-- Discussion containing changed information from previous version are highlighted. --
676
FXUS64 KHUN 212205
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
505 PM CDT Wed May 21 2025

...New AVIATION...

.NEAR TERM...
(Rest of today and tonight)
Issued at 1257 PM CDT Wed May 21 2025

In the mid/upper-levels, a cold core vortex will retrograde
southwestward across eastern Ontario over the course of the near
term period, as a peripheral disturbance lifts east-northeastward
from IL into the Lake Erie vicinity. This configuration will
maintain WNW flow aloft of 55-65 knots across the TN Valley. At
the surface, high pressure (initially centered across eastern
TX/western LA) will build progressively east-northeastward into
central portions of MS/AL by 12Z Thursday, as one surface low
drifts northeastward across the eastern Great Lakes while a
secondary low evolves across eastern NC and deepens as it lifts
off the Mid-Atlantic coast. The resultant pressure gradient will
maintain gusty WNW winds that will subside overnight. We expect
dry conditions to prevail today, with only a few high clouds and
max temps in the u70s-l80s.

Late this afternoon, thunderstorms are predicted to develop
across NE/KS in the vicinity of a cold front (which will remain
nearly stationary from the central High Plains into the OH
Valley), with this activity initiated by a subtle shortwave trough
(currently across southern WY). Beneath strong WNW flow aloft,
this convection may organize into a into a small cluster as it
travels southeastward into the Ozarks by 6Z and perhaps into
northern portions of our CWFA between 8-12Z. However, in spite of
sufficiently strong flow aloft to support storm organization,
elevated CAPE appears quite low (perhaps only 250-500 J/kg) and
this should result in only occasional lightning and perhaps a few
strong wind gusts up to 30-35 MPH with any storms. Due to an
increase in mid/high-level cloudiness early Thursday morning, lows
will be in the 55-60F range.

&&

.SHORT TERM...
(Thursday through Friday night)
Issued at 1257 PM CDT Wed May 21 2025

Latest short range model data suggests that an upper low across
eastern Ontario will drop southward into the northern Great Lakes
by 12Z Friday, before eventually becoming absorbed within the
circulation around a new cyclone to its east on Friday/Friday
night. As a result of this, WNW flow aloft across our region will
remain in the 55-65 knot range through Friday morning, before
falling into the 40-50 knot range late in the short term period.
At the surface, the polar front is finally predicted to spread
southward through the TN Valley on Thursday night/early Friday
morning, with prefrontal dewpoints in the m50s-l60s being replaced
by a drier continental airmass featuring dewpoints in the
u40s-l50s. A few residual showers and thunderstorms will be
possible late tomorrow morning (remnants of tonight`s NW flow
MCS), with redevelopment of isolated convection also possible
tomorrow afternoon as diurnal warming of the lingering moist
airmass will support CAPE in the 500-1000 J/kg range. A final
round of showers and perhaps a few storms will be possible with
the actual frontal passage late Thursday night/early Friday
morning. Although deep-layer shear will remain sufficient for
storm organization (and perhaps a local enhancement in lightning
production and gusty winds up to 30-35 MPH), low instability
(aside from Thursday afternoon) will limit both the coverage and
intensity of convection.

Light northerly winds will lead to a drier and slightly cooler
day on Friday (highs in the l-m 70s), as a high pressure cell
slowly builds into the region from the northwest. However, to our
west, thunderstorms are predicted to develop across central
portions of KS/OK within the return flow regime to the east of a
lee cyclone that will become established across southeastern CO.
Present indications are that this activity will grow into another
MCS that should track southeastward into the Mid-South region by
late Friday night and into our forecast area by 12Z Saturday.
Fortunately, it appears as if the storms will elevated, as the MCS
should remain on the cool side of the warm front (which will
extend from southeastern AR/northwestern MS into north FL), with
lightning and perhaps a few wind gusts up to 30-35 MPH the main
concerns.

&&

.LONG TERM...
(Saturday through Tuesday)
Issued at 330 AM CDT Wed May 21 2025

Upper level northwest flow will become more zonal by late
weekend, with ripples of shortwaves moving over the region through
early next week. Although, there is model disagreement if a more
pronounced shortwave trough will dig over the Ohio and Tennessee
Valleys Monday into Tuesday. Surface high pressure looks to shift
east over the Appalachians by Saturday as a low pressure system
develops over the central CONUS. This feature will then gradually
track eastward over the Mississippi River Valley on Sunday and the
Tennessee Valley on Monday. A cold front associated with this
system is expected to progress over the local area sometime on
Monday as well.

Overall, for early in the weekend, low to medium (15-30%) chances
of showers and storms will remain possible. The main timeframe of
higher precipitation probabilities (40-70%) is Sunday afternoon
through Monday afternoon as the previously-mentioned storm system
approaches the region. While general thunderstorms will be
possible throughout this time, the main time period of concern for
possible stronger to severe storms looks to be Monday afternoon
ahead of the cold front. Guidance suggests bulk shear between
30-40 knots and instability between 1500-2000 J/kg. However, this
is towards the end of the forecast period and much can change over
the coming days. We will therefore continue to watch trends as
this event gets closer in time.

Lingering chances (10-30%) of showers and storms persist into
Tuesday via the NBM, but this could be due to synoptic model
disagreement. In terms of temperatures, highs go on a bit of a
roller coaster through the extended. Values begin in the mid 70s
to around 80 degrees on Saturday then jump into the lower to mid
80s by Sunday. With increasing precipitation chances on Monday,
highs are then forecast to be a bit cooler, in the mid 70s to
around 80 degrees once again. Lows will follow a similar trend,
but mainly remain in the 60s; although, conditions look to be
warmer Sunday night comparatively.

&&

.AVIATION...
-- Changed Discussion --
(00Z TAFS)
Issued at 505 PM CDT Wed May 21 2025

VFR flight weather conditions are forecast.
-- End Changed Discussion --

&&

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

$$

NEAR TERM...70
SHORT TERM....70
LONG TERM....26
AVIATION...17