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Area Forecast Discussion (AFD)

Issued by Huntsville, AL (HUN)

FXUS64 KHUN 200823

Area Forecast Discussion
National Weather Service Huntsville AL
323 AM CDT Tue Mar 20 2018

.NEAR TERM...(Today)
Issued at 323 AM CDT Tue Mar 20 2018

After a very rough afternoon and evening yesterday, quiet weather 
has returned to northern Alabama and Southern Middle Tennessee. 
However, with clear skies and light to calm winds that settled over 
the area around 10 PM last night, patchy dense fog has developed and 
continues east of I-65. Further west, that was the case as well 
between 10 PM yesterday and 1 AM this morning, but a re-enforcing 
frontal boundary that has drier air and stronger winds behind 
currently is stretching from Athens southward to west of West Point 
has dissipated the fog in those locations as of 3 AM. Patchy dense 
fog will continue though in far northeastern Alabama through about 7 
AM. Therefore, a special weather statement continues to highlight 
this threat through 7 AM east of I-65. Lows should drop a bit more 
towards daybreak east of I-65 into the upper 40s to around 50 
degrees. Expect a bit of warming early this morning, as yet another 
stronger cold front pushes southeast into and then through the area 
this afternoon and evening. A good 30 to 35 knot 850 mb jet develops 
along and behind the front aloft. Soundings show the atmosphere being
able to mix up to that wind energy and translate some of it to the 
surface. Thus, it will be brisk today with northwest winds 15 to 20 
mph with gusts near 30 mph. These strong winds will efficiently 
advect cooler and drier air southeast into the area this 
afternoon/evening. Enough lift at 700 mb with this front and enough 
moisture around 700 mb and below should allow for scattered to more 
numerous light rain showers to develop along and behind it, 
especially in locations north of the Tennessee River. Temperatures 
will remain well above freezing through the day, so this should 
remain all rain.

SHORT TERM...(Tonight through Wednesday night) 
Issued at 323 AM CDT Tue Mar 20 2018

As we move into the evening hours today, temperatures will fall into
the mid to upper 30s primarily. This could cause lingering scattered 
precipitation to become a mix of light rain and snow in Southern
middle Tennessee and in northern Jackson county in Alabama. However,
this looks to move northeast of the area just after 10 PM. So not
expecting any accumulation of snowfall at this time. Could see some
flakes of snow in those areas, but not many other locations. Skies
should clear around and after midnight from west to east. This along
with strong cold air advection should allow low temperatures to drop 
just to or below freezing for a few hours before daybreak on

The colder air really moves southeast into the area behind the
departed front by Wednesday, as highs only climb into the mid 40s to
lower 50s despite abundant sunshine. A return to more widespread
freezing conditions look to shape up on Wednesday morning, as winds
lighten as high pressure builds into the area and good radiational
cooling occurs. Could see some locations dip into the upper 20s in
Southern Middle Tennessee. 

.LONG TERM...(Thursday through Monday) 
Issued at 323 AM CDT Tue Mar 20 2018

A sprawling surface high pressure remains in control of the local 
weather on Thursday. Aloft, we will be under northwesterly flow on 
the back side of a trough departing the northeast. However, a mid 
level ridge will be centered over LA and help push up heights and 
therefore, a warming trend. Thursday should be sunny and highs will 
warm into the upper 50s to around 60 degrees.

Clouds will increase slightly Thursday night as a shortwave dives
southeast along the upper trough. Lows will also be able to warm 
above freezing and into the mid 30s to lower 40s. There will be a 
slight chance of rain showers with that shortwave. 

A weak upper low will develop over the midwest Friday evening with
surface cyclogensis in the KS/MO area. Looks like a warm front will
be extending southeast with guidance showing QPF along it down
through most of the forecast area. There is quite a bit of
uncertainty with the system this weekend especially moving into 
Saturday. The surface low shifts east-southeast over SE MO with the
frontal boundary ahead of it. This boundary eventually dissipates
before another frontal boundary moves in Sunday ahead of an upper
trough digging into the desert southwest. Really tough to tell at 
this point where the rainfall gradient will be and when the highest 
rain chances will be. At this point, just left the blended chance 
pops in the forecast from Friday through Tuesday with the highest 
chances int the Monday/Tuesday range. Although thunderstorm 
parameters aren't impressive, with the area in the vicinity of 
multiple fronts, kept isolated thunder in for Sat through Monday. 

In terms of temps, southwest winds and rising heights push highs
Friday to the upper 50s/lower 60s and upper 60s/lower 70s for 
Sat/Sun/Mon. Lows will also slowly warm and be back into the mid 50s 
by Sat night. 


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1232 AM CDT Tue Mar 20 2018

VSBYS at KHSV are still LIFR and oscillating between 1/4 and 3/4 of 
a mile. Expect this to continue through 20/09Z, before winds increase
with a re-enforcing front just to the west of KMSL. Already have 
seen VSBYS become VFR quickly as a result of this boundary at KMSL 
and expect them to remain VFR, as winds remain between 5 and 10 knots
through daybreak. Expect this to occur at KHSV after 20/09Z. Then 
expect cigs to lower and become MVFR after approximately 20/15Z at 
both terminals with showers near both terminals through the afternoon
hours. For now only put VCSH both terminals. This should linger into
the evening hours, before cigs improve and become VFR towards 





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