Special Weather Statement, NWS Huntsville, AL

Area Forecast Discussion
National Weather Service Huntsville AL
240 PM CDT Sat Jun 12 2021

.NEAR TERM...(Remainder of this Afternoon and Tonight)
Issued at 200 PM CDT Sat Jun 12 2021

Visible satellite imagery and sfc observations early this afternoon
has indicated convergence of the low-lvl wind field aligned
generally N-S across central parts of the area. This is taking place
underneath a southward moving vort max, and combined with the humid,
unstable environment, showers and thunderstorms have developed in the
region. The main dynamic forcing so far has generally confined
convection along the N-S axis from Lincoln County southward into
Morgan County. Convection-generated outflow boundaries have caused
further convection to develop outside of the main convergence axis
and this is likely to continue into the afternoon and early evening.
In the moist environment, SBCAPE values have been analyzed ~5000
J/kg, while MLCAPE values are a respectable ~3500 J/kg. Low-lvl lapse
are around 8 C/km and PWATs ~1.7-1.9 inches. Due to the
orientation/magnitude of shear vectors and thermodynamic setup, cells
are pulsing up very rapidly, but are tending to become sheared
quickly while pulsing down rapidly as well. Nevertheless, the
environment is giving rise to a damaging wind threat with convection
this afternoon. Further convection will tend to develop along outflow
boundaries, with some further dynamic support from the N-S
traversing short wave. As insolation begins to wane later this
afternoon into the early evening however, the activity will likewise
gradually decrease in coverage/intensity.

Otherwise, fog may tend to develop later tonight, especially in
locations which received heavy rainfall today. Thus, at this point,
some fog would appear likely in areas from Lincoln southward into
Morgan and Cullman Counties later tonight.

.SHORT TERM...(Sunday through Monday)
Issued at 200 PM CDT Sat Jun 12 2021

On Sunday, another short wave will rotate southward across the
region, although timing with this one is a little more uncertain,
with some disagreement among global/regional models. Nevertheless, a
moist, unstable air mass will again be in place on Sunday (similar
to today), with PWs ~1.7-1.9 inches, 0-3km lapse rates ~8 C/km and
MLCAPE values again north of 3000 J/kg. Deep layer shear will again
be limited under a deep layer northerly wind flow regime. So, cells
will tend to pulse up/down rapidly with north to south movement. Given
thermodynamic parameters, a damaging wind threat would be present
again tomorrow, especially during during peak heating in the
afternoon. Thunderstorms will also be very heavy rainfall producers,
so a slight risk for local flash flooding in low-lying areas and in
urban areas will be present.

Sunday will likely represent the last day for shower and thunderstorm
activity for several days as an air mass change will begin to take
shape early next week. On Monday, upr level ridging will move
southward across the region during the morning before deep northerly
again returns to the area. Ahead of an impending upr trough, warm
low-lvl temps will ensure another hot day, but dew point
temperatures will gradually begin to fall, with temperatures feeling
a little cooler than today or Sunday.

.LONG TERM...(Monday night through Friday)
Issued at 200 PM CDT Sat Jun 12 2021

A high-amplitude ridge (West CONUS) and trough (East CONUS) pattern
will begin to take shape by Tuesday. Cool/dry air advection will
begin in the TN Valley on Tuesday as a modified Canadian air mass
moves into the region. This air mass will be present for much of the
week, and dew point temperatures will likely mix down into the 50s
during the afternoons beginning as early as Tuesday, but certainly by
Wednesday, extending perhaps into Friday. With the low moisture
environment in place, diurnal convection will not occur. The only
other potential for shower/thunderstorm activity will occur from NW-
SE digging shortwaves around the western flank of the broad upr
trough. However, the main effects from these features are expected to
occur well to our N-NE, and this will represent the only caveat to
the dry forecast at this time.

Otherwise, a reinforcing/digging trough will begin to develop by next
weekend with a possible attendant sfc front crossing southward into
the area on Saturday. Showers and thunderstorms may occur with this
front, with only 30 POPs in the forecast for Saturday at this time, due
to uncertainty with timing and southward extent of the front.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1230 PM CDT Sat Jun 12 2021

An upper-lvl system will be moving southward across the area this
afternoon, instigating SHRA/TSRA development. In fact, an area of
SHRA/TSRA has already developed and will likely impact KHSV through
~21Z. Given sctd nature of TSRA activity, TEMPO group will address
threat/impact for KHSV. If the strongest part of cell impacts the
location, vis/ceiling impacts could be further decreased to IFR
range. SHRA/TSRA may develop near KMSL later as upr-low moves SWRD
across the area, but lower confidence in impacts there. SHRA/TSRA
activity is expected to decrease with the loss of daytime heating and
as the upr-lvl system begins to move away especially after 21-00Z.

&&

.HUN WATCHES/WARNINGS/ADVISORIES...
AL...NONE.
TN...NONE.
&&

NEAR TERM...KDW
SHORT TERM...KDW
LONG TERM...KDW
AVIATION...KDW

For more information please visit our website
at weather.gov/huntsville.

Hazardous Weather Outlook
National Weather Service Huntsville AL
245 PM CDT Sat Jun 12 2021

ALZ001>010-016-TNZ076-096-097-131100-
Lauderdale-Colbert-Franklin AL-Lawrence-Limestone-Madison-Morgan-
Marshall-Jackson-DeKalb-Cullman-Moore-Lincoln-Franklin TN-
245 PM CDT Sat Jun 12 2021

This Hazardous Weather Outlook is for north Alabama and portions of
southern middle Tennessee.

.DAY ONE...Tonight...

A few strong to marginally severe storms will be possible into the
early evening with locally damaging wind gusts possible. These
storms will also produce heavy rainfall with localized flash flooding
possible.

Patchy dense fog may develop later tonight, especially in areas that
received heavy rainfall today.

.DAYS TWO THROUGH SEVEN...Sunday through Friday...

A few strong to marginally severe thunderstorms are possible again on
Sunday. Some of these thunderstorms may be capable of producing
damaging wind gusts.

.SPOTTER INFORMATION STATEMENT...

Activation of storm spotters and emergency management personnel is
not anticipated at this time.

Special Weather Statement
National Weather Service Huntsville AL
226 PM CDT Sat Jun 12 2021

ALZ004>007-016-122015-
Lawrence AL-Madison AL-Morgan AL-Limestone AL-Cullman AL-
226 PM CDT Sat Jun 12 2021

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHWESTERN MADISON...
SOUTHEASTERN LIMESTONE...NORTH CENTRAL CULLMAN...MORGAN AND
SOUTHEASTERN LAWRENCE COUNTIES UNTIL 315 PM CDT...

At 226 PM CDT, Doppler radar was tracking a strong thunderstorm over
Priceville, or 7 miles northeast of Hartselle, moving south at 25
mph.

Pea size hail and winds in excess of 40 mph will be possible with
this storm.

Locations impacted include...
Decatur, Hartselle, Priceville, Falkville, Vinemont, Somerville, Eva,
Mooresville, Belle Mina and Basham.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Strong gusty winds will be capable of knocking down small tree limbs
along with other small unsecured items. Seek safe shelter until this
storm has passed.

Very heavy rainfall is also occurring with this storm, and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.

&&

LAT...LON 3471 8695 3455 8673 3421 8674 3433 8716
TIME...MOT...LOC 1926Z 014DEG 20KT 3454 8687

GH

Special Weather Statement
National Weather Service Huntsville AL
316 PM CDT Sat Jun 12 2021

ALZ004-007-016-122100-
Lawrence AL-Morgan AL-Cullman AL-
316 PM CDT Sat Jun 12 2021

...SIGNIFICANT WEATHER ADVISORY FOR NORTHWESTERN CULLMAN...WESTERN
MORGAN AND SOUTHEASTERN LAWRENCE COUNTIES UNTIL 400 PM CDT...

At 315 PM CDT, Doppler radar was tracking a strong thunderstorm near
Trinity, or near Decatur, moving southwest at 15 mph.

Winds in excess of 40 mph will be possible with this storm.

Locations impacted include...
Decatur, Hartselle, Moulton, Trinity, Chalybeate Springs, Speake,
Neel, Massey, Caddo and Basham.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Very heavy rainfall is also occurring with this storm, and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.

&&

LAT...LON 3465 8704 3444 8689 3426 8706 3458 8738
TIME...MOT...LOC 2015Z 052DEG 11KT 3454 8704

GH

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