FXUS64 KHUN 290915 AAA

Area Forecast Discussion...UPDATED
National Weather Service Huntsville AL
415 AM CDT Fri May 29 2020

.NEAR TERM...(Today)
Issued at 415 AM CDT Fri May 29 2020

A 500-mb trough currently centered across the Mid-South region will
continue to weaken and lift northeastward this morning as it becomes
absorbed in the flow around a stronger northern stream trough
digging southeastward into the Upper-MS Valley. Deep-layer
southwesterly flow to the east of the trough axis will maintain an
environment favorable for the development of scattered convection
across the region during the predawn hours, and based on the recent
redevelopment of showers across north-central MS we have increased
early morning POPs into the low chance range. Aside from the threat
for a few showers/thunderstorms, we will continue to monitor the
development of fog in the river valleys of northeast AL, but at this
point the coverage/density of fog does not appear to warrant an SPS.

As for the remainder of the day, latest model guidance indicates
that rapid drying aloft will occur beginning shortly after sunrise,
as winds in the 700-500 mb layer veer to the west-southwest
immediately downstream from the remnant trough axis. Although this
will likely limit the areal coverage of convection compared to
previous days, a subtle wind shift axis at the surface may still
initiate scattered showers/storms across the southeastern portion of
the CWFA late this morning/early this afternoon. Additional
thunderstorms related to a prefrontal surface trough may also spread
southeastward into northwest AL/southern middle TN late this
afternoon. MLCAPE should be able to reach the 1000-2000 J/kg range
for most of the region as temps warm into the l-m 80s, but given the
weakening trend in flow/shear noted in forecast soundings, the main
threats from any storms today will be lightning and occasional wind
gusts in the 30-40 MPH range.

.SHORT TERM...(Tonight through Sunday night)
Issued at 415 AM CDT Fri May 29 2020

Isolated to widely scattered showers and thunderstorms tied to the
prefrontal surface trough mentioned above will likely continue for an
hour or so after 00Z this evening, before dissipating. Light
northerly flow will occur for the remainder of the night in the wake
of the trough axis, but should not advect a substantially cooler or
drier airmass into the region, with lows Saturday morning expected
to only fall into the lower 60s once again. Patchy fog will also be
possible in the wind-protected valleys of northeast AL. Based on low-
level moisture progs from the global models, it appears as if the
true synoptic cold front will arrive during the day on Saturday,
perhaps initiating a few showers south of the TN River during the
late morning/early afternoon hours as it crosses the region.

Northwest flow aloft will remain in place across the TN Vally from
Saturday night-Sunday night, as a broad scale longwave trough slowly
amplifies across the eastern half of North America. This will
maintain clear and dry conditions, with only a limited coverage of
high clouds anticipated through the period. Although max temps will
still reach the lower 80s on Saturday, temps will be a few degrees
cooler on Sunday, primarily as a result of a cooler start to the day.
Sunday night appears to be the most favorable period for radiational
cooling, with lows falling into the l-m 50s.

.LONG TERM...(Monday through Thursday)
Issued at 415 AM CDT Fri May 29 2020

High pressure over the Tennessee Valley in combination with building
500-mb heights will lead to warming temperatures next week. Many
locations will see 90 for the first time this year Wednesday or
Thursday. Overnight low temperatures will also be climbing with many
places not dropping below 70 by the end of the week. With high
pressure over the region, not expecting any precipitation through
midweek. Some models show an upper-level trough riding over the ridge
later next week, possibly bringing a few diurnal showers to the
Tennessee Valley Thursday afternoon/evening, but confidence is low in
the details that far out in the forecast.


.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1239 AM CDT Fri May 29 2020

No changes to previous aviation forecast reasoning, and with
mid/high cloud cover in place, VFR conds should prevail into the
daytime hrs Fri. Sct shra/tsra are again possible going into the
afternoon period, and a PROB30 group has been added during the 17-23Z
time frame. Sfc winds will generally remain out of the SW near 7-9kt
thru the period.






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