Area Forecast Discussion

FXUS64 KBRO 180634 AAA
Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
1234 AM CST Sun Nov 18 2018
.DISCUSSION...Updated for latest aviation discussion below.
.AVIATION...Satellite and radar images as well as surface 
observations indicate low to mid level clouds across the CWA late 
tonight with light rain showers across the coastal sections. Ceilings 
were near 1100ft at KMFE to near 5500ft at KHRL. Expect MVFR to near 
IFR conditions across the Rio Grande valley the rest of tonight into 
Sun morning as low to mid level moisture increases ahead of a cold 
front moving into south Texas Sun morning. Showers and isolated 
thunderstorms will develop along and ahead of the front as it moves 
across deep south Texas Sunday. Expect MVFR conditions with 
thunderstorms in the vicinity of local aerodromes Sun afternoon. 
MVFR to IFR conditions will develop across the Rio Grande valley Sun 
night in the wake of the cold front moving through the area Sun 
.PREV DISCUSSION... /issued 632 PM CST Sat Nov 17 2018/ 
DISCUSSION...Updated for latest aviation discussion below.
AVIATION...BKN to OVC skies will continue through the night as
moisture surges across the region with a moderate to strong low-
level jet. MVFR to possibly IFR ceilings can be expected overnight 
with fog also possible across the Mid Valley due to lightening 
winds. A cold front will approach from the north at the end of 
this forecast period with models still struggling with timing. 
Confidence is moderate to high, though, that rain chances will 
increase during the day with MVFR ceilings.
PREV DISCUSSION... /issued 251 PM CST Sat Nov 17 2018/ 
SHORT TERM (Tonight through Sunday Night):A mostly cloudy day 
across much of the CWA today as low level moisture continues to 
increase with the southerly or slight southeasterly flow continuing. 
A good number of folks have received at least a spit or two of rain 
out there across the coastal counties today. Rain chances begin to 
increase overnight tonight as a cold front and parent UL trough 
begin to push closer to the region.
Ahead of the front, expect continued return flow into Sunday. As the 
upper level impulse and front near, expect rain showers (maybe even 
a clap of thunder or two) to develop across much of Deep South 
Texas. Additionally, surface pressures ahead of the front look 
rather low and in fact a weak surface low may develop along the Rio 
Grande late Sunday. This will 1) keep rain chances going and 2) have 
some implications of timing of the frontal passage here in the lower 
valley. Globals suggest the front will pass later as the low 
interrupts the southern progression. That said, mesoscale guidance 
say a quicker frontal passage as the low ejects quicker OR even 
develops just offshore. For now decided to split the difference and 
bring the front into the northern Ranchlands by late Sunday and 
through the lower RGV between 06z and 12z Monday.  
LONG TERM (Monday through Saturday):Forecasters here are in 
conundrum with the GFS/ECMWF slowing down the front and pulling up 
stationary across the CWA late Sunday night/Monday while the NAM 
with its much stronger cold air surge pushes the front through all 
of Deep South Texas Sunday afternoon and the Lower Valley by sunset 
Sunday. Zonal flow aloft and the development of a low pressure wave 
or weak low along the front may indeed slow the front down but the 
density of the cold air that the NAM is advertising and in fact what 
is observed by current conditions over the TX Panhandle/Plains may 
indeed push the front through the region before becoming stationary 
south of the region. The other issue of uncertainty is the extreme 
high QPF output of the ECMWF and the NAM (although the bulk is shown 
offshore the Lower Texas Coast). Very high uncertainty and low 
confidence forecast with a potential bust may play out early on in 
the forecast.  Temperature spreads between the cold NAM and warmer 
GFS/ECMWF Monday are as high as 16 degrees across portions of the 
RGV. Precipitation amounts also range drastically with ECMWF/NAM 
showing over a foot of rain falling over the Gulf and 1-3 inches 
along the coastal strip (associated with the low pressure/sfc 
trough) with the GFS a more reasonable 0.50-2 inches along the 
With all this said will continue to trend on the slightly cooler 
side but continue high pops (Mid/Lower RGV) and light to moderate 
QPF amounts on Monday into Tuesday. All models do show the entire 
system moving to the east later Wednesday into Thursday as a strong 
shortwave trough swings through Texas and the Central Plains. Rain 
chances may persist, especially closer to the coast, through 
Wednesday with some resemblance of a coastal trough lingering but is 
expected to be lifting northeast Wednesday afternoon/evening leaving 
the RGV/DSTX much drier and mild for Thanksgiving Day and into 
Black Friday and early next weekend. 
MARINE:(Tonight through Sunday Night): Generally light to moderate 
southerly or southeasterly flow will prevail through much of the 
short term marine period. There will be a transition to a more north 
or northwesterly flow toward the end of the period as a cold front 
pushes through the region. There is a bit of uncertainty with the 
passage of the front, however, at this time winds and sea should 
remain mainly moderate with cautionary wording possible. Given that 
at times we'll be nearing Small Craft Advisory thresholds, cannot 
rule them out at this time, however, if a SCA is needed it will only 
be a lower end advisory. 
Monday through Thanksgiving Day...Cold front is expected to pull 
up stationary over of just southeast of the coastal waters Monday 
into Tuesday. There is a potential for an earlier frontal passage 
over the northern coastal waters Sunday afternoon/evening. Either 
way moderate northern flow to develop to help build seas. Low end 
small craft advisories are possible by Tuesday as the front and 
weak low pressure area moves just east of the coastal waters. The 
front and low gets shoved eastward Wednesday and Thursday with 
weak high pressure building over the Northwest gulf maintaining a 
slight to moderate north-northeast flow and moderate persistent 
sea state. 
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