Winter Part Deux
Posted by JAC on 1/23/2010, 9:23 pm
| 500mb Heights are building back up over Hudsun Bay. Hopefully, this won't create a big block like last month. However, looks to be getting back to colder temps for at least the next week.   EXTENDED FORECAST DISCUSSION NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD 305 PM EST SAT JAN 23 2010 VALID 12Z TUE JAN 26 2010 - 12Z SAT JAN 30 2010 WE ARE STILL SEEING A LARGE AREA OF OF HIGH LATITUDE BLOCKING FROM ALASKA ACROSS CANADA TO NWRN EUROPE IN CONJUNCTION WITH A NEGATIVE NAO. TWO CENTERS WITHIN THIS AREA WILL DOMINATE. AT THE BEGINNING OF THE PERIOD...A POSITIVE HEIGHT ANOMALY OVER NW CANADA WILL WEAKEN AND SLIDE SE...WHILE TREMENDOUS DEEPENING AND COOLING OCCURS BETWEEN THE GREAT LAKES AND HUDSON BAY. FARTHER E...A NEW STRONG POSITIVE ANOMALY CENTER DEVELOPING W OF THE BRITISH ISLES WILL BE DOMINANT. BOTH OF THESE ANOMALY CENTERS FAVOR BELOW NORMAL HEIGHTS OVER SE CANADA/THE NE CONUS AND COLD WEATHER OVER THAT PORTION OF NOAM. THE TRICKY PART OF THIS MEDIUM RANGE FORECAST WILL COME LATE NEXT WEEK...CONCERNING THE INTERACTION OF THE NEXT SRN STREAM SYS OVER THE SERN CONUS WITH NRN STREAM ENERGY. ENSEMBLE MEANS AND ENSEMBLE SPAGHETTI PLOTS SHOW RELATIVELY HIGH UNCERTAINTY FRI-SAT OVER THE ERN CONUS N OF ABOUT 37 DEGREES LATITUDE. UPSTREAM OVER THE ERN PACIFIC...PERSISTENT TROUGHING NEAR THE 145TH MERIDIAN WILL SUPPORT A MEAN WESTERN CONUS RIDGE EXTENDING N TOWARDS THE CANADIAN HEIGHT POSITIVE HEIGHT ANOMALY NEAR 55N/110W. MODELS/ENSEMBLES GENERALLY AGREE ON THIS IDEA. DETAIL-WISE...THE FINAL GRAPHICS STAYED WITH THE BLEND OF THE 00Z CANADIAN/00Z ECMWF USED IN THE PRELIM PROGS....WITH THE 12Z/23 CANADIAN SUPPORTING ITS 00Z COUNTERPART RATHER WELL. THE 12Z/23 DETERMINISTIC GFS IS QUITE CONSISTENT THRU DAY 6 WITH ITS EARLIER 00Z RUN...WHICH LEAVES IT STILL FASTER BY FRI DAY 6 WITH THE NEXT SRN STREAM SYS OVER THE SRN PORTIONS OF THE PLAINS AND MS VLY THAN OUR PREFERRED BLEND OF THE 00Z/23 CANADIAN AND ECMWF. THE NEW 12Z/23 CANADIAN IS ALSO QUITE CONSISTENT WITH ITS PRIOR 00Z CONTINUITY BUT HAS TRENDED A BIT FASTER...TOWARDS THE GFS...WITH THE SRN STREAM SYS APPROACHING THE LOWER MS VLY BY FRI DAY 6. WHILE THE 12Z/23 UKMET HAS DECENT CONTINUITY THRU DAY 6 WITH THE FIRST SRN STREAM SYS MOVING ACROSS THE SWRN BORDER STATES...IT MAKES A HUGE CHANGE FROM ITS 00Z CONTINUITY FOR FRI BY DAY 6 IN PULLING THE POLAR VORTEX OVER FAR ERN CANADA BACK TOWARDS HUDSON BAY. THIS HAS THE EFFECT OF MAKING THE PATTERN OVER THE GREAT LAKES AND NEW ENG CONSIDERABLY WARMER AT THAT TIME. THE NEW 12Z/23 ECMWF HAS ALSO TRENDED SW WITH THE CANADIAN VORTEX BY THU EVE....AND HAS A WARMER LOOK OVER THE NERN CONUS THAN ITS 00Z CONTINUITY. WE THINK THAT THE UKMET/ECMWF WARMING HERE IS OVERDONE AND WILL ACCEPT ONLY A SLIGHTLY WARMER SCENARIO THAN CONTINUITY. CONCERNING THE SRN STREAM SYS...THE 12Z/23 ECMWF SHEARS IT APART FRI/SAT DAYS 6-7 IN A COMPLEX INTERACTION WITH NRN STREAM ENERGY...A LOW CONFIDENCE PROPOSITION AT BEST. IN OUR FINALS...WE ARE STAYED WITH 00Z ECMWF AND 00Z/12Z CANADIAN SCENARIO. THERE IS STILL LOTS OF UNCERTAINTY OVER THE SERN STATES TOWARDS THE END OF NEXT WEEK. AS THE FIRST SRN STREAM SYS REACHES THE SERN STATES SAT IT MAY SUPPORT A LOW MAY MOVING ACROSS THE GULF STATES TOWARDS THE S ATLANTIC COAST NEXT WEEKEND. THIS SYSTEM COULD BRING SNOWS TO THE MID-ATLANTIC STATES AND NEW ENGLAND....DEPENDING ON ITS EXACT TRACK. THE CANADIAN/ECMWF ALSO SHOW DECENT AGREEMENT ON THE SECOND SRN STREAM SYS APPROACHING CA NEXT WEEKEND. FLOOD |
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