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Area Forecast Discussion (AFD)

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

                            
000
FXUS64 KBRO 181022
AFDBRO

Area Forecast Discussion
National Weather Service Brownsville TX
422 AM CST Fri Jan 18 2019

.SHORT TERM (Today through Saturday): Areas of fog have developed
this morning, with pockets of dense fog over the Lower Valley. So
far the fog has not been widespread enough for a dense fog 
advisory, but that could still happen in the next few hours. Fog 
will burn off this morning, with conditions becoming partly to 
mostly cloudy with moderate south winds by this afternoon. High 
temperatures today will be in the mid 70s to near 80. South winds 
will continue through this evening, finally veering to southwest 
and then northwest after midnight in advance of an approaching 
cold front. Low temperatures will be in the mid to upper 50s 
tonight, and a few showers may develop near the coast in the early
morning.

A mid-level, 500 mb trough axis will swing over south Texas
tonight, with an associated surface cold front moving through the
RGV and deep south Texas around sunrise Saturday. Deep moisture
ahead of this cold front looks limited, and most of the upper
energy will be to the north, but a rumble of thunder will be
possible right along the front. Clearing will be quick Saturday
afternoon from west to east as dry air surges over the area. High
temperatures will be able to creep into the upper 60s to near 70
Saturday afternoon, before the best CAA is able to take full
control. Strong winds will develop near the coast Saturday
afternoon, with a wind advisory possible right at the coast. It
should be just windy farther inland, and breezy for upper Valley
locations.


.LONG TERM (Saturday Night through Thursday): Northerly winds along
with CAA will occur through Saturday evening and into the 
overnight hours. Although skies become mostly clear, winds of 7-10
knots (at least) will keep things well mixed preventing 
temperatures from reaching their full radiational cooling 
potential.

High pressure builds into the region on Sunday keeping skies mostly
clear. With ample sunshine, temperatures will warm, yet be around
5 degrees or so cooler than Saturday. With the mild temperatures 
and dry air, elevated fire weather conditions can't be ruled out, 
especially in the upper Ranchlands. That said, again with high 
pressure near, winds will be significantly less on Sunday limiting
the overall potential. 

As high pressure begins to slide eastward late in the day, surface 
return flow will set up across the region by late Sunday and early
Monday. This will have important implications in terms of low 
temps on Monday. With a hint of a return flow, temperatures will 
not drop as low as previous forecasts have indicated. That said, 
last couple of packages have captured this trends effectively so 
made no real changes to MinTs Sunday or Monday morning. 

As upper level heights continue to increase with the ridge
arriving early next week along with strong warm surface return 
flow, expect temperatures to increase in rapid order after Sunday.
Another strong cold frontal boundary is expected to surge 
southward as a strong upper level trough digs south and eastward 
by midweek. Globals are still having trouble resolving the timing 
of this frontal boundary. Previous runs have shows the GFS being 
faster with an earlier passage. The latest 00z guidance actually 
switches around a bit with the GFS slower (Wednesday morning 
passage) and the ECM has sped up with a 00z Wednesday passage.

After the frontal passage, cyclogenesis is expected to occur over
the Gulf with GFS developing the low a bit closer to us than the
ECM. GFS is showing a slower evolution than the ECM and
consequently a bit wetter midweek as stratiform/isentropic upglide
shower activity develops. Regardless, globals show the surface low
deepening and moving north and east away from the region by
Thursday allowing for surface high pressure to be in control here
in Deep South Texas. 


&&

.MARINE (Today through Saturday): Deepening low pressure over
the southern Plains will interact with retreating Gulf high 
pressure, resulting in stronger southeast to south winds today and
tonight. Moderate winds may become fresh tonight, with small 
craft should exercise caution conditions on the Gulf. A cold front
will sweep over the waters mid-Saturday morning, with gale force 
gusts possible on the Gulf after the front through late Saturday 
evening or night. Wave heights offshore may reach 10 to 12 feet 
late Saturday afternoon or early evening.

(Saturday Night through Thursday): Hazardous marine conditions
expected Saturday night and early Sunday before some improvement
takes place on Sunday. Rather benign marine conditions expected
Sunday evening through much of the daylight hours of Monday before
conditions decline as southerly flow increases ahead of our next
frontal boundary due into the region late Tuesday or early
Wednesday. Behind the front, strong northerly flow and building
seas can be expected to round out the long term marine period.

&&

.FIRE WEATHER...A cold front will sweep into the Gulf of Mexico
Saturday, with dry and breezy TO WINDY post-frontal conditions.
Strong northwest winds of 20 to 30 mph will be possible, and even
slightly higher for a few hours over Coastal Willacy and Coastal
Cameron Counties. Relative humidity values will drop into the 20
to 30 percent range Saturday afternoon behind the front. Fuels are
currently cured. The elevated fire weather parameters will raise
the threat of enhanced wildfire growth and spread. Felt that
conditions will be shy of red flag criteria for now, however.

&&

.PRELIMINARY POINT TEMPS/POPS...
BAYVIEW/PORT ISABEL  75  61  68  48 /  10  20  20   0 
BROWNSVILLE          77  61  69  47 /  10  20  20   0 
HARLINGEN            77  60  69  46 /  10  20  10   0 
MCALLEN              79  59  71  46 /  10  10   0   0 
RIO GRANDE CITY      80  58  70  44 /  20  10   0   0 
SOUTH PADRE ISLAND   72  60  67  51 /  10  20  20   0 

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...None.
GM...Gale Watch from Saturday morning through Saturday afternoon for 
     GMZ150-155-170-175.

&&

$$

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

Short Term/Aviation/Fire Weather...54
Long Term...Frye-55
Graphicast/Upper Air...67