Just posted by Paul Kocin at HPC :
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1058 AM EST TUE DEC 31 2013
VALID 12Z FRI JAN 03 2014 - 12Z TUE JAN 07 2014
A VERY WINTRY SCENARIO IN THE EAST STARTS OFF THE MEDIUM RANGE
FORECAST WITH A QUICK WARM UP IN THE CENTER OF THE COUNTRY. THE
WARM UP IS SHORT LIVED AS A NEW AND SIGNIFICANT OUTBREAK OF COLDER
AIR BEGINS TO ENTER THE NORTHERN ROCKIES AND PLAINS BY DAY
4/SATURDAY AND PROGRESSES EASTWARD BY SUNDAY DAY 5. WITH LARGE
UNCERTAIN IT STILL APPEARS THAT SOME FORM OF PRECIPITATION EVENT
WILL FORM IN ASSOCIATION WITH THIS NEXT OUTBREAK OF COLD AIR ON
DAY 5 INTO DAY 6/MONDAY...WITH A HUGE RANGE OF SOLUTIONS FROM A
FRONTAL PASSAGE TO A MAJOR CYCLONE. BY DAY 7/TUESDAY...MUCH OF
THE CENTRAL AND EASTERN US IS UNDER THE INFLUENCE OF BELOW TO MUCH
BELOW NORMAL TEMPERATURES.
A CUTOFF UPPER RIDGE OVER GREENLAND/NORTHEAST CANADA WILL HELP
RETAIN AN UPPER LOW OVER SOUTHEASTERN CANADA THAT CONTINUES TO
FORCE A TROUGH MOVING TOWARD THE EASTERN US TO REMAIN ON A PATH
CONDUCIVE TO SNOW OVER PORTIONS OF THE NORTHEAST US ON DAY 3.
WHILE THE DETAILS OF THE TROUGH EVOLUTION SEEM FAIRLY
STRAIGHTFORWARD DURING THE BEGINNING OF THE MEDIUM RANGE PERIOD
FOR THE ENSEMBLE MEANS AND THE EVOLUTION OF A COLD CANADIAN HIGH
BUILDING EASTWARD ACROSS SOUTHEASTERN CANADA ARE ALSO
STRAIGHTFORWARD...THE DETAILS OF THE ACTUAL TROUGH EVOLUTION AND
RESULTING SURFACE BAROCLINIC STRUCTURE REMAINS COMPLEX.
SIGNIFICANT MODEL SPREAD DUE TO THE LIKELIHOOD OF SEVERAL CENTERS
OF LOW PRESSURE OF VARYING STRENGTH COMING TOGETHER TO EVENTUALLY
FORM A CYCLONE OVER THE WESTERN ATLANTIC CONTINUES TO MAKE THIS A
CHALLENGING FORECAST EVEN AT THE START OF THE MEDIUM RANGE. IN
GENERAL...CONTINUITY FROM THE OVERNIGHT FORECAST IS MAINTAINED
BASED ON THE CONSISTENCY OF THE ECMWF ENSEMBLE MEANS WITH INPUT
FROM THE 00Z ECMWF AND 06Z GFS...BOTH OF WHICH MAINTAIN A SIMILAR
SPEED AND AMPLITUDE OF THE TROUGH NEARING THE EAST COAST. WITH THE
MAIN TROUGH NEARING THE EAST COAST BY FRIDAY MORNING...A MULTIPLE
CENTER SURFACE SYSTEM IS STILL EXPECTED WITH THE REMAINING
QUESTION BEING HOW INTENSE THE WESTERNMOST SURFACE LOW RESPONDS TO
THE UPPER LEVEL TROUGH WHILE OTHER SURFACE CENTER OR CENTERS SCOOT
FARTHER EASTWARD. IN ANY EVENT...WHATEVER SNOW IS FALLING ON
FRIDAY MORNING SHOULD BE MOVING EASTWARD OUT TO SEA DURING THE DAY
AS THE SYSTEM CONTINUES EASTWARD.
WITH A MEAN UPPER RIDGE TRENDING TO BUILD OVER THE EASTERN PACIFIC
FROM THE SHORT RANGE INTO THE MEDIUM RANGE...SEVERAL SHORTWAVE
SYSTEMS WILL BEGIN TO PROGRESS SOUTH AND EASTWARD OVER WESTERN
CANADA WHILE ANOTHER LARGE UPPER LOW OVER NW CANADA ALSO BEGINS TO
MOVE SOUTH AND EASTWARD AS WELL. BY DAY 5...ANOTHER LARGE VORTEX
WILL BE FOUND ACROSS SOUTH CENTRAL CANADA WITH A HUGE MASS OF
ARCTIC AIR POISED TO MOVE SOUTH AND EASTWARD ACROSS MUCH OF THE
CENTRAL AND EASTERN US. SIGNIFICANT DIFFERENCES ALSO CHARACTERIZE
THIS DEVELOPMENT WITH THE ECMWF ENSEMBLE MEANS SHOWING THE LARGEST
AMPLITUDE AND GREATER SOUTHWARD PUSH OF THE ARCTIC AIR WITH
GFS/NAEFS ENSEMBLE MEANS SHOWING A SLIGHTLY FLATTER
SCENARIO...ESPECIALLY BY DAY 6. WHILE THE 00Z ECMWF CREATES A
POTENTIALLY HISTORIC SCENARIO BY DAY 6...IT REMAINS A VERY LOW
PROBABILITY SOLUTION AS IT REMAINS MUCH MORE AMPLIFIED THAN THE
CORRESPONDING ECMWF ENSEMBLE MEAN SOLUTION. THE 06Z GFS ACTUALLY
LOOKS MORE LIKE THE 00Z ECMWF ENSEMBLE MEAN SOLUTION AND IS
SOMEWHAT FOLLOWED WHILE STILL SHOWING A VERY LARGE COLD OUTBREAK
MOVING INTO THE CENTRAL AND EASTERN US ON DAYS 6 INTO 7...WITH THE
DETAILS OF HOW LOW PRESSURE AT THE SURFACE ULTIMATELY DEVELOPING
ALONG THE LEADING EDGE OF THE COLD AIR STILL VERY MUCH UNCERTAIN
AT THIS POINT WITH A VERY MODEST SYSTEM SHOWN AT THE PRESENT TIME
BUT WILL LIKELY CHANGE SIGNIFICANTLY AS THE DAYS GET CLOSER.
CHANCES ARE THAT THIS NEXT SYSTEM WILL LIKELY ALSO BE A
SIGNIFICANT WINTER WEATHER EVENT SOMEWHERE FROM THE TENNESSEE AND
OHIO VALLEYS EASTWARD INTO THE NORTHEAST.
KOCIN
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1058 AM EST TUE DEC 31 2013
VALID 12Z FRI JAN 03 2014 - 12Z TUE JAN 07 2014
A VERY WINTRY SCENARIO IN THE EAST STARTS OFF THE MEDIUM RANGE
FORECAST WITH A QUICK WARM UP IN THE CENTER OF THE COUNTRY. THE
WARM UP IS SHORT LIVED AS A NEW AND SIGNIFICANT OUTBREAK OF COLDER
AIR BEGINS TO ENTER THE NORTHERN ROCKIES AND PLAINS BY DAY
4/SATURDAY AND PROGRESSES EASTWARD BY SUNDAY DAY 5. WITH LARGE
UNCERTAIN IT STILL APPEARS THAT SOME FORM OF PRECIPITATION EVENT
WILL FORM IN ASSOCIATION WITH THIS NEXT OUTBREAK OF COLD AIR ON
DAY 5 INTO DAY 6/MONDAY...WITH A HUGE RANGE OF SOLUTIONS FROM A
FRONTAL PASSAGE TO A MAJOR CYCLONE. BY DAY 7/TUESDAY...MUCH OF
THE CENTRAL AND EASTERN US IS UNDER THE INFLUENCE OF BELOW TO MUCH
BELOW NORMAL TEMPERATURES.
A CUTOFF UPPER RIDGE OVER GREENLAND/NORTHEAST CANADA WILL HELP
RETAIN AN UPPER LOW OVER SOUTHEASTERN CANADA THAT CONTINUES TO
FORCE A TROUGH MOVING TOWARD THE EASTERN US TO REMAIN ON A PATH
CONDUCIVE TO SNOW OVER PORTIONS OF THE NORTHEAST US ON DAY 3.
WHILE THE DETAILS OF THE TROUGH EVOLUTION SEEM FAIRLY
STRAIGHTFORWARD DURING THE BEGINNING OF THE MEDIUM RANGE PERIOD
FOR THE ENSEMBLE MEANS AND THE EVOLUTION OF A COLD CANADIAN HIGH
BUILDING EASTWARD ACROSS SOUTHEASTERN CANADA ARE ALSO
STRAIGHTFORWARD...THE DETAILS OF THE ACTUAL TROUGH EVOLUTION AND
RESULTING SURFACE BAROCLINIC STRUCTURE REMAINS COMPLEX.
SIGNIFICANT MODEL SPREAD DUE TO THE LIKELIHOOD OF SEVERAL CENTERS
OF LOW PRESSURE OF VARYING STRENGTH COMING TOGETHER TO EVENTUALLY
FORM A CYCLONE OVER THE WESTERN ATLANTIC CONTINUES TO MAKE THIS A
CHALLENGING FORECAST EVEN AT THE START OF THE MEDIUM RANGE. IN
GENERAL...CONTINUITY FROM THE OVERNIGHT FORECAST IS MAINTAINED
BASED ON THE CONSISTENCY OF THE ECMWF ENSEMBLE MEANS WITH INPUT
FROM THE 00Z ECMWF AND 06Z GFS...BOTH OF WHICH MAINTAIN A SIMILAR
SPEED AND AMPLITUDE OF THE TROUGH NEARING THE EAST COAST. WITH THE
MAIN TROUGH NEARING THE EAST COAST BY FRIDAY MORNING...A MULTIPLE
CENTER SURFACE SYSTEM IS STILL EXPECTED WITH THE REMAINING
QUESTION BEING HOW INTENSE THE WESTERNMOST SURFACE LOW RESPONDS TO
THE UPPER LEVEL TROUGH WHILE OTHER SURFACE CENTER OR CENTERS SCOOT
FARTHER EASTWARD. IN ANY EVENT...WHATEVER SNOW IS FALLING ON
FRIDAY MORNING SHOULD BE MOVING EASTWARD OUT TO SEA DURING THE DAY
AS THE SYSTEM CONTINUES EASTWARD.
WITH A MEAN UPPER RIDGE TRENDING TO BUILD OVER THE EASTERN PACIFIC
FROM THE SHORT RANGE INTO THE MEDIUM RANGE...SEVERAL SHORTWAVE
SYSTEMS WILL BEGIN TO PROGRESS SOUTH AND EASTWARD OVER WESTERN
CANADA WHILE ANOTHER LARGE UPPER LOW OVER NW CANADA ALSO BEGINS TO
MOVE SOUTH AND EASTWARD AS WELL. BY DAY 5...ANOTHER LARGE VORTEX
WILL BE FOUND ACROSS SOUTH CENTRAL CANADA WITH A HUGE MASS OF
ARCTIC AIR POISED TO MOVE SOUTH AND EASTWARD ACROSS MUCH OF THE
CENTRAL AND EASTERN US. SIGNIFICANT DIFFERENCES ALSO CHARACTERIZE
THIS DEVELOPMENT WITH THE ECMWF ENSEMBLE MEANS SHOWING THE LARGEST
AMPLITUDE AND GREATER SOUTHWARD PUSH OF THE ARCTIC AIR WITH
GFS/NAEFS ENSEMBLE MEANS SHOWING A SLIGHTLY FLATTER
SCENARIO...ESPECIALLY BY DAY 6. WHILE THE 00Z ECMWF CREATES A
POTENTIALLY HISTORIC SCENARIO BY DAY 6...IT REMAINS A VERY LOW
PROBABILITY SOLUTION AS IT REMAINS MUCH MORE AMPLIFIED THAN THE
CORRESPONDING ECMWF ENSEMBLE MEAN SOLUTION. THE 06Z GFS ACTUALLY
LOOKS MORE LIKE THE 00Z ECMWF ENSEMBLE MEAN SOLUTION AND IS
SOMEWHAT FOLLOWED WHILE STILL SHOWING A VERY LARGE COLD OUTBREAK
MOVING INTO THE CENTRAL AND EASTERN US ON DAYS 6 INTO 7...WITH THE
DETAILS OF HOW LOW PRESSURE AT THE SURFACE ULTIMATELY DEVELOPING
ALONG THE LEADING EDGE OF THE COLD AIR STILL VERY MUCH UNCERTAIN
AT THIS POINT WITH A VERY MODEST SYSTEM SHOWN AT THE PRESENT TIME
BUT WILL LIKELY CHANGE SIGNIFICANTLY AS THE DAYS GET CLOSER.
CHANCES ARE THAT THIS NEXT SYSTEM WILL LIKELY ALSO BE A
SIGNIFICANT WINTER WEATHER EVENT SOMEWHERE FROM THE TENNESSEE AND
OHIO VALLEYS EASTWARD INTO THE NORTHEAST.
KOCIN
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