Severe Storm Outlook Narrative (AC)
Issued by NWS

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ACUS01 KWNS 251253
SWODY1
SPC AC 251252

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0652 AM CST THU DEC 25 2014

VALID 251300Z - 261200Z

...NO TSTM AREAS FORECAST...

...SUMMARY...
THUNDERSTORMS WILL BE UNLIKELY TODAY AND TONIGHT.

...SYNOPSIS...
RECENT MOISTURE-CHANNEL IMAGERY DETECTS A MID-LEVEL SHORTWAVE TROUGH
CONTINUING TO DIG OVER THE GREAT BASIN. THIS FEATURE WILL FURTHER
AMPLIFY WHILE MAKING SLIGHT NET EWD PROGRESS...AS AN EMBEDDED LOW
CLOSES OFF NEAR THE FOUR CORNERS. AS THIS OCCURS...A STREAM OF
STRENGTHENING MID-LEVEL SWLYS WILL BRANCH NEWD FROM THE BASE OF THE
TROUGH -- FROM SERN AZ TO THE GREAT LAKES. MEANWHILE...A COMPACT
MID-LEVEL CYCLONE WILL CONTINUE ADVANCING NWD THROUGH QUEBEC WHILE
DECELERATING ALONG ITS TRAJECTORY...AS AN ARCING VORTICITY BANNER
TRAILING S OF THE CYCLONE MOVES OFF THE ATLANTIC COAST. THE SFC
FRONT RELATED TO THIS CYCLONE AND RELATED VORTICITY FIELD ALOFT HAS
ALREADY MOVED OFFSHORE -- EXCEPT FOR THE NEW ENGLAND COAST...WHICH
WILL BE CLEARED BY THIS BOUNDARY BY MID DAY. CONTINENTAL AIR WILL BE
PREVALENT ACROSS MOST OF THE CONUS IN THE WAKE OF THIS FRONT...WHILE
A REINFORCING COLD FRONT ADVANCES SWD/SEWD ACROSS THE PLAINS IN
ASSOCIATION WITH A MIGRATORY...NRN-STREAM IMPULSE NEAR THE CNTRL
CANADIAN BORDER.

...PORTIONS OF THE CNTRL GREAT BASIN TO SOUTHEAST ARIZONA...
COOLING MID-LEVEL TEMPERATURES ASSOCIATED WITH THE AFOREMENTIONED
DIGGING TROUGH WILL OVERLIE A DIURNALLY HEATED BOUNDARY LAYER TO
RESULT IN SCANT...ALBEIT NON-ZERO...BUOYANCY ACROSS PORTIONS OF THE
AREA THIS AFTERNOON. DIURNALLY ENHANCED OROGRAPHIC CIRCULATIONS MAY
BREED SHALLOW CONVECTION FROM THE FOUR CORNERS AREA WWD AND
NWWD...AND AN ISOLATED LIGHTNING STRIKE OR TWO CANNOT BE ENTIRELY
RULED OUT. HOWEVER...A DEARTH OF TROPOSPHERIC MOISTURE WILL LIKELY
PROVE DETRIMENTAL FOR SUBSTANTIAL PRECIPITATION GROWTH /
BUOYANCY...TO GREATLY STUNT OPPORTUNITIES FOR CHARGE SEPARATION AND
THUNDERSTORMS.

FARTHER SOUTH -- ACROSS SOUTHEAST ARIZONA -- THE RISK FOR A
THUNDERSTORM OR TWO MAY BE RELATIVELY HIGHER...YET STILL NOT
SUFFICIENTLY HIGH FOR GENERAL-THUNDERSTORM DESIGNATION. DEEP SWLYS
ACCOMPANYING THE DIGGING TROUGH MAY INTERACT WITH A RIBBON OF
MODESTLY ENHANCED PW CURRENTLY DETECTED NEAR/OFF THE COAST OF SRN CA
PER GPS PW DATA AND THE 12Z MIRAMAR /CA/ RAOB -- E.G. PW VALUES OF
0.5-0.8 INCH. AS SIMILAR MOISTURE IS ADVECTED INLAND...A
NE/SW-ORIENTED BAND OF HIGH-BASED CONVECTION COULD DEVELOP NEAR/W OF
THE TUCSON METRO AREA BY LATE AFTERNOON AND SPREAD EWD ACROSS SERN
AZ INTO THE EVENING. SUBSEQUENT OUTLOOKS WILL RE-EVALUATE THE
POSSIBLE NEED FOR GENERAL-THUNDER DELINEATION...THOUGH THE 12Z RAOB
TAKEN AT TUCSON PORTRAYS A SUBSTANTIAL PAUCITY OF ANTECEDENT
LOW/MID-LEVEL MOISTURE. THIS CASTS DOUBT ON THE OVERALL PROSPECTS
FOR LATER-DAY CONVECTIVE DESTABILIZATION AND THUNDERSTORM
POTENTIAL...SUCH THAT GENERAL-THUNDERSTORM DELINEATION HAS NOT BEEN
INCLUDED AT THIS TIME.

...COASTAL MIAMI-DADE COUNTY IN SOUTH FLORIDA AND THE FLORIDA
KEYS...
SFC OBSERVATIONS AND RADAR IMAGERY INDICATE THAT THE LEADING EDGE OF
COOLER/DRIER AIR HAS MOVED OFFSHORE. A NARROW BAND OF SHALLOW
CONVECTION ALIGNING WITH THIS LEADING EDGE HAS RECENTLY MOVED E OF
BISCAYNE BAY AND EXTENDS S TO THE COASTAL WATERS E OF THE UPPER
FLORIDA KEYS AND FARTHER S INTO THE STRAITS OF FLORIDA. BEHIND THE
CORRESPONDING FRONT...THE INFLUX OF CONTINENTAL TRAJECTORIES WILL BE
RESPONSIBLE FOR THE EROSION OF ANY RESIDUAL ELEVATED BUOYANCY WHILE
DEEP-LAYER ASCENT WEAKENS. AS SUCH...THE RISK FOR THUNDERSTORMS HAS
DIMINISHED.

..COHEN/EDWARDS.. 12/25/2014




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