Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Brownsville Texas
1259 am CDT sun may 24 2015
Discussion...updated for latest aviation discussion below.
Aviation...ongoing convection at mfe will continue to move
eastward and approach hrl and bro in the next couple of hours.
Mainly MVFR conditions expected through middle morning. Will mention
a tempo at all Rio Grande Valley taf sites for gusty winds and
brief IFR conditions. Additional thunderstorms are possible later
this morning and this afternoon but due to more stable air and
cloud cover will not include for this taf cycle. Southeast winds
will increase later this morning with gusts around 25 knots this
Previous discussion... /issued 1100 PM CDT Sat may 23 2015/
Discussion...bro radar shows a line of thunderstorms extending from
Hebbronville to near Falcon dam. This line is expected to move
eastward through the rest of the tonight. The main impacts with
this line of thunderstorms will be strong to damaging
winds...isolated tornadoes and heavy rain. A Severe Thunderstorm
Watch has been issued for all counties of deep south Texas and for the
Laguna Madre until 4 am.
Previous discussion... /issued 717 PM CDT Sat may 23 2015/
Discussion...updated for latest aviation discussion below.
Aviation...breezy southeast winds will gradually decrease across
the area this evening. Satellite imagery and surface observations
indicate mostly clear skies across deep south Texas this evening
with high level cloudiness approaching from the west. A large area
of convective over northern Mexico is forecast move west to east
into all of deep south Texas and the Rio Grande Valley overnight.
Short term model data suggest that showers and thunderstorms will
affect the aerodromes mainly after 06z...will mention thunderstorms in the vicinity
overnight with tempo groups beginning at 08z mfe...09z hrl and
10z at bro for thunderstorms and rain...gusty winds and MVFR conditions. The
convective system moves east of deep south Texas by late Sunday
morning with improving conditions anticipated by Sunday
Previous discussion... /issued 356 PM CDT Sat may 23 2015/
Short term /tonight through Sunday night/...scattered convection is
currently affecting the central and eastern portions of the bro County warning forecast area
with additional convection likely to develop over the western
portion due to an outflow boundary moving west-northwest through the
Tonight...a Flash Flood Watch remains in effect for the entire Rio
Grande Valley and all of deep south Texas beginning at 1 am CDT.
Expectation is that the approach and passage of a 500 mb shortwave
will initiate convection over the neighboring states of Mexico...
which will then pass through the bro County warning forecast area. Storm Prediction Center
currently has a marginal risk of severe weather west of a roughly
Baffin Bay to Sullivan City line. With portions of deep south Texas
and the Rio Grande Valley still saturated from recent rains...main
threat will be flash flooding...however large hail and damaging
winds cannot be ruled out.
Sunday...the previously-mentioned Flash Flood Watch remains in
effect until 12 PM CDT. Storm Prediction Center places nearly all of
the bro County warning forecast area (except Zapata county) in a slight risk of severe
weather...featuring large hail...damaging winds...and isolated
tornadoes. Disturbances riding within a southwest-to-northeast middle-
level flow overhead will continue to be the initiator for showers
Sunday night...previoously-mentioned slight risk of severe weather
area remains in effect...with no significant changes in synoptic
factors for convection.
Long term /Memorial Day through Saturday/...one final 500 mb
trough axis will clear through central and northern Texas on Monday
which will give the state another potential round of conv. Mean relative humidity
fields show a pretty decent feed of Gulf moisture pushing from
south to north across the central and eastern portions of the
state on Memorial Day. This should allow the atms to remain fairly
unstable for the end of the Holiday break maintaining the
conv potential over deep south Texas. The big question is which of
the longer range models will get it right for Monday. The European model (ecmwf) is
the wetter of the two longer range model sets with the GFS showing
most the conv remaining concentrated well north of the rgv and the
rest of deep south Texas. Considering the degree of spread between
the two models will opt for a 50/50 blend as am not confident
enough to buy into the drier GFS solution. Once this last 500 mb
trough axis clears the state 500 mb ridging will build into the
area for Wednesday and Thursday diminishing the conv potential. Another
shallower 500 mb trough then pushes from west to east across the
south Central Plains states Friday and Sat which may boost up our
conv potential a bit. So will include a mention of some 20 to 30 %
probability of precipitation late in the forecast period.
For temperatures opted for a fairly straight forward strategy. With
linger conv potential on Monday will undercut mex/European model (ecmwf) temperature guidance
a bit here. Then will go closer to or a little above the GFS mex
MOS/European model (ecmwf) guidance as the 500 mb ridging rebuilds over the area.
Overall longer term forecast confidence is generally above
average with the exception of the conv potential on Monday.
Confidence here with the rain chances is only average due to the
serious model spread between the GFS and the European model (ecmwf).
Marine /tonight through Sunday night/...buoy 42020 reported
south- southeast winds around 16 knots gusting to around 19 knots
with seas slightly over 5 feet with a period of 6 seconds at 14
CDT/19 UTC. Broad high pressure over the Gulf of Mexico will
interact with low pressure over the Central Plains throughout the
forecast period. Winds will increase and seas will build as a
result of the pressure systems interacting...and Small Craft
Advisory winds and seas are forecast for the Lower Texas coast
beginning tonight...and likely persisting through at least Sunday
Memorial Day through Thursday...the combination of surface ridging
over the Gulf of mex and the surface low pressure system expected
to spin up over the central states later this weekend into early
next week will tighten up the pgf. This will likely keep the Bay
and Gulf conditions close to Small Craft Advisory levels through at least Memorial
Day. The pgf will then steadily weaken later next week which will
allow for a little weaker surface flow and slightly lower seas.
Hydrology...recent water releases from the el Cuchillo and marte
r. Gomez reservoirs on the Mexican side of the Rio Grande will
result in higher than normal flows on the southern end of the Rio
Grande. Currently the river stage at the San Benito gauge on the
Rio Grande is expected to rise steadily over the next several
days. The San Benito gauge is expected to crest near 47.4 feet on
late Tuesday night/early Wednesday morning. Flood stage at the
San Benito gauge is 55.0 feet. No flooding is expected. The latest
river stage and forecast information can be found on our office
web Page at www.Weather.Gov/rgv on the rivers/lakes section.
Texas...Flash Flood Watch until noon CDT today for txz248>257.
High rip current risk through Monday evening for txz251-256-257.
GM...Small Craft Advisory until 1 PM CDT this afternoon for gmz150-
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