171
FXUS64 KOUN 211942
AFDOUN

Area Forecast Discussion
National Weather Service Norman OK
242 PM CDT Tue May 21 2024

...New SHORT TERM, LONG TERM...

.UPDATE...
Issued at 1004 AM CDT Tue May 21 2024

Only minor updates needed to the forecast this morning, mainly to
increase cloudiness from the Guadalupe Mountain-induced cirrus
plume spreading northeast through western north Texas and into
central Oklahoma. Despite this increased cirrus, the hourly
temperatures are still on target and will not make any adjustments
to max temperatures with this update. /26

&&

.SHORT TERM...
(This evening through Wednesday)
Issued at 241 PM CDT Tue May 21 2024

Within the short term period alone, three distinct regimes of active
convection are expected, each carrying a risk of severe weather.
This active forecast will largely be centered along and southeast of
I-44, with an attendant risk for flooding especially by tomorrow
afternoon and evening.

The first round will occur this evening. The dryline has been mixing
eastward rapidly throughout the day with winds veering out ahead of
it. Some radar echoes have been noted across south central Oklahoma
as of the time of this writing, though there is some uncertainty
about whether they mature and become surface-based. If they do, the
environment is characterized by moderate-to-strong instability
(2,000-3,000 J/kg of MLCAPE) and rather impressive deep-layer shear.
Therefore, the concern will be for large to very large hail with any
storms that can mature into supercells. Additional development is
possible late this evening from south central to southeast Oklahoma
as a weak cold front impinges on the dryline, with a similar concern
mostly for hail. To the west of the dryline, expect a hot one with
highs jumping into the 90s.

A much stronger frontal push is expect to reach the area after
midnight, impinging on the original washed-out boundary near I-40
sometime after midnight. Warm advection aloft associated with the
NLLJ will lead to the development of strong to extreme (2,000-4,000
J/kg) of instability atop a stable surface layer. Initial storm
development in central to north central Oklahoma near the 850
frontal surface is expected, with storms propagating southward along
the crashing/outflow-reinforced surface boundary. Initial
development may be cellular or supercellular with sufficient speed
shear above the base of the warm nose for a large hail threat. Given
the crashing nature of the front, upscale growth into a squall line
is probable, with the potential for damaging wind gusts with an MCS
along and south of I-40 in south central/southeast Oklahoma.

The existence, strength, and duration of this MCS will determine the
geographic scope of tomorrow afternoon`s severe threat. A stronger
and progressive MCS might help wash the front entirely south of our
area with an attendant reduction in the severe threat. A nonexistent
or weaker MCS would stall the boundary closer to the Red River,
which would most likely prime our environment for redevelopment of
storms in south central and southern Oklahoma by early afternoon.
The risk for severe weather here will be primarily damaging-wind-
driven along and south of the front, with a chance for marginally
severe hail north of the front. North of the front there may be a
chance for repeated rounds of thunderstorms in the afternoon and
evening, which will start to increase the risk for excess runoff and
local flooding issues. HREF 75h percentile 24-hour QPF values in
southeast Oklahoma will reach about 2.50 inches tomorrow evening.
Therefore, a flood watch has been issued for that area.

Highs tomorrow will be much cooler than today thanks to the cold
front and associated widespread cloud cover. Most places will
struggle to reach 80 degrees.

Meister

&&

.LONG TERM...
(Wednesday night through next Monday)
Issued at 241 PM CDT Tue May 21 2024


Continuing chances for storms and severe weather will occur through
the weekend, so bear with us.

The first, and potentially one of the more impactful rounds of
severe weather will occur Thursday afternoon and evening. Most
guidance indicates impressive mass response to return most or all of
our area into the warm sector (no doubt aided by
evapotranspiration). Subtle height falls along an eastern-mixing
dryline should favor an environment favorable for all types of
severe weather. Hydrologic issues will continue in areas that have
received pre-conditioning in the short term timeframe.

The risk will continue on Friday in what might look like a very
similar day to today - a cold front looks like it will impinge on
the northwestern half of our area and might act as a focusing
mechanism for severe weather. Highs will rise into the low 90s south
of the front but will remain in the "cooler" low 80s north of the
front. If you`re looking for a sign that summer is coming, the
temperatures this week will be it.

Another potentially high-impact environment is being shown by global
models on Saturday, although uncertainty continues to rise each day.
Severe weather will be possible particularly along and east of I-35
(per SPC/machine learning guidance). Meanwhile, highs will begin to
heat up even further out to the west of the dryline, with upper 90s
possible in western north Texas.

Sunday might be one last day with a dryline near I-35 with severe
chances to the east of it and building heat to the west. After that,
there is a strong signal beginning Monday for ridging to build in
across the Plains. This might reduce the chance for severe weather
(and/or shift it to north of I-40 in more of a northwest flow
regime), and it would seem to mean that heat will start to build in
next week (although interestingly some global guidance is keeping
highs cooler within the northwest flow regime).

Meister

&&

.AVIATION...
(18Z TAFS)
Issued at 1251 PM CDT Tue May 21 2024

Scattered showers and thunderstorms will affect the area around
KDUA this afternoon. Otherwise most of the showers and
thunderstorms will be Wednesday morning across the area. There are
still some MVFR ceilings across southeastern and portions of
central Oklahoma right now, but those will slowly rise to VFR with
time this afternoon. A front will move into the area overnight
into Wednesday morning increasing the potential for the showers
and storms, but also bringing a wind shift into the area. Some
MVFR and perhaps even localized IFR ceilings will be possible
Wednesday morning, especially north of the front.

&&

.PRELIMINARY POINT TEMPS/POPS...
Oklahoma City OK  62  75  62  83 /  30  40  30  50
Hobart OK         61  79  62  89 /  20  20  20  30
Wichita Falls TX  70  81  66  88 /  10  50  30  40
Gage OK           54  78  56  91 /  10  10  10  10
Ponca City OK     59  75  59  83 /  20  30  20  50
Durant OK         73  82  67  84 /  20  80  70  60

&&

.OUN WATCHES/WARNINGS/ADVISORIES...
OK...Flood Watch from late tonight through late Thursday night for
     OKZ032-041>043-046>048-050>052.

TX...None.
&&

$$

SHORT TERM...04
LONG TERM....04
AVIATION...26