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Area Forecast Discussion (AFD)

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

                            
999 
FXUS64 KBRO 241740 AAB
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
1140 AM CST Sat Feb 24 2018

.DISCUSSION...Winds have continued to increase across portions of
the lower to middle Rio Grande valley late this morning and with a
strong low level jet across the lower Texas coast...have expanded
the wind advisory to include Hidalgo and Kenedy counties.
&&

.AVIATION...Satellite images and surface observations indicate
mostly clear skies across the CWA late this morning with a few low
to mid level clouds across the western portions. In
addition...very strong south to southeast winds continue to
develop across the eastern portions of the Rio Grande valley.
Ceilings were near 2200ft at KAPY to near 3600ft at KBKS. Expect
VFR conditions to prevail across the Rio Grande valley this
afternoon into this evening with very strong southerly winds
across the coastal sections of the CWA. A weak cold front will 
move into the northern ranchlands tonight and low to mid level 
moisture will increase ahead of the boundary. Expect MVFR to near 
IFR conditions to develop with low clouds/fog late tonight into 
early Sun morning. In addition...showers and thunderstorms will 
develop across portions of the northern ranchlands tonight and 
possibly move into the Rio Grande valley early Sun morning.
&&

.PREV DISCUSSION... /issued 546 AM CST Sat Feb 24 2018/ 
DISCUSSION...Updated for latest aviation discussion below.

AVIATION...Ceilings are showing signs of lifting at KBRO and 
KHRL with MVFR likely to be the dominate category this morning.
Stronger winds, 35-45kts 1-3k feet above the surface, to slowly
mix to the surface later this morning mixing out the surface
moisture with VFR conditions developing. KMFE will see conditions
improve later in the morning or early this afternoon. Winds weaken
this evening and low clouds to move off the gulf and spread over
northwest overnight. MVFR with spotty of IFR cigs are anticpated
before midnight. Showers and thunderstorms are expected to
increase later tonight although the majority of the storms look to
remain north of the air terminals can not rule out a band of
storms moving across the airports after midnight with KMFE having
the highest chances. Any fog development will favor KBRO later
tonight with low probabilities of fog dipping to IFR levels.

PREV DISCUSSION... /issued 421 AM CST Sat Feb 24 2018/ 

SHORT TERM (Today through Sunday): Shortwave trough moving out of 
the Rockies and into the Plains today/tonight with surface low 
pressure deepening. Low level jet strengthening as of this writing 
with 925-850 winds increasing to the 35-45kt range this 
morning/early afternoon. The stronger winds to partially mix to the 
surface later this morning with deeper mixing this afternoon as 
lapse rates increase as surface temperatures climb well into the 80s 
and lower 90s. Strongest winds are still expected over the Lower 
Valley and the Coastal regions warranting a wind advisory across 
Cameron and Willacy and Small Craft Advisories for the coastal 
waters. 

Tonight into Sunday...Broad upper trough with deep southwest flow 
will be the forebears of a slow moving cold front and upper level 
impulses increasing the chance for showers and thunderstorms. An 
elongated impulse moving out of Mexico this evening/tonight to 
initiate thunderstorms and with the strengthening upper jet 
atmosphere dynamics become marginally favorable for some strong 
storms with an isolated severe storm not out of the possibility. 
Strong winds and some marginally severe hail along a southwest to 
northeast path from the Zapata, Starr to jim Hogg/Brooks counties 
look like the best locations with increasing 0-6km shear values into 
the 40-55kt range and MU CAPE values 1200-2000j/kg range expected in 
these areas. Northern Hidalgo can not rule out a strong storm as the 
storms track eastward but believe much of the I-2 and lower portions 
of the 69C/E regions may escape the strongest storms tonight. The 
front enters the CWA Sunday morning and moves south at a snails pace 
through the day. GFS shows a few stronger vort maxes moving across 
the region during the day and with dynamics still in place for a few 
clusters of thunderstorms are still possible this time favoring 
counties farther to the east. Expect some pockets of heavy rain with 
Pwats well above normal can not rule of some localized flooding in 
poor drainage areas where showers or thunderstorms could taking on a 
training affect. Temperatures to cool off towards normal behind the 
front but with the slow eastward progress temperatures in the Lower 
Valley to approach or exceed 80. 

LONG TERM (Sunday Night through Friday): The long term starts
with a cold frontal boundary through the region late Sunday and
early Monday. Although the front remains parallel to the upper
level southwest flow, mesoscale influences will help push the
surface front just south of the mouth of the Rio Grande by early
Monday. As the front stalls just south, expect isentropic lift to
keep clouds and showers/drizzle around the region on Monday.
Daytime high will also be cooler as CAA and cloudy conditions 
keep temps down on Monday. The front decides to roar back
northward as a warm front on Tuesday allowing southerly return
flow to help push drizzle/showers/fog potential northward out of
the CWA. 

Behind the warm front WAA will help boost temperatures on Tuesday
and especially on Wednesday as southwest FA may jump into the 
lower 90s. Winds will also begin to pick up on Wednesday due to 
1)intense surface warming allowing afternoon mixing and 2) 
increase in surface pressure gradient between a departing high 
east and troughing west. The front should finally push through the
region overnight (should be a mostly dry passage). High pressure 
drops southward into eastern Texas by early Friday helping relieve
some of the breezy conditions. As this high pushes eastward into 
the southeast, coastal troughing may form by early next weekend, 
which will keep the area cloudy, cool, and damp. 

MARINE (Today through Sunday): Pressure gradient continues to 
strengthen as low pressure moves out of the 4 corners region and 
into the Southern/central Plains through tonight. Southerly flow 
strengthens this morning with increasing winds and building seas 
through the day. Small Craft Advisories are in place for later this 
morning and into the early evening hours. A cold front moves into 
South Texas overnight and slows down considerably moving off the 
coast late Sunday into Sunday night. Winds and seas to slowly lower 
as the gradient weakens with the approach of the front while showers 
and thunderstorms will be on the increase. 

Marine fog remains patchy at best with occasional patches of dense 
fog over the near shore waters. A Dense fog advisory will remain in 
effect until mid morning when the onshore flow strengthens and some 
mixing of slight drier air works its way to the surface.  

Sunday Night through Friday: Moderate winds and seas expected as 
we begin the long term period as coastal trough sets up just off 
shore. Very little improvement expected through much of the week, 
in fact conditions will slowly decline by midweek as a cold 
frontal boundary moves through the region Wednesday night or early
Thursday. This will push winds/sea close to if not exceeding 
Small Craft Adv thresholds. High pressure will then drop into 
eastern TX which may help bring seas and winds down finally by 
Friday...though the easterly fetch across the Gulf may increase 
swells the end of next week. &&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...Wind Advisory until 5 PM CST this afternoon for TXZ251-253>257.

GM...Small Craft Advisory for winds until 6 PM CST this evening for 
     GMZ130-132-135.

     Small Craft Advisory until 9 PM CST this evening for GMZ150-155-
     170-175.
&&

$$

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

Short term/Aviation...61/62 
Long term...52 
PSU/Graphicasts...62