Quantitative Precipitation Forecast
Issued by NWS

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496
FOUS11 KWBC 290758
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
357 AM EDT SAT APR 29 2017

VALID 12Z SAT APR 29 2017 - 12Z TUE MAY 02 2017

...CENTRAL/SOUTHERN ROCKIES TO THE CENTRAL PLAINS AND UPPER
MISSISSIPPI VALLEY...

A LATE SEASON SNOW EVENT WILL IMPACT THE CENTRAL/SOUTHERN ROCKIES
TO THE CENTRAL PLAINS AND UPPER MISSISSIPPI VALLEY THIS WEEKEND.

THE HEAVIEST SNOW AND HIGHEST ACCUMULATIONS WITH THIS EVENT SHOULD
BE OVER THE SANGRE DE CRISTO MOUNTAINS OF SOUTHEAST COLORADO AND
NORTHEAST NEW MEXICO AS MOISTURE WRAPS AROUND A CLOSED LOW MOVING
ACROSS NORTHERN NM TO THE OK PANHANDLE.  LOW LEVEL FLOW BACKING
TOWARDS THE NORTHEAST GETS LIFTED IN WINDWARD TERRAIN TO AUGMENT
THE STRONG 700-500 MB ASCENT TO PRODUCE HEAVY SNOW IN THE
FOOTHILLS AND MOUNTAINS OF SOUTHEAST CO/NORTHEAST NM. POST-FRONTAL
COLD ADVECTION IN THE PLAINS OF SOUTHEAST CO AND WESTERN KS ALLOWS
A TRANSITION FROM RAIN TO SNOW WITH HEAVY SNOW ALSO LIKELY IN
THESE AREAS. THE RAIN-SNOW TRANSITION LINE DRIFTS EAST TOWARDS
CENTRAL KS SAT...WITH THE LIMITING FACTOR IN CENTRAL KS THE
DURATION OF SNOW.

ON SUN THE LOW MOVES NORTHEAST ACROSS THE CENTRAL PLAINS TOWARDS
THE UPPER MS VALLEY. THE CHANCE FOR SNOW WILL BE ON THE WESTERN
QUADRANT OF PRECIPITATION DEVELOPING WITHIN A STRENGTHENING MID
LEVEL DEFORMATION ZONE.  HOWEVER...MODEL GUIDANCE REMAINS
UNCERTAIN WITH LOW LEVEL THERMAL PROFILES AND HOW MUCH SNOW CAN
ACCUMULATE. THERE IS LIKELY TO BE A POOL WHERE IT IS COLD ENOUGH
FOR SNOW WEST OF THE LOW LEVEL CYCLONE BUT PRECIP IN THE FORM OF
RAIN IS ALSO LIKELY IN NORTHEAST NEBRASKA AND EASTERN SD.

THE NAM CONTINUES TO BE ON THE COLDER SIDE OF MODEL SPREAD AND
HIGHEST WITH SNOWFALL ACCUMULATIONS...WHICH IS PARTLY DUE TO
SLOWER CYCLONE MOVEMENT AND MORE QPF IN THE WESTERN PORTION OF OF
THE CIRCULATION IN NORTH CENTRAL KS TO NORTHEAST NEBRASKA.
THE ECMWF CONTINUES TO REPRESENT THE WARMER SIDE OF MODEL
SPREAD...WITH LOWER SNOW ACCUMULATIONS AS A RESULT. HOWEVER THE
00Z ECMWF HAS TRENDED COOLER WITH FORECASTS OF SEVERAL INCHES OF
SNOW IN NORTH CENTRAL KANSAS AND CENTRAL NEBRASKA.

ON MON THE CYCLONE EXITS THE UPPER MS VALLEY INTO ONTARIO WITH THE
PRIMARY THREAT ACROSS CENTRAL TO NORTHEAST MN.  THE GFS/GEFS/21Z
SREF CONTINUE TO ADVERTISE POTENTIAL
FOR HIGHER AMOUNTS THAN THE ECMWF/ECMWF ENSEMBLE MEAN PRIMARILY
DUE TO TEMPERATURE DIFFERENCES AND POTENTIAL DURATION OF SNOW. THE
NAM HIGHER AMOUNTS ARE A COMBINATION OF COLDER TEMPERATURES AND
MORE COLD SECTOR PRECIP DUE TO THE SLOWER MOTION OF THE LOW.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.

PETERSEN

$$





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