Another shot for severe thunderstorms and tornadoes, including some strong tornadoes, possible for the South on Thursday. A Level 4 risk of severe thunderstorms is in place Thursday for a good chunk of the South, including Jackson, MS; Memphis, TN; Birmingham, AL; and Nashville, TN.
The severe threat will start west of the Mississippi River early in the day and spread east throughout the afternoon and evening hours. It is possible parts of the Level 4 risk area may be upgraded to a Level 5.
A dangerous severe weather outbreak will unfold across parts of the country over the next three days. This severe weather outbreak will lead to strong, violent tornadoes, large hail and damaging winds.
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Wednesday is shaping up to be the first significant severe weather and high-impact tornado threat for Dixie Alley and the Mid-South. A potent upper level storm system will approach the region, allowing a surface low to develop and intensify, pulling in deep moisture and warm air into the region.
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With the increased moist and warm airmass at the surface, and colder air moving over the region with the approaching upper-level storm system, the Convective Available Potential Energy (CAPE) will be high in the Mid-South and Dixie Alley. The higher the CAPE values, the more unstable the atmosphere; thus, producing stronger updrafts, leading to more severe weather possibilities.
The approaching upper-level storm system will provide favorable wind speeds and directions across the region. Winds will change directions and speed with height, which provides a favorable environment for severe thunderstorms and tornadoes. This is known as directional and speed shear. Directional shear is wind direction changing with height while speed shear is the change in wind speeds with height.
Strong vertical wind shear is crucial for the development and longevity of severe thunderstorms, and wind shear looks favorable for severe thunderstorms late-Wednesday. From 500 mb (around 18,700 feet) down to 925 mb (around 2,500 feet), the winds change direction and speed, which suggests severe thunderstorms and tornadoes are possible with other favorable atmospheric parameters.
The aforementioned setup indicates not only significant severe weather is possible but tornadoes are also possible late-Wednesday. When looking at such a setup, it is important to look dive into the history and look at similar weather patterns in the past and investigate what they have produced. This is known as analogs.
Looking at the analogs, they indicate similar atmospheric events in the past have led to strong, long-track tornadoes across the region, so this event needs to be monitored closely! It should be noted: this is still far out so the specifics cannot be identified at this point but that will be ironed out over the coming days.
This is supported by the significant tornado parameter values Wednesday afternoon across the region. The significant tornado parameter is a complex composite index, consisting of multiple ingredients. It factors in 0-6 km bulk wind difference (6BWD), 0-1 km storm-relative helicity (SRH1), surface parcel CAPE (sbCAPE), and surface parcel LCL height (sbLCL). To put this in laymen terms, it’s a great tool to identify where strong tornadoes may occur. High significant tornado parameter values are forecast to be present, which suggest tornadoes, some strong or violent, are a possibility across parts of western Tennessee, Mississippi, and western Alabama.
While there are considerable questions surrounding this event, it appears thunderstorms will develop early-Wednesday west of the Mississippi River in Arkansas and Louisiana. These storms will move east through Wednesday afternoon into Wednesday evening for areas east of the Mississippi River, including Tennessee, Mississippi, Alabama, and eventually Georgia, and the Florida Panhandle.
Due to the severe potential, the Storm Prediction Center has highlighted the Mid-South and Mid-Mississippi Valley for severe weather Wednesday. A Level 3 risk for severe weather is in place Wednesday for the red shaded area. This includes southwestern Tennessee, eastern Arkansas, northeastern Louisiana, Mississippi, and Alabama. A Level 2 and Level 1 risk surrounds the Level 3 risk in the orange and yellow shaded areas.
Now is the time to prepare! Do not panic but have a plan in place in case a Tornado Watch or Tornado Warning is issued for your area. Make sure you have a few reliable sources to receive weather information from as this event approaches.
It is also a good time to refresh your memory on tornado terminology. A tornado watch means conditions are favorable for tornadoes to form. A tornado warning means a tornado has been indicated or spotted. A tornado emergency means a severe threat to human life and catastrophic damage to property is likely.
A historic winter storm will cripple parts of the Rockies and Plains over the weekend. Some areas will experience feet of snow, which will create significant travel impacts, allow for power outages, as well as damage to trees. A few areas that will see the biggest impacts are Colorado, Wyoming, and parts of Nebraska.
A potent upper-level system is moving over the Southwest. This system will move northeast into the Rockies over the weekend, followed by the Plains early next week. Deep moisture is feeding north ahead of the system, which will contribute to the heavy snow as the moisture is forced up the Front Range of the Rockies.
Current Winter Weather Alerts
A plethora of winter weather alerts have been issued across Colorado, Wyoming, and parts of Nebraska. A blizzard warning is in effect for southeastern Wyoming and the northern Nebraska Panhandle where heavy snow and strong winds will lead to white out conditions. A winter storm warning has been issued for central Colorado, southern & central Wyoming, the southern Nebraska Panhandle, and South Dakota where heavy snow will fall. A winter storm watch has been issued for parts of northwestern Nebraska and southwestern South Dakota for heavy snow potential.
Snow Accumulations and Impacts
Heavy snow and strong winds are likely for the Front Range of the Rockies and the Plains, leading to whiteout conditions. 1 to 2 feet of snow will fall along the I-25 corridor in the region. The 1 foot totals will extend into the western Plains. Parts of the Front Range may see 3 to 4 feet of snow. Heavy snow accumulations of a foot will extend south into the northern mountains of New Mexico. Denver, Cheyenne, Fort Collins, and Boulder will see significant accumulations.
The winter storm is currently over the Southwest and will begin impacting all of the Four Corners states overnight Friday into Saturday. The snow will also begin impacting slight impacts from the system in the Plains and Front Range of the Rockies overnight Friday.
Bigger impacts will arrive for the Front Range of the Rockies and the Plains Saturday through Sunday. Heavy snow and wind will stick around through the entire weekend, continuing into early-Monday morning before shutting down.
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.
Laura has begun to develop deep convection (thunderstorms) over the past several hours as it skirts along the southeastern Cuba coastline. We expect Laura to mostly continue on a northwestward trajectory on Monday, and even though it’ll continue riding along the southern Cuban coastline for another 24 hours or so, part of the storm will remain over open water the entire time. Sea surface temperatures south of Cuba run in the 30-31°C (~86-88°F) range, which are more than sufficient to allow Laura to maintain its current intensity or even strengthen in the short-term, despite its interaction with the mountainous terrain of Cuba.
Most model guidance a couple days ago had Laura’s center moving through Cuba, but the storm has had a tendency to move a little farther south than most model projections. When a tropical cyclone moves parallel to a chain of landmasses, especially ones that have mountainous terrain, a few dozen mile difference in track can make a dramatic difference in current intensity, subsequent intensity change, and even track. As Laura emerges over the Gulf of Mexico by early Tuesday, we anticipate that the system will be more intact than it otherwise would have been. Thus, it should take less time for Laura to capitalize on the anomalously warm waters beneath it.
A strong, deep-layer high pressure system currently sits just off the Southeast coast, which currently places Laura to the south of the feature. As Laura treks northwestward, this ridge will continue expanding westward, which will prevent the storm from simply turning northward toward Florida once departing Cuba. Hurricane Marco will actually help strengthen the ridge as well. Tropical cyclones, like Laura and Marco, extract heat energy from the underlying ocean via evaporation. This process helps further moisten the air above, and that heat from the ocean gets released into the atmosphere when clouds and deep thunderstorms develop. Thanks to Marco assisting in the strengthening and westward expansion of the ridge, Laura will continue on a northwestward track longer, which 1) will give Laura more time over the warn Gulf of Mexico and 2) will put Louisiana/Texas at a higher risk for a Laura landfall.
Marco will stay weaker due to a mid-to-upper level trough that currently extends southwestward into eastern Texas/northeastern Mexico and over the Gulf of Mexico. Thus, Marco will encounter vertical wind shear, keeping its intensity at bay. However, the trough will retrograde westward by the time Laura makes it into the Gulf of Mexico, which means that Laura should encounter considerably less wind shear.
We expect Laura to rapidly intensify over the Tuesday to Wednesday timeframe, which corresponds to an intensity increase of at least 35 mph (30 knots) over a 24-hour period. The National Hurricane Center currently predicts that Laura will reach upper-end category 2 status in 72 hours. However, it’s possible that most model guidance is underestimating how much strengthening will occur, especially if Laura’s low/mid-level center manages to stay mostly off the Cuban coast over the next 24 hours. Also, Laura is expected to move at a relatively fast pace over the Gulf of Mexico, which will decrease the odds that upwelling of cooler sub-surface ocean waters will hinder Laura’s intensification. Thus, it’s plausible that Laura could become a category 3+ storm.
With all of this said, it’s very important to understand that severe winds are not the only hazard associated with hurricanes. While the strongest winds remain closest to the storm center, flooding often becomes a much more widespread risk, well away from the center. As of now, the heaviest rainfall will fall across much of the Mid-South and potentially extend into eastern parts of the Southern Plains. In the projected 7-day rainfall totals, the axis of heaviest rainfall totals curves around the periphery of the westward-expanding ridge, which corresponds with Laura’s projected path.
We’ll reassess the forecast again on Monday to determine the effect that Laura’s interaction with Cuba will have on its intensification in the Gulf of Mexico. Please understand that the forecast will likely change, especially over the next 24 hours, but afterwards, forecast confidence will hopefully increase.