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Area Forecast Discussion (AFD)

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

FXUS64 KBRO 162309

Area Forecast Discussion
National Weather Service Brownsville TX
509 PM CST Wed Jan 16 2019

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


.AVIATION...Strong low-level moisture on the periphery of a
coastal low will continue to stream overhead tonight with weaker 
northerly surface winds. This will maintain overcast low ceilings 
overnight with areas of fog also possible. Flight conditions are
expected to drop to IFR and eventually LIFR after midnight. Models
do indicate conditions may improve towards the end of the
period Thursday afternoon, though it will be gradual as drier air
moves into the region.


.PREV DISCUSSION... /issued 255 PM CST Wed Jan 16 2019/ 

SHORT TERM (Now through Thursday Night): The 500 mb short wave 
moving over the TX coastline today will shift eastwards later 
tonight and Thurs. This will allow the surface coastline troffing 
near the lower TX coast to weaken or move out away from the region. 
Meanwhile drier air will start to move into the region from the west 
tomorrow. This will tend to lower down the pops for the region 
throughout the short term period. However, will still mention some 
slgt chcs pops mainly near the coastline and offshore throughout 
tonight and tomorrow as 500 mb PVA may linger over the region long 
enough to spark some patchy light rain. Despite drier air aloft 
working into the region gradually from the west, the low low winds 
will be shifting around from a more southerly direction throughout 
tomorrow and tomorrow night. This will maintain enough residual low 
level moisture to maintain the potential for fairly abundant cld 
cover. Also the rebounding low level moisture will combine with the 
generally light surface winds tonight and tomorrow night to allow 
for areas of late night and early morning fog to form up. Areas of 
dense fog will be possible. However will not post up a Dense Fog 
Advisory at this time as will like to see how the vsbys respond 
throughout the evening hours. 

The returning southerly low level flow will warm temps up back above 
climo for mid January. 

The short term temp guidance is in generally good agreement for 
highs and lows through Thurs Night. The NAM is the coolest for highs 
tomorrow with the GFS and ECMWF coming in much warmer. Believe that 
the NAM is underestimating the expected warmup tomorrow. So will 
lean closer to the warmer GFS/ECMWF numbers. 

LONG TERM (Friday through Wednesday): Unsettled weather expands 
across the CONUS on Friday as the next big winter system begins to
take shape in the Plains. Increasing southerly flow at the 
surface and southwesterly flow in mid levels will help 
temperatures peak well above normal Friday afternoon across Deep 
South Texas. Increasing moisture, combined with a weak coastal 
trough developing at the surface and small bouts of passing mid 
level instability, could help develop isolated to widely scattered
showers on Friday. Model soundings are beginning to show somewhat
favorable convective parameters by Friday evening along with a 
persistent cap, likely limiting development. Most of any rainfall 
will occur north of the ranchlands. 

As low pressure strengthens across the southern Plains and heads 
toward the Ohio River Valley, a strong cold front will work 
through the CWA Saturday morning. This may be enough to kick up a 
few thunderstorms or elevated convection ahead and along the 
front, mainly toward the northern ranchlands and eastern or 
coastal zones. High pressure dropping south out of central Canada,
combined with the growing winter storm into the east, will open 
the door for cold arctic air to filter through the Plains and into
Texas behind the front. How much cold air makes it to the 
southern tip of the state remains somewhat debatable at this time.

Reinforcing cold air with strong northerly winds drop temperatures 
through the day Saturday and into the 30s and 40s by Sunday 
morning. With dry air and strong winds, fire weather concerns 
become somewhat elevated Saturday and likely on Sunday before 
winds taper off. Pelican landings on coastal roadways and bridges 
are possible Saturday into Sunday. Wind Advisory and Wind Chill 
Advisories may just be out of reach Saturday through Saturday 
night, but conditions should continue to be monitored for each. 

As the arctic high pressure ridge settles southeast, the avenue of
cooler air to Deep South Texas begins to close and temperatures
should begin to level off or improve by Monday. Model guidance has
varied greatly on Monday mornings temperatures, with lows
trending warmer on each new model run lately. Early next week sees
an overall rebound of temperatures before the next front, more
pacific influenced, arrives on Wednesday. 

Marine (Now through Thursday Night): Broad surface ridging over the 
southeastern States and the Gulf of Mexico will maintain a fairly 
light PGF over the region. The surface flow will remain pretty weak 
across both the Bay and Gulf waters throughout tomorrow night. This 
will maintain generally low seas and fairly calm Bay conditions. No 
SCA conditions expected through Thurs Night. 

Friday through Wednesday: Light to moderate seas begin to build
Friday into Saturday as southerly winds increase and low pressure
builds across the Plains. A cold front on Saturday brings stronger
northerly winds across coastal waters by Saturday afternoon,
further agitating marine conditions through Sunday evening. Gale
force wind gusts are possible Saturday afternoon through Sunday
morning. Conditions improve slightly on Monday before
deteriorating once again Tuesday and Wednesday with the approach
of another cold front. 




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