Prognostic Meteorological Discussion
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000
FXUS21 KWNC 281945
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST NOVEMBER 28 2014

SYNOPSIS: AN UPPER-LEVEL TROUGH OF LOW PRESSURE IS EXPECTED TO SLOWLY PROGRESS
INLAND FROM THE EAST PACIFIC NEXT WEEK. A STRONG SURFACE HIGH, CENTERED ACROSS
THE GREAT PLAINS ON MONDAY MORNING, IS FORECAST TO RAPIDLY SHIFT EAST TO NEW
ENGLAND ON TUESDAY. A LOW PRESSURE SYSTEM IS FORECAST TO MOVE FROM THE BERING
SEA INTO THE GULF OF ALASKA EARLY IN THE PERIOD.

HAZARDS

MUCH BELOW NORMAL TEMPERATURES FOR PARTS OF THE PACIFIC NORTHWEST, NORTHERN
ROCKIES, NORTHERN/CENTRAL GREAT PLAINS, AND UPPER MISSISSIPPI VALLEY, MON, DEC
1.

MUCH BELOW NORMAL TEMPERATURES FOR PARTS OF THE UPPER MISSISSIPPI VALLEY, GREAT
LAKES, NEW YORK, AND NORTHERN NEW ENGLAND, TUE, DEC 2.

FREEZING RAIN FOR THE COLUMBIA RIVER GORGE, MON-TUE, DEC 1-2.

HEAVY SNOW FOR THE SIERRAS OF CALIFORNIA, TUE-WED, DEC 2-3.

PERIODS OF HEAVY RAIN FOR PARTS OF NORTHERN/CENTRAL CALIFORNIA, MON-WED, DEC
1-3.

HEAVY RAIN FOR SOUTHERN CALIFORNIA, TUE-WED, DEC 2-3.

HEAVY PRECIPITATION FOR PARTS OF THE KENAI PENINSULA, PRINCE WILLIAM SOUND, AND
EASTERN GULF COAST OF ALASKA, TUE, DEC 2.

SEVERE DROUGHT FOR THE CENTRAL AND SOUTHERN GREAT PLAINS, SOUTHWEST, SOUTHEAST,
PACIFIC NORTHWEST, GREAT BASIN, AND CALIFORNIA.

DETAILED SUMMARY

FOR MONDAY DECEMBER 01 - FRIDAY DECEMBER 05: A 500-HPA TROUGH IS FORECAST TO
SEPARATE FROM WESTERLY FLOW ACROSS THE NORTHEAST PACIFIC PRIOR TO THIS PERIOD.
ALTHOUGH MODEL DIFFERENCES CONTINUE ON HOW FAST THE UPPER-LEVEL TROUGH MOVES
INLAND, MODEL AGREEMENT IMPROVED SINCE YESTERDAY. THE HIGH-RESOLUTION 6Z/12Z
GFS AND 0Z ECMWF MODELS ON NOVEMBER 28 INDICATE THAT THE 500-HPA TROUGH
APPROACHES CALIFORNIA BY TUESDAY AND THEN WEAKENS AS IT ADVANCES ACROSS THE
INTERIOR WEST DURING MID-WEEK. SEVERAL INCHES OF PRECIPITATION (LIQUID
EQUIVALENT) ARE EXPECTED ACROSS THE COASTAL RANGES OF NORTHERN CALIFORNIA AND
THE SIERRAS FROM MONDAY THROUGH WEDNESDAY. SNOW LEVELS ARE EXPECTED TO REMAIN
RELATIVELY HIGH (AROUND 7,000 FEET) FOR THE SIERRAS. TROPICAL MOISTURE IS
EXPECTED TO BECOME ENTRAINED INTO THE UPPER-LEVEL TROUGH AND INCREASE THE
PROSPECTS FOR LOCALLY HEAVY RAIN ACROSS SOUTHERN CALIFORNIA ON DECEMBER 2 AND
3. THE HEAVIEST RAINFALL (LOCALLY MORE THAN 2 INCHES) IS EXPECTED ACROSS THE
MOUNTAINS OF SOUTHERN CALIFORNIA, WHILE AROUND 1 INCH IS EXPECTED FOR COASTAL
AREAS.



THE GFS MODEL REMAINS CONSISTENT WITH PRECIPITATION SPREADING NORTH INTO THE
PACIFIC NORTHWEST ON MONDAY AND TUESDAY AHEAD OF THE EAST PACIFIC TROUGH.
SURFACE TEMPERATURES ARE EXPECTED TO SUPPORT FREEZING RAIN ACROSS THE COLUMBIA
RIVER GORGE ON DECEMBER 2 AND 3.



MEANWHILE, HEAVY RAINFALL ON NOVEMBER 28 IS RESULTING IN RIVER FLOODING ALONG
THE MOST FLOOD-PRONE RIVERS OF THE NORTHERN WASHINGTON CASCADES. THIS RIVER
FLOODING IS EXPECTED TO RECEDE DURING THE WEEKEND.



SNOW IS EXPECTED ACROSS THE HIGHER ELEVATIONS OF THE NORTH-CENTRAL ROCKIES WHEN
THE EAST PACIFIC TROUGH PUSHES INLAND INTO THE INTERIOR WEST BY WEDNESDAY OR
THURSDAY. HOWEVER, THE UPPER-LEVEL TROUGH IS FORECAST TO RAPIDLY WEAKEN AND
ACCELERATE, LIMITING SNOWFALL AMOUNTS.



A 1040-HPA SURFACE HIGH IS EXPECTED TO BRING MUCH-BELOW NORMAL TEMPERATURES TO
PARTS OF THE PACIFIC NORTHWEST, NORTHERN ROCKIES, NORTHERN/CENTRAL GREAT
PLAINS, AND UPPER MISSISSIPPI VALLEY ON DECEMBER 1. A WIDESPREAD AREA OF
SUBZERO MINIMUM TEMPERATURES IS FORECAST FROM MONTANA AND WYOMING EAST TO THE
DAKOTAS, MINNESOTA, AND NORTHERN WISCONSIN ON MONDAY MORNING. THE MOST
ANOMALOUS COLD ON TUESDAY IS EXPECTED TO EXTEND FROM THE GREAT LAKES EAST TO
NORTHERN NEW ENGLAND.



THE HIGH RESOLUTION 0/6Z GFS AND 0Z ECMWF MODELS FROM NOVEMBER 28 INDICATE A
LOW PRESSURE SYSTEM OVER THE BERING SEA ON MONDAY MORNING. THIS SURFACE LOW IS
EXPECTED TO BECOME CENTERED OVER THE GULF OF ALASKA BY MID-WEEK. ONSHORE FLOW
ASSOCIATED WITH THE SURFACE LOW IS EXPECTED TO PROMOTE HEAVY PRECIPITATION
ACROSS THE WINDWARD SIDE OF THE KENAI PENINSULA, PRINCE WILLIAM SOUND, AND
EASTERN GULF COAST OF ALASKA ON TUESDAY.

FOR SATURDAY DECEMBER 06 - FRIDAY DECEMBER 12: THE GFS AND ECMWF ENSEMBLE MEANS
ON NOVEMBER 28 FEATURE ENHANCED FLOW ACROSS THE NORTH PACIFIC WHICH FAVORS
ABOVE-NORMAL TEMPERATURES ACROSS THE LOWER 48. THE ABOVE-NORMAL TEMPERATURES
ARE ALSO CONSISTENT WITH THE PREDICTED EVOLUTION OF THE MJO DURING THE NEXT TWO
WEEKS. MEANWHILE, AN UPPER-LEVEL TROUGH IS FORECAST OVER THE SOUTHWESTERN
CONUS. DOWNSTREAM OF THIS TROUGH, A WET PATTERN IS EXPECTED FOR THE SOUTHERN
GREAT PLAINS WITH AN INCREASING POTENTIAL OF HEAVY RAINFALL.



THE MOST RECENT U.S. DROUGHT MONITOR, RELEASED ON NOVEMBER 27, INDICATES A
SLIGHT DECREASE IN THE AREAL COVERAGE OF SEVERE TO EXCEPTIONAL DROUGHT (D2 TO
D4) FROM 17.13 PERCENT TO 16.81 PERCENT ACROSS THE CONTINENTAL U.S. THIS IS THE
LOWEST COVERAGE OF SEVERE TO EXCEPTIONAL DROUGHT SINCE DECEMBER 2013.

FORECASTER: BRAD PUGH

$$



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