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Winter Weather Forecast Discussion
 
(Latest Discussion - Issued 0820Z Mar 29, 2017)
 
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Abbreviations and acronyms used in this product
 
Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White


PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
420 AM EDT WED MAR 29 2017

VALID 12Z WED MAR 29 2017 - 12Z SAT APR 01 2017


...WESTERN U.S....

...WA/OR CASCADES TO THE RANGES OF ID/UT/WY/CO...
CONFLUENT FLOW SUPPORTS A ZONAL UPPER LEVEL JET FORECAST BY THE
GFS TO BE 110 KT CROSSING NORTHERN WA STATE ON WED AND THEN
STREAMING INLAND ACROSS THE ID PANHANDLE AND NORTHWEST MT AND
AREAS FURTHER EAST. DEEP LAYERED ASCENT FROM THE SFC-500 MB
SUPPORTS AN EXTENDED PERIOD OF SNOW IN THE WA CASCADES. THE CATCH
IS AS THE UPPER TROUGH APPROACHES DRYING OCCURS ALOFT...SO SNOW
COVERAGE AND INTENSITY DECLINES WED NIGHT. THE HEAVIEST SNOWS ARE
FORECAST IN THE NORTHERN WA CASCADES...WITH LESSER SECONDARY
MAXIMA IN THE OLYMPICS TO THE ID PANHANDLE AND NORTHWEST MT.
THE SNOW LEVELS ARE THE KEY ISSUE IN THE OR CASCADES AS WARMER
CONDITIONS SUPPORT A MIXTURE WITH RAIN.

THE NEXT UPPER TROUGH AMPLIFIES AND DRIFTS EAST TOWARDS THE
PACIFIC NORTHWEST COAST. UPPER JET MAXIMA EXTEND ONSHORE AND
INLAND ACROSS WA/OR INTO
ID...WITH UPPER DIVERGENCE MAXIMA SUPPORTING ASCENT AND RESULTANT
SNOW IN THE RANGES OF SOUTHERN TO CENTRAL ID.

ON THU...EXPECT THE MID-UPPER LEVEL PATTERN TO BECOME MORE
AMPLIFIED AS A DIGGING SHORTWAVE MOVES ONSHORE.  WELL DEFINED 700
MB CONVERGENCE MAXIMA ARE FCST BY THE GFS TO CROSS THE RANGES OF
SOUTHERN AND CENTRAL ID INTO SOUTHWEST MT IN CONJUNCTION WITH THE
TROUGH AND LOW LEVEL FRONT PROGRESSING ACROSS THE REGION.
LIKEWISE...THE FORMING 700 MB CIRCULATION FOCUSES
CONVERGENCE/ASCENT ALONG ITS PATH ACROSS NV INTO UT...WHERE THE
FRONTAL CIRCULATION IS EXPECTED TO SPREAD THE POTENTIAL FOR
ACCUMULATIONS.

ON FRI...THE MODELS/ENSEMBLES FORECAST THE CIRCULATION TO TURN
EAST FROM SOUTHERN UT/NORTHERN AZ EAST ACROSS SOUTHERN CO/NORTHERN
NM.
THE STRONGEST 700 MB CONVERGENCE DEVELOPS ACROSS AREAS NORTH OF
THE CIRCULATION IN UT AND CO...EXTENDING INTO THE LARAMIE AND
SNOWY RANGES IN WY...AND ALSO THE WIND RIVER MNTNS OF WY/UINTAS OF
UT. MULTIPLE SOLUTIONS FORECAST POTENTIAL FOR A FOOT OF SNOW IN
THE CO FRONT RANGE TO THE WIND RIVER MNTNS DURING THIS 24 HR
PERIOD.  CONDITIONS FOR CONDITIONAL SYMMETRIC INSTABILITY ARE MET
IN THE SANGRE DE CRISTO MTNS FRI NIGHT SO AREAS OF CONVECTIVE SNOW
ARE POSSIBLE.  THE 00Z NAM WAS FASTER IN MOVING THE LOW ON TO THE
PLAINS AND ALLOWED MORE POTENTIAL FOR SNOW TO MOVE OUT OF THE
FOOTHILLS ONTO THE HIGH PLAINS.  THIS SOLUTION WAS GIVEN LESS
WEIGHT DUE TO THE MAJORITY CLUSTER FURTHER WEST AGREEING WELL.

...DAY 1 (WED) ON THE CO/NM HIGH PLAINS AND FOOTHILLS OF THE
SANGRE DE CRISTO MNTNS...
FOR THE DAY 1 PERIOD (WED AND WED NIGHT)...AS THE DEEP LAYER
CYCLONIC CIRCULATION
MOVES FURTHER EAST INTO THE CENTRAL PLAINS...THE HEAVY SNOW THREAT
IS EXPECTED TO WANE...WITH A BRIEF
PERIOD OF SNOW POSSIBLE ON THE HIGH PLAINS AND FOOTHILLS BEFORE
THE SYSTEM MOVES AWAY AND PRECIP ENDS.

...UPSTATE NEW YORK AND WESTERN NEW ENGLAND THU/FRI...
THE MODELS INDICATE HIGH PRESSURE DRIFTING EAST ACROSS QUEBEC
TOWARDS NEW ENGLAND THU-FRI.  AN INVERTED TROUGH DEVELOPS
NEAR THE LAKES AS LOW PRESSURE DRIFTS INTO THE OH VALLEY.  LOW-MID
LEVEL WARM ADVECTION COMBINES WITH UPPER DIVERGENCE MAXIMA IN THE
RIGHT JET ENTRANCE REGION TO SUPPORT SNOW DEVELOPING IN UPSTATE
NY...CONTINUING INTO FRI WITH POTENTIAL FOR HEAVY SNOW IN THE
ADIRONDACKS OF NY AND GREEN MNTNS OF VT/WHITE MNTNS OF NH/ADJACENT
MA. THE DEVELOPING LOW-MID LEVEL CIRCULATION TRACKS NEAR NEW YORK
CITY AND LONG ISLAND...SO SOUTHEAST NY AND COASTAL SOUTHERN NEW
ENGLAND APPEAR TO BE TOO WARM FOR SNOW.

SOUTH OF THE AREA OF SNOW ELEVATED LOCATIONS MAY RECEIVE A MIXTURE
OF PRECIP TYPES...WITH THE POSSIBILITY OF ACCUMULATING FREEZING
RAIN IN THE CATSKILLS AND HILLS OF NORTHWEST CT AND BERKSHIRES.
THE NAM FORECASTS THE MOST ICING....LOCALLY OVER A QUARTER INCH SO
A THREAT FOR SIGNIFICANT FREEZING RAIN IS SHOWN.

THE PROBABILITY OF RECEIVING A QUARTER INCH OF FREEZING RAIN IS
LESS THAN 10 PERCENT DAYS 1-2.

PETERSEN