Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 251142

Area Forecast Discussion
National Weather Service Huntsville AL
542 AM CST Sat Feb 25 2017

For 12Z TAFS.


.NEAR TERM...(Today)
Issued at 400 AM CST Sat Feb 25 2017

The last of the storms are exiting the HUN forecast area early this
morning. Most of the activity during last evening and here in the
early morning hours consisted primarily of general thunderstorm
activity. A few of the stronger storms produced dime size hail, but
those were the largest hail reports received. A few light showers
lingering just behind the surface front but along/ahead of the
elevated portion of the front were still evident on regional radars.
These showers will cross northeastern areas of Alabama early this
morning, and should exit to our east by 6 am. The modified Canadian
air mass will continue to move into the region with cold air
advection (CAA) ongoing all day, driven in part by NW winds ~10-15
mph. Clouds will quickly clear the area from west to east during the
morning, with abundant sunshine counteracting the CAA. Temperatures
will fall into the 40s for nearly all locations later this morning,
before daytime heating pushes temps back up into the low/mid 50s
this afternoon...which is about a 30 degree temperature decrease from
yesterday`s record highs!

.SHORT TERM...(Tonight through Monday)
Issued at 400 AM CST Sat Feb 25 2017

High pressure at the center of the Canadian air mass will move
directly overhead the area on Saturday night. Light winds and clear
sky conditions in the relatively dry air mass will allow
temperatures to cool quickly Saturday night. By sunrise Sunday,
temperatures are likely to be in the mid/upper 20s for most
locations. Locations along/near the larger TN River lakes may just
reach the lower 30s. Nevertheless, a hard freeze is appears likely
for many locations on Sunday morning. As high pressure shifts to the
east of the region on Sunday, winds will veer from NE to SE during
the day, with the inevitable warm up ensuing. High cirrus clouds will
increase from the WNW during the afternoon, as temperatures likely
climb into the mid/upper 50s.

A quasi-zonal flow pattern will gradually evolve across much of the
CONUS by late Sunday, while the southern portion of a highly sheared
(and weakening) upper trough is ejected from the SW CONUS into the
Southern Plains. This feature will move into the TN/OH Valley regions
during the day. In response, low-level flow will veer from the S-SE
on Monday, while flow aloft backs from the NW to SW. Warm/moist
advection and strengthening isentropic ascent will generate light
rain initially from west to east, but rain may become more moderate
during the mid to late morning period as much of the column becomes
saturated amidst deepening/strengthening ascent. Temperatures on
Monday morning will fall into the upper 30s to low 40s, so a cold
rain is expected initially during the morning. The upper trough will
move across the region during the day and deamplify during the
process. Rain will continue into the afternoon, but the best chances
will probably be in southern parts of the area where weak
frontogenesis aloft will likely take place. Weak instability will
develop during the afternoon and may be sufficient for isolated
thunderstorms, but mainly in southern parts of the area. Otherwise,
mainly rain/showers are expected on Monday as temperatures manage to
climb into the upper 50s to near 60 under fairly heavy cloud cover.

.LONG TERM...(Monday night through Friday)
Issued at 400 AM CST Sat Feb 25 2017

An unsettled pattern is in the forecast for the Tuesday/Wednesday
timeframe. The forecast area will be in between high pressure off of
southeast coast, and developing low pressure east of the southern
Rockies. At the start of this period, a warm front south of the
region should move northward during Tuesday. A southerly flow with
the front will bring another period of warmer temperatures to the
Tennessee Valley. After Monday night lows in the lower 50s, highs on
Tuesday should rise into the lower 70s - despite more clouds than
sun. Along with the clouds, scattered showers and a few thunderstorms
will also be present, as deeper moisture moving inland from the Gulf
produces a more unstable atmosphere. Even during Tuesday,
considerable timing difference between the various models as far as
placement of showers.

Better shower/thunderstorm chances across the forecast area will be
realized for the mid week, as the month of March comes in like a
lion. The next surface low forming over the western plains will move
ENE towards the southern Great Lakes towards late Wednesday. It will
bring a strong cold front across the area during this time frame. The
GFS was a bit quicker than the ECMWF per timing of the front by
about 6 hours. Going with an average of timing, a frontal boundary
should move across the forecast area Wednesday evening. Given the
front and good moisture convergence east of the front, widespread
showers/thunderstorms will affect the region during Wednesday.
GFS/ECMWF soundings depict modest instability/shear with this next
system; with neither model particularly suggesting widespread
strong/severe convection on a big picture scheme. That being said,
some of the storms especially on Wednesday afternoon/evening could
become strong to severe in intensity - given both models are
suggesting a QLCS type line moving across the region with the front.
Strong to damaging wind gusts, frequent lightning and locally heavy
rains looks to be the primary threats posed by the stronger storms.

With more showers in the forecast, high temperatures will still
range above normal, warming into the mid 60s on Wednesday. Normal
high temperatures for March 1st are around 60. Colder air rushing
across the region Wednesday night will bring lows a bit below
seasonable levels into the upper 30s, and definitely cooler Thur/Fri
with highs in the mid 50s. Dry weather is also expected
Thursday/Friday next week.


.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 540 AM CST Sat Feb 25 2017

VFR conditions are expected at KHSV and KMSL terminals over the next
24 hours. NW winds will continue today, with gustiness at times.
Winds will quickly diminish in speed by 00Z as the center of an area
of high pressure moves into the TN Valley. Light and variable winds
will occur overnight with clear sky conditions. Fog development is
not currently expected on Sunday morning.





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