Preview of NWS' New Version of Forecast
This preview is not operational and should not be used for support decisions.

Area Forecast Discussion (AFD)

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

                            
000
FXUS64 KBRO 151632 AAB
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
1132 AM CDT Mon Oct 15 2018

.DISCUSSION...Updated winds and temps through 03Z this evening, as
momentum of the cold air appears to be carrying the front through
even a little faster than expected (roughly two hours). Trends
were in good shape; just freshened/sped up with a blend of latest
mesoscale guidance (NAM12/HRRR/HiResARW). Temps have already
fallen into the upper 50s in Zapata, Hebbronville, and at Falcon
Lake. Visible imagery shows the front's leading edge moving into
Hidalgo County at this time; should hit the McAllen metro within
the hour and probably clear the coast by 3-4 PM. Will leave PoP's
alone for now, but may able to trim back some over the NW counties
with afternoon package. Text products updated and sent.

&&

.PREV DISCUSSION... /issued 615 AM CDT Mon Oct 15 2018/ 

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...A cold front will be surging through the Rio Grande
Valley during the afternoon hours. Convection is expected to
develop in advance of the front and persist in wake of the frontal
passage. Flight conditions to deteriorate with VFR rapidly falling
to MVFR and eventually IFR conditions develop a few hours if not
immediate behind the front. IFR, mainly low ceilings, are expected
to persist much of the overnight period with low end MVFR 
possible at KMFE by Tuesday morning. 

PREV DISCUSSION... /issued 407 AM CDT Mon Oct 15 2018/ 

SHORT TERM (Today through Tuesday): As of writing this 
discussion, the highly advertised strong Canadian cold front is 
currently pushing south of the I10 corridor in central Texas. In 
the Austin area, temperatures have dropped around 20 degrees or in
the last couple of hours. The front will continue to surge into 
our CWFA first arriving in Zapata County by mid to late morning 
and then the Valley between 18z and 21z. 

There will be a window where the lower valley will warm
significantly prior to the front. Short term/mesoscale guidance, 
which is used in this package for the frontal passage shows much 
of the lower valley reaching the 90 degree mark just prior to the 
FROPA. 

As the front moves through, rain chances begin to increase. Out 
ahead of the front at least moderate instability will be present.
Can't rule out a strong storm or two with gusty winds and perhaps 
even small hail, however, think the primary concern will be heavy 
rainfall. Locations that experience multiple rounds of heavier 
convective rainfall, or poor drainage areas may experience minor 
flooding.

As the front pushes through a coastal trough will develop. With 
isentropic upglide, think stratiform rain will continue through the 
rest of the short term. Overcast and rainy conditions will keep 
temperatures well below average. In fact, on Tuesday much of the 
region will remain in the 50s and in many cases lower to mid 50s. A 
far cry from our average MaxTs for this time of year (roughly 30 
degrees cooler than average). 

LONG TERM (Tuesday Night through Sunday): Models continue in 
good agreement with the longwave pattern setting up over the 
CONUS. A mean trough over the Midwest and upper low over the 
Desert southwest with ridges over the Pacific northwest and the 
another extending east to west across the Gulf of Mexico. At the 
surface a cold front will be extending across the Gulf with a 
surface trough anticipated to maintain a presence along or just 
off the Texas coast through much of the long term. 

Warm air overriding the cool surface air and disturbances within
the deep southwest flow aloft will keep rain chances rather high
through next weekend. Light stratiform rain is expected Tuesday 
into early Wednesday as the surface front and trough will be 
somewhat removed from the coast. The front and trough begin to 
retreat westward later Wednesday and Thursday with a surge of 
tropical moisture and a stronger disturbance move north along the 
coast. Models continue to advertise an increase in rain chances 
with heavy rain still in the offering Wednesday night and 
Thursday. Deepening on how much rain develops Today with the 
initial frontal passage, might determine if a Flash Flood Watch 
may be necessary for portions of Deep South Texas/RGV Wed 
night/Thursday. Highest QPF values remain along and east of the 
coast but just a slight shift to the west may bring the heaviest 
rain inland. The continued presence of the coastal trough and
another surge of high pressure (front) next week will maintain the
chance of rain. 

Temperatures to start off rather cool and will be running 10-15
degrees below normal the beginning of the long term Tuesday
night/Wednesday. The cool airmass slowly modifies Wed night-Friday 
and next weekend as the coastal trough/front advances closer to 
the coast edging warmer Gulf air closer to the region. With the 
front and trough to remain over the Gulf and a deep overcast and 
the high rain chances will show a slower warming trend keeping 
temperatures closer to the cooler GFS. Another shot of cooler high
pressure is possible next Sunday or Monday but uncertainty among
the models continues so a blend of the guidance is maintained this
package. 

MARINE:(Today through Tuesday): Moderate winds and seas to start 
the short term marine period. This will quickly change later this 
afternoon and evening as a strong Canadian cold front pushes into 
the adjacent waters of Deep South Texas. Winds and seas increase 
into SCA thresholds this afternoon. At this time, cannot rule out a 
few wind gusts up to gale force. Winds and seas are expected to 
remain elevated through the remainder of the short term as a coastal 
trough develops. This should keep winds and seas at SCA thresholds 
perhaps even beyond the scope of this forecast.

Tuesday night through Friday...Very unsettled rough marine
conditions are much of the period. The most unsettled periods
Tuesday night through Thursday morning with a tight pressure
gradient residing along the Lower Coast with high pressure over
Texas and the cold front south of the coastal waters. A coastal
trough and front moves northwest into the coastal water later
Thursday with a gradient weakening but residual rough seas are
likely to continue. The gradient remains weak with the
trough/front continuing over or near the coastal waters. Seas may
have a short window to subside. Overall, Small Craft advisories
are likely to persist through the period for at least the offshore
waters. Widespread rain with embedded showers and thunderstorms at
times and occasional bouts of fog will result in additional poor
marine weather. 

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...None.
GM...Small Craft Advisory until 7 AM CDT Wednesday for GMZ130-132-135-
     150-155-170-175.

&&

$$

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

53-Schroeder/52