DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 290503
SWODY1
SPC AC 290500

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1200 AM CDT SUN SEP 29 2013

VALID 291200Z - 301200Z

...NO SVR TSTM AREAS FORECAST...

...SYNOPSIS...
A STRONG...GENERALLY ZONAL...MID LATITUDE JET STREAK APPEARS LIKELY
TO CONTINUE MIGRATING INLAND OFF THE NORTHEASTERN PACIFIC...THROUGH
THE PACIFIC NORTHWEST...NORTHERN INTERMOUNTAIN REGION...NORTHERN
ROCKIES...AND NORTHERN PLAINS BY LATE TONIGHT. ONE SIGNIFICANT
SHORT WAVE IMPULSE EMBEDDED WITHIN THIS REGIME IS FORECAST TO
CONTINUE INLAND AND TURN EAST NORTHEAST OF THE CANADIAN AND NORTHERN
U.S. ROCKIES...INTO SASKATCHEWAN/MANITOBA BY THE END OF THE
PERIOD...WHILE ANOTHER STRONG IMPULSE PROGRESSES INLAND ACROSS THE
SOUTHERN BRITISH COLUMBIA/PACIFIC NORTHWEST COAST THIS EVENING.

AT THE SAME TIME...A SIGNIFICANT PRECEDING SHORT WAVE TROUGH IS
EXPECTED TO ACCELERATE EAST NORTHEASTWARD THROUGH THE EASTERN
CANADIAN PROVINCES. AND...AS THIS OCCURS...A BLOCKING PATTERN NEAR
THE ATLANTIC SEABOARD OF THE U.S. WILL BEGIN TO WEAKEN. WHILE AN
ASSOCIATED HIGH CENTER SHIFTS EAST OF NORTHERN NEW ENGLAND...A BROAD
LOW TO THE SOUTH MAY BEGIN SHIFT SLOWLY NORTHEASTWARD...AWAY FROM
SOUTH ATLANTIC COAST AREAS.

IN RESPONSE TO THESE DEVELOPMENTS...A STABLE AIR MASS SHOULD REMAIN
ENTRENCHED ACROSS MUCH OF THE ATLANTIC SEABOARD...WHILE A WEAKENING
COLD FRONT ASSOCIATED WITH THE LEAD SHORT WAVE IMPULSE STALLS AND
WEAKENS ACROSS THE LOWER GREAT LAKES THROUGH LOWER OHIO VALLEY AND
WESTERN GULF COAST REGION. SEASONABLY HIGH MOISTURE CONTENT AIR
WILL LINGER WITHIN A CORRIDOR ALONG AND AHEAD OF THE SOUTHERN
PORTION OF THE FRONT...WHERE WEAK DESTABILIZATION WITH DAYTIME
HEATING WILL CONTRIBUTE TO A RISK FOR THUNDERSTORM ACTIVITY TODAY.
ELSEWHERE TO THE EAST OF THE ROCKIES...CONVECTIVE POTENTIAL APPEARS
NEGLIGIBLE. MEANWHILE...ACROSS THE WEST...GENERALLY DRY CONDITIONS
WILL ALSO CONTRIBUTE TO LOW CONVECTIVE POTENTIAL ACROSS MOST
AREAS...WITH THE POSSIBLE EXCEPTION OF THE PACIFIC NORTHWEST COAST.

...PACIFIC NORTHWEST COAST...
THE RISK FOR THUNDERSTORM ACTIVITY WITH A FRONTAL BAND ADVANCING
INLAND AFTER 30/00Z APPEARS VERY LOW BASED ON FORECAST SOUNDINGS.
HOWEVER...MODELS SUGGEST THAT MID-LEVEL COOLING WITH THE ASSOCIATED
UPPER IMPULSE WILL BE STRONGER THAN THE PRIOR SYSTEM...WHICH MAY
RESULT IN MORE SUBSTANTIVE CAPE WITHIN THE MOIST POST-FRONTAL
ONSHORE FLOW OVERNIGHT. GIVEN THE FORECAST STRENGTH OF THIS
REGIME...WITH MEAN WINDS IN THE LOWEST FEW KILOMETERS ON THE ORDER
OF 50+ KT...LOCALIZED CONVECTIVELY ENHANCED GUSTS EXCEEDING SEVERE
LIMITS MAY OCCUR EVEN WITH WEAK THUNDERSTORM ACTIVITY.

..KERR/LEITMAN.. 09/29/2013

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