Area Forecast Discussion
Issued by NWS Corpus Christi, TX

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FXUS64 KCRP 251851
AFDCRP

Area Forecast Discussion
National Weather Service Corpus Christi TX
151 PM CDT Wed Apr 25 2018

.DISCUSSION...

Starting to see some thunderstorms develop just across the boarder
begin to push into the Rio Grande Plains. Nothing is severe just
yet, but the expectation is for a few isolated severe wind gusts
or large hail to develop a little later this afternoon as the cold
front presses in from the north-northwest. The current activity
over our region seems to be tied to an advancing shortwave trough
aloft while back to our north it`s mostly surface cold front
driven, or working in tandem with the shortwave trough. It`s all
about location. South of the front, across the western Brush
Country and Rio Grande Plains, instability is increasing but of
concern is the more south flow in place, rather than southeast
flow which helps increase convergence across the higher terrain to
the west of Laredo. There could be a weak boundary, tied to
difference heating along the cloud edge over on the Mexican side
of the Rio Grande river, that may help to ignite more activity
later this afternoon. Again, there are many players on the field,
just a matter of getting them gel.

18Z aviation cycle below.

&&

.AVIATION...

Today...Mostly VFR. A few showers and thunderstorms develop across
the west, near KCOT, and moves east-southeast later this evening.
Have added TEMPO groups for terminals outside of KLRD for MVFR
showers later this evening as these showers and cold front pass
by. Confidence in lower restrictions is low at this time.

Tonight - Thursday...Mostly VFR. Cold front will be pushing
through later this evening/tonight bringing in some drier air and
allowing CIGS to rebound. Rain showers may take a couple hours
post-frontal to cease but they should remain on the lighter side.
North-northeast winds expected around 10-15 knots. Medium
confidence.

&&

PREVIOUS DISCUSSION... /Issued 638 AM CDT Wed Apr 25 2018/

DISCUSSION...

Updated for the 12Z Aviation Discussion.

Updated forecast for Dense Fog Advisory. Areas of dense fog have
spread this morning and are expected to remain in place until an
hour or so after sunrise.

AVIATION...

Very low VSBYs this morning impacting ALI-VCT. Should see
improvements over the next couple of hours. Some low level clouds
are developing farther west toward LRD, so may see periods of MVFR
CIGs at LRD in the next couple of hours as well. Otherwise, VFR
expected to develop by mid morning. Cold front still expected to
approach the region through the day, kicking off showers and
thunderstorms, especially toward LRD, this afternoon and evening.
Rain coverage is expected to spread farther east to the other TAF
sites this evening as the front pushes farther south. Greatest
chances for thunder remain toward LRD where instability remains
greatest. So for the eastern sites, have only VCSH in TAFs at this
time. Although am expecting predominant VFR, in and around any of
the heavier showers/storms, MVFR will be possible. Southeast
winds 10-15 KTs today will become N-NE behind the front.

PREVIOUS DISCUSSION... /Issued 456 AM CDT Wed Apr 25 2018/

SHORT TERM (Today through Thursday)...

Main concern today will focus with the progression of the surface
cold front and the marginal risk for severe thunderstorms with it.
Mid-level trough currently across the central Plains will move
southeast toward the Lower Mississippi Valley later tonight. This
shortwave will push a cold front south through West Texas and
enter South Texas this late afternoon and evening. At the same
time, another shortwave moving eastward along the northern border
of Mexico this morning will reach the Rio Grande region this
afternoon/evening as well. Persistent southeast flow will continue
to draw moisture northward, especially across the Rio Grande
Plains, where PWATs are expected to reach anywhere between
1.6-1.8 inches.

This increase in moisture combined with the front will kick off
shower and thunderstorm development along the front, especially
across the Rio Grande Plains, with additional storms forming off
of the Sierra Madre. That said, there remains the possibility for
some of the storms, especially those moving east out of Mexico, to
reach strong to severe thunderstorm levels.

This is all supported with the cooling mid-level temperatures
from the combination of the approaching shortwave and trough which
will lead to the steepening of the mid-level lapse rates and the
increase of instability, with MUCAPE values increasing to around
1500-1800 J/kg this afternoon/evening.

The continued main threats for these storms are large hail and
damaging winds.

Greatest focus for the strongest and possibly even severe storms
remains to be across the western areas, toward to the Rio Grande
Plains and western Brush Country. Farther east, scattered showers
and thunderstorms are expected as the front continues to push
farther south. Not expecting much in the way of severe weather
farther east as instability and moisture is not as great when
compared to farther west.

The front is expected to push offshore through early Thursday
morning, however, lingering midlevel energy and moisture should
still be enough to continue showers and thunderstorms Thursday
morning. Drier conditions should develop by mid morning Thursday.

As for temperatures, with the rain activity expected to start more
during the afternoon hours, temperatures should still be able to
warm in the upper 80s near 90 degrees today. Cooler temps are
expected for Thursday with highs in the upper 70s to low 80s.

LONG TERM (Thursday night through Tuesday)...

A short wave trough moving out of the central plains will move
across the Ozarks Thursday night and be over the southern
Mississippi River valley early Friday morning. The associated cold
front will move south through Texas Thursday night and be near the
coast by 12Z Friday. Moisture return will be limited ahead of this
front and expect rain chances will be minimal with this front. A dry
and mild air mass will be over the region Friday. The ridge will
move to the east Saturday with a weak moisture return along the Rio
Grande. A weak short wave trough moving out of northeast Mexico
could provide isolated convection over the western Brush Country
Saturday.  Onshore flow will begin to increase on Sunday as low
pressure forms over the central and southern high plains in advance
of the next upper trough moving into the western US. An upper low is
expected to dig into the Great Basin Monday and Tuesday. Low level
moisture return will gradually increase as the southeast flow
strengthens. Mainly streamer type convection is expected for the
area on Monday. Deeper moisture and the possibility of an impulse in
the southwest flow aloft will lead to a better chance of convection
especially over the northern Coastal Bend into the Victoria
Crossroads region Tuesday. Winds could increase to SCA levels over
the marine areas Tuesday.

&&

.PRELIMINARY POINT TEMPS/POPS...
Corpus Christi    59  79  58  82  59  /  40  10  10  10  10
Victoria          58  79  53  81  55  /  30  10  10   0  10
Laredo            60  80  63  84  62  /  60  10  10  10  10
Alice             59  81  57  85  57  /  40  10  10  10  10
Rockport          59  78  59  80  62  /  30  10  10  10  10
Cotulla           59  80  58  82  58  /  60  10  10  10  10
Kingsville        60  80  57  84  58  /  40  10  10  10  10
Navy Corpus       61  77  62  80  64  /  40  10  10  10  10

&&

.CRP WATCHES/WARNINGS/ADVISORIES...
TX...None.
GM...None.

&&

$$

GH/77...AVIATION



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