Significant Severe Weather Event Likely Wednesday

SUMMARY:

There is a threat for some strong thunderstorms on Tuesday, with a greater threat on Wednesday. On Tuesday, the threat will be mainly south of Cullman, and only a Marginal Threat (Level 1/5) for a severe thunderstorms. Gusty winds of 40-50 MPH and heavy rainfall will be the primary threat during this time.

On Wednesday, a more widespread and more intense chance for severe thunderstorms exists as a warm front moves north. Conditions will be favorable for large hail, damaging straight-line winds (70+ MPH), and tornadoes – one or two which could be strong.

CONCLUSION

  • Round 1/2- Marginal Risk for severe storms mainly south of Cullman to Alexander City. Primary threats: small hail, gusty winds, heavy rain
  • Round 2/2- Enhanced Risk for severe storms Coverage area-wide. All modes of severe weather possible, including damaging straight-line winds of 60-70 MPH, large hail, and tornadoes – one or two which could be strong. Timing: Beginning Wednesday afternoon lasting through the evening
  • Flash flooding threat: minimal due to

DISCUSSION

…SUMMARY…
    A broad area of severe weather potential -- including risk for large
    hail, damaging winds, and several tornadoes -- is anticipated
    Wednesday from  the Arkansas/Louisiana vicinity eastward across the
    central Gulf Coast states/southern Appalachians.
 …Synopsis…
    A vigorous upper low moving across central portions of the U.S. will
    once again be the primary upper feature of interest, as it tracks
    from the Texas/Oklahoma Panhandle vicinity early, to southern
    Missouri through the end of the period.  Ahead of this system,
    moderately strong/accompanying flow will spread across the lower
    Mississippi and Tennessee Valleys and central Gulf Coast states with
    time.
 At the surface, a low is forecast to cross Oklahoma during the day,
    and then should cross the Ozarks through the evening eventually
    reaching the western Illinois vicinity by 18/12Z.  Widespread
    thunderstorms, and substantial/accompanying severe risk, can be
    expected in advance of this system.
 …The AR/LA vicinity eastward to portions of TN/GA and the FL
    Panhandle…
    Showers and thunderstorms are forecast to be ongoing from Kansas
    southward to Texas ahead of the advancing upper system and
    associated cold front, and eastward across the central Gulf Coast
    states in a zone along a west-to-east warm front.  Some ongoing
    severe risk will likely exist at the start of the period.
 With time, as moisture streams northward from the Gulf of Mexico
    beneath steepening lapse rates, modest heating will push
    surface-based CAPE into the 1000 to 2000 J/kg range with a broad
    warm sector stretching from the AR/LA vicinity eastward to the
    southern Appalachians.  Convection is forecast to increase in
    response to the destabilization, as persistent UVV occurs not only
    in the vicinity of the cold and warm fronts, but also more broadly
    within the general warm-advection regime.
 Southerly low-level flow, veering and increasing to around 50 kt
    from the west/southwest at mid levels will provide shear favorable
    for supercells.  Additionally, ample low-level shear is expected to
    evolve through the day -- particularly near the aforementioned warm
    front which should drift northward across Arkansas and align
    west-northwest to east-southeast from far southern MO to central GA
    by early evening.  As such, tornado risk may be maximized near this
    boundary -- across the AR area during the day, and then later
    increasing eastward across AL and perhaps into GA as well, as
    low-level flow increases into the evening/overnight.  
 In addition to tornado potential -- including the risk for a couple
    of significant tornadoes across a broad area represented by the
    ENH/30% risk area, large hail and damaging winds will also occur in
    some areas.  Risk will continue through the overnight hours,
    tapering from west to east across the lower Mississippi Valley but
    continuing across the central Gulf Coast states and into the
    southern Appalachians through 18/12z.

11:00 AM Winter Weather Update

Many in north and central Alabama are waking up to dry snowflakes. This snow is accumulating onto surfaces, vehicles, and likely bridges and overpasses. Slight amounts of sunshine are aiding in the drying of water on roadways, making travel slightly less dangerous – but caution is still advised – especially on bridges and overpasses. Little to no more accumulations are anticipated across north Alabama, but a Special Weather Statement is in place:

[spoiler title=”Special Weather Statement from NWS HUN”]

Special Weather Statement
National Weather Service Huntsville AL
621 AM CST Tue Feb 16 2021

ALZ001>010-016-TNZ076-096-097-162100-
Lauderdale-Colbert-Franklin AL-Lawrence-Limestone-Madison-Morgan-
Marshall-Jackson-DeKalb-Cullman-Moore-Lincoln-Franklin TN-
621 AM CST Tue Feb 16 2021

...Scattered Light Snow Showers across North Alabama and Southern
Middle Tennessee Will Continue Through Late Morning...

...Icy Roadways Will Persist Through Much of the Day Across
All of North Alabama and Southern Middle Tennessee...

Light snow showers will continue to move across portions of north
Alabama and southern Middle Tennessee through the late morning hours.
In some cases, these light snow showers may leave light accumulations
of around one half inch to inch. These kind of snowfall accumulations
will be very localized and most areas will not see much in the way
of additional impacts from the light snow flurries that are falling,
as roads everywhere are already very treacherous.

Black ice has developed across much of the road network across the
area, due to ice, sleet, and light snow accumulations. This black
ice will remain in place on area roadways throughout the day as
temperatures will remain below the freezing mark.

It will likely be exceedingly difficult, if not impossible
to travel, especially during the typical hours of the morning rush
hour commute. Bridges and overpasses, are especially at risk. Do not
assume that a well traveled road will be free of ice. Additionally,
some roads may also be blocked by falling trees or tree limbs.

For a list of affected roadways, consult local media outlets.

Stay tuned to NOAA Weather Radio, or a favorite local media outlet,
for further statements or updates from the National Weather Service
in Huntsville.[/spoiler]

There are currently Winter Weather Advisories for central Alabama that expire at noon, where small additional accumulations are possible.

[spoiler title=”Winter Weather Advisory Expiring At Noon From NWS BMX”]

URGENT - WINTER WEATHER MESSAGE
National Weather Service Birmingham AL
731 AM CST Tue Feb 16 2021

...Light Snow and Cold Temperatures May Result in some Minor Snow
Accumulations...

ALZ011>014-022-030-031-161800-
/O.NEW.KBMX.WW.Y.0005.210216T1331Z-210216T1800Z/
/O.CON.KBMX.WC.Y.0001.000000T0000Z-210216T1500Z/
Marion-Lamar-Fayette-Winston-Pickens-Sumter-Greene-
Including the cities of Hamilton, Sulligent, Vernon, Fayette,
Double Springs, Carrollton, Livingston, and Eutaw
731 AM CST Tue Feb 16 2021

...WINTER WEATHER ADVISORY IN EFFECT UNTIL NOON CST TODAY...
...WIND CHILL ADVISORY REMAINS IN EFFECT UNTIL 9 AM CST THIS
MORNING...

* WHAT...For the Winter Weather Advisory, snow. Additional snow
  accumulations of up to one half inch. For the Wind Chill
  Advisory, very cold wind chills. Wind chills as low as 5 below
  zero.

* WHERE...Portions of northwest and west central Alabama.

* WHEN...For the Winter Weather Advisory, until noon CST today.
  For the Wind Chill Advisory, until 9 AM CST this morning.

* IMPACTS...Plan on slippery road conditions. The hazardous
  conditions could impact the morning commute. The cold wind
  chills could result in hypothermia if precautions are not
  taken.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Slow down and use caution while traveling.

Use caution while traveling outside. Wear appropriate clothing, a
hat, and gloves.

&&

$$

ALZ015-017>021-023>029-032>050-161800-
/O.NEW.KBMX.WW.Y.0005.210216T1331Z-210216T1800Z/
Walker-Blount-Etowah-Calhoun-Cherokee-Cleburne-Tuscaloosa-
Jefferson-Shelby-St. Clair-Talladega-Clay-Randolph-Hale-Perry-
Bibb-Chilton-Coosa-Tallapoosa-Chambers-Marengo-Dallas-Autauga-
Lowndes-Elmore-Montgomery-Macon-Bullock-Lee-Russell-Pike-Barbour-
Including the cities of Jasper, Oneonta, Gadsden, Anniston,
Centre, Heflin, Tuscaloosa, Birmingham, Hoover, Columbiana,
Pelham, Alabaster, Pell City, Moody, Talladega, Sylacauga,
Ashland, Roanoke, Greensboro, Moundville, Marion, Centreville,
Clanton, Rockford, Alexander City, Dadeville, Valley, Lanett,
Lafayette, Demopolis, Linden, Selma, Prattville, Fort Deposit,
Hayneville, Wetumpka, Tallassee, Montgomery, Tuskegee,
Union Springs, Auburn, Opelika, Phenix City, Troy, and Eufaula
731 AM CST Tue Feb 16 2021

...WINTER WEATHER ADVISORY IN EFFECT UNTIL NOON CST TODAY...

* WHAT...Snow. Additional snow accumulations of up to one half inch.

* WHERE...Portions of central, east central, northeast,
  southeast and west central Alabama.

* WHEN...Until noon CST today.

* IMPACTS...Plan on slippery road conditions. The hazardous
  conditions could impact the morning commute.[/spoiler]

Winter Storm Watch In Effect

SUMMARY: Winter Storm Watches and Winter Weather Advisories are in effect as a strong cold front approaches from the west. Sunday night through Monday night dangerous travel conditions can be expected due to water freezing on roadways.

DISCUSSION: Light drizzle/rain will begin to change over to all heavy precipitation across northwest Alabama Sunday evening and overnight. Travel is going to be very dangerous as any precipitation will quickly freeze causing slick driving conditions. There is also the potential for ice accumulations which could freeze on branches, power lines and cause power outages.

A Winter Storm Watch has now been issued for much of the Tennessee Valley. Significant ice accumulations from Sunday evening thru Monday night will translate into very hazardous travel conditions due to ice & sleet covered roadways. Limit travel if at all possible late Sunday thru Monday night & have your Winter Emergency Kit ready!

URGENT - WINTER WEATHER MESSAGE
 National Weather Service Huntsville AL
 230 PM CST Sat Feb 13 2021
 ALZ001>005-TNZ076-096-097-140600-
 /O.NEW.KHUN.WS.A.0001.210215T0000Z-210216T1200Z/
 Lauderdale-Colbert-Franklin AL-Lawrence-Limestone-Moore-Lincoln-
 Franklin TN-
 Including the cities of Florence, Muscle Shoals, Sheffield,
 Tuscumbia, Russellville, Red Bay, Moulton, Town Creek, Athens,
 Lynchburg, Fayetteville, Winchester, Sewanee, Decherd,
 Estill Springs, and Cowan
 230 PM CST Sat Feb 13 2021
 …WINTER STORM WATCH IN EFFECT FROM SUNDAY EVENING THROUGH LATE
 MONDAY NIGHT…
 WHAT…Heavy mixed precipitation possible. Total snow and sleet
 accumulations of up to 3 inches and ice accumulations of one tenth
 to one quarter of an inch possible.
 WHERE…Lauderdale, Colbert, Franklin, Lawrence and Limestone
 counties.
 WHEN…From Sunday evening through late Monday night.
 IMPACTS…Travel could become extremely hazardous.
 ADDITIONAL DETAILS…Two periods of wintry precipitation are
 expected. A period of freezing rain or freezing drizzle is
 expected to develop Sunday evening and overnight. This will
 produce icy conditions, especially on bridges and overpasses.
 A mixture of freezing rain and sleet will develop Monday
 afternoon and last into Monday night. The precipitation may mix
 with or change to snow for a period Monday night. 
 PRECAUTIONARY/PREPAREDNESS ACTIONS…
 A Winter Storm Watch means there is a potential for significant
 snow, sleet, or ice accumulations that may impact travel. Continue
 to monitor the latest forecasts.
URGENT - WINTER WEATHER MESSAGE
 National Weather Service Huntsville AL
 230 PM CST Sat Feb 13 2021
 ALZ006-007-016-140600-
 /O.NEW.KHUN.WS.A.0001.210215T2100Z-210216T1200Z/
 Madison-Morgan-Cullman-
 Including the cities of Huntsville, Decatur, and Cullman
 230 PM CST Sat Feb 13 2021
 …WINTER STORM WATCH IN EFFECT FROM MONDAY AFTERNOON THROUGH
 LATE MONDAY NIGHT…
 WHAT…Heavy mixed precipitation possible. Total snow and sleet
 accumulations of up to one inch and ice accumulations of one tenth
 to two tenths of an inch possible.
 WHERE…In Alabama, Madison, Morgan and Cullman counties. In
 Tennessee, Moore, Lincoln and Franklin counties.
 WHEN…From Monday afternoon through late Monday night.
 IMPACTS…Travel could become extremely hazardous.
 ADDITIONAL DETAILS…Rain will change to freezing rain and sleet
 late Sunday afternoon evening and overnight. The precipitation
 may mix with or change to snow for a period Monday night. 
 PRECAUTIONARY/PREPAREDNESS ACTIONS…
 A Winter Storm Watch means there is a potential for significant
 snow, sleet, or ice accumulations that may impact travel. Continue
 to monitor the latest forecasts.

URGENT - WINTER WEATHER MESSAGE
 National Weather Service Birmingham AL
 306 PM CST Sat Feb 13 2021
 …A mixture of winter weather expected to impact west Alabama
 beginning Sunday night and lasting through Monday evening…
 ALZ011-012-014-140500-
 /O.NEW.KBMX.WW.Y.0003.210215T0000Z-210215T1200Z/
 /O.NEW.KBMX.WS.A.0001.210215T1200Z-210216T0600Z/
 Marion-Lamar-Winston-
 Including the cities of Hamilton, Sulligent, Vernon,
 and Double Springs
 306 PM CST Sat Feb 13 2021
 …WINTER WEATHER ADVISORY IN EFFECT FROM 6 PM SUNDAY TO 6 AM CST
 MONDAY…
 …WINTER STORM WATCH IN EFFECT FROM MONDAY MORNING THROUGH
 MONDAY EVENING…
 WHAT…For the Winter Weather Advisory, freezing rain expected.
 Total ice accumulations of around one tenth of an inch. For the
 Winter Storm Watch, a mixture of freezing rain and sleet likely.
 Total ice accumulations of one tenth to three tenths of an inch.
 WHERE…Marion, Lamar and Winston Counties.
 WHEN…For the Winter Weather Advisory, from 6 PM Sunday to 6
 AM CST Monday. For the Winter Storm Watch, from Monday morning
 through Monday evening.
 IMPACTS…Power outages and tree damage are possible due to ice
 accumulations. Travel could be nearly impossible. 
 PRECAUTIONARY/PREPAREDNESS ACTIONS…
 A Winter Weather Advisory means that periods of sleet or freezing
 rain will cause travel difficulties. Be prepared for slippery
 roads and limited visibilities…and use caution while driving.
 A Winter Storm Watch means there is a potential for significant
 accumulations of freezing rain or sleet that may impact travel.
 Monitor the latest forecasts for updates on this situation.