Area Forecast Discussion
Issued by NWS San Angelo, TX

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FXUS64 KSJT 302102

402 PM CDT TUE SEP 30 2014


/Tonight and Wednesday/

Isolated showers have been affecting the Big County this afternoon,
embedded within the mid-level moist axis streaming across the Lone
Star State from southwest to northeast. The RAP Mesoanalysis
indicates a narrow axis of MLCAPE values approaching 1500 J/kg
across the western counties this afternoon, but even the cu
development as been rather limited, suggesting a pretty strong cap.
We are seeing a bit more vertical development in the cu field over
the Trans-Pecos area, however, and any convection that develops may
drift into the southwest zones. Thus, the slight chance PoPs were
retained this evening, mainly west of a line from Ozona, to Robert
Lee, to Miller Creek Reservoir. Winds will be a few mph stronger
than what was observed last night and, combined with the increasing
low-level moisture, should support min temps in the mid to upper 60s.

On Wednesday, the thermal ridge axis will shift east, resulting in
850mb temps of 24-25C across the Big Country and Concho Valley by
peak heating. With low-level adiabatic lapse rates during the
afternoon hours, we should have little problem warming into the
lower 90s across much of the area. These warm temperatures may
strain the cap to its breaking point by late afternoon, so the
mention of showers and thunderstorms was retained after 20z (3 PM).
Coverage is expected to remain very limited, but any storms that
develop could be strong.


/Wednesday night through Monday/

Afternoon water vapor imagery shows a strengthening trough
progressing southeast across the Inter-mountain West, upper-level
moisture streaming northeast across west central Texas from Tropical
Depression Rachel, and a shortwave trough lifting northeast across
the Dakotas. A dryline observed in surface observations extends
south through the Texas Panhandle, with a few showers developing
ahead of this feature. Ahead of this dryline, southeasterly surface
winds continue to advect moisture into the region from the Gulf of

The trend in the model solutions the past few days has been to delay
the arrival of a cold front. This trend has continued today with the
GFS and ECMWF trending towards the NAM model. Convective
temperatures are expected to be reached tomorrow evening. With
sufficient moisture/good instability in place, shower and
thunderstorm development will be possible, mainly north and west of
a line from San Angelo to Baird. Forecast soundings show SBCAPEs in
excess of 2000 J/kg, around 20-25 Kts of 0-6km shear, and T/TD
spreads around 30 degrees F. With this type of environment, a few
strong thunderstorms will be possible.

With the arrival of the upper trough Thursday, a cold front will
cross the area during the day. For Thursday, moisture, instability,
and shear will increase ahead of the cold front, with forecast
soundings indicating convective temperatures being reached, and a
higher potential for strong thunderstorms/possibly a few severe/ if
frontal timing in the models are correct. Friday will feature cooler
temperatures, with highs near 80 degrees. Another disturbance will
cross the Central Plains this weekend sending a weak cold front
south. This front will stall across the area on Sunday, with
increasing surface moisture likely south of the front. However,
moisture return looks insufficient for shower development at this
time. Overall confidence is moderate in rain chances


Abilene  69  92  72  92  56 /  10  10  20  20   5
San Angelo  69  93  73  89  57 /  10   5  10  20  10
Junction  66  91  73  90  60 /   5   5   5  20  20




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