Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 231642 AAC

Area Forecast Discussion...UPDATED
National Weather Service Huntsville AL
1142 AM CDT Tue May 23 2017

For 18Z TAFS.


.NEAR TERM...(Rest of Today)
Issued at 832 AM CDT Tue May 23 2017

Showers and sprinkles were beginning to exit southern middle TN and
northeast AL. Short range mesoscale models indicate a definitive
break in the activity late this morning into most of the afternoon
hours. Visible imagery is showing some breaks in the clouds
coinciding with model RH fields, which should lead to modest heating
in our western counties today. By late afternoon, this could lead to
sufficient CAPE to generate isolated showers or thunderstorms.

.SHORT TERM...(Tonight through Thursday Night)
Issued at 350 AM CDT Tue May 23 2017

Tonight is when things start to get interesting with widespread
rainfall making its return. As the upper trough gets closer, upper
waves moving SW to NE in the upper flow interact with a jet streak,
located near NW AL to help provide lift for additional showers. This
occurs ahead of the next cold front. Although the mention of thunder
is still in the forecast due to the dry mid levels and increasing
instability, the column will need to fully saturate again. Therefore,
this round should just be scattered showers and a few thunderstorms.
At the same time, another upper jet streak moves into the Gulf Coast
region, developing another area of showers/thunderstorms.

Between 6-12z tonight, the leading edge of the base of the upper
trough starts to swing into NW AL as a surface cold front moves
along with it. I do believe the coastal convection will indeed cut
us off from the additional moisture and instability we need to have
strong to severe storms. Although we do saturate, our dew points
don`t increase at all during this time and lapse rates are
unimpressive. However, with the extreme lift coming through, coupled
with 30-40kts (50-60kts closer to 12z) of bulk shear and around 500
J/KG of instability, a strong storm is a possibility. The stronger
storms will be efficient lightning producers with heavy rain and
gusty winds will also be a concern. Did not see the coverage of
storms to be too high so will match neighbors and agree with just a
chance of thunder.

The front and heaviest rain should be out of NE AL by 15z Wednesday
but the upper low won`t lift through the area until almost 00z
Friday. Low level moisture lingers through this time with at least
isolated to scattered showers expected. POPs do start to taper off
and will only impact the northeast areas by 12z Thursday and it
should be completely dry by 00z Friday. With drying moving into the
mid layers by late Wednesday morning, we become pretty capped and
thinking the thunder chances will be low. Therefore, ran with an
isolated thunderstorm for the day and then just showers Wed night
through Thu. Overall basin averaged rainfall amounts are only around
an inch but locally heavier amounts will definitely occur.

The cold front won`t impact lows tonight which remain mild, near 60.
However, the cooler air and lingering clouds/rain will keep highs in
the upper 60s/near 70 for Wednesday with lows dropping to the lower
50s. Temps start to rebound Thu with highs in the lower to mid 70s
and lows in the mid 50s.

.LONG TERM...(Friday through Monday)
Issued at 350 AM CDT Tue May 23 2017

Dry wx and warmer temps will return for the end of the work week over
the cntrl TN Valley, with the passage of a cold front previously in
the week. This front should be well off the mid/srn Atlantic Coasts
by the onset of this forecast period while another sfc ridge of high
pressure gradually makes its way ewd across the Gulf region. The
upper low/trough axis associated with the departing front should also
continue to lift newd away from the local area/more into the NE
region giving way to weak ridging aloft over much of the wrn/cntrl
Gulf states. With cloud cover diminishing on Fri, seasonably warm
temps are xpcted into the first half of the weekend period, with
highs both Fri/Sat mainly in the mid/upper 80s range. However, the
dry spell may be short lived with the latter half of the model suites
hinting at a series of embedded shrtwvs traversing ewd across much
of the SE region starting late Sat. Look for showers/tstms to become
more enhanced heading into the new work week, as yet another area of
low pressure out of the mid Plains lifts newd into the Midwest states
while the attendant cold front sweeps ewd over the Lower MS/TN
Valley areas thru Mon. This should translate into showers/tstms
developing along/ahead of the approaching sfc boundary as this
activity/precip spreads ewd. All in all, the latter part of this
forecast package looks fairly wet as we start the new week leading up
to the Memorial Day weekend, although long range forecast progs hint
at some of this rainfall tapering off by mid week following the
passage of this next front.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1142 AM CDT Tue May 23 2017

Ceilings will be VFR this afternoon into this evening (030-050agl).
Isolated showers and possibly a thunderstorm remain possible, but
areal coverage is expected to be too limited to place in the TAF. An
upper level system and cold front will approach late tonight from the
west, produce numerous showers and a few thunderstorms. These will
arrive in the KMSL vicinity around 06Z and in the KHSV vicinity
around 08Z. These will produce MVFR ceilings (020-030agl) and
visibility (3-5sm). The cold front should pass through around 12-14Z
at KMSL and KHSV respectively, with a wind shift to the west-
northwest around 10kt.





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