Severe Thunderstorm Warning 41, NWS Huntsville, AL

Area Forecast Discussion
National Weather Service Huntsville AL
1200 AM CDT Thu Apr 9 2020

.UPDATE...
For 06Z TAFS.

&&

.NEAR TERM...(Rest of tonight)
Issued at 947 PM CDT Wed Apr 8 2020

Clusters of supercells/tstms are marching SE across west/mid TN this
Wed evening, along and ahead of a pre-frontal boundary stretching SW
front the MO Bootheel into north cntrl AR. Several warnings are in
effect with many of these storms, and it is likely the cntrl TN
Valley will be dealing with similar storms heading into the late
evening/overnight hrs. A Tornado Watch is in effect for all of the
Mid South region and it is also likely this Tornado Watch will be
extended into the local area later this evening given the amount of
low level shear in place below 1km coupled with unusually excessive
amounts of buoyant energy/instability. The main window for severe wx
looks to be from 11 pm thru 4 am. Large hail, damaging winds and a
few tornadoes are the main threats with any severe tstms. Any tstms
should then quickly taper off heading into the early morning hrs Thu,
as a cold front moves ewd across the area. Overnight lows will trend
seasonably warm with the cloud cover/rainfall, with lows xpcted to be
in the upper 50s/lower 60s for most spots.

.SHORT TERM...(Thursday through Friday night)
Issued at 314 PM CDT Wed Apr 8 2020

Latest global model consensus indicates that deep-layer flow will
continue to gradually veer to the northwest on Thursday and Thursday
night, as a deepening vort max (initially over southern Ontario)
pivots northeastward into northern New England and eventually carves
out a broad longwave trough over the eastern CONUS. Although modest
low-level CAA will occur during the day on Thursday, abundant
insolation during the late morning/afternoon hours should allow temps
to reach the u60s-l70s in valley locations and l-m 60s in elevated
terrain. However, a reinforcing surge of colder/drier air will arrive
early Friday morning, as the axis of the broader longwave trough
crosses the region. A subtle increase in synoptic scale ascent
related to this feature will provide an increase in mid/high-level
cloud cover, but profiles remain too dry for the inclusion of any
shower activity with the passage of the reinforcing cold front. With
stronger CAA in the wake of the secondary front forcing lows into the
u30s-l40s Friday morning, temperatures will have difficulty reaching
the m-u 50s on Friday afternoon, and this could set the stage for
frost across portions of the region Friday night/Saturday morning, as
a surface ridge spreads eastward into the southern Appalachians and
provides ideal conditions for radiational cooling.

.LONG TERM...(Saturday through Tuesday)
Issued at 314 PM CDT Wed Apr 8 2020

On Saturday, high pressure overhead will begin to shift eastward
ahead of a deepening upper trough across the desert southwest. Under
partly cloudy skies, afternoon temperatures rise up into the upper
60s to near 70. The upper trough will continue to move east
throughout the day and by the evening a SFC low will develop across
TX. Rain and thunderstorm chances increase starting late Saturday
night as a warm front lifts northeastward through the Tennessee
Valley. By Sunday, the aformentioned low pressure system ejects north
and east through northern Alabama and southern Tennessee with a cold
front swinging through by the late afternoon into the evening.

While model guidance has generally honed in on the timing of this
system, there are considerable differences in the position and track
of the low pressure system. The GFS at the moment is an outlier with
a more southern track compared to the Canadian and ECMWF based on the
latest operational runs. A southern track would limit the severe
potential to our south, whereas if it were to move farther to the
north, greater instability would be able to filter into the region
bringing an increased risk for all modes of severe weather. Given the
differences in models, will only mention strong to severe storms in
the HWO at this time. However, the biggest concern may be the heavy
rain with the potential for 1-2" by Monday morning.

Dry weather returns Monday and Tuesday with high pressure once again
positioned overhead. Much cooler air advects into the region behind
a secondary cold front Monday night. Highs on Tuesday and Wednesday
will only be in the low to mid 60s with overnight lows in the lower
40s.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1200 AM CDT Thu Apr 9 2020

Clusters of shra/tsra continue to move ESE across parts of west/mid
TN into extreme NE MS. This activity will begin to approach the KMSL
terminal within the next hr and prob the KHSV airport within the next
few hrs. Brief IFR cigs/vis are possible in/near any +tsra, with vrb
winds gusting near 35-40kt at times. The shra/tsra are then xpcted to
quickly taper off from the WNW heading into the early morning period
following the passage of a cold front. Cloud cover should also begin
to diminish/sct with the onset of the morning hrs Thu. Sfc winds out
the SW near 8-10kt will turn toward the NW around 12-14kt with higher
gusts Thu morning in the wake of the frontal passage.

&&

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

NEAR TERM...09
SHORT TERM...70/DD
LONG TERM...GH
AVIATION...09

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

Hazardous Weather Outlook
National Weather Service Huntsville AL
1100 PM CDT Wed Apr 8 2020

ALZ001>010-016-TNZ076-096-097-091100-
Lauderdale-Colbert-Franklin AL-Lawrence-Limestone-Madison-Morgan-
Marshall-Jackson-DeKalb-Cullman-Moore-Lincoln-Franklin TN-
1100 PM CDT Wed Apr 8 2020

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

.DAY ONE...Tonight...

Clusters of thunderstorms are expected to move southeast into much
of the outlook area heading into the overnight hours. Some of these
storms may be strong to severe in nature, and will be capable of
damaging winds, large hail and a brief tornado. The thunderstorm
threat is expected to quickly taper off from the northwest early
Thursday morning following the passage of a cold front.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday...

A strong upper level disturbance moving across the region will
translate into scattered thunderstorms from Sunday into Sunday night.
A few of these storms may be strong to severe with the potential for
damaging wind gusts. Heavy rainfall is also expected with this storm
system and rises on area rivers may be possible early next week.

.SPOTTER INFORMATION STATEMENT...

Activation of storm spotters and emergency management personnel is
requested during the overnight hours.

Please relay any information about observed severe weather to the
NWS while following all local, state, and CDC guidelines.

Special Weather Statement
National Weather Service Huntsville AL
105 AM CDT Thu Apr 9 2020

ALZ001>007-016-090645-
Lawrence AL-Madison AL-Lauderdale AL-Morgan AL-Franklin AL-
Limestone AL-Colbert AL-Cullman AL-
105 AM CDT Thu Apr 9 2020

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHWESTERN MADISON...
SOUTHEASTERN LAUDERDALE...CENTRAL LIMESTONE...SOUTHEASTERN COLBERT...
NORTHWESTERN CULLMAN...EASTERN FRANKLIN...MORGAN AND LAWRENCE
COUNTIES UNTIL 145 AM CDT...

At 104 AM CDT, Doppler radar was tracking a line of strong
thunderstorms extending from Rogersville to 9 miles west of Moulton
to 7 miles north of Weston. Movement was east at 50 mph.

Pea size hail and winds in excess of 40 mph will be possible with
these storms.

Locations impacted include...
Western Huntsville, Decatur, Madison, Athens, Cullman, Hartselle,
Russellville, Moulton, Redstone Arsenal and Priceville.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Frequent cloud to ground lightning is occurring with these storms.
Lightning can strike several miles away from a thunderstorm. Seek a
safe shelter inside a building or vehicle.

Portions of these storms may intensify, so be certain to monitor
local radio stations and available television stations for
additional information and possible warnings from the National
Weather Service.

&&

LAT...LON 3456 8758 3489 8735 3478 8658 3425 8679
      3409 8711 3430 8711 3432 8805
TIME...MOT...LOC 0604Z 291DEG 45KT 3480 8730 3446 8745 3427 8802

30

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