Quantitative Precipitation Forecast
Issued by NWS

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FOUS11 KWBC 182103
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
402 PM EST SUN FEB 18 2018

VALID 00Z MON FEB 19 2018 - 00Z THU FEB 22 2018


DAYS 1-3...

...WESTERN U.S....

AN UPPER TROUGH WILL CONTINUE TO AMPLIFY ACROSS THE WESTERN
U.S....WITH A VIGOROUS SHORTWAVE DIGGING SOUTH FROM THE PACIFIC
NORTHWEST INTO THE SOUTHWESTERN U.S. ON MON.  BY MON EVENING THE
GFS SHOWS 500MB HEIGHT STANDARDIZED ANOMALIES 2-3 DEVIATIONS BELOW
NORMAL ACROSS MUCH OF THE WESTERN U.S.  THE HEAVY SNOW THREAT IS
FORECAST TO DIMINISH ACROSS THE NORTHWEST AND NORTHERN ROCKIES SUN
NIGHT...SHIFTING FURTHER SOUTH INTO THE CENTRAL AND SOUTHERN
ROCKIES ON MON.  DEEP SOUTHWESTERLY INFLOW AHEAD OF THE PREVIOUSLY
NOTED SHORTWAVE ALONG WITH STRONG MID-UPPER LEVEL FORCING IS
EXPECTED TO SUPPORT HEAVY SNOW ACCUMULATIONS ALONG THE
UINTAS...WASATCH AND THE WESTERN CO RANGES...ESPECIALLY THE SAN
JUANS.  WPC DAY 1 PROBABILITIES (ENDING 00 UTC TUE)...INDICATE
THAT ACCUMULATIONS OF 8-INCHES OR MORE ARE LIKELY FOR PORTIONS OF
THIS REGION.  FURTHER NORTH...UPSLOPE FLOW IN THE WAKE OF AN
ARCTIC BOUNDARY SLIDING SOUTH...ALONG WITH LOW TO MID LEVEL
FRONTOGENESIS...WILL SUPPORT SOME HEAVIER AMOUNTS FROM THE
SOUTHEASTERN WY RANGES INTO THE HIGH PLAINS AND BLACK HILLS REGION.

DAY 2 PROBABILITIES (ENDING 00 UTC WED) SHOW THE HEAVY SNOW THREAT
CONTINUING TO DIMINISH ACROSS MUCH OF THE WESTERN U.S. AS THE
UPPER TROUGH BEGINS TO SHIFT EAST.  SNOWS CONTINUING INTO TUE
NIGHT MAY PRODUCE SOME ADDITIONAL HEAVY ACCUMULATIONS ACROSS CO
MOUNTAINS...WITH WPC PROBABILITIES INDICATING THE POTENTIAL FOR
ACCUMULATIONS OF 8-INCHES OR MORE ACROSS A SMALL PORTION OF THE
HIGHER TERRAIN.  OTHERWISE...SNOWS ARE EXPECTED TO DIMINISH ACROSS
MUCH OF THE REGION...WITH ADDITIONAL HEAVY TOTALS NOT EXPECTED.

...CENTRAL PLAINS/LOW MO VALLEY/MID MS VALLEY/UPPER GREAT LAKES...

ONGOING SNOWS ACROSS NORTHERN MN ARE EXPECTED SHIFT FURTHER
NORTHEAST SUN EVENING AS THE ASSOCIATED UPPER LEVEL SHORTWAVE AND
SURFACE LOW MOVE FROM THE NORTHERN PLAINS INTO SOUTHERN ONTARIO.

ON MON...GUIDANCE SHOWS A WEAK WAVE ASSOCIATED WITH SHEARED
SOUTHERN STREAM ENERGY LIFTING NORTHEAST FROM THE MID MS VALLEY.
GUIDANCE CONTINUES TO SHOW MIXED PRECIPITATION POSSIBLY PRODUCING
LIGHT ICE ACCUMULATIONS FROM THE LOWER MO AND MID MS VALLEY
NORTHEASTWARD INTO THE UPPER GREAT LAKES REGION.

ON TUE...A STRIPE OF LIGHT TO MODERATE SNOW ASSOCIATED WITH AN
AXIS OF LOW TO MID LEVEL FRONTOGENESIS IS EXPECTED TO EXTEND FROM
THE CENTRAL HIGH PLAINS NORTHEASTWARD INTO THE UPPER MS VALLEY AND
GREAT LAKES...WITH WPC PROBABILITIES INDICATING A SLIGHT RISK OR
GREATER FOR ACCUMULATIONS OF 4-INCHES OR GREATER ACROSS THE
REGION.  MEANWHILE...A MORE AMPLIFIED SHORTWAVE IS FORECAST TO
DEVELOP ALONG THE RIGHT-ENTRANCE REGION OF A STRENGTHENING UPPER
JET...LIFTING ONCE AGAIN FROM THE MID MS VALLEY.  THIS IS EXPECTED
TO PRODUCE ANOTHER ROUND OF FROZEN PRECIPITATION...WITH GUIDANCE
INDICATING A GREATER THREAT FOR SIGNIFICANT ICE ACCUMULATIONS.
WPC DAY 2 PROBABILITIES (ENDING 00 UTC WED) SHOW A SLIGHT RISK OR
GREATER FOR ICE ACCUMULATIONS OF 0.25 INCH OR MORE EXTENDING
NORTHEAST FROM THE LOWER MO VALLEY INTO SOUTHERN WISC AND NORTHERN
LOWER MI.  PROBABILITIES CONTINUE TO HIGHLIGHT A MODERATE RISK FOR
PORTIONS OF SOUTHERN WI.

ON WED...AS THE PREVIOUSLY NOTED LOW LIFTS ACROSS THE GREAT
LAKES...ITS TRAILING COLD FRONT WILL PUSH SOUTHEAST ACROSS THE MID
AND LOWER MS VALLEY.  PRECIPITATION IS EXPECTED ALONG AND BEHIND
THE FRONT...WITH PRECIPITATION CHANGING TO FREEZING RAIN BEFORE
ENDING ACROSS SOME LOCATIONS.  MODELS DIFFER WITH HOW QUICKLY THE
COLD AIR ARRIVES...WITH THE NAM ONE OF THE MORE AGGRESSIVE
SOLUTIONS...BRINGING THE COLD AIR IN MORE QUICKLY...PRODUCING A
NARROW STRIPE OF VERY HEAVY ICE ACCUMULATIONS FROM EASTERN OK TO
CENTRAL IL.  WPC DAY 3 PROBABILITIES SHOW ONLY A SLIGHT RISK FOR
ICE ACCUMULATIONS OF 0.25 INCH OR MORE ACROSS THIS
REGION...INDICATING THE GUIDANCE IS FAR FROM AGREEMENT.

PEREIRA


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