Climate Prediction Center

US HAZARDS ASSESSMENT
NWS CLIMATE PREDICTION CENTER CAMP SPRINGS MD
300 PM EST NOVEMBER 19 2008

SYNOPSIS: A COLD, DRY PATTERN CONTINUES TO BE FORECAST FOR MUCH OF THE EASTERN LOWER 48 STATES DURING THIS ASSESSMENT PERIOD. DOWNWIND OF THE GREAT LAKES, SNOW SQUALLS WILL LIKELY FOLLOW THE OCCASIONAL PASSAGE OF STORM SYSTEMS. THE WESTERN CONUS IS LIKELY TO HAVE ABOVE-NORMAL TEMPERATURES FOR THIS PERIOD, WITH A SIGNIFICANTLY INCREASED CHANCE OF HEAVY PRECIPITATION OCCURRING OVER THE PACIFIC NORTHWEST DURING WEEK 2. LONG-TERM DROUGHT AREAS ARE EXPECTED TO PERSIST, THOUGH NORTHERN CALIFORNIA SHOULD SEE SOME RELIEF DURING THIS ASSESSMENT. AN INCREASE IN THUNDERSTORMS AND HEAVY SHOWERS ARE ALSO PREDICTED FOR THE HAWAIIAN ISLANDS, ESPECIALLY IN THE EARLY STAGES OF THIS PERIOD.

HAZARDS

MUCH BELOW NORMAL TEMPERATURES OVER THE EASTERN QUARTER OF THE CONUS, NOVEMBER 22-23.
HEAVY LAKE EFFECT SNOWS DOWNWIND OF THE WESTERN GREAT LAKES ON NOVEMBER 24TH.
HEAVY LAKE EFFECT SNOWS DOWNWIND OF THE EASTERN GREAT LAKES ON NOVEMBER 22ND, AND ALSO ON NOVEMBER 25TH.
LOCALLY HEAVY RAINS FOR THE HAWAIIAN ISLANDS, ESPECIALLY SOUTH AND SOUTHEAST FACING SLOPES, NOVEMBER 22-23.
CONTINUED SEVERE DROUGHT IN PARTS OF THE WEST, SOUTHERN TEXAS, NORTHERN WISCONSIN, SOUTHEAST AND OHIO VALLEY, WITH SOME RELIEF IN CALIFORNIA.

DETAILED SUMMARY

FOR SATURDAY NOVEMBER 22 - MONDAY NOVEMBER 24: COLD HIGH PRESSURE WILL DOMINATE THE EASTERN STATES THIS WEEKEND, WITH SOME MODERATION IN TEMPERATURES BY MONDAY. DEEPENING LOW PRESSURE NEAR WESTERN NEWFOUNDLAND WILL BRING GUSTY WINDS TO MAINE AS IT CONTINUES TO MOVE AWAY TO THE NORTHEAST. IN THE EASTERN GREAT LAKES REGION, SNOW SQUALLS AND REDUCED VISIBILITIES ARE LIKELY TO POSE A PROBLEM FOR DOWNWIND AREAS. ACROSS THE MIDDLE PART OF THE NATION, A FRONTAL SYSTEM WILL BRING CLOUDINESS AND PRECIPITATION, WITH THE HEAVIER AMOUNTS (0.60") EXPECTED OVER ARKANSAS AND WESTERN TENNESSEE. OUT WEST, SURFACE TEMPERATURES ARE PREDICTED TO RANGE FROM NEAR NORMAL TO ABOVE NORMAL. PRECIPITATION IS EXPECTED ACROSS THE PACIFIC NORTHWEST AS A SHORTWAVE TROUGH MOVES THROUGH THE REGION. THE HIGHEST TOTALS (LIQUID EQUIVALENTS NEAR 0.75") ARE LIKELY ALONG WINDWARD SLOPES OF THE COASTAL RANGES AND CASCADES OF WASHINGTON STATE. AS THE TROUGH MOVES INTO THE NORTHERN ROCKIES, HIGH PRESSURE WILL BUILD AT THE SURFACE IN ITS WAKE OVER THE NORTHERN GREAT BASIN. ELSEWHERE, A DEEPENING TROUGH IN THE WESTERLIES WILL APPROACH THE HAWAIIAN ISLANDS FROM THE NORTHWEST, DESTABILIZING THE ATMOSPHERE AND TEMPORARILY DISRUPTING THE USUAL TRADEWIND PATTERN. THIS WILL MEAN AN INCREASE IN SHOWER AND THUNDERSTORM ACTIVITY, AND SOME OF THE RAIN MAY BE LOCALLY HEAVY. IN ALASKA, COLD HIGH PRESSURE FROM THE PRECEDING PERIOD WILL PREVAIL THROUGHOUT THIS PERIOD FOR MOST AREAS. SOME MODERATION IN TEMPERATURE IS PROJECTED FOR SOUTH-CENTRAL AND SOUTHEASTERN ALASKA AS A RELATIVELY DEEP STORM (976-HPA) OVER THE GULF OF ALASKA STEERS MOIST AND MILD AIR INTO THESE REGIONS FROM THE SOUTH.

FOR TUESDAY NOVEMBER 25 - SATURDAY NOVEMBER 29: BROAD LOW PRESSURE FROM THE BERING SEA TO THE NORTHWEST GULF OF ALASKA IS INDICATED BY MODELS SUCH AS TODAY'S 12Z GFS AND THE LATEST AVAILABLE ECMWF PROG. THIS WILL RESULT IN WIDESPREAD MODERATION IN SURFACE TEMPERATURES AND WETTER THAN MEDIAN CONDITIONS ACROSS SOUTHERN AND CENTRAL ALASKA AS THE CYCLONIC CIRCULATION DRIVES MOIST, MILD AIR INTO THESE AREAS FROM THE GULF. WITH A RIDGE AXIS ANTICIPATED OVER THE ROCKIES AND A TROUGH AXIS LOCATED NEAR 75W, TEMPERATURES WILL LIKELY BE WARMER THAN NORMAL OVER MUCH OF THE WESTERN CONUS, AND A MIX OF NEAR TO BELOW NORMAL TEMPERATURES IS ANTICIPATED OVER THE EAST. THIS TYPE OF LONGWAVE PATTERN IS TYPICALLY ASSOCIATED WITH WIDESPREAD AREAS OF DRYNESS.

FOR SUNDAY NOVEMBER 30 - WEDNESDAY DECEMBER 03: NO SPECIFIC HAZARDS CAN BE IDENTIFIED RELIABLY AT THIS RANGE, OTHER THAN THE LONG-TERM DROUGHT AREAS DEPICTED ON OUR NATIONAL COMPOSITE MAP. SOME RELIEF IS EXPECTED OVER NORTHERN CALIFORNIA. THERE ARE TROPICAL/EXTRATROPICAL INDICATIONS FROM THE MJO THAT THE PACIFIC JET STREAM COULD BE FOCUSED ACROSS THE PACIFIC NORTHWEST DURING THIS TIME, WHICH WOULD CONTRIBUTE TO MORE HEAVY RAIN/SNOW FOR THAT REGION.

FORECASTER: ANTHONY ARTUSA

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