Dangerous Cold and Ice & Snow

An active weather pattern is upon us with in the lower 48 for the next several days. A strong arctic cold front will usher in dangerously cold temperatures to end the year and start off the new year. And, there is still the chance for wintry precipitation tonight into Friday for parts of the Southeast and parts of the Southern Plains (see end of article for details).

Introduction/Discussion of Cold Air
Currently, a frigid airmass is building across northern and western Canada, which will ooze southward down the leeward side of the Rockies over the next couple of days (see Fig. 1). This arctic air will arrive in Oklahoma on Saturday, northern Texas Saturday evening, and push into the coastal areas of Texas by Sunday (locations further east: Mississippi, Alabama, Tennessee, etc. will also see the arctic front move in Saturday into Sunday). Dangerously cold wind chills and high temperatures below freezing are likely for much of Oklahoma, northern Texas, much of Arkansas, much of Tennessee, northern Mississippi, and northern Alabama. In fact, temperatures may not get above freezing for 2-5 days depending on the location; and windchills may drop below zero for northern Texas and northwestern Mississippi, while parts of the Texas Panhandle, much of Oklahoma, and northern Arkansas see windchills 10-30 below zero. Windchill Advisories are likely for much of the western Gulf States (see Fig. 2).

Fig. 1: Cold Temperatures Building

Fig. 2: Forecast Windchills NYE

Wintry Precipitation
If the cold temperatures were not enough, wintry precipitation is possible, too. As the arctic airmass advects southward, moisture will move on top of this cold airmass. This will set the stage for freezing drizzle for much of Oklahoma, Arkansas, northern and central Texas, Tennessee, northern and central Mississippi, and northern and central Alabama. The freezing drizzle may mix with light snow flurries for parts of Oklahoma, Arkansas, Mississippi, and possibly far western Tennessee. The chance for wintry precipitation arrives in Oklahoma on Saturday continuing into Sunday (see Fig. 3), while northern Texas will see the chance by Saturday night (see Fig. 4). Arkansas, Mississippi, and Alabama will see the chance for wintry precipitation by early Sunday morning continuing into Sunday afternoon (see Fig. 5). Amounts of freezing rain should be less than 1/10th of an inch, and there is the possibility for light snow accumulations on top of the freezing rain accumulations across parts of Oklahoma, Arkansas, and northern Mississippi.

Fig. 3: Southern Plains Wintry Precipitation Late Saturday Night

Fig. 4: Southern Plains Wintry Precipitation Sunday Afternoon

Fig. 5: Southeast Wintry Precipitation Sunday Evening

Outlook After NYE/NYD
The arctic airmass will be hard to nudge out of the South and Southeast. This will force us to keep an eye on a shortwave that is modeled to dive into Texas by Tuesday and then into the Southeast on Wednesday (see Fig. 6 and Fig. 7). This shortwave could generate enough lift to cause precipitation across the Gulf States (from Texas to the Carolinas). With the arctic airmass in place, wintry precipitation looks possible. It is too early to say with certainty this event will occur, but it needs to be closely monitored.

Fig. 6: Future Radar Tuesday Evening

Fig. 7: Future Radar Wednesday Morning

Even if your area is not expecting wintry precipitation, please protect yourself (see Fig. 8) and your animals (see Fig. 9) from this cold weather. This cold weather will be deadly. Check on your elderly neighbors. Make sure you have detectors in your home for fires and harmful chemicals, and be safe with those moveable heaters. It would also be wise to protect your pipes and plants.

Fig. 8: Protect Your Skin From The Cold

Fig 9: Protect Your Animals From The Cold

Wintry Precipitation Tonight
This weekend into next week is not the only time-frame in which wintry weather may occur. As early as tonight, freezing drizzle/freezing rain is possible for parts of the Southeast (see Fig. 10). Winter Weather Advisories go into effect tonight at 11:00PM Eastern for the eastern Carolinas (see Fig. 11). Freezing drizzle amounts should be less than 1/10th of an inch, but this will be enough to make roadways (especially elevated roads) dangerous for the Friday morning commute (see Fig. 12). It should be noted, light freezing drizzle may occur across parts of Oklahoma and northern Texas early Friday morning (see Fig. 13).

Fig 10. : Areas That Have a Chance to See Wintry Precipitation Tonight

Fig. 11: Future Radar Around 5:00AM Eastern

Fig. 12: Winter Weather Advisories

Fig. 13: Light Freezing Rain Early Friday Morning

I will continue to monitor this evolving forecast and have the latest updates as needed, so please keep checking back.

Key Takeaways
I. Wintry precipitation is possible as early as tonight for eastern South Carolina, eastern North Carolina, and southeastern Georgia. It is also possible across western Texas and Oklahoma.
II. Dangerously cold air will impact all of the Southern Plains and Southeast. Protect yourself, pets, plants, and pipes.
III. Wintry precipitation will likely occur Saturday-Sunday.
IV. A potential winter storm is being monitored for Tuesday into Wednesday for the Gulf Coast States.

Wintry Precipitation Tuesday Into Wednesday

Introduction
Wintry precipitation is possible today into Wednesday for parts of the South and Southeast. Cold surface temperatures are already in place across these regions, but another reinforcing surge of colder air is advecting southward as an arctic high builds across northern parts of the country. This will set the stage for wintry precipitation across these regions.

Precipitation Chances
A mid-level shortwave will move in from the west, generating lift, which will create light precipitation from Texas and eventually into parts of the Southeast late Tuesday night into Wednesday. Amounts should remain light, less than 2/10ths of an inch, but it does not take much freezing precipitation to cause issues. The areas shaded in pink have a chance to see freezing rain/drizzle, and the areas shaded in blue have the chance to see light snow/flurries. Parts of the Texas Panhandle, Kansas, northern North Carolina, and eastern Virginia may see light snow accumulations.

Wintry Precipitation Forecast

More wintry precipitation is likely by Thursday for the Southeast. I will have an update on that forecast later today.

Christmas Eve Snow

Light snow is possible Saturday night into Christmas Eve for a large part of the mid-section of the U.S. A broad shortwave trough will dig southeastward into Kansas and then move eastward into the Ohio Valley. This shortwave will generate strong vertical motion, which will aid in the development of snow from Kansas eastward into West Virginia. On the southern side of this shortwave, it is possible a few flurries may occur as far south as northern Oklahoma, northern Arkansas, and northern Tennessee.

Locations closer to the shortwave have the best chance to see accumulating snowfall. This region, near the Ohio Valley, will see the strongest lift and modeled soundings show the entire column will be below freezing. More importantly, the dendritic growth zone in the modeled soundings is near saturated. This is favorable for snow accumulation enhancement in which 1-3″ is likely. I would not be surprised to see 2-4″ in parts of central/northern Indiana and Ohio.

Snowfall Forecast

Wintry Weather Still A Possibility For The Southern Plains

Introduction/discussion:
Wintry precipitation still remains a possibility for parts of the Southern Plains this upcoming Christmas weekend. A strong cold front will move through Oklahoma and Texas on Thursday and Friday. Numerical guidance is struggling with the timing of the cold front, but the faster guidance is likely correct due to the density of the arctic air. This will cause temperatures to plummet just ahead of the weekend. It should be noted, patch drizzle may occur late Thursday night behind the cold front in Oklahoma. With temperatures in the 20s at this point, anything that falls would freeze on contact. This should not be a widespread event, but I will keep a close eye on the situation.

High temperatures will remain in the 30s (see Fig. 1) for most of Oklahoma on Friday, and high temperatures in Texas will likely occur on the morning of Friday before falling into the 30s/40s (outside of far south Texas where a later frontal passage is expected). High temperatures on Saturday will range from the 20s in northwestern Oklahoma to near 50 close to the Texas coast (see Fig. 2)–it is possible the models may be too warm with this arctic airmass, too.

Fig. 1: Friday afternoon temperatures (GFS)

Fig. 2: Saturday afternoon temperatures (GFS)

Light snow possible:
If the airmass behind the Thursday/Friday cold front was not cold enough, a secondary surge of arctic air will advance into Texas and Oklahoma by Saturday into Sunday. A robust shortwave will dive southeastward into the Southern Plains, sending a secondary shot at cold air (see Fig. 3). It is possible light snow will develop along and just behind this cold front as model guidance has been strongly hinting at mid-level frontogenesis.

Fig. 3: Shortwave diving into Texas/Oklahoma Panhandle Sunday morning (GFS)

Precipitation would likely fall in the form of light snow (forecast soundings show a favorable snow profile) Saturday evening into Sunday for Oklahoma and possibly northern Texas (see Fig. 4).

Fig. 4: Forecast sounding Sunday morning (GFS)

It should be noted, I am keeping an eye on southern Texas Christmas morning. Some guidance hints at moisture hanging around this area, with cold surface temperatures and very cold temperatures aloft, so this scenario needs to be watched carefully. I also plan to have an article out later this week discussing the continued cold/active period expected between Christmas and NYE for parts of the south.

Accumulations:
It is too early to accurately forecast accumulations. As of right now, accumulations appear to be light, but enough to possibly lead to a white Christmas for some in Oklahoma and north Texas (since the snow will remain on the ground into Christmas morning). Climatologically, frontogenesis snow events in this region produce between 1-3″ of snowfall where the most intense banding takes place. So, I will go out on a limb and say these are the highest totals likely with this event unless something changes. The most favored areas to see snowfall are in far northern Texas and Oklahoma (see Fig. 5).

Fig.5: Potential snowfall map

Wintry Precipitation Around Christmas?

Christmas time-frame discussion and what the guidance is showing:

A big pattern shift by the end of next week into Christmas weekend will occur for the Southern Plains potentially bringing a favorable setup for wintry precipitation and the coldest air of the season. Guidance has indicated anomalously cool temperatures during the Christmas time-frame for the Southern Plains due to a long-wave trough digging into the region (see Fig. 1).

Fig. 1: GEFS 500mb Indicating Long-Wave Trough Across the Central-U.S.

The reason the guidance is showing this pattern is because the eastern Pacific Oscillation (EPO) will tank after the 18th of December (see Fig. 2), which favors a ridging over northwestern parts of North America. The ridging in this region is favorable for arctic air to invade parts of the lower-48. To evaluate which parts of the lower-48 may see the most anomalously cold temperatures, it is important to evaluate the Pacific/North American (PNA) phase. The PNA will become negative over the weekend (see Fig. 2). A negative PNA is most favorable for the coldest temperatures to occur in the western and central parts of the lower-48. The Southeast is generally ‘protected’ from the cold air is this scenario due to amplification of the SE ridge when the PNA is negative.

Fig. 2: Forecasts of Teleconnection Indices

Forecast breakdown for this time-frame:

It appears the advertised arctic airmass will move into Oklahoma and Texas on Thursday of next week. The exact timing is uncertain, but numerical guidance usually struggles with arctic airmasses and is too slow with the movement of such a dense airmass (however, guidance is in concurrence of a Thursday arrival). Out west, an upper-level low will develop at the base of the aforementioned long-wave trough, possibly cutting off, setting the stage for overrunning precipitation. The timing of the potential precipitation event(s) is unknown at this time, but it does appear the first round of precipitation may occur next Friday night into Saturday. Potentially followed by another round or two of precipitation depending on the evolution of the upper-level low and track between the 22nd and 26th of December.

While too early to establish an exact area, amounts, timing, and precipitation type; confidence, is increasing that somewhere across Texas/Oklahoma will see wintry precipitation periodically between the dates listed above. With the shallow nature of an arctic airmass, it is possible a freezing rain scenario may develop across central and eastern Texas. This is because surface temperatures appear to be below freezing at this time, but just above our heads, temperatures may be above freezing. Further west, the airmass is deeper, thus, more of a snow setup comes to fruition if precipitation is present.

The GFS is showing such a scenario by next Saturday in north Texas. Forecast soundings show the surface well below freezing with a very deep warm layer (above freezing) just a couple thousand feet above our heads (see Fig. 3). This means snowflakes would develop, fall, melt just above our heads, then those melted snowflakes would fall as rain at the surface but immediately freeze upon contact. This is not what we want because freezing rain can be devastating. Further west in Texas, near the upper-level low, temperatures aloft are much colder so snow is more likely in this region (see Fig. 4).

Fig. 3: GFS Forecast Sounding Next Saturday (north Texas)

Fig. 4: GFS Forecast Sounding Next Saturday (west Texas)

Again, it is too early for exact predictions, but this is something I am monitoring. The finer details will be worked out over the next several days, but I am becoming more confident in the large scale setup across North America. Models do not handle arctic airmasses well, so if the airmass is colder and deeper than forecast, if precipitation occurs, it is possible more of a sleet/snow scenario may evolve. If temperatures are warmer, then potentially a cold rain–if precipitation develops. I will have updates as needed.

Predominantly Colder Pattern Could Develop Across Heartland Of U.S. By Late Next Week

Brief Discussion On Early to Midweek Weather:

We’re about to briefly shift out of the pattern that has been responsible for the recent colder weather across the eastern United States and warmth out west. The pattern has previously been characterized by an amplified ridge that has extended from the western U.S. through western Canada and into Alaska. Downstream of the ridge, deep troughing has persisted and in fact, even brought colder conditions all the way into Florida. Remarkably, parts of the panhandle of Florida and over the open waters of the Gulf had snow on the backend of the system that dumped copious amounts of snow across parts of the Southeast. This amplified pattern is going to flatten out next week, allowing for relatively warmer conditions to prevail across most of the U.S. through mid-week. With that said, there will be a quick-moving trough that’ll trek across the Northern Plains early next week and then eastward over New England by mid-week. That’ll bring a quick intrusion of cold air from the Northern Plains over into the Great Lakes and over parts of New England, but that cold will remain mostly confined to those regions. We will eventually have to discuss that system on Firsthand Weather, since it will most likely be bringing a swath of precipitation (rain) across the eastern third of the U.S. Parts of the Northern Plains, Great Lakes, and inland regions of New England could get some snow out of the system, so we’ll have to watch that.

Overview Of Long-Range Forecast Discussion For Late Next Week Through Just Beyond Christmas:

Let’s go ahead and fast forward to the end of next week through the Christmas timeframe and just slightly beyond that. That’s really the entire purpose of this article, and I want to begin digging into how the pattern could begin to evolve after the early to mid-week warmup. Temperatures have mostly been below average across the majority of the eastern third of the nation over the last seven days, while the core of the warmth (relative to climatological averages) has been centered over the Northern Plains and has extended westward into Montana, Wyoming, and Colorado. Additional parts of the western third of the U.S. have also been quite warm. Now if you read Firsthand Weather’s winter forecast that was published about a month ago, you probably noticed that we were bullish on the cold across the Northern Plains and into the Rockies, so if you’re located across any of those locations, you might be wondering what’s going on with the forecast. Get ready, changes are on the way!

It’s not all that uncommon to hear a lot of talk about the North Atlantic Oscillation (NAO) and the Arctic Oscillation (AO) in many of the medium and longer-range forecast discussions that get published on the internet; however, the eastern Pacific Oscillation (EPO) is a lesser known index that honestly should be discussed more often than it is in the U.S. The negative phase of the EPO is characterized by ridging over Alaska with troughing to its south. It’s simply a dipole pattern similar to the NAO, but its location is in the northeastern Pacific. Any atmospheric feature(s) that is present upstream of the U.S. can have important implications for how our weather in the U.S. may evolve with time.

It’s important to note that simply determining whether the EPO is negative or positive doesn’t give the whole picture. It’s just as important to determine the position of the Alaska ridge or trough, its orientation, and its amplitude. For example, a ridge can extend well into Alaska, but its position may be far enough offshore that the downstream trough centers itself over the western and central U.S. This, in effect, can open the door for ridging to develop across the Southeast and along the East Coast. The moral of the story is that a negative EPO pattern is one to watch closely in the U.S. since it can oftentimes signal widespread cold, but it’s important to dig a bit deeper to fully determine where those coldest anomalies will be located. That’s what we’ve been in the process of doing at Firsthand Weather and will continue doing through the weekend and early next week.

How Will This Impact The Weather In The United States:

While the GFS model is generally more aggressive with the development of Southeast ridging, the European features a weaker ridge. Nonetheless, the pattern that will likely evolve from very late next week into Christmas will feature widespread cold across the heartland of the country. The coldest anomalies should be centered over the Northern Plains and upper Midwest, and it won’t be uncommon for that Arctic air to spill southward into the Rockies and the central/southern Plains. Additional regions to watch for very cold conditions will be the Ohio Valley, northwestern parts of the Tennessee Valley, and Northeast (especially inland regions away from the coast). The Pacific Northwest could also get in on some of these colder conditions, and that colder air could spill into the Mid-Atlantic at times, too. To summarize this into one sentence, this pattern will likely feature widespread cold, which differs quite drastically from the eastern-focused cold earlier in the month.

european model 500 mb height anomalies
Figure 1: Latest European model features long-wave trough centered over the central U.S.

The next image from the Climate Prediction Center (NOAA) shows the probability that temperatures will be above or below average from December 21 to December 27. That’s not a bad compromise across the Southeast, given that the guidance does tend to develop ridging across the Southeast but at times, colder air will make it into those regions. Notice that the probability for below-average temperatures is depicted over a large region of the U.S. Keep in mind that this particular graphic tells you nothing about the magnitude of the cold. Its purpose serves to show you which regions could simply have above or below average temperatures.

8-14 day temperature anomaly probabilities
Figure 2: The latest 8-14 day (Dec. 21 to 27) temperature probability outlook from the CPC

The next analysis takes GEFS forecast model data and produces a temperature anomaly map (from December 23 to 25, in this case) based on previous similar pattern setups. Based on this kind of setup, you’d generally expect storm systems to swing southeastward through the Rockies, into the central/southern Plains and then hook northeastward across the mid-south, the northwestern Tennessee Valley, Ohio Valley, and across inland regions of the Northeast. Even though I didn’t draw in that storm track, I mostly agree with this analysis. The region to watch most closely for wintry weather (including ice) over this period will generally extend from the central/southern Plains over into the Ohio Valley and into inland regions of the Northeast. That puts parts of the Tennessee Valley and the mid-south (parts of Arkansas, western Tennessee, far northward Mississippi) in a zone that could swing either way; however, it’s a region to watch nonetheless. To make it easy, take a glance at the map, and if you’re relatively close to the storm track drawn on the map and located on the northern/northeastward side, take notice. This is meant to give you a general overview of what the dominant storm track could look like, so please understand that this isn’t depicting a particular system.

Cold in central U.S. with storm track
Figure 3: Projected temperature anomalies (for Dec. 23 to 25) from CIPS Analog Guidance using GEFS model data and analogs

I suspect that most of the Southeast (the red-shaded zone across parts of the South in the image above) will transition to a predominantly wetter and a warmer pattern through Christmas and maybe just a bit beyond. With that said, some of the guidance does have the colder air spilling into the Southeast at times through the period (notice the back and forth in temperature anomalies depicted in the two images below), which seems realistic to me. Essentially, this is a pattern that favors wetter and warmer conditions, which can then be followed by colder and drier conditions, and then the cycle continues. If you’re located just east and southeast of the Appalachians, it’s worth noting that surface high pressure moving across the Northeast can result in surface temperatures being at freezing just outside of the mountains across those locations as precipitation is moving across the Southeast. That’s a scenario to watch for with this kind of pattern and can cause icy conditions (not snow though); however, that’s a very localized threat that often doesn’t even reach into cities like Birmingham or Atlanta and doesn’t occur across locations west and southwest of the Appalachians. Unless the ridging that is expected to build into Alaska is farther east than I’m anticipated, I expect most of the wintry weather to occur across the locations I specified in the previous paragraph.

european model temperature anomalies 1
Figure 4: Projected temperature anomalies from latest European model on Friday morning, Dec. 22

european model temperature anomalies 2
Figure 5: Projected temperature anomalies from latest European model on Saturday morning, Dec. 23

Chris is planning on posting an article for the Pacific Northwest and one for the Southern Plains sometime soon. In the meantime, I’ll also be working on regional forecasts across additional areas. Hopefully this article gives everyone a general overview of the pattern we’re going to be dealing with, and we’ll get into the nitty-gritty specifics throughout the month. Of course, any changes to the overall pattern could require me to make revisions to this forecast, so most definitely be aware of that! I don’t have all of the answers and do make mistakes, so please follow Firsthand Weather continuously.

Winter Weather to impact the East Coast

Winter Weather Advisories have been put into effect from Louisiana through parts of Northern Georgia.   This system is going to head toward the coast and move up the Eastern Seaboard with minor to moderate impacts.

Matt and Chris already have good coverage for the forecast for the Southern Plains and the Southeast, so my focus will be from the Delmarva Peninsula northward into New England.   A cold front associated with a system that moved up into Canada, has pushed well into the Gulf and off the east coast, spanning from near Greenland back to Mexico.  The cold air is well established with snow as far south as the Texas and Mexico border and advisories to nearly the Gulf Coast.

One of the challenges with this system will be the usual early season marine influence.   Sea surface temperatures are still warm and any easterly winds will impact surface temperatures over the land.  This will be a major impact along the coast down in Virginia and for Cape Cod as well as the islands.  Coastal areas should expect to see a heavier wetter snow once the snow starts to fall.  This set up may also trigger a few ocean effect bands, which could make for small areas of higher snow totals right next to areas of lower totals.

The NAM model is being for more aggressive with snowfall accumulations across the region than other modelling, though this is common for the NAM.   The expected snowfall accumulations occur for most locations later on Saturday into Saturday night.  The GFS shows a far lower area of accumulation as well as lower overall totals.

Figure 1: NAM model snowfall accumulation forecast through Sunday afternoon. Source: Tropical Tidbits

winter

Figure 2: GFS model snowfall accumulation forecast through Sunday afternoon. Source: Tropical Tidbits

Despite the differences, both models show plowable snows into the I-95 corridor with some higher snowfall total further east where the rain/mix doesn’t hold totals down.   I’ll be doing some follow ups on this as the track and actual conditions get closer.   There is another chance for a storm early next week that we’ll also be keeping an eye on as cold and windy conditions are expected to take hold in the Eastern United States, but we’ll get through this first storm first and focus on the longer term risks as they get closer.

 

Rob

 

 

 

 

Early-Season Winter Event Looking More Likely For Parts Of The Southeast

It’s only December 6th and we’re already talking about the potential for a winter event across parts of the Southern Plains and the Southeast. Since we’ve already covered the forecast for the Southern Plains, I’m going to focus primarily on the Southeast. A system earlier in the week moved across the Northern Plains and has now trekked northeastward into Canada. A cold front associated with that system pushed across the eastern U.S. earlier in the week and has now made its way to the Gulf coast and along the East coast. Behind the front, a broad trough has become established over the eastern two-thirds of the nation. With this kind of setup, mid to upper-level wind flow across the southeastern U.S. is generally from the southwest; thus, the initial cold front has already slowing down and will eventually stall out near the Gulf coast and East Coast. The shortwave feature that will be responsible for bringing snow to Texas is going to interact with the broad trough and a second shortwave feature. This interaction is going to sharpen the trough, which will eventually extend into the Southeast. Given that the frontal boundary will be stalled out near the coast as all of this is unfolding, this is going to induce the development of a surface low pressure system that will ride along that boundary along the Gulf coast and up the East coast.

For those in the Southeast, most who have lived in that region for any extended period of time know that most winter storms that unfold across that region involve a low pressure system developing near the coast along the Gulf of Mexico, which then crosses over and moves off or along the East coast. Since cold air is often limited, forecasting these events can be challenging throughout the extent of the event. Since it’s still early December, that even adds additional challenges.

First and foremost, it should be noted that most of the model guidance suggests at least some wintry weather (snow!!) across the Southeast (more on specific locations in a bit). However, snowfall accumulation projections range from no accumulations to several inches of snow for parts of the Gulf coast northeastward to the East coast. For events such as these, I either like to see that a pre-existing colder air mass has become established over the region before the event, or that there is going to be sufficiently cold air provided by a certain atmospheric feature in time for the event (for example, high pressure over the Northeast). The first cold front that has now pushed through the region has brought in much colder conditions, but given the broadness of the trough and the time of the year, there really needs to be an additional source of colder air spilling into the region. Throughout the day on Thursday, the colder air to the north-northwest of the area will continue pushing southeastward, but despite that, we’re still going to be dealing with the classic borderline winter storm/event in the South.

The NAM model has generally been the most aggressive with snowfall accumulations across the Southeast, which extend those accumulations down the Gulf coast. The hefty snowfall accumulations occur for most locations later on Friday into Friday night, even though it has precipitation (mostly rain) spreading across many locations in the Southeast tomorrow. If you’re looking to get noteworthy accumulating snow, it’s best this event occur later on Friday like what the NAM is showing for many locations, and given that it would be getting dark or already dark, this would greatly increase the odds that temperatures would be sufficiently cold throughout the atmosphere to support snow or a transition from rain to wet snow. This would also allow more time for colder air to seep southeastward. The GFS is less aggressive, primarily because it has the heaviest precipitation moving out more quickly. The European model, which is generally more reliable, falls somewhere in between with accumulations. Remarkably, all of the guidance is at least showing some accumulating snowfall for some locations in the Southeast. However, it should be noted that these maps depict a 10:1 snow to liquid ratio, but given the warmer ground temperatures and the fact that rain will mix in (at least initially), these totals could be overestimated for some locations on all three models. However, higher snowfall rates across some locations could offset some of these hindrances for snowfall accumulations.

NAM model snowfall map

Figure 1: NAM model snowfall accumulation forecast for the next 72 hours. Source: Tropical Tidbits

GFS model snowfall map

Figure 2: GFS model snowfall accumulation forecast for the next 72 hours. Source: Tropical Tidbits

European model snowfall map

Figure 3: European model snowfall accumulation forecast for the next 90 hours. Source: Ryan Maue

Remarkably, residents living in southeast Louisiana, southern Mississippi and possibly extending into western parts of Alabama have the greatest chance of this event unfolding for them. Since this region will be some of the first locations to feel the effects of the colder air mass digging southeastward, precipitation developing and moving across the region will have the greatest chance of making the transition to snow either late Thursday or early Friday. Predicting snowfall accumulations from eastern parts of Alabama into Georgia and South Carolina gets quite challenging. The later this event unfolds for those locations on Friday, the better for accumulating snowfall. The more aggressive snowfall totals that span across parts of North Carolina into southeastern Virginia are warranted. That’s another region that I feel has a pretty decent chance of this event unfolding.

Due to the uncertainty that exists, this will require me to post a follow-up update tomorrow. However, residents in the general swath of accumulations that are being depicted by the model guidance should prepare for this event. I expect the majority of accumulations to occur over grassy surfaces; however, issues on the roadways could occur for localized regions where the snowfall rates are higher. That will be something that we’ll have to determine tomorrow. Nonetheless, it is still very early in the meteorological winter, and it’s remarkable that we even have an event such as this to forecast! Firsthand Weather will keep everyone updated as much as possible before and during this event and will be posting numerous updates on our Facebook page.

Wintry Precipitation Chances Extended Into North Texas

Wintry precipitation chances will return to parts of Texas this week. It is currently warm in much of Texas, with some areas close to 90, but the weather will chance drastically overnight into Tuesday.

The setup
At this hour, a chilly Canadian airmass is advancing southward into Oklahoma and the Texas Panhandle. This cold front will move through all of Oklahoma and Texas by the end of the day on Tuesday; followed by a reinforcing shot of cold/dry air moving in Wednesday night. This Canadian airmass is what is setting the stage for a cold enough temperature profile to support wintry precipitation. The only ingredient missing is a lifting mechanism to generate precipitation–this will change by Wednesday. A robust upper-level shortwave will traverse (from west to east) across Texas Wednesday into Thursday. The robust nature of this shortwave will act as the lifting mechanism to generate precipitation across parts of Texas.

GFS 500mb Vorticity Map (Wednesday Morning)

A band of precipitation will initially develop in western Texas Tuesday night, and as the shortwave gets closer, the band will evolve into a large band of precipitation across much of the I-20 corridor in Texas. Throughout the day on Wednesday, this band will shift southward into central and southern Texas. This was a trend I noticed in the guidance (the northward trend in precipitation) that I mentioned in yesterday’s article. The northward trend continued today, thus, the introduction of wintry precipitation chances now extending into north Texas (the best chances along and south of I-20).

Precipitation type
Forecast atmospheric soundings show a profile that would support wintry precipitation. Initially, the precipitation would begin as a rain then rain/sleet mixture in northern Texas. The same is likely for central parts of Texas. Surface temperatures will be borderline (upper 30s), but wetbulbing will drop temperatures to allow for this wintry precipitation transition. Further southwest, in the Rio Grande, Edwards Plateau, and parts of the Texas hill country, a rain/snow mixture looks to be the primary precipitation type due to a colder atmospheric profile.

GFS Forecast Sounding: North Texas (Wednesday Morning)

GFS Forecast Sounding: Texas Hill Country (Wednesday Night)

Where is snow most likely and accumulations
At this time, the best chance for snow will remain in west Texas, the Rio Grande, the Texas hill-country, and the Edwards Plateau.

NAM Future Radar (Wednesday Morning)

NAM Future Radar (Wednesday Night)

Accumulations do look possible. It is extremely difficult to forecast accumulations this far in advance, in the south, especially when precipitation types may be a mixture; but, light accumulations will likely occur in west Texas and the Texas hill country. A slushy inch may accumulate on elevated surfaces with 1-2″ in the higher terrain. The rain/sleet mixture in north Texas and central Texas should not cause any travel issues but will be fun to watch fall from the sky.

NAM Accumulations

Update: Texas Snow Looking Likely This Upcoming Week

Confidence is growing that parts of Texas will receive snowfall this upcoming week, so enjoy the warm temperatures while they last.

The setup
A chilly Canadian airmass will settle into the Southern Plains by early to mid-week. The initial cold front will move into Oklahoma and Texas Monday into Tuesday with a reinforcing front moving in Wednesday afternoon/evening. This will set the stage for the thermodynamic profile to be supportive of wintry precipitation. Things get interesting by mid-week when a robust upper-level shortwave traverses (from west to east) across Texas Wednesday night into Thursday, and work in tandem with the upper-level trough axis that will dive southward into the Southern Plains.

GFS 500mb Vorticity Map (Wednesday Night)

This will increase lift and likely generate a band of precipitation from western Texas into the Texas hill-country. Forecast atmospheric soundings show a profile that would support a rain/snow mixture quickly changing to snow. Initially surface temperatures will be borderline for snow (upper 30s), but wetbulbing will drop temperatures to near or below freezing Wednesday night.

GFS Forecast Sounding (Wednesday Night)

Where is snow most likely
Right now, the best chance for snow will remain south of I-20 in west Texas, the Rio Grande, the Texas hill-country, and the Edwards Plateau. Latest guidance is trying to nudge the precipitation closer to I-20, so rain/snow chances may be introduced into locations further north as we get closer to Wednesday.

GFS Future Radar (Wednesday Evening)

Accumulations
Accumulations do look possible. It is extremely difficult to forecast accumulations this far in advance, but light accumulations will likely occur in the aforementioned areas. Right now, it appears a slush inch may accumulate on elevated surfaces with 1-2″ in the higher terrain.

GFS Snow Forecast (Wednesday Evening-Thursday Morning)

Again, the finer details need to be ironed out in this forecast, but I will have updates as needed. Expect an accumulation map from me tomorrow evening, so keep checking back for details.