Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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FXUS64 KHGX 261019
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
419 AM CST Sun Feb 26 2017

.DISCUSSION...
High pressure has moved over the Mid-South this morning allowing
for SE winds to develop off the coast. Winds have decoupled over
much of the area allowing for temperatures to drop into the 40s.

Upper level pattern maintains a broad trough mainly over the
eastern half of the country with a ridge out over the Pacific.
There are several fast moving short wave troughs moving through
the mean flow across the country. One shortwave was about to push
inland over California with a stronger system on its heals over
the Pacific NW.

This first shortwave trough will help initiate convection mainly
west and north of Houston this afternoon and tonight. Showers
should develop from Victoria to College Station. The axis of
shower activity shifts to the NE towards the Arklatex overnight. A
few strong/severe storms will be possible per SPC day 1 outlook
of a marginal risk. Marginal risk does include areas from College
Station to Crockett. HRRR/WRF hi res models show stronger
convection forming mainly from Austin towards Tyler and Texarkana
north of the forecast area. Farther south there may be some
isolated showers but any threat of strong storms will be north of
the area tonight into Monday morning. The forecast will keep
higher precipitation chances from Madisonville to Crockett.

Monday into Tuesday there are several parameters that suggest
scattered showers and thunderstorms for much of SE Texas, but that
potential largely depends upon any forcing and capping from the
elevated mixed layer. At first glance, there is respectable
instability around 1000-2000 J/kg, strong deep layer shear with a
strong 90kt jet aloft on Monday, and moisture with precipitable
water of 1.4 inches. This kind of environment carries over into
Tuesday but there are a couple of factors that will likely limit
thunderstorm chances.

First there is strong flow at 850mb from the SW with temperatures
increasing from 12C to 16C on Monday. This only increases the
capping over the area especially to the SW of Houston. Second
there are some slight height rises late Monday as the first
shortwave departs the area after passing by Sunday night into
Monday morning. Height rises continue into Tuesday in response to
the digging trough upstream over the southern Rockies. Flow at
850mb continues to increase from the SW and this will only
maintain temperatures of 16-18C. The forecast will maintain some
higher PoPs to the E and NE of the forecast area but for the most
part keep 20-30 percent for the area. Of particular notice is that
the convective allowing WRF ARW/NMM and Texas Tech WRF do not
break out much convection at all on Monday and think they are on
track given the environment.

Overall think the NAM/GFS/ECMWF/CMC are all on track with the next
cold front pushing through on Wednesday. All of them are pushing
the second short wave trough out of the Rockies into the Plains by
Wednesday morning. It then shifts into the Great Lakes by
Wednesday night with good NW flow aloft over the plains helping
drive the front south into the Gulf. The CMC looks a touch slower
than the other models and appears to be overdoing precipitation
along the front. Forecast follows the GFS/ECMWF timing more
closely and clears any precip out of the area Wed night. We are
going to have to keep an eye out for a few strong storms along the
front Wednesday morning. There is still some instability and lift
from the front may be enough to erode any capping. Deep layer
shear will still be strong enough for organized convection like a
squall line. The main issues limiting the severe threat will be
capping and the degree of instability available.

Behind the front high pressure remains in control through the end
of the week. Forecast gets interesting next weekend as both the
GFS/ECMWF bring a weak upper low over Mexico. The CMC even hints
at this but is faster than the GFS/ECMWF. As such a coastal low
forms in the NW Gulf which will trigger quite a bit of shower
activity along with a few thunderstorms that could produce heavy
rainfall. The good thing is that the models keep the heavy
rainfall off the coast. Regardless there will still be good rain
chances for next weekend so will keep 40/50 PoP on the day 7/8
forecast. There are some timing issues between the models so look
for further adjustments in when the best rain chances will occur.

Overpeck

.MARINE...
Onshore has still been somewhat indirect tonight remaining light and
more out of the east, but these winds will continue to veer towards
southeast by mid-day Sunday. As the winds veer, they should also
become stronger as high pressure exits to the east. Caution flags
are up for today, and onshore winds at least near that caution
threshold will continue for much of the first half of the week. With
this elevated onshore flow, expect some higher than normal tides as
well.

A cold front will pass through the area Wednesday night, with
strengthening offshore winds behind it. Confidence is increasing in
the need for a small craft advisory, with some gusts approaching
gale force as the colder air increases instability over the
relatively warmer water. Winds should veer back around to being
onshore by the weekend, though a weak, backdoor front or possibly
even a coastal low may back winds towards the northeast Sunday
night. Stay tuned, as there is still considerable uncertainty about
these scenarios at the range.

Luchs

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      70  63  81  66  83 /  40  40  30  10  30
Houston (IAH)              74  65  82  68  84 /  20  30  30  10  20
Galveston (GLS)            73  67  76  68  78 /  10  20  30  10  10

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...SMALL CRAFT SHOULD EXERCISE CAUTION from 9 AM CST this morning
     through this evening 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...39
Aviation/Marine...25



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