Climate Prediction Center

US HAZARDS ASSESSMENT
NWS CLIMATE PREDICTION CENTER CAMP SPRINGS MD
300 PM EST NOVEMBER 23 2009

SYNOPSIS: AN INTENSE STORM IS FORECAST TO TRACK NORTHWARD THROUGH THE MID-ATLANTIC AND NEW ENGLAND STATES DURING THURSDAY THROUGH FRIDAY, BRINGING WIDESPREAD RAIN, STRONG WINDS, AND HIGH-ELEVATION AND LAKE-EFFECT SNOWS. ANOTHER STORM IS FORECAST TO AFFECT THE EASTERN HALF OF THE NATION EARLY NEXT WEEK. IN THE NORTHEAST PACIFIC, A SERIES OF INTENSE LOW PRESSURE SYSTEMS IS EXPECTED TO CONTINUE TO BRING WIND, RAIN, AND SNOW TO ALASKA. ANOTHER PERIOD OF RAIN AND WIND IS FORECAST FOR THE PACIFIC NORTHWEST LATER THIS WEEK.

HAZARDS

HIGH WINDS AND HIGH WAVES ACROSS THE SOUTHERN COAST OF ALASKA NOVEMBER 26.
LOCALLY HEAVY SNOW FROM OHIO INTO NORTHERN VERMONT NOVEMBER 27-28.
HIGH WINDS FOR THE EASTERN GREAT LAKES REGION INTO THE NORTHEAST NOVEMBER 27-28.
ONGOING RIVER FLOODING IN ILLINOIS, LOUISIANA, AND SOUTHERN TEXAS.
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 THURSDAY NOVEMBER 26 - SATURDAY NOVEMBER 28: AN UPPER-LEVEL CUTOFF LOW IS FORECAST TO SLOWLY MOVE EASTWARD FROM THE OHIO VALLEY TO THE MID-ATLANTIC REGION. AS A RESULT, A SURFACE LOW OFF THE COAST OF THE CAROLINAS IS LIKELY TO INTENSIFY AND TRACK NORTHWARD TO NORTHERN NEW ENGLAND BY SATURDAY. THE STRONG PRESSURE GRADIENT ASSOCIATED WITH THE LOW AS THE SYSTEM INTENSIFIES IS FORECAST TO BRING POTENTIALLY DAMAGING NORTHWESTERLY WINDS ACROSS THE EASTERN GREAT LAKES INTO WESTERN NEW ENGLAND BY SATURDAY. COLD AIR RUSHING IN BEHIND THE LOW IS EXPECTED TO CHANGE THE RAIN TO SNOW BY SATURDAY DOWNWIND OF LAKES ERIE AND ONTARIO, AND OVER THE HIGHER TERRAIN FROM WEST VIRGINIA THROUGH PENNSYLVANIA INTO NORTHERN VERMONT.

ON THE WEST COAST, MODELS FORECAST A SHORTWAVE AND A SURFACE LOW TO MOVE INLAND, BRINGING RAIN AND WIND TO WESTERN PORTIONS OF WASHINGTON AND OREGON. WINDS COULD REACH HAZARDOUS LEVELS BRIEFLY, ESPECIALLY ON THURSDAY, AND OFFSHORE WAVES MAY REACH DANGEROUS LEVELS AS WELL. AT THIS TIME, THE INTENSITY AND DURATION OF THE EVENT DOES NOT APPEAR TO WARRANT DEPICTION OF A HAZARD, BUT FORECAST MODELS WILL NEED TO BE MONITORED.

IN THE NORTHEAST PACIFIC, THE PATTERN CONTINUES TO FAVOR A SERIES OF DEEP LOW PRESSURE SYSTEMS AFFECTING ALASKA. A HIGH WIND EVENT FOR THE SOUTH COAST OF ALASKA HAS THE HIGHEST CONFIDENCE FOR HAZARDOUS WEATHER AT THIS TIME, WITH THE TIMING OF LATER STORMS MAKING IT DIFFICULT TO DELINEATE HAZARDS FOR SPECIFIC LATER DATES.

ONGOING FLOODING FROM EARLIER RAINFALL EPISODES IS FORECAST FOR THE ILLINOIS RIVER IN ILLINOIS AND SEVERAL RIVERS IN NORTHERN LOUISIANA AND SOUTHERN TEXAS. 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 FLORIDA, RAINFALL ASSOCIATED WITH THE EASTERN STORM IS EXPECTED TO OFFER SOME RELIEF FROM RECENT SHORT-TERM DRYNESS.

FOR SUNDAY NOVEMBER 29 - THURSDAY DECEMBER 03: THE INTENSE NORTHEAST LOW PRESSURE SYSTEM IS FORECAST TO MOVE NORTHWARD INTO ATLANTIC CANADA ON SUNDAY. STRONG CYCLONIC FLOW IS EXPECTED TO BRING ANOTHER DAY OF POTENTIALLY DAMAGING WINDS TO THE NORTHEAST ON SUNDAY, WHILE SOME SNOW WILL LINGER OVER NEW YORK AND NEW ENGLAND.

THE SHORTWAVE THAT EARLIER ENTERED THE PACIFIC NORTHWEST IS FORECAST BY THE MODELS TO DIG SOUTHEASTWARD AND LEAD TO A STRONG UPPER LEVEL TROUGH OVER THE GREAT PLAINS ON MONDAY. MODELS HAVE NOT BEEN CONSISTENT ON THE DETAILS OF THE ASSOCIATED LOW PRESSURE CENTER, WITH THE ECMWF TODAY SHOWING THE STORM FARTHER SOUTH COMPARED WITH TODAYS GFS OPERATIONAL RUN. REGARDLESS OF THE DETAILS, IT APPEARS THAT MUCH OF THE EASTERN HALF OF THE CONUS WILL SEE INCLEMENT WEATHER DURING MONDAY THROUGH WEDNESDAY, AND A HAZARD MAY BE POSTED LATER THIS WEEK FOR HEAVY PRECIPITATION.

COLD AIR BEHIND THIS SYSTEM OFFERS THE POSSIBILITY OF SNOW FALLING UNUSUALLY FAR SOUTH IN THE SOUTHERN PLAINS AND EVEN THE DEEP SOUTH.

THE WEST IS FORECAST TO SEE A FAIRLY DRY PATTERN THIS PERIOD WHILE, FARTHER NORTH, PACIFIC STORMS CONTINUE TO STRIKE ALASKA. A VERY INTENSE LOW PRESSURE SYSTEM IS LIKELY TO AFFECT THE STATE AROUND SUNDAY OR MONDAY, BUT THE STRONGEST WINDS ARE FORECAST TO BE MOSTLY PARALLEL TO THE COAST, REDUCING THE POTENTIAL FOR DAMAGING WIND SPEEDS OVER LAND.

FOR FRIDAY DECEMBER 04 - MONDAY DECEMBER 07: RECENT GFS ENSEMBLES SUGGEST A CHANGE TO A NEGATIVE AO/NAO PATTERN, WITH WEAK RIDGING NEAR THE WEST COAST AND TROUGHING OVER THE EASTERN HALF OF THE CONUS. THE POSITIVE PNA ALONG WITH THE NEGATIVE NAO/AO SUGGEST A COLD PATTERN FOR THE CENTRAL AND EASTERN U.S. THE CURRENT MJO ACTIVITY DOES INCREASE UNCERTAINTY AS SOME FORECAST GUIDANCE (OPERATIONAL GFS SOLUTIONS) INDICATES POTENTIAL EXTENSION OF THE PACIFIC JET. THIS IS CONSISTENT WITH THE FORECAST PHASE OF THE MJO AND MAY LEAD TO ABOVE-AVERAGE RAINFALL FOR PRIMARILY THE CENTRAL U.S. WEST COAST.

FORECASTER: DOUG LECOMTE

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