Prognostic Meteorological Discussion
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FXUS21 KWNC 021922
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST DECEMBER 02 2016

SYNOPSIS: DURING WEEK-1 A SURFACE LOW PRESSURE SYSTEM IS FORECAST TO LIFT
NORTHWARD THROUGH THE MISSISSIPPI VALLEY TOWARDS THE GREAT LAKES. ANOTHER
SURFACE LOW PRESSURE MAY FORM ALONG THE MID-ATLANTIC AS THE AFOREMENTIONED
SYSTEM REACHES THE GREAT LAKES. BEHIND THESE DISTURBANCES ARCTIC AIR IS
EXPECTED TO SPILL SOUTHWARD DUE TO AN UNSEASONABLY STRONG SURFACE HIGH PRESSURE
EXPECTED TO BE POSITIONED OVER THE YUKON. UNSETTLED CONDITIONS ARE ANTICIPATED
IN THE NORTH PACIFIC THROUGHOUT WEEK-1 THAT COULD IMPACT THE WEST COAST. DURING
WEEK-2, MID-LEVEL HIGH PRESSURE IS FORECAST ALONG THE PACIFIC COAST WITH LOW
PRESSURE EXPECTED OVER THE GREAT LAKES.

HAZARDS

SEVERE WEATHER ACROSS PORTIONS OF THE SOUTHEAST AND THE LOWER MISSISSIPPI
VALLEY, MON, DEC 5.

HEAVY RAIN ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY, THE TENNESSEE
VALLEY, THE MID-ATLANTIC, THE SOUTHERN APPALACHIANS, AND THE SOUTHEAST,
MON-TUE, DEC 5-DEC 6.

FLOODING POSSIBLE ACROSS PORTIONS OF EASTERN TEXAS, MON-TUE, DEC 5-6.

MUCH BELOW-NORMAL TEMPERATURES ACROSS PORTIONS OF THE NORTHERN AND CENTRAL
PLAINS, THE ROCKIES, THE GREAT BASIN, THE PACIFIC NORTHWEST, AND THE SOUTHWEST,
TUE-WED, DEC 6-DEC 7.

HEAVY RAIN ACROSS WESTERN PORTIONS OF CALIFORNIA AND OREGON, THU, DEC 8.

MUCH BELOW-NORMAL TEMPERATURES ACROSS PORTIONS OF THE SOUTHWEST, THE GREAT
BASIN, THE ROCKIES, GREAT PLAINS, THE LOWER AND MIDDLE MISSISSIPPI VALLEY, THE
TENNESSEE AND OHIO VALLEYS, THE MID-ATLANTIC, THE CENTRAL AND SOUTHERN
APPALACHIANS, AND THE SOUTHEAST, THU-FRI, DEC 8-DEC 9.

MUCH BELOW NORMAL TEMPERATURES ACROSS PORTIONS OF THE ALASKA PANHANDLE AND
MAINLAND ALASKA, MON-FRI, DEC 5-DEC 9.

HIGH WINDS ACROSS PORTIONS OF THE ALASKA PANHANDLE, TUE-WED, DEC 6-DEC 7.

SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR PORTIONS OF THE GREAT PLAINS,
THE GREAT BASIN, THE NORTHERN AND CENTRAL ROCKIES, THE UPPER AND MIDDLE
MISSISSIPPI VALLEY, AND THE PACIFIC NORTHWEST, SAT-THU, DEC 10-DEC 15.

MODERATE RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR PORTIONS OF THE ALASKA
PANHANDLE, SAT-SUN, DEC 10-DEC 11.

SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR PORTIONS OF THE ALASKA
PANHANDLE, MAINLAND ALASKA, AND THE ALEUTIANS, SAT-THU, DEC 10-DEC 15.

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 05 - FRIDAY DECEMBER 09: AS WEEK-1 BEGINS, A SURFACE LOW
PRESSURE SYSTEM IS FORECAST OVER THE LOWER MISSISSIPPI VALLEY ASSOCIATED WITH A
NEGATIVELY-TILTED TROUGH AT 500-HPA.  DYNAMICAL MODEL GUIDANCE CONTINUES TO
FORECAST THIS SYSTEM TO SHIFT NORTHWARD TOWARDS THE GREAT LAKES, HOWEVER,
FORECASTS NOW PORTRAY A SECONDARY COASTAL SYSTEM DEVELOPING OFF THE
MID-ATLANTIC BY MID-WEEK. THIS SECONDARY DEVELOPMENT WOULD LIMIT SNOW AND WIND
POTENTIAL ACROSS THE NORTHEASTERN QUARTER OF THE COUNTRY FROM EITHER SYSTEM.
INSTEAD AN EASTWARD SHIFTING HEAVY RAIN HAZARD (EXCEEDING 1 INCH IN 24 HOURS)
IS THE MOST LIKELY THREAT ACROSS THE SOUTHEASTERN U.S. ON MON-TUE, DEC 5-6. THE
STORM PREDICTION CENTER ALSO ANTICIPATES A 15% RISK OF SEVERE WEATHER ADJACENT
TO THE GULF OF MEXICO ASSOCIATED WITH THIS SYSTEM AS LOCALLY SEVERE WINDS AND
TORNADOES COULD BE POSSIBLE ON MON, DEC 5. SIGNIFICANT RIVER FLOODING IS
POSSIBLE ASSOCIATED WITH THIS SYSTEM ACROSS PARTS OF SOUTHEASTERN TEXAS ON
MON-TUE, DEC 5-6.



NORTHERLY WINDS ARE ANTICIPATED IN THE WAKE OF THE AFOREMENTIONED LOW PRESSURE
SYSTEM AS IT STRENGTHENS AND MOVES NORTHWARD. STRONG SURFACE HIGH PRESSURE IS
ALSO FORECAST IN THE YUKON DURING WEEK-1, THAT WILL FURTHER HELP BRING COLD,
ARCTIC AIR SOUTHWARD OVER THE CONUS. MUCH BELOW-NORMAL TEMPERATURES ARE
POSSIBLE MON-TUE, DEC 4-5 FOR THE GREAT BASIN, ROCKY MOUNTAINS, AND GREAT
PLAINS. HERE MINIMUM TEMPERATURES COULD BE 12-20 DEGREES F BELOW NORMAL. THE
MUCH BELOW-NORMAL TEMPERATURE HAZARD REGION IS EXPECTED TO PUSH EASTWARD INTO
THE SOUTHEAST AND OHIO AND TENNESSEE VALLEYS FOR THU-FRI, DEC 6-7.



PERSISTENT SURFACE LOW PRESSURE IS FORECAST IN THE GULF OF ALASKA AND NORTH
PACIFIC LATE IN WEEK-1, INCREASING THE LIKELIHOOD OF ONSHORE FLOW OFF THE
PACIFIC FOR MUCH OF THE WEST COAST. HEAVY RAIN IS POSSIBLE FOR COASTAL PORTIONS
OF NORTHERN CALIFORNIA AND OREGON ON FRI, DEC 9 AS THE COLD FRONT ASSOCIATED
WITH THIS SYSTEM IS EXPECTED TO BE COMING ASHORE.



ALASKA IS ALSO FORECAST TO BE IMPACTED BY THE ANOMALOUSLY COLD WEATHER, AS
POLAR AIR IS FORECAST TO WRAP WESTWARD AROUND THE BASE OF SURFACE HIGH PRESSURE
POSITIONED OVER THE YUKON. THIS SCENARIO WOULD POTENTIALLY RESULT IN A REGION
OF MUCH BELOW-NORMAL TEMPERATURES FORECAST ACROSS MUCH OF ALASKA FOR TUE-FRI,
DEC 6-9 WHERE ANOMALIES COULD EXCEED -25 DEGREES F. WITHIN THIS REGION THE
HAZARD IS EXPECTED TO SHIFT EASTWARD AND SOUTHEASTWARD OVER THE COURSE OF
WEEK-1. THIS SETUP ALSO SUPPORTS THE POTENTIAL DEVELOPMENT OF EASTERLY HIGH
WINDS (EXCEEDING 50 MPH) FOR EXPOSED AREAS ACROSS THE ALASKA PANHANDLE SOUTH OF
YAKUTAT ON TUE-WED, DEC 6-7.

FOR SATURDAY DECEMBER 10 - FRIDAY DECEMBER 16: THE ANOMALOUS 500-HPA FORECAST
PATTERN FOR WEEK-2 FAVORS RIDGING ALONG THE PACIFIC COAST AND BERING SEA, WITH
TROUGHING OVER THE GREAT LAKES. THE BIGGEST DIFFERENCE AMONG THE ENSEMBLE MEAN
FIELDS LIES IN THE TREATMENT OF THE RIDGING IN THE PACIFIC, WITH THE GEFS MORE
AMPLIFIED AND EXTENDING THROUGH SOUTHERN CANADA THAN THE WEAKER EUROPEAN
SOLUTION WHICH CONFINES WEAKER RIDGING TO THE SOUTHWEST INSTEAD. HOWEVER, THE
GEFS IS LESS AMPLIFIED THAN THE ECMWF ENSEMBLES IN THE ANOMALOUS RIDGE OVER THE
BERING SEA, WHICH WOULD RESULT IN LESS TRANSPORT OF SIBERIAN AIR TOWARDS NORTH
AMERICA. THE EUROPEAN SOLUTION RESULTS IN COLDER AIR ACROSS MUCH OF NORTH
AMERICA, HOWEVER BOTH ENSEMBLES APPEAR LESS BULLISH ON THE COLD AIR POTENTIAL
OVER NORTH AMERICA THAN PRIOR RUNS.



GIVEN THE SOMEWHAT WARMER SOLUTIONS IN ENSEMBLE GUIDANCE TODAY, PROBABILITIES
FOR MUCH BELOW-NORMAL TEMPERATURES ARE DAMPED RELATIVE TO THE PREVIOUS
FORECAST. A SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES IS NOW FORECAST FOR
APPROXIMATELY THE NORTHWESTERN QUARTER OF THE CONUS FOR SAT-THU, DEC 10-15.
ROUGHLY THE SOUTHERN TWO-THIRDS OF ALASKA, WITH THE EXCEPTION OF MOST OF THE
ALEUTIANS, HAS A SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR SAT-MON, DEC
10-12, WITH THIS RISK BECOMING FOCUSED ALONG THE CANADIAN BORDER AND ALASKA
PANHANDLE OVER THE COURSE OF THE WEEK. WITHIN THIS REGION, PARTS OF THE ALASKA
PANHANDLE HAVE A MODERATE RISK OF MUCH BELOW-NORMAL TEMPERATURES SAT-SUN, DEC
10-11.



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: DANIEL HARNOS

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