Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 230918

Area Forecast Discussion
National Weather Service Brownsville TX
418 AM CDT Tue May 23 2017

.SHORT TERM (Today through Wednesday): The quasi-stationary front that
has been meandering along and north of the Northern Ranchlands the
last 24 hours is currently extending east to west from the Western
Gulf into Central Kenedy County and into Hidalgo and Starr counties.
Convection has been developing along the boundary mainly over the
Laguna Madre between 1-3am with some isolated convection starting up
over Central Starr and Northern Hidalgo.  Expecting convection to
increase in coverage this morning/today as warm moist low level flow
flows over this boundary adn with large scale ascent increasing in
advance of southeast moving upper trough over the Central Plains.
Several disturbances within the cyclonic flow to help initial
possible several clusters of thunderstorm through the day and
especially tonight with the main impulse and a cold front moving
through the CWA. SPC maintains a slight risk of severe weather for
all Deep South Texas today and tonight but believe the best timing
for severe weather in our region will be between 6pm and 3 am. Main
threat with the potential storms will be large hail and damaging
winds but can not rule out a brief spin up tornado with shear values
increasing overnight as the cold front and upper trough approaches.
The strongest disturbance and lift will coincide with the moderately
strong cold front moving through the CWA between 9 pm and 3 am.
Instability, CAPE values 2500-3000j/kg, lapses rates at least 8.0
C/km are forecast this evening with the approach of upper
disturbance and the cold pool aloft associated with the upper
trough.  Most models suggest convection to initiate over the Sierra
Madre around 6 pm and move southeast near or into Zapata and Starr
county through the evening hours...while additional convection to
form along the cold front and sweep through the region between 9pm
and 3 am. Uncertainty creeps into the forecast if the Sierra Madre
convection, which could be the most intense, does move into the
forecast area or stays just south of the River.

Once the front moves through convection should end within a few
hours with relatively cooler and drier air filtering across Deep
south Texas by sunrise. Wednesday will be much less humid as dew
points fall into the 40s and 50s as the large scale upper trough
ushers in a brief shot of modified Canadian air. Highs will be
around 10 degrees lower then the last few days.

.LONG TERM (Wednesday Night through Monday): Northwest flow aloft
and surface high pressure across the western Gulf of Mexico will
continue to bring drier air and slightly cooler temperatures
across the area Wednesday night. Low temperatures Wednesday night
expected to be a few degrees below normal with temperatures
falling into the 60s in most locations. Mid level ridging over
the southern and central Plains Thursday will continue to provide
subsidence across Deep South Texas even as low level moisture
begins to increase due to the return of onshore flow. Temperatures
will return to above normal Thursday with high temperatures mainly
in the 90s. A subtropical ridge develops over northern Mexico
Friday and into the weekend resulting in temperatures well above
normal. Moisture will continue to increase across Deep South Texas
and the Rio Grande Valley through the weekend and into early next
week as a weak cold front moves southward across Texas. This will
provide a chance of showers and thunderstorms across the region
Sunday night into Monday.


.MARINE (Now through Wednesday): A modest swell has developed over
the Coastal waters with the persistent east-southeast flow over the
Gulf. This swell to persist today in advance of a cold front that
will sweep through tonight. Showers and thunderstorms to increase in
areal coverage and intensity today and especially tonight before
ending as the cold front passing through. Northeast winds and sea to
increase approaching small craft advisory levels by midday Wednesday
before slowly lowering by sunset.

Wednesday Night through Saturday Night...Light northeast winds
initially will gradually become southeast by late Wednesday night
as surface high pressure moves eastward. Southeast winds will
steadily increase on Thursday as the pressure gradient tightens
across the western Gulf of Mexico due to low pressure across the
west Texas interacts with high pressure across the northern Gulf.
Moderate to strong southeast winds will support SCEC to low-end
SCA conditions across portions of the lower Texas coastal waters
Thursday through Saturday night.


BAYVIEW/PORT ISABEL  92  70  84  71 /  30  40  10   0
BROWNSVILLE          94  71  87  71 /  30  40  10   0
HARLINGEN            94  67  87  68 /  30  40   0   0
MCALLEN              97  70  90  69 /  30  60   0   0
RIO GRANDE CITY      96  67  90  68 /  30  60   0   0
SOUTH PADRE ISLAND   84  75  81  75 /  30  50  10   0




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