Quantitative Precipitation Forecast
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FOUS11 KWBC 240727
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
327 AM EDT TUE OCT 24 2017

VALID 12Z TUE OCT 24 2017 - 12Z FRI OCT 27 2017


...DAY 1...
...GREAT LAKES...

MOST OF THE GUIDANCE SHOWS A LOW MOVING INTO THE EASTERN U.P.
EARLY TUE.  BY TUE AFTERNOON-EVENING...MODELS SHOW ENOUGH COLD AIR
ON THE BACKSIDE OF THE SYSTEM FOR RAIN CHANGING TO SNOW ACROSS
PORTIONS OF THE WESTERN U.P. INTO FAR NORTHERN WISCONSIN.
GUIDANCE IS IN GOOD AGREEMENT THAT WARM BOUNDARY LAYER CONDITIONS
WILL HAMPER THE POTENTIAL FOR SIGNIFICANT ACCUMULATIONS OUTSIDE OF
THE HIGHER TERRAIN OF THE U.P.  THE 00 UTC MODELS AND 21 SREF MEAN
SHOWED SUPPORT FOR 2-4 INCHES OF SNOW ACROSS THE HURON
MOUNTAINS...WITH THE NAM SHOWING FASTER COOLING AND HEAVIER
QPF...LEADING TO HEAVIER TOTALS. THE WPC PROBABILITIES...WHICH
INDICATE A SLIGHT RISK FOR ACCUMULATIONS OF 8-INCHES OR MORE BY
THE END OF THE DAY 1 PERIOD (ENDING 00 UTC WED).

...DAYS 2-3 FRONT RANGE OF THE ROCKIES FROM MT TO WT/CO/NORTHERN
NM...
THE MODELS INDICATE A COLD FRONT MOVES STEADILY SOUTH DOWN THE
FRONT RANGES OF THE ROCKIES STARTING IN MT AND WY ON DAY 2 AND
THEN CONTINUING SOUTH ACROSS CO INTO NM ON DAY 3.  POST-FRONTAL
BRIEF UPSLOPE FLOW AND FRONTOGENESIS LEAD TO A PERIOD OF LIFT AND
SNOW IN THE MOUNTAINS.  THE SNOW LASTS SEVERAL HOURS BUT THE
MODELS ALSO SHOW DRYING ALOFT AFTERWARD THAT LIMITS THE DURATION
OF SNOW.  THE THREAT IS LIMITED TO WHERE TERRAIN ENHANCES LIFT AND
WHERE TEMPERATURES ARE COLD LONG ENOUGH FOR ACCUMULATIONS TO
OCCUR...ON THE FRONT RANGE AND ADJACENT FOOTHILLS OF THE MT/WY/CO
ROCKIES TO SANGRE DE CRISTO MTNS FROM SOUTHEAST CO/NORTHEAST NM.

...DAY 3 UPPER MIDWEST...
A SHORTWAVE IS FORECAST TO MOVE OUT OF THE NORTHERN PLAINS TOWARDS
THE UPPER MIDWEST...WITH A SURFACE LOW PROGRESSING ACROSS NORTH
DAKOTA AND MINNESOTA TO WISCONSIN IN THE ECMWF/GFS/ECMWF ENSEMBLE
MEAN FORECASTS.  GUIDANCE SHOWS THE POTENTIAL FOR A STRIPE OF
SIGNIFICANT SNOWS NORTH OF THE LOW CENTER...WITH THE HEAVIEST
AMOUNTS MOST LIKELY TO FALL ACROSS SOUTHERN CANADA NORTH OF MN.
THE WPC PREFERENCE WAS FOR A LOW TRACK A LITTLE FURTHER SOUTH THAN
THE NAM...WITH A LITTLE MORE SNOW ACCUMULATIONS THAN THE NAM
ACROSS NORTHERN MINNESOTA...SIMILAR TO THE GFS AND THE ECMWF.
UNCERTAINTY INVOLVES PRECIP TYPE WITH INITIAL CONDITIONS TOO WARM
FOR SNOW AND A CHANGE OVER WITH TEMPERATURES QUICKLY FALLING WITH
THE LOW PASSAGE IN EAST ND/NORTHERN MN.

FOR DAYS 1-3...THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN
10 PERCENT.

PETERSEN

$$





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