Flash Flood Warning 12, NWS San Angelo, TX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN ANGELO TX
610 PM CDT Mon May 18 2015

.AVIATION...
/00Z TAFS/
Mainly VFR conditions are expected through much of this evening.
Widespread stratus will spread north across West Central Texas late
tonight through much of Tuesday, with MVFR/IFR ceilings at the
terminals. Also, a few storms are possible this evening along the
I-10 corridor, and will add a VCTS to the KSOA terminal. Also, a
complex of storms will probably move across the Big Country
Tuesday morning and early afternoon and gone with 5SM -TSRA and
the KABI terminal between 12Z and 15Z.

&&

.PREV DISCUSSION... /ISSUED 338 PM CDT Mon May 18 2015/

SHORT TERM...
(Tonight and Tuesday)

..Flash flood watch midnight tonight through 7 PM Tuesday for the
Big Country and N. Concho Valley...

Complex of storms is expected to develop in the Permian Basin and
South Plains, then move east into the Big Country late tonight and
Tuesday. With precipitable waters increasing to 1.5 inches, locally
heavy rainfall possible. A weak cold front will approach the Big
Country late tonight, providing a low level focus for storm
development. An upper shortwave will be moving in from the west
at the same time, producing mid level lift. Outflow from the
storms may push into the northern Concho Valley...thus Sterling,
Coke and Runnels counties were added into the Flash Flood Watch.

Isolated to scattered thunderstorms may develop earlier this
afternoon and evening, mainly in Crockett and Sutton counties, the
Concho Valley and Western Big Country. There is an isolated severe
threat, with large hail and damaging winds. Localized flooding
will also be possible near the stronger storms.

04

LONG TERM...
(Tuesday night through Monday)

The forecast in a nutshell: It's not going to rain every day at
any particular location, but we are looking at several rounds of
potentially heavy rainfall over the next week. Localized rainfall
amounts exceeding 5 inches are not out of the question. However,
where the heaviest rainfall occurs will be dependent on the
location of certain mesoscale features. Numerical guidance will
likely have a poor handle on the mesoscale features further out in
time, so there will be plenty of forecast fine-tuning that needs
to be done over the coming days. Overall, the severe weather
threat is relatively low, but flash flooding will be a significant
concern. Now let's drill down for some details.

Southwest flow aloft will be the theme this week, as has been the
case for most of the month of May. As we begin the long-term
portion of the forecast (Tuesday night), a potent shortwave trough
will be lifting northeast across the southern Plains. Convection
will be possible overnight, especially across the Big
Country/Heartland counties, but the strongest lift will be moving
east and should limit the amount of precipitation.

A cold front is forecast to dip south into West Central TX on
Wednesday into Wednesday evening. There remains some disagreement
within the 12z model suite regarding how quickly this boundary
moves south into the area. The GFS is notably slower, bringing
the front south of I-20 by midday Thursday, a good 12-18 hours
slower than the NAM, GEM, and ECMWF. The thinking is that with
convection along/north of the boundary, the front will move south
more quickly, more in line with the faster solutions. This
presence of this front will be a player in the potential for heavy
rainfall again on Wednesday afternoon and evening. Precipitable
water values are progged to be in the 1.3 to 1.6" range by this
time, providing ample moisture for convective development. Winds
at 850 mb are forecast to remain from the south at near 15 mph,
maintaining the fetch of moisture from the Gulf.

Additional model differences arise on Thursday. The NAM and ECMWF
dry out the boundary layer quite a bit more than the GFS, which
maintains dewpoints in the mid/upper 60s. Regardless, Thursday is
likely to be a relative lull in precipitation as short-wave
ridging aloft traverses the area. By Thursday night and Friday,
however, the models are indicating another shortwave trough
lifting northeast across Far West TX, providing additional
synoptic scale ascent over the region. This lift, combined with
the presence of the decaying frontal boundary, will likely aid in
additional rainfall.

This pattern will persist through the weekend, keeping at least
chance PoPs in the forecast areawide. A strong shortwave trough is
forecast to lift northeast across West TX over the weekend. This
will provide another shot at heavy rainfall and stronger
thunderstorms. Temperatures will run near to slightly below normal
for much of the period with highs in the mid 70s to lower 80s and
overnight lows generally in the 60s.

Johnson

&&

.PRELIMINARY POINT TEMPS/POPS...
Abilene 	 68  78  67  81  62 /  50  70  40  40  50
San Angelo 	 69  84  67  85  64 /  50  50  30  30  50
Junction 	 70  84  69  85  66 /  30  40  20  20  50

&&

.SJT WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH from Midnight CDT tonight through Tuesday
evening FOR THE FOLLOWING ZONES: Callahan...Coke...Fisher...
Haskell...Jones...Nolan...Runnels...Shackelford...Sterling...
Taylor...Throckmorton.

&&

21

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE SAN ANGELO TX
334 PM CDT MON MAY 18 2015

TXZ049-054-064>066-071>073-076>078-098-099-113-114-127-128-139-
140-154-155-168>170-192045-
FISHER-NOLAN-STERLING-COKE-RUNNELS-IRION-TOM GREEN-CONCHO-
CROCKETT-SCHLEICHER-SUTTON-HASKELL-THROCKMORTON-JONES-SHACKELFORD-
TAYLOR-CALLAHAN-COLEMAN-BROWN-MCCULLOCH-SAN SABA-MENARD-KIMBLE-
MASON-
334 PM CDT MON MAY 18 2015

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF WEST CENTRAL
TEXAS.

.DAY ONE...THIS AFTERNOON AND TONIGHT

A FLASH FLOOD WATCH IS IN EFFECT FOR HEAVY RAINFALL OVER THE BIG
COUNTRY AND NORTHERN CONCHO VALLEY...AFTER MIDNIGHT AND THROUGH
7 PM TUESDAY. FLOODING IN URBAN AREAS AND LOW LYING AREAS IS
POSSIBLE. AN ISOLATED SEVERE THUNDERSTORM IS POSSIBLE LATE THIS
AFTERNOON AND THROUGH THE EVENING...MAINLY OVER CROCKETT COUNTY...THE
CONCHO VALLEY AND WESTERN BIG COUNTRY. THE MAIN THREATS ARE LARGE
HAIL AND DAMAGING WINDS.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY

HEAVY RAINFALL AND POTENTIAL FLASH FLOODING WILL CONTINUE TUESDAY
ACROSS THE BIG COUNTRY AND NORTHERN CONCHO VALLEY.

SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE INTO NEXT WEEK. SOME
STORMS MAY BECOME STRONG TO SEVERE...WITH LARGE HAIL AND DAMAGING
WINDS BEING THE MAIN CONCERNS. IN ADDITION...DANGEROUS CLOUD TO
GROUND LIGHTNING AND HEAVY RAINFALL WILL ALSO BE POSSIBLE.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED LATER THIS AFTERNOON OR TONIGHT.

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