Quantitative Precipitation Forecast
Issued by NWS

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FOUS11 KWBC 242027
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
426 PM EDT THU APR 24 2014

VALID 00Z FRI APR 25 2014 - 00Z MON APR 28 2014


DAY 1...

...UPPER MS VALLEY/UPPER GREAT LAKES...

AN UPPER LEVEL SHORTWAVE TROUGH WILL CLOSE OFF OVERNIGHT OVER
NORTHEASTERN MINNESOTA WITH SNOW CONTINUING OVERNIGHT BEFORE
TAPERING OFF BY MORNING. THE HEAVIEST SNOW WILL LIKELY FALL
NORTHEASTWARD ACROSS THE ARROWHEAD REGION WITH A MEDIUM TO HIGH
PROBABILITY OF GREATER THAN 4 INCHES AFTER 00 GMT.  TOTAL
ACCUMULATIONS COULD TOTAL UP TO A FOOT THE FARTHER NORTHEAST YOU
GO IN THE REGION FROM SNOW THIS AFTERNOON INTO OVERNIGHT.  WITH A
SHORT DURATION FORECAST SUCH AS THIS...A BLEND OF SEVERAL MODELS
WAS USED TO GENERATE THE FORECAST QPF...WHILE THE MAJORITY OF THE
12Z RUNS SHOWED A QPF MAXIMUM NEAR AN INCH CLOSE TO THE NORTHEAST
MINNESOTA/CANADIAN BORDER...ALLOWING FOR AT LEAST 4O TO 70 PERCENT
PROBABILITIES OF GREATER THAN 8 INCHES OF SNOW.

DAYS 1 THROUGH 3...

...WEST COAST/GREAT BASIN/NORTHERN AND CENTRAL ROCKIES...

AN AMPLIFYING LONG WAVE TROUGH OVER THE WESTERN US WILL SPREAD
THREE DAYS OF WINTER WEATHER OVER THE HIGHER ELEVATIONS OF THE
WEST. A MULTI MODEL BLEND WAS AGAIN USED FOR THE QPF/THERMAL
PROFILES BUT THERE WAS AN EMPHASIS ON THE 00Z/12Z ECMWF VERSUS THE
12Z GFS IN THE LARGE SCALE DETAILS WITH THE 03Z/09Z SREFMEANS
PROVIDING LOCAL ENHANCEMENTS. THE 06Z AND 12Z BIAS CORRECTED MULTI
MODEL ENSEMBLE MEAN ALSO APPEARED TO PROVIDE SOME GOOD INFORMATION
AS WELL.

ON DAY 1...THE UPPER TROUGH AMPLIFIES SOUTHEASTWARD OVER THE
EASTERN PACIFIC AND MOVES TOWARD THE CENTRAL CALIFORNIA COAST BY
LATER FRIDAY.  WHILE DROPPING FREEZING LEVELS WILL PROGRESS SLOWLY
EASTWARD ACROSS THE NORTHWEST...IT WILL DROP DRAMATICALLY OVER
NORTHERN CALIFORNIA AS RAIN AND SNOW SPREAD SOUTHEASTWARD ACROSS
NORTHERN INTO CENTRAL CALIFORNIA.  SNOWFALL LEVELS ARE EXPECTED TO
DROP AS LOW AS 4000 TO 4500 FEET...ALLOWING SNOW TO FALL ACROSS
THE KLAMATH AND CASCADE RANGES INCLUDING MOUNT SHASTA AND THEN
SPREAD ACROSS THE SIERRA NEVADA. THE HEAVIEST SNOW IS MORE LIKELY
TO FALL ACROSS THE SIERRA WITH 6 TO 12 INCH AMOUNTS COMMON BY
FRIDAY EVENING WITH SNOW CONTINUING INTO DAY 2. SNOW WILL ALSO
OCCUR OVER THE WASHINGTON AND OREGON CASCADES...BUT IS NOT
EXPECTED TO PARTICULARLY HEAVY SINCE MOST OF THE LIFT WILL OCCUR
FARTHER SOUTH.  SNOW WILL ALSO FALL ACROSS INTERIOR OREGON...THE
SAWTOOTH AND BITTERROOTS IN IDAHO AND WESTERN MONTANA...PARTS OF
MOSTLY NORTHWESTERN NEVADA AND NORTHWEST WYOMING. MOST OF THE
SNOWFALL WILL NOT BE EXCESSIVE BUT THERE IS A LOW TO EVEN HIGH
CHANCE OF 4 TO 8 INCHES ESPECIALLY ACROSS THE SAWTOOTH RANGE IN
IDAHO.

THE FULL EXTENT OF THE UPPER TROUGH MOVES OVER THE WEST ON DAY
2/FRIDAY EVENING TO SATURDAY EVENING. AS IT DOES SO...MUCH OF THE
SNOWFALL OVER THE WASHINGTON AND OREGON CASCADES ENDS.  THE SNOW
CONTINUES ACROSS THE SIERRAS AND SPREADS SOUTHWARD AND SIGNIFICANT
SNOW IS EXPECTED ACROSS THE HIGHER ELEVATIONS OF
NEVADA...PARTICULARLY ACROSS THE CENTRAL AND EASTERN REGIONS.
SIGNIFICANT SNOW ALSO SPREADS TO THE UTAH WASATCH RANGE...WITH
SOME OF THE HEAVIEST SNOW EXPECTED ACROSS SOUTHERN UTAH.
FINALLY...SNOW ALSO CONTINUES ACROSS THE MOUNTAINS OF NW
WYOMING...THE SAN JUAN MOUNTAINS IN SW COLORADO...THE BITTERROOTS
AND ESPECIALLY ACROSS NORTHWESTERN MONTANA.  SOME OF THE HEAVIEST
SNOW IS EXPECTED ACROSS THE AREAS JUST TO THE NORTH OF THE INTENSE
500 MB VORTICITY LOBE WHICH CROSSES SOUTHERN CALIFORNIA/NORTHERN
ARIZONA AND NEW MEXICO. HERE AGAIN...MOST OF THE HEAVIEST SNOW IS
EXPECTED GENERALLY TO BE IN THE 4 TO 8 INCH RANGE WITH LOW
PROBABILITIES OF A FOOT OR MORE BUT THE COMBINED 2 DAY SNOWFALL
ACROSS THE SIERRA WILL LIKELY EXCEED ONE FOOT IN MANY PLACES.

BY DAY 3...THE DEEP TROUGH IS CHARACTERIZED BY A DEVELOPING CUTOFF
LOW AS IT SLOWLY MOVES TO THE NORTHEAST.  AS A RESULT...THE
HEAVIER SNOW HAS ALSO SHIFTED WITH THE BULK OF THE SNOW EXPECTED
ACROSS THE COLORADO ROCKIES WITH A GENERAL WIDESPREAD AREA OF 4 TO
12 INCHES OF SNOW.

IN ADDITION...A NEW TROUGH IS EXPECTED TO SLIDE SOUTHEASTWARD
ACROSS THE PACIFIC NORTHWEST...INCREASING THE CHANCES FOR MORE
SNOW ACROSS THE WASHINGTON AND OREGON CASCADES.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.


KOCIN

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