Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 240526

Area Forecast Discussion
National Weather Service Huntsville AL
1126 PM CST Thu Feb 23 2017

For 06Z TAFS.


.NEAR TERM...(Tonight)
Issued at 817 PM CST Thu Feb 23 2017

Temperatures are still warm as of 8pm with most areas in the middle
50s to lower 60s. Earlier mid level clouds have dissipated with just
a few cirrus clouds streaming across from the west. Mid-level ridging
continues to strengthen overnight with only slight drops in the 850mb
temps noted in the northeastern areas. With the mostly clear skies,
temps will fall but the 5-10mph wind and the continued warm southerly
flow will only allow them to drop to the lower to upper 50s. The
coolest values will be in the east. Did not make many changes from
the previous forecast other than lowering temps a deg or two in the

NARRE/SREF guidance has now picked up on the low level cloud deck
moving in from the south that was more uncertain earlier this
evening. Highest chances of this happening will be in areas west of
Interstate 65, due to greater isentropic lift, but cannot rule out a
few in the east as well. Will keep skies mostly clear in the grids
and bring clouds back in around 10-11z.

.SHORT TERM...(Friday through Saturday)
Issued at 230 PM CST Thu Feb 23 2017

The upper level ridge will strengthen through the morning hours on
Friday as an upper level low pushes into the Central Plains. Skies
will remain partly cloudy, with plentiful sunshine aiding in the
southerly flow to warm max temperatures in the upper 70s. A few
spots may reach the 80 degree mark, especially across the west,
before the eastern periphery of the upper trough pushes into the

As the upper low moves east-northeast during the day Friday, a
surface low will develop and trail a cold front southward. This
system will track into the Great Lakes region during the late
afternoon hours, with the cold front reaching the MS Valley by
sunset. Ahead of this system, dewpoints will rise into the upper
50s, as southerly flow continues. Showers and thunderstorms will
develop to our west and north and move into the forecast area
between 00Z and 03Z and then quickly push eastward, exiting the
forecast area between 06Z and 09Z when the cold front is expected to
clear the area.

There will be several limiting factors in terms of the coverage and
strength of storms. First, the upper dynamics will remain well north
of the forecast area, with limited lift this far south. Meanwhile, a
capping inversion is expected to remain in place, which is more than
plausible considering the strength of the retreating upper ridge.
So, despite the fact that we will be fairy warm, dewpoints remaining
in the 50s will certainly not help us break the cap and get any
surface based instability. Additionally, this cap may prevent much
of the area from seeing much in the way of convection as several
hires models show very little precip south of TN.

Saturday will be quite cool compared to the past week, as strong CAA
occurs behind the cold front. The front looks to pass through
quickly enough for our overnight lows to drop into the upper 40s
Saturday morning, with little warming through the day. High pressure
building southward will keep skies clear and afternoon highs will
only make it into the low to mid 50s. With the clear skies and calm
winds Saturday night, decent radiational cooling conditions will
mean temps falling below freezing.

.LONG TERM...(Saturday night through Wednesday)
Issued at 230 PM  CST Thu Feb 23 2017

Sunday will start off on a chilly note with temps around 30 degrees,
making it feel a bit more like a typical February morning. As the
sfc high overhead shifts eastward, the southeasterly winds will warm
temps up nicely towards 60 degrees.

Our next chance of rain will be on Monday morning to kick off an
unsettled weather pattern. As a shortwave swings from the Plains to
the OH Valley, a sfc low will move across the MS Valley. With
plentiful moisture and warm air ahead of this system, showers will
develop and spread into our area as we head into the day Monday.

Latest guidance is in disagreement with development of a sfc low and
potential front. The GFS develops a stronger sfc low and pushes a
front through the area on Tuesday. On the other hand, the ECMWF never
really develops a sfc low and an associated front and is therefore
considerably lower with QPF. With this in mind, used a blend between
the two but leaned towards the GFS and held onto higher POPs just a
little bit longer in our eastern zones on Tuesday. Even with the
potential rain and frontal passage, temps will still warm towards 70
degrees. Overnight lows Tues/Wed will be in the upper 50s, which is
more like our seasonable daytime highs for this time of year.

A sfc low up in the Great Lakes will send another cold front down to
the TN Valley on Wednesday. As a result, showers and thunderstorms
are possible Wednesday. Included thunderstorms as the cap that
prevails on Tuesday erodes, allowing for some decent CAPE (~200-600
J/kg) and shear (~60kt 0-6km) by the time the cold front arrives.
Strong to potentially severe storms are possible with the front on
Wednesday. Models agree on pushing this front out fairly quickly and
filtering in cooler and drier air behind it.


.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1125 PM CST Thu Feb 23 2017

VFR conditions and wind around 5-10kt continue through much of the
night. Continued with lower CIGS around 2500ft with this update.
Confidence is not high regarding if these clouds will move in and the
eventual height so this will need to be monitored. BKN040 will
prevail through much of the day Friday with winds gusting to 20-25kt
in the afternoon. A cold front will approach toward the end of the
TAF period and introduced -SHRA at KMSL at 01z and KHSV 03z. The
front itself should move through around 5-6z at KMSL. Did not include
thunder at this time but that may need to be added in future





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