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Area Forecast Discussion (AFD)

Issued by Huntsville, AL (HUN)

FXUS64 KHUN 230538

Area Forecast Discussion
National Weather Service Huntsville AL
1238 AM CDT Mon Apr 23 2018

For 06Z TAFS.


.NEAR TERM...(Tonight)
Issued at 731 PM CDT Sun Apr 22 2018

Deepening low pressure system across the Ozarks/Mississippi Valley 
will continue to shift eastward into the Tennessee Valley overnight.
A strengthening 850 mb jet is rotating into Northern Alabama from the
southeast ahead of this low, while a pronounced dry slot has
developed across Mississippi into Southwest/West Central Alabama. A
meso-low has developed across Northwest Alabama, which in 
conjunction with the low-level jet, has generated some strong wind 
gusts in the 25 to 40 mph range across much of the Huntsville CWA. 
Over the past couple of hours, these gusts were noted across the 
Shoals, with KMSL gusting as high as 30-40 mph. Have expanded the 
Wind Advisory across the entire area to account for these strong 
winds which may be capable of producing some localized tree and power
line damage through around 06z. 

In addition to the strong gradient winds, deep moisture continues to
advect into the region from the SE/SSE. Have noted an uptick in
reflectivity on radar over the last hour or two as the low-level jet
kicks in. with this broad area of moderate to locally heavy showers 
generally producing about 0.3 to 0.6 inches per hour within the 
heaviest bands. In general, think the flash flood threat is fairly 
low given the higher FFG values -- and the fact that the heaviest 
activity is moving gradually east with time. However, will need to 
watch for some areal flooding concerns on a localized level in areas 
where training does occur. Forecasted rainfall totals of 1.5 to 3
inches through Monday morning seems on track given the latest radar 
trends and model data.

The greatest rainfall potential will occur from 00z to 06z, before 
drier air moves in from the west, weakening this activity and 
eventually tapers it off late tonight. Most models, especially 
mesoscale guidance, continue to suggest show this abrupt end to 
precipitation occurring in this 06-08z timeframe from west to east as
dry air entrains in. This will also coincide with the LLJ shifting 
north and west of the region, diminishing lift over the area. Due to 
the cloud cover, precipitation, and breezy/gusty, southerly winds, 
temperatures will remain quite mild and in the 50s overnight.

.SHORT TERM...(Monday through Tuesday)
Issued at 250 PM CDT Sun Apr 22 2018

As the upper low and vort max move over the area on Monday we can
expect a few isolated to scattered showers and storms to develop.
Models over the last 24 hours have shifted the low track a bit more
to the north and have adjusted PoPs in that direction. Could be a
situation where the further south you are on Monday the lower the
PoPs and higher your chances for a few peeks of sunshine. Temps will
end up a few degree warmer Monday compared to todays values with 
highs in the mid to upper 60s. 

The low begins to pull away from the area on Tuesday but some
lingering wrap around moisture could allow for a few light showers
and have continued lower end PoPs through Tuesday afternoon. Highs on
Tuesday end up close to Mondays values. 

.LONG TERM...(Tuesday night through Saturday)
Issued at 250 PM CDT Sun Apr 22 2018

Weak CAA on the backside of the departing system could allow for a
shallow inversion to develop Tuesday night and with the recent rains
could support some fog potential. Don't have anything in the forecast
at this time but something to keep an eye on. Tuesday night through
Wednesday afternoon will be one of the few dry periods in the
forecast. A weak trough is forecast to drop S/SE out of the northern
Plains towards the Gulf Coast. Models differ on just how far south 
to dig this feature and could be the difference between only a few 
light showers Wednesday night/Thursday to more scattered to 
widespread rain on Thursday. Because of this uncertainty have kept 
PoPs more broad brushed but tried to show some gradient north to 
south in PoPs. 

Beyond Thursday models begin to diverge on another trough that is
forecast to drop SE out of the northern Plains. The GFS has the core
of the trough over the OH Valley with the TN Valley remaining dry.
The GEM has the trough moving across the TN Valley bringing another
round of showers on Friday. The ECMWF on the other hand is between 
these two solutions with only a few light showers. Ensembles are also
not very supportive to any of these solutions and have just slight
chance PoPs for Friday afternoon to account for these differences.
Winds remains out of the N/NW through the extend period and should
allow for a few cool mornings with the colder morning likely
occurring Saturday morning. Clearer skies over the weekend would
support temps in the 70s despite the weak CAA. 


.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1239 AM CDT Mon Apr 23 2018

Very strong winds continue near the KHSV airport, with the ASOS
reporting gusts near 50KT still. These winds are xpcted to diminish
after 01Z, although cigs near/just below 1K ft look to become
entrenched across much of the area heading into the early morning
hrs. Cigs may then lift more into the MVFR range or 1-2K ft Mon
morning, with the onset of daytime heating/mixing. VFR conds may
develop late in the TAF period, as cigs lift above 3K ft.


AL...Wind Advisory until 1 AM CDT early this morning for ALZ001>010-016.

TN...Wind Advisory until 1 AM CDT early this morning for TNZ076-096-097.



LONG TERM...Stumpf

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