Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 290252

Area Forecast Discussion
National Weather Service Huntsville AL
952 PM CDT Tue Mar 28 2017

.NEAR TERM...(Rest of tonight)
Issued at 952 PM CDT Tue Mar 28 2017

Under mostly clear skies, temperatures had fallen into the upper 50s
to lower 60s across the TN Valley, with dewpoints just a few degrees
cooler. Surface high pressure will continue to shift to the east
across the Great Lakes region and winds will become more easterly by
sunrise, though expecting winds to remain below 5 mph overnight. The
low pressure system to the west will continue to move eastward, and
low level winds will shift to the south after midnight. This will
bring an increase in moisture northward and low level clouds may
develop in response to this. Despite the cloud cover, temperatures
are still expected to fall into the upper 40s across the north to mid
50s across the south. This will allow dewpoint depressions to drop
to around 3 degrees and patchy fog may develop. Previous forecast was
on track, so not major changes were needed.

.SHORT TERM...(Wednesday through Thursday)
Issued at 323 PM CDT Tue Mar 28 2017

Any fog that`s present at daybreak should quickly burn off shortly
after sunrise. Light/variable winds in the morning should become
southeasterly as the surface high moves towards the east coast. The
high moving to our east and a return southerly flow will bring the
frontal boundary south of the area back as a warm front. The return
of this front could bring an isolated shower and/or thunderstorm
Wednesday afternoon.

Better rain chances are in the forecast on Thursday/Thursday night
as a system currently affecting the southern High Plains heads
eastward. Model output from the various model suites overall was in
similar agreement, but of course disagreements in the details. The
NAM/GFS were a bit deeper/faster than the ECMWF/Canadian. Also, the
models were picking up on possible development along Gulf coast,
which would intercept some of the moisture/ instability from the
Gulf. This would tend to temper overall storm strength during
Thursday. Also, the fact the heaviest rains comes through after dusk
Thursday would encounter a cooler, slightly more stable environment
which helps keep convection weaker too. Convection during Friday
should wind down from west to east as this next system`s cold front
moves across the Tennessee Valley.

High temperatures should approach 80 tomorrow, and mid/upper 70s on
Thursday as the showers/storms commence. Friday will trend cooler
with highs around 70.

.LONG TERM...(Thursday night through Monday)
Issued at 323 PM CDT Tue Mar 28 2017

We start the long-term period with a system exiting the area to the
east. A few lingering light showers might be possible across the
eastern half of the area Friday evening. But expect those to be very
isolated. Drier air quickly filters into the area Friday night and
lows could dip into the upper 40s by Saturday morning. An upper
level ridge builds over the TN Valley on Saturday and we can expect
a warming trend in temps both Saturday and Sunday. Highs on Sunday
could approach the 80 degree mark.

While we are sitting high and dry over the weekend a system will be
impacting the desert southwest. This system begins to shift east on
Sunday into the TX Panhandle. However, there is some disagreement
between the latest GFS/ECMWF in terms of just how quickly this
system kicks eastward. The 500mb ensemble means from the
GFS/CMC/NAEFS all seem to have a similar handle on the timing, which
would line up a bit more with the 12Z GFS. The ECMWF might be under
doing the influence of the departing ridge. In either case though,
it appears that as the system shifts out of the desert SW and into
southern US and begins to take on a slight negative tilt, that a MCS
could develop over eastern TX and ride along the Gulf Coast. The
strongest jet does remain to our south and would tend to point
towards the MCS along the Gulf idea. This would likely cut us off
from the deeper moisture and limit the overall strong/severe
thunderstorm threat. But with the main upper level dynamics moving
over the area, thunderstorms are still likely as lapse rates do
steepen aloft but any instability would remain elevated. Due to the
timing differences though have gone with a blend in the guidance but
leaning a bit more towards the latest GFS.

Beyond early next week the forecast remains a bit uncertain and
potentially unsettled as we could see another one or two systems
move across the TN Valley. Went with a blend of long-term guidance
with some model disagreements.


.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 620 PM CDT Tue Mar 28 2017

VFR conditons are expected at the KMSL and KHSV terminals through the
next 6 hours, as winds become light and skies remain generally mostly
clear. An abundance of low level moisture, along with the clear skies
and light winds, will give way to MVFR fog development around 10Z at
both terminals. Although guidance suggests MVFR cigs as well early
Wednesday morning, confidence is not high enough to include with this
issuance. Visibilities, and low cigs should they develop, will
improve after 14Z, with VFR conditions expected through the remainder
of the period.




LONG TERM...Stumpf

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