065
FXUS21 KWNC 151842
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT MAY 15 2023
SYNOPSIS: A BROAD AREA OF MID-LEVEL HIGH PRESSURE ACROSS MUCH OF THE NORTHERN
CONTIGUOUS UNITED STATES (CONUS) FAVORS GENERALLY ABOVE-NORMAL TEMPERATURES BUT
WITH LIMITED CHANCES FOR REACHING HAZARDS THRESHOLD. 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. IN
ALASKA, RIVER-ICE BREAK-UP COULD LEAD TO FLOODING AND ICE JAMS IN THE INTERIOR
ALONG MAJOR RIVERS.
HAZARDS
POSSIBLE FLOODING FOR PORTIONS OF CALIFORNIA, NEVADA, UTAH, WYOMING, WESTERN
MONTANA, IDAHO, OREGON, AND WASHINGTON.
POSSIBLE FLOODING ALONG PORTIONS OF THE RED RIVER OF THE NORTH, 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 THURSDAY MAY 18 - MONDAY MAY 22:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR TUESDAY MAY 23 - MONDAY MAY 29: THERE IS FAIR 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 EXCLUDING THE
SOUTHEAST WHERE NEAR TO SLIGHTLY BELOW-NORMAL HEIGHTS ARE FORECAST AND ALONG
THE IMMEDIATE WEST COAST WHERE THE EUROPEAN AND GEFS DISAGREE ON WEAKLY
POSITIVE OR WEAKLY NEGATIVE 500-HPA HEIGHT ANOMALIES, RESPECTIVELY. IN ALASKA,
POSITIVE 500-HPA HEIGHTS ACROSS THE WESTERN THIRD OF THE STATE ARE FORECAST,
WITH NEAR TO SLIGHTLY BELOW-NORMAL HEIGHTS IN THE EAST.
ABOVE-NORMAL TEMPERATURES ARE FAVORED ACROSS MUCH OF THE CONUS DURING WEEK-2.
THE ECMWF AND GEFS BOTH FORECAST TEMPERATURES EXCEEDING THE 85TH CLIMATOLOGICAL
PERCENTILE IN PORTIONS OF NORTHERN CONUS FROM THE PACIFIC NORTHWEST TO THE
GREAT LAKES DURING THE PERIOD. HOWEVER, THERE IS LIMITED SUPPORT FOR THESE
TEMPERATURES EXCEEDING 85 DEGF. THEREFORE, NO CORRESPONDING HAZARD SHAPES ARE
POSTED. EARLY IN THE PERIOD, IN THE NORTHEAST, THERE IS SOME SUPPORT FOR
TEMPERATURES FALLING BELOW THE 15TH PERCENTILE AND 40 DEGF WHICH COULD IMPACT
VULNERABLE VEGETATION. HOWEVER, TEMPERATURES FALLING BELOW 32 DEGF LOOK LIMITED
TO JUST THE HIGHEST ELEVATIONS, THEREFORE, NO CORRESPONDING TEMPERATURE HAZARD
IS POSTED.
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 IS ONGOING OR ANTICIPATED ALONG PARTS OF THE PORTNEUF,
BEAR, HUMBOLDT, NACHES, AND OKANOGAN RIVERS, AMONG OTHERS. FLOODING CONTINUES
TO BE POSSIBLE ALONG SOME RIVERS IN THE NORTH-CENTRAL CONUS. HOWEVER, DUE TO
SNOW COVER BECOMING NEARLY DEPLETED IN THIS AREA AND ADJACENT CANADA, THE RIVER
FLOODING RISK IS ANTICIPATED TO WANE OVER THIS AREA.
AT THE BEGINNING OF THE PERIOD, MULTIPLE MODELS INDICATE THE POTENTIAL FOR A
SURFACE LOW OVER THE WESTERN PORTIONS OF THE FOUR CORNERS, SOUTHERN NEVADA AND
SOUTHERN CALIFORNIA. THIS PATTERN MAY SUPPORT ENHANCED MOIST SOUTHERLY FLOW TO
PARTS OF THE FOUR CORNERS, RESULTING IN ENHANCED PRECIPITATION IN THE REGION.
BOTH REFORECAST TOOLS INDICATE A BROAD AREA WITH AT LEAST A 20% CHANCE OF 3-DAY
RAINFALL EXCEEDING THE 85TH CLIMATOLOGICAL PERCENTILE, PRIMARILY DURING DAYS 8
TO 10, BUT LIMITED SUPPORT FOR PRECIPITATION EXCEEDING HALF AN INCH. THE ECMWF
TOOLS SHOW THE HIGHEST CHANCES (>40%) OF EXCEEDING THESE THRESHOLDS ACROSS
NORTHERN ARIZONA, SOUTHERN UTAH AND SOUTHERN NEVADA. DUE TO THIS BEING THE
DRIEST TIME OF THE YEAR IN A RELATIVELY ARID REGION OF THE COUNTRY, ONLY A FEW
TENTHS OF AN INCH FOR A ONE-WEEK PERIOD IS CONSIDERABLY ABOVE NORMAL. IN ALMOST
130 YEARS OF RECORD, MAY MONTHLY TOTALS AT PHOENIX, AZ HAVE ONLY EXCEEDED AN
INCH FOUR TIMES, AND ONLY THE EUROPEAN REFORECAST SHOWS A NON-TRIVIAL CHANCE
FOR PRECIPITATION TOTALS TO EXCEED A HALF AN INCH. THE UNCALIBRATED ENSEMBLE
MEANS HAVE LESS AGREEMENT COMPARED TO THE REFORECAST TOOLS, WITH THE GEFS
HAVING A GREATER SIGNAL FOR ENHANCED PRECIPITATION THAN THE ECMWF. BASED ON
SIGNIFICANT UNCERTAINTY REGARDING HEAVY PRECIPITATION POTENTIAL AND CONSIDERING
CLIMATOLOGY AT THIS TIME OF THE YEAR, NO HAZARD IS POSTED AT THIS TIME.
IN PORTIONS OF NORTHEAST KANSAS, NORTHWEST MISSOURI, AND SOUTHWEST IOWA, RAIN
OVER THE WEEKEND HAS REDUCED THE CHANCES FOR RAPID ONSET DROUGHT. NEAR-NORMAL
PRECIPITATION IS ALSO FORECAST DURING THE WEEK-2 PERIOD. THEREFORE, THE RAPID
ONSET DROUGHT RISK INTRODUCED LAST WEEK HAS BEEN REMOVED. THIS AREA WILL
CONTINUE TO BE MONITORED AS PRECIPITATION TOTALS OVER THE LAST 30 AND 60 DAYS
REMAIN BELOW NORMAL FOR THOSE PERIODS. SOIL MOISTURE IN THESE REGIONS IS ALSO
WELL BELOW-NORMAL WITH NASA SPORT SOIL MOISTURE ANALYSIS OF THE TOP 100CM
SHOWING MUCH OF THE AREA BELOW THE 30TH PERCENTILE.
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 KOBUCK RIVERS.
FORECASTER: RYAN BOLT
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