Quantitative Precipitation Forecast
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FOUS11 KWBC 190904
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
403 AM EST MON FEB 19 2018

VALID 12Z MON FEB 19 2018 - 12Z THU FEB 22 2018


DAYS 1-3...

...WESTERN U.S...

WIDESPREAD SNOWFALL IS EXPECTED FROM CALIFORNIA TO THE FOUR
CORNERS STATES ON MONDAY AS A HIGHLY ANOMALOUS UPPER TROUGH
CONTINUES TO AMPLIFY OVER THE WESTERN U.S..  THE LOWERING HEIGHTS,
COMBINED WITH DEEP SOUTHWESTERLY INFLOW AHEAD OF THE AMPLIFYING
TROUGH, SHOULD RESULT IN PERIODS OF HEAVY SNOW ALONG THE FAVORED
TERRAIN, WITH THE HIGHEST TOTALS EXPECTED OVER THE SAN JUAN
MOUNTAINS IN SOUTHWEST COLORADO WHERE WPC DAY 1 PROBABILITIES
(VALID 12Z MON - 12Z TUES) ARE SHOWING A HIGH RISK OF SNOWFALL
ACCUMULATIONS IN EXCESS OF A FOOT.

THE WIDESPREAD HEAVY SNOW ACROSS THE WEST SHOULD FINALLY BEGIN TO
DIMINISH ON TUESDAY WHILE THE UPPER TROUGH AXIS SHIFTS EASTWARD.
HOWEVER, MULTIPLE SHORTWAVES DIGGING INTO A RELOADING UPPER TROUGH
COULD BRING AN ADDITIONAL CHANCE FOR SNOW TO PORTIONS OF THE
WESTERN U.S. WEDNESDAY INTO THURSDAY.  THERE IS STILL SOME
UNCERTAINTY WITH THE EXACT DETAILS OF THESE FEATURES, BUT THE BEST
MODEL CONSENSUS SUGGEST THAT LIGHT TO MODERATE SNOW WILL BE
POSSIBLE OVER THE PACIFIC NORTHWEST AND NORTHERN CALIFORNIA AS
SUCCESSIVE SHORTWAVES DROP THROUGH THE REGION.  ALSO, A WEAK
SHORTWAVE CROSSING THE FOUR CORNERS STATES COULD LEAD TO
ADDITIONAL LIGHT TO MODERATE ACCUMULATIONS OVER THE SAN JUAN AND
SANGRE DE CRISTO MOUNTAINS.


...CENTRAL/NORTHERN PLAINS TO THE MIDDLE/UPPER MISSISSIPPI VALLEY,
GREAT LAKES, AND OHIO VALLEY...

WINTRY WEATHER WILL IMPACT A LARGE PORTION OF THE CENTRAL U.S. AS
A HIGHLY ANOMALOUS WESTERN U.S. TROUGH EDGES EASTWARD DURING THE
FIRST HALF OF THE WORK WEEK.

MONDAY INTO TUESDAY, MODERATE TO LOCALLY HEAVY SNOW SHOULD DEVELOP
WITHIN AN AXIS OF LOW TO MID LEVEL FRONTOGENESIS SETTING UP FROM
EASTERN WYOMING NORTHEASTWARD INTO THE NORTHERN PLAINS.  WPC
PROBABILITIES ARE CURRENTLY HIGHLIGHTING A BROAD MODERATE RISK OF
SNOWFALL ACCUMULATIONS EXCEEDING 4-INCHES ACROSS THE REGION WITH A
RELATIVELY EXPANSIVE HIGH RISK AREA CENTERED OVER SOUTH DAKOTA.
FARTHER EAST, WEAK SHORTWAVE ENERGY LIFTING NORTHEASTWARD AHEAD OF
THE WESTERN U.S. TROUGH AND AN ASSOCIATED SURFACE WAVE TRACKING
FROM THE MIDDLE MISSISSIPPI VALLEY TO THE UPPER GREAT LAKES SHOULD
RESULT IN SWATH OF ACCUMULATING SNOW ACROSS MINNESOTA, NORTHERN
WISCONSIN, AND THE U.P. OF MICHIGAN. WPC PROBABILITIES INDICATE
THE GREATEST CHANCE FOR SNOWFALL ACCUMULATIONS IN EXCESS OF
4-INCHES SHOULD BE JUST SOUTH OF YESTERDAY`S(SUNDAY`S) SNOWFALL.
FREEZING RAIN IS EXPECTED SOUTH OF THE HEAVY SNOW, AND WPC
PROBABILITIES ARE HIGHLIGHTING A MODERATE RISK OF ICE
ACCUMULATIONS GREATER THAN 0.25-INCHES ACROSS CENTRAL/SOUTHERN
WISCONSIN.

THE THREAT FOR HEAVY SNOW SHOULD BEGIN TO DIMINISH BY TUESDAY.
HOWEVER, ADDITIONAL ICE ACCUMULATIONS WILL BE POSSIBLE FROM THE
MIDDLE/UPPER MISSISSIPPI VALLEY TO THE GREAT LAKES ON TUESDAY AS
STRONG SOUTHERLY FLOW AHEAD OF THE WESTERN U.S. TROUGH DRAWS WARM
MOIST AIR ACROSS THE TOP OF AN INVADING SHALLOW ARCTIC AIRMASS,
WITH THE THREAT FOR FREEZING RAIN EXPECTED TO SHIFT SLIGHTLY SOUTH
AND EAST ON WEDNESDAY.  THERE IS STILL SOME UNCERTAINTY WITH THE
EXACT TIMING OF PRECIPITATION AND ARRIVAL OF ARCTIC AIR, BUT WPC
PROBABILITIES REMAINED CONSISTENT IN ADVERTISING A SLIGHT RISK OF
ICE ACCUMULATIONS GREATER THAN 0.25 INCHES EXTENDING FROM
SOUTHWESTERN MISSOURI TO NORTHWESTERN INDIANA DURING THE DAY 2
PERIOD (12Z TUE - 12Z WED).

PLEASE REFER TO WPC`S QPF DISCUSSION (QPFPFD) FOR THE LATEST
INFORMATION ON THE HEAVY RAINFALL THREAT WITH THIS SYSTEM.


GERHARDT


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