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Area Forecast Discussion (AFD)

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

                            
896 
FXUS64 KBRO 260551 AAB
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
1251 AM CDT Tue Mar 26 2019

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

&&

.AVIATION...Front progressing through south Texas right now, with
moisture starting to pool ahead of it. Lower cigs and vis are
focused close to the front, so have backed away from lowest TAF
conditions until front gets closer to airport locations. A few
showers are possible, but chances remains very low and focused
around midday.

&&

.PREV DISCUSSION... /issued 701 PM CDT Mon Mar 25 2019/ 

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...As a weak cold front approaches the area, winds will 
become light and dew point depressions will decrease overnight. 
This, combined with a stable layer, will be a good recipe for low 
clouds and patchy to area wide fog. The TAFs reflect lowering 
ceilings after midnight, with visibility also decreasing toward 
dawn. The NAM guidance is a little more aggressive, taking 
conditions down to IFR around dawn, with the GFS seeming to stay 
more in MVFR territory. Dramatic clearing is not expected as the 
front pushes through during the morning, with a wind shift to east
northeast in the lower Valley after daybreak and continued mostly
cloudy skies. The NAM guidance brings conditions back to MVFR to 
match the GFS mid to late morning as light to moderate east 
northeast winds become better established. The current 20 to 30 
percent chance of rain could support a few showers Tuesday 
morning as well.

PREV DISCUSSION... /issued 305 PM CDT Mon Mar 25 2019/ 

SHORT TERM (Now through Tuesday Night): Cloud cover associated 
with a pre-frontal trough/shear line has slowed warming a bit 
today, so earlier had nudged max/hour temps down a degree or two. 
Weak cold front currently draped across south-central TX (per WPC 
analysis) will sag through the CWA over the next 12-18 hours. NAM 
is actually a bit slower than the GFS in this case. Initial wind- 
shift to northerly appears to reach the northern zones between 09-
12Z early tomorrow morning with winds then quickly veering back 
to NE. Ahead of the front, low temp/dewpoint spreads along with 
light pre-frontal winds should lead to some patchy mist/fog from 
late tonight through mid-morning tomorrow when the NE winds pick 
up a bit and mix out the fog. Went with areas of fog wording for 
the coastal zones.

Front has doesn't have too much to work with in terms of upper-level 
support, with a dry WNW flow ahead of a ridge over the Desert SW 
already established.  Best column RH pools over the western CWA, 
along the Rio Grande, against the higher terrain.  Showers should be 
light.  Forecast charts and soundings show some instability with 
little CIN remaining around mid-afternoon tomorrow, but too much dry 
air aloft would seem to be entrained into any updrafts, so have 
removed any thunder mention.  Front will be slow-moving, so chance 
PoP's will drift southward through the day, possibly lingering over 
far western areas into the evening.

As far as temps go, lows tonight expected to be in the mid-60s 
pretty  much everywhere.  Airmass behind the front won't be much 
cooler, but cloud cover and NE flow off the Gulf should still yield 
temps 3-7 degrees or so cooler than today, most pronounced over the 
N. Ranchlands.

LONG TERM (Wednesday through Monday):The long term could end up 
being a tale of two seasons. The first half seeing a warming trend
with increasing southerly winds as mid level high pressure 
traverses the state. The second half may see a late season strong 
cold front with a shot of thunderstorms late Saturday/Sunday 
followed by a few days of below normal temperatures. 

Wednesday looks to be a transition day in wake of Tuesday's cold 
front as winds turn southeast with surface high pressure tracking 
east. Temperatures rebound a few degrees approaching normal, maybe 
more if the clouds decrease and the sun makes a longer appearance. 
Thursday and Friday heights falls across the west with the departing 
mid-level ridge and approaching Pacific trough will allow for 
southerly flow to increase with the pressure gradient peaking 
Friday. The stronger south winds will push temperatures and dew 
points up with both the GFS/ECMWF guidance in tandem. 

As for the next front models continue to show similarities in the 
surface features but differ in the placement of the mid/upper level 
trough. Even though confidence is increasing timing and strength of 
the front is still uncertain this far out. The front could move 
through as early as Saturday afternoon or passing through the lower 
Valley Sunday morning. Look for the potential for a line of 
thunderstorms along the front with much cooler temperatures as a 
1035+mb high moves into Oklahoma. Latest EC guidance is much cooler 
showing only a high of 59 degrees for Brownsville (GFS only 71) next 
Sunday wont go that cool just yet but a model blend of deterministic 
and ensemble lowers temperatures 10-14 degrees below normal next 
Sunday. Both the GFS/EC show some energy lingering west of the 
region after the frontal boundary so affects of the front, cooler and 
wetter, may linger into early next week. This may be no April
Fools front. 

MARINE:(Now through Tuesday Night):  Light winds and low-to-
moderate seas will prevail tonight ahead of a modest cold front. 
This front is expected to move through the Lower Texas coastal 
waters early Tuesday morning, with northeast breezes briefly 
becoming fresh before settling back to moderate. Seas build to 
moderate levels Tuesday afternoon.  Locally dense sea fog may be a 
concern tonight, especially over the relatively cooler nearshore 
waters (still at 66-67F).  Fog should break up once the 
aforementioned NE breezes kick in Tuesday morning.

Wednesday through Friday: Moderate onshore flow Wednesday 
strengthens Thursday and Friday as Gulf high pressure interacts with 
low pressure deepening over West Texas. The gradient may peak 
Friday, could remain strong into Saturday, with small craft 
advisories looking more likely for the Laguna Madre with the 
stronger winds shifting east Friday night. Next cold front surge may 
be as early as late Saturday afternoon or Sunday morning. 

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...None.
GM...None.
&&

$$

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