FXUS21 KWNC 181815
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER CAMP SPRINGS MD 300 PM EDT MAY 18 2012

SYNOPSIS: A WEAK LOW PRESSURE SYSTEM IS FORECAST TO DEVELOP NEAR THE MID-ATLANTIC AND LINGER ALONG THE EAST COAST EARLY IN THE WEEK. AN UPPER-LEVEL RIDGE OF HIGH PRESSURE MAY STRENGTHEN AND BRING UNSEASONABLY WARM TEMPERATURES TO THE EASTERN U.S. LATE IN THE WEEK. TROPICAL MOISTURE IS EXPECTED TO PERSIST OVER SOUTH FLORIDA. AN UPPER-LEVEL TROUGH OF LOW PRESSURE IS FORECAST TO REPLACE AN UPPER-LEVEL RIDGE OF HIGH PRESSURE NEXT WEEK ACROSS THE WESTERN U.S. A SURFACE LOW IS EXPECTED TO STRENGTHEN ACROSS THE NORTHERN PLAINS WITH A TRAILING FRONT SLOWLY ADVANCING ACROSS THE GREAT PLAINS. A LOW PRESSURE SYSTEM IS FORECAST TO WEAKEN ACROSS THE GULF OF ALASKA.

HAZARDS

RIVER FLOODING CONTINUING FOR PARTS OF NORTHERN WASHINGTON, MAY 21-22.

MUCH ABOVE NORMAL TEMPERATURES FOR PARTS OF THE WESTERN U.S., MAY 21.

MUCH ABOVE NORMAL TEMPERATURES FOR THE CENTRAL AND SOUTHERN HIGH PLAINS, MAY 22-23.

HIGH WINDS, BLOWING DUST, AND ENHANCED WILDFIRE DANGER FOR THE SOUTHWESTERN U.S., MAY 22-24.

PERIODS OF HEAVY RAIN FOR SOUTH FLORIDA, MAY 21-27.

SEVERE DROUGHT FOR PARTS OF THE SOUTHEAST, CENTRAL ROCKIES, SOUTHERN PLAINS, SOUTHWEST, INTERIOR PORTIONS OF CALIFORNIA, THE GREAT BASIN, AND HAWAII.

DETAILED SUMMARY

FOR MONDAY MAY 21 - FRIDAY MAY 25: AN AMPLIFIED UPPER-LEVEL RIDGE IS EXPECTED TO RESULT IN MUCH ABOVE NORMAL TEMPERATURES (MORE THAN 12 DEGREES F) ACROSS THE WESTERN U.S. BEFORE AN UPPER-LEVEL TROUGH MOVES INLAND FROM THE EAST PACIFIC. ACROSS THE LOWER DESERTS OF SOUTHERN ARIZONA, MAXIMUM TEMPERATURES ARE LIKELY TO EXCEED 105 DEGREES F ON MONDAY. MUCH ABOVE NORMAL TEMPERATURES ARE FORECAST TO SPREAD EAST ONTO THE CENTRAL AND SOUTHERN HIGH PLAINS BY TUESDAY.

MULTIPLE WILDFIRES HAVE RECENTLY DEVELOPED IN ARIZONA. THE LARGEST WILDFIRE IN MARICOPA COUNTY HAS BURNED MORE THAN 12,000 ACRES. AS AN UPPER-LEVEL TROUGH SHIFTS EAST, HIGH WINDS ARE EXPECTED TO DEVELOP ACROSS THE SOUTHWESTERN CONUS BY MID-WEEK. CRITICAL WILDFIRE DANGER CONDITIONS MAY RETURN TO THE SOUTHWESTERN U.S. DURING THE EARLY TO MIDDLE PART OF NEXT WEEK DUE TO GUSTY WINDS, HOT TEMPERATURES, LOW RELATIVE HUMIDITY VALUES, AND DRY FUELS. GUSTY WEST TO SOUTHWEST WINDS CAN CREATE BLOWING DUST AND REDUCED VISIBILITIES.

AN AMPLIFYING TROUGH ACROSS THE WESTERN CONUS IS FORECAST TO SPAWN A SLOW-MOVING SURFACE LOW ACROSS THE NORTHERN PLAINS. SINCE THE LATEST MODEL RUNS FROM 12Z/MAY 18 DIFFER ON THE LOCATION OF HEAVY RAINFALL, A HEAVY RAINFALL HAZARD IS NOT POSTED FOR THE NORTHERN PLAINS. UNCERTAINTY IN THE TIMING OF INDIVIDUAL SHORTWAVE TROUGHS EMERGING FROM THE LONGWAVE WESTERN CONUS TROUGH PRECLUDES DESIGNATION OF A SEVERE WEATHER HAZARD ACROSS THE GREAT PLAINS.

RAPID SNOW MELT HAS CREATED SHARP RISES ON RIVERS ACROSS THE EASTERN SLOPES OF THE CASCADES, IDAHO PANHANDLE, AND NORTHWEST MONTANA. RIVERS ARE FORECAST TO REMAIN AROUND FLOOD STAGE INTO NEXT WEEK. PLEASE SEE THE LATEST HYDROGRAPHS AT: HTTP://WATER.WEATHER.GOV/AHPS/INDEX.PHP.

DEEP TROPICAL MOISTURE ORIGINATING FROM THE WESTERN CARIBBEAN IS EXPECTED TO BRING THE THREAT OF HEAVY RAINFALL TO THE FLORIDA KEYS AND SOUTH FLORIDA FOR AN EXTENDED PERIOD. MODEL GUIDANCE VARIES ON THE NORTHERN EXTENT OF THE HIGH PRECIPITABLE WATER VALUES. A HEAVY RAINFALL HAZARD IS POSTED FOR SOUTH FLORIDA, BUT THE AXIS OF HEAVIEST RAINFALL MAY REMAIN OVER THE BAHAMAS AND CUBA.

ALTHOUGH NO RAINFALL OR WIND HAZARDS ARE POSTED WITH A WEAK EAST COAST LOW PRESSURE SYSTEM, MINOR COASTAL FLOODING MAY OCCUR ACROSS PARTS OF THE MID-ATLANTIC AT THE BEGINNING OF THE PERIOD DUE TO PERSISTENT, ONSHORE FLOW.

FOR SATURDAY MAY 26 - FRIDAY JUNE 01: THE THREAT OF HEAVY RAINFALL IS EXPECTED TO CONTINUE INTO WEEK-2 ACROSS SOUTH FLORIDA. THE UPPER-LEVEL ENVIRONMENT AND ABOVE NORMAL SEA SURFACE TEMPERATURES REMAIN CONDUCIVE FOR AN EARLY SEASON TROPICAL CYCLONE IN THE WESTERN CARIBBEAN. THE EXPECTED LONGWAVE PATTERN COULD RESULT IN HEAVY RAINFALL/SEVERE WEATHER ACROSS THE GREAT PLAINS DUE TO AN AMPLIFIED WESTERN CONUS TROUGH. A BUILDING SUBTROPICAL RIDGE OVER THE SOUTHEASTERN CONUS MAY RESULT IN MUCH ABOVE NORMAL TEMPERATURES ACROSS PARTS OF THE EAST-CENTRAL U.S. DURING THE MEMORIAL DAY WEEKEND.

FORECASTER: BRAD PUGH

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