Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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FXUS64 KHGX 251745
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1245 PM CDT MON JUL 25 2016


.AVIATION...
SHRA developing rapidly in the moist axis (2.2-2.4" PW) from SHV-
LFK- GLS and these should deepen becoming scattered to numerous
thunderstorms in the coming hour or so. Winds should steer this
band west through the Metro hubs between 1730-2300z with
intermittent direct impacts (VISBY/VRB gusty winds) at the hubs
before storms depart to the west. Seabreeze storms should move
inland to the northwest impacting the LBX/SGR sites through 22z
then expect some clearing as line continues northwest but will be
fighting increasing capping/subsidence late this afternoon. The
area will remain very moist but slightly capped overnight so can`t
rule out isolated showers but thinking that most will hold off
until after 11z with rapid increase in coverage and intensity
after 14z TUE. 45

45

&&

.PREV DISCUSSION... /ISSUED /

UPDATE...
Only minor adjustments this morning, mainly to keep temperatures
and skies on track. A little unsure about PoPs for the next few
hours. Convection to this point is almost entirely over the water,
and while heating should erode any convective inhibition as we
head towards afternoon, that cloud deck covering much of the area
has me wondering if rain chances are a touch high before 18Z. If I
were to totally believe the consensus of short term models, I
should be very worried. But, since the expectation is still for
things to become more active around 18Z and uncertainty could well
allow for rain to develop a bit early, will leave things mainly
untouched beyond a slight adjustment to blend better with the
neighbors and removing the small region of "likely" precip. In the
end, the focus is still on the afternoon for the main show.

PREV DISCUSSION... /ISSUED 636 AM CDT MON JUL 25 2016/

AVIATION...
Moderate confidence in the forecast. The models were trending
toward a peak period of best thunderstorm chances to be generally
from 19Z to 23Z. The HRRR and RAP13 both show the showers along
the coast spreading inland between 15Z and 17Z. Think that the
coverage will diminish by 02Z this evening. Overnight tonight,
some of the models were indicating storms will regenerate south
and east of KIAH and KHOU. There is enough uncertainty to keep the
mention out of both sites for now.

40

PREV DISCUSSION... /ISSUED 355 AM CDT MON JUL 25 2016/

DISCUSSION...
At 3 am, weak low pressure was noted near El Paso with high
pressure over the eastern Gulf of Mexico. At 850 mb, a weak area
of low pressure was noted over Louisiana with a plume of deeper
moisture extending E-NE into the Ohio River valley. A weak high
pressure system was located over SE OK. A very weak 850 trough
axis extended east-west from about Galveston Bay into the west
central Gulf. At 500 mb, a weak upper low was located over LA with
a plume of deeper moisture over western LA with a stronger upper
low over the eastern Gulf. An upper level high was located over
the desert southwest and 500 heights have only fallen about 10
meters at FWD and SHV since yesterday. At 300 mb, the center of an
expansive upper ridge was located over west central Texas with
another lobe of high pressure over central AZ. The flow between
the weak low over LA and the ridge to the west will allow a strong
vort lobe to rotate into the area from the northeast later today.
PW values are progged to increase to between 2.20 and 2.40 inches
with convective temps between 88-92. It seems reasonable to expect
shra/tsra today with the best chance this aftn as the disturbance
approaches SE TX. PW values remain high tonight with the NAM12
particularly aggressive with PW values approaching 2.60 inches.
Will maintain chance PoPS all night but having trouble finding a
catalyst for precip. Storm motion will be between 5 and 10 knots
so some of the storms will have the potential to produce brief but
locally heavy rain this afternoon. Will maintain likely PoPs
today. High temps are tricky today. The day will start out warm
and conditions should heat up fast but depending on when clouds
begin to develop and the onset of precip will determine just how
warm it`ll get. Went just a shade above numerical guidance due to
the warm AM temps.

The upper low over the eastern Gulf will shift west and phase
with the upper low over LA by Tuesday 12z and become more of an
inverted trough. PW values remain AOA 2.25 inches. Convective
temps are between 87-91 degrees. A weak disturbance will again
rotate into the region during the afternoon so would expect an
increase in shra/tsra on Tuesday aftn as the upper level
disturbance and the inverted trough near the area. Have
maintained likely PoPs for Tuesday

On Wednesday, SE TX will lie on the east side of the inverted
trough axis and this is a favorable position for additional
shra/tsra. Another strong upper level disturbance will pivot into
the region from the northeast. PW values lower to between 1.95 and
2.15 inches but convective temps remain between 88-91 degrees.
Fcst soundings do show some capping try to redevelop around 500 mb
but at this time, the cap still looks weak and breakable. Will
maintain high end chance PoPs west and bumped PoPs to likely over
the east.

Thursday through the weekend looks like a return to more typical
summer conditions with daytime high temps warming into the
mid/upper 90s. PW values remain around 2.00 inches with some
drying noted over the weekend. Upper level ridging will be both
east and west of the area with a weakness centered over the
central/southern plains. This pattern should allow for diurnally
driven shra/tsra each day. 43

MARINE...
Weak surface ridging will keep a general light wind pattern in place
today. However, computer models were showing moderate southerly
winds will develop Tuesday and Wednesday. A deep layer of upper
level moisture is expected to bring better chances for showers and
thunderstorms today through Wednesday. Rain and thunderstorm chances
then lower over the second half of the week. Given the model
forecast sounding for GLS, still think isolated short-lived
waterspouts will be possible this morning and again on Tuesday
morning.

40

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      95  76  92  75  93 /  60  30  60  30  50
Houston (IAH)              93  77  91  77  92 /  70  40  60  30  60
Galveston (GLS)            90  79  88  81  89 /  60  50  70  30  60

&&

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

$$

Discussion...25
Aviation/Marine...45


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