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Area Forecast Discussion (AFD)

Issued by Huntsville, AL (HUN)

FXUS64 KHUN 190325

Area Forecast Discussion
National Weather Service Huntsville AL
925 PM CST Sun Feb 18 2018

.NEAR TERM...(Tonight)
Issued at 914 PM CST Sun Feb 18 2018

The weak area of convergence/forcing that brought some scattered 
light to briefly moderate rainfall to portions of northern Alabama 
this evening has pushed further north. This convergence/forcing now 
is near a line from Rome to Nashville. Some lingering light rain 
showers are hanging on over eastern Jackson and DeKalb counties, but 
will push east into Georgia and eastern Tennessee shortly. Not sure 
how much further east the area of convergence over Georgia will make 
it, due to the strength of the surface ridge through daybreak. 
Guidance seems to pick up on this and redevelops some scattered 
showers over northeastern Alabama between 3 am and 6 am on Monday as
an additional weak area of forcing moves north across the area. Thus,
keeping isolated to scattered showers in the forecast through 
daybreak mainly near and east of the I-65 corridor.

Further west, low clouds could break up a bit between now and 2 am. 
If this occurs, with very thin high clouds, some patchy fog may 
develop west of I-65 between now and 2 am. Lowered winds based on 
current observations a tad and kept this trend through about 3 or 4 
am. Models show that next round of possible scattered precipitation 
toward daybreak occurring as another piece of weak energy moves north
through the area towards daybreak into the early morning hours on 
Monday. This forcing looks weak also, but the increase in low level 
moisture and enough lift will likely allow mostly cloudy to cloudy 
conditions to redevelop west of I-65 after about 3 AM. Lows look on 
track and should be just a few degrees cooler than they are now, 
likely in the lower to mid 50s in most locations. Winds should stay 
high enough in most locations to not see widespread fog formation, 
but west of I-65, where clearing could occur, sheltered areas could 
see patchy fog formation.

.SHORT TERM...(Monday through Tuesday night)
Issued at 258 PM CST Sun Feb 18 2018

Earlier analysis of 12Z upper air data revealed an upper low moving
southward along the Pacific NW coast. This low will help carve out 
a deep trough over the western CONUS, kept from moving eastward in 
part by a strong upper high situated north of the Bahamas and east of
Florida. This more amplified pattern will result in slower eastward 
movement of the systems to our west eastward. It will also bring more
warmer air northward across the region. Thus lower to mid 70s for 
highs are expected for Washingtons Birthday/Monday. Normals this time
of year are in the mid to upper 50s. 

Even warmer temperatures expected tomorrow night and Tuesday. 
Nighttime lows will fall only into the mid 50s to lower 60s. Highs on
Tuesday will rise into the mid/upper 70s. Record high temperatures 
tomorrow and Tuesday could be given a run for the money (especially 
on Tuesday). Respective standing records then are 79/1917 and 
79/1986, in Muscle Shoals and Huntsville respectively. 

Another change from the recent wet trend, decided to keep Mon-Tue 
dry, but brought scattered showers back into the picture Tuesday 
night, as deeper moisture and better lift is realized across the 
Tennessee Valley. 

.LONG TERM...(Wednesday through Saturday) 
Issued at 258 PM CST Sun Feb 18 2018

The forecast area will be situated between an upper trough extending
through the Intermountain West and a fairly strong subtropical ridge
over the southeastern CONUS and eastern seaboard at the start of the
long term period. A cold front will be meandering over the central 
CONUS and approach the TN Valley on Wednesday. Ahead of this front,
moisture will continue to advect northward as southerly flow 
persists at the surface and southwesterly flow persists aloft. The 
upper trough over the west will weaken quite a bit as it progresses 
eastward, while the upper ridge maintains a strong hold to our 
southeast. This will make it hard for the cold front to make much 
progression, which is evident in the models forecasts, as they 
continue to struggle with the evolution of this system. At this 
point, it does seem clear that the front will make it at least into 
the Mississippi Valley, with rain chances increasing across the TN 
Valley during the day on Wednesday. The GFS continues to be the more 
progressive model, swinging the front through on Wednesday, before it
stalls to our south. Meanwhile, the ECWMF hangs it up just to our 
north, leaving the potential for outflow boundaries to move into the 
region and generate precip. Still too far to go into much detail 
about mesoscale features, but for these reasons, have maintained the
blended guidance of likely pops on Wednesday, with higher chances on
Wednesday night given the possibility of the front sagging through 
the area. 

The front looks to be within the vicinity of the TN Valley from 
Thursday through Saturday. Meanwhile, southerly flow through the 
vertical column will keep a rather moist profile across the area. 
This will mean a continued wet pattern for the TN Valley at the end 
of the week. It's difficult to pinpoint which days will have the 
higher potential for rain, so have kept chance pops in the forecast 
for Thursday night and onward. The front looks to finally move
through the area on Saturday, bringing a higher chance for showers
Saturday and Saturday night, along with isolated thunderstorms. 
Still a lot of uncertainty, so undercut the guidance a little due 
the discrepancies noted in the midweek front. 

Temperatures through much of the extended period will be well above
normal for late February given the strength of the ridge and upper
level heights. Rain and cloud cover may help, but the slow movement
of the cold front and continued WAA will likely overcome any precip
to help temps warm into the upper 60s to upper 70s during the period.
The warmest day will likely be on Wednesday, as the front remains to
our north at this time. Overnight lows will be on the warm and muggy
side, with temps remain in the upper 50s to lower 60s.  


.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 522 PM CST Sun Feb 18 2018

A weak warm front will continue to keep MVFR cigs in place through 
the night. Some scattered showers may continue to affect both 
terminals at times this evening as this feature moves north, but due
to low confidence/pop have kept only VCSH in the forecast from now 
to 04Z at KMSL and 05Z at KHSV. Will have to watch late tonight at 
KMSL if we get some brief clearing around and just after midnight. 
This may allow some brief light fog to form, but left out for now due
to uncertainty. A 1000 to 1500 foot deck should return to KMSL 
around 07Z. Winds should stay between 5 and 10 knots through the 
night. By 16Z, expect strong winds to mix down aloft and some gusts 
up to 20 knots are possible through tomorrow afternoon. Expect cigs 
to come up as well to VFR around 5000 feet or higher tomorrow.





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