DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 221245
SWODY1
SPC AC 221243

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0643 AM CST SAT DEC 22 2012

VALID 221300Z - 231200Z

...NO SVR TSTM AREAS FORECAST...

...SYNOPSIS...

A MID TO UPPER-LEVEL LOW CENTERED NEAR 53N/-137W AS OF 12Z WILL
RETROGRADE NWWD THROUGH THE GULF OF AK WITH A SERIES OF VORTICITY
MAXIMA PIVOTING THROUGH THE BASE OF THE PARENT SYSTEM ONTO THE
PACIFIC NW AND NRN CA COASTS. DOWNSTREAM...BROAD RIDGING FROM THE
ROCKIES THROUGH MS RIVER VALLEY WILL FLATTEN IN RESPONSE TO THE NEWD
PROGRESSION OF THE INTENSE SYNOPTIC SYSTEM CURRENTLY OVER THE NERN
STATES...AND THE TRANSLATION OF VORTICITY MAXIMA FROM THE PACIFIC
COAST THROUGH THE INTERMOUNTAIN WEST.

...PACIFIC NW AND NRN/CNTRL CA COASTS INTO THE SACRAMENTO VALLEY OF
NRN CA...

EARLY MORNING RADAR IMAGERY AND LIGHTNING DATA INDICATE THE ONSHORE
MOVEMENT OF AT LEAST TWO DISTINCT FORCED CONVECTIVE BANDS WITH
LIGHTNING...ONE NEAR SFO AND THE OTHER NEAR/NW OF UKI. THIS
ACTIVITY IS ASSOCIATED WITH DCVA/HEIGHT FALLS ATTENDANT TO A STRONG
VORTICITY MAXIMUM CURRENTLY MOVING ONTO THE ORE AND NRN CA COASTS.
A TRAILING VORTICITY LOBE IS EXPECTED TO MOVE ONTO THE NRN CA COAST
/INVOF SFO/ LATER TODAY...WHILE ANOTHER PERTURBATION REACHES THE
ORE/WA COASTS IN THE 23/06Z-12Z TIME FRAME.

MOIST...ONSHORE FLOW IN THE LOW LEVELS WILL ALIGN WITH 500-MB
TEMPERATURES GENERALLY COLDER THAN -25C TO FOSTER STEEP MIDLEVEL
LAPSE RATES AND WEAK CONVECTIVE INSTABILITY. BURSTS OF LIGHTNING
WILL BE POSSIBLE ALONG THE COAST AND OVER THE IMMEDIATE OFFSHORE
WATERS...ESPECIALLY AHEAD OF THE ABOVE-MENTIONED VORTICITY MAXIMA
WHERE DEEP-LAYER ASCENT IS ENHANCED.

ADDITIONALLY...LOW-TOPPED STORMS WILL BE POSSIBLE IN THE SACRAMENTO
VALLEY THIS AFTERNOON AND EVENING. HERE...OROGRAPHICALLY CHANNELED
FLOW WILL YIELD A WIND PROFILE SUPPORTIVE OF WEAK UPDRAFT ROTATION.
WHILE SOME SMALL HAIL IS POSSIBLE WITH STRONGER UPDRAFTS...THE
MARGINAL INSTABILITY IS EXPECTED TO LIMIT THE POTENTIAL FOR SEVERE
STORMS.

..MEAD/LEITMAN.. 12/22/2012

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