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Area Forecast Discussion (AFD)

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

FXUS64 KBRO 201730 AAB

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
1230 PM CDT Sat Apr 20 2019

.DISCUSSION...Updated for latest aviation discussion below.


.AVIATION...VFR conditions prevail through the TAF period with
southeasterly winds picking up this afternoon across the RGV.
Gusts are expected to briefly diminish overnight before strong
southeasterly winds return late Sunday morning into Sunday 
afternoon. Some high clouds will begin to work in overnight and
become more numerous on Sunday. 


.PREV DISCUSSION... /issued 627 AM CDT Sat Apr 20 2019/ 

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...Dry atmosphere persist across South Texas with VFR 
continuing today and tonight with low confidence of a few lower 
clouds prior to sunrise Sunday. Southeast winds increase this 
afternoon with some gusts around 20 knots...lingering moderate 
winds tonight becoming breezy to windy, 20-25 knots Sunday.

PREV DISCUSSION... /issued 410 AM CDT Sat Apr 20 2019/ 

SHORT TERM (Today through Sunday): Mid level high pressure
overhead to provide another beautiful day for Deep South Texas. 
Despite surface winds returning from the southeast today, dry air 
over the Gulf will take at least another 12-24 hours to modify 
keeping our region rather comfortable. Morning low temperatures 
dipping well into the 50s with the dry atmosphere, rebound nicely 
with full sunshine pushing afternoon highs well into the 80s and 
lower 90s out west. Thermal gradient strengthens today with the 
warm inland temperatures combining with the relative cooler near 
shore Gulf waters providing breezy southeast winds. Strongest 
winds are anticipated over the coastal counties. 

A more substantial pressure gradient develops later tonight into 
Sunday as pressures lower across the Southern and Central Plains as 
the mid level ridge axis gets shunted east with the approach
of an up stream upper trough. Low level 925-850mb winds are 
strongest (35kts) on the GFS with guidance continuing to show 
surface winds approaching but not exceeding wind advisory (30+ mph
sustained) Sunday. Latest forecast also to keep winds just shy of
wind advisory at this time but any strengthening of the gradient 
could allow us to exceed the threshold. Otherwise, dew points 
steadily increase and will be at least 10 degrees higher tonight 
and Sunday which will make it feel more humid while overnight 
temperatures are expected to be 10-12 degrees warmer (mid 60 to 
near 70), Highs Sunday to remain near seasonal normals in the mid 
80s to lower 90s.

LONG TERM (Sunday Night through Friday): As we go into Sunday
night, a strong H5 trough will begin digging across the desert
southwest. At the surface, strong pressure gradient will remain,
keeping southerly surface winds gusty on the western periphery of 
the departing high across the northeast Gulf of Mexico. Very 
springlike for Deep South Texas, if you will as high pressure is 
dominant east and leeside troughing is dominant to our west. This 
gusty pattern continues through early next week. Moderate 
southerly flow will draw more low level moisture into the region 
leading to eventually a higher percentage of cloud cover. 

As we progress more into the upcoming week, the aforementioned H5
trough begins to shift eastward as it continues to dig south and 
west. This will provide a relatively active southwesterly flow 
aloft. Eventually, weak surface cyclogenesis is expected near SAT
or perhaps just south of this region on Wednesday. As low level 
moisture increases, instability could climb to the 2000 to 3000 
J/KG range late in the day Wednesday. This coupled with 0-6km bulk
shear values topping out at just under 50kt does suggest 
thunderstorm activity may be possible across the region for 
Wednesday night/early Thursday. There will be an EML present 
during the daylight hours across the region, however, as upper 
level height falls move across the area, expect this to help 
erode the cap slowly allowing again for the potential for a few 
thunderstorms. Not a fan of global CAPE forecasts at this range so
at the moment we'll acknowledge the chances for storms at this 
time and continue to monitor as mesoscale guidance begins to come 
into range for a clearer, less fuzzy picture. 

A cold front will drop southward clearing the area by Thursday
morning. With dry northwesterly flow taking shape as an upper 
level ridge builds across west Texas by early next weekend, expect
mostly tranquil weather Friday and into Saturday. As high 
pressure settles into the region expect winds to subside just a 
bit. Temperatures are expected to gradually well into the 80s for
most and perhaps reaching the 90s for some out west through the
week. Temperatures will remain around average or perhaps slightly
above even post frontal. 

MARINE (Today through Sunday): Winds return onshore today as 
high pressure moves to the east. The onshore flow strengthens 
locally with the strongest winds, but remain just below small
craft advisory, over the Laguna Madre this afternoon before the 
moderate flow develops across the Gulf waters tonight. Pressure 
gradient gradually strengthens Sunday as pressures lower over the 
Southern Plains. Small Craft advisories are likely on the Laguna 
Sunday with exercise caution conditions for the Gulf waters. 
Slight seas today remain low tonight with gradual building Sunday 
as winds increase. 

(Sunday Night through Friday): A tight pressure gradient between
high pressure across Florida and developing low pressure across
northern Mexico will cause surface winds to increase across the
region. Expect at the very least cautionary wording early next
week. Small Craft Advisories may be possible at some point early
next week, however, become increasingly likely from Tuesday
through early Thursday as a cold front passes through the region.
This long term marine cycle looks to end on a much better note as
high pressure builds into the region allowing for winds and seas
to return to more tranquil conditions by Friday. 




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