Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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000
FXUS64 KHGX 240913
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
413 AM CDT TUE MAY 24 2016

.DISCUSSION...
Warm and humid conditions continue this morning with temperatures
in the low 70s and high clouds moving across SE Texas. Latest
surface analysis has weak low pressure in SW Kansas and SE
Colorado. Pressure gradient across SE Texas is not too tight but
still enough to support some light winds this morning. Winds are
stronger offshore in the Gulf of Mexico where 15 knot winds are
common. Water vapor imagery shows an upper level low off the coast
of the mid-Atlantic states. Upper level ridging stretched from SE
Texas towards the Great Lakes. Another upper level low was
organizing over California as a couple lobes of vorticity look to
merge. This system will be responsible for upcoming thunderstorm
chances on Friday.

Today and Wednesday the forecast is very similar to that of
yesterday. There may be a few isolated showers and thunderstorms.
The 00z CRP sounding did show a weak cap from the EML around
750-700mb. Models show upper level ridging building as 500mb
heights increase over the region through Wednesday. This ridging
will be in response to upstream troughing over the Desert SW.
Moisture levels gradually increase today into Wednesday so will
keep mention of an isolated storm in the forecast with 20 PoP.

Upper level low over the southern Rockies slowly moves into the
Plains Thursday into Friday. Timing of the upper low moving into
the Plains has become more consistent between the GFS/ECMWF with a
slow progression and negative tilt on Friday. This means there
will be large scale ascent to weaken capping from the EML. The
upper level jet becomes more favorable with one jet streak
becoming south/north oriented over the Plains placing E Texas in
the right entrance region. Meanwhile the southern branch of the
jet moves across Mexico into S Texas with SE Texas in the left
entrance region. Flow at 850mb increases to around 30 knots off
the Gulf of Mexico and even becomes a bit convergent. Precipitable
water values increase to 1.8 inches on Thursday and then over 2
inches on Friday which is more than previous forecasts. CAPE
should reach 2000-3000 J/Kg across the area combined with decent
low level shear of 10-20kts. Deep layer shear will be increasing
during the day to around 30-40kts. Shear parameters should support
organized convection. The overall pattern along with deep moisture
supports a heavy rainfall threat. Models are really hitting north
Texas hard with precipitation and then bringing higher QPF into SE
Texas late Friday. Most likely axis of heavy rainfall will
stretch from Columbus west of Houston NNE to the Arklatex region.
It is possible for most of the heavy rainfall to be north of
Houston but any mesoscale boundary that develops south of the main
convection could push into the Houston area. It would then be
possible for mesoscale processes to become dominate and given
strong inflow from the Gulf, heavy rainfall could shift farther
south into Houston. Again this is an alternate scenario dependent
on the mesoscale evolution that will be difficult to resolve. On
top of the heavy rainfall threat, severe weather may be possible
given the CAPE/shear combinations. Hail and downburst winds would
be the main hazards but there may be a small tornado threat if
there is enough low level shear.

For the weekend, thunderstorm chances will linger but lower
chances than Friday. While overall moisture decreases with
precipitable water values under 1.7 inches for the weekend, the
atmosphere may still be weakly capped that diurnally driven
convection could still develop. Thunderstorm activity may become
more widely scattered on Saturday with more isolated activity
expected Sunday/Monday.

Overpeck

&&

.MARINE...
Winds and seas will continue to slowly strengthen through the week
in response to a tightening gradient between lower pressures in the
lee of the Rockies and higher pressures off to our east. Caution
flags over the offshore waters may need to be expanded these next
few days, and advisories might be needed. Look for decreasing winds
and seas over the Memorial Day weekend. 42

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      88  74  88  74  84 /  20  10  20  10  50
Houston (IAH)              87  75  88  75  86 /  20  10  10  10  30
Galveston (GLS)            83  78  83  78  83 /  10  10  10  10  30

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...SMALL CRAFT SHOULD EXERCISE CAUTION 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...42


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