FXUS21 KWNC 252030
PMDTHR
US HAZARDS ASSESSMENT
NWS CLIMATE PREDICTION CENTER CAMP SPRINGS MD
300 PM EST NOVEMBER 25 2009
SYNOPSIS: AN INTENSE STORM IS FORECAST TO TRACK NORTHWARD FROM MAINE INTO 
CANADA THIS WEEKEND. STRONG WINDS ARE FORECAST TO AFFECT THE NORTHEAST INTO 
SATURDAY, WITH LOCALLY HEAVY SNOW IN PARTS OF THE REGION. ANOTHER STORM IS 
FORECAST TO MOVE NORTHWARD FROM THE GULF OF MEXICO EARLY NEXT WEEK, SPREADING 
RAIN ACROSS A LARGE PORTION OF THE EASTERN HALF OF THE COUNTRY. IN THE 
NORTHEAST PACIFIC, A SERIES OF INTENSE LOW PRESSURE SYSTEMS IS EXPECTED TO 
CONTINUE TO BRING WIND, RAIN, AND SNOW TO ALASKA. 
HAZARDS
HIGH WINDS AND HIGH WAVES ACROSS THE SOUTHERN COAST OF ALASKA NOVEMBER 
28-DECEMBER 1.
HEAVY RAIN AND SNOW OVER THE ALASKAN PANHANDLE NOVEMBER 29-DECEMBER 1. 
HIGH WINDS FROM PENNSYLVANIA INTO NEW ENGLAND NOVEMBER 28.
ONGOING RIVER FLOODING IN ILLINOIS, LOUISIANA, AND ARKANSAS.
HEAVY RAINS AND FLOODING OVER PORTIONS OF THE SOUTH NOVEMBER 30-DECEMBER 1.
CRITICAL WILDFIRE CONDITIONS IN SOUTHERN CALIFORNIA NOVEMBER 29-30.
SEVERE DROUGHT IN PARTS OF WISCONSIN, TEXAS, AND AREAS IN THE WESTERN U.S. SOME 
RELIEF IS EXPECTED ACROSS MOST OF THESE AREAS, EXCLUDING AREAS IN ARIZONA, 
SOUTHERN CALIFORNIA, AND NEVADA.
DETAILED SUMMARY
FOR SATURDAY NOVEMBER 28 - MONDAY NOVEMBER 30: AN INTENSE NORTHEAST LOW 
PRESSURE SYSTEM IS FORECAST TO SLOWLY MOVE NORTHWARD FROM THE MAINE AREA ON 
SATURDAY INTO CANADA ON SUNDAY. THE STRONG PRESSURE GRADIENT ASSOCIATED WITH 
THE LOW IS FORECAST TO BRING POTENTIALLY DAMAGING NORTHWESTERLY WINDS ACROSS 
THE EASTERN GREAT LAKES INTO NEW ENGLAND ON SATURDAY, WITH WEAKENING WINDS ON 
SUNDAY. LOCALLY HEAVY SNOW IS LIKELY OVER THE HIGHER TERRAIN OF THE NORTHEAST 
ON SATURDAY AS WELL AS ACROSS THE NORTHERN PARTS OF VERMONT, NEW HAMPSHIRE, AND 
MAINE. BANDS OF HEAVY SNOW COULD DEVELOP DOWNWIND OF LAKES ERIE AND ONTARIO.   
A FRONTAL SYSTEM IS FORECAST TO MOVE INTO THE PLAINS ON SATURDAY. MODELS 
INDICATE A HIGHLY AMPLIFIED UPPER-LEVEL TROUGH MOVING ACROSS THE WEST THIS 
PERIOD, WITH A CUTOFF LOW DEVELOPING OVER THE SOUTHWEST BY SUNDAY. AN 
ASSOCIATED SURFACE LOW PRESSURE AREA OVER THE SOUTHWEST AND TEXAS IS LIKELY TO 
LEAD TO WIDESPREAD PRECIPITATION EXTENDING FROM ARIZONA INTO TEXAS AND THE 
LOWER MISSISSIPPI VALLEY. ENOUGH COLD AIR MAY BE IN PLACE TO BRING SNOW FROM 
NEW MEXICO INTO WEST TEXAS ON SUNDAY AND MONDAY. ALTHOUGH A NUMBER OF FORECAST 
MODELS INDICATE THE POTENTIAL FOR SNOW TO EXTEND UNUSUALLY FAR SOUTH, THERE IS 
ENOUGH UNCERTAINTY ABOUT THE EVENT TO PRECLUDE PLACING A HAZARD AREA ON THE MAP 
AT THIS TIME.  
HIGH PRESSURE OVER THE GREAT BASIN ON SUNDAY INTO MONDAY IS FORECAST TO LEAD TO 
POTENTIALLY STRONG DOWNSLOPE WINDS AND LOW RELATIVE HUMIDITY OVER SOUTHERN 
CALIFORNIA, RESULTING IN AN AREA OF ENHANCED FIRE DANGER.  
SURFACE LOW DEVELOPMENT NEAR THE LOWER MISSISSIPPI VALLEY BY MONDAY IS FORECAST 
TO RESULT IN HEAVY RAIN INTO THE SOUTH. WITH RIVERS ALREADY HIGH FROM RECENT 
RAINS, THE ADDITIONAL MOISTURE COULD EASILY TRIGGER FLOODING IN SEVERAL STATES. 
THERE IS SOME POTENTIAL FOR SEVERE WEATHER OVER THE GULF STATES BY MONDAY AHEAD 
OF THE STORM SYSTEM, BUT MODEL UNCERTAINTIES PREVENT DEPICTION OF AN AREA AT 
THIS TIME. 
ONGOING FLOODING FROM EARLIER RAINFALL EPISODES IS FORECAST FOR THE ILLINOIS 
RIVER IN ILLINOIS AND SEVERAL RIVERS IN NORTHERN LOUISIANA. RAIN OR SNOW IS 
EXPECTED TO BENEFIT DROUGHT AREAS IN WISCONSIN, WASHINGTON, AND NORTHERN 
CALIFORNIA. LITTLE CHANGE IS SEEN FOR DROUGHTS IN ARIZONA, NEVADA, AND SOUTHERN 
CALIFORNIA. 
IN THE PACIFIC, AN INTENSE LOW PRESSURE SYSTEM FORECAST TO MOVE EASTWARD ACROSS 
THE GULF OF ALASKA ON SATURDAY AND SUNDAY IS LIKELY TO BRING HIGH WINDS AND 
WAVES TO COASTAL AREAS OF ALASKA, WHILE HEAVY RAIN AND SNOW IS FORECAST TO 
STRIKE THE PANHANDLE ON SUNDAY AND MONDAY. 
FOR TUESDAY DECEMBER 01 - SATURDAY DECEMBER 05: BIG DIFFERENCES EXIST BETWEEN 
MODELS FOR THIS PERIOD REGARDING THE EVOLUTION OF THE LOW PRESSURE SYSTEM OVER 
THE SOUTH AND GULF OF MEXICO, MAKING DELINEATION OF THE TRACK AND INTENSITY OF 
THE DEVELOPING STORM OVER THE SOUTH QUITE DIFFICULT. TODAY'S 12Z GFS MODEL RUN 
INDICATES A CLOSED UPPER-LEVEL LOW OVER WEST TEXAS ON TUESDAY, LEADING TO A 
SURFACE LOW IN THE GULF SOUTH OF LOUISIANA. BOTH TODAY'S ECMWF AND GFS MODEL 
RUNS SHOW A SEPARATE LOW TRACKING ACROSS THE NORTHEAST. REGARDLESS OF THE 
DETAILS OF ANY FORECAST SURFACE LOW, THERE IS A LIKELIHOOD THAT HEAVY RAINS 
WILL SPREAD EASTWARD FROM THE LOUISIANA-ARKANSAS AREA EARLY IN THE PERIOD, 
RESULTING IN INCREASED ODDS FOR FLOODING IN AREAS THAT HAVE RECENTLY SEEN MUCH 
RAIN. THERE IS ALSO AN ELEVATED CHANCE FOR SEVERE WEATHER OVER THE SOUTHEAST 
WITH THIS STORM SYSTEM, BUT MODEL UNCERTAINTIES PRECLUDE DELINEATION OF AN AREA 
AT THIS TIME. 
ANOTHER UPPER-LEVEL TROUGH IS FORECAST TO DEEPEN OVER THE PLAINS BY THURSDAY, 
ALLOWING COLD CANADIAN AIR TO DROP SOUTHWARD INTO THE ROCKIES AND PLAINS, AND 
POSSIBLY RESULTING IN AN INTENSE LOW PRESSURE SYSTEM AFFECTING THE MIDWEST BY 
FRIDAY.   
OVER THE PACIFIC, ANOTHER IN THE SERIES OF STORMS IS FORECAST TO AFFECT ALASKA 
INTO TUESDAY, BRINGING THE LIKELIHOOD FOR ADDITIONAL HEAVY PRECIPITATION AND 
HIGH WINDS AND WAVES TO COASTAL AREAS. 
FOR SUNDAY DECEMBER 06 - WEDNESDAY DECEMBER 09: RECENT GFS ENSEMBLES CONTINUE 
TO SHOW A POSITIVE PNA PATTERN THIS PERIOD, FEATURING WEAK RIDGING NEAR THE 
WEST COAST AND TROUGHING OVER THE CENTRAL OR EASTERN STATES. THE PATTERN 
SUGGESTS COLD WEATHER OVER MUCH OF THE COUNTRY AWAY FROM THE WEST COAST, WITH 
THE POTENTIAL FOR ADDITIONAL WET WEATHER ACROSS THE SOUTH AND EAST. 
FORECASTER: DOUG LECOMTE 
$$