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Area forecast discussion 
National Weather Service Brownsville Texas
302 PM CST sun Mar 1 2015

Short term /now through Monday night/...for a second day in a
row...mesoscale features are winning the battle and keeping a winter-
like (valley-style) day for the region...with continued chill
holding tough across the Rio Grande plains and ranchlands where 2 PM
temperatures were still struggling just above 50. That
said...breaks and some lifting ceilings were encroaching on the Rio
Grande and with a warm atmosphere above the cold dome temperatures
become a tricky proposition. Have been monitoring and adjusting
through the day and now have low to middle 60s for the middle/Upper Valley
population...and around 60 in the Lower Valley as peak heating upon
US. Across the Jim Hogg to King ranchlands of Kenedy...temperatures
will only reach the low to middle 50s. For the coast...one last high
tide of surf toward the dunes this afternoon...and that will be it
with swells gradually tapering down. Will let coastal flood
statement expire at 3 PM. A great day for experienced surfers...such
days don't come around that often.

Which brings US to the next 36 hours. NAM/sref continue in the
cool/cold Camp for one more day while the GFS/European model (ecmwf) bring the soup
beginning late tonight and especially Monday. For Monday...the third
day in a row...model differences are up to 20 degrees on high
temperatures. And for a third day in a row...we'll be throwing out
the blends and going very closely with the NAM/sref concept. As
mentioned in this morning's update...a reinforcing bubble of Great
Plains high pressure noses into south Texas and northern Mexico
overnight and into Monday courtesy of two features: upper level
convergence whipping across the northern plains into the Mississippi
Valley and slow moving trough across Southern California into the
intermountain west. Each help build upper ridge from the Gulf to
the Central Plains and support the slow moving surface ridge. This
ridge will combine with already chilly air from land through the
shallow nearshore waters to enhance the **northwest** surface
pattern which has been key to keeping the chill in the air.

The GFS/European model (ecmwf) which lack the ability to handle mesoscale surface
density differences...as shown the past two days...were tossed in
favored of the NAM for this package. Even the NAM forecast is a bit
tricky for Monday afternoon and overnight since the last vestige of
the weakening ridge will be fighting both early March sunshine and
intrusion of very warm subtropical atmosphere...as shown by presence
of 591 dm height contour just to our southeast Monday afternoon.

For the sensible weather: rest of today...watching a pocket of
partial to mostly sunny skies crossing the Rio Grande by 3 PM in
Hidalgo County...as well as lifting ceilings and some breaks up
river near Falcon dam. If full sunshine reaches McAllen...they could
shoot up to 68 before the lowering sun...so for now have nudged to
the middle 60s. Farther north and east...no chance for such a break so
highs will level out in the middle 50s from Hebbronville to Sarita and
upper 50s to around 60 in Harlingen/Brownsville. Have dropped most
of the mentionable precipitation as well.

For tonight...the northwest flow and arrival of ridge 'nose' will
reform low stratus soon after sunset...and temperatures will fall
steadily into the 50s in the warmer areas...and back into the middle to
high 40s in the cooler areas...by midnight. With humidity near 100
percent and sharp low level inversion expect patchy to areas of fog
and patchy drizzle to develop once again after midnight. Northwest
flow should keep true dense fog from developing but will have to
keep an eye as visibility did fall near one-half mile toward the
coast earlier today.

Monday begins murky and will likely remain so through noon in the
valley before ceilings begin to lift...allowing temperatures to
slowly climb. Across the ranchlands to the Rio Grande plains...the
murkiness may well hold in for most of the day...and no reason to
Buck recent trends. Hence...nearly identical temperature forecast to
today's verifying numbers with mainly 50s for the ranchlands inching
to 60-63 across the Rio Grande Valley.

Monday night could set the stage for widespread dense fog. Light
northwest flow returns during the evening...but with surface high
finally dissolving the winds may lay down completely. At the same
time...southeast winds will likely begin migrating west from the
dissipating coastal trough and with plenty of warm moist air just
off the surface and very dry air arriving on deepening southwest
flow above 850 mb (mean relative humidity in the 850-300 mb layer falls to 5
percent) the stage is set for a sock-in after midnight and
continuing after daybreak Tuesday. With no more cold air to
drain...temperatures will be nearly steady and could rise a shade
after midnight...the perfect setup for dense fog.

Long term /Tuesday through Sunday/...warm air advection increases
across south Texas Tuesday in response to low pressure across the
Central Plains. The global models continue to be in agreement with
a blast of cold Arctic air makes its way into the central United
States Wednesday with the cold front moving through North Texas Wednesday
morning and through south Texas Wednesday night. As the front comes through
the Rio Grande Valley Wednesday night...a 500mb trough across the
southwest U.S./Northwest Mexico provides a window for
convection...likely elevated...Wednesday night as the shallow cold air
filters into the area. Overrunning conditions develop Thursday
with warm and moist air aloft moving across the colder air at the
surface. Light rain and drizzle will develop Thursday and continue
through the rest of the week into the weekend as a coastal trough
develops offshore the Lower Texas coast Friday into Saturday. Cold
and wet conditions to continue through the rest of the forecast
period as a result.
&&

Marine...
now through Monday night...swell period continues at 7-8
seconds but sea heights gradually subsiding...now down to 5 feet or
so. Expect this trend to stabilize overnight into Monday with 3-5
foot seas holding with a slight uptick in northerly flow as the
surface ridge quickly noses in...then out...of the waters. Have
nudged down wind and waves Monday night owing to the slower
departure of the cold pattern. Unfortunately...the lighter
winds/slight seas will come with potentially very dense fog making
for a difficult if not impossible start to the fishing day on
Tuesday.

Tuesday through Friday...moderate to strong southeast winds will
prevail across the coastal waters Tuesday as low pressure
across the Central Plains and high pressure across the northeast
United States tightens the pressure gradient across the western
Gulf of Mexico. Winds should diminish Wednesday before a strong
cold front moves offshore the Lower Texas coast Wednesday night. Light to
moderate south to southeast winds Wednesday will shift to the
north and increase Wednesday night with gusts to near gale force likely.
Very strong north winds will prevail across the Lower Texas coast Thursday
and diminish slightly Thursday night into Friday as the pressure
gradient remains very strong across the western Gulf. Small craft
advisories will be needed for the offshore waters Tuesday and gale
watches/warning will likely be needed for all of the coastal
waters Wednesday night into Thursday.
&&

Preliminary point temps/pops...
Bayview/Port Isabel 52 62 56 76 / 20 20 10 10
Brownsville 52 62 56 77 / 10 20 10 10
Harlingen 50 62 54 80 / 10 20 10 10
McAllen 48 62 56 83 / 10 20 10 10
Rio Grande City 47 62 57 86 / 10 20 10 10
South Padre Island 52 61 58 72 / 20 20 10 10
&&

Bro watches/warnings/advisories...
Texas...none.
GM...none.
&&

$$

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