Prognostic Meteorological Discussion
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FXUS21 KWNC 051920
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST DECEMBER 05 2016

SYNOPSIS: A STRONG AREA OF SURFACE HIGH PRESSURE IS FORECAST TO SHIFT SOUTH
FROM CANADA THIS WEEK AND BECOME CENTERED OVER THE EASTERN U.S. DURING THE
WEEKEND. MULTIPLE WAVES OF SURFACE LOW PRESSURE ARE EXPECTED TO PUSH INLAND
INTO THE PACIFIC NORTHWEST, NORTHERN CALIFORNIA, AND NORTHERN ROCKIES THROUGH
AT LEAST EARLY NEXT WEEK. DURING WEEK-2, ARCTIC HIGH PRESSURE IS LIKELY TO
AFFECT THE NORTHERN GREAT PLAINS. 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 MUCH OF MAINLAND ALASKA AND THE ALASKA
PANHANDLE.

HAZARDS

MUCH BELOW-NORMAL TEMPERATURES FOR PARTS OF THE WESTERN AND CENTRAL U.S., THU,
DEC 8.

MUCH BELOW-NORMAL TEMPERATURES SHIFTING FROM THE CENTRAL TO SOUTHEASTERN U.S.,
FRI-SAT,  DEC 9-10.

HEAVY, LAKE-EFFECT SNOW DOWNWIND OF THE GREAT LAKES, THU-FRI, DEC 8-9.

FREEZING RAIN FOR PARTS OF THE PACIFIC NORTHWEST, THU, DEC 8.

HEAVY PRECIPITATION (RAIN AND HIGH-ELEVATION SNOW) FOR PARTS OF THE PACIFIC
NORTHWEST AND NORTHERN CALIFORNIA, THU-MON, DEC 8-12.

HIGH WINDS FOR THE PACIFIC NORTHWEST, THU, DEC 8.

HEAVY PRECIPITATION (RAIN AND HIGH-ELEVATION SNOW) FOR THE NORTHERN SIERRA
MOUNTAINS, THU-FRI, DEC 8-9.

HEAVY SNOW FOR PARTS OF THE NORTHERN ROCKIES, THU-SAT, DEC 8-10.

MUCH BELOW NORMAL TEMPERATURES ACROSS PORTIONS OF THE ALASKA PANHANDLE AND
MAINLAND ALASKA, THU-MON, DEC 8-12.

HIGH WINDS FOR THE NORTHERN ALASKA PANHANDLE, THU-FRI, DEC 8-9.

A SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR MUCH OF THE CENTRAL AND
EASTERN U.S. AND PARTS OF THE PACIFIC NORTHWEST AND NORTHERN ROCKIES, TUE-MON,
DEC 13-19.

A MODERATE RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR PARTS OF THE NORTHERN AND
CENTRAL GREAT PLAINS, UPPER MISSISSIPPI VALLEY, GREAT LAKES, NORTHERN ROCKIES,
AND NORTHERN INTERMOUNTAIN WEST, TUE-SAT, DEC 13-17.

A HIGH RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR PARTS OF THE NORTHERN GREAT
PLAINS AND NORTHERN ROCKIES, TUE-THU, DEC 13-15.

A SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR PARTS OF EASTERN MAINLAND
ALASKA AND THE ALASKA PANHANDLE, TUE-MON, DEC 13-19.

A MODERATE RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR THE ALASKA PANHANDLE,
TUE-SAT, DEC 13-17.

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

DETAILED SUMMARY

FOR THURSDAY DECEMBER 08 - MONDAY DECEMBER 12: A 1044-HPA SURFACE HIGH IS
FORECAST TO BRING MUCH BELOW-NORMAL TEMPERATURES INITIALLY TO THE WEST-CENTRAL
U.S. DURING MID-WEEK BEFORE SHIFTING INTO THE SOUTHEASTERN U.S. BY THE MORNING
OF DEC 10. THE MUCH BELOW-NORMAL TEMPERATURE HAZARD IS POSTED FOR AREAS WHERE
THE MINIMUM TEMPERATURE IS 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 8 AND 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.



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.



AN INCREASING RISK OF FREEZING RAIN EXISTS ACROSS PARTS OF THE INTERIOR PACIFIC
NORTHWEST DURING MID-WEEK AS PRECIPITATION ARRIVES WHEN SURFACE TEMPERATURES
ARE SLOW TO WARM ABOVE FREEZING. THE COLUMBIA RIVER GORGE, WILLAMETTE VALLEY,
AND EASTERN PARTS OF THE PORTLAND, OREGON METRO AREA ARE MOST LIKELY TO RECEIVE
FREEZING RAIN WITH SIGNIFICANT ICE ACCUMULATIONS THROUGH THURSDAY, DEC 8. A
STRONG PRESSURE GRADIENT IS EXPECTED TO RESULT IN HIGH WINDS (SPEEDS ABOVE 35
MPH) ACROSS OREGON AND WASHINGTON ALSO ON DEC 8. ELSEWHERE, WAVES OF LOW
PRESSURE ARE FORECAST TO BRING PERIODS OF HEAVY RAIN AND HIGH-ELEVATION SNOW TO
PARTS OF THE PACIFIC NORTHWEST AND NORTHERN CALIFORNIA FROM DEC 8 TO 12. TOTAL
PRECIPITATION AMOUNTS, LIQUID EQUIVALENT, ARE LIKELY TO EXCEED 5 INCHES ACROSS
THE SOUTHERN CASCADES DURING THIS TIME PERIOD. THE MOST LIKELY TIME FOR HEAVY
PRECIPITATION (RAIN AND SNOW AT ELEVATIONS ABOVE 7,000 FEET) ACROSS THE
NORTHERN SIERRAS IS ON DEC 8 AND 9. THE WAVES OF LOW PRESSURE ARE ALSO EXPECTED
TO BRING PERIODS OF HEAVY SNOW (MORE THAN 6 INCHES PER 24 HOURS) TO PARTS OF
THE NORTHERN ROCKIES FROM DEC 8 TO 10.



ALASKA IS FORECAST TO BE AFFECTED BY ANOMALOUSLY COLD TEMPERATURES, AS ARCTIC
HIGH PRESSURE REMAINS CENTERED OVER EASTERN ALASKA OR WESTERN CANADA. THE 6Z
GFS ENSEMBLE MEAN GENERALLY INDICATES THAT TEMPERATURES WILL AVERAGE 16 DEGREES
F OR MORE BELOW NORMAL ACROSS THE AREA OF ALASKA OUTLINED WITH A MUCH
BELOW-NORMAL TEMPERATURE HAZARD. THE STRONG SURFACE HIGH OVER THE YUKON
SUPPORTS THE DEVELOPMENT OF HIGH EASTERLY WINDS (EXCEEDING 50 MPH) FOR EXPOSED
AREAS ACROSS THE NORTHERN ALASKA PANHANDLE THROUGH DEC 9.

FOR TUESDAY DECEMBER 13 - MONDAY DECEMBER 19: ENSEMBLE MEANS AGREE THAT
ANOMALOUS RIDGING ALOFT PERSISTS ACROSS THE BERING SEA WHICH IS LIKELY TO
RESULT IN ANOTHER ARCTIC HIGH SHIFTING SOUTH FROM CANADA INTO THE NORTHERN
GREAT PLAINS BY THE BEGINNING OF 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 ARE POSTED FOR AREAS WHERE THE GEFS REFORECAST TOOL INDICATES THAT
DAILY MINIMUM TEMPERATURES HAVE 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 MORE THAN 25 DEGREES F BELOW
NORMAL ACROSS THE NORTHERN HIGH PLAINS EARLY IN WEEK-2. NO ADDITIONAL WINTER
WEATHER HAZARDS ARE POSTED DURING WEEK-2 AS MODEL SOLUTIONS VARY ON THE TIMING
OF HEAVY SNOW ACROSS THE WESTERN U.S. AND THERE IS NO CLEAR SIGNAL FOR THE
LOCATION OF HEAVY SNOW AND/OR FREEZING RAIN ACROSS THE CENTRAL AND EASTERN U.S.




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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