Quantitative Precipitation Forecast
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FOUS11 KWBC 302046
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
346 PM EST FRI JAN 30 2015

VALID 00Z SAT JAN 31 2015 - 00Z TUE FEB 03 2015


DAY 1...

...NORTHEAST...

A NEGATIVELY TILTED AND AMPLIFYING TROUGH APPEARS TO BE SLIGHTLY
FARTHER EAST THAN EARLIER FORECASTS HAVE INDICATED IMPLYING THAT
SOME WRAP AROUND PRECIPITATION COULD BE SLIGHTLY FARTHER EAST OFF
THE CENTRAL NEW ENGLAND COAST.  HOWEVER...THERE IS STILL A HIGH
PROBABILITY THAT HEAVY SNOW WILL STILL OCCUR THROUGH CENTRAL AND
EASTERN MAINE. ADDITIONAL ACCUMULATIONS AFTER 00Z WILL LIKELY BE
IN THE 6 TO 12 INCH RANGE ACROSS THE EASTERN THIRD OF MAINE WITH A
LOW TO MODERATE PROBABILITY FOR AMOUNTS EXCEEDING 12Z INCHES. THE
TROUGH WILL LIFT NORTHWARD TOWARD NOVA SCOTIA WITH SNOW ENDING
ACROSS EASTERN MAINE BY SATURDAY EVENING. WITH A DAY 1
FORECAST...A MULTI MODEL BLEND WAS USED IN GENERATING THE
DETERMINISTIC PORTION OF THE SNOWFALL.

...SOUTHWEST/SOUTHERN ROCKIES...

A LONGWAVE TROUGH WILL CONTINUE TO INFLUENCE THE WEATHER AND
PRODUCE SIGNIFICANT SNOW OVER THE HIGH ELEVATIONS OF THE FOUR
CORNERS REGION OF THE SOUTHWEST. MOIST SOUTHWESTERLY FLOW ALOFT
WILL CONTINUE  TO INFLUENCE THE REGION UNTIL THE UPPER TROUGH
MOVES SOUTHEASTWARD AS A SEPARATE TROUGH DIVES SOUTHEASTWARD
ACROSS THE CENTRAL PLAINS...HELPING SHIFT THE TROUGH AXIS
SOUTHEASTWARD INTO NORTHERN MEXICO EFFECTIVELY SHUTTING OFF THE
MOISTURE SUPPLY/LIFT FOR SNOWFALL IN THE SOUTHWEST ON SUNDAY.

HEAVIEST SNOW IS EXPECTED TO AFFECT THE HIGHER ELEVATIONS OF NEW
MEXICO AND THE SAN JUAN/SANGRE DE CRISTO PEAKS ACROSS SOUTHERN
COLORADO. PORTIONS OF THE SOUTHERN WASATCH IN UTAH CAN EXPECT SOME
SIGNIFICANT SNOWFALL AS WELL AS THE HIGHEST PEAKS WITHIN THE
MOGOLLON RIM IN ARIZONA. IN GENERAL THERE IS A MODERATE TO HIGH
PROBABILITY FOR AN ADDITIONAL 4 TO 8 INCHES OF SNOW FOR THE MOST
PART.



DAYS 1 THROUGH 3...

...UPPER MISSISSIPPI VALLEY/OHIO VALLEY/LOWER GREAT LAKES/NORTHERN
MID ATLANTIC/NORTHEAST...

A WIDESPREAD POTENTIALLY HIGH IMPACT SNOW EVENT APPEARS TO BE
SHAPING UP ACROSS A LARGE SWATH OF THE NORTHERN TIER EXTENDING
FROM THE UPPER MISSISSIPPI VALLEY ACROSS THE LOWER LAKES/OHIO
VALLEY...NORTHERN MID ATLANTIC AND ACROSS CENTRAL AND SOUTHERN NEW
ENGLAND.

OVER THE PAST COUPLE DAYS...THE SYSTEM HAS TRENDED FROM A SHEARED
LIGHT QPF SYSTEM TO ONE THAT THREATENED SNOW FARTHER SOUTH THAN
CURRENT FORECASTS INDICATED.  IT IS STILL UNCLEAR IF THIS APPARENT
NORTHWARD TREND WILL CONTINUE OVER THE NEXT COUPLE DAYS OR EVOLVE
IN SOME UNANTICIPATED MANNER.  A SHARPER TROUGH COULD RESULT IN
MORE EASTERN RIDGING AND THUS A MORE NORTHWARD TREND...WHILE
PERHAPS A LESS AMPLIFIED SOLUTION WILL CONTINUE THE CURRENT
SCENARIO.  AT THIS POINT...THIS IS PURELY SPECULATION.

WITH ALL THE UNCERTAINTY REGARDING WHERE THOSE CRUCIAL SNOW/NO
SNOW GRADIENTS SET UP AND WHERE THE CHANGEOVER REGION
OCCURS...THIS SYSTEM APPEARS TO HAVE THE POTENTIAL FOR A SWATH OF
6 TO 12 INCHES OF SNOW SOMEWHERE IN THE CORRIDOR FROM THE SOUTHERN
MIDWEST ACROSS THE NORTHEAST...WITH PRESENTLY ONLY A SMALL
PROBABILITY OF GREATER THAN A FOOT OF SNOW.  WITH SEVERAL FORECAST
CYCLES COMING UP...THESE NUMBERS AND LOCATIONS WILL LIKELY CHANGE.

WHILE THE SOUTHWESTERN TROUGH HEADS SOUTHWARD INTO MEXICO...ENERGY
AND MOISTURE EJECTING EASTWARD ACROSS THE PLAINS AND MISSISSIPPI
VALLEY WILL COMBINE WITH THE AMPLIFYING TROUGH MOVING
SOUTHEASTWARD ACROSS THE NORTHERN ROCKIES ON SATURDAY NIGHT AND
BECOME A SIGNIFICANT TROUGH OVER THE MISSISSIPPI VALLEY BY SUNDAY.
THE CONSOLIDATION OF THESE SYSTEMS APPEAR TO PRODUCE A HIGH
PROBABILITY OF GREATER THAN 4 INCHES OF SNOW FROM IOWA/NORTHEAST
MISSOURI TO NORTHERN ILLINOIS/INDIANA AND OHIO ON DAY 2...
SATURDAY EVENING INTO SUNDAY EVENING.   THERE IS A LOW PROBABILITY
OF GREATER THAN 12 INCHES OF SNOW ACROSS NORTHERN ILLINOIS INTO
NORTHERN INDIANA.  AS THIS STORM DEVELOPS...MUCH COLDER AIR WILL
BUILD NOT ONLY BEHIND THE SYSTEM AS A LARGE ARCTIC ANTICYCLONE
HEADS SOUTHWARD INTO THE NORTHERN PLAINS...BUT COLDER AIR WILL
ALSO BLEED EASTWARD AS PRESSURES RISE OVER SOUTHEASTERN CANADA AND
NORTHERN NEW ENGLAND IN ASSOCIATION WITH A PRONOUNCED UPPER
CONFLUENCE ZONE.  THE COMBINATION OF THESE TWO SYSTEMS WILL HELP
GENERATE A INCREASINGLY BAROCLINIC ZONE UPON WHICH THE DEVELOPING
SURFACE LOW WILL MOVE ALONG.  ON DAY 3...SUN EVENING INTO MON
EVENING...A MODERATE TO HIGH RISK FOR 4 TO 8 INCHES COVERS MUCH OF
NEW YORK/PENNSYLVANIA...AND CENTRAL AND SOUTHERN NEW ENGLAND.

THE PREVAILING SHIFT IN THE 12Z MODELS WAS TO CONTINUE A MORE
NORTHERLY TRACK WITH THIS SYSTEM...WHICH IS REFLECTED IN THE WPC
FORECAST...PARTICULARLY FROM LATE DAY 2 ONWARD.  HOWEVER FORECAST
CONFIDENCE IS TEMPERED BY THE RUN-TO-RUN INCONSISTENCIES THE
MODELS HAVE SHOWN ALONG THE WITH DISTINCT POSSIBILITY THAT THE
MODELS MAY REVERSE TRENDS IN SUBSEQUENT RUNS.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.

KOCIN

$$




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