370
FXUS21 KWNC 311939
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT MAY 31 2023
SYNOPSIS: THE SYNOPTIC PATTERN DURING THE WEEK-2 PERIOD IS CHARACTERIZED BY
MID-LEVEL HIGH PRESSURE OVER CENTRAL AND WESTERN CANADA AND THE NORTHWESTERN
CONTIGUOUS UNITED STATES (CONUS) THAT GRADUALLY WEAKENS, WITH WEAK MID-LEVEL
LOW PRESSURE ACROSS MUCH OF THE REST OF THE CONUS. THIS PATTERN FAVORS
RELATIVELY QUIET WEATHER FOR MOST OF THE CONUS. WITH AN ANOMALOUS MID-LEVEL
RIDGE OVER THE NORTHWEST CONUS AT THE BEGINNING OF WEEK-2, THERE WILL BE
INCREASED CHANCES FOR A PERIOD OF EXCESSIVE HEAT ACROSS THE REGION. A
FAVORABLE ENVIRONMENT FOR THUNDERSTORMS AND HEAVY RAINFALL ACROSS PORTIONS OF
THE SOUTH-CENTRAL AND SOUTHEASTERN CONUS REMAINS POSSIBLE DURING 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 ENHANCED
HEAT INDEX VALUES. 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.
HAZARDS
SLIGHT RISK FOR EXCESSIVE HEAT FOR PARTS OF THE NORTHWEST, THU-FRI, JUN 8-9.
SLIGHT RISK FOR HEAVY PRECIPITATION FOR PORTIONS OF THE SOUTHERN PLAINS, LOWER
MISSISSIPPI AND TENNESSEE VALLEYS, AND SOUTHEAST, SAT-MON, JUN 10-12.
SLIGHT RISK FOR HIGH WINDS FOR PARTS OF SOUTHWEST ALASKA AND ALEUTIAN ISLANDS,
THU-FRI, JUN 8-9.
POSSIBLE FLOODING FOR PORTIONS OF CALIFORNIA, NEVADA, UTAH, WYOMING,
SOUTHWESTERN MONTANA, AND IDAHO.
POSSIBLE FLOODING ALONG PORTIONS OF THE JAMES RIVER IN SOUTH DAKOTA.
RAPID ONSET DROUGHT RISK ACROSS PORTIONS OF THE UPPER MIDWEST, AND THE MIDDLE
MISSISSIPPI AND OHIO VALLEYS.
DETAILED SUMMARY
FOR SATURDAY JUNE 03 - WEDNESDAY JUNE 07:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR THURSDAY JUNE 08 - WEDNESDAY JUNE 14: THE WEEK-2 MID-LEVEL, 500-HPA HEIGHT
PATTERN CONTINUES TO LOOK RELATIVELY PERSISTENT WITH AN AREA OF NEGATIVE
500-HPA HEIGHT ANOMALIES ACROSS THE EASTERN AND SOUTHERN CONUS AND POSITIVE
500-HPA HEIGHT ANOMALIES UPSTREAM ACROSS THE NORTHWEST. MEANWHILE, AN AREA OF
MID-LEVEL TOUGHING IS FORECAST ACROSS THE ALEUTIAN ISLANDS. THIS PATTERN
SUPPORTS RELATIVELY QUIET WEATHER ACROSS MUCH OF THE CONUS DURING WEEK-2.
COMPARED TO YESTERDAY, TODAY'S ECMWF ENSEMBLE MEAN 500-HPA POSITIVE HEIGHT
DEPARTURES ARE SLIGHTLY WEAKER, WHEREAS THE GEFS FAVORS A STRONGER MEAN
SOLUTION. BOTH MODEL ENSEMBLE MEANS GENERALLY INDICATE WEAKER ANOMALOUS
TROUGHING ACROSS THE EAST, WITH THE GEFS NOW INDICATING A CUTOFF LOW ALONG THE
COAST OF CALIFORNIA EARLY IN WEEK-2.
WITH AMPLIFIED MID-LEVEL RIDGING PREDICTED OVER THE NORTHWEST FROM THE END OF
WEEK-1 INTO THE BEGINNING OF THE PERIOD, THE GEFS, ECMWF, AND CANADIAN
REFORECAST TOOLS ARE IN GOOD AGREEMENT INDICATING INCREASED CHANCES FOR
TEMPERATURES TO EXCEED THE 85TH CLIMATOLOGICAL PERCENTILE EARLY IN WEEK-2. THE
REFORECAST TOOLS SHOW THE GREATEST POTENTIAL ON DAY 8, WITH AT LEAST A 40%
CHANCE OF TEMPERATURES EXCEEDING THESE THRESHOLDS ACROSS MUCH OF THE
HIGHLIGHTED RISK AREA. EVEN THOUGH THERE IS RELATIVELY HIGH PROBABILITIES FOR
THIS HEAT POTENTIAL, TEMPERATURES ARE ANTICIPATED TO REMAIN IN THE LOW 90S DEG
F AND NOT BE VERY EXTREME, THUS ONLY A SLIGHT RISK IS DESIGNATED FOR JUNE 8 TO
9. THE RISK AREA IS LIMITED TO EAST OF THE CASCADES, AS TODAY'S GUIDANCE FAVORS
TEMPERATURES REMAINING BELOW 90 DEG F FURTHER WEST. TEMPERATURES ARE
ANTICIPATED TO MODERATE THEREAFTER AS THE RIDGE WEAKENS AND SHIFTS WESTWARD BY
THE MIDDLE OF WEEK-2.
REFORECAST AND RAW DYNAMICAL TOOLS CONTINUE TO SHOW INCREASED CHANCES FOR
EXCESSIVE HEAT IN THE RIO GRANDE VALLEY AS MID-LEVEL HEIGHTS INCREASE SLIGHTLY
OVER THE SOUTH-CENTRAL CONUS BY THE MIDDLE OF WEEK-2. CALIBRATED HEAT TOOLS
SUGGEST HEAT INDEX VALUES POSSIBLY APPROACHING 105 DEG F IN THIS REGION, WHICH
ARE LIKELY TO BE THE HOTTEST TEMPERATURES SO FAR THIS SEASON. THE CALIBRATED
GEFS HEAT INDEX TOOL CONTINUES TO HAVE THE STRONGEST HEAT SIGNAL, ALTHOUGH THE
CALIBRATED WEEK-2 HEAT TOOL SHOWS A SLIGHTLY WEAKER SIGNAL COMPARED TO
YESTERDAY. THE GEFS AND CANADIAN REFORECAST TOOLS HAVE A GREATER HEAT SIGNAL
COMPARED TO THE ECMWF COUNTERPART. HOWEVER, DUE TO CONTINUING CONCERNS THAT
COLDER TEMPERATURES EARLIER IN THE PERIOD MAY LINGER IN THE AREA, NO ADDITIONAL
RELATED HEAT HAZARD IS DESIGNATED.
IN THE MIDWEST, THE ECMWF AND CANADIAN REFORECAST TOOLS INDICATE AT LEAST A 40%
CHANCE OF TEMPERATURES EXCEEDING THE 85TH CLIMATOLOGICAL PERCENTILE AND 90 DEG
F. HOWEVER, DUE TO THESE TOOLS NOT SHOWING ENHANCED RISK OF REACHING 95 DEG F
AND THE LACK OF SUPPORT FROM THE GEFS, A CORRESPONDING HEAT HAZARD IS NOT
POSTED. THIS HEAT EVENT WOULD LIKELY BE DRIVEN BY ABSOLUTE TEMPERATURES RATHER
THAN BEING MOISTURE DRIVEN, THUS REACHING HAZARDOUS THRESHOLDS WOULD BE LESS
LIKELY.
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.
LOW-LEVEL RETURN FLOW OFF THE GULF OF MEXICO IS PREDICTED TO INCREASE CHANCES
FOR HEAVY PRECIPITATION ACROSS PARTS OF THE SOUTH-CENTRAL AND SOUTHEASTERN
CONUS DURING THE MIDDLE OF WEEK-2. THE SLIGHT RISK OF HEAVY PRECIPITATION HAS
BEEN EXTENDED EASTWARD COMPARED TO YESTERDAY BASED ON GOOD AGREEMENT AMONG THE
UNCALIBRATED GEFS AND ECMWF REFORECAST TOOLS. PORTIONS OF THE SOUTHERN PLAINS,
LOWER MISSISSIPPI AND TENNESSEE VALLEYS, AND SOUTHEAST ARE HIGHLIGHTED WITH A
SLIGHT RISK OF HEAVY PRECIPITATION, JUNE 10-12, WHERE THE GEFS AND ECMWF
REFORECAST TOOLS INDICATE AT LEAST A 20% CHANCE OF 3-DAY ACCUMULATED RAINFALL
TOTALS EXCEEDING THE 85TH CLIMATOLOGICAL PERCENTILE AND 1 INCH. FURTHERMORE,
SOME PARTS OF THE SOUTHERN PLAINS HAVE SEEN OVER 200% OF NORMAL PRECIPITATION
IN THE PAST 30 DAYS, MUCH OF THAT COMING FROM LAST WEEK. ATMOSPHERIC CONDITIONS
MAY ALSO BE SUPPORTIVE OF LOCALIZED THUNDERSTORMS.
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. WITH
INCREASED CHANCES FOR ABOVE NORMAL PRECIPITATION PREDICTED FOR MUCH OF THE
WESTERN CONUS DURING WEEK-2, POSSIBLE FLOODING CONTINUES TO BE HIGHLIGHTED.
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. THE POSSIBLE FLOOD AREA FOR THE SOURIS RIVER IN
NORTH DAKOTA IS REMOVED IN TODAY'S OUTLOOK DUE TO GAUGES INDICATING FLOOD
IMPROVEMENT, NEAR TO BELOW NORMAL PRECIPITATION FAVORED FOR WEEK-2, AND LITTLE
PRECIPITATION PREDICTED FOR WEEK-1.
THE POSSIBLE FLOOD RISK ACROSS ALASKA HAS BEEN REMOVED DUE TO THE ANTICIPATION
OF SNOWMELT IMPACTS SIGNIFICANTLY DECREASING BY WEEK-2. AS OF 12Z TODAY,
TYPHOON MAWAR IS LOCATED EAST OF TAIWAN WITH WINDS NEAR 75 MPH TRACKING
NORTHEASTWARD. THIS STORM MAY REMAIN A POTENT STORM SYSTEM, WITH RECENT
DETERMINISTIC GFS SOLUTIONS INDICATING ITS REMNANT CIRCULATION WILL BECOME
ABSORBED IN THE WESTERLIES, AND LEAD TO AN AMPLIFICATION OF THE PATTERN
DOWNSTREAM OVER SOUTHWESTERN ALASKA BY WEEK-1, POTENTIALLY LINGERING INTO THE
BEGINNING OF WEEK-2. GIVEN THE AMPLIFIED TROUGHING ALOFT, AND DEEPENING LOW
SURFACE PRESSURE FAVORED, THE GREATEST HAZARD POTENTIAL IS FOR HIGH WINDS.
WHILE REFORECAST TOOLS HAVE LIMITED SUPPORT, THE PREDICTED SYNOPTIC PATTERN
SUPPORTS, A SLIGHT RISK OF HIGH WINDS FOR THE ALEUTIAN ISLANDS AND SOUTHWEST
ALASKA FOR JUNE 8-9.
FORECASTER: MELISSA OU
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