Valid Monday, December 09, 2013 to Friday, December 20, 2013

Summary of Forecasts and Hazards

US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST DECEMBER 06 2013

SYNOPSIS: A STRONG AND VERY COLD AREA OF UPPER-LEVEL LOW PRESSURE IS FORECAST OVER THE WEST-CENTRAL CONTIGUOUS U.S. WHILE AN AREA OF UPPER-LEVEL HIGH PRESSURE IS EXPECTED OVER THE SOUTHEASTERN U.S. DURING THE FIRST FEW DAYS OF THE HAZARDS OUTLOOK PERIOD. A LOW PRESSURE SYSTEM IS ANTICIPATED TO AFFECT THE EAST COAST STATES EARLY IN THE PERIOD BEFORE TRACKING INTO EASTERN CANADA, ALLOWING ARCTIC HIGH PRESSURE TO BUILD IN BEHIND IT. TOWARDS THE MIDDLE TO LATTER PART OF NEXT WEEK, A LOW PRESSURE SYSTEM IS ANTICIPATED TO APPROACH THE PACIFIC NORTHWEST COAST. AN AREA OF UPPER-LEVEL HIGH PRESSURE IS FORECAST TO SHIFT WESTWARD ACROSS THE BERING SEA, SIGNIFYING A COOL DOWN FOR MOST OF THE STATE.

HAZARDS

• MUCH BELOW-NORMAL TEMPERATURES FOR THE SOUTHWEST, THE CENTRAL INTERMOUNTAIN REGION, MUCH OF THE ROCKIES AND GREAT PLAINS, AND THE MIDWEST, MON-TUE, DEC 9-10.
• MUCH BELOW-NORMAL TEMPERATURES FROM EASTERN MONTANA ACROSS NORTH DAKOTA TO NORTHERN MINNESOTA, MON-FRI, DEC 9-13.
• MUCH BELOW-NORMAL TEMPERATURES FOR THE GREAT LAKES REGION, THE NORTHERN AND MIDDLE ATLANTIC COAST STATES, THE OHIO VALLEY, THE LOWER MISSISSIPPI VALLEY, AND THE LOWER SOUTHERN PLAINS, WED-THU, DEC 11-12.
• MUCH BELOW-NORMAL TEMPERATURES FOR THE ALASKA PANHANDLE AND SOUTHEAST PORTIONS OF THE MAINLAND, WED-FRI, DEC 11-13.
• HIGH WINDS FOR THE NORTHERN GREAT PLAINS, MON-TUE, DEC 9-10.
• FREEZING RAIN FOR EASTERN OHIO, AND WESTERN AND CENTRAL PENNSYLVANIA, MON, DEC 9.
• PERIODS OF HEAVY RAIN FROM CENTRAL LOUISIANA NORTHEASTWARD TO SOUTHEASTERN VIRGINIA, MON-TUE, DEC 9-10.
• PERIODS OF HEAVY RAIN FOR NORTHWESTERN CALIFORNIA, WED-THU, DEC 11-12.
• PERIODS OF HEAVY SNOW FOR THE LOWER GREAT LAKES REGION, TUE-WED, DEC 10-11.
• FLOODING POSSIBLE FROM WEST VIRGINIA TO CENTRAL TENNESSEE, MON-TUE, DEC 9-10.
• FLOODING OCCURRING OR IMMINENT OVER EXTREME SOUTHWESTERN UTAH, MON-TUE, DEC 9-10.
• SEVERE DROUGHT FOR PARTS OF THE MIDWEST, GREAT PLAINS, RIO GRANDE VALLEY, ROCKIES, SOUTHWEST, GREAT BASIN, CALIFORNIA, AND HAWAII.

DETAILED SUMMARY

FOR MONDAY DECEMBER 09 - FRIDAY DECEMBER 13: ARCTIC AIR IS FORECAST TO DOMINATE THE WEATHER PATTERN ACROSS MOST OF THE CONUS DURING THE FIRST HALF OF THE OUTLOOK PERIOD. THEREFORE, WIDESPREAD AREAS OF MUCH BELOW-NORMAL TEMPERATURES ARE INDICATED ON THE HAZARDS MAP. A LOW PRESSURE SYSTEM APPROACHING THE EAST COAST IS PREDICTED TO BRING PERIODS OF HEAVY RAIN TO THE SOUTHEAST, FROM CENTRAL LOUISIANA NORTHEASTWARD TO SOUTHEASTERN VIRGINIA, AND FREEZING RAIN FROM EASTERN OHIO TO CENTRAL PENNSYLVANIA. JUST PRIOR TO THE START OF THIS PERIOD, AN ICY MIX IS ANTICIPATED FARTHER SOUTH ACROSS WESTERN AND CENTRAL PORTIONS OF VIRGINIA AND MARYLAND, BUT MODEL RUNS GENERALLY SUPPORT A RAPID TRANSITION TO ALL RAIN AS WARM AIR ADVECTS INTO THIS REGION.

FLOODING IS POSSIBLE OVER PORTIONS OF WEST VIRGINIA, FAR SOUTHERN OHIO, EASTERN KENTUCKY, AND CENTRAL TENNESSEE ON MONDAY AND TUESDAY. FLOODING IS OCCURRING OR IMMINENT OVER EXTREME SOUTHWESTERN UTAH DURING THIS SAME PERIOD.

DURING THE EARLY TO MIDDLE PORTIONS OF THIS PERIOD, BACK-TO-BACK COLD FRONTS ARE FORECAST TO MOVE ACROSS THE GREAT LAKES, FOLLOWED BY LAKE-ENHANCED SNOW SQUALLS DOWNWIND OF THE LOWER GREAT LAKES. POST-FRONTAL WEST-NORTHWEST TO WEST-SOUTHWEST WINDS ARE PARTICULARLY FAVORABLE FOR SIGNIFICANT SNOWFALL DOWNWIND OF LAKES ONTARIO AND ERIE.

THE DETERMINISTIC 00Z ECMWF BOUNDARY LAYER WIND FORECASTS INDICATE THE POSSIBILITY OF HIGH WINDS (20-30 KNOTS) OVER THE NORTHERN GREAT PLAINS ON DEC 9-10. THESE HIGHER WINDS ARE ASSOCIATED WITH A COLD FRONT, FORECAST TO DIVE SOUTHWARD OUT OF SOUTH-CENTRAL CANADA ACROSS THIS REGION. COMPARED TO THE CORRESPONDING GFS BOUNDARY LAYER WIND PREDICTIONS, THE ECMWF MODEL IS USUALLY MORE CONSERVATIVE, LENDING MORE CONFIDENCE TO THIS EVENT.

TOWARDS THE END OF THIS PERIOD, A PACIFIC STORM SYSTEM IS ANTICIPATED TO APPROACH THE PACIFIC NORTHWEST COAST. PERIODS OF HEAVY RAIN (SEVERAL INCHES) ARE PREDICTED TO OVERSPREAD NORTHWESTERN CALIFORNIA AND SOUTHWESTERN OREGON. FROM THE CASCADE RANGES EASTWARD, THE PRECIPITATION TYPE IS MOST LIKELY TO BE SNOW.

A RIDGE IS EXPECTED TO SHIFT WESTWARD ACROSS THE BERING SEA, WHICH ALLOWS THE 500-HPA HEIGHTS OVER ALASKA TO FALL, AND THE INFLUX OF COLDER AIR. MUCH BELOW-NORMAL TEMPERATURES ARE FAVORED FOR THE ALASKA PANHANDLE AND SOUTHEASTERN MAINLAND, AS COLD AIR WORKS ITS WAY WESTWARD FROM BRITISH COLUMBIA. THE DETERMINISTIC 06Z AND 12Z GFS TEMPERATURE ANOMALY FORECASTS ARE GENERALLY 15 TO 30 DEGREES BELOW NORMAL FOR THIS REGION.

FOR SATURDAY DECEMBER 14 - FRIDAY DECEMBER 20: TODAY'S DYNAMICAL MODELS ARE GENERALLY PREDICTING A DEAMPLIFICATION OF THE LONG WAVE PATTERN OVER THE CONUS, FAVORING A TRANSITION FROM WIDESPREAD BELOW-NORMAL TEMPERATURES TO NEAR- AND ABOVE-NORMAL TEMPERATURES. THIS KIND OF PATTERN ALSO FAVORS AN INCREASE IN PRECIPITATION ACROSS THE NORTHERN TIER OF STATES.

ACCORDING TO THE U.S. DROUGHT MONITOR VALID DECEMBER 3 (RELEASED DECEMBER 5),THE SPATIAL COVERAGE OF SEVERE TO EXCEPTIONAL DROUGHT ACROSS THE CONTINENTAL U.S. BARELY CHANGED DURING THE PAST WEEK (16.50 PERCENT THIS WEEK COMPARED TO 16.49 PERCENT LAST WEEK). THE UPDATED MAP SHOWS RELATIVELY MINOR CHANGES TO THE PREVIOUS MAP, SOME OF WHICH INCLUDE A SLIGHT EXPANSION OF ABNORMAL DRYNESS (D0) ACROSS THE PACIFIC NORTHWEST, AND A SLIGHT REDUCTION IN D0 COVERAGE IN THE MID-ATLANTIC REGION.

FORECASTER: ANTHONY ARTUSA

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