Prognostic Meteorological Discussion
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FXUS21 KWNC 091935
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST DECEMBER 09 2016

SYNOPSIS: AS THE FORECAST PERIOD BEGINS, A SURFACE LOW PRESSURE SYSTEM IS
ANTICIPATED TO BE SHIFTING FROM THE GREAT LAKES TOWARDS THE CANADIAN MARITIMES.
BEHIND THIS SYSTEM A COLD FRONT IS EXPECTED TO USHER IN A BLAST OF ARCTIC AIR
AS SURFACE HIGH PRESSURE LOOKS TO BUILD SOUTHWARD OUT OF THE YUKON INTO THE
GREAT PLAINS. STORM ACTIVITY IS EXPECTED TO INCREASE OFF THE PACIFIC COAST
TOWARDS THE MIDDLE OF WEEK-1. MID-LEVEL HIGH PRESSURE WILL POTENTIALLY BUILD
ACROSS THE SOUTHEAST IN WEEK-2, LIMITING POTENTIAL GROWTH OF THE ARCTIC AIR
MASS. THE MOST BITTERLY COLD AIR IS EXPECTED TO RETREAT INTO CANADA BY THE
LATTER HALF OF WEEK-2.

HAZARDS

HEAVY SNOW ACROSS PORTIONS OF THE NORTHEAST, MON, DEC 12.

LOCALLY HEAVY LAKE-EFFECT SNOW ACROSS DOWNWIND PORTIONS OF THE GREAT LAKES,
TUE-FRI, DEC 13-16.

MUCH BELOW-NORMAL TEMPERATURES ACROSS PORTIONS OF THE NORTHERN AND CENTRAL
PLAINS, THE NORTHERN ROCKIES, THE UPPER AND MIDDLE MISSISSIPPI VALLEY, AND THE
NORTHERN GREAT BASIN, MON-FRI, DEC 12-16.

MUCH BELOW-NORMAL TEMPERATURES ACROSS PORTIONS OF THE NORTHERN AND CENTRAL
PLAINS, THE MISSISSIPPI VALLEY, THE CENTRAL APPALACHIANS, THE OHIO AND
TENNESSEE VALLEYS, THE GREAT LAKES, THE NORTHERN ROCKIES, THE NORTHERN GREAT
BASIN, AND THE PACIFIC NORTHWEST, WED-FRI, DEC 14-16.

HEAVY PRECIPITATION ACROSS PORTIONS OF THE GREAT BASIN, THE NORTHERN AND
CENTRAL ROCKIES, CALIFORNIA, AND THE PACIFIC NORTHWEST, WED-FRI, DEC 14-DEC 16.

HIGH WINDS ACROSS PORTIONS OF CALIFORNIA, THE SOUTHWEST, THE SOUTHERN ROCKIES,
AND THE SOUTHERN PLAINS, FRI, DEC 16.

MUCH BELOW-NORMAL TEMPERATURES ACROSS PORTIONS OF THE ALASKA PANHANDLE,
MON-TUE, DEC 12-13.

SIGNIFICANT WAVE HEIGHTS AND POTENTIAL ASSOCIATED COASTAL FLOODING FOR THE
ALEUTIANS AND WESTERN PORTIONS OF MAINLAND ALASKA, THU-SUN, DEC 15-18.

HIGH RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR PORTIONS OF THE NORTHERN AND
CENTRAL PLAINS, THE NORTHERN ROCKIES, THE NORTHERN GREAT BASIN, AND THE PACIFIC
NORTHWEST, SAT-MON, DEC 17-19.

MODERATE RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR PORTIONS OF THE NORTHERN
AND CENTRAL PLAINS, THE GREAT BASIN, THE NORTHERN AND CENTRAL ROCKIES, THE
UPPER AND MIDDLE MISSISSIPPI VALLEY, NORTHERN CALIFORNIA, AND THE PACIFIC
NORTHWEST, SAT-WED, DEC 17-21.

MODERATE RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR PORTIONS OF THE
MID-ATLANTIC AND NEW ENGLAND, SAT-SUN, DEC 17-18.

SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR APPROXIMATELY THE NORTHERN
TWO-THIRDS OF THE LOWER-48 STATES, SAT-FRI, DEC 17-23.

SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR PORTIONS OF THE ALASKA
PANHANDLE, SAT-SUN, DEC 17-18.

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

DETAILED SUMMARY

FOR MONDAY DECEMBER 12 - FRIDAY DECEMBER 16: A SURFACE LOW PRESSURE IS FORECAST
OVER THE GREAT LAKES AT THE BEGINNING OF THE OUTLOOK PERIOD, AND IS EXPECTED TO
LIFT EAST-NORTHEAST TOWARDS THE CANADIAN MARITIMES. ON THE NORTHERN PERIPHERY
OF THIS SYSTEM A REGION OF HEAVY SNOW (3" OR MORE IN 24 HOURS) IS FORECAST FOR
PORTIONS OF UPSTATE NEW YORK AND NORTHERN NEW ENGLAND ON MON, DEC 12. BEHIND
THE AFOREMENTIONED SYSTEM COLDER AIR IS ANTICIPATED, ALONG WITH 850-HPA FLOW
OUT OF THE WEST AND NORTHWEST OVER THE NEXT SEVERAL DAYS. THIS SCENARIO,
COUPLED WITH WATER TEMPERATURES IN GREAT LAKES IN THE 40S AND 50S, IS EXPECTED
TO RESULT IN PERIODIC LOCALLY HEAVY LAKE-EFFECT SNOW IN DOWNWIND COASTAL AREAS
OF THE GREAT LAKES FOR TUE-FRI, DEC 13-16.



HAZARDOUS MUCH BELOW-NORMAL TEMPERATURES ARE ANTICIPATED TO BUILD ACROSS MUCH
OF THE U.S. DURING WEEK-1 ASSOCIATED WITH HIGH PRESSURE SHIFTING SOUTHWARD OUT
OF THE YUKON AND INTO THE CENTRAL CONUS. INITIALLY THE COLDEST AIR IS FORECAST
TO EXTEND EASTWARD FROM WASHINGTON STATE INTO THE FAR WESTERN GREAT LAKES, AND
SOUTHWARD TOWARDS NEBRASKA FOR MON-TUE, DEC 12-13. MUCH BELOW-NORMAL
TEMPERATURES ARE THEREAFTER ANTICIPATED FOR AN EVEN BROADER REGION FROM
APPROXIMATELY PUGET SOUND EASTWARD THROUGH THE APPALACHIANS, WITH A SOUTHERN
EXTENT EAST OF THE ROCKIES THROUGH THE CENTRAL PLAINS AND OHIO VALLEY FOR THE
REST OF WEEK-1, WED-FRI, DEC 14-16. ASSOCIATED WITH THE AFOREMENTIONED
TEMPERATURE HAZARDS, MINIMUM TEMPERATURE ANOMALIES OF 12-25 DEGREES F BELOW
NORMAL ARE POSSIBLE.



HEAVY PRECIPITATION (EXCEEDING 3-5" LIQUID EQUIVALENT, WITH HIGHER ALTITUDE
SNOW AND RAIN OTHERWISE) IS POSSIBLE ACROSS PORTIONS OF NORTHERN CALIFORNIA AND
OREGON EASTWARD THROUGH WYOMING AND COLORADO ON WED-FRI, DEC 14-16. THIS
PRECIPITATION IS EXPECTED TO BE ASSOCIATED WITH ONSHORE FLOW AHEAD OF A SURFACE
LOW PRESSURE SYSTEM ANTICIPATED TO BE COMING ASHORE OVER NORTHERN CALIFORNIA
LATE IN WEEK-1. IN THE WARM SECTOR OF THIS SYSTEM HIGH WINDS (EXCEEDING 35 MPH)
OUT OF THE SOUTH ARE POSSIBLE FROM SOUTHERN CALIFORNIA THROUGH WEST TEXAS ON
FRI, DEC 16.



ALASKA IS NOT EXPECTED TO BE SPARED FROM THE ANOMALOUS COLD THAT THE CONUS IS
EXPECTING, WITH MUCH BELOW-NORMAL TEMPERATURES FORECAST FOR PARTS OF THE ALASKA
PANHANDLE MON-TUE, DEC 12-13.  HERE MINIMUM TEMPERATURE ANOMALIES ARE FORECAST
TO EXCEED 16 DEGREES F BELOW NORMAL. SOUTHERLY FLOW IS ANTICIPATED ACROSS THE
BERING AND CHUKCHI SEAS LATE IN WEEK-1. THIS PERSISTENT FLOW COULD LEAD TO
SIGNIFICANT WAVES EXCEEDING 20` AND POTENTIAL ASSOCIATED COASTAL FLOODING FOR
WINDWARD FACING REGIONS OF WESTERN ALASKA AND THE ALEUTIANS THU-SUN, DEC 15-18
(NOTE THIS HAZARD EXTENDS TWO DAYS INTO WEEK-2).

FOR SATURDAY DECEMBER 17 - FRIDAY DECEMBER 23: DYNAMICAL MODEL GUIDANCE IS IN
BETTER AGREEMENT REGARDING THE WEEK-2 500-HPA CIRCULATION RELATIVE TO EARLIER
IN THE WEEK. THE ECMWF ENSEMBLES HAVE TRENDED TOWARDS THE COLDER GEFS SOLUTION
FEATURING ANOMALOUS 500-HPA TROUGHING ACROSS THE WEST, WHILE THE GEFS HAS
SHIFTED CLOSER TO THE WARMER ECMWF FORECAST FAVORING ANOMALOUS RIDGING BUILDING
ACROSS THE SOUTHEAST THROUGHOUT WEEK-2. THE COMBINED IMPACT OF THESE CHANGES IS
A CONTINUATION OF THE COLD-RELATED HAZARDS ACROSS THE NORTHERN TIER OF THE U.S.
DURING WEEK-2, BUT A WESTWARD SHIFT IN THE HIGHEST RISK AREAS RELATIVE TO
OUTLOOKS FROM EARLIER IN THE WEEK. A HIGH RISK OF MUCH BELOW-NORMAL
TEMPERATURES IS NOW FORECAST TO EXTEND FROM THE PACIFIC NORTHWEST THROUGH THE
NORTHERN AND CENTRAL PLAINS FOR SAT-MON, DEC 17-19. AN ATTENDANT AREA OF
MODERATE RISK OF MUCH BELOW-NORMAL TEMPERATURES EXTENDS FROM NORTHERN
CALIFORNIA THROUGH THE UPPER MISSISSIPPI VALLEY FOR SAT-TUE, DEC 17-20. A
SECOND AREA WITH A MODERATE RISK OF MUCH BELOW-NORMAL TEMPERATURES IS
INTRODUCED FOR THE NORTHEAST SAT-SUN, DEC 17-18. ROUGHLY THE NORTHERN
TWO-THIRDS OF THE CONUS IS GIVEN A SLIGHT RISK OF MUCH BELOW-NORMAL
TEMPERATURES FOR THE ENTIRETY OF WEEK-2, SAT-FRI, DEC 17-23. THE COLD RISK IS
EXPECTED TO WANE EAST OF THE MISSISSIPPI THROUGHOUT WEEK-2 AS ANOMALOUS
MID-LEVEL RIDGING MAY BUILD IN THE SOUTHEAST. THE SLIGHT, MODERATE, AND HIGH
RISK AREAS CORRESPOND CLOSELY TO THE 20TH, 40TH, AND 60TH PERCENT CHANCES OF
BEING BELOW THE 15TH CLIMATOLOGICAL PERCENTILE OF MINIMUM TEMPERATURE ACCORDING
TO THE GEFS.



SOUTHERN PARTS OF THE ALASKA PANHANDLE ARE ALSO GIVEN A SLIGHT RISK OF MUCH
BELOW-NORMAL TEMPERATURES FOR SAT-SUN, DEC 17-18. MODEL GUIDANCE SUGGESTS STORM
ACTIVITY COULD RESUME IN THE GULF OF ALASKA LATE IN THE WEEK-2 TIMEFRAME. STORM
ACTIVITY IS ALSO INDICATED EAST OF THE MISSISSIPPI DURING WEEK-2, YET
INCONSISTENCIES IN TIME AND SPACE REGARDING FORECAST CYCLONES LIMIT CONFIDENCE
IN A SPECIFIC HAZARD FORECAST.



ACCORDING TO THE LATEST U.S. DROUGHT MONITOR (USDM) VALID ON DECEMBER 6, THE
COVERAGE OF SEVERE OR GREATER DROUGHT FOR THE CONUS DECREASED BY OVER 2.5% TO
13.97%. MOST OF THE IMPROVEMENTS WERE FOCUSED OVER THE SOUTHEASTERN QUARTER OF
THE COUNTRY WHERE RAINS PROVIDED 1 TO 2 CLASS IMPROVEMENTS IN DROUGHT
CONDITIONS WHILE ALSO HELPING WITH FIREFIGHTING EFFORTS TIED TO THE LONG-TERM
DRYNESS. SOME DEGRADATION OF DROUGHT CONDITIONS WAS NOTED FOR THE GREAT PLAINS.

FORECASTER: DANIEL HARNOS

$$



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