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Area forecast discussion 
National Weather Service Corpus Christi Texas
641 PM CDT Tuesday Apr 21 2015

Discussion...see aviation below for 00z taf update.

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Aviation...ceilings will lower this evening and
overnight...brining MVFR to occasionally IFR conditions to south
Texas. Patchy fog will also impact the area...with MVFR visibilities at
all terminals during the early morning hours on Wednesday. Will
maintain lower ceilings throughout the day on Wednesday...along with
showers possible in the vicinity of all terminals. A thunderstorm
may develop within this activity tomorrow...but current confidence
is not high enough to include mention of thunderstorms and rain at this time. Winds
will generally be light out of the southeast through the period
as well.

&&

Previous discussion... /issued 343 PM CDT Tuesday Apr 21 2015/

Short term (tonight through Wednesday night)...isolated showers
across the eastern zones continue to struggle with any further
development with Low Cape values. Farther west toward
Laredo...thick cloud coverage has hindered much in
warming...although an isolated shower remains possible as laps
analysis suggests instability shifting farther west. Main
convection should quiet down...with a patchy light stratiform
rain developing overnight as a coastal trough develops and lifts
slowly north.

For Wednesday...the question continues to be whether or not
scattered or widespread convection will develop. NAM and Euro
continue to bring in much higher probability of precipitation while GFS has been backing
down. A few factors support for the higher solutions. Cape values
increase to near 2500-3500 j/kg with little to no cin per the
NAM. GFS shows similar cape values however with much more
inhibition. The main factors that support less activity are the
slight increase in midlevel ridging and the upper jet lifting
north. This would lead to a bit more subsidence across the region.
In addition...a light to moderate south to southwest flow is forecast
to develop off the Sierra Madre...keeping a much warmer layer at
850 mb. This capping and subsidence is typical in keeping rain
chances...more so severe weather...at a minimum. Moisture
increasing in the boundary layer will keep showers developing
under the cap...although an isolated thunderstorm will remain
possible. Storm Prediction Center continues to keep the northeastern zones toward
Victoria under a slight risk for severe thunderstorms. That part
of the County Warning Area has a relatively weaker cap than farther south and
west. But again...best upper level support remains north of the
region...and midlevel subsidence could help suppress development.
Thunderstorms are going to have a hard time to develop...but if
parcels can break through the cap...with the amount of instability
available...severe weather can not be ruled out with large hail
and damaging winds as the main threats.

Long term (thursday through tuesday)...a potent shortwave embedded
within the strong subtropical jet nosing into West Texas/nm region is
expected to trigger a mesoscale convective system by late Thursday afternoon/evening across the Sierra
Madre. This mesoscale convective system is expected to continue developing as it propagates
east-northeastward across south Texas aided by convective available potential energy of 3000-4000+ j/kg and 0-6km
shear at or above 50 knots. Will thus continue with the highest probability of precipitation for Thursday
night especially across the brush country. Large hail and winds will
be the primary severe weather threats for Thursday night and this lines up well
with the Storm Prediction Center slight risk prognosticated during this timeframe. Depending
upon the expected evolution of this mesoscale convective system will determine the sensible weather
for Friday. For now...will maintain at least chance probability of precipitation as a corridor of
decent moisture and extreme instability is still expected to occur
across the County Warning Area on Friday. A weakening Pacific front/dryline bisecting
the County Warning Area on Saturday may trigger some isolated convection. Slightly
drier conditions on Sunday will keep rain chances even lower although
cannot totally rule out a storm or two. Guidance for Monday and
Tuesday becomes a bit more diverse with its handling of the next
Pacific shortwave. For now will be a bit conservative with probability of precipitation and only
go with slight chance probability of precipitation early next week.

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Preliminary point temps/pops...
Corpus Christi 70 81 72 85 74 / 20 30 20 20 30
Victoria 67 82 70 86 72 / 20 40 20 20 30
Laredo 67 85 71 93 74 / 30 20 10 20 40
Alice 69 83 71 89 74 / 20 30 10 20 40
Rockport 73 77 72 79 75 / 20 30 20 10 30
Cotulla 68 84 70 91 72 / 30 30 10 20 50
Kingsville 70 83 72 88 75 / 20 30 10 20 30
Navy corpus 73 78 72 81 74 / 20 20 20 10 20

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Crp watches/warnings/advisories...
Texas...none.
GM...none.

&&

$$

Lk/84...aviation

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