Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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000
FXUS64 KHGX 230912
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
412 AM CDT MON MAY 23 2016

.DISCUSSION...
Saturday deep moisture returned to SE Texas more quickly than
forecasted with no capping resulting in widespread thunderstorm
activity producing hail and heavy rainfall. Sunday thunderstorm
activity formed ahead and along a stationary frontal boundary and
this activity was expected to develop inland as it pushed SW.
Instead the frontal boundary had a stronger push to it which
shifted the convection into the Gulf and effectively limited any
convection as moisture decreased across the area. This has made
forecasting quite a challenge since none of the short range models
have done a good job with moisture evolution. If the models have
resolved these features, it has been too late in the forecast
cycle to make much of difference. Hopefully today more diligent
analysis helps make a better short range forecast.

.Short Term...Today/Tomorrow.
Latest water vapor imagery and 00z upper air analysis showed a
somewhat omega block pattern with an upper low over the mid-
Atlantic and another broad upper low over the Rockies. A ridge was
sandwiched in between from the western Great Lakes to the
Arklatex. The southern branch of the jet was still active across
Mexico into Texas. At the surface, surface dewpoints were in the
upper 60s to low 70s which is about 5 degrees lower than the last
couple of mornings. Higher moisture was noted across S Texas with
dewpoints in the mid/upper 70s. Based on available short range
guidance, this moisture should be increasing through central Texas
with some of that moisture increasing over SE Texas mainly west of
I-45. Based on NAM/GFS soundings, convective temperatures should
be in the mid/upper 80s. Max temperatures today should be very
close to those numbers. Forecast will go with 20 PoPs for the area
but would not be surprised if there was more activity in the
moisture axis region which would require 30-40 PoPs. The forecast
highly depends upon moisture evolution, amount of subsidence from
ridging aloft and divergence from 300mb jet streak. The divergence
from the jet may be enough to offset any subsidence which could
allow for deep convection. Instability will be pushing 2000-3000
J/Kg of CAPE and model soundings show little if any capping. Deep
layer shear will be close to 30 knots so if storms form there
could see pulse/multicellular convection which could support a
downburst/hail threat close to severe levels. Brief heavy rainfall
will be an issue again if storms develop. There does not seem to
be much change in the atmosphere for Tuesday so will keep a
similar forecast. If anything, capping may be stronger than on
Monday. Subsidence from upper level ridging may also be stronger
with less divergence from the jet.

.Long Term...Wednesday through end of week.
Upper level ridging continues to build on Wednesday as an upper
level low develops over the Pacific coast and Desert SW. Ridging
should begin to break down Wednesday night into Thursday as the
upper level trough moves across the southern Rockies. This system
will lift into the Plains Thursday/Friday with a negative trough
axis over Texas. GFS/ECMWF/Canadian all show the potential for
heavy rainfall from north of Houston through Northeast Texas.
Forecast will keep 60-70 PoPs given the consistency and the
potential for heavy rainfall and severe weather. Precipitable
water values increase to 1.8 to 2.0 inches Friday with 30kt winds
at 850mb. There will certainly be enough large scale ascent over
the region with no capping that widespread thunderstorm activity
will be possible. CAPE could reach 2500 J/Kg with 35-40kts of deep
layer shear which would support a threat of severe weather. Again
the greatest threat will be Houston northward with lower
thunderstorm chances along the coast.

Thunderstorm chances decrease over the weekend as the trough lifts
in the the Midwest and heights begin to rise over the area.
Saturday into Sunday moisture should be decreasing with
precipitable water values dropping closer to 1.5 inches. Wind
profiles will be weaker but still could be enough instability for
storms to develop. Capping is not expected to build over the area
but large scale lift will be weaker and likely only boundaries for
storms to form along will be the sea breeze. The forecast will
keep 20 to 30 PoPs and any thunderstorm activity will be rather
isolated in coverage.

Overpeck

&&

.MARINE...
Look for gradually increasing southeast winds along with building
seas this week in response to a tightening pressure gradient between
lower pressures in the lee of the Rockies and higher pressures off
to our east. Caution flags are anticipated, and advisories might be
needed.
42

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      87  72  88  74  88 /  20  10  20  10  10
Houston (IAH)              86  73  87  76  88 /  20  10  20  10  10
Galveston (GLS)            82  76  83  78  83 /  20  10  10  10  10

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...NONE.
&&

$$

Discussion...39
Aviation/Marine...42


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