Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 240900

Area Forecast Discussion
National Weather Service Huntsville AL
400 AM CDT Tue Oct 24 2017

.NEAR TERM...(Today)
Issued at 359 AM CDT Tue Oct 24 2017

Clear skies and light winds have allowed temperatures across the TN
Valley as of 08Z to drop into the lower 50s to upper 40s. Under these
conditions, fog development, some dense, has occurred near the
rivers and in the valleys, especially in NE AL. RGB Nighttime
Microphysics highlights the fog well and the Fort Payne sfc ob has
observed a quarter mile or less for the past two hours. The foggy
conditions will improve as winds pick up ahead of the re-inforcing
front that is currently located along the MS River.

As for the rest the day, the main story is all about the cold air
advection. With northwesterly winds 10-15 mph and gusts 20-25 mph
streaming cooler air into the TN Valley, daytime highs will only
reach the lower 60s despite the sunshine.

.SHORT TERM...(Tonight through Thursday)
Issued at 359 AM CDT Tue Oct 24 2017

High pressure will begin to build into the region Tuesday night
allowing for calm winds and mostly clear skies through the night.
This will allow for temps to drop into the mid/upper 30s and possible
patchy frost development by early Wednesday morning. Will let the
day shift make the call for potential frost advisory. As it looks
currently Southern Middle TN will be most at risk. Wednesday`s
daytime highs will be cooler with highs reaching the upper 50s and
lows in the upper 30s/lower 40s. Temps will be a little warmer on
Thursday as a ridge builds into the region with highs in the upper

.LONG TERM...(Thursday night through Monday)
Issued at 359 AM CDT Tue Oct 24 2017

Friday should be the warmest day of the week with good southerly
return flow and enough sunshine to help push highs into the upper 60s
to around 70 degrees. Clouds will be on the increase later in the
afternoon as a strong cold front approaches the region. A few
isolated to scattered showers will be possible late in the afternoon,
though most locations will remain dry.

A dramatic change in the forecast will occur Friday night into
Saturday as the aforementioned cold front and strong upper-level
trough pushes into the Tennessee Valley. A broad area of showers
(some locally heavy) will accompany this front as it moves into the
region. Models are still in good agreement with the timing, with the
best chances for precipitation areawide being 06z to 18z on Saturday,
before gradually tapering off from west to east later in the day on
Saturday. Given the lack of instability, have kept a mention of
thunder out of the forecast. However, given the dynamics that one
might expect with such a strong frontal system, it would not take
much instability to generate thunderstorms, so will keep an eye on
this in the coming days.

The notable change with respect to the weather will be the air mass
itself, as significantly cooler air will moves in. Given the clouds,
rain and this cooler air mass, highs on Saturday will only climb
into the low to mid 50s! Then as precipitation tapers off Saturday
evening, strong cold air advection will take place and lows will drop
into the mid 30s by early Sunday morning -- and a few spots in
Southern Middle Tennessee potentially reaching the freezing mark. A
mostly sunny day on Sunday will do little to warm us up under this
stout northerly flow, as highs in the 50s will be common once again.
A more widespread freeze is possible Sunday night into early Monday
morning across much of the Tennessee Valley as good radiational
cooling will take place. Will certainly need to monitor for the need
for frost/freeze products this weekend. Thereafter, high pressure
will build in, prompting a subtle warming trend heading into the
middle of next week.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1220 AM CDT Tue Oct 24 2017

Winds have weakened over the past few hours but should start to
pick back up as a front approaches the area. Expect an increase in
winds out of the SW between 06-09z and then switching to the NW by
12z with speeds increasing through the morning hours. Gusts by late
Tuesday morning through the afternoon hours could be upwards of
20-25kts at times. VFR conditions are forecast for the TAF period
with a SCT 5,000ft cloud deck possible between 15-22z Tuesday.





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