Severe Thunderstorm Warning 12, 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

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SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE SAN ANGELO TX
1111 AM CDT THU APR 16 2015

TXZ064>066-071>073-076>078-139-140-154-155-168>170-161800-
STERLING-COKE-RUNNELS-IRION-TOM GREEN-CONCHO-CROCKETT-SCHLEICHER-
SUTTON-COLEMAN-BROWN-MCCULLOCH-SAN SABA-MENARD-KIMBLE-MASON-
INCLUDING THE CITIES OF...STERLING CITY...ROBERT LEE...BRONTE...
BALLINGER...WINTERS...MERTZON...SAN ANGELO...EDEN...OZONA...
ELDORADO...SONORA...COLEMAN...BROWNWOOD...BRADY...SAN SABA...
MENARD...JUNCTION...MASON
1111 AM CDT THU APR 16 2015

...THUNDERSTORMS INCREASING IN COVERAGE AND STRENGTH LATE THIS MORNING...

AT 11 AM...NATIONAL WEATHER SERVICE RADAR INDICATED SCATTERED THUNDERSTORMS
ACROSS THE AREA SOUTHEAST OF A LINE FROM ELDORADO TO COLEMAN. THE STORMS
WERE MOVING NORTHEAST AT 25 MPH AND WERE INCREASING IN COVERAGE AND
STRENGTH. A FEW OF THESE STORMS COULD PRODUCE HAIL AND FREQUENT
LIGHTNING. BRIEF VERY HEAVY RAINFALL COULD CAUSE PONDING OF WATER ON
ROADS OR MINOR STREET FLOODING. THE STORMS ARE EXPECTED TO CONTINUE
INTO AT LEAST THE EARLY AFTERNOON HOURS.

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE SAN ANGELO TX
1136 AM CDT THU APR 16 2015

TXZ168>170-161715-
KIMBLE TX-MASON TX-MENARD TX-
1136 AM CDT THU APR 16 2015

...SIGNIFICANT WEATHER ADVISORY EFFECTIVE UNTIL 1215 PM CDT FOR
KIMBLE...MASON AND MENARD COUNTIES...

POTENTIAL STORM HAZARDS INCLUDE...
  GUSTY WINDS AND SMALL HAIL

AT 1131 AM CDT...A BAND OF STRONG THUNDERSTORMS WAS OVER NORTHEASTERN
KIMBLE COUNTY. THE STRONGEST STORM WITHIN THIS BAND WAS LOCATED 2
MILES WEST OF YATES CROSSING...OR ABOUT 10 MILES NORTHEAST OF
JUNCTION... AND WAS MOVING NORTHEAST AT 30 MPH.

DIME TO NICKEL SIZE HAIL...FREQUENT LIGHTNING AND VERY HEAVY RAIN
WILL ACCOMPANY THESE STORMS...ALONG WITH WIND GUSTS TO 40 MPH.

POTENTIAL STORM IMPACTS INCLUDE...
  A FEW WEAK BRANCHES BROKEN...
  AN ISOLATED POWER OUTAGE POSSIBLE...
  HAZARDOUS DRIVING CONDITIONS WITH PONDING OF WATER ON ROADS...

THE STRONG THUNDERSTORMS WILL BE NEAR...
  LONDON BY 1145 AM CDT
  SALINE BY 1150 AM CDT
  US-377 NEAR THE KIMBLE-MENARD COUNTY LINE BY 1155 AM CDT
  ERNA BY NOON CDT
  STREETER BY 1210 PM CDT

LAT...LON 3093 9944 3085 9921 3072 9903 3044 9954
      3058 9978
TIME...MOT...LOC 1633Z 223DEG 26KT 3059 9963

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE SAN ANGELO TX
1224 PM CDT THU APR 16 2015

TXZ154-155-170-161800-
MCCULLOCH TX-MASON TX-SAN SABA TX-
1224 PM CDT THU APR 16 2015

...SIGNIFICANT WEATHER ADVISORY EFFECTIVE UNTIL 100 PM CDT FOR
SOUTHERN MCCULLOCH...SAN SABA AND NORTHERN MASON COUNTIES...

POTENTIAL STORM HAZARDS INCLUDE...
  GUSTY WINDS...HAIL AND DEADLY LIGHTNING

AT 1219 PM CDT...A CLUSTER OF STRONG THUNDERSTORMS WAS LOCATED 2 MILES
NORTHWEST OF KATEMCY...OR ABOUT 14 MILES NORTH OF MASON...MOVING NORTHEAST
AT 30 MPH. THESE STORMS WILL CONTAIN FREQUENT LIGHTNING AND VERY HEAVY
RAIN. SMALL HAIL AND WIND GUSTS TO 45 MPH ARE ALSO POSSIBLE.

POTENTIAL STORM IMPACTS INCLUDE...
  SOME BROKEN SMALL TREE BRANCHES...
  AN ISOLATED POWER OUTAGE POSSIBLE...
  A FEW LOOSE OBJECTS TOPPLED...
  HAZARDOUS DRIVING CONDITIONS AND POSSIBLE MINOR FLOODING ON SOME ROADS...

THE STRONG THUNDERSTORMS WILL BE NEAR...
  CAMP SAN SABA BY 1225 PM CDT
  VOCA AND FREDONIA BY 1235 PM CDT
  SLOAN AND US-190 NEAR THE MCCULLOCH-SAN SABA COUNTY LINE BY 100 PM
  CDT

LAT...LON 3092 9857 3091 9863 3092 9895 3084 9896
      3076 9931 3095 9943 3119 9936 3131 9902
      3120 9864
TIME...MOT...LOC 1720Z 228DEG 25KT 3095 9927