Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 201718

Area Forecast Discussion
National Weather Service Huntsville AL
1118 AM CST Sat Jan 20 2018

.NEAR TERM...(Rest of Today)
Issued at 1118 AM CST Sat Jan 20 2018

A weak cutoff mid/upper-level low currently drifting from LA into
southern MS is forecast to advance eastward to near the southern MS-
AL border by late this afternoon. Weak diffluent flow aloft and
associated vertical motions to the northeast of this feature has
supported a broken-overcast layer of high-based stratus clouds this
morning. However, this cloud deck is expected to lift/scatter during
the afternoon hours as the diffluent regime is replaced by a COL
region/weak steering currents to the north of the Gulf coast

At the surface, light but steady southerly winds will continue
throughout the day as the region will remain to the northwest of a
high centered across southeastern AL/southwestern GA and the western
FL panhandle. With current observations indicating temperatures
running several degrees above forecasted values, we have increased
max temps into the m50s-around 60 degree range based on persistent
southerly winds and greater insolation anticipated this afternoon.

.SHORT TERM...(Tonight through Monday)
Issued at 245 AM CST Sat Jan 20 2018

Partly to mostly cloudy skies will continue tonight, as more
moisture from the south returns further inland. The worked over Gulf
will not be yielding as much lower level moisture yet, given
dewpoints should rise to around 40 Sunday morning, and briefly into
the lower 50s on Monday. Even warmer temperatures should end the
week, with highs later today rising into the low to mid 50s. Even
warmer conditions are forecast on Sunday, rising into the lower 60s.

A powerful storm system now moving across the west coast will
translate eastward, and produce a new surface low late Saturday
night across the Colorado Divide and adjacent High Plains. This new
cyclone should deepen as it moves NE towards the Great Lakes. A cold
front trailing southward from this low approaching the region, will
bring rain chances back to the Tennessee Valley beginning early
Monday. Have stayed close to previous timing regarding the chances of
showers, with the models in relatively good agreement timing wise.
The Canadian and to a lesser extent the NAM/GFS were hinting at a
squall line type setup possible preceding the front. But with limited
instability and a good separation between this area and the parent
low, think that gusty winds are the main threat from the heavier
showers and/or stronger storms.

.LONG TERM...(Monday night through Friday)
Issued at 245 AM CST Sat Jan 20 2018

Cold front will likely be crossing thru the mid TN Valley by the
start of Mon night, with showers/perhaps a few embedded tstms ongoing
along/just ahead of the sfc boundary mainly E of the I-65 corridor.
The cold front and lingering convection will then be well E of NE AL
by the start of Tue, as the parent sfc low lifts into the Great Lakes
states. High pressure out of the Plains states will also begin to
build ewd into the Midwest/Lower MS Valley regions during the day
Tue, with overall wx conditions improving into the cntrl TN Valley.
With the oncoming sfc high in the wake of the frontal passage, some
cooler air will begin to stream into the area from the NW late Tue
into Tue night. However, with the flow pattern aloft turning more
towards the WNW, this influx of cooler air will not be arctic driven
as compared to the last couple of frigid outbreaks. Overall temps in
fact look to turn more seasonal going into mid week, with highs well
in the mid 50s for most locations Tue into Wed, and overnight lows
trending closer to the freezing mark.

As the sfc high begins to translate ewd into more of the ern CONUS,
little change in these overall conditions looks to develop, with
afternoon highs remaining in the mid 50s nearing the end of the work
week and early morning lows predom near 30F. These seasonal temps may
begin to warm slightly as next weekend approaches, as the sfc high
becomes more layered across the mid/nrn Atlantic Basins and another
low pressure system and attendant cold front translates ewd out of
the Plains states.


.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 535 AM CST Sat Jan 20 2018

An area of VFR stratus (cloud bases generally above 3500 ft AGL)
should continue this morning, as a weak mid level system translates
across the region. Cloud coverage should thin somewhat this afternoon
as the disturbance moves further to the east, and drier air aloft is
realized. Additional VFR clouds should return late in the TAF, mainly
over the KMSL terminal. MVFR CIGs will be close, but should stay west
of the airport. Light SE winds this morning will become southerly
around 10 kt this afternoon, then diminish to around 5 kt after dusk.





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