Quantitative Precipitation Forecast
Issued by NWS

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FOUS11 KWBC 200755
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
254 AM EST TUE JAN 20 2015

VALID 12Z TUE JAN 20 2015 - 12Z FRI JAN 23 2015


...DAYS 1 TO 2...

...NORTHERN PLAINS/UPPER MISSISSIPPI VALLEY/GREAT LAKES/MIDDLE
ATLANTIC/SOUTHERN NEW ENGLAND...

A SERIES OF WEAK UPPER LEVEL SHORTWAVE DISTURBANCES EMBEDDED
WITHIN NORTHWESTERLY UPPER FLOW OVER THE NORTHERN ROCKIES/NORTHERN
PLAINS WILL CONTINUE MOVING EAST SOUTHEASTWARD WITH A MORE WELL
DEFINED SHORTWAVE TROUGH CROSSING THE OHIO VALLEY BY WEDNESDAY
MORNING.  A WEAK JET EXIT REGION WILL NEAR THE MID ATLANTIC COAST
WHILE CONFLUENT FLOW ALOFT OVER NEW ENGLAND MAINTAINS HIGH
PRESSURE OVER THAT REGION.

HAVE CONFERRED WITH THE LOCAL WFOS ABOUT A POSSIBLE CHANGE TO THE
FORECAST FROM EARLIER TODAY SUGGESTED BY THE 00Z GFS/CANADIAN AND
ECMWF THAT APPEARS TO SHIFT HEAVIER SNOWFALL SOUTHWARD IN THE MID
ATLANTIC REGION BY WEDNESDAY WITH 2 TO 4 INCH AMOUNTS COMMON IN
THE WASHINGTON/BALTIMORE/PHILADELPHIA REGION AS OPPOSED TO FARTHER
NORTH TOWARD NEW YORK CITY. THE GFS/CANADIAN AND NOW THE 00Z ECMWF
ARE SOMEWHAT CONSISTENT FROM NORTHERN VIRGINIA/DELMARVA TO
SOUTHERN NEW JERSEY. HOWEVER...IT SHOULD BE NOTED THAT THIS CHANGE
IS STILL NOT THE FINAL WORD BUT DOES SUGGEST A SHIFT AT THIS STAGE
OF THE FORECAST PROCESS WITH UNCERTAINTIES REMAINING OVER FINAL
ACCUMULATIONS.

DESPITE THE INDIVIDUAL FORECASTS SUGGESTING GREATER THAN 4 INCHES
OF SNOW IN PORTIONS OF THE MID ATLANTIC...THERE WERE NO AREAS
REPORTING AN OVERALL PROBABILITY OF GREATER THAN 4 INCHES ANYWHERE
IN THE MID ATLANTIC DEPENDING ON THE 58 MEMBER ENSEMBLE SYSTEM.
EVEN OVER SOUTHEAST NORTH DAKOTA/NORTHEAST SOUTH
DAKOTA/SOUTHWESTERN MINNESOTA...THE COMBINATION OF MODEL BLENDS
AND THE DETERMINISTIC FORECAST STILL REPRESENTED LESS THAN A 10
PERCENT CHANCE OF GREATER THAN 4 INCHES OF SNOW.

THE SHORTWAVE TROUGH WILL EXIT THE NORTHEAST COAST ON EARLY
THURSDAY TAKING MOST OF THE SNOW WITH IT...ALTHOUGH THE 00Z
NAM/21Z SREF CONTINUES TO BRING SOME ADDITIONAL SNOW ACROSS
SOUTHERN NEW ENGLAND INTO DAY 3.  FOR THE TIME BEING...THIS IS
BEING DISCOUNTED.

...DAYS 1 TO 3...

...SOUTHERN ROCKIES/SOUTHWEST/SOUTHERN HIGH PLAINS...

AN INITIALLY BROAD UPPER TROUGH NEAR THE CALIFORNIA COAST WILL
AMPLIFY OVER THE SOUTHWEST AS ANOTHER SHORTWAVE SYSTEM MOVES
SOUTHWARD ACROSS THE ROCKIES TO THE EAST OF STRONGLY AMPLIFYING
RIDGE OVER THE WEST COAST ON WEDNESDAY.  THESE TWO SYSTEMS WILL
INTERACT ON WEDNESDAY INTO THURSDAY INTO A POSITIVELY TILTED BUT
HIGHLY AMPLIFIED TROUGH MOVING EASTWARD ACROSS THE SOUTHERN PLAINS
BY THURSDAY INTO EARLY FRIDAY.

WHILE THIS SYSTEM WILL BEGIN FAIRLY MOISTURE STARVED...SNOW WILL
BEGIN TO BREAK OUT EARLY WEDNESDAY FROM SOUTHERN COLORADO INTO
NORTHERN NEW MEXICO AND PORTIONS OF THE MOGOLLON RIM WITH
WIDESPREAD QPF DEVELOPING OVER THE SOUTHERN ROCKIES INTO TEXAS BY
LATER WEDNESDAY INTO THURSDAY MORNING.  WHILE THE PRECIPITATION
WILL MAINLY BE RAIN ACROSS CENTRAL TEXAS...SIGNIFICANT SNOW WILL
DEVELOP ESPECIALLY ACROSS SOUTH AND SOUTHEASTERN COLORADO ACROSS
NORTHERN TO CENTRAL NEW MEXICO INTO THE PANHANDLES OF TEXAS AND
OKLAHOMA. THERE WAS QUITE GOOD AGREEMENT BETWEEN THE OPERATIONAL
00Z ECMWF/GFS AND THE ECMWF AND GEFS ENSEMBLE MEANS.  IN GENERAL
THERE WAS A MODERATE TO HIGH PROBABILITY FOR 4 TO 8 INCHES OF SNOW
FROM NORTH TEXAS INTO MUCH OF NORTHERN NEW MEXICO WITH A LOW TO
MODERATE CHANCE OF 8 INCHES OR MORE ESPECIALLY ACROSS NORTHEAST
NEW MEXICO.

AS THE TROUGH BECOMES MORE POSITIVELY TILTED ON THURSDAY...SNOW
WILL DIMINISH FROM NORTH TO SOUTH AND ONLY AMOUNTS TO A FEW INCHES
ON DAY 3 ACROSS EASTERN NEW MEXICO INTO WESTERN TEXAS WITH LIGHT
FREEZING RAIN POSSIBLE NEAR THE RIO GRANDE.  THERE ARE A FEW SMALL
AREAS IN SOUTHEAST NEW MEXICO AND WESTERN TEXAS WITH A LOW
PROBABILITY OF GREATER THAN 4 INCHES OF SNOW.

THE PROBABILITY OF 0.25 INCHES OF ICE IS LESS THAN 10 PERCENT
ACROSS THE CONTIGUOUS US.

KOCIN

$$




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