Quantitative Precipitation Forecast
Issued by NWS

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389
FOUS11 KWBC 140843
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
342 AM EST SAT JAN 14 2017

VALID 12Z SAT JAN 14 2017 - 12Z TUE JAN 17 2017


...SOUTHWEST AND SOUTHERN/CENTRAL PLAINS TO THE MIDDLE MISSISSIPPI
VALLEY...OHIO VALLEY...AND MID-ATLANTIC REGION...

A MAJOR ICING EVENT IS FORECAST ACROSS AREAS OF THE NORTHERN TX
PANHANDLE ACROSS NORTHWEST OK AND MUCH OF KS INTO EASTERN NE...

AN ICE STORM IS EXPECTED FROM THE SOUTHERN/CENTRAL PLAINS TO THE
MIDDLE MISSISSIPPI VALLEY THIS WEEKEND...INTO PORTIONS OF THE
NORTH CENTRAL PLAINS ON MONDAY...AS A WARM MID LEVEL LAYER MELTS
FALLING SNOW WITH RAIN REACHING A SUBFREEZING GROUND.  PORTIONS OF
OKLAHOMA AND KANSAS ARE EXPECTED TO SEE HIGH ICE ACCUMULATIONS
WITH THIS EVENT...WITH ACCUMULATIONS SEEN ONCE EVERY COUPLE OF
YEARS.  ON DAY 1 THE ICING THREAT EXTENDS ACROSS THE NORTHEAST TX
PANHANDLE ACROSS NORTHWEST OK AND SOUTHWEST TO EASTERN KS AND
NORTHWEST MO.

LIGHT AMOUNTS OF ICING STRETCH DOWNSTREAM INTO THE OHIO VALLEY AND
PORTIONS OF MID ATLANTIC...WHERE LIGHT LIQUID EQUIVALENTS LEAD TO
LIGHT ICING ACCUMULATIONS. THE NAM PREVIOUSLY OVER FORECAST HOW
QUICKLY SUB FREEZING AIR WOULD PLUNGE SOUTH AND HAS BACKED OFF IN
ICING POTENTIAL IN SOUTHERN MD AND ADJACENT VA.

ON DAY 2/SUN...AS THE MID LEVEL CIRCULATION TURNS NORTHEAST FROM
NM TOWARDS THE TX PANHANDLE...THE THREAT FOR SIGNIFICANT
ACCUMULATIONS DOWNSTREAM FROM THE LOW EXTENDS NORTHEAST FROM
SOUTHWEST KS ACROSS NORTHEAST KS AND SOUTHEAST NE AND NEAR THE
MO/IA BORDER.
THERE ARE STILL MODEL DIFFERENCES ON QPF AMOUNTS THAT NEED TO BE
RESOLVED WITH A SPLIT AS TO HOW MUCH WARM SECTOR PRECIP FALLS VS
THE COLD SECTOR.

ON DAY 3/MON...THE MID LEVEL CIRCULATION CONTINUES MOVING
NORTHEAST ACROSS THE CENTRAL PLAINS TOWARDS THE UPPER MS VALLEY.
ICING THREAT CONTINUES DOWNSTREAM FROM SOUTHEAST NE NORTHEAST
ACROSS NORTHWEST IA AND SOUTHERN MN/NORTHERN WI.  THE DAY 3 AXIS
IS SUBJECT TO CHANGE DEPENDING THE TRACK OF THE MID LEVEL
CIRCULATION...WHICH DIVERGES AMONGST THE MODEL/ENSEMBLE SOLUTIONS.

SUNDAY AND MONDAY...HEAVY SNOW IS EXPECTED ALONG AND LEFT OF THE
700 MB LOW TRACK AS IT CROSSES NM INTO CO AND POSSIBLY THE
ADJACENT OK PANHANDLE. ACCUMULATIONS OVER A FOOT ARE EXPECTED IN
THE SANGRE DE CRISTO MOUNTAINS OF NORTHERN NM AND SOUTHEAST
CO....WITH SEVERAL INCHES OF SNOW ON THE HIGH PLAINS OF SOUTHEAST
CO.  THE MODELS SPREAD ON THE TIMING OF MIXED PRECIP TYPES TO SNOW
ON DAY 2 REMAINS WITH THE GFS SLOWER TO TRANSITION TO SNOW IN
EASTERN CO/WESTERN KS THAN THE NAM/ECMWF/SREF ARW MEMBERS...WHICH
WERE GIVEN MORE WEIGHT IN THE FORECAST.

THE 700 MB LOW LIFTS NORTHEAST ON MONDAY AND THE AXIS OF SNOW
ALONG WITH IT.
MODEL DIVERGENCE MAKES THE CONFIDENCE ON THE DAY 3 FORECAST LOWER.
 THE MODELS HAVE BOTH TIMING DIFFERENCES WITH THE GFS/NAM
FASTER...AND NOW THE 00Z ECMWF HAS TRENDED FASTER IN MOVING THE
LOW NORTHEAST. THEY WOULD RESULT IN THE AXIS OF SNOW EXTENDING
ACROSS CENTRAL NE TO SOUTHEAST SD AND ADJACENT SOUTHWESTERN NM.
THERE REMAINS MODEL SPREAD WITH THE EXACT EVOLUTION OF THE UPPER
LOW AND THE DETAILS OF HOW IT INTERACTS WITH A NORTHERN STREAM
SHORTWAVE...WHICH REDUCES CONFIDENCE IN MODEL THERMAL PROFILES AND
THE EXACT SNOW AND ICE ACCUMULATIONS.   MORE WEIGHTING WAS GIVEN
TO THE 00Z ECMWF AND 21Z SREF MEAN QPF/TEMPERATURE PROFILES.

...PACIFIC NORTHWEST...
THE MODELS INDICATE AN UPPER LEVEL TOUGH OVER THE NORTHEAST
PACIFIC SLOWLY MOVING EAST IN THE DIRECTION OF BRITISH COLUMBIA.
CONFLUENT DEEP LAYER FLOW GRADUALLY COMES ONSHORE FROM THE PACIFIC
INTO VANCOUVER ISLAND AND EVENTUALLY NORTHWEST WA.  THERE ARE
TIMING DIFFERENCES AS TO WHEN PRECIP DEVELOPS...WITH HIGHER
AMOUNTS EXPECTED BEYOND THIS PERIOD IN THE MOST OF MODELS. THE
12Z-00Z ECMWF HAS ACCUMULATIONS AT THE HIGHER PEAKS OF THE
OLYMPICS AND NORTHERN WA CASCADES WHILE THE 00Z NAM WAITS BEYOND
THIS PERIOD FOR ACCUMULATING SNOW TO DEVELOP. ALSO LIGHT ICING IS
POSSIBLE WHERE TRAPPED SFC COLD AIR PERSISTS IN SOME OF THE
CASCADES MOUNTAIN PASSES AND IN THE COLUMBIA RIVER GORGE.

PETERSEN

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