Severe Storm Outlook Narrative (AC)
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11
000
ACUS48 KWNS 180952
SWOD48
SPC AC 180950

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0350 AM CST THU DEC 18 2014

VALID 211200Z - 261200Z

...DISCUSSION...
THE AMPLIFICATION OF SHORT WAVE PERTURBATIONS WITHIN AN INITIALLY
ZONAL...INTENSE MID-LATITUDE PACIFIC JET STILL APPEARS LIKELY TO
LEAD TO THE TRANSITION TO A BLOCKIER REGIME ACROSS THE CENTRAL AND
EASTERN PACIFIC.  HOWEVER...THE SPREAD OF POSSIBLE SOLUTIONS EVIDENT
IN THE MEDIUM RANGE MODELS AND MODEL ENSEMBLES REMAINS LARGE...AND
THE IMPACTS ON THE DOWNSTREAM PATTERN EVOLUTION ACROSS NORTH AMERICA
LATE THIS WEEKEND THROUGH THE CHRISTMAS HOLIDAY IS UNCLEAR.

ONE DEVELOPMENT IN WHICH CONFIDENCE CONTINUES TO GROW IS
AMPLIFICATION OF LARGE-SCALE UPPER RIDGING NEAR THE PACIFIC COAST
THIS WEEKEND...WHICH COULD PERSIST INTO EARLY NEXT WEEK...FOLLOWED
BY LARGE-SCALE UPPER TROUGH AMPLIFICATION OVER THE
PLAINS/MISSISSIPPI VALLEY INTO THE EASTERN U.S. BY THE MIDDLE OF
NEXT WEEK.  THIS PROBABLY WILL BE ACCOMPANIED BY STRONG SURFACE
CYCLOGENESIS...WHICH COULD OCCUR IN TWO STAGES...ONE ACROSS THE
NORTHERN PLAINS AND UPPER MISSISSIPPI VALLEY INTO THE GREAT LAKES
REGION...THE OTHER ACROSS THE CENTRAL/EASTERN GULF COAST...THEN UP
THE ATLANTIC SEABOARD TO THE LEE OF THE APPALACHIANS.  IT REMAINS
UNCLEAR WHICH WILL BE MOST PROMINENT.  IF IT IS THE LATTER...THERE
WOULD SEEM TO BE AT LEAST SOME POTENTIAL FOR ORGANIZED SEVERE STORM
DEVELOPMENT ACROSS THE EASTERN GULF STATES AND SOUTHERN/MID ATLANTIC
COAST STATES LATE NEXT TUESDAY THROUGH CHRISTMAS EVE.  BUT THE
POTENTIAL FOR SUBSTANTIVE BOUNDARY LAYER MOISTURE RETURN OFF THE
EASTERN GULF OF MEXICO AND WESTERN ATLANTIC ALSO REMAINS UNCLEAR AT
THE PRESENT TIME.

GIVEN THE PREDICTABILITY ISSUES ASSOCIATED WITH THE PATTERN
EVOLUTION AND THE EXTENDED /DAY 6-7/ TIME FRAME...AMONG OTHER
UNCERTAINTIES...SEVERE WEATHER PROBABILITIES STILL SEEM TO REMAIN
BELOW THE MINIMUM 15% THRESHOLD THROUGH THE PERIOD.

..KERR.. 12/18/2014


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.