Prognostic Meteorological Discussion
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FXUS21 KWNC 062124
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST DECEMBER 06 2016

SYNOPSIS: A STRONG AREA OF SURFACE HIGH PRESSURE IS FORECAST TO SHIFT SOUTH
FROM CANADA THIS WEEK AND THEN SHIFT OFFSHORE OF THE EAST COAST BY DECEMBER 12.
NEXT WEEK, ARCTIC HIGH PRESSURE IS EXPECTED TO BUILD SOUTHEAST ACROSS MUCH OF
THE CONTINENTAL U.S. MULTIPLE WAVES OF LOW PRESSURE ARE EXPECTED TO PUSH INLAND
INTO THE PACIFIC NORTHWEST, NORTHERN CALIFORNIA, AND NORTHERN ROCKIES DURING
THE NEXT WEEK. A STRONG AREA OF UPPER-LEVEL HIGH PRESSURE IS EXPECTED TO REMAIN
ANCHORED OVER THE BERING SEA DURING THE NEXT TWO WEEKS WITH ARCTIC HIGH
PRESSURE PERSISTING ACROSS SOUTHEASTERN MAINLAND ALASKA AND THE ALASKA
PANHANDLE.

HAZARDS

MUCH BELOW-NORMAL TEMPERATURES FOR THE GREAT PLAINS AND LOWER MISSISSIPPI
VALLEY, FRI, DEC 9.

MUCH BELOW-NORMAL TEMPERATURES FOR THE SOUTHEASTERN U.S., SAT, DEC 10.

MUCH BELOW-NORMAL TEMPERATURES RETURNING TO THE NORTHERN GREAT PLAINS, MON-TUE,
DEC 12-13.

HEAVY, LAKE-EFFECT SNOW DOWNWIND OF THE GREAT LAKES, FRI, DEC 9.

PERIODS OF HEAVY PRECIPITATION (RAIN AND HIGH-ELEVATION SNOW) FOR PARTS OF THE
PACIFIC NORTHWEST AND NORTHERN CALIFORNIA, FRI-TUE, DEC 9-13.

PERIODS OF HEAVY SNOW FOR PARTS OF THE NORTHERN ROCKIES, FRI-TUE, DEC 9-13.

MUCH BELOW NORMAL TEMPERATURES ACROSS THE ALASKA PANHANDLE, FRI-TUE, DEC 9-13.

HEAVY LAKE-EFFECT SNOW DOWNWIND OF THE GREAT LAKES, WED-THU, DEC 14-15.

A SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR MUCH OF THE CONTINENTAL
U.S. AND THE ALASKA PANHANDLE, WED-TUE, DEC 14-20.

A MODERATE RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR PARTS OF THE PACIFIC
NORTHWEST, NORTHERN ROCKIES, GREAT PLAINS, MIDWEST, GREAT LAKES, AND ALASKA
PANHANDLE, WED-SUN, DEC 14-18.

A HIGH RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR PARTS OF THE NORTHERN ROCKIES
AND NORTHERN GREAT PLAINS, WED-SUN, DEC 14-18.

SEVERE DROUGHT ACROSS PARTS OF THE EASTERN U.S., GREAT PLAINS, MISSOURI RIVER
VALLEY, CENTRAL ROCKIES, INTERMOUNTAIN WEST, CALIFORNIA AND HAWAII.

DETAILED SUMMARY

FOR FRIDAY DECEMBER 09 - TUESDAY DECEMBER 13: A SURFACE HIGH, WITH AN INITIAL
STRENGTH OF 1052-HPA OVER WESTERN CANADA, IS FORECAST TO BRING MUCH
BELOW-NORMAL TEMPERATURES TO THE CENTRAL U.S. ON FRIDAY, DEC 9 BEFORE SHIFTING
INTO THE SOUTHEASTERN U.S. BY SATURDAY MORNING, DEC 10. THE MUCH BELOW-NORMAL
TEMPERATURE HAZARD IS POSTED FOR AREAS WHERE THE MINIMUM TEMPERATURE ARE
FORECAST TO AVERAGE 12 DEGREES F OR MORE BELOW NORMAL. SUBZERO MINIMUM
TEMPERATURES ARE EXPECTED TO EXTEND AS FAR SOUTH AS THE CENTRAL HIGH PLAINS ON
DEC 9.  ALTHOUGH HARD FREEZES ARE LIKELY ALONG THE GULF COAST ON DEC 8 AND 9,
FREEZING TEMPERATURES ARE NOT EXPECTED ACROSS THE MAJOR CITRUS GROWING AREAS OF
SOUTH TEXAS AND THE FLORIDA PENINSULA AT THIS TIME. EARLY NEXT WEEK, ARCTIC
HIGH PRESSURE IS LIKELY TO RESULT IN MUCH BELOW-NORMAL TEMPERATURES ACROSS
NORTHERN GREAT PLAINS WHERE MINIMUM TEMPERATURES BELOW -10 DEGREES F ARE
FORECAST ON DEC 13 ACROSS EASTERN MONTANA AND NORTH DAKOTA.



STRONG COLD AIR ADVECTION IS FORECAST TO PROMOTE HEAVY LAKE-EFFECT SNOW
DOWNWIND OF THE GREAT LAKES THROUGH FRIDAY, DEC 9. TOTAL SNOWFALL AMOUNTS ARE
EXPECTED TO EXCEED ONE FOOT IN THE MOST FAVORED SNOW BELTS SOUTH AND EAST OF
THE GREAT LAKES.



WAVES OF LOW PRESSURE ARE FORECAST TO BRING PERIODS OF HEAVY RAIN AND
HIGH-ELEVATION SNOW (TOTAL AMOUNTS OF MORE THAN 5 INCHES, LIQUID EQUIVALENT) TO
PARTS OF THE PACIFIC NORTHWEST AND NORTHERN CALIFORNIA FROM DEC 9 TO 13.
SEVERAL FEET OF SNOW ARE EXPECTED ACROSS THE HIGHER ELEVATIONS OF THE SOUTHERN
CASCADES OF OREGON, NORTHERN SIERRA MOUNTAINS OF CALIFORNIA, AND NORTHERN
ROCKIES DURING THE NEXT WEEK.



ARCTIC HIGH PRESSURE OVER WESTERN CANADA AND ANOMALOUS EASTERLY FLOW IS
EXPECTED TO RESULT IN MUCH BELOW-NORMAL TEMPERATURES ACROSS THE ALASKA
PANHANDLE FROM DEC 9 TO 13. THE 6Z GFS ENSEMBLE MEAN GENERALLY INDICATES THAT
TEMPERATURES WILL AVERAGE 16 DEGREES F OR GREATER BELOW NORMAL ACROSS THE
ALASKA PANHANDLE.

FOR WEDNESDAY DECEMBER 14 - TUESDAY DECEMBER 20: ENSEMBLE MEANS AGREE THAT
ANOMALOUS RIDGING ALOFT PERSISTS ACROSS THE BERING SEA AND WESTERN ALASKA
THROUGH WEEK-2. MUCH BELOW-NORMAL TEMPERATURES ARE LIKELY TO AFFECT AT LEAST
THE NORTH-CENTRAL U.S. AND PARTS OF ALASKA THROUGH MID-DECEMBER. THE SLIGHT,
MODERATE, AND HIGH RISK OF MUCH BELOW-NORMAL TEMPERATURES IS BASED GENERALLY ON
AREAS WHERE THE GEFS REFORECAST TOOL INDICATES DAILY MINIMUM TEMPERATURES WITH
A 20, 40, OR 60 PERCENT CHANCE, RESPECTIVELY, OF FALLING BELOW THE 15TH
PERCENTILE COMPARTED TO CLIMATOLOGY. THE 6Z GFS ENSEMBLE MEAN INDICATES
TEMPERATURES AVERAGING AS MUCH AS 30 DEGREES F BELOW NORMAL ACROSS THE NORTHERN
HIGH PLAINS EARLY IN WEEK-2. THE LARGEST DIFFERENCE AMONG THE MODEL GUIDANCE IS
ACROSS THE PACIFIC NORTHWEST WHERE THE 0Z ECMWF ENSEMBLE MEAN INDICATES MORE
UPPER-LEVEL RIDGING ALONG THE WEST COAST. IF THE GFS ENSEMBLE MEANS VERIFY WITH
A LARGER AREA OF ARCTIC HIGH PRESSURE, THEN A GREATER RISK OF RECORD COLD
EXISTS ACROSS THE PACIFIC NORTHWEST.



THE NEXT OUTBREAK OF ARCTIC AIR IS EXPECTED TO RESULT IN HEAVY LAKE-EFFECT SNOW
DOWNWIND OF THE GREAT LAKES ON DEC 14 AND 15. NO ADDITIONAL WINTER WEATHER
HAZARDS ARE POSTED DURING WEEK-2 AS ONSHORE FLOW IS EXPECTED TO EASE ACROSS THE
WESTERN U.S., REDUCING CONFIDENCE ON HEAVY SNOW ACROSS THE SIERRA MOUNTAINS AND
NORTHERN/CENTRAL ROCKIES. ELSEWHERE, PRECIPITATION AMOUNTS ARE UNCERTAIN ACROSS
THE CENTRAL AND EASTERN U.S. ASSOCIATED WITH ANY WAVES OF LOW PRESSURE
PRECEDING OR ALONG THE ARCTIC FRONT.



ACCORDING TO THE LATEST U.S. DROUGHT MONITOR (USDM) VALID ON NOVEMBER 29, THE
COVERAGE OF SEVERE OR GREATER DROUGHT FOR THE CONUS DECREASED NEARLY A HALF
PERCENT TO 16.6%. IMPROVEMENTS WERE NOTED FOR PORTIONS OF THE LOWER MISSISSIPPI
VALLEY AND NEW YORK STATE. WHILE THE MOST RECENT USDM SHOWS DETERIORATION OF
DROUGHT CONDITIONS IN THE SOUTHEAST, RAINS FOLLOWING THE LATEST RELEASE MAY
YIELD IMPROVEMENT FOR THE NEXT PUBLICATION.

FORECASTER: BRAD PUGH

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