444
FXUS02 KWBC 081815
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
115 PM EST MON FEB 08 2010
VALID 12Z THU FEB 11 2010 - 12Z MON FEB 15 2010
..SOUTHERN SNOW POSSIBLE THURSDAY THROUGH SATURDAY
TELECONNECTIONS WITH A STRONG POSITIVE ANOMALY IN THE MID-LEVELS
OVER NORTHEAST CANADA /BETWEEN 3 AND 4 STANDARD DEVIATIONS ABOVE
NORMAL/ FAVORS PROGRESSIVE CLOSED CYCLONES UNDER ITS BASE IN THE
LOWER 40S LATITUDE. THIS ALLOWS US TO DISCARD THE 00Z CANADIAN
WHICH LEAVES A CLOSED CYCLONE QUASI-STATIONARY IN THE NORTHERN
PLAINS/UPPER MIDWEST LATE IN THE PERIOD. SHORTWAVE ENERGY IN THE
SOUTHERN STREAM IS EXPECTED TO REMAIN PROGRESSIVE ACROSS THE
SOUTHERN TIER OF THE COUNTRY THROUGH THE FORESEEABLE FUTURE. DUE
TO THE PROGRESSION EXPECTED IN THE NORTHERN AND SOUTHERN STREAMS
AS WELL AS QUESTIONS REGARDING FUTURE INTERACTIONS BETWEEN THE TWO
STREAMS... CONFIDENCE IN THE FORECAST LATE THIS WEEKEND INTO EARLY
NEXT WEEK IS LOW IN ANY PARTICULAR PIECE OF DETERMINISTIC
GUIDANCE...WHICH IS LIKELY TO SHOW RUN-TO-RUN AND DAY-TO-DAY
DIFFERENCES REGARDING PROGRESSION AND PHASING. BOTH THE 06Z GEFS
MEAN AND 00Z ECMWF ENSEMBLE MEANS ARE IN REASONABLE AGREEMENT
THROUGH THE PERIOD. IN ORDER TO RESOLVE DETAIL ISSUES...CHOSE TO
COMPROMISE BETWEEN THE 00Z ECMWF AND 06Z GEFS MEAN
SOLUTIONS...WITH SOME MODIFICATIONS MADE PER 00Z MULTI-MODEL
ENSEMBLE LOW PRESSURE AREA CLUSTERING...SUCH AS THIS WEEKEND NEAR
FLORIDA AND LATE IN THE PERIOD IN THE GULF OF MEXICO.
DEEP CYCLONE MOVING BY THE PACIFIC NORTHWEST SATURDAY/SUNDAY...
A COMPROMISE OF THE 06Z GEFS MEAN/00Z ECMWF KEPT THIS SYSTEM
WITHIN THE MIDDLE OF THE ENSEMBLE SPREAD POSITION-WISE. HEAVY
PRECIPITATION IS EXPECTED WITH THE SYSTEM FROM WASHINGTON
STATE/THE OLYMPIC PENINSULA NORTHWARD TO VANCOUVER ISLAND. AT
THIS TIME...THE CASCADES ARE EXPECTED TO HAVE LESSER AMOUNTS...BUT
ONLY A SLIGHT SHIFT TO THE SOUTH WOULD BRING MUCH HEAVIER
PRECIPITATION INTO THE MOUNTAIN RANGE.
GREAT LAKES...
AS A STRONG AND DEEP CYCLONE MOVES OFFSHORE THE NORTHEAST AND
RETROGRADES INTO ATLANTIC CANADA...COLD AIR WITHIN THE CYCLONIC
FLOW ON ITS BACK/SOUTHWEST SIDE SETS THE STAGE FOR LAKE EFFECT
SNOWS THROUGH THE PERIOD.
SOUTHERN STREAM SYSTEM MOVING THROUGH FLORIDA FRIDAY...
THE ECMWF SHOWS A TWO DAY TREND TOWARDS SLOWING THIS SYSTEM
DOWN...AND ITS 00Z SOLUTION LIES WITHIN THE SOUTHERN PORTION OF
THE ENSEMBLE ENVELOPE. TO ACCOUNT FOR THE TREND...TOOK THE LOW ON
A SLOWER/MORE NORTHERLY PATH...WITHIN THE NORTHWEST SIDE OF THE
00Z MULTI-MODEL ENSEMBLE LOW ENVELOPE. THIS SYSTEM IS EXPECTED TO
BE QUITE WET ALONG THE GULF COAST AND FLORIDA...WITH STRONG
THUNDERSTORMS POSSIBLE ACROSS THE FLORIDA PENINSULA TO THE SOUTH
OF ITS TRACK AS THE LOW PASSES THROUGH. MEASURABLE SNOW IS
POSSIBLE WITHIN ITS NORTHERN PERIPHERY FROM TEXAS EASTWARD ACROSS
THE DEEP SOUTH INTO SOUTH CAROLINA FROM THURSDAY INTO SATURDAY AS
1000-500 HPA THICKNESS VALUES WITH THE PREFERRED MODEL BLEND ARE
ANTICIPATED TO BE BELOW 5400 METERS.
ROTH
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