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Area Forecast Discussion (AFD)

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

FXUS64 KBRO 231255 AAC

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
655 AM CST Fri Feb 23 2018

.DISCUSSION...Updated for latest marine discussion below.


.MARINE...Dense fog has formed over portions of the Laguna Madre
and near shore waters and a dense fog advisory has been issued
through 11 am. 


.PREV DISCUSSION... /issued 549 AM CST Fri Feb 23 2018/ 

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...Poor flying conditions prevail this morning as a warm
front moves on shore. LIFR cigs and IFR vsbys are expected through
mid morning then a steadily improvement late this morning and into
the afternoon as the front moves north of the region and 
southeasterly winds increase. MVFR mixing with occasional VFR
conditions this afternoon lower back to MVFR Friday evening.
Pressure gradient strengthens today and tonight with moderate
southeast winds developing. Winds are not expected to relax
overnight with gust remaining around 20 knots tonight. 

PREV DISCUSSION... /issued 331 AM CST Fri Feb 23 2018/ 

SHORT TERM (Today through Saturday): Warm front still lurking
offshore is slowly moving westward. Hi-res Rapid Refresh and NAM 
suggest the front to move inland mid-morning and accelerate N-NW 
this afternoon. Lingering showers and light fog this morning to 
dissipate and lift northeast as the front progresses through Deep 
South Texas. In it wake, southerly flow strengthens as pressures 
lower over the Southern Plains. Breezy conditions expected with 
the the lower Valley seeing the strongest wind with gusts near 30 
mph later this afternoon. Temperatures warm up significantly with 
the southerly flow and with mid level RH's lower this drier air 
should help mix out the surface moisture for some sun to warm much
of the Lower and Mid Valley back into the lower 80s. 

Tonight Low level jet strengthens as upper trough moves into the 4 
corners area and surface low deepens over the southern plains. Low 
clouds and a constant breeze to keep temperature well above normal. 
Not expecting fog tonight due to the higher winds lingering. Higher 
dew point air along the cooler shelf waters and the Laguna Madre may 
allow for the sea fog to reform. 

Saturday Low level jet remains strong over the eastern half of the 
CWA in the morning with model averages near 40 knots in the 850-
925mph layer. Model guidance continues to show winds approaching 
wind advisory criteria through the first half of the afternoon 
before the jet lifts to the northeast and offshore. Confidence in a 
slam dunk advisory is lower with the last few model guidance runs 
trending slightly lower with overall wind speeds but none the less 
windy conditions are expected in the Lower Vally with breezy 
conditons in the Mid Valley.  Low pressure trough moves into the 
western counties with a weak downslope component developing in the 
afternoon. The downsloping and sufficient mixing in the east should 
push temperatures up into the upper 80s to lower 90s Saturday 

LONG TERM (Saturday Night through Thursday): The long term period
will begin with a frontal boundary located over the CWFA. This
should provide support for some showers/storms. Similar to the 
frontal passage this week, this front looks to be parallel to the 
mid level southwesterly flow, however, if convection does fire, 
mesoscale features (i.e. cold pool) would likely be the driving 
force behind a complete passage. Regardless, held temperatures 
down with rainfall and overcast skies anticipated.

Monday looks continued cool and damp as the front, just south of 
the mouth of the Rio Grande River (assuming it is able to slide
completely through) will generate enough isentropic lift to keep 
a solid deck of low stratus over the RGV, though there may be a 
few breaks across the northern Ranchlands. The frontal boundary 
will lift northward fairly quickly Monday night allowing for the 
surface flow to shift southerly once again. This will help 1) 
allow breaks in the clouds and 2) help temperatures boast back 
into the lower and middle 80s as WAA begins. Wednesday looks like
another very breezy day across the RGV. Additionally, it looks 
fairly warm too, especially for this time of year with upper 80s 
to near 90 degrees expected inland close to the river. 

Our next front will be due into the region on Thursday. Globals
are in agreement that the front will again push through the region
once again allowing temperatures to cool going into late next
week. Overall, the synoptic flow doesn't really change much with
active southwesterly flow aloft being the dominant feature.  

MARINE (Today through Saturday): Web cameras not showing to much 
dense fog this morning but patches are still expected with the warm 
front offshore. Some mixing of the boundary layer should result in 
thiner areas of fog through the day with the potential of thicker fog 
reforming tonight and Saturday morning. Pressure gradient 
strengthens the next 24-36 hours with southerly flow increasing with 
a moderate wind and seas regime today. Stronger winds develop 
Saturday with Small craft advisory conditions anticipated over the 
Laguna Madre and marginal SCA wind and seas over the Gulf waters.

(Saturday night through Thursday): Marine conditions will begin to
improve from earlier adverse conditions on Saturday. A cold front
will begin to stall across the Saturday night which should allow
winds to subside a bit. Sunday through Monday looks somewhat quiet
with winds residing somewhere between 10-15kts. Wave heights will
remain somewhat elevated with moderate northerly flow, however, 
should remain below SCA criteria. On Wednesday another cold front 
rolls toward the region. This time SCA thresholds look to be met 
with winds approaching 20 kts (especially over the Laguna) and 
wave heights approach 7 ft plus. Winds should begin to lighten by 
Thursday as high pressure moves southward into eastern TX. 


GM...Dense Fog Advisory until 11 AM CST this morning for GMZ130-132-



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