Quantitative Precipitation Forecast
Issued by NWS

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000
FOUS11 KWBC 242048
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
348 PM EST SAT FEB 24 2018

VALID 00Z SUN FEB 25 2018 - 00Z WED FEB 28 2018


...UPPER MS VALLEY/UPPER GREAT LAKES...

A DEVELOPING AREA OF SNOW ACROSS MN MOVES NORTHEAST IN TANDEM WITH
THE STRONGER 700 MB LIFT WITHIN  STRONG THETA-E MAXIMA AHEAD OF A
PROGRESSIVE TROUGH CROSSING THE UPPER MS VALLEY THIS EVENING AND
THEN LK SUPERIOR SUNDAY MORNING.  SNOW POTENTIAL OF 6-12 INCHES IS
EXPECTED NEAR THE LK SUPERIOR SHORELINE OF MN/NORTHWEST WI. THE
SNOW DEVELOPS AHEAD OF A LOW LEVEL CYCLONE THAT CROSSES LK
SUPERIOR SUN MORNING AND THEN ACROSS THE BORDER INTO CANADA.  THE
PRECIP TYPE TRANSITION ZONE OCCURS ACROSS WI AND THEN THE MIDDLE
AND EASTERN UP OF MI.  LIGHT ICING IS POSSIBLE IN THESE AREAS
OVERNIGHT.

THE EVENT QUICKLY TAPERS ON SUNDAY WITH THE CYCLONE MOVING INTO
ONTARIO. THE MODELS HAVE COME INTO GOOD AGREEMENT...ALLOWING A
CONSENSUS BASED APPROACH FOR ACCUMULATIONS AND QPF/TEMPERATURE
PROFILES...WITH EACH SOLUTION EQUALLY WEIGHTED IN THE
PROBABILITIES.


...PACIFIC NORTHWEST/CA/NORTHERN ROCKIES/GREAT BASIN...

THE MODELS INDICATE FLOW WILL BE BACKING OVERNIGHT INTO
SUNDAY...WITH THE DEVELOPMENT OF LOW SHEARS WESTERLY FLOW COMING
OFF THE PACIFIC OCEAN INT THE WA/OR CASCADES.  LAYER RELATIVE
HUMIDITY IS FORECAST TO BE 90-100 PERCENT.  WITH THE 700 MB JET OF
50-60 KT CROSSING THE CASCADES...POCKETS OF STRONG CONVERGENCE AND
LOFT ARE EXPECTED IN THE W/OR CASCADES.  LIFT WILL ALSO BE AIDED
LATE SUN AFTERNOON/NIGHT BY INCREASING LAPSE RATES TO 7-8 DEG
C/KM. BY MON MORNING SNOW TOTALS IN THE WA/OR CASCADES ARE
EXPECTED TO REACH 2 TO 3 FEET. SECONDARY MAXIMA ARE EXPECTED IN
THE RANGE OF ID AND WY AS THE 700 MB CONTINUES INLAND INTO THESE
AREAS...ALONG WITH WELL DEFINED CONVERGENCE BANDS.

AS THE TROUGH MOVES SOUTH ACROSS CA AND NV ON MON A CLOSED MID TO
UPPER LOW DROPS DOWN THE NORTHERN/CENTRAL CA COASTLINE. THE
DOWNSTREAM LOW LEVEL CONVERGENCE BANDS FOCUS N THE CA SIERRA
NEVADA RANGE AND DOWNSTREAM ACROSS NORTHERN NV INTO NORTHERN
UT...WITH SNOW OCCURRING IN WINDWARD TERRAIN. HIGHER AMOUNTS ARE
FCST IN THE CA SIERRA NEVADA DUE TO GREATER AMOUNTS OF AVAILABLE
MOISTURE IN PLACE...WITH POTENTIAL FOR A FOOT ON DAY 2.  WITH
FALLING HEIGHTS AND TEMPS COMBINED WITH UPPER DIVERGENCE MAXIMA
NEAR THE APPROACHING CLOSED LOW...SNOW IS EXPECTED TO DEVELOP
LATER MONDAY IN THE RANGES OF SOUTHERN CA...SUCH AS THE SAN
BERNARDINO MOUNTAINS.

...INTERIOR NEW YORK AND CENTRAL/NORTHERN NEW ENGLAND...

INITIAL CONDITIONS ARE ABOVE FREEZING IN THE LOW LEVELS BUT MODEST
COLD DRAINING INTO INTERIOR NEW YORK AND NEW ENGLAND SETS THE
STAGE A MULTI-PRECIP TYPE EVENT SUNDAY AS STRONG MID LEVEL
WARM/MOIST ADVECTION RESULTS IN A SURGE OF PRECIPITATION.  INITIAL
PRECIP STARTING AS SNOW IN VT/NH GRADUALLY CHANGES OVER TO
SLEET/FREEZING RAIN...WITH LIGHT ACCUMULATIONS IN THE
BERKSHIRES/GREEN/WHITE MOUNTAINS.  ON THE ORDER A QUARTER INCH OF
ICING IS POSSIBLE IN THE SOUTHERN ADIRONDACKS AND BERKSHIRES OF
MA/GREEN MOUNTAINS OF VT.
THE UNCERTAINTY REVOLVES AROUND HOW LONG COLD AIR REMAINS IN PLACE
AND HOW LONG EACH PRECIP TYPE LASTS. THE SNOW LASTS A LITTLE
LONGER DEEPER INTO THE COLD AIR IN INTERIOR MAINE.  THE EVENT
QUICKLY WINDS DOWN SUN EVENING AS THE DEEP LAYER JET AND LIFT
DEPARTS INTO THE CANADIAN MARITIMES.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT DAYS
2 AND 3.

PETERSEN

$$





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