Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 252033
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
333 PM CDT Thu Apr 25 2019

.NEAR TERM...(Tonight)
Issued at 333 PM CDT Thu Apr 25 2019

Light-moderate rain will continue to advance eastward across the
forecast area this afternoon, along the northern periphery of a
deeper convective complex across central AL. Scattered-numerous
heavier showers will also continue to develop along an outflow
boundary immediately preceding the shield of lighter precipitation.
However, lightning activity has been essentially nonexistent with
this activity, and with near term forecast soundings indicating a
weakening trend in lapse rates aloft, we feel that this will
continue.

Recent model guidance indicates that a mid-level shortwave
disturbance across the mid-South region early this evening will lift
east-northeastward over the TN Valley and into the southern
Appalachians by 12Z, becoming increasingly phased with a northern
stream wave digging into the lower-OH Valley. A deepening surface low
related to the broader trough will eject rapidly northeastward into
the vicinity of Lake Erie, with the passage of a surface trough axis
and subsequent wind shift to west-southwest bringing the threat for
widespread precipitation rapidly to an end from W-to-E during the
late evening/early morning hours. Regardless, we have left high POPs
in the forecast for all areas this evening, based on current radar
observations to our west and expectations that deep-layer ascent will
remain rather strong with the passage of both the low and mid- level
trough axis. A few thunderstorms will also be possible amidst
numerous-widespread showers, but the primary concern with any storms
will be lightning and perhaps a brief strong wind gust. Temperatures
should fall into the mid 50s as precipitation comes to an end, with
low stratus clouds and some patchy light fog continuing through
sunrise.

.SHORT TERM...(Friday through Saturday night)
Issued at 333 PM CDT Thu Apr 25 2019

The northern stream wave digging into the lower-OH Valley overnight
is expected to track further southeastward into the southern
Appalachians Friday morning, with weak ascent downstream from this
feature perhaps maintaining light shower activity across the
northeastern corner of the forecast area during the morning. However,
as deep-layer flow veers to the north-northwest and strengthens
throughout the day, the southward advection of drier air will lead to
a rapid end to any lingering precipitation by late morning, with
clouds expected to clear from W-to-E during this period as well. At
the surface, the true synoptic cold front will cross the region
between 10-16Z, with gusty north-northwest flow developing in its
wake. In fact, current wind and wind gust grids would marginally
support a Wind Advisory for elevated terrain locations, with
sustained speeds around 25 MPH and gusts around 35 MPH. However, we
will let the overnight shift make the final decision on the issuance
of an NPW.

In the presence of moderately strong low-level CAA, highs should
struggle to reach the u60s-l70s tomorrow afternoon. Conditions will
be favorable for radiational cooling Friday night as a surface ridge
shifts eastward across the region, and early morning temps will
likely fall into the l-m 40s (warmest near large bodies of water).
South-southwesterly return flow between the departing ridge and a
strong northern stream trough shifting eastward over the northern
Plains will begin after sunrise on Saturday, and should promote max
temps in the m-u 70s once again. As the northern stream wave travels
further eastward into the Great Lakes on Saturday night, the trailing
cold front will drift southeastward, extending along an axis from
southwestern TN into central KY by 12Z Sunday. Scattered showers and
perhaps a few thunderstorms will be possible early Sunday morning, as
deeper moisture (characterized by PWATs in the 1-1.2 inch range)
returns northward in advance of the front.

.LONG TERM...(Sunday through Wednesday)
Issued at 333 PM CDT Thu Apr 25 2019

The second half of the weekend period will begin with a weakening
frontal boundary dropping into the mid TN Valley from the NW. The
latest global model suites continue to show most/if not all of the
diminishing showers/tstms along the front tapering off to the east,
as the sfc boundary stalls invof the gen area. Even with precip
tapering off to the ENE early Sun, lingering cloud cover may be slow
to clr the area later in the day given a more stagnant west to east
flow regime in place over much of the region. Even with the lingering
clouds in place, afternoon temps again look to climb well into the
mid/upper 70s for most spots.

Cloud cover should begin to diminish/sct heading into the evening
hrs Sun, as high pressure quickly moves ewd across the OH Valley/mid
Atlantic states. The Bermuda Ridge then looks to become established
across the mid/srn Atlantic going into the new work week, while upper
ridging builds ewd over most of the Gulf region into mid week. This
should translate into quiet and unseasonably warm wx conditions thru
at least Tue, with afternoon highs climbing into the lower/mid 80s
while lows trend in the upper 50s/lower 60s. Rain chances return to
the forecast late in the period, as a highly sheared upper trough
axis and its associated low pressure system traverse ewd across the
mid/srn Plains Tue and into the Midwest region Wed. This system will
have an elongated frontal boundary approaching the area from the NW
late Wed, with perhaps low chances of showers/tstms developing along
or just ahead of this next front.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 102 PM CDT Thu Apr 25 2019

An area of lgt-mod rain will continue to build northeastward into
northern AL, along the northern flank of deeper convection moving
eastward across central AL. Although heavier SHRA and perhaps a TSRA
will continue to develop along an outflow boundary immediately
preceding this activity, we have only included SHRA in a 3-hr tempo
group at both terminals, along with MVFR cig/vsby. The threat for
SHRA will end from W-to-E early this evening, as a surface trough
axis shifts eastward veering low-level flow to WSW by 01Z/MSL and
03Z/HSV. As winds diminish in the wake of the surface trough, we
expect development of both light fog and lower stratus, with cigs
initially falling to arnd 1500 ft AGL, before descending into the IFR
range early Friday morning. Conditions will begin to improve before
sunrise as flow veers to WNW, with even more pronounced clearing
occurring by 15Z as a cold front pushes southeastward through the
region. NNW winds will likely gust to around 20 knots (and perhaps
higher) in the wake of this front.

&&

.HUN WATCHES/WARNINGS/ADVISORIES...
AL...NONE.
TN...NONE.

&&

$$

NEAR TERM...70/DD
SHORT TERM...70/DD
LONG TERM...09
AVIATION...70/DD

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