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000
FXUS64 KHUN 192255
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
555 PM CDT Fri Apr 19 2024

...New AVIATION...

.NEAR TERM...
(Remainder of today and tonight)
Issued at 250 PM CDT Fri Apr 19 2024

Current surface observations suggest that a cold front continues
to push very slowly southeastward into our northwest AL/southern
Middle TN zones this afternoon. However, it appears as if a weak
prefrontal surface trough (or remnant outflow boundary) lies
across our southeastern counties, and it is this feature that will
serve as the initiating mechanism for any thunderstorm activity
in our CWFA for the remainder of the afternoon. Breaks in the
stratus layer in this region could allow MLCAPE to reach 1500-2000
J/kg given dewpoints in the m-u 60s, and with mid-level westerly
flow of 35-45 knots providing sufficient bulk shear, gusty winds
(up to 40-50 MPH), small hail and frequent lightning will be
possible should a stronger updraft develop. However, based on data
from the 12Z CAMs, coverage of storms should remain scattered at
best before ending shortly after 0Z as the cold front drifts
southeastward and out of the region.

Zonal flow aloft (between a cold core upper low over Ontario and
a subtropical ridge across Central America) will persist across
much of the south-central/southeastern CONUS overnight, with the
surface cold front expected to drift southward into southern
portions of the Gulf Coast states before stalling. A subtle mid-
level disturbance embedded in the subtropical stream will lift
northeastward from northern Mexico into central TX early Saturday
morning, initiating the development of widespread convection well
to our west (across the Red River Valley of OK/TX). Although this
activity will not impact our CWFA, weak warm advection induced by
the disturbance (above the shallow layer of cool air at the
surface) may support the development of some drizzle or very light
rain beneath a low stratus deck. Due to a modest increase in
northerly flow/CAA, lows should fall into the l-m 50s by 12Z.

&&

.SHORT TERM...
(Saturday through Monday night)
Issued at 250 PM CDT Fri Apr 19 2024

Nocturnal convection developing across the southern Plains late
tonight (in the regime discussed above) may organize into one or
two broader clusters during the day on Saturday that would
subsequently track east-southeastward into MS/AL. Although the
risk for thunder with this activity should remain confined to
locations along and immediately north of the stalled frontal
boundary to our south, we will maintain a very low probability for
a few lightning strikes tomorrow afternoon (mainly south of the
TN River) as the northern portions of the storm clusters begin to
spread light rain eastward into our forecast area. Temperatures
will struggle to rise 10-15 degrees above morning lows due to an
abundance of cloud cover and northerly winds of 10-15 MPH (gusting
up to 20 MPH at times), and we have indicated highs in the l-m
60s.

This precipitation regime will persist into the evening hours on
Saturday, as another large mass of rain and embedded thunderstorms
(associated with a slightly stronger wave in the subtropical jet)
spreads northeastward from central TX. Models suggest that the
initiating mid-level disturbance may intensify a bit as it tracks
northeastward across the Lower MS Valley early Sunday morning,
with synoptic scale lift expected to be maximized across our
forecast area this period. However, the layer of cool/dry air in
the low-levels will be deepening with time, presenting some
concern about the northward extent of rainfall with the second
wave (Sunday morning). Although any rain will end in our
southeastern zones early Sunday afternoon, clouds will be slow to
clear the region and highs will struggle to make it out of the
u50s-l60s.

A weakening surface ridge of high pressure will shift eastward
into the Ozarks by early Monday morning, before crossing the TN
Valley Monday and building further northeastward off the Mid-
Atlantic coast Monday night. This, along with a low-amplitude
ridge aloft, will support dry conditions and clear skies, with
some patchy frost possible early Monday morning (especially across
our southern Middle TN zones) when dewpoints will be in the l-m
30s. Highs will rebound into the m-u 60s on Monday afternoon.

&&

.LONG TERM...
(Tuesday through Thursday)
Issued at 233 AM CDT Fri Apr 19 2024

Afternoon Update: Based on the 12Z suite of global models, all
thoughts mentioned in the extended discussion (below) remain valid
this afternoon.

For how volatile late-April can be for our area, next week looks
pretty pleasant, relatively speaking. Surface high pressure will
keep higher rain chances at bay and high temperatures in the
mid-70s. A few things to monitor will be a shortwave trough
digging into the Great Lakes region with an attendant surface low
that may drag a cold front into the South. For now, low rain
chances (20-30%) are in the forecast for late Tuesday into
Wednesday. The greatest potential for rain with this system will
stay farther north, but that could change if the trough digs
farther south. The second feature to watch is a longwave trough
that will set up over the Western US late next week. This may lead
to ridging and warmer temperatures over the Southeast in addition
to sending several impulses through the area, which would lead to
multiple periods of showers and thunderstorms next weekend.

&&

.AVIATION...
(00Z TAFS)
Issued at 555 PM CDT Fri Apr 19 2024

MVFR conditions are forecast through the TAF period at both KMSL
and KHSV as low clouds continue to move into the TN Valley.
After 19Z Saturday, a PROB30 group has been added to account for
low chances of light showers leading to decreased visibilities and
continued lowered ceilings.

&&

.HUN WATCHES/WARNINGS/ADVISORIES...
AL...None.
TN...None.
&&

$$

NEAR TERM...70
SHORT TERM....70
LONG TERM....30
AVIATION...HC