Severe Thunderstorm Warning 16, NWS San Angelo, TX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN ANGELO TX
1217 PM CDT Thu Apr 16 2015

.AVIATION...
/18Z TAFS/
Expect VFR conditions to prevail today across all terminals.
However, as scattered showers and thunderstorms develop this
afternoon and evening, terminals may experience temporary lower
visibility and ceilings. Gusty winds will likely accompany these
storms as well. After midnight, MVFR ceilings are expected to
develop across the KBBD, KSOA, and KJCT terminals and persist
through the early morning hours.

&&

.PREV DISCUSSION... /ISSUED 1124 AM CDT Thu Apr 16 2015/

UPDATE...
Scattered showers and thunderstorms have increased in coverage
across the area roughly southeast of a line from Eldorado to Coleman.
This may be associated with a weak embedded impulse in the
southwest flow aloft. An increase in strength is also occurring
as the storms move into an increasingly unstable environment.

The SPC Day1 Convective Outlook extended the Enhanced Risk for
severe storms southeast across the northern third of our area.
This is roughly along a weak, nearly stationary surface boundary
which extends from the Texas Pahnandle southeast across the Big
Country. Thunderstorms which develop to the northwest in the mid
to late afternoon could congeal into a Mesoscale Convective System
and propagate southeast along this boundary this evening.

The current forecast looks on track with PoPs and the severe
wording for this afternoon and early evening. Will monitor and
make further updates to the forecast as needed.

19

PREV DISCUSSION... /ISSUED 648 AM CDT Thu Apr 16 2015/

AVIATION...
/12Z TAFS/

Currently, all sites are VFR this morning, with a few showers
moving through areas near KSOA, KJCT, and KSJT. MVFR to IFR CIGS
are lurking just south and east of our forecast area, and are
expected to affect our region for at least a few hours this
morning, so we have included at least TEMPO groups for MVFR CIGS
at all sites this morning, with these CIGS expected to scatter out
during the mid to late morning time frame. Later today, scattered
showers and thunderstorms are expected to develop. It appears that
the KBBD and KABI are most likely to be affected so we have
included a VCTS at these two sites during the afternoon and
evening hours. With less confidence in storms affecting KJCT,
KSOA, and KSJT, have left the mention of thunder out for now, but
this can be added later. MVFR CIGS should return to at least
southern sites tonight. However, the coverage of CIGS across the
entire area will dependent on coverage and placement of any overnight
thunderstorm activity that is able to develop. 20

PREV DISCUSSION... /ISSUED 345 AM CDT Thu Apr 16 2015/

SHORT TERM...
(Today and Tonight)

Isolated to scattered showers and thunderstorms are affecting
areas mainly less than Interstate 10 as a shortwave embedded in
the subtropical jet stream moves across Mexico and south Texas.
This activity is expected to diminish over the next few hours.

Otherwise, a large upper level low continues to move into the
four corners area while becoming cut off from the main northern
jet stream across southern Canada. Low level southerly flow across
the area due to surface pressure falls to our west and northwest
has resulted in increased moisture, and this southerly flow will
continue through today. Along with clearing and warm temperatures,
this moisture will result in an unstable air mass (2000-3000 J/kg
CAPE) across the area today. A shortwave embedded in
southwesterly flow will move into the area today, interact with
this unstable air mass, and should result in scattered showers and
thunderstorms developing by this afternoon across the area,
especially east of a Sweetwater to Mason line. Although 0-6km
shear will only be in the 20 to 30 knot range, some of the storms
will likely be able to strengthen to severe levels due to the
unstable air mass. The main hazards will be large hail and
damaging wind gusts.

Tonight, additional development will be possible as the dryline
tightens up, and moves east into the area. The NAM and ECMWF are
slower moving the dryline east into the area than the GFS, which
would result in a later arrival of thunderstorms into our counties
if they develop. Considering these factors, there is less
confidence in the chances for precipitation, and will only go
with a chance for the overnight period as opposed to likely. With
more limited instability during the overnight period, and the
possibility that we may not even see activity until very late or
early Friday morning, will not mention severe wording for the
overnight.

20

LONG TERM...
(Friday through Wednesday)

An upper low will be over northern New Mexico Friday morning as a
dryline advances into the western CWA. The best chance of
thunderstorm activity will migrate east across the forecast area
Friday and Friday night as the upper low spins northward into
central Colorado and the dryline advances deeper into the CWA.
The upper low is expected to move east over the Central Plains on
Saturday with any thunderstorm activity over the forecast area
ending from west to east by late Saturday. Temperatures Friday
afternoon will be in the upper 70s over the forecast area under
cloudy and rainy skies. Afternoon highs will warm into the lower
80s on Saturday as skies begin to clear from the west. Morning
lows will be in the mid 50s. A cold front will push south through
the forecast area on Sunday keeping afternoon highs in the 70s,
below seasonal norms. Dry weather is on tap Sunday into Monday in
the wake of the departing upper low.

Models are showing periodic upper disturbances moving over a
stationary dryline positioned over far West Texas beginning late
Monday and continuing into mid-week. This scenario will keep a
slight chance of thunderstorms over the forecast area through
this time period. Afternoon highs will continue to be in the 70s
with a warm-up to seasonal normals beginning on Wednesday.

15

&&

.PRELIMINARY POINT TEMPS/POPS...
Abilene 	 59  78  57  81  54 /  50  50  30  30  20
San Angelo 	 59  79  56  83  55 /  50  50  20  20  10
Junction 	 62  79  58  83  56 /  50  60  30  40  20

&&

.SJT WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

99/99/18

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE SAN ANGELO TX
219 PM CDT THU APR 16 2015

TXZ049-054-064>066-071>073-076>078-098-099-113-114-127-128-139-
140-154-155-168>170-171930-
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-
219 PM CDT THU APR 16 2015

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

.DAY ONE...THIS AFTERNOON AND TONIGHT

SCATTERED THUNDERSTORMS ARE EXPECTED THIS AFTERNOON AND TONIGHT
ACROSS ALL OF WEST CENTRAL TEXAS. A FEW OF THESE STORMS COULD
BECOME SEVERE WITH THE MAIN HAZARDS BEING LARGE HAIL...DAMAGING
WINDS AND DEADLY LIGHTNING.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY

ADDITIONAL THUNDERSTORMS ARE POSSIBLE FRIDAY AND SATURDAY ACROSS
MOST OF THE AREA. SOME OF THESE STORMS MAY ALSO BECOME SEVERE WITH
THE MAIN HAZARDS BEING LARGE HAIL...DAMAGING WINDS...AND DEADLY
LIGHTNING.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED THIS AFTERNOON THROUGH LATE
EVENING...AND AGAIN ON FRIDAY.

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