Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 280511
AFDBRO

Area Forecast Discussion
National Weather Service Brownsville TX
1211 AM CDT Sun May 28 2017

.DISCUSSION...Updated for latest aviation discussion below.

&&

.AVIATION...MVFR ceilings have developed at all area terminals.
Expect ceilings to stay in the MVFR range tonight, but would not
be surprised to see a brief period of IFR ceilings. MVFR
conditions will continue through mid-morning Sunday before
lifting and scattering out. Moderate southeasterly winds expected
overnight, staying in the 10 to 12 knot range. Winds pick up again
by mid-morning Sunday and become breezy and gusty, but not quite
as strong as today, as the pressure gradient will be slightly
weaker.

&&

.PREV DISCUSSION... /issued 644 PM CDT Sat May 27 2017/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...A near-repeat of conditions from the last 24 hours to
the next 24 is anticipated. Current breezy SE winds will decrease
to moderate this evening and overnight, then pick up again Sunday
mid-morning. Wind speeds likely to be a bit lighter than today`s,
though, as the pressure gradient will be relaxed somewhat as a
front moves into central Texas.

Main challenge is onset times of MVFR ceilings overnight at the
terminals. Basically blended persistence from last night with MOS
guidance products and RUC BUFKIT time-height sections. Thinking is
that CIG`s will move inland from the coast, beginning shortly
after sunset. Only two obs from last night recorded IFR CIG at
BRO, so will not mention in this TAF set. High clouds will be in
the mix throughout the next 24 hours as well (as mentioned by
previous forecaster), courtesy of both a speed max at jet level
and anvil cirrus from thunderstorms over the Mexican plateau.
Lower cloud deck should again mix out by early afternoon Sunday.

PREV DISCUSSION... /issued 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.

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...None.
GM...None.
&&

$$

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