Climate Prediction Center

US HAZARDS ASSESSMENT
NWS CLIMATE PREDICTION CENTER CAMP SPRINGS MD
300 PM EDT MAY 06 2009

SYNOPSIS: DURING THE WEEKEND, LOW PRESSURE SHOULD EXIT THE NORTHEAST AS A FRONTAL BOUNDARY PROGRESSES TOWARDS THE GULF COAST WHILE AN UPPER-LEVEL RIDGE DOMINATES THE SOUTHWEST. FROM MAY 11 – 13, A WARM FRONT IS EXPECTED TO LIFT NORTH INTO THE CENTRAL PLAINS AND MIDDLE MISSISSIPPI VALLEY, USHERING IN WARM, MOIST AIR. BY THE MIDDLE PART OF NEXT WEEK, AN ACTIVE STORM TRACK MAY DEVELOP FROM THE PLAINS INTO THE MISSISSIPPI VALLEY AND MIDWEST.

HAZARDS

ON MAY 9, HEAVY RAIN FOR THE CENTRAL APPALACHIANS.
FROM MAY 9 - 11, HEAVY RAIN ACROSS EASTERN PARTS OF THE SOUTHERN PLAINS, OZARKS, AND LOWER MISSISSIPPI VALLEY.
FROM MAY 9 - 11, MUCH ABOVE NORMAL TEMPERATURES FOR THE DESERT SOUTHWEST.
ONGOING FLOODING FOR PORTIONS OF THE NORTHERN PLAINS AND UPPER MIDWEST INCLUDING THE RED RIVER VALLEY OF THE NORTH, THE SHEYENNE RIVER AND THE JAMES RIVER.
ONGOING FLOODING FOR THE ILLINOIS RIVER.
ONGOING FLOODING FOR THE YUKON RIVER IN ALASKA.
SEVERE DROUGHT PERSISTS ACROSS PARTS OF CALIFORNIA, NEVADA, NEW MEXICO, TEXAS, WISCONSIN, AND FLORIDA.

DETAILED SUMMARY

FOR SATURDAY MAY 09 - MONDAY MAY 11: FAST, ZONAL FLOW SHOULD CONTINUE INTO THE WEEKEND ACROSS THE LOWER 48. ON SATURDAY, A SHORTWAVE TROUGH AND ASSOCIATED SURFACE LOW SHOULD TRACK INTO THE MID-ATLANTIC AND NORTHEAST. ALONG THE PATH OF THIS LOW PRESSURE SYSTEM, HEAVY RAIN (1 – 3 INCHES) MAY FALL IN THE CENTRAL APPALACHIANS INCLUDING THE HEADWATERS OF THE POTOMAC RIVER. DUE TO PRESENT SATURATED SOILS AND HIGH STREAM FLOWS, MINOR FLOODING COULD OCCUR ON THE UPPER POTOMAC RIVER.

DESPITE RECENT DRYNESS, RIVER FLOODING ALONG THE RED, SHEYENNE, AND JAMES RIVERS IN THE NORTHERN PLAINS CONTINUES AND SHOULD LINGER INTO NEXT WEEK. FLOODING WILL ALSO PERSIST ALONG THE ILLINOIS RIVER.

DUE TO RIDGING ALOFT, MUCH ABOVE NORMAL TEMPERATURES ARE FORECAST IN THE SOUTHWEST WHERE MAXIMUM TEMPERATURES SHOULD EXCEED 100 °F. BY THE MIDDLE PART OF NEXT WEEK, A DECREASE IN 500-HPA HEIGHTS SHOULD BRING COOLER TEMPERATURES TO THE SOUTHWEST.

DURING THE PAST WEEK, SNOWMELT AND ICE JAMS TRIGGERED RIVER FLOODING IN PARTS OF ALASKA. EAGLE, ALASKA-NEAR FAIRBANKS-EXPERIENCED ITS WORST FLOODING IN RECORDED HISTORY. THE YUKON RIVER CONTINUES TO RISE FROM EAGLE TO CIRCLE CITY AND ADDITIONAL ICE JAMS ARE EXPECTED TO DEVELOP.

FOR TUESDAY MAY 12 - SATURDAY MAY 16: MODEL GUIDANCE INDICATES THAT AN AMPLIFICATION TO THE LONGWAVE PATTERN SHOULD OCCUR OVER THE LOWER 48 AS A DEEP TROUGH EVOLVES IN THE WESTERN CONUS AND A RIDGE DEVELOPS IN THE SOUTHEASTERN CONUS. AT THE BEGINNING OF THIS PERIOD, A WARM FRONT RETREATING NORTH MAY PROVIDE THE FOCUS FOR HEAVY RAINFALL IN THE CENTRAL PLAINS, LOWER OHIO VALLEY, AND MIDDLE MISSISSIPPI VALLEY. DOWNSTREAM OF THE AMPLIFYING WESTERN TROUGH, SEVERAL DAYS OF STORMY WEATHER INCLUDING THE POTENTIAL FOR SEVERE WEATHER, HEAVY RAINFALL, AND FLOODING MAY AFFECT THE PLAINS, MISSISSIPPI VALLEY, AND THE MIDWEST.

LATER NEXT WEEK, AN INCREASE IN 500-HPA HEIGHTS ACROSS THE SOUTHEASTERN CONUS SHOULD RESULT IN A GRADUAL DRYING TREND FOR THE EXCESSIVELY WET AREAS OF THE MID-SOUTH. IT SHOULD BE NOTED THAT THE OPERATIONAL RUNS OF THE 0Z GFS AND 0Z ECMWF INDICATE A HIGHLY AMPLIFIED PATTERN WITH 500-HPA HEIGHTS AT OR GREATER THAN 588 DM IN THE SOUTHEAST BY THE MIDDLE PART OF NEXT WEEK. THIS UPPER-LEVEL PATTERN COULD BRING A SPELL OF MUCH ABOVE NORMAL TEMPERATURES TO THE SOUTHEAST.

FOR SUNDAY MAY 17 - WEDNESDAY MAY 20: THE SPREAD AMONG THE INDIVIDUAL 0Z GFS ENSEMBLE MEMBERS BECOMES LARGE REGARDING THE DURATION OF THE WESTERN CONUS TROUGH. THE OPERATIONAL MODEL RUNS OF THE 0Z AND 6Z GFS INDICATE THAT THE WESTERN CONUS TROUGH MAY PERSIST LATE INTO THE WEEK 2 PERIOD WHICH WOULD PROLONG THE THREAT OF SEVERE WEATHER, HEAVY RAINFALL, AND FLOODING IN THE PLAINS, MISSISSIPPI VALLEY, AND MIDWEST. THE EXPECTED LONGWAVE PATTERN FEATURING ABOVE NORMAL 500-HPA HEIGHTS FROM THE SOUTHERN PLAINS INTO THE SOUTHEASTERN CONUS SHOULD MAINTAIN ABOVE NORMAL TEMPERATURES ACROSS MUCH OF THE SOUTHERN CONUS.

NO DROUGHT RELIEF IS EXPECTED IN FLORIDA AND WILDFIRE DANGER WILL REMAIN ELEVATED. THE MEDIAN ONSET OF THE RAINY SEASON IN SOUTH FLORIDA IS MAY 21.

FORECASTER: BRAD PUGH

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