Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 272316

Area Forecast Discussion
National Weather Service Huntsville AL
516 PM CST Mon Feb 27 2017

For 00Z TAFS.


.NEAR TERM...(Tonight)
Issued at 312 PM CST Mon Feb 27 2017

After the initial rainfall this morning, most of the rest of the day
has been dry for the Huntsville CWFA. While short-range model
guidance has suggested a dry period until late evening, radar is
picking up on additional showers over north-central MS perhaps
associated with another weak shortwave (as suggested by water vapor
imagery). Meanwhile, persistent cloud cover has made it tough to warm
up much from early lows in the upper 40s, but most of the area has
made it to at least the mid 50s.

Tonight`s forecast was going to be mostly dry through 06Z or so,
before transitioning to a wetter pattern as the next weak mid-level
shortwave trough and warm front move into the mid-Mississippi
valley. There is greater confidence in clouds lowering and thickening
more as isentropic lift strengthens. Either way, the temperature is
not going to fall that much tonight in general, but the low will
occur early in the night with temperatures rising towards daybreak.

.SHORT TERM...(Tuesday through Wednesday)
Issued at 312 PM CST Mon Feb 27 2017

Scattered showers and thunderstorms will continue into tomorrow; the
question is whether any of these storms can become severe. The low-
level and deep-layer wind shear are both strong. Instability is there
too; the question in our mind is whether the low-to-mid level
capping develops as hinted by the operational models. Elevated storms
capable of producing large hail look more likely, but it will take
more effort to produce any surface-based storms (though it is not out
of the question). PoPs for Tuesday will stay in the 50-60% range
given the relatively weak forcing. High temperatures in the warm
sector will easily be 10-15 degrees warmer than today and could
potentially flirt with records for the date.

Wednesday continues to be the main focus, as the parent long wave
troughs phase over the Plains and drive a strong cold front eastward,
likely creating a squall line/QLCS. There is no doubt that the
forcing Wednesday is much better and instability more pronounced.
However, the most unstable lapse rates (late in the day) and
strongest shear (earlier in the day) are displaced from one another.
A few tornadoes are possible, particularly if there are line breaks,
or if storms develop earlier when they can take advantage of more
favorable shear. However, wind damage looks like the more significant
threat with the expected timing (late morning thru afternoon).

.LONG TERM...(Wednesday night through Sunday)
Issued at 312 PM CST Mon Feb 27 2017

As the surface front continues southeastward into the Florida
panhandle Wednesday night, a decent pressure gradient will still be
in place, as cold air advection continues behind the front. This
will keep northwest winds between 10 and 15 mph with higher gusts to
between 20 and 25 mph above 1000 feet. These winds will slowly
diminish to between 5 and 10 mph with some higher gusts above 1000
feet after midnight. Since this air mass is Pacific in origin, very
cold air will not be advected in despite the strong northwesterly
winds. Also, mixing will likely help to temper low temperatures as
well, low temperatures will still drop into the upper 30s to around
40 degrees. It will be cooler on Thursday, as highs in the mid to
upper 50s are expected despite abundant sunshine. Higher elevations
above 1000 feet will be even cooler with highs only topping out in
the lower 50s.

Another weak and dry front is forecast by models to push southeast
through northern Alabama Thursday evening. There should be very
little cloud cover associated with this front. Behind the front on
Friday, even colder air into the Tennessee Valley. Lows in the lower
to mid 30s look reasonable. As colder air moves into the region,
highs on Friday will likely be cooler than guidance. Forecasted
highs in the lower 40s in Southern Middle Tennessee to the lower 50s
south of the Tennessee River. This may be generous given 925
temperatures. However, enough uncertainty exists with these
temperatures to not go much lower than stated temperatures.

A warmup looks to be in store for the weekend, as southerly to
southwesterly low level flow develops as the surface high pushes off
the Georgia coast. Highs should climb into the lower to mid 60s
again by Sunday. Models hint at weak forcing and maybe deep enough
moisture for showers to developing by Sunday night. Included isolated
to scattered showers during that period.


.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 516 PM CST Mon Feb 27 2017

Tricky CIG forecast for the next few hours with KMSL still reporting
clear skies and KHSV fluctuating from BKN023 to FEW023. Will
continue the current conditions at both terminals with KMSL dropping
to around 1500ft by 4Z and KHSV staying down, even though they could
briefly jump back up. Confidence is not high on how low the CIGS go
tomorrow afternoon with some guidance indicating CIGS as low as
500ft. With afternoon mixing, do not think we will stay this low and
have brought them to BKN015. Amendments may be necessary for the
CIGS. Have also added -SHRA in at both terminals late Tue morning. No
thunder is in the TAFs at this time due to low confidence but we may
get a rumble or two late Tue morning/early Tue afternoon.





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