March 1st was the first day of meteorological spring, and now spring-like thunderstorms are in the forecast over the next several days. Severe thunderstorms will begin over the Southern Plains and slowly spread east into the Mid-South.
The severe thunderstorm event will be triggered by the jet stream plunging south over the western-half of the lower-48. This dip in the jet stream will create a nice uptick in moisture across the western lower-48, including parts of California and the Four Corners states (YAY!). What comes down, must go up! A seesaw will take place. As the jet stream dips over the western lower-48, the jet stream will surge north over eastern parts of the country, which will lead to well above average temperatures.
This pattern will set the stage for severe thunderstorms from the Southern Plains into the Mid-South as gulf moisture and warmth feeds north, east of the Rockies, along with strong winds and colder temperatures slowly spreading east in the upper-levels of the atmosphere.
Severe thunderstorm forecast
The first threat for severe thunderstorms begins Wednesday across the Southern Plains. The main area to see thunderstorms will occur from western Missouri, southwest into central and eastern Kansas, down into central Oklahoma. The main hazards are gusty winds and hail.
The severe thunderstorm threat continues Thursday, slightly shifting south. The main area to see thunderstorms will occur from southern Missouri, southwest into southern Kansas, down into central and western Oklahoma as well as western Texas. The main hazards are gusty winds and hail.
Friday, Saturday, Sunday
A more impactful severe weather threat begins Friday, continuing through the weekend as the dip in the jet stream out west begins to move east. This will allow the hail and wind threat to continue along with an uptick in the chance for tornadoes.
The enhanced severe threat will begin Friday across far southern Kansas, northern and western Oklahoma, extending down into northwestern Texas.
The severe thunderstorm risk area expands on Saturday from southern Kansas, all of Oklahoma, down through northern and central Texas.
By Sunday, the severe threat slowly shifts east into the Mid-South. Eastern Kansas, southern and central Missouri, eastern Oklahoma, eastern Texas, Arkansas, northern and central Louisiana, far western Tennessee, and far northwestern Mississippi will all be under the gun for severe thunderstorms.
All modes of severe thunderstorms are possible Friday, Saturday, and Sunday.
As the dip in the jet stream advances east early next week, the associated cold front will seep into the Ohio Valley and Southeast. The thunderstorm threat will shift east, too, but there are too many uncertainties at this point for a severe hazard to be outlined.
All eyes are on an upper-level low over the Southern Plains. This upper-level low will race to the east overnight into Saturday and begin to open into a shortwave over the Mid-South tonight. Despite the upper-level system opening into a shortwave, it will be rather vigorous as it moves into the Southeast on Saturday.
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As the shortwave treks over the Southeast, strong lift, and a gradual moistening of the atmosphere will occur. This will lead to an uptick in cloud cover across the South & Southeast beginning tonight and continuing through Saturday morning. A light band of precipitation should develop with the increased lift ahead of the shortwave overnight into early-Saturday morning across northeastern Alabama, northern Georgia, far southeastern Tennessee, southeastern North Carolina, and far western Upstate South Carolina.
Initially, the precipitation from this band will fall into dry air at the surface; thus, the majority of the precipitation will evaporate before reaching the surface. This evaporation process will lead to a gradual moistening of the atmosphere, leading to precipitation reaching the ground Saturday morning. The precipitation band will increase in coverage and intensity throughout the morning hours Saturday. Here is where the forecast gets interesting. The temperature profile of the atmosphere is supportive of a rain/snow mixture. Almost the entire column of the atmosphere, from the ground to where the jets fly, will be below freezing. This will allow snow or a rain/snow to fall across the aforementioned regions.
High-resolution models are suggesting .05″ to .20″ of precipitation falling across northeastern Alabama, northern Georgia, far southeastern Tennessee, southeastern North Carolina, and far western Upstate South Carolina.
With temperatures supporting wintry weather, precipitation amounts of .05″ to .20″ would equate to a few areas seeing accumulating snow. Models are suggesting up to 1″ of snow possible.
Firsthand Weather is forecasting flurries from northeastern Alabama, northern Georgia, far southeastern Tennessee, southeastern North Carolina, and far western Upstate South Carolina Saturday morning with light accumulations possible across the higher terrain of northeastern Georgia. Within this area of accumulations, due to banding, isolated 2″ amounts cannot be ruled out but most areas will see lesser accumulations.
It should be noted: this event is marginal. Slight deviations in weather variables may significantly change the forecast so keep checking back for updates.
It is now meteorological spring but why does the calendar say spring starts on March 20?
Meteorological seasons are based on the annual temperature cycle and are more consistent for that reason. Astronomical spring, March 20, is based on the position of the Earth in relation to the sun. It is also called the vernal equinox, which marks the moment the sun’s rays are shining directly on the equator. This is when the day and night are equal lengths.
Meteorologists like to break down the seasons into three-month groups, which consist of winter (December, January and February), spring (March, April and May), summer (June, July and August), and fall (September, October and November). Hence, why it is now meteorological spring. Meteorological spring, March 1st through May 31st, is the transition period between the three coldest months and the three warmest months of the year.
Regardless of meteorological spring or astronomical spring, the days are getting longer–a lot longer! Most of the lower-48 will gain at least 50-minutes of daylight throughout the month of March. This is wonderful news for all of you outdoors people, gardeners, and farmers.
The northwestern Gulf of Mexico is still recovering from the February Arctic intrusion that impacted Texas. As of early-March, water temperatures are well below average. The below average water temperatures will undoubtedly have an impact on convection and severe thunderstorms west of the Mississippi throughout March.
The Gulf of Mexico waters are an important variable in convection and severe thunderstorms for areas east of the Rockies. Generally speaking, when the Gulf of Mexico water temperatures are above average, this leads to more instability for convection and severe thunderstorms by supplying the atmosphere with added moisture and warmth. Instability acts as fuel for thunderstorms, and many times, the greater the instability, the stronger the thunderstorm if other variables are favorable. Thus, the added moisture and warmth bolsters instability, creating increased severe thunderstorms.
Research shows the warmer the Gulf of Mexico water temperatures, the more hail and tornadoes occur throughout March, April, and May. With the water temperatures running below average in the northwestern Gulf of Mexico, it is possible this will have implications on convection and severe thunderstorms throughout the month of March due to the decreased availability of moisture and warmth added to the atmosphere. This may lead to less intense convection or a decrease in tornado and large hail frequencies during the month of March for areas west of the Mississippi River. It should be noted: severe thunderstorms are still possible throughout March but the frequency and intensity may be impacted. Areas farther east into Dixie Alley and the Southeast will likely not see a decrease in thunderstorm intensity and frequency as Gulf of Mexico water temperatures are above average in the eastern-half of the Gulf.
Above average temperatures are forecast for the region throughout March so this will allow the Gulf of Mexico water temperatures to slowly recover, possibly returning to average or even climbing above average by April, which could lead to an increase in severe weather during April and May.
A strong shortwave approaching the Southern Plains has already resulted in a precipitation shield developing across much of Oklahoma and upper Texas. As the wave treks across the two states overnight, precipitation will fill in across the eastern half of Texas tonight before doing the same across Arkansas, Missouri, and Louisiana overnight into Wednesday morning. The Arctic air mass remains well entrenched over much of the Southern Plains and Mid-South. Surface high pressure over the Ohio Valley will begin departing eastward of Wednesday, but with recent snow/sleet cover, plenty of cold air will remain in place to help pull off another powerful winter storm across recently impacted areas.
In this article, I will focus primarily on the ice storm threat with the coming system. A mixture of freezing rain and sleet will likely lead to scattered to widespread power outages across parts of eastern Texas, lower Arkansas, Louisiana, and Mississippi on Wednesday/Wednesday night and across parts of North Carolina and the Virginias on Thursday.
Southern Plains & Mid-South Ice Storm Impacts and Timeline
Temperatures will continue to plummet overnight tonight across the Plains and Mid-South. Widespread 20s already overspread the region of interest, and many of those areas will drop into the teens overnight. Precipitation will reach Arkansas, far northern Louisiana, and northwestern Mississippi early enough Wednesday to fall mainly as snow at first. An associated surface low will skirt along the southeast Texas and then across the Louisiana coast on Wednesday. This low will transport warmer air overtop colder air at the surface. This warm nose will lead to a nasty freezing rain moving across eastern Texas, the northern two-thirds of Louisiana, lower Arkansas, and western/central/northern parts of Mississippi.
Due to strong, low-level warm air advection, the latest NAM guidance results in freezing rain/sleet transitioning to a cold rain more quickly across much of Louisiana and Mississippi later on Wednesday. Warm advection will partially be offset by melting on Wednesday, since the ice-to-liquid phase change is a cooling process. Plus, dry air in the low levels will result in evaporational cooling keeping colder air in place for longer. For these reasons, I favor the colder HRRR model guidance, which has an ice storm impacting areas farther to the south. The latest HREF ice accretion projections for Wednesday and Wednesday night provides some idea as to where the heaviest freezing rain accumulations will occur. A large swath of 0.5-1+ inch freezing rain accumulations could fall, resulting in widespread power outages. Due to the self-limiting nature of ice storms, freezing rain accumulations these high can be challenging to reach. However, surfaces already well below freezing will allow accumulations to occur immediately. To provide some perspective, amounts as little as 0.05-0.1 inches can cause major issues on roads, especially on bridges and overpasses.
Carolina and Mid-Atlantic Ice Storm Impacts and Timeline
The surface high across the Ohio Valley on Wednesday will shift into New England late Wednesday into Thursday. Surface ridging will build down the east side of the Appalachians, setting up a cold air damming setup. As mid-level ridging along the East Coast amplifies on Thursday, the surface low along the Gulf coast will take on a northeastward trajectory. As the feature moves across central Georgia and South Carolina during the day, rain will overspread much of the Southeast. However, enough cold air at the surface will allow a major ice storm to unfold across western/central/northern parts of North Carolina, much of Virginia, southeastern West Virginia, and into the Delmarva peninsula.
Strong warm air advection in the low levels will eventually result in a transition from sleet and/or freezing rain to a cold rain across upper South Carolina and lower parts of North Carolina. The timing on this transition will determine ice totals in that region. The latest HRRR guidance doesn’t depict any significant totals since it has sleet transitioning directly to rain, but HREF ensembles indicate a more prolonged period of freezing rain down to the North Carolina/South Carolina border. Ice totals in northern Virginia into the Delmarva peninsula should receive lower ice totals relative to areas to the south due to more snow in the beginning. For areas in between, the ice storm could bring totals reaching or even exceeding 0.25-0.5 inches.
A longwave trough with quite a broad base will remain almost stationary across the northern half of the U.S. this upcoming week into at least next week. A ridge will persist just off the West Coast, while a block sits over western Greenland. Another ridge will remain positioned over the southeastern quadrant of the U.S. This ridge will initially keep temperatures well above average across the Southeast; however, northern troughing will prohibit the ridge from amplifying unabated. A baroclinic zone will become established across the Southern Plains, Mid-South, Missouri Valley, Tennessee Valley, Southeast, Ohio Valley, and Mid-Atlantic. This setup will bring several opportunities for snow, ice, and rain across the mentioned regions over the next two weeks.
We discussed around a week ago how longwave troughing can suppress the storm track too far southward to bring any meaningful wintry precipitation. Instead, conditions are generally very dry and cold. If you recall, model guidance had a lobe of the tropospheric polar vortex digging as far south as the Tennessee Valley for early this week. Instead, we got a flatter trough with some Southeast ridging. In most guidance now, we’re stuck with a long-lasting broad-based trough that likely won’t keep the southern stream storm track suppressed.
Cross polar flow extending from Siberia over into western Canada has allowed Arctic air to pool over western Canada. That brutally cold airmass has already begun spilling into the upper Plains and Midwest. But essentially, we now have the available cold air to tap as numerous storm systems parade from the Southwest/Southern Plains in an east or northeastward direction. One major drawback to the expected pattern configuration is that ice (sleet/freezing rain) could become the more predominant frozen precipitation-type across the Southern Plains, Mid-South, Southeast, and even into the lower Ohio Valley and Mid-Atlantic. With broad troughing centered across the central U.S. and a Southeast ridge to the east, southwesterly flow will transport warm air above the surface. However, Canadian high pressure will wrap around very cold air at the surface. This will produce atmospheric profiles that support sleet/freezing rain versus snow.
Systems We’re Currently Watching
We have a slew of systems we’re currently watching that will bring impacts in the foreseeable future. We’re going to post articles and social media updates on each system individually, but we will introduce those threats here.
February 10-12, 2021 (Wed.-Fri.): Shortwaves embedded in mostly westerly flow will bring widespread precipitation across the Southern Plains, Mid-South, Missouri Valley, Southeast, Tennessee, along and south of the Ohio River, and the Mid-Atlantic. Canadian high pressure has continued to advect cold air at the surface across northern portions of where precipitation will develop. We expect a prolonged period of sleet/freezing rain to fall across northern Texas, central/eastern Oklahoma, northern/central Arkansas, lower Missouri, western Tennessee, upper Mississippi, and Kentucky. North of the Ohio River and areas across much of the Mid-Atlantic will experience mostly snow, although lower and central parts of the Virginias may get a mixture of snow/ice. For areas south, expect rain.
February 13-14, 2021 (Weekend): Forecast model guidance indicates HIGH uncertainty for this potential event. The outcome of this potential winter storm depends on the interaction of three features: a shortwave entering lower California late week, a shortwave entering the Pacific Northwest around the same time, and a lobe of the tropospheric polar vortex spinning over the northern Plains/Midwest. The European model continues to indicate that the California wave gets suppressed so far south that it passes across the Gulf of Mexico. This feature would bring rainy conditions to Florida and areas along and relatively close to the Gulf coast over much of the weekend. On the other hand, the GFS often has the California wave phasing with the Pacific Northwest wave somewhere over the central U.S. This scenario would result in the phased systems eventually taking on a northeastward trajectory. This scenario would potentially bring a significant winter storm to the central/southern Plains, the Mid-South, the Missouri Valley, the lower Midwest, the Ohio Valley, the lower Great Lakes, and Northeast over the weekend. I will admit that this is a tough forecast, and at the moment, I need additional time to study this event.
February 15-17, 2021 (Mon.-Wed.): A strong shortwave will enter the western U.S. later in the weekend and dig southeastward into the Four Corners region. As the wave continues eastward, the tropospheric polar vortex lobe will move eastward across the Great Lakes and Northeast. These two features will create a region of confluent flow across the Ohio Valley and Mid-Atlantic/New England, which will support Canadian high pressure moving eastward into the Northeast. This high will likely result in cold air damming as far south as the Carolinas and Georgia. A surface low will likely develop along the Gulf coast in response to the shortwave approaching the region. Cold air will already be in place across the Southern Plains, Mid-South, and much of Tennessee to support wintry precipitation. With cold air damming in place, the Carolinas, northern Georgia, and northeastern Alabama need to closely monitor the potential for an ice storm next week. This system could potentially bring an impactful winter storms to parts of the Ohio Valley, Mid-Atlantic, and (maybe) the Northeast. We have about a week to get into specifics. I advise against making any changes to current plans until confidence increases over the next two to three days.
A potent shortwave will dive southeastward across the Rockies and enter the Southern Plains on Wednesday. The feature will develop into a closed low on Thursday over the Mid-South, triggering the development of a surface cyclone along the Gulf coast the same day. By early Friday, the system will reach the Georgia/South Carolina coast and trek up along the Southeast coast on Friday.
This system has a chance to bring a round of accumulating snowfall on Wednesday to far eastern Oklahoma and Kansas, northwestern Arkansas, southern/western Missouri and areas northward on Wednesday. A snowstorm will impact parts of the Southeast late Thursday into Friday, potentially including far northern Alabama and Georgia, eastern Tennessee, far southeastern Kentucky, far southern Virginia, Upstate South Carolina, and western/central North Carolina.
As the low strengthens late Thursday into early Friday, a warm nose will attempt to works its way into southeastern Tennessee, northern Georgia, northern South Carolina, and western North Carolina. However, the passage of the strong mid-level closed will offset the magnitude of warming that otherwise would have occurred in the low levels. Strong frontogenesis across northern Georgia, upstate South Carolina, and central North Carolina could provide the necessary forcing to bring the freezing/melting level close to the surface in those areas. Evaporational cooling will also initially lower temperatures at and just above the surface. Despite lackluster cold in place across lower elevation regions in Georgia, the Carolinas, and even Southeast Tennessee, the dynamics of this storm system may actually ‘make up’ for it. Plus, the system will pass during a timeframe when temperatures are normally colder anyway (at night and early morning!).
We have quite an interesting scenario taking shape for the end of the week. The surface low on Thursday into Friday will take the classic track that favors significant winter weather across the Southeast. However, the pre-existing air mass across the region will only be marginally cold. Although colder air will get wrapped around the backside of the storm system, even it will be marginal. As a result, most regions across the Mid-South and western half of the Southeast region will likely just get a nasty, cold rain on Thursday.
Snow Accumulation Forecast (Attempt #1)
I included a 5–10+ inch accumulation zone in the mountains of Georgia, South Carolina, North Carolina, and Tennessee, where soil temperatures are already relatively cool and low-level temperatures should be sufficient for snow (or a rain to snow transition).
I expect noteworthy accumulations to fall across the Cumberland Plateau, far northern Alabama, northern Upstate South Carolina, and western central North Carolina. A transition of rain to snow will likely occur as the mid-level and surface low wraps around colder air.
Far southeastern Kentucky and lower Virginia could get accumulating snow; however, if the surface low jogs slightly south, most precipitation will remain south of the area.
I outlined a region in pink, where this storm system could potentially bring unexpected accumulating snowfall. I currently have included the northern metro of Atlanta in this zone. Again, strong forcing will need to offset the very marginal air mass in place. Otherwise, expect a cold rain.
I expect only a cold rain across the rest of the Southeast and Mid-South.
Please stayed tuned for subsequent forecasts on this potential winter storm. Don’t forget to download our Southern Snow app. Our app provides you with snow forecasts from both Firsthand Weather AND your local National Weather Service office. Check it out!
Now that we’re less than 7 days from Christmas, our Southern Snow app will provide you a super-localized forecast on the upcoming snow potential this Christmas week. Our written forecast discussions, such as this one, should provide a nice ‘heads up’ that may or may not be currently reflected in the daily forecasts. You sort of get the best of both worlds if you have the app.
A strong shortwave will enter the Pacific Northwest on Tuesday and sweep across the Rockies on Tuesday and Wednesday. This system will add to existing snow cover across the Cascades, the northern Sierra Nevada region and most of the Rockies, ensuring a White Christmas.
Snow cover from last week’s nor’easter will begin rapidly melting on Christmas Eve and Christmas Day. However, areas that picked up feet of snow across the Mid-Atlantic and Northeast will still have snow cover from the event, even at lower elevations.
The upper Midwest and the Great Lakes region will have several opportunities for snow in the coming days. A weaker system will pass through the area early this week, and a stronger storm system will set the stages for lake-effect snow on the backend on Christmas Eve and Day.
The same mid-week system has the potential to bring noteworthy snow accumulations to areas along and west of the Appalachians, along with western areas of New York.
One could make the argument that some areas included in the possible probabilities category should eventually get bumped up to moderate chances. I concur. As one shortwave swings across the Midwest and Great Lakes mid-week, another wave will dig southeastward into the Plains and mid/lower Mississippi Valley. As a result, a second surface low could develop farther south early Christmas Day, bringing snow chances as far south as eastern Tennessee and the northern Gulf coast states.
The air mass behind the advancing strong cold front will be very dry, so there remains much uncertainty on moisture availability. Nonetheless, snow-to-rain ratios will be high behind the front, so even a little moisture and lift would do the trick. Climatologically, these setups have a relatively high probability of being a bust for snow, especially farther south. However, if I see that short-range guidance supports higher totals, I’ll probably need to bump up probabilities to a moderate for some.
Before coming eastward, the same wave will have the potential to produce accumulations east of the Rockies across Colorado, Wyoming, and into parts of the Northern/Central Plains before Christmas Day. It’s quite likely some of those areas will get pushed into moderate probabilities in a subsequent update by Firsthand Weather.
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This week’s storm system of interest has now moved away from the West Coast and begun to dig into the Four Corners region. The vigorous shortwave will continue amplifying across the Southern Plains on Tuesday. By Wednesday, it’ll begin lifting east northeastward across the Mid-South, Mississippi Valley, and Tennessee Valley. Later Wednesday, the wave will push into the Ohio Valley, the Mid-Atlantic, and New England, bringing a powerful winter storm along the East Coast from Wednesday into Thursday.
After dropping snow across the Rockies, precipitation will develop along and ahead of the shortwave across the central and southern Plains on Tuesday. The wave will trigger the development of a surface low along the Gulf coast on Wednesday, as a large swath of precipitation overspreads the Southeast, Tennessee Valley, Ohio Valley, and Mid-Atlantic. Precipitation will then begin to overspread southeastern New England by Wednesday evening, continuing into Thursday. Rain and possible storm development in the warm sector of the system will aid in the amplification of a downstream ridge. The strength of this ridge will determine how closely the surface low rides along the Mid-Atlantic and southeastern New England coast after departing North Carolina and Virginia.
Forecast Model Discussion
The operational, along with many of its ensemble members, have continued to show a more southern track of the surface low, primarily due to a weaker downstream ridge. In such a scenario, the axis of heaviest snowfall rates and accumulations would occur from around D.C. (and northern Virginia) to Philly to Long Island to Cape Cod. Areas just northwest of this line would still get noteworthy but lower amounts. The GFS-parallel, a version of the GFS still in its testing phase, has consistently been the northern outlier. This solution would largely be a miss for D.C., Philly, New York City, Long Island, and Cape Cod, but copious amounts of snow would fall northwest of this line, including over Boston.
The European model, along with the shorter-range 12km NAM, has the surface low trekking quite close to the Mid-Atlantic after moving just offshore. Both models keep the low far enough off the southeastern New England coast for the heaviest snow accumulations to still fall over Philly, NYC, Long Island, and Cape Cod.
Most model guidance indicates that downstream ridging mid-week will be flattened by the current storm system exiting New England today. However, this ridge should be more amplified than what models suggest. For that reason, I gave the GFS-parallel and the shorter-range RGEM model (not discussed above) more weight in the snow accumulation forecast below. If there’s not a northward shift in most model guidance by tomorrow afternoon, I’ll adjust my forecast to align more closely with the operational GFS, European, and other short-range guidance.
Matthew’s Snowfall Accumulation Forecast for Select Cities
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