Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 232334

Area Forecast Discussion
National Weather Service Huntsville AL
534 PM CST Thu Nov 23 2017

For 00Z TAFS.


.NEAR TERM...(Tonight)
Issued at 113 PM CST Thu Nov 23 2017

Afternoon GOES-16 water vapor imagery shows that the mid-level
trough axis has moved across north Alabama/southern Tennessee. The
lingering clouds in northeast Alabama have cleared, leaving the
entire region clear and dry. Despite a cold start this morning (most
dropped into the 20s), the full sunshine is causing temperatures to
respond nicely, with everyone in the low-mid 50s.

Another clear/cold night with light/variable winds is on tap for
tonight with high pressure. Radiational cooling will be maximized,
so the forecast will undercut guidance by several degrees across a
large portion of the forecast area. A slight difference in low-
level moisture across northeast Alabama will keep temperatures a few
degrees higher there.

.SHORT TERM...(Friday through Saturday)
Issued at 113 PM CST Thu Nov 23 2017

Friday should be another pleasant day, albeit warmer, as weak
southerly flow ahead of an approaching cold front boosts temperatures
by another 5 degrees or so. With still fairly minimal moisture return
to speak of (despite the southerly flow), there should not be much
cloud cover during the day. Highs should reach well into the lower
60s, and based on guidance biases, the forecast will have a few spots
reaching the mid 60s. Friday night will be mild, but cloud cover will
increase markedly after midnight.

A weak front will move across the region Saturday afternoon. Moisture
remains limited to areas above ~700mb so the front should produce only
an increase in clouds. The 12Z GFS generated a little QPF (just
0.01-0.02 inches) but there is little support for this from the SREF
or NAEFS probabilities. Still, a sprinkle or two cannot be entirely
ruled out, mainly north of the Tennessee River.

.LONG TERM...(Saturday night through Wednesday)
Issued at 113 PM CST Thu Nov 23 2017

Another dry and seasonable period will follow behind the Saturday
front. Temperatures Sunday and Monday will hover right around normal
for late November.

The pattern becomes a little more interesting Tuesday into Wednesday
as a deep Pacific-originating trough digs into the southern Plains,
setting up robust southerly flow ahead of the trough. Deterministic
models (GFS/ECMWF) have consistently been far apart in terms of
timing, as one might expect with a feature of this amplitude.
While most of the ensembles (GEFS/NAEFS and even ECMWF) are faster
with this feature, the already-amplified pattern favors a slower
progression. So the forecast will continue to spread low-moderate
PoPs over the broader time period, Wednesday through Thursday. Even
then, there is not much confidence in receiving a lot of rain, since
few extended-range models create much moisture return despite the
southerly flow. The forecast will trend warmer than blends/MOS
Tuesday amidst prefrontal warm advection, but more towards the mean
Wed-Thu given the uncertainty about the timing of the trough.


.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 630 PM CST Thu Nov 23 2017

VFR conditions are expected at KHSV/KMSL TAF sites over the next 24
hours. Despite clear sky/lgt wind conditions, fog development is not
anticipated at TAF sites tonight. A ridge axis will move SEWRD
across the area tonight and early Friday resulting in lgt/vrb sfc
winds. However, winds will return from the SSW by about 16Z as the
ridge axis shifts to our SE tomorrow.





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