Area Forecast Discussion
Issued by NWS San Angelo, TX

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FXUS64 KSJT 230507
AFDSJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN ANGELO TX
1207 AM CDT Sat May 23 2015

.AVIATION...
/06Z TAFS/
MVFR to IFR CIGS are starting to fill in across southern and
eastern areas. The onset of the lower VIS and CIG may be delayed
somewhat by high clouds from convection to the west. With rain
still expected tomorrow afternoon and evening, no significant
changes were made beyond the overnight hours.

&&

.PREV DISCUSSION... /ISSUED 647 PM CDT Fri May 22 2015/

AVIATION...
/00Z TAFS/
No significant changes to the previous set of TAFs. Expecting the
SCT clouds at MVFR heights to fill in and become OVC within a
couple hours across the area after 00Z/7PM this evening, and then
lower to IFR as they did last night with similar conditions in
place. Tomorrow, we are still expecting showers with possibly some
embedded isolated thunderstorms to move into the area during the
morning hours, mainly after 12Z/7AM. There is a better chance for
thunderstorm activity tomorrow afternoon as temperatures warm, so
have introduced VCTS after 20Z at most sites tomorrow, with
possibly some slight improvement in CIG heights during the
afternoon. Winds will be southeasterly throughout the time period,
hovering around 12 knots, with intermittent gusts near 20 knots at
times. 20

PREV DISCUSSION... /ISSUED 347 PM CDT Fri May 22 2015/

SHORT TERM...
(Tonight and Saturday)

.Heavy rainfall expected across West Central TX this weekend...

Low clouds beginning to erode this afternoon as a warm front lifts
north across the CWA. Temperatures have warmed into the upper 70s
across the southwest quadrant of the CWA, with dewpoints in the mid
60s. The resultant MLCAPE values are nearing 1000 J/kg in the
vicinity of the Pecos River. A few storms are likely to develop over
the Trans-Pecos area and Permian Basin this afternoon and could
drift into the western portion of the CWA. However, weaker
instability in our neck of the woods will limit convection intensity
and and its eastward extent. Low clouds will redevelop tonight as
southerly flow increases over the boundary layer. Isentropic ascent
at 300K may also result in some patchy drizzle. That said, the
coverage of measurable rainfall will be limited during the
overnight hours.

By Saturday morning, synoptic scale forcing for ascent will be
increasing over west TX as a strong shortwave trough moves across
the southern Rockies. West Central TX will be favorably located in
the right entrance region of the a N-S oriented jet streak over the
High Plains, enhancing mesoscale ascent over the southern Plains.
Precipitable water values are forecast to approach 1.60",
essentially in the 99th percentile of climatology. This moist,
uncapped airmass will support the development of widespread showers
and thunderstorms throughout the day Saturday. The abundance of
cloud cover may limit instability sufficiently to ward off a
significant severe weather threat; however, a few strong to severe
storms are certainly possible across the CWA, as highlighted in the
Day 2 outlook from the SPC. The primary concern will be flash
flooding as widespread rainfall amounts of 1 to 3 inches are
expected between Saturday morning and Sunday afternoon, with locally
higher amounts.

Johnson

LONG TERM...
(Saturday night through next Friday)

The active weather pattern will continue through Memorial Day,
with main focus on heavy rainfall Saturday night and early Sunday,
and the potential for severe weather Monday afternoon into Monday
night.

Widespread coverage of showers and thunderstorms with heavy
rainfall Saturday night will shift into our eastern counties
overnight. By Sunday morning, have the highest PoPs across our
eastern counties. Drier air will overspread the western part of
our area during the day, but with another disturbance rotating
through the base of the trough and into our area Sunday afternoon,
will have a possibility of additional isolated to scattered
thunderstorm development, mainly across the eastern third of our
area.

Any intrusion of drier low-level air on Sunday will be short-lived,
as return flow brings the moisture back by late Sunday night. The
12Z GFS and ECMWF both show a shortwave trough moving east across
New Mexico on Memorial Day. This will bring an increased chance of
thunderstorms Monday afternoon into Monday night across our area.
With very unstable air (CAPEs in excess of 3000 J/KG) and adequate
vertical shear, severe weather will certainly be possible. Storms
may initially develop along a dryline in West Texas, and then grow
upscale into a Mesoscale Convective System across our area. Heavy
rainfall will again be possible. Have increased the PoPs across
our area Monday and Monday night.

Very warm and humid conditions are expected for much of next week.
Rain chances look low for Tuesday into Wednesday, as heights aloft
temporarily build with weak shortwave ridging over Texas.

Another upper trough is progged to move east across the
southwestern states on Wednesday and Thursday. Approach of this
system into a very unstable airmass will support an increased
chance for thunderstorms across our area Thursday into Friday.

19

&&

.PRELIMINARY POINT TEMPS/POPS...
Abilene  67  76  65  83  65 /  30  80  80  50  10
San Angelo  68  78  66  85  65 /  30  80  80  50  10
Junction  69  78  67  83  67 /  30  70  80  50  20

&&

.SJT WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH from 10 AM CDT Saturday through Sunday morning
FOR THE FOLLOWING ZONES: Brown...Callahan...Coke...Coleman...
Concho...Crockett...Fisher...Haskell...Irion...Jones...Kimble...
Mason...McCulloch...Menard...Nolan...Runnels...San Saba...
Schleicher...Shackelford...Sterling...Sutton...Taylor...
Throckmorton...Tom Green.

&&

$$





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