Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 240839

Area Forecast Discussion
National Weather Service Huntsville AL
239 AM CST Wed Jan 24 2018

.NEAR TERM...(Today)
Issued at 239 AM CST Wed Jan 24 2018

Quiet weather across the Tennessee Valley early this morning, with
high pressure at the surface beginning to nose its way in from the
west. RGB imagery shows a stratus deck around 3kft across Middle and
East Tennessee that has grazed portions of far Northern and
Northeast Alabama and Southern Middle Tennessee. Drier air to the
southwest is eroding this cloud shield as directional flow gradually
nudges it further to the ENE. As a result, an early morning overcast
sky across Southern Middle Tennessee and far Northeast Alabama will
quickly join the rest of the CWA in becoming mostly clear by 12-15z.
Northwest flow at the surface and aloft, however, will maintain this
slightly "cooler" and drier air mass. This will limit the effects of
daytime heating somewhat as highs will be similar to yesterday,
peaking in the upper 40s to lower 50s. A shortwave trough and weak
cold front will bring some breezy NW winds and another shot of cooler
air late this afternoon into this evening. While there may be some
high clouds that filter into the area with this feature, moisture
will be very limited and a mostly clear sky is expected to prevail.

.SHORT TERM...(Tonight through Friday)
Issued at 239 AM CST Wed Jan 24 2018

A mostly clear night will be on tap for tonight as cooler air filters
into the region overnight. The calm winds and dry boundary layer will
support good radiational cooling and have nudged low temperatures
down a degree or two. Most areas will drop below the freezing mark by
Thursday morning, generally bottoming out in the mid to upper 20s. High
pressure will build into the region at the surface and aloft during
the middle to end of the work week, promoting dry conditions and a
gradual warming trend. With plenty of sunshine and winds veering to
the SE/SSE, temperatures will climb back into the mid to upper 50s by
Thursday and closer to 60 degrees by Friday. As winds veer more to
the south to SSW, Gulf moisture will also begin to creep back into
the region by Friday afternoon into Friday night ahead of an
approaching upper-trough that will be deepening over the Central
Plains and mid/lower Mississippi Valley. Weak isentropic lift ahead
of this system will bring some low/mid level cloudiness by Friday
evening as well as some isolated light rain showers after midnight
Friday night. However, the best chances for any meaningful shower
coverage and precipitation will occur later on this weekend.

.LONG TERM...(Saturday through Tuesday)
Issued at 239 AM CST Wed Jan 24 2018

The long term period starts with an approaching broad longwave trough.
Models have come into better agreement with the past few runs and
all show a more broad trough. The ECMWF/CMC models were showing a
more amplified pattern but latest runs have backed away from that
solution. Good southerly flow for much of Friday and continuing into
Saturday will result in above normal temps with highs in the
afternoon close to 60 degrees. Increasing clouds through the day is
about the only thing preventing temps from going higher than that.

The uncertainty with this forecast period is going to be related to
upper level energy moving N/NE out of the western Gulf of Mexico and
towards the LA/MS/AL coasts. The GFS wants to keep much of this
bottled up over the northern Gulf, while the ECMWF/CMC pull the
energy further north as the main longwave trough approaches and moves
it across the area on Saturday. The differences between these
solutions would be very little rain on Saturday if the energy stays
south (GFS solution) due to widespread convection along the coast or
an extended period of showers continuing for much of the day Saturday
(ECMWF/CMC solutions) as much of that activity moves over the area.
Ensemble guidance doesn`t paint any clearer of a picture with pretty
good spread in QPF forecasts. So, have gone with a blend, but worth
noting that the ECMWF/CMC were trending towards the less amplified
solution that the GFS has been advertising so there could be some
weight in lower QPF amounts for Saturday.

Lows Saturday night into Sunday remain warm due to clouds and WAA
with values in the mid to upper 40s. By sunrise on Sunday a cold front
will be entering NW AL and spreading east through the morning hours.
Good forcing along the front and from the trough axis should allow
for upwards of 0.5 of rain as the front moves across the area.
Cold and dry air is in place to start next week with lows Monday morning
near freezing but with sunny skies afternoon highs should be near
the 50 degree mark. Another night with temps at or below freezing is
expected Monday night into Tuesday as a surface high moves over the
area. Thankfully, the overall pattern is fairly progressive and the
high kicks off to the east and winds shift back to the south allowing
for above normal temps for the latter half of next week.


.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1110 PM CST Tue Jan 23 2018

Low clouds have pushed southward and into the KMSL and KHSV terminals
over the last hour. These clouds, currently around 3000 feet, have
eroded from the west, and are now east of KMSL. Trends suggest that
the clouds will continue to erode over the next couple of hours and
push out of the KHSV terminal by 08Z. This will leave VFR conditions
through the remainder of the period. Winds will remain from the
north-northwest and may become gusty during the afternoon on




LONG TERM...Stumpf

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