Drought in Texas, December 15 to 21, 2020

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
1029 PM CST Mon Dec 14 2020

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

.AVIATION...VFR to MVFR conditions are expected through the next
24 hours. The latest suite of TAFs will reflect the passage of a
cold front Tuesday evening.
&&

.PREV DISCUSSION... /issued 540 PM CST Mon Dec 14 2020/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...VFR is expected through the next 24 hours. Winds will
veer in advance of the next cold front passage.

PREV DISCUSSION... /issued 252 PM CST Mon Dec 14 2020/

SHORT TERM (Now through Tuesday Night):  The initial part of the
short term is fairly straightforward. A shallow layer of cold air is
in place under a strong inversion. Lift is weak, however, with
little precip possible. Overnight temperatures will be below normal,
mainly in the 40s, and a few spots across the Ranchlands could dip
into the upper 30s tonight. High pressure will shift to the east
overnight, with wind direction veering slowly from north to
southeast. Conditions will remain dry on Tuesday, but return flow
from the south could result in a few Gulf and coastal showers during
the day. Mostly sunny skies will return to western sections while
more cloudy conditions remain along the coast. High temperatures
will edge back up to near if not slightly above seasonal normal 70s.

A cold front will surge across West Texas Tuesday during the day,
enroute to deep South Texas and the lower RGV by Tuesday night. An
initial wind shift to north may occur by late afternoon, with the
front moving across the Upper Valley in the evening, and reaching
the coast as early as midnight or thereafter. With nighttime CAA,
low temperatures Tuesday night will dip into the 40s area wide,
except for the immediate lower Valley coast, where it will remain
nearer to 50 degrees. The probability for some upper 30s across the
north appears to be higher on Tuesday night than for tonight. Rain
chances will be very low with this dry front, but a few showers
could develop over the open Gulf with the additional moisture
source there.

LONG TERM (Wednesday through Monday): Relatively short-wavelength
but also relatively low-amplitude Pacific storm track should
maintain a progressive pattern across the CONUS into early next
week. Locally, we expect to see two cold frontal passages: Tuesday
evening (see above) and sometime on Saturday, though no wild
temperature swings are expected. Unfortunately, these two frontal
passages will be mainly dry, with light precip accumulations only
occurring east of I-69E/Hwy. 77 (at best) over the next seven
days, which won't be of much help for our developing moderate+
drought conditions.

First front should be well clear of the coast by Wednesday
morning, with zonal flow at upper levels taking hold and a cool NW
flow at low levels. Afternoon temps reach the mid-upper 60s, which
is several degrees below normal, even for mid-December. Relative
humidity values bottom out in the 20-25% range west of the coastal
counties. 20-ft. winds out of the NNW progged in the 10-15mph
range, so will have to monitor for a potential Fire Danger
Statement.

Thursday morning is very likely to be the coldest of the period,
as dry air at the surface, light winds, and very limited cloud
cover combine to allow strong radiational cooling. Sheltered
locations across the northern Ranchlands could dip briefly below
freezing. Interestingly, MET guidance holding those lows in the
mid-upper 30s, while blended guidance is more low-mid 30s. As an
example, NBM probabilistic guidance for Falfurrias has values in
the 20th-70th percentile ranges between 30-34F. Too early yet for
any headlines, but this will bear watching over the next 24
hours.

Weak onshore flow returns for Thursday, with some modest warming
(to near 70F along the Rio Grande). Low-level southerly flow sets
up Thursday night in response to troughing in the lee of the
Rockies. Temperatures climb back above normal, pushing 80F in
spots, with dewpoints rising as well. This moistening leads to a
return of slight chances for rain right along the coast and
offshore by Friday night, with widely scattered coverage possible
east of Hwy. 77 during the day on Saturday. Column moisture never
becomes particularly deep (reaching about 750mb), but some decent
vertical motion values could lead to a rumble of thunder or two as
the front and short-wave trough aloft pass sometime during the day
on Saturday.

There are some differences between the GFS and ECMWF in the
handling of a pair of shortwaves over the weekend, though the
effect on sensible weather in Deep South Texas would appear to be
limited. ECM is sharper with the initial wave (mentioned above),
whereas the GFS hangs back another piece and brings it through
Sunday, along with a reinforcing push of cool air. At any rate,
Sunday and Monday look mostly sunny due to a very dry column
again. Short-wave ridging aloft next Monday may provide a few
degrees of warming, to just above normal.

MARINE (Now through Tuesday Night): Marine conditions will
improve today through Tuesday with high pressure spreading over
the area. North winds today will veer to southeast by Tuesday.
Small craft should exercise caution the rest of this afternoon
with wave heights still lowering. A cold front will arrive Tuesday
night, producing strong north winds and building seas. Small
craft advisory conditions due to strong north winds will be
possible late Tuesday night continuing into Wednesday and wave
heights will respond in turn.

Wednesday through Sunday: Small Craft Advisories (SCA) are likely
to be ongoing Wednesday morning, in the wake of Tuesday evening's
frontal passage. These conditions may persist for much of the day,
especially on the outer Gulf waters, as seas take time to subside.
Lighter onshore flow takes hold for Thursday, with seas further
subsiding to 2-3 ft. Southerly flow then increases, in response to
a tightened pressure gradient, beginning Thursday night. Periods
of Small Craft Exercise Caution (SCEC) are likely, with SCA
possible offshore by Friday night. Another cold front arrives
sometime Saturday, with at least moderate to fresh north winds
behind it, so SCEC to lower-end SCA likely. Seas look to build
near 6 ft. offshore by early Sunday as well.
&&

.PRELIMINARY POINT TEMPS/POPS...
BAYVIEW/PORT ISABEL  50  76  48  63 /   0   0   0   0
BROWNSVILLE          50  78  49  65 /   0   0   0   0
HARLINGEN            47  78  46  65 /   0   0   0   0
MCALLEN              47  78  46  67 /   0   0   0   0
RIO GRANDE CITY      43  76  44  67 /   0   0   0   0
SOUTH PADRE ISLAND   56  72  55  60 /   0   0   0   0
&&

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

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

Hazardous Weather Outlook...UPDATED
National Weather Service Brownsville TX
553 PM CST Mon Dec 14 2020

TXZ248>257-351-353-151215-
Zapata-Jim Hogg-Brooks-Inland Kenedy-Starr-Southern Hidalgo-
Inland Willacy-Inland Cameron-Coastal Willacy-Coastal Cameron-
Coastal Kenedy-Northern Hidalgo-
553 PM CST Mon Dec 14 2020

This Hazardous Weather Outlook is for portions of Deep South
Texas.

.DAY ONE...Tonight

There is a moderate risk of rip currents on the area beaches.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday

Rip current risk will be elevated again Tuesday night through
Thursday.

Elevated fire weather conditions may develop Wednesday behind a
dry cold front.

Temperatures may approach freezing in a few exposed locations
across the northern and western Ranchlands Thursday morning.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will not be needed.

GMZ130-132-135-150-155-170-175-151215-
Laguna Madre from the Port of Brownsville to the Arroyo Colorado-
Laguna Madre from the Arroyo Colorado To 5 NM north of Port
Mansfield TX-
Laguna Madre from 5 nm north of Port Mansfield to Baffin Bay TX-
Coastal waters from Port Mansfield to the Rio Grande out 20 nm-
Coastal waters from Baffin Bay to Port Mansfield out 20 nm-
Waters from Port Mansfield to the Rio Grande extending from 20 to
60 nm-
Waters from Baffin Bay to Port Mansfield extending from 20 to
60 nm-
553 PM CST Mon Dec 14 2020

This Hazardous Weather Outlook is for portions of The Gulf of
Mexico and The Laguna Madre.

.DAY ONE...Tonight

No hazardous weather is expected.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday

Additional Small Craft Advisories may be needed late Tuesday
night into Wednesday and again Friday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will not be needed.

Speece