094
FXUS21 KWNC 121829
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT MAY 12 2023
SYNOPSIS: A BROAD AREA OF MID-LEVEL HIGH PRESSURE CONTINUES TO FAVOR
PREDOMINANTLY ABOVE-NORMAL TEMPERATURES ACROSS THE NORTH-CENTRAL STATES, AND IN
MOST AREAS FROM THE ROCKIES WESTWARD TO THE PACIFIC COAST BRINGING CHANCES FOR
HAZARDOUS TEMPERATURES TO PARTS OF THE PACIFIC NORTHWEST. UNSEASONABLY WARM
SPRING TEMPERATURES COULD ENHANCE THE SNOWMELT RATE WHERE DEEP SNOWPACK IS
STILL IN PLACE ACROSS THE HIGHER ELEVATIONS, INCREASING THE POTENTIAL FOR
FLOODING ALONG SOME RIVERS, ESPECIALLY ACROSS THE NORTHWESTERN QUARTER OF THE
CONTIGUOUS U.S. (CONUS). ANTECEDENT AND FORECASTED DRYNESS ACROSS THE CENTRAL
PLAINS LEADS TO AN INCREASED RISK OF RAPID ONSET DROUGHT.
HAZARDS
SLIGHT RISK OF EXCESSIVE HEAT FOR PORTIONS OF THE PACIFIC NORTHWEST AND THE
CENTRAL VALLEY OF CALIFORNIA, SAT-MON, MAY 20-22.
RAPID ONSET DROUGHT RISK IN NORTHEAST KANSAS, NORTHWEST MISSOURI, AND SOUTHWEST
IOWA.
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 YUKON, KUSKOKWIM, AND
TANANA RIVERS.
DETAILED SUMMARY
FOR MONDAY MAY 15 - FRIDAY MAY 19:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR SATURDAY MAY 20 - FRIDAY MAY 26: THERE CONTINUES TO BE GOOD AGREEMENT IN
THE MEAN WEEK-2 500-HPA HEIGHT ANOMALY FORECASTS BETWEEN THE DYNAMICAL MODELS.
AMPLIFIED MID-LEVEL RIDGING IS FORECAST OVER THE NORTHWESTERN CONUS AT THE
BEGINNING OF THE PERIOD, GRADUALLY WEAKENING THROUGHOUT WEEK-2 AND EXPANDING TO
THE SOUTH AND EAST. AT THE ONSET OF THE PERIOD, THE ECMWF, GEFS AND CANADIAN
FORECAST INDICATE HEIGHT ANOMALIES GREATER THAN OR NEAR 180M OVER PORTIONS OF
THE PACIFIC NORTHWEST. THIS PATTERN FAVORS ANOMALOUS WARM TEMPERATURES ACROSS
THE WEST, WITH THE GEFS AND ECMWF REFORECAST TOOLS SHOWING THE HIGHEST
PROBABILITIES (>60% CHANCE) OF MAXIMUM TEMPERATURES EXCEEDING THE 85TH
CLIMATOLOGICAL PERCENTILE ACROSS MUCH OF THE NORTHWEST AT THE BEGINNING OF THE
PERIOD, AND SLIGHTLY WEAKER CHANCES EXTENDING SOUTH INTO THE CENTRAL VALLEY OF
CALIFORNIA. THESE TOOLS, AS WELL AS UNCALIBRATED GUIDANCE ALSO SHOW CHANCES FOR
TEMPERATURES TO REACH 90 DEG F IN PARTS OF EASTERN WASHINGTON AND 95 DEG F IN
PARTS OF THE CENTRAL VALLEY EARLY IN THE PERIOD. UNLIKE THE CHANCES FOR
HAZARDOUS HEAT DURING WEEK-1, STRONG EASTERLY WINDS APPEAR TO BE LESS LIKELY,
REDUCING CHANCES FOR HAZARDOUS HEAT ALONG THE IMMEDIATE PACIFIC COAST.
THEREFORE, A SLIGHT RISK OF EXCESSIVE HEAT IS POSTED FOR PARTS OF THE
WILLAMETTE VALLEY, EASTERN WASHINGTON, AND THE SNAKE RIVER VALLEY FOR SAT -MON,
MAY 20-22. RELATIVE TO YESTERDAY, THE EXCESSIVE HEAT HAZARD IS EXPANDED
SOUTHWARD INTO THE CALIFORNIA VALLEY WHERE THERE IS INCREASED SUPPORT FOR
TEMPERATURES REACHING HAZARDS CRITERIA.
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
SURFACE HIGH PRESSURE FORMING OVER THE SOUTH-CENTRAL CONUS WHILE A SURFACE LOW
FORMS 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, AND A HALF AN INCH OVER
THE SOUTHWESTERN CONUS, PRIMARILY DURING DAYS 8 TO 10 (MAY 20-22). THESE TOOLS
SHOW THE HIGHEST CHANCES (>40%) OF EXCEEDING THESE THRESHOLDS ACROSS ARIZONA
AND SOUTHERN UTAH. 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,
PRECIPITATION TOTALS OVER THE LAST 14, 30, AND 60 DAYS HAVE BEEN BELOW HALF OF
NORMAL FOR THOSE PERIODS. SOIL MOISTURE IN THESE REGIONS IS ALSO WELL
BELOW-NORMAL WITH NASA SPORT SOIL MOISTURE ANALYSIS SHOWING MUCH OF THE AREA
BELOW THE 20TH PERCENTILE. FORECASTS FROM THE WEATHER PREDICTION CENTER (WPC)
SHOW LITTLE PRECIPITATION IN THESE REGIONS DURING THE WEEK-1 PERIOD, AND THE
CPC WEEK-2 FORECAST FAVORS BELOW-NORMAL PRECIPITATION IN THESE REGIONS. AS WE
MOVE INTO THE SUMMER SEASON, THE RAPID ONSET DROUGHT RISK IS EXPECTED TO
INCREASE IN THESE AREAS AND SUBSEQUENT HAZARD IS POSTED FOR THE WEEK-2 PERIOD.
IN INTERIOR ALASKA, WARMER TEMPERATURES DURING THE PAST WEEK HAVE LED TO RISES
IN MANY OF THE RIVERS IN THIS REGION. MUCH OF THE TANANA RIVER NOW HAS OPEN
WATER AS RIVER ICE CONTINUES TO MELT. MEANWHILE, THE YUKON RIVER NEAR THE
CANADIAN BORDER WATER LEVELS HAVE RISEN 7 FEET WITH WATER LEVELS CONTINUING TO
RISE AND ICE JAMS OCCURRING. RIVER ICE IS EXPECTED TO CONTINUE BREAKING UP
ALONG THE YUKON RIVER OVER THE NEXT SEVERAL WEEKS. WITH WARMER TEMPERATURES
DURING THE WEEK-1 PERIOD SIGNIFICANT RIVER RISES DUE TO SNOW AND ICE MELT MAY
CONTINUE INTO WEEK-2. FURTHERMORE, RIVER ICE BREAKUP COULD LEAD TO ICE-JAMS ON
THE MAJOR RIVERS, INCLUDING THE KUSKOKWIM RIVER LEADING TO INCREASED CHANCES
FOR POSSIBLE FLOODING.
FORECASTER: RYAN BOLT
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page