Flash Flood Warning 25, NWS Norman, OK

Area Forecast Discussion
National Weather Service Norman OK
634 PM CDT Wed May 1 2024

...New AVIATION...

.SHORT TERM...
(This afternoon through Thursday night)
Issued at 129 PM CDT Wed May 1 2024

***This Afternoon into Tonight***

As a wise man once said: It's gonna be May.

We're ringing in the traditional most active month of the year with
a highly complex forecast for both severe and flooding potential
this evening. This morning's convection has left a rather
substantial cold pool with theta-E perturbations on the order of
4-10 Kelvin across central Oklahoma. Recovery is uncertain within
our area, but West Texas Mesonet observations show a narrow plume
of upper-60s dewpoints gradually advancing northwestward across
the eastern Texas panhandle. Currently, the dryline is retreating
westward, but with increased diurnal heating it will likely
advance back into the eastern panhandle. The third boundary of
note in our forecast is what appears to be the synoptic-scale warm
front, which meets the dryline at a triple point low near
Perryton and extends east-northeast from there toward Medford.

Convection initiation appears probable in spite of the intrusion of
the cold pool into central Oklahoma. The two likeliest zones for CI
are:

-Along the outflow boundary in the southeastern TX panhandle
-Near the triple point in the northeastern TX panhandle

Outflow boundary region:

The presence of near-70 dewpoints and 3,000 J/Kg of MLCAPE will
encourage thunderstorm development likely by mid afternoon. The
initial mode will favor supercells capable of very large hail. Over
time, CAMs show a tendency to weaken the 500 mb winds while
increasing the LLJ. This will probably encourage supercells to grow
upscale into an eastward-propagating squall line. Given the depth of
boundary-layer winds and drying in the mid-levels to raise DCAPE to
1,400 J/kg, damaging wind gusts will become a threat toward sunset
with a potential in southwest Oklahoma and western north Texas for
significant (70+ mph) wind gusts. The tornado threat is conditional,
and may be most focused in the spatiotemporal window where the LLJ
is increasing directly along the remnant OFB. After sunset, this
cluster will continue eastward toward south central Oklahoma, likely
weakening over time. A second threat will occur overnight with this
cluster - flooding. One-hour flash flood guidance sits as low as 1.6-
2 inches of rain across much of southwest Oklahoma and as low as 1
inch in the Arbuckles. Even a small residence time of storms in this
area overnight could trigger recurrence of flooding.

Triple point region:

Storm coverage is more uncertain here as ongoing stratus/need for
further moisture advection cast doubt on reaching convective
temperatures. However, CAM guidance (notably the HRRR and MPAS) has
become much more bullish in the late morning hours on depicting the
development of scattered supercells by late afternoon. The longevity
of these storms will be dependent on sufficient theta-E advection to
overcome the development of a modest capping inversion after sunset.
However, shear profiles will be sufficient for supercellular
structures with the potential for large to very large hail. The
frontal boundary may also become a focus for tornado potential
toward sunset as the LLJ enlarges. CAM guidance is less bullish on
the potential for an overnight MCS across north central Oklahoma;
thus, it is anticipated that this activity will weaken after sunset.

Meister

***Thursday into Thursday Night****

By tomorrow (Thursday) afternoon, a slowly-advancing cold front will
be located somewhere in close proximity of I-44. The location of
this cold front will likely be affected by tonight's convection
with some spread among guidance. In addition, a dryline will be
located in the eastern Texas panhandle or western north Texas.
Both of these surface boundaries will be likely focus for
convective during the afternoon and evening hours as convective
inhibition weakens with daytime heating.

Effective bulk shear will be weak to modest at only ~30 knots, so
transient supercell structures are possible. Even so, significant
hail is possible given the modest cloud layer shear (~50 knots),
weak low-level shear, and significant instability (MLCAPE >3000
J/kg). In addition, large downdraft CAPE (>1000 J/kg) may result
in damaging wind gusts. The tornado risk is generally low, but if
a supercell could constructively interact with the cold front or
an outflow boundary, the tornado potential would be higher
(especially given the magnitude of instability). Thunderstorms
may grow upscale into clusters and move to the southeast late
evening into the overnight hours. Flooding will become a hazard,
especially for locations that have had recent heavy rainfall.

Mahale

&&

.LONG TERM...
(Thursday night through next Tuesday)
Issued at 300 PM CDT Wed May 1 2024

An active pattern will continue into early next week with periods
of showers and thunderstorms as shortwave troughs lift northeast
within the west to southwest flow. Currently, it appears the
greatest risk of severe weather during this period will be on
Monday. Heavy rainfall/flooding will be the primary hazard on the
other days. Here are the specific details:

Friday: Isolated to scattered daytime thunderstorms are possible
as a subtle shortwave trough/PV anomaly moves through in a weakly
capped environment.

Friday Night into Saturday: A complex of thunderstorms associated
with a cold front is expected to move through the area. Heavy
rainfall and flooding will be the primary hazard.

Sunday: Another shortwave trough is progged to lift into the
Southern Plains with a threat for heavy rainfall and flooding.

Monday: A negatively-tilted trough is progged to lift into the
Plains. Currently, it appears the strongest synoptic-scale ascent
and associated surface low will develop across the northern
Plains. However, a trailing dryline will likely be located
somewhere in the Southern Plains with a moist, unstable air mass
with sufficient shear for supercells and severe weather. This is
the next potential for significant severe weather if the
ingredients come together.

Mahale

&&

.AVIATION...
(00Z TAFS)
Issued at 630 PM CDT Wed May 1 2024

Overall, much of the forecast period tonight and tomorrow morning
expected to be MVFR most terminals. Gusty southerly winds will
continue through the night. TSRA chances will be highest across
southwest Oklahoma and northwest Texas tonight, with possibility
for activity to progress eastward across the southern half of
Oklahoma overnight into tomorrow morning. Cold front will move
into northern Oklahoma toward and after 12Z, with slow progress
southward during the day tomorrow. TSRA will be possible along the
front late in the forecast period, but will leave out for now due
to timing and possibility that cloudiness during the day will
limit coverage.

&&

.PRELIMINARY POINT TEMPS/POPS...
Oklahoma City OK  64  78  60  77 /  50  70  50  30
Hobart OK         61  79  57  76 /  60  40  40  30
Wichita Falls TX  64  82  61  80 /  70  20  40  20
Gage OK           57  76  50  76 /  30  30  20  30
Ponca City OK     64  76  56  75 /  50  80  40  20
Durant OK         66  79  64  81 /  70  70  60  30

&&

.OUN WATCHES/WARNINGS/ADVISORIES...
OK...Flood Watch through Thursday morning for OKZ035>041-044>046-050.

TX...Flood Watch through Thursday morning for TXZ084>090.

&&

SHORT TERM...04
LONG TERM....10
AVIATION...11

Hazardous Weather Outlook...UPDATED
National Weather Service Norman OK
1115 PM CDT Wed May 1 2024

OKZ004>048-050>052-TXZ083>090-030415-
Harper-Woods-Alfalfa-Grant-Kay-Ellis-Woodward-Major-Garfield-
Noble-Roger Mills-Dewey-Custer-Blaine-Kingfisher-Logan-Payne-
Beckham-Washita-Caddo-Canadian-Oklahoma-Lincoln-Grady-McClain-
Cleveland-Pottawatomie-Seminole-Hughes-Harmon-Greer-Kiowa-Jackson-
Tillman-Comanche-Stephens-Garvin-Murray-Pontotoc-Coal-Cotton-
Jefferson-Carter-Johnston-Atoka-Love-Marshall-Bryan-Hardeman-
Foard-Wilbarger-Wichita-Knox-Baylor-Archer-Clay-
1115 PM CDT Wed May 1 2024

This hazardous weather outlook is for portions of northern...
western...central...and southern Oklahoma...and western north
Texas.

.DAY ONE...Tonight...

.Thunderstorms...
An area of strong to severe thunderstorms will move east across
the southern half of Oklahoma and north Texas overnight. Hail to
the size of quarters and damaging wind gusts to 80 mph will be the
main hazards, along with a low tornado risk.

.Strong winds...
An area of strong winds will be possible north of the
thunderstorms overnight across west central into central Oklahoma.
Winds gusts of 45 to 55 mph will be possible.

.Heavy Rainfall and Flooding...
Heavy rainfall could lead to flooding across portions of western
north Texas and southwestern and southern Oklahoma overnight.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday...

.Thunderstorms...
There will be a daily chance of thunderstorms through Monday. The
greatest risks for severe weather are on Thursday and Monday.

.Heavy Rainfall and Flooding...
Repeated rounds of thunderstorms with heavy rainfall could lead to
localized flooding in some areas through early next week

Get graphics and more details at weather.gov/norman...and follow
our weather forecast office on Twitter and Facebook.

Mahale

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