DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 280551
SWODY1
SPC AC 280550

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1150 PM CST THU FEB 27 2014

VALID 281200Z - 011200Z

...NO SVR TSTM AREAS FORECAST...

...SYNOPSIS...
THE CENTER OF THE COLD EASTERN CANADIAN UPPER VORTEX APPEARS TO BE
IN THE PROCESS OF REDEVELOPING A BIT BACK TO THE NORTH...TOWARD THE
HUDSON BAY REGION. ANOTHER SIGNIFICANT IMPULSE IS PIVOTING AROUND
ITS WESTERN PERIPHERY...BUT MODELS SUGGEST THAT IT WILL BECOME
INCREASINGLY DEFORMED...AS ITS SOUTHWARD PROGRESSION BECOMES
SUPPRESSED NEAR THE WESTERN AND CENTRAL CANADIAN/U.S. BORDER. THIS
IS EXPECTED TO OCCUR AS A MORE SUBSTANTIAL UPPER TROUGH...WITHIN A
BELT OF WESTERLIES EXTENDING ACROSS THE MID LATITUDE PACIFIC THROUGH
THE SOUTHERN TIER OF THE U.S...BEGINS TO PROGRESS INLAND ACROSS THE
PACIFIC COAST TODAY...AND DOWNSTREAM RIDGING BUILDS ACROSS THE
CENTRAL AND SOUTHERN ROCKIES/PLAINS AND MISSISSIPPI VALLEY.

DESPITE THE TREND TOWARD A MORE ZONAL MID/UPPER FLOW REGIME EAST OF
THE ROCKIES...A STRONG COLD SURFACE RIDGE IS FORECAST TO GRADUALLY
BUILD BENEATH THE CONFLUENCE OF THE TWO STREAMS OF FLOW...AND BEGIN
TO NOSE SOUTHWARD THROUGH THE PLAINS AND MISSISSIPPI VALLEY. AT THE
SAME TIME...THE BOUNDARY LAYER OVER MUCH OF THE REMAINDER OF THE
SOUTH AND EAST MAY CONTINUE TO SLOWLY MODIFY IN THE WAKE OF A PRIOR
COLD INTRUSION...BUT GENERALLY STABLE CONDITIONS ARE EXPECTED TO
PERSIST WITH LOW CONVECTIVE POTENTIAL.

MID-LEVEL DESTABILIZATION ASSOCIATED WITH A REMNANT SOUTHERN STREAM
IMPULSE MAY BE SUPPORTIVE OF LOW THUNDERSTORM PROBABILITIES TODAY
ACROSS PARTS OF THE OZARK PLATEAU INTO THE CENTRAL GULF STATES.
HOWEVER...THE PRIMARY CONVECTIVE POTENTIAL FOR THIS PERIOD APPEARS
TO ACCOMPANY THE INLAND PROGRESSING UPPER TROUGH...ACROSS CALIFORNIA
AND PORTIONS OF THE GREAT BASIN AND SOUTHERN PLATEAU. GUIDANCE
SUGGEST THAT THE MID-LEVEL COLD CORE OF THIS SYSTEM MAY NOT BE
ESPECIALLY COLD /AROUND -22 TO -24C/... BUT AN INFLUX OF MOISTURE
FROM LOWER LATITUDES OF THE EASTERN PACIFIC PROBABLY WILL CONTRIBUTE
TO SUFFICIENT DESTABILIZATION FOR THUNDERSTORM ACTIVITY.

...CALIFORNIA INTO THE SRN GREAT BASIN/SOUTHERN PLATEAU...
RAINFALL ASSOCIATED WITH PRE-COLD FRONTAL LOW/MID-LEVEL WARM
ADVECTION...AND PERHAPS A BAND OF FRONTAL CONVECTION...OVERSPREADING
THE REGION BETWEEN NOW AND MID DAY WILL CONTRIBUTE TO BOUNDARY LAYER
MOISTENING. AS STRONGER MID-LEVEL COOLING SPREADS INLAND AFTER 12Z
THIS MORNING...STEEPENING LOWER/MID TROPOSPHERIC LAPSE RATES ARE
EXPECTED TO CONTRIBUTE TO INCREASING POTENTIAL FOR THUNDERSTORM
ACTIVITY. THE EXTENT TO WHICH INSOLATION WILL CONTRIBUTE TO
INSTABILITY REMAINS UNCLEAR...BUT DEEP LAYER SHEAR BENEATH THE
MID-LEVEL JET AXIS /70-90+ KT AT 500 MB/...NOSING AROUND THE EASTERN
PERIPHERY OF THE LOW/MID-LEVEL CYCLONIC EMBEDDED WITHIN THE
APPROACHING UPPER TROUGH...SEEMS TO SUPPORT CONTINUING AT LEAST LOW
PROBABILITIES FOR SEVERE HAIL/WIND IN STRONGER STORMS.

OROGRAPHIC BACKING OF THE LOW-LEVEL FLOW MAY EVEN ENHANCE HODOGRAPHS
ENOUGH TO SUPPORT LOW PROBABILITIES FOR A TORNADO OR TWO BY MID DAY
ACROSS THE LOS ANGELES BASIN...PERHAPS PARTS OF THE SAN JOAQUIN
VALLEY AS WELL.

EVENTUALLY...BY LATE AFTERNOON...MODEL FORECAST SOUNDINGS SUGGEST
SUFFICIENT DESTABILIZATION IN THE PRESENCE OF STRONG SHEAR TO
SUPPORT AN ENVIRONMENT MARGINALLY SUPPORTIVE OF SEVERE WIND AND HAIL
ACROSS PARTS OF THE SOUTHERN GREAT BASIN INTO SOUTHERN PLATEAU.

..KERR/DARROW.. 02/28/2014

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