342
FXUS21 KWNC 171742
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT MAY 17 2023
SYNOPSIS: A BROAD AREA OF MID-LEVEL HIGH PRESSURE FORECAST ACROSS MUCH OF THE
NORTHERN CONTIGUOUS UNITED STATES (CONUS) FAVORS GENERALLY ABOVE-NORMAL
TEMPERATURES BUT WITH LIMITED CHANCES FOR REACHING HAZARDS THRESHOLDS. HOWEVER,
WARM TEMPERATURES COULD ENHANCE THE SNOWMELT RATE WHERE DEEP SNOWPACK REMAINS
IN PLACE ACROSS THE HIGHER ELEVATIONS, INCREASING THE POTENTIAL FOR FLOODING
ALONG SOME RIVERS. HEAVY PRECIPITATION IS POSSIBLE IN PARTS OF THE GREAT PLAINS
WHERE MOIST, SOUTHERLY FLOW MAY INTERACT WITH A WEAK LOW-PRESSURE SYSTEM, AND
ACROSS THE SOUTHEAST COAST AND FLORIDA, DUE TO A POTENTIAL CUT-OFF SYSTEM. IN
ALASKA, RIVER-ICE BREAK-UP COULD LEAD TO FLOODING AND ICE JAMS IN THE INTERIOR
ALONG MAJOR RIVERS.
HAZARDS
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF FLORIDA AND EXTENDING
NORTHWARD THROUGH THE COASTAL CAROLINAS, THU-MON, MAY 25-29.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE SOUTHERN AND CENTRAL
PLAINS, THU-SAT, MAY 25-27.
POSSIBLE FLOODING FOR PORTIONS OF CALIFORNIA, NEVADA, UTAH, WYOMING, WESTERN
MONTANA, IDAHO, OREGON, AND WASHINGTON.
POSSIBLE FLOODING ALONG PORTIONS OF THE JAMES RIVER AND THE MISSISSIPPI RIVER.
POSSIBLE FLOODING IN PARTS OF INTERIOR ALASKA ALONG THE TANANA, YUKON,
KUSKOKWIM, KOYUKUK, AND KOBUK RIVERS.
DETAILED SUMMARY
FOR SATURDAY MAY 20 - WEDNESDAY MAY 24:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR THURSDAY MAY 25 - WEDNESDAY MAY 31: THERE IS GOOD AGREEMENT IN THE MEAN
WEEK-2 500-HPA HEIGHT HEIGHT FORECASTS ACROSS THE DYNAMICAL MODELS TODAY.
POSITIVE 500-HPA HEIGHT ANOMALIES ARE FORECAST ACROSS MUCH OF THE CONUS, WITH
THE LARGEST POSITIVE ANOMALIES ACROSS THE GREAT LAKES AND NORTHEAST. THIS
FAVORS ABOVE-NORMAL TEMPERATURES ACROSS MANY AREAS, ALTHOUGH NO WIDESPREAD
AREAS OF HAZARDOUS TEMPERATURES ARE INDICATED. WARM TEMPERATURES ARE
ANTICIPATED TO ENHANCE THE SNOWMELT RATE ACROSS THE WESTERN CONUS, INDUCING
RIVER FLOODING ESPECIALLY ACROSS HIGHER ELEVATIONS IN THE WEST AND THE SOUTHERN
CANADIAN ROCKIES, WHERE A FEW SITES STILL REPORT OVER 50 INCHES OF SNOW WATER
CONTENT. THE ABOVE-NORMAL TEMPERATURES MAY CAUSE RAPID SNOWMELT IN PARTS OF THE
SIERRA NEVADA, GREAT BASIN, NORTHERN ROCKIES, AND PACIFIC NORTHWEST, RESULTING
IN AREAS AT HIGH RISK OF FLOODING AND MUDSLIDES ALONG MANY RIVERS, AND IN AREAS
ADJACENT TO THE HIGHER ELEVATIONS; HOWEVER, EXPANSIVE, MULTI-STATE FLOODING IS
NOT EXPECTED TO ENVELOP LARGE AREAS OF THE INTERIOR WEST. FLOODING CONTINUES TO
BE POSSIBLE ALONG SOME RIVERS IN THE NORTH-CENTRAL CONUS DUE TO PREVIOUS
SNOWMELT.
THE ABOVE-AVERAGE TEMPERATURES COMBINED WITH LITTLE PRECIPITATION FORECAST AND
ALREADY DRY SOILS MAY LEAD TO INCREASING DROUGHT CONCERNS ACROSS THE PARTS OF
THE OHIO VALLEY DURING THE PERIOD. HOWEVER, BECAUSE SOME PRECIPITATION IS
FORECAST IN WEEK-1, WHICH MAY TEMPORARILY ALLEVIATE SOME OF THE CONCERN, NO
RAPID ONSET DROUGHT HAZARD IS ISSUED AT THIS TIME. HEAT LEVELS MAY INCREASE
ACROSS PARTS OF THE LOWER MISSISSIPPI VALLEY, CENTRAL GULF COAST, AND
SOUTHEAST, WITH THE SKILL WEIGHTED ECMWF/GEFS HEAT TOOL INDICATING ELEVATED
PROBABILITIES (20-30 PERCENT) FOR HEAT INDICES TO EXCEED 100 DEG F IN SOME OF
THESE AREAS LATER IN WEEK-2. HOWEVER, IT IS UNLIKELY HEAT INDICES WILL REACH
105 DEG F PRECLUDING A RELATED HEAT HAZARD.
A CUT-OFF MID-LEVEL LOW IS FORECAST TO DEVELOP ACROSS THE SOUTHEAST LATE IN
WEEK-1 AND PERSISTING INTO WEEK-2. THIS FAVORS INCREASING CHANCES OF HEAVY
PRECIPITATION ACROSS PARTS OF FLORIDA AND NORTHWARD ALONG PARTS OF THE
MID-ATLANTIC AND SOUTHEAST COASTS. THE UNCERTAINTY LIES IN WHETHER OR NOT THE
HEAVIEST PRECIPITATION REMAINS OFF THE COAST OR COMES FURTHER INLAND. THE
ECMWF, GEFS, AND CANADIAN REFORECAST TOOLS ALL DEPICT AT LEAST A 20 PERCENT
CHANCE 3-DAY PRECIPITATION TOTALS EXCEED THE 85TH PERCENTILE AND 1-INCH ACROSS
PARTS OF FLORIDA AND NORTHWARD THROUGH THE COASTAL CAROLINAS, WITH THE ECMWF
REFORECAST TOOL CONTINUING TO DEPICT THE HIGHEST PROBABILITIES (UPWARDS OF 40
PERCENT). GIVEN THE CONTINUED SUPPORT AND FAVORABLE SET-UP, A SLIGHT RISK OF
HEAVY PRECIPITATION REMAINS POSTED ACROSS FLORIDA AND COASTAL AREAS OF THE
SOUTHEAST FROM MAY 25-29. THE UNCALIBRATED DYNAMICAL MODEL ENSEMBLES ALSO BRING
ENHANCED PRECIPITATION INTO THE MID-ATLANTIC, ALTHOUGH PROBABILITIES IN THE
REFORECAST TOOLS DO NOT SUPPORT A NORTHWARD EXTENSION OF THE HAZARD, SUGGESTING
PRECIPITATION WILL NOT BE AS HEAVY COMPARED TO FURTHER SOUTH. IN ADDITION TO
THE POTENTIAL RAINFALL, BELOW-NORMAL TEMPERATURES AND EASTERLY SURFACE WINDS
ARE EXPECTED TO LEAD TO OVERALL DAMP AND COOL CONDITIONS LEADING UP TO AND
POSSIBLY CONTINUING INTO THE MEMORIAL DAY WEEKEND ACROSS COASTAL PARTS OF THE
SOUTHEAST AND MID-ATLANTIC.
WEAK SURFACE LOW PRESSURE FORECAST ACROSS THE SOUTHWEST, ALONG WITH INCREASED
SOUTHERLY FLOW ACROSS THE GREAT PLAINS, MAY LEAD TO EPISODES OF HEAVY
PRECIPITATION AND THUNDERSTORMS ACROSS PARTS OF THE PLAINS EARLY IN THE PERIOD.
THE GEFS AND ECMWF REFORECAST TOOLS DEPICT AT LEAST A 20 PERCENT CHANCE 3-DAY
PRECIPITATION TOTALS EXCEED 1-INCH DURING THE MAY 25-27 TIMEFRAME ACROSS PARTS
OF THE CENTRAL AND SOUTHERN PLAINS, CORRESPONDING WITH A SLIGHT RISK FOR HEAVY
PRECIPITATION. ELEVATED CHANCES OF ABOVE-NORMAL PRECIPITATION ALSO EXTEND BACK
THROUGH PARTS OF THE FOUR CORNERS, ROCKIES, AND SOUTHWEST CONSIDERING THE
RELATIVELY DRY CLIMATOLOGY OVER THESE AREAS. HOWEVER, 3-DAY PRECIPITATION
TOTALS ARE GENERALLY FORECAST TO BE UNDER A HALF-INCH, PRECLUDING A RELATED
HEAVY PRECIPITATION HAZARD FOR THESE REGIONS.
IN INTERIOR ALASKA, WARMER TEMPERATURES DURING THE PAST WEEK HAVE LED TO RISES
IN MANY OF THE RIVERS IN THE REGION. THERE ARE CURRENTLY SEVERAL FLOOD WATCHES
AND ADVISORIES POSTED THROUGHOUT INTERIOR ALASKA. MUCH OF THE TANANA RIVER NOW
HAS OPEN WATER AS RIVER ICE CONTINUES TO MELT BUT THERE ARE LINGERING CONCERNS
FOR SNOWMELT FLOODING INTO THE WEEK-2 PERIOD. THE ICE FRONT ALONG THE YUKON
RIVER IS PROGRESSING DOWNRIVER AND MAY BRING FLOODING CONCERNS TO AREAS
DOWNRIVER OF FAIRBANKS BY WEEK-2. OTHER RIVERS OF CONCERN FOR RIVER ICE BREAK
UP LEADING TO THE POTENTIAL FOR POSSIBLE FLOODING AND ICE JAMS ARE THE
KUSKOKWIM, KOYUKUK, AND KOBUK RIVERS.
FORECASTER: THOMAS COLLOW
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page