Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 260739

Area Forecast Discussion
National Weather Service Huntsville AL
239 AM CDT Thu Apr 26 2018

.NEAR TERM...(Today)
Issued at 238 AM CDT Thu Apr 26 2018

A rainy Thursday is in store for the TN Valley as an upper low
currently over northern AR moves SE through the day. The surface low
associated with this system was forming over central MS and should
move E/NE as the upper low enters the area. Moisture advection and
lift on the southern flank of the low has generated a band of
showers that are moving towards the TN Valley. However, drier air
evident in the 00z soundings from BMX/OHX have prevented some of this
initial push of radar echoes from reaching the surface as of 05-06z.
The latest obs from MSL show light rain starting to fall. All of
this activity will shift eastward through the morning hours and it`s
looking like a wet commute for much of the TN Valley.

Instability will be limited initially and any embedded thunderstorms
should be focused near the center of the surface low. As the upper
system moves east we`ll see some slight steepening of the lapse rates
and by mid to late morning we could see a few embedded thunderstorms
over our area but chances are low. Think any thunderstorms that do
develop remain to our south where the better low level moisture and
jet dynamics will be focused. In fact a majority of the hires and
latest HREF guidance point to this idea of heavier showers/storms
developing more to the south of the area. These models also show a
quicker end to the initial round of precip today as a dry slot aloft
works it`s way into the area. Then as the upper low moves overhead we
could see more scattered showers with a few embedded thunderstorms.
All activity should be east of the area by sunset tonight.

The clouds and rain will keep temps below normal today with highs
only warming 4-5 degrees from the current values.

.SHORT TERM...(Tonight through Friday night)
Issued at 238 AM CDT Thu Apr 26 2018

A shallow cool airmass rushes in behind the departing system and
should result in a low level inversion developing tonight. With
recent rainfall and whatever rain we get today expect some moisture
to be trapped beneath this inversion and patchy fog/low level stratus
to develop tonight. The benefit of the fog/low clouds will be that
temps never really get a chance to bottom out and lows remain in the
mid to upper 40s.

An elongated/sheared vorticity axis moving across the Plains today
ends up producing two distinct upper level systems overnight. One
moves across OK/TX and the other stronger system across the Great
Lakes. The OK/TX system continues to drop S/SE and will pass to our
S/SW on Friday. Models do show some remnants of the sheared vorticity
axis and have it going across the area Friday afternoon. There might
be just enough lift and lingering low level moisture to support a few
isolated light showers Friday afternoon. Have low end PoPs for
Friday to account for this. Otherwise, expect mainly dry and partly
cloudy skies on Friday. With the late April sun, even with a few
clouds around we should be able to warm up into the upper 60s to
lower 70s on Friday. High pressure moving in behind this feature
remains to our west and keeps the stronger CAA at bay for Friday
night. Expect temps to be close to Thursday nights values, maybe even
a degree or two warmer.

.LONG TERM...(Saturday through Wednesday)
Issued at 238 AM CDT Thu Apr 26 2018

An upper-trough centered over the eastern Great lakes, extending
south along the spine of the Appalachian Mountains will continue to
pull away from the Tennessee Valley this weekend. In its wake, high
pressure will build into the area from the west, which will promote a
mostly clear and sunny sky -- along with dry weather this weekend
into early next week. Initially, north to northeasterly flow will
help to keep temperatures in check by a few degrees this weekend,
with highs warming into the upper 60s to lower 70s. These readings
are about 5-8 degrees below normal for late April despite the ample

The aforementioned high will intensify as it shifts east into the
Tennessee Valley, eventually becoming established over the Southern
Appalachians by Tuesday (just east of the area). With winds veering
back to the south to southwest, moisture will gradually be on the
rise, along with temperatures. Breezy SW winds will enhance warming,
along with increased thickness values and temperatures aloft (~ 5
degrees Celcius higher at 850 mb) by Tuesday and Wednesday. This
will result in highs reaching to upper 70s to lower 80s by the middle
of the new week. A cold front advancing southeast from the Central
Plains and Missouri Valley will approach the Mid South late in the
period. Will likely see result in some denser cloud cover late
Wednesday into Wednesday night. However, any shower/thunderstorm
activity should remain well to the northwest. Most guidance is holding
off on any PoPs/QPF until late in the week, beyond the scope of this
forecast package.


.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1228 AM CDT Thu Apr 26 2018

An area of low pressure will move into the region, bringing lower
ceilings and widespread areas of -RA starting early this morning
through mid/late afternoon. By daybreak, ceilings and visibilities
will drop to MVFR levels are remain there through most of the day.
This -RA will taper off after 21z, but broken to overcast low stratus
decks around 1 kft will remain in place through the remainder of the
period. Winds will also quickly veer from the SE to SW between 18-21z
as a cold front moves through the region.




NEAR TERM...Stumpf

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