567
FXUS21 KWNC 241907
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT MAY 24 2023
SYNOPSIS: THE SYNOPTIC PATTERN DURING THE WEEK-2 PERIOD IS CHARACTERIZED BY
WIDESPREAD MID-LEVEL HIGH PRESSURE OVER CANADA AND WEAK LOW PRESSURE ALONG BOTH
COASTS OF NORTH AMERICA. THIS RESULTS IN MOSTLY WARMER, QUIETER WEATHER FOR
MOST OF THE CONTIGUOUS U.S. (CONUS). A FAVORABLE ENVIRONMENT FOR THUNDERSTORMS
TYPICAL FOR THIS TIME OF YEAR OVER THE CENTRAL AND SOUTHERN PLAINS MAY RESULT
IN POTENTIALLY IMPACTFUL PRECIPITATION. THE POTENTIAL FOR RIVER FLOODING
RELATED TO THE SPRING THAW CONTINUES FOR PORTIONS OF THE WEST AND ALASKA, AS
WELL AS ALONG THE JAMES RIVER IN SOUTH DAKOTA.
HAZARDS
MODERATE RISK FOR HEAVY PRECIPITATION FOR PORTIONS OF THE SOUTHERN PLAINS,
THU-FRI, JUN 1-2.
SLIGHT RISK FOR HEAVY PRECIPITATION FOR PORTIONS OF THE SOUTHERN AND CENTRAL
PLAINS, THU-MON, JUN 1-5.
SLIGHT RISK FOR EXCESSIVE HEAT FOR PORTIONS OF THE GREAT LAKES, AND THE OHIO,
MIDDLE AND UPPER MISSISSIPPI VALLEYS, WED-FRI, JUN 1-2.
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 IN PARTS OF WESTERN MAINLAND ALASKA, ALONG THE YUKON,
KUSKOKWIM, KOYUKUK, AND KOBUK RIVERS.
RAPID ONSET DROUGHT RISK ACROSS PORTIONS OF THE MIDDLE MISSISSIPPI AND OHIO
VALLEYS.
DETAILED SUMMARY
FOR SATURDAY MAY 27 - WEDNESDAY MAY 31:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR THURSDAY JUNE 01 - WEDNESDAY JUNE 07: THE WEEK-2 SYNOPTIC PICTURE AS
DEPICTED BY ENSEMBLE MODEL SOLUTIONS FOR 500-HPA HEIGHT ANOMALIES RESEMBLES AN
OMEGA BLOCK WITH WEAK TROUGHING ALONG BOTH COASTS OF NORTH AMERICA AND
EXPANSIVE RIDGING OVER MUCH OF CANADA. THIS FEATURE ENDURES THROUGHOUT THE
FORECAST PERIOD AND RESULTS IN WARMER BUT RELATIVELY QUIET WEATHER FOR MUCH OF
THE CONUS. ONE EXCEPTION TO THIS IS OVER THE GREAT PLAINS, WHERE INCREASED
LOW-LEVEL JET (LLJ) ACTIVITY FAVORS INCREASED PROBABILITIES OF HEAVY
PRECIPITATION WITH PERIODIC THUNDERSTORMS FOR THE REGION. REFORECAST TOOLS FROM
THE GEFS, ECMWF, AND CMCE ALL INDICATE AT LEAST A 20% PROBABILITY OF EXCEEDING
THE 85TH CLIMATOLOGICAL PERCENTILE AND 1 INCH FOR 3-DAY PRECIPITATION OVER
PORTIONS OF THE GREAT PLAINS, THEREFORE A SLIGHT RISK FOR HEAVY PRECIPITATION
IS POSTED FOR THE REGION FOR JUN 1-5. ADDITIONALLY, THE ECMWF INDICATES A 40%
PROBABILITY OF EXCEEDING THE 85TH PERCENTILE FOR PORTIONS OF THE SOUTHERN
PLAINS. THE GEFS REFORECAST IS NOT QUITE AS BULLISH BUT DOES HAVE PROBABILITIES
OVER 30% FOR THE FIRST 3-DAY PERIOD OF WEEK-2. GIVEN THIS, THE CONSISTENCY OF
THE SIGNAL FOR SEVERAL DAYS, AND GOOD INDICATIONS FROM MULTIPLE MODELS OF AN
ENHANCED LLJ EARLY IN WEEK-2, A MODERATE RISK FOR HEAVY PRECIPITATION IS POSTED
FOR THE TEXAS PANHANDLE AND ADJACENT AREAS FOR JUN 1-2.
EXPANSIVE RIDGING OVER MUCH OF CENTRAL NORTH AMERICA IS LIKELY TO RESULT IN
WARMER TEMPERATURES, PARTICULARLY FOR THE NORTH-CENTRAL CONUS. THE REFORECAST
TOOLS ALL INDICATE A 20% CHANCE OF EXCEEDING THE 85TH PERCENTILE FOR MAXIMUM
TEMPERATURES FOR THIS REGION FOR JUN 1-2, WITH THE SIGNAL DROPPING OFF
SOMEWHAT AFTER THIS DATE. THE ECMWF AND CMCE IN PARTICULAR FAVOR A WARMER
SOLUTION WITH AT LEAST 40% PROBABILITIES OF EXCEEDING THE 85TH PERCENTILE. DEW
POINTS AND THEREFORE HEAT INDICES ARE NOT EXPECTED TO BE TOO ELEVATED, BUT
NONETHELESS THERE IS THE POTENTIAL TO EXCEED THE 90F THRESHOLD FOR PORTIONS OF
THE UPPER MIDWEST FOR THE FIRST TIME THIS SEASON. GIVEN THIS A SLIGHT RISK FOR
EXCESSIVE HEAT IS POSTED FOR MOST OF ILLINOIS AND WESTERN INDIANA, AND
EXTENDING NORTHWESTWARD TO INCLUDE PORTIONS OF IOWA, WISCONSIN, AND MINNESOTA
FOR JUN 1-2. LATE IN THE FORECAST PERIOD MODEL ENSEMBLES DEPICT A RETROGRESSION
OF THE EXPANSIVE RIDGE OVER CANADA, WHICH COULD BRING MUCH ABOVE-NORMAL
TEMPERATURES TO THE NORTHWESTERN CONUS TOWARDS THE END OF WEEK-2. THERE IS
STILL A LOT OF UNCERTAINTY WITH REGARD TO THIS POTENTIAL FOR HAZARDOUS HEAT SO
NO CORRESPONDING HAZARD IS POSTED AT THIS TIME.
DROUGHT CONCERNS ARE FORECAST TO INCREASE ACROSS PARTS OF THE EASTERN CORN BELT
DURING THE WEEK-2 PERIOD DUE TO THE AFOREMENTIONED WARMTH. SOIL MOISTURE IS
BELOW THE 30TH CLIMATOLOGICAL PERCENTILE OVER SOME AREAS, AND 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.
SNOWMELT SEASON 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 MANY 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.
WEAK MID-LEVEL FLOW ACROSS ALASKA FAVORS ONLY A SLIGHT TILT TOWARD ABOVE AND
BELOW NORMAL TEMPERATURE PROBABILITIES ACROSS PARTS OF NORTHERN AND SOUTHERN
ALASKA RESPECTIVELY. HOWEVER, REGARDLESS OF TEMPERATURES, 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 THROUGHOUT THE ALASKAN INTERIOR. THERE ARE
CURRENTLY SEVERAL FLOOD WATCHES AND ADVISORIES POSTED THROUGHOUT INTERIOR AND
WESTERN ALASKA. 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: DANNY BARANDIARAN
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