Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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FXUS64 KHGX 251522
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1022 AM CDT Sat Mar 25 2017

.UPDATE...
A cold front has cleared the vast majority of Southeast Texas, but
stretches from Trinity Bay through League City, Angleton, and Bay
City, towards Palacios. Behind it, skies have cleared quickly and
the forecast is largely on track. Ahead of it, warm, moist air
remains with scattered to broken skies. Showers and storms are
beginning to redevelop, particularly over Galveston and Chambers
counties. Indeed, with these storms and the suddenly slow movement
of the front, an urban and small stream flood advisory was needed
due to slow moving storms around I-10 in northeast Chambers
County. Mesoanalysis shows 1000-2000 j/kg of MLCAPE ahead of the
front, so there is potential for thunderstorms until the front can
move offshore around noon.

Though moving slowly, the front is moving, and still expect it to
clear the coast before fully stalling. But thanks to the warm
start this morning, did bump up high temps 2-5 degrees from
Houston coastward. Also, of course had to raise POPs to account
for the current storms, and potential for more showers and storms
along the front in the next few hours. From there, largely blended
back into the previous forecast, as things should more or less go
to plan once the entire area is in a post-frontal airmass.

Luchs

&&

.PREV DISCUSSION... /ISSUED 619 AM CDT Sat Mar 25 2017/

AVIATION...
Cold front was moving into the Houston metro area at 11Z. Expect
that the line of showers and isolated thunderstorms will move past
IAH and HOU by 13Z, KLBX by 14Z, and KGLS between 14Z and 15Z. The
front may slow down as it reaches the coast or continue its
current speed; however, the latest NAM12 slows the front down
right along the coastline before returning it back inland.
Actually like the latest HRRR and catered the terminals close to
its output. Am expecting VFR conditions by late morning.

There is an outside chance that MVFR to IFR conditions could
develop away from the coast late tonight. Guidance may be a bit
overdone and went closer to the raw model output.

40

PREV DISCUSSION... /ISSUED 407 AM CDT Sat Mar 25 2017/

DISCUSSION...
SE TX is getting a brief respite after an active night of storms.
A weak cold front that extends from near paris to Waco to Ozona
will continue to push east and should move into SE TX prior to
sunrise. The front is expected to trigger additional showers and
thunderstorms...with the precip becoming more numerous as the
front nears the coast. Short term guidance is very bullish with
high rain chances this morning. Will be watching trends closely
and if short term guidance is correct, the radar should begin to
start lighting up around 4 AM. Conds should dry out quickly as
drier air moves into SE TX. PW values are progged to fall to 0.60
inches by afternoon. Clear skies are expected tonight with some
light ground fog possible in rural areas toward sunrise.

On Sunday a weak area of low pressure will develop over North
Texas and this feature will drag a weak cold front across the
state late Sunday night into Monday. The front should stall before
reaching SE TX. A strong upper level disturbance will move across
the southern plains Sunday night and this feature might be close
enough to generate a few showers and thunderstorms over mainly
the northern half of SE TX. Fcst soundings show a capping
inversion near 850 mb and very dry air above 850 mb. Fcst
soundings show a weak capping inversion in place through Tuesday
with moisture profiles looking rather meager. A slight warming at
850 mb supports slightly warmer sfc temps both Monday/Tuesday.

Another potent upper level low will approach Texas on Wednesday.
This feature is trending much further north than yesterdays model
runs. Global models are in good agreement that the low will track
northeast across the southern plains. Jet dynamics still look
impressive with this feature and SE TX will lie in a splitting jet
structure. PW values now only increase to around 1.55 inches (was
1.80 inches yesterday). There should still be enough lift to
generate shra/tsra on Wednesday but the threat for severe wx/heavy
rainfall has diminished somewhat. SPC has shifted their outlook
for Wednesday further north. A weak disturbance rotating around
the broad upper low may bring some showers/storms to the area Wed
night and Thursday before conditions dry out on Friday. Low
pressure will develop over West Texas on Friday and approach the
region on Saturday. The low will drag a cold front across the
region and bring another chance of shra/tsra. 43

MARINE...
The moderate to strong onshore winds are expected to diminish this
morning as the surface pressure gradient diminishes ahead of a weak
cold front. Another round of showers will be possible later this
morning ahead of the front. Westerly winds may briefly develop
later today over the Gulf waters and bays; however, onshore winds
are expected to return by Sunday.

Another system moving across the plains will help strengthen the
onshore winds Sunday night. Another system will help develop
moderate to strong onshore winds again Tuesday night, Wednesday, and
Wednesday night. Although caution conditions are expected Sunday
night, advisory conditions will be possible beginning on Wednesday.

40

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      78  57  85  66  84 /  10  10  10  20  10
Houston (IAH)              82  61  85  68  86 /  20  10  10  10  10
Galveston (GLS)            80  69  82  71  81 /  50  10  10  10  10

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...SMALL CRAFT SHOULD EXERCISE CAUTION until 1 PM CDT this
     afternoon for the following zones: Coastal waters from
     Freeport to the Matagorda Ship Channel out 20 NM...Coastal
     waters from High Island to Freeport out 20 NM.

     Small Craft Advisory until noon CDT today for the following
     zones: Waters from Freeport to the Matagorda Ship Channel
     from 20 to 60 NM...Waters from High Island to Freeport from
     20 to 60 NM.

     SMALL CRAFT SHOULD EXERCISE CAUTION until 4 PM CDT this
     afternoon for the following zones: Waters from Freeport to
     the Matagorda Ship Channel from 20 to 60 NM...Waters from
     High Island to Freeport from 20 to 60 NM.

&&

$$

Discussion...25



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