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Next 12 Hours

Forecast data from the National Digital Forecast Database.

5 Day Forecast

• Sunday
• 
• High: 88 °
• Low: 75 °
• Partly Cloudy

• Monday
• 
• High: 91 °
• Low: 75 °
• Mostly Cloudy

• Tuesday
• 
• High: 90 °
• Low: 75 °
• Partly Cloudy

• Wednesday
• 
• High: 91 °
• Low: 75 °
• Partly Cloudy

• Thursday
• 
• High: 90 °
• Low: 75 °
• Partly Cloudy

Area forecast discussion...updated 
National Weather Service Brownsville Texas 
610 PM CDT Sat may 18 2013 


Discussion...updated for latest aviation discussion below. 
&& 


Aviation...no changes were needed to the previous taf forecast 
package. Previous discussion: 


Generally a broken record forecast into Sunday afternoon. Slowly 
developing/moving upper level trough across the northern plains 
will enhance the semi-permanent pressure gradient between the Lee 
of the Sierra Madre and the western Gulf for one more day. That 
means gusty south/southeast winds from middle to late morning through 
early evening with sustained values ramping into the low-middle 20s 
and gusts at or above 30 knots for a few hours...followed by the 
nocturnal drop toward but not below 10 knots overnight. 


As for clouds...dry air within the inversion ensures rapid mix-out 
of the late night through early morning soup...which will flirt 
with the IFR/MVFR boundary at 1k feet between 06z and 13z. Once 
mixed...scattered to occasionally broken cirrus prevails though 
high level drying appears Sunday afternoon. 


Last but not least...smoke from the last of agricultural burning in 
Yucatan state will continue on a trajectory toward the valley and 
should lead to high MVFR visibility restrictions under the 
inversion overnight and early morning as haze/mist. Visibility 
should rise above thresholds near the ground...but haze aloft 
looks to be in the cards for Sunday which could restrict 
visibility a little in the mixing layer...3 to 5k feet or so...on 
approach. 
&& 


Previous discussion... /issued 157 PM CDT Sat may 18 2013/ 


Short term /now through Sunday night/...Summer swelter has arrived 
for this weekend as temperatures and humidity will be more like late 
June and early July than middle may. That said...the past several years 
have had stretches in may that were similar if not hotter...and the 
biggest difference between now and July is the general strength of 
the southerly flow which owes to deepening surface low pressure 
ahead of developing upper trough sliding across the central and 
northern plains. In addition to the winds...hazy skies and moderate 
to unhealthy air quality courtesy of the last of the agricultural 
burning in Yucatan don't typically come with late June/July heat. 


Subtle changes in the middle/upper flow into early Monday will do 
little to affect sensible weather...which will continue to feature 
sultry nights with low clouds quickly developing and becoming 
overcast by midnight or so...bookending a hazy hot and breezy day on 
Sunday. The subtle change...which involves a flattening 500 mb 
ridge and veering winds above 700 mb toward the northwest...should 
reduce the amount of cirrus on Sunday afternoon compared with this 
(saturday) afternoon. 


Otherwise...with low level thickness...1000-500 mb thickness...850 
temperature...etc. Pretty much status quo expect nearly the same 
surface temperature and humidity on Sunday as they were on Friday 
and today. This means highs in the 90s except just over 100 across 
the Zapata plains...lower 80s at the beaches...and feels like 
temperatures a little over 100 in all areas each afternoon. 
Nighttime temperatures will fall into the upper 70s toward the coast 
by middle evening and hold all night...with lower to middle 80s well 
inland by midnight falling into the 70s before daybreak. 


As for air quality...values for fine particulate 
matter...dust/haze/smoke et cetera...passed 100 this morning Middle Valley 
which puts Hidalgo/western Cameron/Starr in unhealthy for sensitive 
groups. Expect similar conditions on Sunday with nothing to change 
the type of air mass and the long fetch coming from the Yucatan. 
While the wind trajectory brings the particulates...the strength of 
the wind mixes them to a degree and should keep values from rising 
into more dangerous territory. For more...surf to 
http://tceq.Texas.Gov and click on "air". 


Long term /Monday through Saturday/...a large closed low/trough will 
be positioned from the Midwest to The Four Corners at the 
beginning of the long term. The trough will be slow in moving east 
with the trough axis not moving east of Texas until early Thursday. 
A hot and increasingly unstable atmosphere will set up over south 
Texas through midweek but moisture will be the limiting factor to 
provide any higher then the slight chance of thunderstorms that is 
already in the forecast anytime from Tuesday night through 
Wednesday night. Best chances still remain in the western half of 
the County Warning Area where model guidance continues to favor this area. As 
mentioned in previous discussion...initiation of convection is 
likely over central Texas where a quasi-stationary front is 
prognosticated to be located or over the Lee side of the Sierra Madre. 
West to northwest flow could allow for some convection to work its 
way into and possible through portions of deep south Texas. Models 
remain persistent on this scenario but guidance probability of precipitation remain rather 
low with moisture depth limited up to 800mb. Once this trough axis 
passes to the east and strong 500mb high builds back north from 
Mexico the threat for thunder and any chance of rain ends. The 
latter half of the forecast period remains dry. 


Temperatures start off hot with the warmest 850mb temperatures of 
the week running 23-25c. As the trough moves into Texas and 
heights and thickness lower temperatures drop off into the upper 
teens to around 20c by Thursday. Surface temperatures follow this trend 
with the maximum temperatures peaking Monday and lowering to normal by middle 
week. Overnight lows to remain rather warm and sultry with 
southeast winds not abating much at least into Wednesday. 


Marine...this afternoon through Sunday...status quo here as 
well...with the usual flip-flop of stronger winds across the Gulf 
and lighter winds across the Laguna Madre overnight becoming 
stronger across the Laguna Madre and somewhat lighter over the 
deeper Gulf where the marine layer should be able to overcome 
synoptic forcing provided by the low pressure trough...which never 
really strengthens owing to the steady state condition of the 
central/northern plains upper low. 


Thus...expect another round of Small Craft Advisory/winds for Laguna 
Madre waters on Sunday...with caution conditions at most during the 
day across the open Gulf waters. For tonight and Sunday 
night...expect surface winds to edge close to advisory levels but 
remain just below. Winds in the 850-925 layer sit in the 25-29 knot 
range tonight which...when combined with water temperatures at or a 
few degrees lower than ambient air should provide a rare nocturnal 
marine layer to keep sustained winds in the 16-18 knot range with a 
few gusts up to 20-23 knots or so. Sunday night could push across 
the 20 knot sustained threshold as low level winds increase a couple 
knots with the surface trough strengthening just a tad. For 
now...have worded as 'near 20 knots'. 


Seas have risen toward 5 feet this afternoon offshore and expect 
values to maintain or rise a little more overnight. Did not pop a 6 
foot forecast just yet but will need to monitor over the next couple 
of days. 


Monday through Thursday...the first half of the week to remain 
near scec levels or even periods of Small Craft Advisory 
especially across the Laguna. The gradient strengthens a bit 
Monday and Tuesday with a low pressure trough moving into Texas. 
The trough axis moves along the upper Gulf Coast Wednesday with 
some slackening of the gradient. The trough moves east Thursday 
and high pressure builds in for the weekend with winds and seas 
lowering slightly. 
&& 


Bro watches/warnings/advisories... 
Texas...none. 
GM...Small Craft Advisory for winds until 7 PM CDT this evening for 
gmz130-132-135. 
&& 


$$ 


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