Area Forecast Discussion
Issued by NWS San Angelo, TX

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FXUS64 KSJT 191753 AAC

1253 PM CDT Fri Sep 19 2014

/18Z TAFS/

The main aviation forecast concerns are with showers/thunderstorms
and associated reductions in ceilings and visibilities this
afternoon into tonight, and with possible IFR/LIFR conditions
late tonight and early Saturday morning, with low cloud ceilings.
Area of showers persists early this afternoon from north of Brady
to around Sweetwater. New band of convection has developed from
just southeast of Brady, south across eastern Mason County. Other
showers developing west and southwest of San Angelo. All of this
convective activity is moving very slowly north-northeast. Expect
an increase in coverage of showers with scattered thunderstorms
this afternoon and evening. Carrying VCSH/VCTS groups in the area
TAFs, and will update as needed. Additional showers and
thunderstorms are expected tonight, with the best chance across
our western and northwestern counties. The models were on target
with the extent of low cloud development that occurred early this
morning. Outside of convective activity, anticipate that this will
occur again late tonight and early Saturday morning. Carrying low
cloud (IFR) ceilings at the TAF sites.




A forecast update is in order this morning. Satellite imagery
shows widespread cloud cover, and surface observations have
indicated widespread IFR and LIFR ceilings. Radar imagery shows a
band of rain showers with moderate to occasionally heavy rain,
extending from Eden northwest into southwestern Nolan County. Area
of moderate to heavy rain over West Texas is slowly shifting east or
east-southeast (referenced in the Satellite Precipitation Estimates
product from NESDIS). Will update the forecast, at this time to
increase cloud cover and re-work the PoP field for today.



/12Z TAFS/

Ceilings have come down in many places to less than 2000 ft, but
trying to pin down a prevailing height is akin to playing
whack-a-mole with Mother Nature. In general, ceilings will bounce
around between IFR and MVFR, briefly dropping to less than 500 ft
at times over the next few hours. Visibilities have followed suit
along the I-20 corridor, ranging from 1/4 to 3 miles in the past
hour. Generally improving conditions are anticipated by mid/late
morning, with prevailing VFR conditions anticipated after 16z.

Current convection is expected to weaken this morning, but
additional development is expected this afternoon and tonight. A
VCSH group was appended to all sites excluding KABI this
afternoon. Any cells that develop may produce brief IFR
visibilities and/or MVFR ceilings. Rain chances increase tonight
across the north. Expect a general easterly wind at 10 kts or



(Today and tonight)

A split flow pattern persists over the western CONUS with a
relatively deep trough along the West Coast, cut off from the
stronger westerlies over the northern tier. The mid/upper-level
ridge remains in place over the southern Rockies and Plains, but
the remnants of Odile are trapped beneath this ridge, moving
very slowly to the east across NM this morning. Copious tropical
moisture has been advected into the region, as evidenced by the
precipitable water values from the 00z raobs. Both the FWD and DRT
precipitable water values are just below two standard deviations
above climatology. However, the 1.95" PWAT at KMAF is above the
99th percentile. In other words, pretty rare! GPS PWAT data
indicates values over 2.00" east of DRT. Southerly 850mb winds of
15-20 kts will continue to advect this moisture poleward
throughout the day.

Analysis of the wind field hints at a very weak surface boundary
(or trough) extending from northwest to southeast across the
CWA. The RAP Mesoanalysis also indicates a bit of a theta-e
gradient over the southwest zones, in the vicinity of the stronger
convection earlier in the evening. The convection over our neck of
the woods continues to weaken this morning, as does the
precipitation moving into the Permian Basin. However, we should
still see at some activity around through the morning hours.
Despite the abundant cloud cover, temperatures are forecast to
warm into the mid/upper 80s across the southern and eastern zones,
which should promote the development of additional convection by
midday. Most of the models favor the southwest half of the
forecast area for the development of showers and thunderstorms
today, likely focusing a bit farther north, primarily over the
western Big Country and Concho Valley tonight.

The hi-res CAMS are suggesting that convection during the daytime
period will be more cellular in nature, keeping the threat for
flash flooding on the low side. However, tonight, as the low-
level jet begins to intensify, we may see this activity grow
upscale. Given the lower flash flood threat for today, no Flash
Flood Watch will be issued at this time. That said, a watch may be
warranted next shift, focused on the overnight period.

(Saturday into Thursday)

Potential for heavy rainfall and flooding will continue this
weekend. Remnants of Odile are expected to push northeast into the
Panhandle and Northwest Texas early Saturday. A cold front then
moves through West Central Texas, from northeast to southwest,
Saturday afternoon and night, acting as a continuing focus for
heavy rainfall.

Both the GFS and NAM models indicate heavy rainfall amounts of 1
to 3 inches in the Big Country and Concho Valley, Saturday and
Saturday night. Locally heavier amounts possible as the tropical
atmosphere will be a efficient rainfall producer. Sunday afternoon,
the heavy rainfall focus moves to the Concho Valley and areas
southwest including Crockett county. This occurs, as more stable air
moves in from the northeast. The main potential for heavy rainfall
then moves southwest of the region Sunday night, with Crockett
county having the best chance of rain. Flash flood watches may be
needed this weekend. Of course, rainfall and runoff will be
extremely beneficial as reservoirs are at extremely low levels and
much West Central Texas is in moderate to extreme drought.

Kept a slight chance of showers on Monday with low/mid level
moisture remaining. Rainfall amounts will be light, if the occur.
A more stable atmosphere remains over the region the rest of the
week, as weak surface high pressure builds in.



Abilene  84  69  83  70  85 /  80  50  60  50  30
San Angelo  84  70  86  70  86 /  60  50  60  50  40
Junction  87  72  86  72  87 /  50  30  40  40  30



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