Climate Prediction Center

US HAZARDS ASSESSMENT
NWS CLIMATE PREDICTION CENTER CAMP SPRINGS MD
300 PM EST JANUARY 05 2009

SYNOPSIS: AN ACTIVE WEATHER PATTERN IS EXPECTED TO CONTINUE EARLY DURING THE PERIOD ESPECIALLY ACROSS THE PACIFIC NORTHWEST AND PORTIONS OF ALASKA. A SERIES OF STRONG LOW PRESSURE CENTERS WILL IMPACT THESE REGIONS WITH HEAVY PRECIPITATION AND HIGH WINDS WITH CONTINUING FLOODING ANTICIPATED FOR AREAS IN WASHINGTON AND OREGON. TWO STORM SYSTEMS MOVING AWAY FROM THE NORTHEAST US - ONE PRIOR AND ANOTHER DURING THE EARLY-MID PART OF THE FORECAST PERIOD - WILL RESULT IN A NORTHWEST FLOW OF COLDER AIR ACROSS THE NORTH-CENTRAL AND NORTHEAST US LIKELY RESULTING IN TWO EPISODES OF LAKE EFFECT SNOW. THEREAFTER, A LESS ACTIVE WEATHER PATTERN THAN IN PREVIOUS WEEKS IS EXPECTED FOR MUCH OF THE CONTINENTAL US AS HIGH PRESSURE WILL DOMINATE.

HAZARDS

HEAVY PRECIPITATION FOR PORTIONS OF THE PACIFIC NORTHWEST JANUARY 8.
HEAVY RAIN AND INLAND SNOW FOR PARTS OF SOUTHEAST ALASKA AND THE ALASKAN PANHANDLE JANUARY 9-11.
HIGH WINDS FOR THE ALASKAN PANHANDLE JANUARY 10.
LAKE EFFECT SNOW FOR THE GREAT LAKES JANUARY 9 AND JANUARY 11.
RIVER FLOODING FOR PORTIONS OF ILLINOIS, THE WESTERN MID-ATLANTIC, OHIO VALLEY AND TENNESSEE VALLEY JANUARY 8-10.
STRONG DOWNSLOPE WINDS FOR PORTIONS OF SOUTHERN CALIFORNIA JANUARY 9-12.
RIVER AND URBAN FLOODING FOR PORTIONS OF WASHINGTON AND OREGON JANUARY 8-11.
SEVERE DROUGHT CONTINUES IN PARTS OF THE WEST, SOUTHERN PLAINS, NORTHERN WISCONSIN, OHIO VALLEY, AND THE SOUTHEAST. SOME RELIEF IS EXPECTED ACROSS THE OHIO VALLEY AND SOUTHEAST.

DETAILED SUMMARY

FOR THURSDAY JANUARY 08 - SATURDAY JANUARY 10: AT THE START OF THE FORECAST PERIOD, A STRONG STORM SYSTEM WILL IMPACT THE PACIFIC NORTHWEST WITH CONTINUED HEAVY RAINFALL AND GUSTY WINDS. THIS IN COMBINATION WITH CONTINUED SNOWMELT - AS A RESULT OF ABOVE AVERAGE TEMPERATURES - MAKES THE CONTINUATION OF RIVER AND URBAN FLOODING LIKELY ACROSS AREAS IN WASHINGTON AND OREGON. LATER DURING THIS FORECAST PERIOD, A STRONG UPPER-AIR TROUGH SOUTH OF ALASKA AND A BUILDING RIDGE ALONG THE WEST COAST WILL SHIFT THE FOCUS OF STORMINESS TO THE NORTH. A POTENT STORM SYSTEM WILL IMPACT SOUTHEAST ALASKA AND THE ALASKAN PANHANDLE WITH HEAVY PRECIPITATION (COASTAL RAIN AND INLAND SNOW) AS WELL AS HIGH WINDS.

A LOW PRESSURE CENTER WILL MOVE NORTHEAST AWAY FROM NEW ENGLAND PRIOR TO THE PERIOD AND RESULT IN STRONG NORTHWESTERLY FLOW AND USHER IN BELOW NORMAL TEMPERATURES FOR MUCH OF THE NORTHERN TIER OF THE CENTRAL AND EASTERN US. THE COLD AIR MOVING ACROSS THE GREAT LAKES IN COMBINATION WITH GENERALLY ICE-FREE WATER IS EXPECTED TO RESULT IN A PERIOD OF HEAVY LAKE EFFECT SNOW. THE LAKE SURFACE AND 850-HPA TEMPERATURE DEPARTURES ARE EXPECTED TO BE ABOVE NECESSARY LEVELS FOR LAKE EFFECT SNOW.

LATER IN THE PERIOD, HIGH PRESSURE WILL BUILD IN ACROSS THE WESTERN US. THIS STRONG HIGH PRESSURE IN COMBINATION WITH AN INVERTED TROUGH TO THE SOUTH IS EXPECTED TO RESULT IN A STRONG PRESSURE GRADIENT AND OFFSHORE WINDS. CONSEQUENTLY, THERE EXISTS THE POTENTIAL FOR STRONG DOWNSLOPE WINDS BUT UNCERTAINTY REMAINS HIGH AT THIS TIME.

HEAVY RAINFALL PRIOR TO THE ASSESSMENT PERIOD IS EXPECTED TO WORSEN FLOODING PROBLEMS ACROSS PORTIONS OF THE MID-ATLANTIC AND OHIO AND TENNESSEE RIVER VALLEY'S. ALSO, FLOODING IS EXPECTED TO CONTINUE IN ILLINOIS DUE TO RISING RIVERS BEING FED BY SNOWMELT.

FOR SUNDAY JANUARY 11 - THURSDAY JANUARY 15: DURING THIS PERIOD, A UPPER-AIR RIDGE WILL FURTHER DEVELOP AND CONTINUE TO SUPPORT STRONG HIGH PRESSURE ACROSS THE WESTERN US. OFFSHORE WINDS ARE EXPECTED TO CONTINUE AND MAY RESULT IN INCREASED FIRE RISK FOR PORTIONS OF SOUTHERN CALIFORNIA LATER IN THE WEEKEND AND EARLY NEXT WEEK. A SECOND ROUND OF LAKE EFFECT SNOW IS EXPECTED ACROSS AREAS NEAR THE GREAT LAKES AS ANOTHER STORM SYSTEM RESULTS IN A COLD AIR INTRUSION OVER THE ICE-FREE GREAT LAKES.

THE UPPER-AIR RIDGE IN THE WEST WILL DRY OUT MOST OF THE CONUS, BUT COULD CAUSE SIGNIFICANT FLOODING IN THE WEST DUE TO RAPID SNOWMELT. ALSO, COLD AIR OUTBREAKS ARE LIKELY ACROSS THE NORTH-CENTRAL AND NORTHEAST US TO POTENTIALLY THE DEEP SOUTH. HOWEVER, CONSIDERABLE MODEL DIFFERENCES AND UNCERTAINTY DOES NOT ALLOW THE DELINEATION OF SPECIFIC HAZARDOUS COLD AT THIS TIME.

FOR FRIDAY JANUARY 16 - MONDAY JANUARY 19: RECENT MODEL SOLUTIONS INDICATE GENERAL PERSISTENCE OF THE 6-10 DAY UPPER LEVEL PATTERN DURING THIS PERIOD. THERE IS FAIRLY HIGH CERTAINTY WITH THIS FORECAST AS THE SPREAD AMONGST INDIVIDUAL ENSEMBLE MEMBERS IS RELATIVELY SMALL FOR THIS TIME RANGE. THE SEVERE DROUGHT AREAS ARE EXPECTED TO REMAIN FOR MOST AREAS.

FORECASTER: JON GOTTSCHALCK

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