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Area Forecast Discussion (AFD)

Issued by Brownsville/Rio Grande Valley, TX (BRO)

FXUS64 KBRO 171127 AAA

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
627 AM CDT Wed Oct 17 2018

...12z Aviation Update...

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


.AVIATION...Continued clouds and intermittent pockets of drizzle 
to start the TAF cycle. Flight categories will flirt with the 
IFR/MVFR transition height through mid morning or so. Beyond mid 
to late morning Wednesday generally MVFR conditions can be 
expected through around sunset before another drop to the 
MVFR/IFR transition height again. Rain chances will be rather low 
up through the morning, but gradually increase through the 
afternoon hours and especially the evening and overnight. Best 
rain chances look to reside across the coastal terminals. 
Northerly surface winds will continue to remain elevated through 
this cycle similar to the last 24 hours.


.PREV DISCUSSION... /issued 416 AM CDT Wed Oct 17 2018/ 

SHORT TERM (Today through Thursday): After a very damp, gloomy, 
and cool day on Tuesday, Wednesday will see very little 
improvement. Temperatures may be a degree or two warmer than 
Tuesday with the lower valley approaching the middle and upper 
60s, however, the northern Ranchlands will likely hang onto upper 
50s and lower 60s today. Similar to yesterday, some pockets of 
drizzle will be possible and winds will be gusting to 20 to 25 mph
again at times. Again, very similar to Tuesday. 

Later, an upper level disturbance will begin to slide northward 
around an upper level high across the Florida Peninsula later 
tonight and Thursday. At this time it looks like the best chance 
for rain will be right along the coast, however, much of the 
region will see at least some measurable precipitation from this 
feature. Models have trended a little further west with the main 
vort axis so we'll need to monitor this trend and perhaps bring 
the heavier rain a bit further west. The highest QPF again as of 
now will be focused right along the immediate coast. 

The end of the period will be similar to the start with rainfall 
chances beginning to decrease, however, the strong surface coastal
trough remains in place with continued breezy, damp, gloomy, and 
cool weather prevailing.

LONG TERM (Thursday night through Tuesday): Mid level ridging 
centered over the mid Atlantic region will support surface high 
pressure pushing into deep south Texas and the RGV Thursday night. A 
surface trough will lie just offshore, enhancing rain there and 
along the coast. Upstream, a rex block appears over the West Coast. 
Rain chances will remain elevated Thursday night with high pressure 
still interacting or supporting the trough offshore. Totals over 
land should be in the tenths if the heaviest activity behaves and 
remains just offshore. Should heavier rain develop along the coast, 
a few tenths Thursday night into Friday could easily turn into an 
inch or two of rain.  Friday into Saturday a cold front will push 
south over the plains and into Texas as mid level ridging builds 
from Texas to the Pacific Northwest. The ridging will help strong 
Canadian high pressure spill south. The GFS brings the front across 
the door step Saturday afternoon and evening, and the ECMWF is also 
pretty close to that timing. Cameron and Willacy counties will have 
the best chance of continuous light to moderate rain Saturday 
through Monday, accumulating around a quarter of an inch every six 
hours. Both long range models actually develop a weak surface low 
early next week. As that develops, enhanced rainfall looks possible 
Monday, with an inch possible for Cameron county alone that day. 
Tuesday looks a little better as the areas of concentrated rainfall 
shift away from the area. Highs will be in the 70s while lows will 
be in the 50s and 60s, near or perhaps slightly below average for 
this time of year. Given that the models are in fairly good 
agreement, confidence is medium to above medium with this forecast. 
Other issues that will be of concern will be elevated rip current 
risk and possible minor coastal flooding with the elevated wave 
heights from the east and northeast.

Today through Thursday: Adverse marine conditions expected to 
continue through this marine short term period. This morning at 
the time of this discussion Buoy 42020 was showing wind gusts 
above SCA thresholds, however, wave heights have been a bit 
lackluster for this event...now down to 4 to 5 feet. Northwesterly
flow is limiting the fetch for our coastal waters, which is 
having little impact on seas. Eventually, winds will begin to 
shift to a more northerly direction adding a bit more of a fetch 
and eventually higher waves. This should begin later tonight. With
a high likelihood of continued adverse marine conditions...went 
ahead and extended the current Small Craft Adv through Thursday 

Thursday night through Sunday night: Little improvement in marine 
conditions is expected in the long term. Moderate to fresh east 
winds will prevail initially, due to high pressure across the north 
Gulf and a lingering coastal trough over the western Gulf. Wave 
heights will be in the 5 to 7 feet range offshore. Winds will back 
to northeast and increase Saturday to Saturday night with the 
arrival of another cold front. Strong northeast winds and high seas 
will develop Saturday night behind the front. Small craft should 
exercise caution to low end small craft advisory conditions will 
prevail on the Gulf waters Thursday night through Saturday, with 
small craft advisory conditions expected Saturday night through 
Sunday night.


GM...Small Craft Advisory until 1 PM CDT Thursday for GMZ130-132-135-



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