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Area Forecast Discussion (AFD)

Issued by Huntsville, AL (HUN)

FXUS64 KHUN 192328

Area Forecast Discussion
National Weather Service Huntsville AL
528 PM CST Mon Feb 19 2018

For 00Z TAFS.


.NEAR TERM...(Tonight)
Issued at 222 PM ST Mon Feb 19 2018

What a wonderful warm day today has turned out to be with partly
cloudy skies and 2PM temps in the lower to mid 70s. As of 2PM 
Huntsville hit 76, breaking its high temp record of 75 which was set 
in 1939. Muscle Shoals is at 75 and needs 76 to tie its record. A 
strengthening mid level ridge developing off the SE coast has helped 
usher in a warmer, southerly flow as well as a steady stream of mid 
level moisture. Clouds should continue to scatter out for the next 
few hours and leave a few mid level and cirrus clouds overnight. A 
few hires models, and even NAM soundings, indicate another stratus 
layer moving back in overnight, mostly in the western areas. With 
winds remaining elevated, around 10mph, overnight, and continued warm
advection, it may be hard to get the cooling necessary for enough 
saturation for an overcast stratus later. Will stick with a partly 
cloudy sky overnight but additional updates may be needed. All of the
above factors will make lows tonight even warmer, in the lower 60s. 

.SHORT TERM...(Tuesday through Thursday)
Issued at 222 PM CST Mon Feb 19 2018

Tuesday will be similar to Monday in synoptic terms with the mid
level ridge continuing to strengthen and 850mb temps warming. The
atmosphere will quickly mix out Tuesday morning, once again
producing 10-15MPH sustained winds with gusts up to 25 mph. This 
will be slightly higher than Monday due to a bit higher mixing. 

The continued southwesterly moisture stream along the ridge and weak
isentropic lift has caused guidance to show some very light QPF after
18z Tuesday. It's going to be tough to get any showers with the
drying associated with the mixing but given the higher moisture and 
lift, and even a bit of instability (we didn't have any Monday) a 
20% chance of a shower seems reasonable at this time. Even so, highs 
should get even warmer than Monday-in the upper 70s, possibly 80 in a
few places out west. Record highs for Tuesday are: 79 in Huntsville 
that was set in 1986 and 79 also in Muscle Shoals, set in 1917.

Even though the instability decreases Tuesday night, the continued 
lift in the warm sector ahead of an approaching cold front/upper 
trough, warrants a slight chance to chance of showers. The cold front
will be near central AR Wednesday morning but it is well ahead of 
its parent upper trough, being propelled by a weak upper shortwave 
and it's movement has slowed every model run this week, due to the 
strength of the upper ridge. Have continued to back off the POPs, 
only introducing likely in the NW areas for Wed afternoon with 
showers possible out ahead of it. The remaining precip with the front
will overspread the area Wednesday night. It weakens/washes out on 
Thursday with scattered showers through the day. In terms of thunder,
Wednesday has good instability/shear and no cap to support 
thunderstorms but very little, if any, lift. Wednesday night has the 
lift, but not much else. But will continue the mention of isolated 
storms. Can't make much of an argument for storms on Thursday but 
given the pattern, won't remove it at this point. 

Temps once again will be warm Wednesday and Thursday but slightly
cooler due to rain/clouds. Highs will be mid to upper 70s Wednesday
and lower to mid 70s on Thursday. Lows each night will be in the mid

.LONG TERM...(Thursday night through Sunday)
Issued at 222 PM CST Mon Feb 19 2018

The inconsistencies over the past few days with the midweek system 
make it somewhat uncertain with regard to the forecast at the start 
of the long term. However, whether we get a true front through in on 
Thursday or if it stalls before it reaches our area, southerly flow 
will return in earnest by Friday morning. Given some warm air 
advection and weak lift Thursday night, we could see some isolated to
scattered light showers, though these won't amount to much. Temps 
will remain on the mild side, with lows expected to be in the 60s. 
The subtropical ridge will begin to break down through the day on 
Friday, as a strong upper trough begins to dig into the Desert 
Southwest. Despite the lowering heights, continued southerly to 
southwesterly flow through the vertical column will keep a steady 
stream of warm and moist air across the area. This will help highs 
warm into the mid to upper 70s. Might see an isolated light shower 
again on Friday, but again not much in the way of precip. 

The upper trough will eject into the southwestern Plains on 
Saturday, eventually developing into a cut-off low. As it
strengthens, surface cyclogensis will occur over the TX Panhandle, 
with a cold front trailing south of the low. This system will slowly 
track to the northeast through the day on Saturday, reaching the Mid 
Mississippi Valley by Saturday evening. As stated above, there 
remains some inconsistencies among models with the mid range 
forecast, however with this system, there is considerable agreement 
among the models, along with run to run consistencies as well. 
Therefore, a bit more confidence exists with the weekend system. 
Ahead of the arrival of the front/precip, an abundance of moisture 
will be in place and temperatures will be well above normal. 
Temperatures will be a few degrees lower than those observed Friday, 
given the lower upper heights as the trough inches closer, but we 
will still break the 70 degree mark. The front will enter the area 
Sunday night, with showers and thunderstorms moving ahead of the 
system. It's a bit too early to start nailing down threats with this 
cold front, however given the overall setup, this may bring our first
shot of organized thunderstorms this year. The front will exit the 
area on Sunday, bringing some cooler and drier air across the region.


.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 528 PM CST Mon Feb 19 2018

VFR conditions should prevail across north AL/southern middle TN
until 10-12Z when MVFR cigs (around 2500 feet) may develop over the 
gulf coast and lift north across MS/AL. These clouds will be more
likely near KMSL/NW AL, but have included in KHSV as well until 18Z.
Southerly wind speeds of 14 kts gusting to 25 kts have diminished to
around 9-11 kts. However, these winds will strengthen to 14-15 kts 
gusting to 20 kts after 14-15Z.





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