939
FXUS21 KWNC 181811
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT MAY 18 2023
SYNOPSIS: A CUT-OFF MID-LEVEL LOW IS FORECAST TO DEVELOP ACROSS THE
SOUTHEASTERN U.S. (CONUS) PRIOR TO THE START OF WEEK-2, WITH IMPACTS CONTINUING
INTO THE FORECAST PERIOD. THERE ARE ELEVATED CHANCES OF HEAVY PRECIPITATION
ACROSS PARTS OF THE SOUTHEAST AND SOUTHERN MID-ATLANTIC, WITH POTENTIAL FOR
INCREASED WINDS ALONG THE COAST. WHILE THERE REMAINS CONSIDERABLE UNCERTAINTY
AS TO WHETHER THE HEAVIEST PRECIPITATION WILL REMAIN OFFSHORE OR MOVE FURTHER
INLAND, TODAY’S FORECAST HEDGES MORE AGGRESSIVE CONSIDERING THE START OF
MEMORIAL DAY WEEKEND COINCIDES WITH THESE POTENTIAL IMPACTS. ELSEWHERE, ACROSS
THE CONUS, BROAD MID-LEVEL HIGH PRESSURE AND ABOVE-NORMAL TEMPERATURES ARE
FORECAST, WHICH COULD LEAD TO LOCALIZED FLOODING DUE TO SNOW MELT OVER HIGHER
ELEVATIONS OF THE WEST, AS WELL AS WORSENING DROUGHT CONDITIONS ACROSS THE CORN
BELT DUE TO LITTLE PRECIPITATION FORECAST. IN ALASKA, RIVER-ICE BREAK-UP COULD
LEAD TO FLOODING AND ICE JAMS IN THE INTERIOR ALONG MAJOR RIVERS.
HAZARDS
MODERATE RISK OF HEAVY PRECIPITATION FOR THE COASTAL CAROLINAS, FRI-SAT, MAY
26-27.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE SOUTHEAST AND SOUTHERN
MID-ATLANTIC, FRI-MON, MAY 26-29.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE GREAT PLAINS AND UPPER
AND MIDDLE MISSISSIPPI VALLEY, FRI-SAT, MAY 26-27.
SLIGHT RISK OF HIGH WINDS ALONG THE SOUTHEAST AND MID-ATLANTIC COASTS, FRI-SAT,
MAY 26-27.
POSSIBLE FLOODING FOR PORTIONS OF CALIFORNIA, NEVADA, UTAH, WYOMING, WESTERN
MONTANA, IDAHO, OREGON, AND WASHINGTON.
POSSIBLE FLOODING ALONG PORTIONS OF THE JAMES RIVER.
POSSIBLE FLOODING IN PARTS OF INTERIOR ALASKA ALONG THE TANANA, YUKON,
KUSKOKWIM, KOYUKUK, AND KOBUK RIVERS.
RAPID ONSET DROUGHT RISK ACROSS PORTIONS OF THE EASTERN CORN BELT.
DETAILED SUMMARY
FOR SUNDAY MAY 21 - THURSDAY MAY 25:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR FRIDAY MAY 26 - THURSDAY JUNE 01: 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 THE JAMES RIVER IN SOUTH DAKOTA DUE TO PREVIOUS SNOWMELT.
DROUGHT CONCERNS ARE FORECAST TO INCREASE ACROSS PARTS OF THE EASTERN CORN BELT
DURING THE WEEK-2 PERIOD. HIGH TEMPERATURES ARE FORECAST TO BE WELL INTO THE
80S DEG F, WITH THE ECMWF ENSEMBLE DEPICTING TEMPERATURES NEAR 90 DEG F. IN
ADDITION, SOIL MOISTURE IS BELOW THE 30TH CLIMATOLOGICAL PERCENTILE OVER SOME
AREAS, AND ASIDE FROM A PASSING FRONT EARLY IN WEEK-1, VERY LITTLE
PRECIPITATION IS FORECAST THROUGH WEEK-2. DUE TO THESE FACTORS, A RAPID ONSET
DROUGHT RISK IS HIGHLIGHTED ACROSS PARTS OF THE EASTERN CORN BELT, SPECIFICALLY
SOUTHEASTERN IOWA, CENTRAL ILLINOIS AND INDIANA, AND SOUTHWESTERN OHIO. THERE
ARE ALSO DROUGHT EXPANSION CONCERNS ACROSS THE NORTHERN MID-ATLANTIC, BUT WITH
ADDED UNCERTAINTY DUE TO THE INCREASING ONSHORE FLOW FORECAST EARLY IN WEEK-2
AND THE NORTHWARD EXTENT OF PRECIPITATION.
A CUT-OFF MID-LEVEL LOW IS FORECAST TO DEVELOP ACROSS THE SOUTHEASTERN CONUS
LATE IN WEEK-1 AND PERSISTING INTO WEEK-2, LEADING TO UNSETTLED WEATHER DURING
MEMORIAL DAY WEEKEND OVER PARTS OF THE SOUTHEAST AND MID-ATLANTIC. THE ECMWF,
GEFS, AND CANADIAN REFORECAST TOOLS ALL DEPICT AT LEAST A 20 PERCENT CHANCE OF
3-DAY PRECIPITATION TOTALS EXCEEDING THE 85TH PERCENTILE AND 1-INCH ACROSS
PARTS OF THESE AREAS, WITH THE ECMWF REFORECAST TOOL CONTINUING TO DEPICT THE
HIGHEST PROBABILITIES (UPWARDS OF 40 PERCENT). A MODERATE RISK OF HEAVY
PRECIPITATION IS POSTED ALONG THE NORTH AND SOUTH CAROLINA COASTS WHERE THE
UNCALIBRATED 0Z ECMWF, GEFS, AND CANADIAN ENSEMBLES DEPICT THE HEAVIEST
PRECIPITATION TOTALS EARLY IN WEEK-2 (MAY 26-27). A SLIGHT RISK OF HEAVY
PRECIPITATION REMAINS POSTED ACROSS A BROADER AREA OF THE SOUTHEAST AND
SOUTHERN MID-ATLANTIC FROM MAY 26-29. SOME PRECIPITATION MAY ALSO EXTEND INTO
THE NORTHERN MID-ATLANTIC, ALTHOUGH AMOUNTS ARE EXPECTED TO BE LOWER COMPARED
TO FARTHER SOUTH. IN ADDITION TO THE POTENTIAL RAINFALL, A TIGHT PRESSURE
GRADIENT FAVORS INCREASED EASTERLY SURFACE WINDS ALONG THE COAST, JUSTIFYING A
SLIGHT RISK FOR HIGH WINDS ALONG THE COAST FROM NORTHEASTERN FLORIDA TO
SOUTHERN MARYLAND FOR MAY 26-27. THIS COULD PROMOTE INCREASED SURF AND RIP
CURRENTS ACROSS THE BEACHES.
INCREASED SOUTHERLY SURFACE FLOW ACROSS THE CENTRAL CONUS, COMBINED WITH WEAK
LOW PRESSURE FORECAST ACROSS THE ROCKIES, MAY LEAD TO EPISODES OF HEAVY
PRECIPITATION AND THUNDERSTORMS ACROSS THE GREAT PLAINS AND UPPER AND MIDDLE
MISSISSIPPI VALLEY EARLY IN THE PERIOD. THE UNCALIBRATED 0Z GEFS, ECMWF, AND
CANADIAN ENSEMBLES DEPICT THE HIGHEST PRECIPITATION CHANCES ACROSS THESE AREAS
ON MAY 26-27, WITH SOME CONTINUED SUPPORT FROM THE ECMWF AND CANADIAN
REFORECAST TOOLS, WHICH DEPICT AT LEAST A 20 PERCENT CHANCE PRECIPITATION
TOTALS EXCEED THE 85TH CLIMATOLOGICAL PERCENTILE AND 1-INCH OVER PARTS OF THE
CENTRAL AND SOUTHERN PLAINS EARLY IN WEEK-2. THEREFORE, A SLIGHT RISK OF HEAVY
PRECIPITATION CONTINUES TO BE HIGHLIGHTED FOR MAY 26-27, AND IS EXPANDED
NORTHWARD COMPARED TO YESTERDAY ACROSS THE NORTHERN PLAINS AND UPPER
MISSISSIPPI VALLEY DUE TO THE INCREASED SIGNALS IN THE UNCALIBRATED GUIDANCE.
ELEVATED CHANCES OF ABOVE-NORMAL PRECIPITATION ALSO EXTEND BACK THROUGH PARTS
OF THE WEST CONSIDERING THE RELATIVELY DRIER CLIMATOLOGY. HOWEVER, 3-DAY
PRECIPITATION TOTALS ARE GENERALLY FORECAST TO BE UNDER A HALF-INCH, PRECLUDING
A RELATED HEAVY PRECIPITATION HAZARD FOR THESE REGIONS.
WEAK TROUGHING OVER THE BERING SEA AND ALASKA IS FORECAST TO RESULT IN A PERIOD
OF NEAR- TO BELOW-NORMAL TEMPERATURES ACROSS THE STATE DURING WEEK-2. HOWEVER,
RIVERS ARE EXPECTED TO CONTINUE TO RISE ACROSS MAINLAND ALASKA DUE TO ICE JAMS.
THERE ARE CURRENTLY SEVERAL FLOOD WATCHES AND ADVISORIES POSTED THROUGHOUT
INTERIOR AND WESTERN 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
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