381
FXUS21 KWNC 301857
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT MAY 30 2023
SYNOPSIS: THE SYNOPTIC PATTERN DURING THE WEEK-2 PERIOD IS CHARACTERIZED BY
WIDESPREAD MID-LEVEL HIGH PRESSURE OVER CANADA AND THE WESTERN CONTIGUOUS
UNITED STATES (CONUS) AND WEAK MID-LEVEL LOW PRESSURE OVER THE EASTERN CONUS.
THIS RESULTS IN WARMER AND RELATIVELY QUIET WEATHER FOR MOST OF THE CONUS. WITH
AN ANOMALOUS MID-LEVEL RIDGE OVER THE NORTHWEST CONUS, THERE WILL BE INCREASED
CHANCES FOR A PERIOD OF EXCESSIVE HEAT EARLY IN WEEK-2 FOR THE REGION. A
FAVORABLE ENVIRONMENT FOR THUNDERSTORMS AND HEAVY RAINFALL IN THE SOUTHERN
PLAINS AND LOWER MISSISSIPPI VALLEY REMAINS POSSIBLE THROUGH THE MIDDLE OF
WEEK-2 WITH MOIST LOW-LEVEL INFLOW. IN THE RIO GRANDE VALLEY, HEAT AND HUMIDITY
IS ANTICIPATED TO BUILD BY THE END OF THE PERIOD ENHANCING CHANCES FOR
EXCESSIVE HEAT. THE POTENTIAL FOR A RECURVING CYCLONE IN THE PACIFIC INCREASES
THE LIKELIHOOD FOR HIGH WINDS TO SOUTHWEST ALASKA AND THE ALEUTIAN ISLANDS. THE
POTENTIAL FOR RIVER FLOODING MOSTLY RELATED TO THE SPRING THAW CONTINUES FOR
PORTIONS OF THE WEST CONUS, ALASKA, AND ALONG PORTIONS OF THE JAMES RIVER IN
SOUTH DAKOTA AND SOURIS RIVER IN NORTH DAKOTA.
HAZARDS
SLIGHT RISK FOR HEAVY PRECIPITATION FOR PORTIONS OF THE SOUTHERN PLAINS AND
SOUTHEAST, WED-SAT, JUN 7-10.
SLIGHT RISK FOR EXCESSIVE HEAT FOR PARTS OF THE NORTHWEST, WED-FRI, JUN 7-9.
SLIGHT RISK FOR HIGH WINDS FOR PARTS OF SOUTHWEST ALASKA AND ALEUTIAN ISLANDS,
WED-FRI, JUN 7-9.
POSSIBLE FLOODING FOR PORTIONS OF CALIFORNIA, NEVADA, UTAH, WYOMING,
SOUTHWESTERN MONTANA, AND IDAHO.
POSSIBLE FLOODING ALONG PORTIONS OF THE JAMES RIVER IN SOUTH DAKOTA.
POSSIBLE FLOODING ALONG PORTIONS OF THE SOURIS RIVER IN NORTH DAKOTA.
POSSIBLE FLOODING IN PARTS OF WESTERN MAINLAND ALASKA AND ALONG THE YUKON,
KUSKOKWIM, KOYUKUK, AND KOBUK RIVERS.
RAPID ONSET DROUGHT RISK ACROSS PORTIONS OF THE UPPER MIDWEST, AND THE MIDDLE
MISSISSIPPI AND OHIO VALLEYS.
DETAILED SUMMARY
FOR FRIDAY JUNE 02 - TUESDAY JUNE 06:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR WEDNESDAY JUNE 07 - TUESDAY JUNE 13: THE WEEK-2 MID-LEVEL, 500-HPA, HEIGHT
PATTERN LOOKS RELATIVELY STAGNANT WITH AN AREA OF NEGATIVE 500-HPA HEIGHT
ANOMALIES ACROSS THE EASTERN CONUS AND POSITIVE 500-HPA HEIGHT ANOMALIES ACROSS
MUCH OF WESTERN NORTH AMERICA. MEANWHILE, AN AREA OF MID-LEVEL TOUGHING IS
FORECAST ACROSS THE ALEUTIAN ISLANDS. THIS PATTERN SUPPORTS LARGELY QUIET
WEATHER ACROSS MUCH OF THE CONUS DURING WEEK-2.
WITH PERSISTENT RIDGING PREDICTED OVER THE NORTHWEST, THE GEFS, ECMWF, AND
CANADIAN REFORECAST TOOLS ARE INDICATING INCREASED CHANCES FOR TEMPERATURES TO
EXCEED THE 85TH CLIMATOLOGICAL PERCENTILE DURING THE FIRST HALF OF THE PERIOD.
THE ECMWF REFORECAST INDICATES THE HIGHEST PROBABILITIES WITH AT LEAST A 60%
CHANCE OF EXCEEDING THIS THRESHOLD ACROSS MUCH OF THE REGION. STRONGER CHANCES
FOR TEMPERATURES TO EXCEED THE 85TH PERCENTILE HAVE ALSO DEVELOPED WEST OF THE
CASCADES. REFORECAST TOOLS AND UNCALIBRATED ENSEMBLES INDICATE CHANCES FOR
TEMPERATURES TO REACH THE LOW 90’S DEG F EAST OF THE CASCADES AND NEAR 90 TO
THE WEST. THEREFORE, A SLIGHT RISK OF EXCESSIVE HEAT IS POSTED FOR JUN 7-9. BY
THE MIDDLE OF THE PERIOD, PROBABILITIES FOR EXCEEDING THE 85TH PERCENTILE ARE
REDUCED RELATIVE TO THE FIRST THREE DAYS OF WEEK-2 AND SO THE LENGTH OF THE
HAZARD IS ONLY FOR THE FIRST THREE DAYS OF THE PERIOD.
IN THE SECOND HALF OF THE WEEK, REFORECAST TOOLS AND RAW DYNAMICAL TOOLS SHOW
INCREASED CHANCES FOR EXCESSIVE HEAT IN THE RIO GRANDE VALLEY AS MID-LEVEL
HEIGHTS INCREASE SLIGHTLY. MODEL GUIDANCE SUGGESTS HEAT INDEX VALUES
APPROACHING 105 DEGF IN THIS REGION. THESE ARE LIKELY TO BE THE HOTTEST
TEMPERATURES SO FAR THIS SEASON. THE STRONGEST HEAT SIGNAL IS EMERGING IN THE
GEFS REFORECAST AND CALIBRATED TOOLS WITH GOOD RUN TO RUN CONSISTENCY AND WITH
SOME SUPPORT FROM THE ECMWF AND CANADIAN TOOLS. HOWEVER, THERE ARE CONCERNS
THAT COLDER TEMPERATURES EARLIER IN THE PERIOD MAY LINGER IN THE AREA. DUE TO
SIGNIFICANT UNCERTAINTY NO ADDITIONAL RELATED HEAT HAZARD IS DESIGNATED.
LOW-LEVEL RETURN FLOW OFF THE GULF OF MEXICO IS PREDICTED TO INCREASE CHANCES
FOR HEAVY PRECIPITATION ACROSS PARTS OF THE SOUTHERN PLAINS AND LOWER
MISSISSIPPI VALLEY. REFORECAST TOOLS SUGGEST AT LEAST A 20% CHANCE OF THREE DAY
PRECIPITATION TOTALS TO EXCEED THE 85TH CLIMATOLOGICAL PERCENTILE AND 1 INCH OF
PRECIPITATION IN THESE AREAS. FURTHERMORE, SOME PARTS OF THE SOUTHERN PLAINS
HAVE SEEN OVER 200% OF NORMAL PRECIPITATION IN THE PAST 30 DAYS, MUCH OF THAT
COMING FROM THE LAST WEEK. HOWEVER, RAW ENSEMBLE TOOLS HAVE LIMITED SUPPORT FOR
HEAVY RAIN, REDUCING CONFIDENCE IN THE CHANCES FOR HEAVY PRECIPITATION TO PARTS
OF THESE REGIONS. DESPITE THIS UNCERTAINTY, A SLIGHT RISK OF HEAVY
PRECIPITATION IS POSTED FOR JUN 7-10 DUE TO STRONG AGREEMENT AMONG THE
REFORECAST TOOLS.
IN THE MIDWEST THE EUROPEAN AND CANADIAN REFORECAST TOOLS HAVE A FAIRLY STRONG
SIGNAL OF TEMPERATURES EXCEEDING THE 85TH CLIMATOLOGICAL PERCENTILE AND 90 DEG
F. HOWEVER, THERE IS LESS SUPPORT FOR TEMPERATURES REACHING 95 DEG F. THIS HEAT
EVENT WOULD LIKELY BE DRIVEN BY ABSOLUTE TEMPERATURES RATHER THAN BEING
MOISTURE DRIVEN, THUS REACHING HAZARDOUS THRESHOLDS WOULD BE LESS LIKELY.
FURTHERMORE, THE GEFS IS MUCH COOLER ACROSS THE REGION DURING THE PERIOD,
FURTHER REDUCING SUPPORT FOR A POTENTIAL EXCESSIVE HEAT HAZARD. THEREFORE, NO
CORRESPONDING HAZARD IS POSTED TODAY.
DROUGHT CONCERNS ARE FORECAST TO CONTINUE ACROSS PARTS OF THE CENTRAL AND
EASTERN CORN BELT AND ADJACENT AREAS DURING WEEK-2 DUE TO THE EXPECTATION OF
NEAR-NORMAL PRECIPITATION, AND PRECIPITATION TOTALS TWO TO FOUR INCHES BELOW
NORMAL FOR THE PAST 30 TO 60 DAYS. SOIL MOISTURE IS CURRENTLY BELOW THE 30TH
CLIMATOLOGICAL PERCENTILE OVER MANY OF THESE AREAS. DUE TO THESE FACTORS, A
RAPID ONSET DROUGHT RISK IS HIGHLIGHTED ACROSS PARTS OF THE CENTRAL AND EASTERN
CORN BELT, SPECIFICALLY IN MUCH OF SOUTHERN IOWA, NORTHERN MISSOURI, CENTRAL
ILLINOIS AND INDIANA, AND SOUTHERN OHIO.
SNOWMELT CONTINUES ACROSS THE WESTERN CONUS AFTER ACCUMULATING A VERY LARGE AND
IN SOME CASES RECORD-BREAKING SNOWPACK, INDUCING RIVER FLOODING ESPECIALLY
ACROSS HIGHER ELEVATIONS FOR SOME AREAS IN THE WEST, WHERE A FEW SITES STILL
REPORT OVER 40 INCHES OF SNOW WATER CONTENT. AS SNOWMELT CONTINUES IN PARTS OF
THE SIERRA NEVADA, GREAT BASIN, AND NORTHERN ROCKIES, FLOODING MAY CONTINUE TO
OCCUR ALONG SOME RIVERS AND IN AREAS ADJACENT TO THE HIGHER ELEVATIONS.
FLOODING IS ALSO EXPECTED TO CONTINUE ALONG THE JAMES RIVER IN SOUTH DAKOTA AS
RIVER LEVELS HAVE BEEN VERY SLOW TO RECEDE DUE TO SATURATED GROUND CONDITIONS
AND RELATIVELY FLAT TOPOGRAPHY. A SIMILAR SITUATION HAS DEVELOPED ALONG THE
SOURIS RIVER IN NORTH DAKOTA, WHICH SHOULD CAUSE ONGOING MINOR TO MODERATE
FLOODING TO CONTINUE INTO WEEK-2.
SOUTHERLY MID-LEVEL FLOW ACROSS ALASKA FAVORS ABOVE NORMAL TEMPERATURES ACROSS
PARTS OF NORTHERN AND CENTRAL ALASKA DURING THE WEEK-2 PERIOD. RIVERS ARE
EXPECTED TO CONTINUE TO RISE ACROSS WESTERN MAINLAND ALASKA DUE TO ICE JAMS,
WHILE INCREASING SNOWMELT ACROSS EASTERN ALASKA IS ANTICIPATED TO CONTINUE THE
POTENTIAL FOR RIVER FLOODING THROUGH A LARGE PART OF THE ALASKAN INTERIOR.
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.
ANOTHER FACTOR WHICH COULD IMPACT PARTS OF ALASKA IS THE EVOLUTION OF TYPHOON
MAWAR, CURRENTLY NORTHEAST OF THE PHILIPPINES IN THE PACIFIC OCEAN WITH WINDS
NEAR 85 MPH. THE TYPHOON IS BEGINNING TO RECURVE, TURNING TO THE NORTHEAST JUST
EAST OF TAIWAN. AFTER TURNING, THE STORM IS ANTICIPATED TO BECOME EXTRATROPICAL
WHILE CONTINUING NORTHEASTWARD, BUT STILL REMAIN A POTENT STORM SYSTEM. TOOLS
ARE IN BETTER AGREEMENT, BRINGING THE REMNANTS OF MAWAR CLOSE TO ALASKA DURING
WEEK-2, WHICH COULD IMPACT THE ALEUTIANS AND SOUTHWEST ALASKA WITH HIGH WINDS.
WHILE REFORECAST TOOLS HAVE LIMITED SUPPORT, RAW ENSEMBLES ARE IN BETTER
AGREEMENT FOR A STRONG SUMMER LOW-PRESSURE SYSTEM TO IMPACT THIS PART OF THE
STATE. THEREFORE, A SLIGHT RISK OF HIGH WINDS IS FORECAST FOR THE ALEUTIAN
ISLANDS AND SOUTHWEST ALASKA FOR JUNE 7-9.
FORECASTER: RYAN BOLT
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