Severe Thunderstorm Warning 19, NWS Huntsville, AL

Area Forecast Discussion...UPDATED
National Weather Service Huntsville AL
1145 AM CST Wed Mar 1 2017

.UPDATE...
For 18Z TAFS.

&&

.NEAR TERM...(Rest of Today)
Issued at 913 AM CST Wed Mar 1 2017

The line moving into northwestern Alabama has become more broken over
the last hour. The most recent development of this broken line has
formed along the approaching cold front, which is quickly moving
southeast over the past few hours. Shear remains very high and low
level helicity remains high (at least 300-400 m2s2 at both 0-1 and
0-3 km layers). Temperatures have risen into the lower 70s west of
I-65 with dewpoints in the lower to mid 60s. Thus, surface based
CAPE has risen south of this developing line to over 1000 J/KG from
some mesoscale analysis. Given these parameters and given potential
of individual supercell development given broken line and
thermodynamic conditions, the tornado threat has increased near and
south of the Tennessee River. Given parameters can not rule out the
development of a stronger tornado. Damaging winds remains the primary
threat and large hail also remains possible. Timing of severe
thunderstorms is between now and 2 pm north of a line from Southern
Middle Tennessee t near the Muscle Shoals area through 2 pm. This
will push southeast to locations near the Tennessee River between
noon and 3 PM, before affecting Cullman county east through southern
DeKalb county between 1 and 4 PM.

.SHORT TERM...(Tonight through Thursday night)
Issued at 351 AM CST Wed Mar 1 2017

Much quieter wx conditions are expected for the TN Valley starting
tonight and continuing through Thu. What lingering rainfall is left
across NE AL should continue to diminish/translate ewd during the
early evening hrs, as cloud cover begins to diminish/sct. The cold
front itself should also make its way out of the local area to the
s/e later this evening, as a strong dome of high pressure out of the
mid/srn Plains states builds ewd into the SE region. With the
oncoming sfc high, cooler/drier air should also begin to filter into
the area from the n, with more seasonal like temps xpcted into Thu.
Lows tonight look to fall back into the mid/upper 30s for most
locations while temps on Thu trend fairly mild, with highs mainly in
the 55-60F range. Temps Thu night look to be even cooler, with lows
falling close to the freezing mark for many areas.

.LONG TERM...(Friday through Tuesday)
Issued at 351 AM CST Wed Mar 1 2017

A rather pleasant end to the work week looks to be in store across
the TN Valley, as the axis of an upper level trough pushes to the
east of the area. Highs on Friday will be on the cool side, behind a
reinforcing shot of cold air. Forecast max temps will only warm into
the lower to mid 50s, with a few spots across our NE counties
struggling to make it out of the 40s. Overnight lows will fall into
the lower 30s under mostly clear skies and calm winds. The cool
spell will be short-lived as upper ridge begins to build into the TN
Valley over the weekend. Plenty of sunshine persist on Saturday and
help our temps reach into the upper 50s to lower 60s.

Forecast models begin to diverge on their evolution of the upper
patten beginning on Sunday. The ECMWF is a little more progressive
with a strengthening shortwave moving through overnight Sunday,
bringing scattered showers across the area. Meanwhile, the GFS
maintains the upper ridging but does indicate a weak shortwave
moving around the northern periphery of the ridge. Either way, our
overnight lows Sunday night will be well above normal and only fall
into the 50s. Discrepancies increase regarding the progression of an
upper level trough that will eject east of the Rockies late in the
long-term period. A cold front will trail southward from the parent
surface low over the Great Lakes and then move eastward into the TN
Valley. Once again, the ECMWF is a little bit quicker bringing this
front through as early as Monday night, though the upper forcing
looks much weaker. The GFS, on the other hand, is roughly 12 hours
slower and shows decent forcing across the TN Valley. Given the
uncertainties, have maintained a blend of the guidance. Also kept a
mention of isolated thunderstorms for Monday through Tuesday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1140 PM CST Wed Mar 1 2017

MVFR cigs/vsbys are expected starting around 01/17Z at KMSL. The
line will move southeast and begin affecting KMSL terminal in earnest
between 01/18Z and 01/20Z. During this time cigs should drop at
times to IFR criteria. This should happen a bit later at KHSV,
between 01/19Z and 01/21Z. Some of these storms could be strong to
severe. Expect VFR conditions to return quickly this afternoon,
around 02/00Z at KHSV and around 01/23Z at KMSL. Winds will diminish
and become northwesterly early this evening.

&&

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

NEAR TERM...KTW
SHORT TERM...09
LONG TERM...73
AVIATION...KTW

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

Hazardous Weather Outlook...UPDATED
National Weather Service Huntsville AL
1158 AM CST Wed Mar 1 2017

ALZ001>010-016-TNZ076-096-097-020100-
Lauderdale-Colbert-Franklin AL-Lawrence-Limestone-Madison-Morgan-
Marshall-Jackson-De Kalb-Cullman-Moore-Lincoln-Franklin TN-
1158 AM CST Wed Mar 1 2017

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

.DAY ONE...This Afternoon and Tonight...

A tornado watch has been issued until 6 PM for all counties in
the Huntsville Forecast Area. Strong to severe thunderstorms are
expected...pushing southeast and affecting areas along and north of a
line from Southern Middle Tennessee to near the Muscle Shoals area
in the late morning to early after hours. These strong to severe
storms will push southeast to near the Tennessee River in the early
afternoon hours and affect our southeastern counties through the late
afternoon hours. All modes of severe weather are possible, although
damaging winds up to 70 mph will be the primary threat. A stronger
tornado and large hail cannot be ruled out.

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

Isolated thunderstorms return to the Tennessee Valley next Monday
and Tuesday as another cold front approaches from the west.

.SPOTTER CALL TO ACTION STATEMENT...

Activation of storm spotters and emergency management personnel is
requested today.

ktw

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