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Displaying AFOS PIL: AFDBRO Received: 2019-01-12 12:29 UTC

FXUS64 KBRO 121229 AAB

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
629 AM CST Sat Jan 12 2019

.DISCUSSION...Satellite images and surface observations indicate
visibilites have dropped to a quarter of a mile across portions of
the CWA this morning. With clear skies and calm winds...areas of
dense fog will continue to develop across the Rio Grande valley
and northern ranchlands before the cold front moves into the
northern portions of the CWA later this morning. Have issued dense
fog advisory for all of the CWA except for the coastal sections of
Cameron...Willacy and Kenedy counties through 9 am today.

.PREV DISCUSSION... /issued 556 AM CST Sat Jan 12 2019/ 
DISCUSSION...Updated for latest aviation discussion below.

AVIATION...Satellite images and surface observations indicate
mostly clear skies with areas of fog across the CWA early this
morning. Ceilings were near 200ft at KAPY to near 700ft at KBKS.
Visibilities were near 1/4SM with fog at KHRL...KEBG...and KAPY to
near 6SM with fog at KPIL. Expect MVFR to IFR conditions across
the Rio Grande valley through 18Z today before a cold front moves
through the area. VFR conditions will prevail after 18Z as drier
air filters into the CWA this afternoon. MVFR conditions will
return across portions of the Rio Grande valley tonight as fog 
redevelops late tonight.

PREV DISCUSSION... /issued 441 AM CST Sat Jan 12 2019/ 
SHORT TERM (Today through Sunday): Line of convection that 
developed across the CWA last night has moved offshore the lower 
Texas coast early this morning as a prefrontal trough continues to
move eastward across the coastal sections. This trough will for 
the most part will bring an end to rain chances across the Rio 
Grande valley today even as a cold front moves through the RGV 
this afternoon. Will likely continue to see patchy fog develop 
across portions of deep south Texas early this morning as clearing
skies and light winds allow fog to continue to develop before the
front moves into the northern ranchlands later this morning. 
Drier air will filter into the Rio Grande valley today and cooler 
air will filter into the area tonight into Sunday as surface high 
pressure builds into south Texas in the wake of the surface low 
pressure across the ARLATEX region this afternoon moving east and 
northeast. Temperatures will be in the upper 70s to near 80 across
the Rio Grande valley this afternoon before falling into the 
lower to mid 50s tonight. Highs will be considerably cooler Sunday
with highs in the lower 60s across the RGV. 

LONG TERM (Sunday Night through Friday): The pattern of winter
2018/19 has been one of changes...from springlike warmth to
winterlike chill...and back again...but without any sharp day to 
day drops - rather temperatures "oozing" into the cool before 
recovering. Such will be the pattern for the next work week, as 
temperatures begin seasonably chilly before warming up into 
springlike levels to close out the week. In getting from the cool 
to the warm, a period of welcome...but still light...rain will 
cover most of Deep S. Texas and the Rio Grande Valley Tuesday and 
Tuesday night.

The pattern aloft features a building 500 mb ridge while west
northwest 500 mb flow across east Texas continues to draw down a
piece of the surface high which originated in the northern Plains
and Canadian prairies over the weekend...and with overrunning
moisture/weak isentropic lift clouds will thicken and a few light
showers/sprinkles can't be ruled out for the eastern half of the
area. Light northerly surface flow in a chilled atmosphere will
keep temperatures in the 50s for most areas...and leaned toward an
ECMWF/NAM-12 blend for highs. 

Monday night a weakening 500 mb trough approaches west Texas from
west central Mexico, with slowly deepening moisture riding up the
Sierra Madre and extending east to the foothills/Rio Grande
Plains, which will increase chances for wetting light rains from
southwest to northeast. ECMWF is fairly robust in bringing rain to
the mid/Upper Valley by daybreak, and chances toward dawn may need
to be increased over the 40 percent for this forecast in time.

That moisture overspreads the entire Valley/Deep S. Texas region
Tuesday, courtesy of the short wave inducing decent isentropic
lift while helping developing a weak but notable surface low east
of northern Tamaulipas. This ensures a damp and chilly day as
surface winds will back to north or even northwest - and while
light, will lock in low temperatures more in line with the cooler
ECMWF and 84 hour NAM-12. Low to mid 50s would not surprise for
the entire region, but with some easterly flow just off the
surface trying to sneak back across the developing surface low
into the Lower Valley, nudged highs up to 60 from South Padre to
Brownsville, with mid to upper 50s elsewhere and the lowest
temperatures across the Upper Valley and Rio Grande Plains.

The weakness moves steadily across the border region overnight,
taking the rainfall with it. GFS is a bit quicker with ending
rainfall from west to east while ECMWF is slower...due to
uncertainty and to keep consistency with prior forecasts kept
likely rainfall across the lower Valley all night, tapering
off/ending across the Rio Grande Plains. WPC QPF determinstic rain
totals range from 0.25 inches in the upper Valley to near 0.75
inches toward the coast for the event...which seems reasonable
given the favorable pattern. For the week, a fairly seasonable
number for the heart of winter.

Thereafter, drier air arrives as 500 mb ridge rebuilds Wednesday
then becomes a zonal flow Thursday and Friday. With no upper level
support (confluence) to bring any strong surface highs southward
through the period, sunshine Wednesday and Thursday will moderate
temperatures nicely, reaching back to seasonable levels (upper 60s
to lower 70s Wednesday) and a bit more into the 70s Thursday. 
Clouds may fill back in with perhaps a shower or two toward the 
coast then, which will temper the warming just a bit. Low level 
southerly flow develops Friday, with southwest flow from 850 to
700 mb potentially bringing a drying and downslope condition by
afternoon. Current forecast brought temperatures to or above 80 in
the Valley and mid to upper 70s for the ranchlands, and this looks
reasonable based on consistency. 

MARINE: Today through Sunday...Seas were near 5 feet with 20 
winds near 14 knots at buoy020 early this morning. Light to 
moderate southwest winds will shift to the north across the 
coastal waters today as a cold front moves offshore the lower 
Texas this afternoon. Winds and seas will increase across the 
western Gulf of Mexico tonight as the pressure gradient increases 
across the lower Texas coast with high pressure building into the 
northwest Gulf in the wake of the front. Moderate to strong 
northeast winds will develop offshore the lower Texas coast 
tonight and small craft advisories may be needed for the far 
offshore waters for seas if not winds. The pressure gradient will 
diminish across the western Gulf slightly on Sunday with high 
pressure across the south-central United States extending into the
northwest Gulf. Moderate northeast winds will prevail across the 
coastal waters on Sunday. 

Sunday night through Wednesday night...Moderate winds and seas 
will be the rule as the period is dominated by the Canadian 
sourced surface high early, followed by the weak low pressure cell
which will form south of the waters and likely roll through the 
20-60 nm leg Tuesday night and early Wednesday. At this point it 
was tricky to place the low, but given cooler nearshore waters and
some northwest flow out to and beyond the beach, have northeast 
winds through Tuesday before winds shift east/southeast at night. 
On Wednesday, more north to northwest close to the coast Wednesday
and southeast in the 20-60 nm leg...before winds turn back to the
northeast but a lighter speeds Wednesday evening and finally veer
to the southeast overnight.

In general, while the ridge is easing across east Texas into
Louisiana, winds may hang in caution range (15 to 18 knots or so)
with seas rising back toward 5 feet. The bigger nuisance for
boaters will be the wetter conditions Tuesday through early to
midday Wednesday, with chilly conditions on Monday.

TX...Dense Fog Advisory until 9 AM CST this morning for TXZ248>255-



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