Area Forecast Discussion
Issued by NWS Brownsville, TX

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400
FXUS64 KBRO 272103 CCA
AFDBRO

Area Forecast Discussion...CORRECTED
National Weather Service Brownsville TX
403 PM CDT Sat May 27 2017

...Corrected for WPC risk of Excessive Rainfall category on
Monday...

.SHORT TERM (Now through Sunday night ): Mid level ridging over
the northwest Gulf will remain in place initially, but will shift
slightly toward the northeast Gulf by Sunday night. Surface high
pressure will remain in control across the Gulf waters. Ample low
level moisture will remain available as moderate southeast winds
continue tonight. Low temps will range from 75 to 80, and may see
isolated convection fire over the Mexican mountains to the west.
Winds may be just slightly weaker on Sun as the upper ridge shifts
east. The heat will continue, however. High temperatures will
again rage from the mid 90s to a few degrees above the century
mark. Heat index values will be borderline for a heat advisory
Sunday, and will therefore defer to later shifts for refinement on
that point.

A front will push into south Texas Sunday, but southward progress
toward the CWA will be slowed as synoptic driven southeast to
south winds strengthen during the day. As the front moves closer
Sunday night, there may be two centers of action. The first will
be upstream over the RGV Plains, where developing convection may
drift south toward the northwest sector of the CWA. The second
will be storms developing along the Middle Texas Coast, moving
south along the coast. The models suggest that the front will
still be a bit too far north Sun night to more than just
marginally affect the northern tier counties of the CWA, but
general thunderstorms will be possible for that area nonetheless.


.LONG TERM (Monday through Saturday):Models continue to trend with
an unsettled, hopefully rainy, period for Deep South Texas for the
coming week. A split flow pattern evolves across North America with
a active subtropical jet stream developing across Northern Mexico
and passing over South Texas and the Western Gulf. Atmospheric
moisture deepens significantly with several shortwave trough
moving along the west to east axis of the subtropical jet. This is
a favorable pattern for scattered to widespread, heavy at times
rainfall for Deep South Texas.

Monday-Monday night: A MCS or even MCC is forecast by the global
models to be ongoing or developing over Deep South Texas Monday
morning with widespread thunderstorm activity through much of the
day. The interaction of a cold front, an upper level disturbance
and anomalous moisture (2+inches pwat) along with increasing upper
level divergence should lead to a likely rain day. Model
guidance, GFS/ECMWF/NAM/Canadian, all pinpointing Monday and
Monday night and even Tuesday with likely to categorical rain
chances. QPF amounts are totaling 2 to 5+ inches with WPC placing
much of our CWA in a Marginal Risk of excessive rainfall. Flash
Flood Guidance remains high with 3/6hr values ranging 3.7 to 6.9
inches, so even with no definite or widespread flooding expected
at this time this bears watching due to past history of rain
events this time of year with the ingredients mentioned.
Atmosphere may become to "water logged" for severe weather but can
not rule of isolated strong to severe storms early on in the
event that may have the potential to produce hail up to one inch
and gusty winds upwards to 50+ mph with sufficient instability,
decent mid level lapse rates and some shear.

Later Tuesday and for the rest of the week: several disturbances
and sufficient moisture (pwats 1.7-2.0) should be enough to keep
at least a chance of showers and thunderstorms each day. Models
eyeing another significant shortwave approaching the Big Bend
vicinity Thursday with increasing divergence in advance of this
disturbance which might lead a bump in the pops towards the end of
the week. Temperatures are not expected to be much a factor this
week under this pattern with near to slightly below normal highs
and near normal lows.

&&

.MARINE:(Now through Sunday night): Mid level ridging and surface
high pressure will dominate, producing moderate southeast to south
winds and moderate seas. Obs from around the Laguna are near 20
knots, with the HRRR maintaining a few 20 knot wind barbs through
the afternoon, so will let the small craft advisory on the Bay ride
until its expiration at 6 pm. Winds Sunday will be a skosh less than
today. A few showers or thunderstorms may develop Sun night across
the northern sections of Lower Texas Coastal Waters as a front
approaches from the north.

Monday through Thursday...light to moderate southeast to east
winds and a low to moderate sea is expected Monday and Tuesday
with a weakening cold front over the Northwest Gulf waters.
Pressure gradient strengthen mid to late in the week with marginal
small craft advisory conditions developing by Thursday mainly for
seas and possibly for wind.

&&

.PRELIMINARY POINT TEMPS/POPS...
BAYVIEW/PORT ISABEL  80  92  79  87 /   0   0  30  60
BROWNSVILLE          80  94  79  89 /   0   0  30  60
HARLINGEN            79  97  77  88 /   0   0  30  70
MCALLEN              79  99  78  90 /   0   0  40  80
RIO GRANDE CITY      78 102  77  89 /   0  10  50  80
SOUTH PADRE ISLAND   80  87  79  81 /  10   0  30  60

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...Heat Advisory until 6 PM CDT this evening for TXZ252-253.

GM...Small Craft Advisory for winds until 6 PM CDT this evening for
     GMZ130-132-135.

&&

$$

This product is also available on the web at:
HTTP://WEATHER.GOV/RGV

54...short term
59...long term



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