Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 221929

Area Forecast Discussion
National Weather Service Brownsville TX
229 PM CDT Mon May 22 2017

.SHORT TERM (Tonight through Tuesday Night): A stalled front resides
over the CWA, with a radar signature pushing slowly across Willacy,
Hidalgo, and Cameron Counties. But despite continued rich low level
moisture and available buoyancy, ongoing isolated to scattered
convection should weaken tonight. The HRRR prolongs convection out
west over the Sierra Madre range into tonight, so can`t rule out a
few storms moving into the Zapata and Starr sector. Overnight low
temperatures will be propped up in the 70s by high dew points, with
low clouds moving in on light southeast marine winds.

Winds will be light to moderate Tuesday, and possibly northeast on
the backside of washing out frontal boundary. Another front will
push south from the southern Plains during the day, edging through
Tuesday afternoon and Tuesday night, with convection increasing in
coverage as the front overtakes the residual stationary front and
interacts with a ready supply of rich low level moisture, supported
to some extent by destabilizing energy aloft. The GFS shows a vort
max moving off the Mexican mountains in the evening which could help
prolong convection and support stronger cells moving toward the
coast. The forecast sounding for Cameron County Tuesday afternoon
boasts a PW of 1.90 inches, historically above the 90th percentile
for the day. The lapse rate will be a healthy 8 deg C per km. CAPE
will be 3700 J/kg with a supercell parameter of 9.0, and a SHiP of
1.9, supportive of supercells and significant hail. The probability
of severe convection Tuesday to Tuesday night in conjunction with
this event is currently rated at slight, or 15%, by SPC, focusing on
the threat of large hail and damaging wind/wind gusts. Brief heavy
downpours will be possible in any stronger storms.

The arrival of cooler, drier air along with the lingering rainfall
potential should put the kibosh on convection later Tuesday night,
and also allow low temps to dip into the 60s for the northwest 2/3
of the CWA.

.LONG TERM (Wednesday through Monday): Surface high pressure will
continue to bring drier air into the Rio Grande valley and
northern ranchlands Wednesday as northwest flow aloft provides
subsidence across the state as the 500mb trough across the
central United States moves eastward. 500mb ridge across the
southern and central Plains Thursday will continue to provide
subsidence across south Texas even as an onshore flow returns at
the surface. A somewhat zonal flow develops across the southern
tier of the country Friday before an upper level trough develops
across western U.S. Saturday and moves eastward across west TX
Sunday. This will allow moisture to increase across portions of
north-central TX through the weekend and convection is progged to
develop across north TX late Sunday and move southward Monday as a
weak cold front moves southward across the state. This will
provide a chance of showers and thunderstorms for the upper
portions of the Rio Grande valley late Monday.

.MARINE (Now through Tuesday night): Light to moderate southeast
to south winds tonight and Tuesday, shifting to moderate north
late Tuesday night in the wake of a cold front. Low to moderate
seas. Scattered showers and thunderstorms, some strong to severe
late Tuesday.

Wednesday through Saturday...Moderate north to northeast winds
will prevail across the coastal waters Wednesday before high
pressure across the lower Texas coast moves eastward Wed night.
Winds will veer to the southeast Wed night and increase Thursday
as the pressure gradient increases across the western Gulf of
Mexico with low pressure across the TX panhandle and high pressure
across the northern Gulf. Moderate to strong southeast winds will
prevail across the lower TX coast Thursday through Saturday. SCEC
to borderline SCA conditions will prevail across portions of the
coastal waters Thursday through Saturday.

BAYVIEW/PORT ISABEL  78  88  72  85 /  40  30  50  10
BROWNSVILLE          78  91  72  87 /  30  30  50  10
HARLINGEN            76  91  70  88 /  40  30  50  10
MCALLEN              77  93  70  89 /  40  30  60  10
RIO GRANDE CITY      76  94  70  90 /  40  30  50  10
SOUTH PADRE ISLAND   78  84  74  82 /  40  40  50  10



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