Quantitative Precipitation Forecast
Issued by NWS

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432
FOUS11 KWBC 270936
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
435 AM EST MON FEB 27 2017

VALID 12Z MON FEB 27 2017 - 12Z THU MAR 02 2017

DAYS 1 THROUGH 3...

...WEST...

HEAVY SNOWFALL IS LIKELY TODAY INTO THE FIRST HALF OF TUESDAY
ACROSS THE HIGHER TERRAIN OF CENTRAL UT...THE MOGOLLON RIM OF
AZ...THE CO ROCKIES AND THE HIGHER TERRAIN OF NORTHERN NM. A
DIGGING TROUGH WILL INTERACT WITH A SUBTROPICAL PLUME OF MOISTURE
MOVING IN FROM THE PACIFIC TO PRODUCE THE HEAVY SNOWFALL AMOUNTS.
GENERALLY LOOKING AT 6-12" OF SNOWFALL...ALTHOUGH LOCALIZED
AMOUNTS OF 1-2 FEET ARE POSSIBLE ACROSS THE HIGHEST TERRAIN OF
CENTRAL AZ AND PORTIONS OF THE SAN JUAN MOUNTAINS NEAR THE CO/NM
BORDER. OVERALL THERE IS GOOD MODEL AGREEMENT WITH THE EVOLUTION
OF THIS SYSTEM...THUS HIGH CONFIDENCE IN THE FORECAST...WITH A
MULTI MODEL BLEND GENERALLY FOLLOWED. SNOWFALL WILL COME TO AN END
BY TUESDAY NIGHT ACROSS THIS REGION AS THE TROUGH MOVES OFF TO THE
EAST AND UPPER LEVEL RIDGING BEGINS TO BUILD INTO THE AREA.

PROLONGED SNOWFALL IS ALSO EXPECTED ACROSS THE NORTHWEST US OVER
THE NEXT SEVERAL DAYS. A WELL DEFINED SHORTWAVE DIVING INTO THE
LONGWAVE TROUGH WILL BE RESPONSIBLE FOR SNOWFALL TODAY ACROSS THE
WA/OR CASCADES AND THE HIGHER TERRAIN OF NORTHERN ID AND WESTERN
MT. A LULL IN THE SNOWFALL IS POSSIBLE TUESDAY...HOWEVER SHOULD
SEE ANOTHER UPTICK IN SNOWFALL COVERAGE AND INTENSITY TUESDAY
NIGHT INTO WEDNESDAY AS ADDITIONAL SHORTWAVE ENERGY AND INCREASED
UPSLOPE FLOW MOVES ACROSS. NOT REALLY EXPECTING SNOWFALL RATES TO
BE THAT INTENSE...HOWEVER THE LONG DURATION OF THE SNOWFALL WILL
RESULT IN TOTALS OF ROUGHLY 10-20 INCHES ACROSS THE WA/OR CASCADES
AND THE HIGHER TERRAIN OF NORTHERN ID AND WESTERN MT THROUGH 12Z
THURSDAY.


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

LONGWAVE TROUGHING WILL BUILD INTO THE CENTRAL PORTION OF THE
COUNTRY INTO MID WEEK RESULTING IN AN UNSETTLED WEATHER PATTERN.
OVERALL...TEMPERATURE PROFILES WILL BE MUCH TOO WARM FOR
SNOWFALL...HOWEVER WE SHOULD BE COLD ENOUGH FOR SOME SNOWFALL
ACROSS PORTIONS OF THE UPPER MS VALLEY INTO THE GREAT LAKES.
OVERALL THERE REMAINS QUITE A BIT OF SPREAD WITH THE EVOLUTION OF
THE SHORTWAVE FEATURES WITHIN THE TROUGH AND THE EVOLUTION OF
SURFACE LOW PRESSURES ALONG THE BAROCLINIC ZONE. OVERALL THE GFS
APPEARS MUCH TOO QUICK AND NORTH...AND PUTS TOO MUCH EMPHASIS ON
THE LEAD AREA OF LOW PRESSURE. THE BETTER OVERALL MODEL CONSENSUS
IS CLOSER TO THE ECMWF/UKMET/GEM/NAM EVOLUTION. THESE SOLUTIONS
STRESS MORE OF A SOUTHERN/SLOWER TRACK WITH THE LEAD LOW THROUGH
TUESDAY...AND A STRONGER TRAILING LOW THAT DEVELOPS NEAR OR JUST
EAST OF MI ON WEDNESDAY. WPC TENDED TO FAVOR THE BETTER CLUSTERING
OF THESE LATTER MODELS...ALTHOUGH CONFIDENCE IN THE DETAILS
REMAINS LOW.

THE APPROACH OF A SHORTWAVE AND INCREASED LOW/MID LEVEL
FRONTOGENESIS NORTH OF THE DEVELOPING SURFACE LOW SHOULD RESULT IN
SOME SNOWFALL MONDAY NIGHT INTO TUESDAY ACROSS PORTIONS OF
NORTHERN MN/WI INTO THE UP OF MI. SOME MODEL DIFFERENCES REMAIN
WITH SNOWFALL AXIS AND MAGNITUDE...ALTHOUGH BEGINNING TO SEE SOME
CONVERGENCE. THE GFS/GEFS REMAIN THE MOST AGGRESSIVE...BUT AS
MENTIONED ABOVE THESE SOLUTIONS ARE GENERALLY NOT PREFERRED. FOR
NOW THE BEST MIDDLE GROUND SOLUTION ENDS UP SOMEWHERE BETWEEN THE
12Z AND 0Z ECMWF...WITH THE 0Z NAM/UKMET/GEM MORE SUPPRESSED AND
THE 0Z GFS FURTHER NORTH AND HEAVIER. THE MOST LIKELY SNOWFALL
CURRENTLY IS IN THE 2-5" RANGE...ALTHOUGH WITH SOME OF THE SREF
MEMBERS AND GFS RUNS MORE AGGRESSIVE...THERE ARE LOW PROBABILITIES
OF 8".

THE OTHER AREA TO WATCH IS MI WEDNESDAY AFTERNOON AND NIGHT AS THE
TRAILING LOW MAY INTENSIFY...WHICH WOULD WRAP IN ENOUGH COLD AIR
FOR A CHANGEOVER TO SNOW. AS MENTIONED ABOVE...THE GFS APPEARS TOO
WEAK WEAK WITH THIS LOW AND IS CURRENTLY NOT PREFERRED. THE 0Z
RUNS OF THE ECMWF/UKMET/GEM/NAM ARE ALL CLUSTERED PRETTY CLOSE
TOGETHER...WITH WPC LEANING IN THAT DIRECTION. STILL SOME
DIFFERENCES AMONGST THESE PREFERRED MODELS WITH REGARDS TO THE
DEGREE OF COLD AIR WRAPPING IN AND THE NORTHWEST EXTENT OF THE
SNOWFALL. THOUGHT THE 0Z NAM WAS LIKELY TOO COLD AND BRINGING
ACCUMULATING SNOWFALL TOO FAR SOUTH...AS IT HAD NO SUPPORT FROM
THE OTHER MODELS NOR THE SREF. WITH REGARDS TO THE NORTHWEST
EXTENT...FAVORED SOMETHING IN BETWEEN THE 12Z AND 0Z ECMWF. THIS
RESULTS IN A MOST LIKELY SNOWFALL OF 2-5" ACROSS PORTIONS OF
CENTRAL MI. ALTHOUGH GIVEN THE MODEL SPREAD AND THREE DAY LEAD
TIME...UNCERTAINTY REMAINS HIGH...WITH THE RANGE OF POSSIBILITIES
STRETCHING FROM 0" TO 6"+ ACROSS CENTRAL MI.


CHENARD



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