Area Forecast Discussion
Issued by NWS Corpus Christi, TX

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FXUS64 KCRP 170454 AAC

Area Forecast Discussion...UPDATED
National Weather Service Corpus Christi TX
1054 PM CST Sat Dec 16 2017


Updated for 06z aviation.



Poor flying conditions will continue across South Texas. Ceilings
range from IFR to MVFR across the area and these trends should
persist overnight into early Sunday morning. Some fog will be
possible as well lowering vsbys to around 1 to 2 miles. Potential
exists for low vsbys to materialize but did not mention in the
tafs just yet. Any fog that develops should mix out mid to late
morning, but ceilings should still remain in the MVFR category
through the afternoon. Ceilings less than 1kft and reduced vsbys
may return late in the period.


.PREVIOUS DISCUSSION... /Issued 944 PM CST Sat Dec 16 2017/


Forecast was cleaned up based on latest trends. Rainfall exiting
the Victoria Crossroads will continue to move to the northeast.
This should pretty much end rain chances for the night, but did
leave a low 20 pop over offshore Gulf Waters. Low clouds are all
ready in place across the area, but some fog will be possible as
well tonight. Confidence is not the great with respect to dense
fog potential, but will continue to monitor this possibility.
Overnight lows look reasonable with 40s inland and low 50s along
the immediate coast.

Updated products all ready sent.

PREVIOUS DISCUSSION... /Issued 602 PM CST Sat Dec 16 2017/


Updated for 00z aviation.


Miserable aviation conditions will persist for the majority of the
taf cycle, with only slight improvements Sunday afternoon. Sfc low
that developed over the Middle Texas Coastal Waters will move NNE
this evening with precip ending from west to east. Precip is all
ready east of LRD with a few more hours of -ra/ra at ALI/CRP/VCT.
In addition to the rain, low clouds blankets the South Texas
terminals with ceilings ranging from MVFR to LIFR. Reduced vsbys
will also occur in areas of light rain. Rain should move east of
the terminals by 06z, but low clouds will persist and patchy fog
may develop. Confidence is not high on dense fog forming, but have
started to trend vsbys downward for the overnight and early
morning hours. Only a slight improvement is expected during the
day on Sunday as ceilings will remain in the MVFR category. Winds
will be predominantly out of the N and NE tonight, becoming more E
and SE by Sunday afternoon. Wind speeds should generally be 8
knots or less through the period.

PREVIOUS DISCUSSION... /Issued 355 PM CST Sat Dec 16 2017/

SHORT TERM (Tonight through Sunday Night)...

Areas of rain continue across western areas with showers developing
offshore and along the coast in vicinity of developing
boundary/surface low. All of this being driven by potent upper level
disturbance currently over far West Texas as well as moisture stream
from the Pacific. Surface low/boundary could clip far northeast CWA
this afternoon. Think any chance for thunderstorms will be limited
to immediate coastal areas in vicinity of the boundary. Models have
pretty good handle on positioning of upper disturbance, increasing
confidence in timing of end of precip shield...expected to be out of
the forecast area by around midnight. Could linger just a bit longer
far northeast. Despite the upper disturbance getting out of the
area, will keep a very thick/low cloud cover over most of the area
tonight. Some vis reductions are possible with this low ceiling/fog.
Some guidance suggests some clearing of mid level clouds far west,
which could enhance fog potential in that area.

Should see an increase in cloud deck by mid-day Sunday, though
generally overcast conditions will continue. Another coastal trough
may develop by late Sunday to providing another low chance for
showers. Fog looks like a good potential for Sunday night as
lingering ground moisture from today`s rain will have nowhere to go
with cool temps and persistent cloud cover.

Min temps tonight drop mainly into the 40s, but expect warmer
temps Sunday night with a general onshore flow. Highs will warm
only into the lower 60s on Sunday.

LONG TERM (Monday through Saturday)...

Anticipate convection across the CWA/MSA Monday/Tuesday as an upper
level disturbance moves across the region (confident in
deterministic NWP output.) Drier Tuesday night/Wednesday as the
upper system moves east. Deterministic GFS/ECMWF predict a strong
disturbance to enter the NW CONUS Wednesday then move SE across the
Rockies. Yet, the GFS/ECWMF diverge with respect to this system,
with the ECMWF becoming progressive and the GFS cuts it off over the
SWRN CONUS. Will follow the GFS ensemble mean, which maintains the
upper trough axis west of TX Friday/Saturday. The ECMWF predict the
development of a surface ridge over Western Canada and coincident
with a polar air mass Tuesday, which is a precursor pattern to cold
air outbreak (CAO) events east of the Rockies. Further, the MSLP
center/polar air mass begins to move SWD into the CONUS as the
foregoing upper system predicted to move SE across the Rockies
Wednesday, which is a large scale meteorological pattern that occurs
during CAO events. Thus, confident that the polar air will enter the
CWA Friday as predicted by deterministic output. If the upper trough
axis remains west of the CWA/MSA Friday/Saturday, a wintry
precipitation scenario could occur as early as Saturday. Yet, will
maintain sfc temperatures above freezing over the CWA Saturday
consistent with the SuperBlend. Further, applying the top down
approach to select GFS deterministic soundings suggest rain over the


Corpus Christi    47  63  59  72  64  /  70  10  30  30  40
Victoria          45  66  57  71  61  /  90  10  20  50  50
Laredo            44  61  55  68  61  /  20  10  10  20  30
Alice             46  63  58  73  63  /  60  10  20  30  40
Rockport          49  63  60  71  64  /  80  10  30  40  50
Cotulla           42  60  54  67  58  /  30  10  10  20  40
Kingsville        46  63  59  74  64  /  60  10  20  30  40
Navy Corpus       51  63  62  72  66  /  70  10  30  40  40


GM...Small Craft Advisory until 2 AM CST Sunday For the following
     zones: Coastal waters from Port Aransas to Matagorda Ship
     Channel out 20 NM...Waters from Port Aransas to Matagorda
     Ship Channel from 20 to 60 NM.



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