Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 181946

Area Forecast Discussion
National Weather Service Huntsville AL
246 PM CDT Wed Oct 18 2017

.NEAR TERM...(Tonight)
Issued at 245 PM CDT Wed Oct 18 2017

Another quiet and cool fall night is in store tonight with a surface
anticyclone over the Appalachians keeping the region dry underneath a
modified continental polar airmass. So, temperatures should drop off
quickly after sunset and reach into the low to mid 40s by Thursday

Similar to what happened this morning, the only main impact for
tonight could be radiation fog formation along rivers, and lakes.
This may occur as a result of warm water interacting with the cooler
airmass. Also, there could be some valley fog formation in the
valleys as dewpoint depressions drop close to 0. Due to this
potential, did add patchy dense fog in the forecast for the rivers,
lakes, and valleys late tonight into early Thursday morning.

.SHORT TERM...(Thursday through Friday night)
Issued at 245 PM CDT Wed Oct 18 2017

Once the fog dissipates on Thursday morning, little change in the
weather is expected on Thursday as a synoptic ridge builds from the
NW Gulf of Mexico to the Southeast as a pair of troughs amplify over
the Intermountain West. Daytime high temperatures may be a degree or
two warmer on Thursday with this ridge building and the resultant
deep southerly flow. One thing the models did should is that at the
surface cold air damming may continue through Friday as the surface
anticyclone doesn`t move much from the central Appalachians.
Overnight lows may be a little warmer on Thursday night into early
Friday morning, but still in the 40s.

As the ridge axis shifts east on Friday, a LLJ will become oriented
over the MS River Valley and should begin to bring cloud cover
further north especially over western portion of the CWA (NW AL).
Surface dewpoints may be slower to rise given the lingering cold air
damming over the eastern half of the country. Temperatures should
also be warmer in the mid 70s by Friday afternoon. These warmer
temperatures will also mean `warmer` temperatures on Friday night:
in the low 50s.

.LONG TERM...(Saturday through Tuesday)
Issued at 245 PM CDT Wed Oct 18 2017

High pressure influencing the short term will persist into Saturday.
This will keep temps warm in the mid/upper 70s, overnight lows
seasonable in the lower 50s and dry conditions.

A major pattern change will finish out the extended forecast,
however models still do not agree on exactly how it will play out,
thus lowering forecast confidence on the event. But they at least
have a general agreement on what will happen. The lingering upper
level ridge will be pushed eastward into the Atlantic as a large
upper-level trough digs across the Midwest this weekend. A sfc low up
in Canada will have a trailing cold front that will move into the TN
Valley Sunday night/Monday bringing showers and thunderstorms with
rain ending on Tuesday. Not expecting any severe weather with this
system, however heavy rainfall is possible as PWATs reach over 1.5
inches on Monday.

Behind this system, look for another taste of Fall as the trough
continues to dig into the Southeast. Highs on Tuesday will be in the
upper 60s with overnight lows back in the lower 40s, with Wednesday
even cooler than that!


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1228 PM CDT Wed Oct 18 2017

VFR conditions are expected to continue across north Alabama/southern
middle Tennessee for the next 24 hours. The main exception is the
potential for fog formation near rivers and valleys that may cause a
drop in VIS between 19/10Z-19/14Z, especially near K4A6, K4A9, K8A0.
There may be some ground fog that affects KMSL around that same time
frame but not confident enough to include reduced VIS in TAFs as
this time.





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