Climate Prediction Center

US HAZARDS ASSESSMENT
NWS CLIMATE PREDICTION CENTER CAMP SPRINGS MD
300 PM EDT MAY 05 2009

SYNOPSIS: FROM FRIDAY INTO SATURDAY, LOW PRESSURE SHOULD TRACK EAST ALONG A FRONTAL BOUNDARY FROM THE SOUTHERN PLAINS INTO THE TENNESSEE VALLEY AND CENTRAL APPALACHIANS. ON SUNDAY, LOW PRESSURE EXITS THE NORTHEAST AS HIGH PRESSURE BUILDS SOUTH AND THE AFOREMENTIONED FRONTAL BOUNDARY SHIFTS SOUTH TOWARDS THE GULF COAST. AN UPPER-LEVEL RIDGE SHOULD REMAIN DOMINANT OVER THE SOUTHWEST.

HAZARDS

FROM MAY 8 - 9, HEAVY RAIN CAN BE EXPECTED ACROSS THE OZARKS, TENNESSEE VALLEY, AND CENTRAL APPALACHIANS.
ON MAY 8, SEVERE WEATHER IS FORECAST IN EASTERN OKLAHOMA, NORTHEAST TEXAS, AND ARKANSAS.
FROM MAY 8 - 11, MUCH ABOVE NORMAL TEMPERATURES ARE EXPECTED IN THE 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 RIVER FLOODING IN PARTS OF ALASKA.
SEVERE DROUGHT PERSISTS ACROSS PARTS OF CALIFORNIA, NEVADA, NEW MEXICO, TEXAS, WISCONSIN, AND FLORIDA.

DETAILED SUMMARY

FOR FRIDAY MAY 08 - SUNDAY MAY 10: A LOW AMPLITUDE SHORTWAVE TROUGH SHOULD RAPIDLY TRACK FROM THE PLAINS INTO THE NORTHEAST. ON FRIDAY, ABUNDANT MOISTURE, STRONG INSTABILITY, AND SUFFICIENT SHEAR SHOULD SUPPORT SEVERE THUNDERSTORM DEVELOPMENT IN THE EASTERN PARTS OF THE SOUTHERN PLAINS. MODEL GUIDANCE SUGGESTS THAT A MESOSCALE CONVECTIVE SYSTEM (MCS) MAY TRACK FROM THE OZARKS INTO THE TENNESSEE VALLEY ON FRIDAY NIGHT. HEAVY RAINFALL IN EXCESS OF 3 INCHES AND ADDITIONAL FLOODING CAN BE EXPECTED IN ARKANSAS AND TENNESSEE. LOCALLY HEAVY RAIN AND RIVER FLOODING MAY ALSO AFFECT PARTS OF THE CENTRAL APPALACHIANS AND MID-ATLANTIC.

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.

ACROSS THE SOUTHERN FLORIDA PENINSULA, EXTREME DROUGHT HAS EXPANDED AND NUMEROUS WILDFIRES HAVE DEVELOPED IN RECENT WEEKS. IN THE BIG CYPRESS NATIONAL PRESERVE IN SOUTHWEST FLORIDA, A LARGE WILDFIRE (MORE THAN 30,000 ACRES BURNT) SPARKED BY LIGHTNING IN LATE APRIL IS 95% CONTAINED.

DUE TO RIDGING ALOFT, MUCH ABOVE NORMAL TEMPERATURES ARE FORECAST IN MUCH OF THE SOUTHWEST. ON FRIDAY, MAXIMUM TEMPERATURES WILL RANGE FROM 95 – 105 °F IN SOUTHEAST NEW MEXICO AND WESTERN TEXAS BEFORE RELIEF FROM THE HEAT ARRIVES THIS WEEKEND. HOT TEMPERATURES, WITH MAXIMUM TEMPERATURES REACHING 100 °F, SHOULD CONTINUE ACROSS THE DESERT SOUTHWEST.

DURING THE PAST WEEK, SNOWMELT TRIGGERED RIVER FLOODING IN PARTS OF ALASKA. FLOODING CONTINUES ALONG THE CHENA AND TANANA RIVERS AT OR OUTSIDE OF FAIRBANKS. ADDITIONAL RIVER FLOODING REMAINS POSSIBLE.

FOR MONDAY MAY 11 - FRIDAY MAY 15: THE GREATEST UNCERTAINTY IS THE LOCATION OF A FRONTAL BOUNDARY THAT HAS RECENTLY PLAGUED THE MID-SOUTH WITH FREQUENT PERIODS OF HEAVY RAIN AND FLOODING. THE OPERATIONAL RUN OF THE 0Z ECMWF CONTINUES THE LIKELIHOOD OF HEAVY RAINFALL IN THE OZARKS AND TENNESSEE VALLEY, WHILE THE OPERATIONAL RUN OF THE 0Z GFS INDICATES A DRIER WEATHER PATTERN. DUE TO CONFLICTING SIGNALS FROM THE MODELS, A HEAVY RAINFALL HAZARD IS NOT DEPICTED BEYOND MAY 9. HOWEVER, THE POTENTIAL FOR HEAVY RAINFALL AND ADDITIONAL FLOODING SHOULD BE CLOSELY MONITORED IN THE OZARKS AND TENNESSEE VALLEY.

LATER NEXT WEEK, AN INCREASE IN 500-HPA HEIGHTS ACROSS THE SOUTH-CENTRAL CONUS SHOULD RESULT IN A GRADUAL DRYING TREND FOR THE EXCESSIVELY WET AREAS OF THE MID-SOUTH, AND EXPAND ABOVE NORMAL TEMPERATURES TO INCLUDE THE SOUTHERN PLAINS, LOWER MISSISSIPPI VALLEY, AND SOUTHEAST. IT SHOULD BE NOTED THAT THE OPERATIONAL RUN OF THE 12Z GFS INDICATES A HIGHLY AMPLIFIED PATTERN WITH 500 H-PA HEIGHTS 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 SATURDAY MAY 16 - TUESDAY MAY 19: THE EXPECTED LONGWAVE PATTERN OF ZONAL FLOW NEAR THE U.S./CANADA BORDER WOULD SHIFT THE PRIMARY STORM TRACK INTO THE UPPER MIDWEST. THE INCREASE IN 500-HPA HEIGHTS NOTED IN THE 0Z AND 6Z GFS ENSEMBLE MEAN SOLUTIONS AT D+11 SHOULD BRING ABOVE NORMAL TEMPERATURES TO MUCH OF THE CENTRAL AND EASTERN U.S. NO DROUGHT RELIEF IS EXPECTED IN FLORIDA AND WILDFIRE DANGER WILL REMAIN ELEVATED. THE MEDIAN ONSET OF THE RAINY SEASON IN FLORIDA IS MAY 21.

FORECASTER: BRAD PUGH

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