Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 220358

Area Forecast Discussion
National Weather Service Huntsville AL
1058 PM CDT Mon Aug 21 2017

For 06Z TAFS.


.NEAR TERM...(Tonight)
Issued at 839 PM CDT Mon Aug 21 2017

High pressure centered over the AL/TN/GA area was able to keep much
of the afternoon showers/thunderstorms at bay. The exception has been
near NW AL where a few isolated storms continue along a weak
convergence axis. Any lingering activity will taper off over the
next few hours leaving clear skies. Even with the clear skies temps
won`t fall too far, due to dewpoints in the low to mid 70s. Did end
up making a few tweaks to temps in the sheltered valley locations
where temps could drop into the upper 60s. Otherwise, expect temps at
sunrise to be in the low to mid 70s. The rest of the forecast is in
good shape and no other changes are needed.

.SHORT TERM...(Tuesday through Wednesday night)
Issued at 222 PM CDT Mon Aug 21 2017

The upper level ridge currently over the southeastern CONUS will
begin to weaken on Tuesday, as a broad upper trough swings into the
upper midwest. Moisture will continue to advect northward across the
areas, sending PW values above 1.5 inches by Tuesday afternoon. The
combination of increased moisture and lower heights will lead to
isolated diurnally driven thunderstorms. The coverage may be a bit
higher, but with little to no large forcing mechanism, will keep the
coverage low for now.

Meanwhile, the upper trough will swing through the Great Lakes
region, with a cold front trailing south of its parent low well to
the north of the TN Valley. Models are in fair agreement that this
front will push slowly southward, with the axis of a prefrontal
trough moving through the forecast area late Tuesday night and into
the early morning hours on Wednesday. Scattered showers and
thunderstorms will move into the area during the late evening hours
and then become more numerous towards daybreak as the greater
forcing enters the forecast area. Not too confident on the coverage
of showers and thunderstorms overnight, given the lack of
instability, but still kept close to forecast guidance. The cold
front will then move through the area on Wednesday, with numerous
showers and storms impacting the region during the day. Given that
most of the upper dynamics will be displaced from the TN Valley, not
anticipating any organized severe convection. Showers and
thunderstorms will end from north to south as the cold front drops
to the south of the area late Wednesday night.

Temperatures on Tuesday will be hot once again as mostly clear skies
prevail. Additionally, dewpoints will remain in the lower 70s,
creating heat indices nearing 100 degrees, especially across the
west. Overnight lows will be mild as cloud cover increases late
Tuesday night. Wednesday will be a bit cooler as overcast skies and
thunderstorms continue through the day. The front should clear the
area quickly enough Wednesday night for CAA to bring in temperatures
in the mid to upper 60s by Thursday morning.

.LONG TERM...(Thursday through Sunday)
Issued at 222 PM CDT Mon Aug 21 2017

Much of the extended portion of the forecast will be pleasant, with
the exception for a few chances of showers/storms here or there.
Daytime temperatures will generally stay in the lower to middle 80s,
with morning lows starting out each day in the lower to middle 60s.
Normal values this time of year are in the 90-93F range for highs
and the 68-71F range for morning lows.

The extended begins Thursday with a cold front displaced well S/E of
the local area, with lower dewpoints filtering into the area thanks
to NW flow aloft. Some locations in Srn Middle TN will likely wake
up to dewpoints in the upper 50s Friday morning, with the rest of
the area in the low 60s! With the upper trof meandering slowly Ewrd,
this will leave the area in NW flow for much of Friday, before
finally translating E of the area. At the sfc, high pressure in
place will do the same, which will allow for winds to become more
SErly, increasing moisture Friday night into Saturday. As
disturbances wobble toward the area this weekend, isolated showers
and storms return Saturday, with longer-range models expecting the
most coverage on Sunday and Monday. Have adjusted PoPs down just a
bit from SuperBlend for this timeframe to the lower 50s, but further
adjustments will likely be warranted over the coming days. By this
point in the forecast, one of these disturbances begins to develop
into an area of low pressure at the base of a departing H5 trof to
our E on Monday. To our W, a ridge aloft begins to encompass much of
the Wrn 2/3 of the CONUS, making for a drier forecast on tap for
late Tuesday morning and beyond.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1058 PM CDT Mon Aug 21 2017

VFR conditions will continue through the TAF period. Winds will be
light and variable tonight but favor a W/SW direction during the day
Tuesday around 5kts. After 17z Tuesday isolated to scattered showers
and thunderstorms could develop. However, uncertainty in timing and
location remains too high to include in TAFs at this time. A front
will approach the area from NW Tuesday evening increasing
thunderstorm chances.




NEAR TERM...Stumpf

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