Flash Flood and Hail in Texas, May 4 to 8, 2023

Area Forecast Discussion
National Weather Service Fort Worth TX
659 PM CDT Thu May 4 2023

...New Short Term, Aviation...

.SHORT TERM... /NEW/
/Through Friday Evening/

Scattered thunderstorms that developed along a dryline late this
afternoon with support from a passing mid-level shortwave are
currently pushing eastward into our forecast area. We are
continuing to monitor two areas for the greatest potential for
thunderstorms and severe weather. The first is across portions of
western north Texas where a cluster of thunderstorms has developed
near the intersection of the dryline and an outflow boundary from
this morning's storms. Locally backed flow may allow for a
slightly better, albeit still low, potential for a tornado or two
through the evening as this activity progresses east-
southeastward. A Tornado Watch is currently in effect for Montague
and Cooke counties until 9PM this evening. The other main area of
concern is across our Central Texas counties where a cluster of
thunderstorms has developed further south along the dryline in an
area of less convective inhibition. Effective bulk shear ~45-55
kts and MLCAPE ~1500-2000 J/kg will promote a large hail and
damaging wind threat with any of these thunderstorms. A Severe
Thunderstorm Watch remains in effect for locations west of the
I-35 corridor until midnight tonight. Observational analysis and
the 00Z FWD sounding show a large capping inversion over the
Metroplex and surrounding areas, which will likely cause storms to
struggle between the two ongoing clusters. However, if a storm
does get going in this "between" area, the environment is
supportive of large hail. Deep moisture and large warm cloud
depths will also support efficient rain rates this evening into
tonight, so we will need to monitor for a localized heavy
rainfall/flash flooding threat especially in the vicinity of
training thunderstorms.

All thunderstorms should exit the area to the east just after
midnight. Low-level cloud cover is expected to blanket the area
later tonight into Friday morning, possibly into early Friday
afternoon for portions of Central Texas, before lifting/clearing.
It'll be a warm/humid night tonight with overnight lows in the mid
to upper 60s expected, nearing 70 degrees across the Metroplex and
portions of the Brazos Valley. Persistent southerly low-level flow
will keep surface dewpoints in the mid to upper 60s across our
area into Friday afternoon. By midday, surface winds are expected
to take on a more southwesterly shift allowing for temperatures to
rise rapidly into the upper 80s to mid 90s Friday afternoon. The
dryline is expected to mix eastward once again Friday afternoon,
perhaps pushing into our western counties. Destabilization
tomorrow afternoon and a passing weak, low-amplitude shortwave
across North Texas late Friday should allow for isolated to
scattered thunderstorms to develop along the dryline by late
Friday afternoon into Friday evening. Although our area will be
displaced from the upper-level jet and deep-layer shear will be
less favorable, high MLCAPE >3000 J/kg, steep mid-level lapse
rates ~7.5-8.0 C/km, and effective bulk shear around 30 knots will
be supportive of cluster of storms capable of producing large
hail and damaging wind gusts late Friday afternoon into Friday
evening. Storm coverage is still uncertain, although the best
potential for isolated to scattered storms seems to be
along/south of the I-20 corridor.

Langfeld

&&

.LONG TERM... /Issued 305 PM CDT Thu May 4 2023/
/Saturday Onward/

Daily chances for thunderstorms will exist through the extended
forecast period, some of which will be strong or severe.

Broad western US troughing will exist to start off the upcoming
weekend with modest southwest flow aloft. Persistent low-level
southerly flow will provide a steady stream of Gulf moisture over
the Southern Plains, bounded by a dryline to the west. This
boundary will mix eastward and retreat westward each day
throughout the extended forecast period, offering a chance for
convective development every afternoon as the boundary layer
destabilizes with diurnal heating. To its east, strong or extreme
instability will materialize with surface dewpoints in the
mid/upper 60s or 70s, ambient temperatures climbing in the upper
80s and 90s, and very steep lapse rates aloft via the eastward
advection of an elevated mixed layer arriving from the higher
terrain of West Texas. In this particular environmental setup, the
main challenge is typically convective initiation due to the
broad and weak nature of ascent near the dryline with minimal
upper support present. However, the volatile buoyant sector
airmass should be sufficient to support at least isolated to
scattered thunderstorm development on nearly a daily basis, even
with only weak lift present.

Both Saturday and Sunday will have a potential for slightly more
organized convection due to a subtropical jet streak impinging on
Texas from the southwest. Strengthened but still modest flow will
result in deep-layer bulk shear magnitudes of at least 30-40 kts,
borderline yet sufficient for storms to acquire supercellular
characteristics. Convection may have a tendency to devolve into
more of a multicellular mode over time, but an environment
favorable for strong cold pooling combined with extraordinary
instability could become favorable for forward-propagating MCS
development. The shear/buoyancy parameter space will favor threats
for large hail with initial cells, transitioning to a damaging
wind threat if convection can grow upscale into one or more
complexes, but weak and disorganized low-level flow will largely
result in hodographs unfavorable for tornadoes. Of course, this
threat can never be ruled out with robust surface-based
convection, especially given the remarkable instability which may
be able to enhance updraft velocities while contributing to
vorticity generation via stretching. With uncertainty in both
placement and coverage of storm development, PoPs ranging from
20-40% remain appropriate, although those with outdoor
events/planned should be prepared to handle rounds of
afternoon/evening thunderstorms either day.

Another weather-related concern during the extended will be the
arrival of seasonable heat and humidity, with heat index values
climbing into the mid 90s just about every day from Saturday into
next week. Ambient highs will be in the upper 80s and 90s over
the weekend while dewpoints climb into the 60s and lower 70s.
Given this will be the first prolonged period of higher heat
indices this year, heat safety messaging will need to become a
bit more prominent.

Flow aloft will weaken further while becoming more zonal heading
into early next week. While a similar overall pattern will remain
in place with moist southerly low-level flow, instability may be
less than the weekend with slightly cooler surface temperatures
along with more modest mid-level lapse rates. There will still be
daily opportunities for convective activity, although not
necessarily all of which will be fueled by the dryline. We could
see a couple rounds of morning activity supported by warm
advection, while other guidance suggests the potential for a weak
cutoff low to develop over South or East Texas which would offer
additional rain chances through the midweek period. With weaker
shear and instability, the potential for any organized severe
convection during this time period presently appears low. Greater
rain chances as well as severe weather potential may return during
the second half of the week if recent guidance's depiction of
deeper western US troughing comes to fruition.

-Stalley

&&

.AVIATION... /NEW/
/00Z TAFs/

The main concern through the TAF period will be the potential for
isolated to scattered showers and thunderstorms this evening and
tomorrow afternoon/evening.

A cluster of thunderstorms across western North Texas may
gradually start to push into the northern parts of the Metroplex
and the D10 airspace later this evening. As such a couple hour
TEMPO group for TSRA was added to the DFW TAF for 02-04Z. We will
continue to monitor this cluster of thunderstorms as it pushes
east-southeastward through this evening. The more robust cells may
be capable of producing hail and frequent lightning. An
additional cluster of thunderstorms will approach ACT in the
03-05Z timeframe.

As thunderstorms push east of all terminals tonight, MVFR cigs are
expected to push into North and Central Texas impacting all
terminals through Friday morning. MVFR could linger at KACT
through early Friday afternoon. More isolated to scattered showers
and thunderstorms will be possible later Thursday
afternoon/evening, and the addition of VCTS will be considered in
future forecast packages.

Langfeld

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    69  94  69  92  70 /  30  20  20  20  20
Waco                68  90  67  89  68 /  40  20  20  20  20
Paris               66  87  69  88  69 /  60  10  10   5  20
Denton              65  94  65  92  66 /  40  20  20  20  20
McKinney            67  92  68  89  68 /  40  10  20  20  20
Dallas              69  94  69  92  70 /  30  20  20  20  20
Terrell             68  90  68  88  69 /  30  20  20  10  20
Corsicana           70  89  70  89  70 /  40  20  20  10  20
Temple              68  90  67  90  68 /  50  30  20  20  20
Mineral Wells       65  95  65  95  65 /  20  20  20  30  20

&&

.FWD WATCHES/WARNINGS/ADVISORIES...
None.
&&

Hazardous Weather Outlook
National Weather Service Fort Worth TX
711 PM CDT Thu May 4 2023

TXZ091>095-100>107-115>123-129>135-141>148-156>162-174-175-052330-
Montague-Cooke-Grayson-Fannin-Lamar-Young-Jack-Wise-Denton-Collin-
Hunt-Delta-Hopkins-Stephens-Palo Pinto-Parker-Tarrant-Dallas-
Rockwall-Kaufman-Van Zandt-Rains-Eastland-Erath-Hood-Somervell-
Johnson-Ellis-Henderson-Comanche-Mills-Hamilton-Bosque-Hill-Navarro-
Freestone-Anderson-Lampasas-Coryell-Bell-McLennan-Falls-Limestone-
Leon-Milam-Robertson-
711 PM CDT Thu May 4 2023

This Hazardous Weather Outlook is for North and Central Texas.

.DAY ONE...Tonight.
Isolated to scattered thunderstorms, some severe, will push east
through our area this evening and into tonight with the primary areas
of concern across western Central Texas and western North Texas near
the Red River Valley. Large hail and damaging wind gusts will be the
main hazards, with a lesser threat for a tornado or two.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.
Additional scattered thunderstorms are possible across most of the
area Friday through Wednesday, particularly during the afternoon and
evening hours each day. Some storms may become strong or severe
during this time period with threats for hail and damaging winds.

.SPOTTER INFORMATION STATEMENT...
Limited spotter activation may be requested along and west of I-
35 this afternoon and evening.