Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 010259

Area Forecast Discussion
National Weather Service Huntsville AL
959 PM CDT Fri Sep 30 2016

Adjusted Sky grids and added Patchy fog.


The upper level low continues to sit and spin near IN/KY this
evening. A raggedy line of clouds has streamed into the northern half
of the area but recent satellite loops indicate these clouds will
break up over the next few hours. This is backed up by latest
SREF/NARRE guidance and recent forecast soundings. Observations to
our NW show dewpoints have nudged up a few degrees from yesterday
evening with values now in the mid to upper 50s. While winds right at
the surface will be virtually calm tonight, there is still a slight
NW wind between 5-10 kts between 1,000-3,000ft above the surface. So,
there might still be some advection of these higher dewpoints into
the region tonight. With increased dewpoints tonight, we are not
expecting temps to fall quite as low as they did yesterday with lows
tonight expected to be at or above the 50 degree mark.

The main question is the potential for fog again tonight. The
scattering out of the clouds as discussed above and slightly higher
dewpoints is favorable for another night of fog formation. However,
recent probabilistic guidance keeps the best chances for fog in TN.
The guidance nailed the dense fog yesterday night into this morning.
So, based on that and what is discussed above added patchy fog
tonight but kept it for areas mainly north of the TN river. The
remainder of the forecast is in good shape and no other updates are
needed at this time.



(Issued 710 PM CDT Fri Sep 30 2016)
For 00Z TAFs: Although skies temporarily cleared across nrn AL late
this aftn, IR satellite imagery suggests that another batch of bkn-
ovc altostratus clouds will invade the region from the nw this
evening. Cigs will likely remain in the 4-8 kft range for majority of
the upcoming forecast period as models indicate this layer of cloud
cover lingering well into Sat aftn. However, if any dissipation in
this cloud deck occurs during the early morning hours, calm winds
will support development of fog and low stratus -- similar to what
occurred this morning. At this time, we will only include a tempo for
vsby reductions to 4SM btwn 01/10-13Z but drops to IFR/LIFR will be
psbl if higher-lvl clouds completely dissipate. Lgt nly sfc flow will
diminish to VRB02 kt within first 1-2 hrs of TAF period, with a lgt
wly flow developing tomorrow morning.





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