128 
FXUS64 KBRO 232327 AAA
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
627 PM CDT Fri Apr 23 2021

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

&&

.AVIATION...Mixed VFR and MVFR ceilings will continue for the next
few hours before lowering again into IFR and eventually LIFR
levels overnight. A cold front will move through the area early
Saturday morning, which may help to kick up a few showers as it
passes through. Short-term guidance continues to indicate fairly
sparse coverage at best, so will keep any mention of showers in
PROB30 groups given the lower confidence. Southeasterly winds 
will weaken in advance of the front which should allow for some 
fog to develop, dropping visibility to MVFR levels. Fog will 
quickly dissipate and ceilings will gradually rise after the front
rolls through and northwesterly winds usher in drier air.

&&

.PREV DISCUSSION... /issued 249 PM CDT Fri Apr 23 2021/ 

SHORT TERM (Now through Saturday Night):Models have backed off on 
the low probability of strong to severe convection overnight with a 
stronger cap/inversion developing over the CWA and much of the 
energy with the 500mb trough being concentrated with the synoptic 
features over Oklahoma and East Texas. Hi-Res and deterministic 
models having a tough time developing convection the rest of today 
and tonight likely due to the strengthening cap and diurnal 
nocturnal minimum reducing the instability somewhat. There remains 
decent elevated CAPE and some shear to support any updrafts within 
any isolated thunderstorms that develop which can produce gusty 
winds and hail. Probability of rain has dipped below 15 percent and 
some models are even below 10 percent. Will continue 20 percent 
after midnight to cover the isolated chances along the boundary.
Otherwise, cloudy skies and humid conditions with temperatures 
remaining in the 70s and winds diminishing. Light patchy fog is 
possible prior to the arrival of the weak front.  

Main challenge turns to the dry airmass shown by the models to 
overspread the CWA Saturday. Rapid drying of the airmass from the 
dew points in the 70s today to 30s and 40s tomorrow. The dry airmass 
and downsloping weak northwesterly winds allow for full sunshine and 
temperatures to heating up rapidly which will allow for relative 
humidity to crash through the afternoon. Hot and dry but a general 
light wind with occasional moderate gusts to 20 mph can be expected. 
These conditions raise a fire weather concern, which is detailed in 
the fire weather discussion below. Surface high pressure moves 
quickly to the east by sunset Saturday with winds already returning 
from east for the evening cutting off the dry air intrusion. A 
cooler evening is in store with lows nearing or dipping just below 
the late April normal of mid to upper 60s. 

LONG TERM (Sunday through Friday): 500 mb ridging will continue to 
build over Texas Monday into Tuesday. This will maintain very warm 
to hot and stable conditions across deep south Texas through at 
least the first half of next week. Another large 500 mb trough will 
dig over the West Coast and into the Rockies early next week then 
swings eastward over the Plains around midweek. The ECMWF and GFS 
are in fairly good agreement with the 500 mb pattern through 
midweek. Models begin to differ towards the end of the period with 
the speed and strength of the West Coast trough. The GFS still 
remains faster and stronger with this feature, while the ECMWF is 
slower and weaker. A slight chance of convection returns around 
midweek as moisture increases and pools ahead of the approaching 
front. The weak cold front is expected to arrive Wednesday into 
Thursday morning. Above normal temperatures will prevail through 
midweek and then temperatures fall to near to below normal Thursday 
into Friday.

MARINE (Now through Saturday Night: The pressure gradient continues 
to strengthen as surface low pressure moves into the Southern 
Plains. Winds over the Gulf are expected to reach SCA levels if not 
at 3 pm by sunset and remain elevated through at least midnight and 
possibly a few hours later before the weak front near the Coastal 
Bend slowly weakening the gradient.  The boundary works its way into 
the coastal waters Saturday morning with not much of a wind shifts 
with weak surface ridging remaining well north of the Gulf Coast. 
Light and variable to light north to northeast winds much of 
Saturday with winds turning quickly to the east by sunset and 
continuing light overnight. Seas remain churned up with the 
strengthening southerly flow much of the night before gradually 
diminishing Saturday. Not expecting much in the way of thunderstorms 
but one or two are possible with a few showers until the front 
passes to the east. 

Sunday through Wednesday: Favorable conditions are expected along 
the lower Texas coast for the remainder of the weekend as high 
pressure settles across the western Gulf. The pressure gradient will 
strengthen on Monday with moderate to strong winds and building 
seas. Small Craft Advisory conditions likely for both the Bay and 
Gulf Waters Tuesday into Wednesday. 

Fire Weather (Saturday): Very dry airmass overspreads the region
Saturday in wake of the frontal boundary. Mean sfc-7000mb RH dips
below 10 percent mid-afternoon west of I 69C. However, weak 
surface ridging and weak pressure gradient behind the front limits
northerly winds well below Red Flag conditions. There remains an 
elevated fire weather concern with extreme and rapid lowering of 
the relative humidity and the very warm temperatures expected in 
the afternoon. Forecast winds do not support a Fire Watch, but a 
Fire Danger Statement will likely be issued for tomorrow, due to 
the near explosive fuel state and well above normal temperatures 
expected. 

&&

.PRELIMINARY POINT TEMPS/POPS...
BAYVIEW/PORT ISABEL  84  72  89  66 /  20  20   0   0 
BROWNSVILLE          87  73  94  65 /  10  20   0   0 
HARLINGEN            90  72  97  63 /  20  20   0   0 
MCALLEN              92  72  98  65 /  10  20   0   0 
RIO GRANDE CITY      97  71  99  62 /  10  20   0   0 
SOUTH PADRE ISLAND   78  72  80  69 /  10  20   0   0 

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...High Rip Current Risk until 7 PM CDT this evening for TXZ256-257-
     351.

GM...Small Craft Advisory until 8 PM CDT this evening for GMZ130-132-
     135-150-155.

     Small Craft Advisory until 1 AM CDT Saturday for GMZ170-175.

&&

$$

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