Quantitative Precipitation Forecast
Issued by NWS

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
000
FOUS11 KWBC 022056
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
355 PM EST MON MAR 02 2015

VALID 00Z TUE MAR 03 2015 - 00Z FRI MAR 06 2015


DAYS 1 THROUGH 2...


...ROCKY MOUNTAINS...

A COMPLEX SERIES OF UPPER TROUGHS INCLUDING ONE LIFTING
NORTHEASTWARD ACROSS THE MOUNTAINS TONIGHT INTO TUESDAY WHILE A
SEPARATE TROUGH BRIEFLY CUTS OFF JUST OFF THE SOUTHERN CALIFORNIA
COAST WILL SHIFT EASTWARD ON TUESDAY AND WEDNESDAY AS A LONGWAVE
RIDGE MOVES ACROSS THE WEST COAST. THE COMBINATION OF THESE TWO
SYSTEMS IN CONCERT WITH AN OUTBREAK OF MUCH COLDER AIR MOVING
SOUTHEASTWARD ALONG THE LESS SLOPES OF THE ROCKIES WILL PROVIDE
SEVERAL MECHANISMS FOR A FAIRLY WIDESPREAD SNOW EVENT EXTENDING
THE LENGTH OF THE ROCKIES. SINCE THIS IS PRIMARILY A DAY 1
EVENT...THERE WAS RELATIVELY GOOD MODEL AGREEMENT WITH MESOSCALE
DETAILS PROVIDED BY THE 12Z NAM/09Z SREF MEANS.  HEAVIEST SNOWS
EXCEEDING 8 TO 12 INCHES WAS FAIRLY COMMON FROM CENTRAL AND
SOUTHERN WYOMING ACROSS THE COLORADO ROCKIES WITH THE HIGHEST
PEAKS EXPECTING AN ADDITIONAL FOOT OR GREATER SNOWFALL.


...NORTHERN PLAINS/MIDWEST/OHIO VALLEY/APPALACHIANS/NORTHEAST...

THE INITIAL TROUGH LIFTING NORTHEASTWARD FROM THE SOUTHWESTERN
UPPER TROUGH WILL COMBINE WITH A NORTHERN STREAM SYSTEM DROPPING
SOUTHEASTWARD FROM NORTHERN CANADA AND PRODUCE A FAIRLY WIDESPREAD
AREA OF SNOW/SLEET AND FREEZING RAIN FROM THE NORTHERN PLAINS
ACROSS THE MIDWEST/OHIO VALLEY/APPALACHIANS AND NORTHEAST. AS AN
AREA OF COLD HIGH PRESSURE AGAIN DRIFTS EASTWARD OFF THE EAST
COAST...GENERALLY LIGHT FREEZING RAIN WILL OCCUR IN ITS WAKE FROM
THE MID MISSISSIPPI VALLEY ACROSS THE OHIO VALLEY/APPALACHIANS AND
THE MID ATLANTIC STATES ON DAY 1/TUESDAY.  FARTHER NORTH...MOSTLY
MODERATE SNOW WILL FALL FROM THE NORTHERN PLAINS ACROSS THE UPPER
MIDWEST. BY DAY 2/TUESDAY NIGHT INTO WEDNESDAY...THE SNOW WILL
MOVE ACROSS NORTHERN NEW YORK INTO NEW ENGLAND WHERE THERE IS A
MODEST CHANCE FOR 4 INCHES OR GREATER FOR CENTRAL TO NORTHERN NEW
ENGLAND.  FARTHER SOUTH...FREEZING RAIN WILL QUICKLY CHANGE TO
RAIN.

DAYS 2 TO 3...


...SOUTHERN PLAINS/LOWER AND MID MISSISSIPPI VALLEY/OHIO
VALLEY/MID ATLANTIC STATES AND NEW ENGLAND...

ALL OF THE SHORTWAVE ENERGY OUT WEST WILL FINALLY PUSH EASTWARD AS
THE MAIN TROUGH IN THE NORTHERN STREAM COMBINES WITH THE REMAINING
SOUTHERN STREAM TROUGH LIFTING EASTWARD FROM THE SOUTHWEST US.
WITH A RATHER HIGH AMPLITUDE RIDGE OVER THE GULF COAST...THE
LIFTING SHORTWAVE SYSTEMS PROGRESS EASTWARD IN A MANNER THAT
GENERATES AN IMPRESSIVE AMPLIFYING UPPER JET OVER THE NORTHERN US.
 THE ENTRANCE REGION OF THIS JET IS ASSOCIATED WITH A WIDESPREAD
OUTBREAK OF PRECIPITATION MUCH OF WHICH WILL FALL BEHIND AN
ADVANCING COLD FRONT.  THE FRONT WILL MAKE ITS WAY SLOWLY SOUTH
AND EASTWARD WITH A WIDESPREAD AREA OF RAIN CHANGING TO FREEZING
RAIN/SLEET AND THEN SNOW.

ONE OF THE MORE DIFFICULT ASPECTS OF THIS FORECAST IS DETERMINING
HOW MUCH OF THE QPF FALLS AS FREEZING RAIN VS SLEET AND THEN HOW
QUICKLY IT CHANGES TO SNOW.  IN GENERAL...THE OPERATIONAL GFS
MODEL HAD BEEN MORE SUPPRESSED THAN THE OTHER OPERATIONAL RUNS BUT
TODAYS 12Z GFS FINALLY MOVED TOWARD THE LESS SUPPRESSED
MODELS...INCLUDING THE ECMWF AND THE UKMET/CANADIAN.  THE NAM MAY
HAVE BEEN FARTHER NORTH THAN THE OTHER MODELS BUT ALSO SEEMED TO
COME UNDER ALIGNMENT.

TO THE NORTH WHERE MOST OF THE PRECIPITATION WILL LIKELY FALLS AS
SNOW...THERE IS STILL SOME UNCERTAINTY TO HOW MUCH WILL FALL WITH
THE MODELS FLIPPING BACK AND FORTH BETWEEN LESS AND MORE SNOWY
SOLUTIONS.  THE MOST RECENT RUNS SUGGEST A S MORE SNOWY PATTERN
BUT THE NAM STILL REPRESENTS A SMALLER ACCUMULATION ESPECIALLY FOR
THE NORTHEAST US WITH JUST A BRIEF PERIOD OF SNOW.

HOWEVER...THERE SEEMED TO BE A MODEL CONSENSUS FOR SIGNIFICANT
SNOW GREATER THAN 4 INCHES ALONG THE OHIO RIVER ON DAY 2 WITH A
MODERATE TO HIGH PROBABILITY OF GREATER THAN 4 INCHES OF SNOW.  BY
DAY 3...AS PRECIPITATION AGAIN CHANGES FROM RAIN/MIXED
PRECIPITATION TO SNOW...AN AREA OF 4 TO 8 INCHES APPEARS TO BE
MODERATELY TO HIGHLY PROBABLE FROM THE UPPER TENNESSEE VALLEYS
ACROSS THE MID ATLANTIC STATES INTO SOUTHERN NEW ENGLAND. SOME
COMBINED TOTALS COULD EXCEED 8 INCHES ESPECIALLY ACROSS PORTIONS
OF THE OHIO VALLEY.  ADDITIONAL FREEZING RAIN/SLEET IS ALSO
EXPECTED AS RAIN TRANSITIONS TO SNOW WITH PERHAPS THE GREATEST
CHANCES OCCURRING ON DAY 2 OVER ARKANSAS INTO WESTERN TENNESSEE
AND ON DAY 3 OVER NORTHERN LOUISIANA ACROSS NORTHERN MISSISSIPPI
INTO NORTHERN ALABAMA AND SOUTHEASTERN TENNESSEE.

KOCIN


$$





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