Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 300536

Area Forecast Discussion
National Weather Service Huntsville AL
1236 AM CDT Tue May 30 2017

For 06Z TAFS.


.NEAR TERM...(Tonight)
Issued at 851 PM CDT Mon May 29 2017

Outside of a few pockets of lingering showers across NW AL, early
evening convection has just about come to an end across the cntrl TN
Valley this Memorial Day. Weak frontal boundary has lifted slightly
to the n closer to the AL/TN state line, although this looks to have
little effect on any lingering showers/tstms. The boundary may
actually drift slightly more to the n during the overnight hrs, and
provide more of a focus for convection across wrn/mid TN during the
day Tue. What showers remain across the area should end over the next
couple of hrs as the last bit of latent heating diminishes and a
weak low level inversion develops. However, with the frontal boundary
moving n coupled with the persistent mid/high cloud cover, patchy
dense fog may not be that much of a concern early tomorrow morning
other than perhaps some light fog in a few spots. As such, rain/tstm
chances were lowered/removed for the remainder of this evening and
patchy fog removed for the early morning hrs Tue.

.SHORT TERM...(Tuesday through Wednesday Night)
Issued at 244 PM CDT Mon May 29 2017

Assuming the frontal boundary pushes south or maybe on top of the
area, an additional upper wave will move across and once again, help
create showers and thunderstorms along the front. This looks to be
mostly south of the area but could clip our southern counties. Looks
like another weak wave could interact with the terrain in the
northeast and produce a few showers/storms as well. In conclusion,
scattered showers/thunderstorms for the entire forecast area seems
like a good bet. A strong storm is not out of the question Tuesday
with instability/lapse rates higher than today. There is more dry air
and slightly lower dew points than what we have been seeing but
there is basically zero shear. Given the uncertainty of the
boundaries, could just be some pop up showers and a storm or two.

Feel that Tue night should be mostly dry with any storms diminishing
by midnight. However, given lingering instability aloft and waves
moving along the upper low, will leave in isolated POPs and match
the neighbors.

With the upper low still lingering in the same location as it is in
right now, another front will be able to develop and approach the
area on Wednesday. Southerly winds ahead of it should be able to
pull dewpoints back into the mid to upper 60s with PW values around
1.25-1.5 inches. Instability/lapse rates will be higher than
previous days and shear at the lower levels will be non zero
(although that`s not saying much). There isn`t much upper support but
I have slightly higher confidence in a few strong storms, maybe 1 or
2 severe for Wednesday. Once again, the front moves through,
shifting winds to the NW and with the loss of daytime heating, storms
end by midnight.

Temps will be near normal with highs Tue-Wed in the lower 80s and
lows in the lower 60s.

.LONG TERM...(Thursday through Sunday)
Issued at 244 PM CDT Mon May 29 2017

During the afternoon hours on Thursday, models push a warm front
northeast into northern Alabama. Most guidance develops at least
scattered showers and thunderstorms in the afternoon along this
boundary. Best coverage with it will be along/near the surface warm
front and the upper level energy associated with it. A fairly moist
boundary layer looks to still be in place, along with dry air aloft
and fairly steep low level lapse rates. There looks to be little
shear (speed or directional) given the weak and low level flow. Thus
would expect typically summertime pulse storms that could become
strong. The main threats with any strong storms would be gusty winds
to around 40 mph, small hail, and frequent lightning given forecast
surface based instability. Clouds and precipitation should keep high
temperatures mainly in the lower 80s. The exception being east of I-
65, which may see a bit more sunshine and thus have highs in the
lower to mid 80s there. As the warm front pushes northeast across
northern Alabama Thursday night, rain chances should increase, but
kept them high chance for now.

More pronounced southerly or southwesterly low level flow will warm
overnight lows into the mid 60s by Friday morning. Models seem to
wash out the boundary (warm front) over or just north of the area
Friday into Saturday, keeping scattered showers and thunderstorms in
the forecast. Similar parameters continue to be in place during this
period. Thus a continuation of strong storms are possible.  Between
the clouds and scattered precipitation, this should keep highs in
the lower 80s.

By Saturday afternoon into Saturday night, both GFS and ECMWF move a
decent longwave trough axis southeast from Texas/Ohio into the
Tennessee Valley. This should increase forcing over the area,
especially Saturday night. Shear still doesn`t look that great, but
again enough instability should be in place for strong storms
capable of frequent lightning and gusty winds. A better coverage of
precipitation is shown by models during this period (especially in
the afternoon/evening). However, given how far out in the forecast
this is, only kept high chance pop for now. With cloud cover and
more widespread rainfall, high temperatures around 80 degrees look
more likely. This may even be too high for temperatures. Lows will
remain pretty warm (upper 60s to around 70 degrees) with southerly
flow expect through Saturday night ahead of the longwave trough axis.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1130 PM CDT Mon May 29 2017

Some reduced vis are in place near the KMSL terminal due to some
-br/fg. Generally xpct these vis to var btwn 2-4SM thru the early
morning hrs Tue before conds quickly improve shortly after 12Z.
Otherwise, with mainly mid/high clouds in place across the area, VFR
conds are generally xpcted thru the TAF period. Only exception may
be some very -br/tempo MVFR conds near the KHSV airport during the
early morning period.





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