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FXUS64 KHUN 181723

Area Forecast Discussion
National Weather Service Huntsville AL
1223 PM CDT Wed Sep 18 2019

For 18Z TAFS.


.NEAR TERM...(Rest of Today)
Issued at 950 AM CDT Wed Sep 18 2019

A few boundaries can seen in surface observations and satellite 
imagery over the southeastern CONUS at 9 AM. A stalled front extends 
from extreme se Georgia northwestwards into the northern Florida 
panhandle. A weak surface low has developed along it near Tallahassee,
FL, with an inverted trough axis extending northward into north 
central/northeastern Alabama. However, looking at both the Altanta,
GA and Birmingham, AL soundings, very dry air is in place near and 
east of the inverted trough axis. They do show some moisture around 
700 mb, however, the rest of the atmospheric profile is very dry 
(much likely too dry for cloud cover or precipitation). 

Guidance does show deeper low level moisture near a fairly strong
back door front over NE Georgia and South Carolina. Models do push
this west, but based on guidance this deeper low level moisture (as 
seen in the Charleston, SC sounding) doesn't arrive until this 
evening in northeastern Alabama. Guidance does show slightly 
stronger convergence/lift later this afternoon. This occurs in the 
drier portions of the atmospheric column. We will likely see some 
partly cloudy conditions pushing into northeastern Alabama late this 
afternoon though (due to moisture around 700 mb and some low level 
lift). This should have little impact on actual high temperatures 
though. Some slightly cooler air should advect into the area from the
east though late this afternoon into northeastern Alabama near this 
backdoor front. This should keep the temperatures in the lower 90s 
there. Further west, it will be hot. Highs near and west of I-65 look
to remain in the 95 to 100 degree range this afternoon. The hot spot
today looks to be the Quad cities area. With such dry air in place 
aloft expect mixing again this afternoon of drier air to the surface.
This should keep heat index values slightly above temperatures in 
the 98 to 102 range primarily west of the I-65 corridor. 

However, Huntsville and 
Cullman will likely reach 96 to 99 degrees. 

.SHORT TERM...(Tonight through Friday night)
Issued at 249 AM CDT Wed Sep 18 2019

The slightly cooler air should continue to gradually spread wwd into
more of the cntrl TN Valley later tonight, with lows falling predom
into the mid 60s to near 70F by early Thu. A strong area of high 
pressure then looks to become layered from the NE/mid Atlantic states
into the srn Atlantic areas starting Thu and continuing thru the end
of the work week. This should translate into near seasonal/stagnant 
temps both Thu/Fri, with highs mainly in the mid to perhaps upper 80s
and lows in the upper 50s/mid 60s into early Sat. An upper ridge axis
also looks to remain in place over much of the SE region into the 
weekend period, translating into quiet/tranquil wx conditions outside
of a few clouds, given some lingering moisture around/below H85.

.LONG TERM...(Saturday through Tuesday)
Issued at 249 AM CDT Wed Sep 18 2019

The dry and warm pattern will persist into the long term period
across the TN Valley, keeping above normal temperatures and below
normal precipitation in the forecast. After a weak shortwave (what
will become the remnants of TD Imelda) passes through the TN Valley
on Saturday, upper ridging will generally maintain its hold over the
region through the latter part of the weekend. An upper trough 
moving through the High Plains and into the Great Lakes region will
help to dampen the ridge a bit on Sunday and Monday, however
persistent southerly flow and mostly clear skies will allow high
temperatures to warm into the upper 80s to lower 90s through Monday,
with overnight lows in the mid to upper 60s. 

As the upper trough continues to track eastward across the Great
Lakes on Monday night, a weak cold front will make its way through
the TN Valley. Models differ on the exact timing and strength of 
this system, being in the latter part of the forecast period. 
However, models do agree that this system won't bring much, if any, 
change to the sensible weather pattern across the region. High 
pressure building into the region on Tuesday will keep north- 
northwesterly flow at the surface and an upper ridge will begin to 
build into the southeast. The northerly flow will be relatively 
light, with little change in the airmass behind the front, so highs 
will still warm into the upper 80s to lower 90s on Tuesday and 
Wednesday. Meanwhile, overnight lows will remain in the 60s, so it 
looks as though the first true taste of fall is still at least a week


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1225 PM CDT Wed Sep 18 

Light and variable winds are expected at both terminals through the early
evening hours with VFR conditions continuing. Winds should pick up around
4Z at KHSV as a backdoor front approaches the terminal from the east. Surface
winds expected to be around 10 knots. This should keep wind shear below
20 knots, despite winds near 925 mb increasing to around 25 knots. However,
southeast winds around 10 knots with gusts around 15 knots are expected
after 4Z at KHSV. This increase in winds should occur a few hours later
around 6Z at KMSL. Even gustier winds to around 20 knots are expected
after 13Z as the winds become more southerly. CIGS between 3000 to 4000
feet after 13Z are expected.





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