Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 282023
AFDHUN

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

.NEAR TERM...(Tonight)
Issued at 323 PM CDT Tue Mar 28 2017

After a wet and stormy start to the work week yesterday, much calmer
weather prevailed across the region this afternoon. A frontal
boundary that moved southward across the area last night has made
it to north of the I-20 corridor. It`s position can be delineated
nicely from new GOES-16 visible data, indicating slightly
drier/cooler air up this way compared to south of the boundary.
Isolated to scattered showers have formed near and south of the
boundary. So far, the showers have remained more tame than
yesterday`s strong and severe convection - with no lightning noted so
far.

The surface low that brought the stormy weather yesterday has made
it to the Mid Atlantic region, pushed eastward by high pressure
building southward from the Upper Mississippi Valley. This high
bringing slightly cooler air and light winds tonight, along with
plenty of residual moisture from the showers of yesterday will create
patchy fog development tonight. Given that clouds will also be on
the increase, have not gone with area of fog and/or widespread dense
fog. Lows will be in the low/mid 50s - a tad cooler than this
morning.

.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 18Z TAFS through 18Z Wednesday afternoon)
Issued at 102 PM CDT Tue Mar 28 2017

Post frontal stratus clouds across the Tennessee Valley were finally
beginning to lift/break up due to daytime heating and mixing. As of
18Z, CIGs over the TAF sites have increased into the MVFR category
(improved from IFR just recently). Continued improvement is expected
for the rest of the day. Tonight, light winds and the presence of
residual moisture from recent heavy rainfall will lead to fog/mist
formation in the late night. Have reduced VIS values to IFR for the
predawn, along with MVFR CIGs. Conditions should improve back to VFR
a few hours after sunrise. Light NW winds this afternoon will become
light/variable overnight, then SE around 5kt after 29/1400Z.

RSB


&&

.HUN WATCHES/WARNINGS/ADVISORIES...
AL...NONE.
TN...NONE.
&&

$$

NEAR TERM...RSB
SHORT TERM...RSB
LONG TERM...Stumpf
AVIATION...09


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