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
000
FOUS11 KWBC 250928
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
427 AM EST SAT FEB 25 2017

VALID 12Z SAT FEB 25 2017 - 12Z TUE FEB 28 2017

DAYS 1 THROUGH 3...

...NORTHEAST...

AN AREA OF LOW PRESSURE MOVING INTO SOUTHERN CANADA WILL DRAG A
COLD FRONT THROUGH NEW ENGLAND TODAY INTO TONIGHT. WARM AIR AHEAD
OF THE FRONT WILL RESULT IN MAINLY A RAIN EVENT. HOWEVER AS THE
TROUGH GOES NEGATIVE TILT WE SHOULD BEGIN TO SEE MORE IN THE WAY
OF POST FRONTAL PRECIPITATION. STRONG COLD AIR CONVECTION BEHIND
THE FRONT WILL PROBABLY LEAD TO RAIN MIXING WITH AND CHANGING TO
SNOW ACROSS THE HIGHER TERRAIN OF NORTHEAST NY INTO PORTIONS OF
NORTHERN NEW ENGLAND. ONLY EXPECTING LIGHT ACCUMULATIONS...AS BY
THE TIME THE COLUMN COOLS ENOUGH FOR SNOW MOST OF THE
PRECIPITATION WILL HAVE EXITED OFF TO THE EAST. THINK SOME OF THE
ALGORITHMS FROM THE VARIOUS MODELS ARE PROBABLY OVERDOING
ACCUMULATIONS...WITH THE PERCENT OF FROZEN PRECIP PARAMETER FROM
THE NAM SHOWING MORE OF A RAIN/SNOW MIX...WITH MOST OF THE
STEADIER PRECIPITATION COMING TO AN END BEFORE THE COLUMN IS COLD
ENOUGH FOR ACCUMULATING SNOW. THUS GENERALLY JUST GOING FOR 1-3"
ACROSS THE AFOREMENTIONED HIGHER TERRAIN REGIONS. GIVEN THE
PROBLEM WITH THE ALGORITHMS...THE WPC AUTOMATED SNOWFALL
PROBABILITIES ARE LIKELY TOO HIGH ACROSS PORTIONS OF NEW YORK AND
NEW ENGLAND WITH THIS SYSTEM.

...WEST...

TROUGHING OVER THE WEST WILL CONTINUE TO ALLOW FOR PERIODIC SNOW
CHANCES OVER THE NEXT COUPLE DAYS. NOT MUCH IN THE WAY OF
ACCUMULATING SNOW EXPECTED ON DAY 1 (12Z SAT -12Z SUN)...HOWEVER
BY EARLY SUNDAY A STRONG SHORTWAVE AND ASSOCIATED SURFACE LOW WILL
MOVE INTO THE PACIFIC NORTHWEST..BRINGING AN INCREASING SNOW
THREAT. SINCE THIS WAVE WILL BE REINFORCING THE TROUGH THAT IS
ALREADY IN PLACE...IT WILL BE MOVING INTO AN ALREADY COLD
AIRMASS...THUS EXPECT SNOW LEVELS TO END UP PRETTY LOW. PORTLAND
AND SEATTLE WILL PROBABLY STAY WARM ENOUGH TO PREVENT ACCUMULATING
SNOWFALL...BUT YOU DO NOT HAVE TO GET MUCH HIGHER BEFORE
ACCUMULATING SNOWFALL BECOMES LIKELY. OVERALL THE SYSTEM LACKS
ANOMALOUS MOISTURE...AND IS QUICK MOVING...BOTH FACTORS THAT WILL
HELP KEEP SNOWFALL AMOUNTS FROM GETTING TOO EXTREME. GENERALLY
LOOKING AT 6-12" ACROSS THE WA/OR CASCADES...AS WELL AS INTO THE
HILLS OF NORTHWEST CA AND SOUTHWEST OR. IT IS A BIT LESS COMMON TO
GET AMOUNTS THIS HIGH THAT CLOSE TO THE COAST...SO THAT FACTOR IS
PROBABLY THE MOST SIGNIFICANT ASPECT OF THIS SYSTEM.

AS THE TROUGH AXIS MOVES INLAND..EXPECT ACCUMULATING SNOWFALL TO
MOVE INTO THE FAVORED TERRAIN OF NORTHERN ID AND WESTERN MT...WITH
6-12" EXPECTED HERE AS WELL. BY MONDAY INTO MONDAY NIGHT THE SNOW
THREAT SHIFTS SOUTH INTO THE CENTRAL ROCKIES AND THE MOGOLLON RIM
AREA OF AZ. UNCERTAINTY IS A BIT HIGHER BY THIS TIME...AS MODELS
HAVE BEEN HAVING A DIFFICULT TIME DEPICTING SHORTWAVE ENERGY AT
THE PERIPHERY OF THE LONGWAVE TROUGH THAT COULD MOVE INTO THE
SOUTHWEST. REGARDLESS OF THE TROUGH/SHORTWAVE EVOLUTION SHOULD SEE
ACCUMULATING SNOW ACROSS THE TERRAIN OF CENTRAL UT INTO
CENTRAL/WESTERN CO...JUST A MATTER OF HOW MUCH. AT THIS TIME
LOOKING AT MODERATE TO HIGH PROBABILITIES OF 6"+ ACROSS PORTIONS
OF THE CENTRAL ROCKIES...WITH STILL LOW PROBABILITIES OF EXCEEDING
A FOOT THROUGH 12Z TUESDAY. GREATER UNCERTAINTY ALONG THE MOGOLLON
RIM WHERE MODEL QPF HAS BEEN VERY INCONSISTENT...RESULTING IN
SNOWFALL AMOUNTS FLUCTUATING FROM 0" TO OVER A FOOT FROM ONE MODEL
CYCLE TO THE NEXT. THUS LOW CONFIDENCE WITH THIS ASPECT OF THE
FORECAST...WITH THE 25TH TO 75TH FORECAST PERCENTILE SNOWFALL
RANGING FROM 0" TO 10"

CHENARD

$$





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