Quantitative Precipitation Forecast
Issued by NWS

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FOUS11 KWBC 250803
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
403 AM EDT SAT MAR 25 2017

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

DAYS 1 THROUGH 3...

...WESTERN U.S....

THE WEST WILL BE AFFECTED BY A COUPLE OF MID/UPPER-LEVEL TROUGHS
THROUGH THE WEEKEND INTO EARLY NEXT WEEK. THE FIRST SHORTWAVE
MOVES ACROSS THE GREAT BASIN AND CENTRAL ROCKIES ON DAY 1 BEFORE
DEPARTING FOR THE PLAINS ON DAY 2 (SUN).
LIGHT TO LOCALLY MODERATE SNOW ARE EXPECTED ACROSS THE RANGES OF
NORTHERN WY (SUCH AS THE BIGHORNS) AND ADJACENT SOUTHERN MT AND IN
NORTHERN UT AND WESTERN CO. THE STEADY FORWARD MOVEMENT OF THE
WAVE PRECLUDES LONGER DURATION SNOWS AND THUS NO AREAS OF HEAVY
SNOW ARE TARGETED.

THE WEST COAST WILL SEE A BREAK BETWEEN SYSTEMS ON DAY 1 WITH THE
NEXT MID/UPPER-LEVEL TROUGH FORECAST TO MOVE ONSHORE ALONG THE
WEST COAST ON DAY 2.
HEIGHTS AND SNOW-LEVELS WILL DROP ACROSS MUCH OF THE WEST AS THE
TROUGH MOVES INLAND AND THEN BEGINS TO FURTHER AMPLIFY ACROSS THE
GREAT BASIN BY LATE MONDAY.  ACROSS THE WA/OR CASCADES, CA SIERRA
NEVADA , AND ID SALMON RIVER/BOISE MNTNS SEVERAL INCHES OF SNOW
ARE EXPECTED WITH LOCALLY HEAVY SNOW POSSIBLE.

ON DAY 3 (MON) THE 700 MB WAVE DEPARTS CA AND IS FORECAST TO CROSS
NV AND UT..POSSIBLY CLOSING OFF BEFORE ENTERING CO MON NIGHT/EARLY
TUE.  LOW LEVEL CONVERGENCE ALONG THE FRONT AS THE CIRCULATION
MOVES ACROSS WESTERN WY AND UT FOCUSES SNOWFALL.

IN THE NORTHWEST...SECONDARY WAVES ROTATE AROUND THE BASE OF THE
NORTHEAST PACIFIC TROUGH AND ROTATE ONSHORE AND INLAND.  PERIODS
OF SNOW ARE EXPECTED WITH EACH WAVE AND IT PROGRESSES ACROSS THE
PACIFIC NORTHWEST AND NORTHERN ROCKIES. SNOW MAY EVEN CONTINUE AS
THE LAST IN THE SERIES OF WAVE MOVES INLAND MON NIGHT AS THE FLOW
OVER THE EASTERN PACIFIC IN CONFLUENT WITH A DEVELOPING WEST-EAST
UPPER JET FORECAST BY THE GFS TO MOVE ONSHORE BY 12Z TUE WITH
UPPER DIVERGENCE MAXIMA COMING INTO THE OLYMPICS AND NORTHERN WA
CASCADES.

THE WPC FORECAST WAS BASED ON A MULTI-MODEL BLEND INCLUDING THE
NAM/GFS/ECMWF.

THE PROBABILITY OF RECEIVING A QUARTER INCH OF FREEZING RAIN IS
LESS THAN 10 PERCENT ACROSS THE WESTERN US.


...GREAT LAKES TO THE NORTHEAST...

A MULTI-DAY PRECIPITATION EVENT IS FORECAST ACROSS PORTIONS OF THE
CENTRAL AND EASTERN U.S. A CLOSED UPPER-LEVEL LOW IS FORECAST TO
DRIFT SLOWLY NORTHEASTWARD TOWARD THE LOWER GREAT LAKES THROUGH
THE WEEKEND.
AT THE SURFACE ARE THAT COLD HIGH PRESSURE WILL BE REINFORCED FROM
EASTERN CANADA AND EXTENDING INTO NEW ENGLAND, BEHIND A COLD FRONT
WHICH WILL CROSS THE REGION EARLY SATURDAY BEFORE BECOMING
STATIONARY ACROSS THE MID-ATLANTIC BY SATURDAY NIGHT/SUNDAY.

SOME LIGHT FREEZING RAIN IS POSSIBLE ON DAY 1 (SAT) FROM PORTIONS
OF NORTHERN WISCONSIN AND THE UP OF MI/NORTHERN LOWER MI TO
INTERIOR EASTERN NEW YORK AND ADJACENT WESTERN NEW ENGLAND AS
BROAD ISENTROPIC LIFT PRODUCES A SHIELD OF PRECIPITATION.

RELATIVELY LIGHT FREEZING RAIN ACCUMULATIONS OF A HUNDREDTH UP TO
A TENCH OF AN INCH ARE POSSIBLE ON DAY 2 (SUN) ACROSS INTERIOR
EASTERN NEW YORK AND INTERIOR MA/VT/NH AS LOW-LEVEL WARM ADVECTION
OCCURS OVER THE SURFACE SUBFREEZING AIR IN THESE AREAS.

ON DAY 3 (MON), FREEZING RAIN AMOUNTS PICK UP A BIT AS THE UPPER
WAVE CROSSES NORTHERN NEW YORK AND INTERIOR NEW
ENGLAND...PRODUCING A BAND OF SNOW IN MAINE AND MIXED PRECIP
TYPES...INCLUDING FREEZING RAIN...IN WESTERN MAINE/NORTHERN NH AND
ADJACENT VT.  SEVERAL MODELS/21Z SREF MEAN INDICATE THE POTENTIAL
FOR AMOUNTS REACHING A QUARTER INCH FOR SOME AREAS. CONSEQUENTLY,
THERE IS A SLIGHT TO MODERATE PROBABILITY OF A QUARTER INCH OF
ICING ACROSS MUCH OF INTERIOR NORTHERN NEW ENGLAND ON DAY 3.

THE STRENGTH OF THE LOW-LEVEL WARM ADVECTION, ALONG WITH THE
STRENGTH OF THE ARCTIC HIGH ACROSS SOUTHEASTERN CANADA WILL
DETERMINE THE EXACT DISTRIBUTION OF PRECIPITATION TYPES DURING
THIS EVENT. AT THIS TIME, GIVEN DUAL UNCERTAINTIES OF PRECIP TYPE
AND AMOUNT...SIGNIFICANT CHANGES IN FORECASTS OF EACH TYPE ARE
POSSIBLE.

THE WPC FORECAST WAS BASED ON A MULTI-MODEL BLEND INCLUDING THE
NAM/GFS/ECMWF.

THE PROBABILITY OF A QUARTER INCH OF ICING IS LESS THAN 10 PERCENT
ON DAY 1.

PETERSEN


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