SWODY2
SPC AC 181727
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1227 PM CDT SUN OCT 18 2009
VALID 191200Z - 201200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
A LOW AMPLITUDE PROGRESSIVE RIDGE WILL SHIFT EWD FROM THE PLAINS/MS
VALLEY REGION TO THE ERN HALF OF THE CONUS...WHILE AN UPSTREAM
PACIFIC TROUGH APPROACHING THE WEST COAST ON DAY 1 UNDERGOES FURTHER
AMPLIFICATION INTO THE GREAT BASIN/LOWER CO RIVER VALLEY. AT 12Z
MONDAY...A SURFACE BOUNDARY SHOULD EXTEND WSWWD FROM WY THROUGH NRN
NV TO NRN CA. WRN EXTENT OF THIS BOUNDARY WILL BECOME MORE
PROGRESSIVE ON MONDAY IN RESPONSE TO THE AMPLIFYING PACIFIC
TROUGH...WITH THIS FRONT MOVING E/SEWD FROM NV/CA TO ERN UT AND THE
SRN CO RIVER VALLEY BY 12Z TUESDAY.
...INTERMOUNTAIN WEST...
A LOWER AMPLITUDE SHORTWAVE TROUGH...CURRENTLY APPROACHING NRN CA
PER WATER VAPOR IMAGERY IS FORECAST TO LOSE AMPLIFICATION ON MONDAY
AS THIS FEATURE TRACKS NE INTO A MORE CONFLUENT FLOW REGIME LOCATED
OVER THE NRN HIGH PLAINS. COOL MID LEVEL TEMPERATURES AND WEAK
ASCENT ATTENDANT TO THIS IMPULSE SHEARING NEWD SHOULD AID IN
SUPPORTING TSTMS THROUGH THE DAY ACROSS THE NRN INTERMOUNTAIN REGION
WHERE TSTMS MAY BE ONGOING AT THE START OF THE FORECAST PERIOD.
ALTHOUGH MOISTURE WILL REMAIN MEAGER ACROSS THE GREAT BASIN...
STRONGER FORCING FOR ASCENT WITH THE AMPLIFYING PACIFIC TROUGH AND
STEEP LAPSE RATES/COOLER MID LEVEL TEMPERATURES WILL AID IN FOCUSING
TSTM DEVELOPMENT ALONG THE FRONT FROM NV INTO UT FROM MONDAY
AFTERNOON INTO THE OVERNIGHT PERIOD.
...ERN WY/SERN MT INTO WRN SD...
A LEE-SIDE SURFACE LOW IS EXPECTED TO DEVELOP OVER WY MONDAY
AFTERNOON...SHIFTING SEWD INTO THE CENTRAL HIGH PLAINS BY 12Z
TUESDAY IN RESPONSE TO HEIGHT FALLS AHEAD OF AMPLIFYING TROUGH INTO
THE GREAT BASIN. STRENGTHENING SLY LOW LEVEL WINDS FROM NEB INTO SD
MONDAY NIGHT WILL SUPPORT INCREASING LOW LEVEL WAA REGIME AND THE
DEVELOPMENT OF ELEVATED TSTMS. DESPITE THE LACK OF GREATER MOISTURE
RETURN...PLUME OF STEEP MID LEVEL LAPSE RATES EXTENDING EWD ACROSS
THIS REGION WILL SUPPORT ELEVATED MUCAPE OF 200-300 J/KG. ALTHOUGH
EFFECTIVE BULK SHEAR /35 KT/ WOULD BE SUPPORTIVE OF ORGANIZED
STORMS...WEAK INSTABILITY SHOULD PRECLUDE A SEVERE WEATHER THREAT...
THOUGH SMALL HAIL IS POSSIBLE.
...SERN AZ/SWRN NM...
TSTMS WILL AGAIN BE POSSIBLE ACROSS THIS REGION WHERE INSTABILITY
WILL BE GREATER WITH MLCAPE REACHING TO AROUND 500 J/KG MONDAY
AFTERNOON. HOWEVER...WEAK FORCING ALOFT AND WEAK EFFECTIVE BULK
SHEAR SHOULD LIMIT THE SEVERE WEATHER THREAT.
..PETERS.. 10/18/2009
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