Accumulations Forecast (Southern Plains, South, and Southeast)

Here’s an updated accumulations forecast for the Southern Plains, South, and Southeast from tonight through Saturday. Many areas will see a transition from one precipitation type to another, which is hard to spatially demonstrate on a small map while making the image legible. Please note, forecasting wintry precipitation for the South is extremely difficult. Any banding, convection, unforeseen temperature inversions, as well as other variables can significantly alter potential wintry accumulations. (If you want to read a detailed discussion about the synoptic setup of the event, please see the previous article for those details.)

Winter Storm Update (Southern Plains, South, and Southeast)

Right Now/The Setup:
Confidence is increasing for wintry precipitation to impact parts of the Southern Plains, South, and Southeast beginning tomorrow in parts of the Southern Plains and continuing into the weekend. Models are in relatively good agreement of the placement of synoptic features for this setup, but there are still a few questions that I will try to iron out in this discussion.

The system that will bring wintry precipitation to southern parts of the country is currently located across the Pacific Northwest. This closed upper-level low will dive southeastward and slowly open up as it approaches the Southern Plains. Ahead of this approaching system, a surge of arctic air will advance southeastward, which will set the thermal profiles for wintry precipitation. As the trough digs into the South and moves away from the Southern Plains, a surface low may develop along the north-central/northeast Gulf Coast. This will setup precipitation chances for parts of the South and Southeast.

Southern Plains:
An area of snow will begin to develop Thursday night into Friday in the Texas Panhandle and central Oklahoma before advancing east-southeastward. This band will eventually impact most of central and southern Oklahoma, northern Texas, and develop eastward into Arkansas, northern Louisiana, and into northern Mississippi/Alabama (more on these areas later in the discussion).
It is important to note, this band of snow will develop into response to lifting associated to frontogenesis. The reason I mention this is because it’s extremely difficult to forecast the exact placement of this frontogenesis. It appears the frontogenesis with this arctic boundary will be pretty significant, which could lead to adequate lift to dump moderate snow for some areas. Typically this type of setup can lead to decent snow amounts for some areas with a tight gradient to no snow just over a small distance. I will continence to monitor the evolution of this band and adjust the forecast accordingly dependent upon where this temperature gradient sets up. It should be noted, the forecast soundings across the Texas Panhandle, Oklahoma, Arkansas, and northern Texas are conducive for high snow ratios (greater than 10:1), which could lead to a quick few inches-especially in Oklahoma and the Texas Panhandle. Right now, it appears the heaviest snow should be just south of the Oklahoma City Metro and remain well north of Dallas; however, these Metro areas will likely see light snow/flurries. It should be noted, some of the short-range guidance is hinting at an area of very light freezing drizzle developing in response to an area of isentropic lift across parts of the Texas Hill County-just outside of Austin. This will need to be monitored early Friday morning because it could make bridges and overpasses slick.

A second chance for light snow may evolve across southern Oklahoma, northern and eastern Texas, southern Arkansas, and pars of Louisiana late Friday as the trough moves across the area. The trough will aid in enough lift to generate some light snow flurries, but moisture is meager at best, so any snow that falls will be very light at best. Locations further southeast, in east and southeast Texas, may see a few sleet pellets looking at the latest forecast soundings. It’s possible the far northern parts of Houston may get in on the ‘fun.’

South and Southeast:
The South and Southeast will see wintry precipitation as well. The aforementioned region of lift associated with the frontogenesis across the Southern Plains will also be a variable in the South. A narrow band of precipitation will develop across southern Arkansas, northern Louisiana, into northern Mississippi, and northern Alabama. As mentioned earlier in this discussion, these setups are extremely difficult to forecast in regards to where the most intense zone of lift develops in response to the significant temperature gradient above our heads (around 700mb)—the surface cold front will be well south into Texas but the front slopes so essentially which creates a unique position of the 700mb temperature gradient in which is the zone the band of snow will develop. Areas beneath this band of snow could see a quick accumulation while areas just outside of this band see nothing—the gradient will be tight. Right now, it appears Birmingham may see snow from this initial band of snow.

As the trough moves east of out of Texas, a weak surface low may develop along the north-central/northeast Gulf and begin to move off to the northeastward. The evolution of this low, if it develops, is still uncertain at this point (and we are a couple days out so I will continue to iron out the details of this feature later in the week). If the low develops, it may wrap some additional moisture into the cold air across the Southeast. This would give Georgia, South Carolina, and North Carolina a chance of snow and a wintry mixture for areas closer to the coast. It is possible an area of enhanced accumulations may occur if the low deepens as it moves off the East Coast. This will be closely monitored. There area many uncertainties with the onset of precipitation, temperature profiles, and the northward extent of the precipitation axis. Small deviations in these variables, or a prolonged mixture of sleet, could drastically impact accumulations.

Preliminary Wintry Precipitation Forecast:
Below is my current thinking on which areas have a shot at wintry precipitation, and which areas have the best chance to see accumulations. Please note, confidence is higher towards the Southern Plains since this event is about 24-36 hours out, but confidence decreases further east. Forecasting wintry events in this region is extremely hard, and accumulations this far out is highly susceptible to changing—this may need adjustments tomorrow. I just wanted to generate a map in order to create a heads up in case the frozen stuff begins to fall in your backyard.

2 storm chances for East Coast

The Southern Storm is the big story with winter weather expected to impact from Texas to the Eastern Seaboard, leaving the first storm expected to form off the coast of the Carolina’s pretty much no attention attention.

 

This weak system is expected to slide up the coast and bring some rain to Eastern North Carolina with light snow from areas of Nebraska into Kentucky to Delaware and New Jersey ahead of the Southern Storm.  Matt has posted a handy map of the Winter Weather Advisories that are currently in place as this weak system moves across the country toward the coast.   This system will combine with the low shown above and slowly intensify as it moves to the Southeast of New England.  This system will bring snow into Southeastern New England with light accumulations during the early morning hours of Friday into Friday afternoon.    Early activity will likely be in the form of snow showers which may limit to coverage area of overall snowfall but the biggest problem to accumulating snow will be the warmth of the ground.   Any snow that does manage to stick will have a difficult time remaining in place for long, with the one thing that may save some areas from an instant melt being the cold temperatures on the way following this system.

Southern Storm

For the main event, which have been covered well by Chris and Matt for the Southern areas that’s will be impacted, the Southern storm looks like it’ll be wide right for many of our readers.  As seen in the previous articles, the system forms in the South and slides off the coast of the Carolina’s, leaving the heavier snow totals expected for that region.  the uncertainty in the speed and exact track of this system is causing some forecast issues, but aside from some lake effect snows  caused by the general flow pattern in the Great Lakes region, this second system looks to leave readers across most of Kentucky, West Virginia, Western and Central Pennsylvania back towards Ohio high and dry.

Southern Storm

The above model data is for 1 PM Saturday.   It shows the storm after it has left Georgia and areas further west and does not indicate that it will not snow there at all.  Just that it will not be snowing there at this particular point in time.

Watching the strength and track

The key question to the track of this system will be the strength of the lows and the energy brought into the pattern.  A strong set up will include more of the Eastern portions of the U.S while a weaker pattern will deprive even New England of any snowfall.  Despite the impressive moisture associated with this system, guidance is now really strengthening these lows very much.   For anyone along the Mid-Atlantic and Northeast, please read the articles Matt and Chris put out about the south to stay informed about this system.   The information they have will be invaluable for track this system up the coast over time.   I’ll be around to keep you up to dat on all the latest for this system and its impacts for this region.   So keep an eye on both facebook and the website for further details.

 

Robert Millette

Firsthand Weather

Quick Update On The Southeast Winter Storm Potential

While this article will not be nearly as extensive and detailed as the one from the other day, I did want to do a brief update on the latest trends, and I will have a much bigger and detailed update on Thursday night.

The biggest issue right now is still trying to pin down the exact track of the low pressure system that is going to develop along the Gulf Coast, which will then move off the Southeast coast (and potentially up the coast some, depending on certain factors).

There are some differences on strength of a northern stream system that will be moving over the Great Lakes region. The other uncertainty remains to be with timing of the vigorous shortwave feature that will be moving into the West Coast and triggering the development of the winter storm that will eventually impact the Southeast.

The models are beginning to come into better agreement, however there are still some differences on the northern extent of the moisture, which makes this forecast still particularly challenging.

The European model isn’t too bullish on bringing adequate moisture into the northern half of Mississippi and Alabama, while the GFS model is somewhat more aggressive. This is one area that is going to have to be watched still, and the threat zone might have to be moved some south. The map that Christopher Nunley put out on Firsthand Weather last night is still a good indication of where wintry precipitation could fall. The big question right now for that region is how much precipitation will move into the region and how heavy it will be. We might actually have a better handle on that by tonight.

The low pressure system is really going to ramp up as it begins to move off the Southeast storm. This could actually be a big winter storm for the Carolinas, and I expect that one stretch will get at least over 4 to 6 inches of snow. The system is going to deepen as it enters into the right entrance of a jet streak that will be located along and just off the Mid-Atlantic coast. The atmosphere should be primed for the strengthening of this cyclone. Northern and central Georgia remains to be a bit of a question mark too because of uncertainties on northern moisture extent. The Weather Prediction Center has gone particularly aggressive with snowfall potentials over northern Georgia and far western South Carolina for Friday night, so it is a region to watch closely. All regions that were mentioned in my last article need to still remain alert. Depending on later trends, I may have to add parts of the Carolina beaches in the threat zone but will hold off on that until tonight or tomorrow.

WPC snow map

Figure 1: Forecast for Friday and Friday night courtesy of the Weather Prediction Center

As you can see below, both the latest GFS and European call for a sizable winter storm across the Carolinas, but pinning down the regions that will receive heaviest snowfall amounts is challenging and honestly impossible at this point.

Carolina snowfall map - Euro

Figure 2: Latest snowfall projections from the European model through Saturday night

GFS snowfall map

Figure 3: Latest snowfall projections from the GFS model through Saturday night (important note: totals are likely elevated in southernmost regions due to sleet/freezing rain possibly skewing totals)

A potentially significant winter storm is looking more likely for the Carolinas. I am also keeping the northern half of Georgia and southern portions of Virginia in a high risk zone for this event, too. I expect some impacts for north-central portions of Mississippi and Alabama, but that is very much contingent on moisture. Extreme southern and extreme eastern parts of Tennessee could see some impacts, too. Christopher Nunley is covering the potential impacts from this system west of the mentioned areas, and Rob Millette is going to cover regions north of that zone.

Probability snow map

Figure 4: The probability that a region will get at least 4 inches of snow (blue circle indicates probability greater than 10%, green circle indicates probability greater than 40%)

One last note. . .a region from the Central Plains over to northern Tennessee, Kentucky and extending into parts of Ohio, West Virginia, Virginia and to the coast (I didn’t name all regions) could get some snowfall tomorrow into early Friday with possible accumulations from a much weaker system ahead of the main storm system. Be sure not to get the two systems confused!

Again, these are just some quick thoughts, and I’ll have a much more extensive update Thursday night including timing, additional details on precipitation type and maps.

Southern Plains, South, and Southeast Snow UPDATE

This forecast is a follow-up on Matthew Holliday’s forecast from last night in regards to the winter storm that may impact parts of the Southern Plains and South/Southeast. There is still great uncertainty regarding the evolution of the winter storm late this week into the weekend, but I’ll discuss what we know and try to explain the pattern leading up to this potential event.

The Setup:
The guidance is struggling with consistency in regards to the placement of synoptic features leading to a potential wintery shot for low-latitudes. The thinking as of tonight (Tuesday), a trough will dig into western Texas late in the week. As the trough digs further into Texas, a surface low will develop along the north-central/northeast Gulf Coast. This will setup precipitation chances for parts of the Southern Plains and Southeast. A cold airmass will be oozing into the area at the same time, which will setup an area of snow, and likely an area of snow/sleet mixture.

Southern Plains:
A cold front has moved into the region today, but even colder air will settle in later this week as a reinforcing cold airmass moves into the area on Thursday. The thermal profiles with this aimrass will be conducive for wintry precipitation. The forecast soundings show mainly a snow profile for much of the Southern Plains with the potential for a snow/sleet mixture towards I-20 in northern Texas/northern Louisiana.

The first chance of light wintry precipitation will occur late Thursday into Friday for the Texas Panhandle, Oklahoma, Arkansas, northern Texas, and northern Louisiana in response to a weak disturbance causing lift; along with a band of frontogenesis due to a relatively defined thermal gradient associated with the reinforcing cold airmass This will act to squeeze out any moisture in the atmosphere; however, the precipitation will be light and brief due to the dry low-levels. Any precipitation should be light and begin in the Texas Panhandle and central Oklahoma/Arkansas, then slowly move southward into northern Texas. Forecasting snowfall totals is extremely difficult this far out, but it appears the snow should remain light. A dusting to 1” cannot be ruled out. It should be noted, if this band of snow moves slower than expected, or the frontogenetic area is more enhanced due to a larger temperature gradient than forecast, snow totals may increase just north of I-20. This will be monitored.

A second snow threat may develop across far eastern/northeastern Texas late Friday night into Saturday as the trough moves across the area. The trough appears to come into the Southern Plains at a positive tilt. This tilt is the least impressive in regards to precipitation chances, but should aid in light precipitation—especially east of Texas. This second threat is more questionable because it’s a battle between dry air. It will also be important to monitor when and if a weak surface low develops near the Gulf Coast. Right now, it appears a low will develop along the north-central/northeastern Gulf, which is too far east to aid in more precipitation for Texas. Southern Arkansas and Louisiana should see light snow, and a light snow/sleet mixture due to this weak low.

South and Southeast:
The aforementioned disturbance trekking across the Southern Plains late Thursday/early Friday may generate light snow/sleet north of the I-20 corridor in Mississippi and possible into far northern Alabama as well. The second threat, outside of the small band in Mississippi on early Friday, begins Saturday for central and southern parts of Mississippi, Alabama, Georgia, and eventually into South Carolina and parts of North Carolina.

As the trough moves east of out of Texas, it should become more neutrally tilted and a weak surface low may develop along the north-central/northeast Gulf. This low may slightly deepen as it begins a northeastward trek into the Southeast, which will wrap moisture into the cold air, and likely create an area of wintry precipitation for the aforementioned areas. It’s too early to determine how much snow will fall due to many unforeseen variables that will come into play. The evolution of the low (if it develops), the track, the position and depth of the cold airmass, and moisture are all critical in determining which areas will see snow, which areas will see a snow/sleet mixture, and how much may fall. It does appear some light accumulations will occur across the South and Southeast, however.

This map shows which areas I am watching for potential winter weather impacts late week into the weekend. Please note, this area will be updated throughout the week, and does not mean accumulations will occur. It’s entirely too early to forecast snowfall totals this far out.

Confidence Increasing For Southeast Winter Storm This Weekend

While much uncertainty still exists on specifics, confidence continues to increase that a winter storm (potentially significant) will be impacting the Southeast, among other regions, this weekend. In this article, I will primarily be focusing on the southeastern U.S. (including the Tennessee Valley), while Christopher Nunley will be posting an article tomorrow, which will address potential impacts across the Southern Plains. This system could produce impacts from coast to coast, including over the Rockies, which will also need to be addressed.

The Pattern Leading Up To The Potential Winter Storm:

When attempting to determine how big of a punch a winter storm might bring, I always take a look at the overall pattern that will precede the event. Currently, a low pressure system is located over the lower Mississippi Valley, which will trek northeastward tomorrow across the Tennessee Valley and Ohio Valley. While this will act to transport warm, moist air into the southeastern U.S. initially, cooler air will rush in behind the low as it moves into Canada.

A series of shortwave troughs, one that will be particularly robust mid-week, will move across the Great Lakes and Ohio Valley and eventually eastward into the Northeast. This will act to maintain the general placement of a longwave trough over the eastern third of the nation, and a strong cold front will eventually sweep all the way through the Gulf Coast states to the East Coast by Wednesday into Thursday.

500 mb map winter storm

Figure 1: On Friday, the latest GFS has a longwave trough over the eastern third of the U.S. with the potential winter storm located over the Rockies.

As far as having the necessary cold air in place for a winter storm across the southern states, this kind of setup is typically what needs to occur. As it seems right now, the cold air will be in place before the system of interest moves across the Southeast. While some regions could start with a mixed bag of precipitation or even just rain, this is shaping up to be an all-snow event for many locations with a rain/snow line setting up somewhere along the Gulf Coast states.

Potential Impacts, Locations To Watch, and Uncertainties:

A vigorous shortwave (the feature that will trigger the development of the winter storm) will move into northern California/ Oregon after midweek, which will dig into the Southern Plains early weekend and trek eastward across the Gulf coast states through the weekend. This will keep the colder air reinforced over the eastern U.S., and this feature will trigger the development of a surface low pressure system that will eventually move along the Gulf Coast states. The low pressure will likely be placed in the right-entrance region of a jet streak (very strong winds aloft) located along the East Coast that could aid in the further strengthening of this low pressure system once it moves just off the Southeast coast.

There are a couple of uncertainties that I have at this point that should somewhat clear up by midweek. First, it is uncertain how far north the region of precipitation will reach. Sometimes the issue with pre-existing cold air masses located over a region is that the moisture can get suppressed quite a bit to the south. Another factor to consider is deep convection (thunderstorms) along the Gulf coast and Florida that could rob moisture from regions farther north. These are some factors that always must be considered with such a setup. This uncertainty is definitely being demonstrated by the forecast models. . .the operational GFS model has a monster of a winter storm for a large portion of the Southeast while the operational European model has generally kept precipitation amounts lighter the farther north one is located. With that said, almost all model guidance has some amount of moisture making it fairly far north, however, this puts locations like Tennessee and southern Kentucky in a “wildcard zone.”

Model differences with southern winter storm

Figure 2: The latest GFS (top two images) has the precipitation field farther north than the latest European model (bottom two images). Ensembles are likely more useful in this range.

While this is subject to change, locations that need to watch the potential of being impacted by a winter event/storm (potentially significant in some of these locations) include the northern half of Mississippi, the northern half of Alabama, the northern half of Georgia, the northern half of South Carolina (including Midlands), much of North Carolina, far southern Tennessee, and southern Virginia.

Additional regions that could be impacted (which will be addressed tomorrow in Christopher’s article) include parts of the Southern Plains, Arkansas, and northern Louisiana. He will be covering those locations during the extent of this event.

Regions that are currently on the line include the rest of Tennessee, southern Kentucky, and the rest of Virginia due to uncertainties on the northern extent of the moisture.

Right now, the focus is currently on the overall pattern and the feature that will be responsible for this potential event. Given the blocking signature currently located over the eastern Pacific, forecast models are especially unreliable at this time. I encourage you to disregard forecasts, such as those produced by weather apps, that are solely based on model data. Over the next two days, we will be able to better specify locations and will make the necessary modifications to the possible impact zones. Throughout the week, we will begin to nail down exact timelines, precipitation-type for your location, and amounts.

This only marks the beginning of the forecasts and coverage that will be doing on this potential event. Be sure to follow Firsthand Weather on Facebook and Twitter, as we will be posting several updates per day on there.