055 
FXUS64 KBRO 201511 AAB
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
911 AM CST Sun Dec 20 2020

.DISCUSSION...The dense fog advisory has been extended through 10
AM along either side of I 69C corridor from Hidalgo County north
through Brooks. Some areas may experience visibilities below one 
quarter mile at times. 

&&

.PREV DISCUSSION... /issued 505 AM CST Sun Dec 20 2020/ 

DISCUSSION...Issued a dense fog advisory through 9 AM for along
either side of the I 69C corridor from Hidalgo County north
through Brooks. Kenedy and Jim Hogg can expected some areas
experience visibilities dropping below one quarter mile at times.
Will be monitoring for lower vsby across across portions of Willacy
and Cameron counties the next few hours. 

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...Some morning patchy fog may produce brief IFR
conditions through 15Z before mixing out and VFR prevails for all
areas through at least 06Z Monday. Fog may redevelop tonight with
light winds, clear skies and sufficient surface moisture. 

PREV DISCUSSION... /issued 349 AM CST Sun Dec 20 2020/ 

SHORT TERM (Now through Monday): The main source of dry air remains 
north of Deep South Texas and there remains enough surface moisture 
under a dry and stable airmass. Clear skies and near clam winds is 
allowing for fog formation with some becoming dense (< 1/4 mi) 
across northern Ranchlands and portions of Lower RGV.  With dew 
point depressions steadily narrowing as radiative processes increase 
would expect the fog to expand through sunrise. Will be considering 
a dense fog advisory for the remainder of the night into mid-morning 
to cover this. Beyond the morning fog, benign but very nice 
conditions along with mild temperatures will be the rule for the 
last day of Autumn and the first official day of Winter tomorrow. 
Short range models in good agreement indicating another shortwave 
trough (seen on mid and upper water vapor channels) moving east of 
Texas today allowing for sfc and upper ridging to settle over South 
Texas bringing another subtle shot of drier conditions. After 
another round of fog, potentially dense in spots, Monday morning no 
other sensible weather is anticipated.  Model guidance in good 
agreement with lows in the 40s and 50s with highs in the 70s both 
today and Monday.  Humidity will be low, especially this afternoon, 
however winds are expected to be less than 10 mph limiting any fire 
weather danger. 

LONG TERM (Monday Night through Saturday): A flat ridging pattern 
will carry through mid week, before the next short wave trough plows 
through the Southern Plains and delivers the next cold front to Deep 
South Texas. Mild temperatures and dry conditions will start off the 
week, and then as the surface high moves off to the east, we get a 
return flow which will bring in warmer and more humid conditions. 
Highs are expected to reach the upper 70s to near 80 on Tuesday, and 
then the lower to mid 80s across Deep South Texas on Wednesday 
afternoon, which is about 10 to 15 degrees above normal. The 
pressure gradient will tighten as the cold front approaches and will 
bring breezy southeast winds to the area on Wednesday. 

The models have come into better agreement for the frontal passage 
on Wednesday night, but there is still about a 6 hour difference 
between the GFS and the ECM. The 0Z GFS slowed down slightly and now 
has the front passing through the area around midnight on Wednesday 
night, while the ECM continues to lag and pushes the front through 
sometime very early Christmas Eve morning. PoPs will increase ahead 
of and along the frontal boundary on Wednesday, with the greatest 
chances offshore and and along the coast. There will be a nice cool 
down behind the front, allowing temperatures on Christmas Eve and 
Christmas day to top out in the 60s with a chilly Christmas Eve in 
the 40s and 30s...and some locations may even approach freezing. 
With the dry and breezy conditions behind the front on Thursday, 
rapid wildfire spread and growth may be a concern. On Saturday,
the surface high will shift east and more mild conditions will be
expected. 

With the model discrepancies, forecast confidence continues to be 
low to moderate Wednesday and beyond. 

MARINE: Now through Monday... Surface high pressure builds over the 
Western Gulf later today and passing slowly to the east Monday. 
Light northerly winds and lowering seas expected today with light 
easterly winds and low seas Monday. 

Monday Night through Thursday...The southeasterly flow 
will pick up on Tuesday and Wednesday as the next cold front 
approaches, and rain chances will begin to increase. SCEC conditions 
are likely Tuesday night into Wednesday. The timing of this next 
cold front is still a bit uncertain, but should be sometime 
Wednesday night. Winds and seas will likely build to SCA criteria 
with the frontal passage...with some of the model guidance 
continuing to hint at Gale conditions. 

&&

.PRELIMINARY POINT TEMPS/POPS...
BAYVIEW/PORT ISABEL  72  53  74  59 /   0   0   0   0 
BROWNSVILLE          75  53  77  60 /   0   0   0   0 
HARLINGEN            76  50  77  57 /   0   0   0   0 
MCALLEN              76  49  78  57 /   0   0   0   0 
RIO GRANDE CITY      78  46  79  54 /   0   0   0   0 
SOUTH PADRE ISLAND   68  62  70  66 /   0   0   0   0 

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...Dense Fog Advisory until 10 AM CST this morning for TXZ249>251-
     253-353.

GM...None.
&&

$$

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68-McGinnis