892
FXUS21 KWNC 261801
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT MAY 26 2023
SYNOPSIS: THE SYNOPTIC PATTERN DURING THE WEEK-2 PERIOD IS CHARACTERIZED BY
WIDESPREAD MID-LEVEL HIGH PRESSURE OVER CANADA AND WEAK MID-LEVEL LOW PRESSURE
ALONG BOTH COASTS OF NORTH AMERICA. THIS RESULTS IN WARMER AND RELATIVELY QUIET
WEATHER FOR MOST OF THE CONTIGUOUS U.S. (CONUS). ENHANCED CHANCES FOR EXCESSIVE
HEAT IN PARTS OF THE MIDWEST ARE ANTICIPATED TO WANE EARLY WEEK-2, BUT AS THE
ANOMALOUS MID-LEVEL RIDGE IN CANADA DRIFTS WEST, THERE WILL BE SLIGHTLY
ENHANCED CHANCES FOR A PERIOD OF NOMINALLY-EXCESSIVE HEAT IN THE NORTHWEST
CONUS. A FAVORABLE ENVIRONMENT FOR THUNDERSTORMS WITH HEAVY RAINFALL IN THE
PLAINS AND SOME ADJACENT PORTIONS OF THE LOWER MISSISSIPPI VALLEY AND ROCKIES
SHOULD SLOWLY RELENT BY THE MIDDLE OF WEEK-2, WHEN MOIST LOW-LEVEL INFLOW
EASES. 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 PLAINS AND ADJACENT
ROCKIES, SAT-TUE, JUN 3-6.
SLIGHT RISK FOR EXCESSIVE HEAT FOR PORTIONS OF THE UPPER MIDWEST, AND THE OHIO,
MIDDLE AND UPPER MISSISSIPPI VALLEYS, SAT, JUN 3.
SLIGHT RISK FOR EXCESSIVE HEAT FOR PARTS OF THE NORTHWEST SAT-FRI, JUN 3-9.
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 MONDAY MAY 29 - FRIDAY JUNE 02:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR SATURDAY JUNE 03 - FRIDAY JUNE 09: 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, SLIGHTLY
BELOW-NORMAL MID-LEVEL 500-HPA HEIGHTS ALONG THE SOUTHERN TIER OF THE CONUS,
AND EXPANSIVE MID-LEVEL RIDGING OVER MUCH OF CANADA. THIS GENERAL CONFIGURATION
CONTINUES THROUGH THE PERIOD, ALTHOUGH THE ANOMALOUS MID-LEVEL RIDGE CENTERED
OVER CANADA IS EXPECTED TO SLOWLY RETROGRESS TOWARD WESTERN CANADA AND WEAKEN
SLIGHTLY AS THE PERIOD PROGRESSES. AS A RESULT, WARM AND GENERALLY QUIET
WEATHER IS PREDICTED TO PREVAIL ACROSS MOST OF THE CONUS. ONE EXCEPTION TO THIS
IS OVER PART OF THE PLAINS AND ADJACENT PORTIONS OF THE ROCKIES AND LOWER
MISSISSIPPI VALLEY, WHERE INCREASED LOW-LEVEL JET (LLJ) ACTIVITY CREATES
ENHANCED PROBABILITIES OF HEAVY PRECIPITATION WITH PERIODIC THUNDERSTORMS FOR
THE REGION UNTIL THE MIDDLE OF WEEK-2. RAINFALL WILL BE ENHANCED AT TIMES BY
UPSLOPING OROGRAPHIC WINDS NEAR THE MOUNTAINS. REFORECAST TOOLS FROM THE GEFS,
ECMWF, AND CMCE ALL INDICATE AT LEAST A 20% PROBABILITY OF EXCEEDING THE 85TH
CLIMATOLOGICAL PERCENTILE AND 0.75 TO OVER 1.0 INCH FOR 3-DAY ACCUMULATED
PRECIPITATION, SUPPORTING A SLIGHT RISK OF HEAVY PRECIPITATION ACROSS THE
REGION, JUN 3-6. THIS SLIGHT RISK AREA IS AGAIN EXTENDED FARTHER NORTH FOR THE
SECOND SUCCESSIVE DAY BASED ON RAW OUTPUT FROM THE CMCE, ECMWF, AND GEFS
ENSEMBLE MEANS.
EXPANSIVE MID-LEVEL RIDGING OVER MUCH OF CENTRAL NORTH AMERICA IS LIKELY TO
RESULT IN WARMER THAN NORMAL TEMPERATURES ACROSS THE CENTRAL AND NORTHERN
PORTIONS OF THE CONUS, CLOSEST TO THE MAXIMUM 500-HPA HEIGHT ANOMALIES
ASSOCIATED WITH THE BROAD MID-LEVEL RIDGE CENTERED IN CANADA. ALL REFORECAST
TOOLS INDICATE AT LEAST A 20% CHANCE OF MAXIMUM TEMPERATURE EXCEEDING THE 85TH
PERCENTILE DURING JUN 3 FROM THE NORTHWESTERN OHIO VALLEY THROUGH THE MIDDLE
AND UPPER MISSISSIPPI VALLEYS AND THE SOUTHWESTERN GREAT LAKES REGION. THE
ECMWF REFORECAST TOOL AND TO A LESSER EXTENT THE CMCE COUNTERPART FAVOR A
WARMER SOLUTION WITH 30% TO 50% PROBABILITIES OF EXCEEDING THE 85TH PERCENTILE,
BUT GEFS-BASED TOOLS ARE COOLER AND BRING IN SIGNIFICANT UNCERTAINTY,
PRECLUDING DESIGNATING ANY AREAS WITH A MODERATE RISK OF EXCESSIVE HEAT. DEW
POINTS AND ASSOCIATED HEAT INDICES ARE NOT EXPECTED TO BE EXTREMELY ELEVATED,
BUT NONETHELESS THERE IS THE POTENTIAL FOR TEMPERATURES TO EXCEED 90 DEG F FOR
PORTIONS OF THE UPPER MIDWEST FOR THE FIRST TIME THIS SEASON. THE PAST ONE TO
TWO MONTHS HAVE BEEN DRIER THAN NORMAL IN THIS REGION, WHICH INCREASES THE ODDS
FOR HIGHER TEMPERATURES BUT LIMITS THE POTENTIAL FOR UNUSUALLY HIGH DEW POINTS.
TAKING ALL OF THIS INTO CONSIDERATION, A SLIGHT RISK OF EXCESSIVE HEAT IS
POSTED FROM WESTERN INDIANA WESTWARD THROUGH NORTHERN MISSOURI AND NORTHWARD
ACROSS SOUTHERN MINNESOTA, INCLUDING PART OF THE CHICAGO METRO AREA, JUN 3.
ENSEMBLES OVERWHELMINGLY FAVOR A SLOW RETROGRESSION AND DE-AMPLIFICATION OF THE
EXPANSIVE RIDGE OVER CANADA, WHICH SHOULD BRING MUCH ABOVE-NORMAL TEMPERATURES
TO THE NORTHWESTERN CONUS THROUGHOUT THE PERIOD. THERE IS STILL A LOT OF
UNCERTAINTY REGARDING THE POTENTIAL FOR HAZARDOUS HEAT, BUT WITH POSITIVE
500-HPA HEIGHT ANOMALIES OVER AND NORTH OF THE REGION THROUGHOUT WEEK-2,
CHANCES ARE SUFFICIENTLY ELEVATED TO POST A SLIGHT RISK FOR EXCESSIVE HEAT OVER
THE NORTHWEST THROUGHOUT THE PERIOD (JUN 3-9), WITH THE BEST CHANCES NEAR THE
MIDDLE OF WEEK-2. PROBABILISTIC TOOLS SHOW LESSER CHANCES FOR IMPACTFUL HEAT TO
THE WEST OF THE CASCADES, AND THE LOWER-LEVEL WIND FLOW PATTERN IS NOT
PARTICULARLY FAVORABLE TO BRING EXCESSIVE HEAT WEST OF THE CASCADES, SO THE
HAZARD HAS BEEN REMOVED FROM THIS AREA. IN CONTRAST, PROBABILISTIC TOOLS BASED
ON ALL THREE MODEL ENSEMBLES SHOW ENHANCED CHANCES FOR TEMPERATURES TOPPING 90
DEG. F IN PARTS OF CENTRAL AND SOUTHWESTERN IDAHO, SO THE SLIGHT RISK HAZARD
HAS BEEN EXTENDED INTO THIS REGION.
DROUGHT CONCERNS ARE FORECAST TO INCREASE ACROSS PARTS OF THE CENTRAL AND
EASTERN CORN BELT AND ADJACENT AREAS DURING WEEK-2 DUE TO THE AFOREMENTIONED
WARMTH, THE EXPECTATION OF BELOW-NORMAL PRECIPITATION, AND PRECIPITATION TOTALS
ONE TO THREE 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.
WEAK MID-LEVEL FLOW ACROSS ALASKA FAVORS ONLY A SLIGHT TILT IN PROBABILITIES
FOR ABOVE AND BELOW NORMAL TEMPERATURES 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 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 CONDITIONS OVER PARTS OF ALASKA IS THE
EVOLUTION OF SUPER TYPHOON MAWAR, CURRENTLY WEST OF GUAM IN THE PACIFIC OCEAN
WITH TOP WINDS NEAR 175 MPH. MAWAR IS NOW THE STRONGEST TYPHOON SINCE 2021, AND
THE FIFTH-STRONGEST MAY TYPHOON ON RECORD. THE TYPHOON IS EXPECTED TO CONTINUE
WESTWARD FOR THE NEXT FEW DAYS BEFORE TURNING TO THE NORTHEAST JUST EAST OF
TAIWAN. AFTER RECURVATURE, THE STORM IS ANTICIPATED TO SLOWLY BECOME
EXTRATROPICAL WHILE CONTINUING NORTHEASTWARD, BUT STILL REMAIN A POTENT STORM
SYSTEM. SOME TOOLS BRING THE REMNANTS OF MAWAR CLOSE TO ALASKA DURING WEEK-2,
WHICH WOULD SIGNIFICANTLY IMPACT SOME PARTS OF THE STATE. HOWEVER, MODEL
GUIDANCE HAS BEEN INCONSISTENT REGARDING HOW FAR NORTH THE STORM TRACKS, AND
TODAY’S RUNS ARE LESS INDICATIVE OF A POTENTIAL THREAT TO ALASKA THAN
YESTERDAY, SO THERE ARE NO HIGHLIGHTED HAZARD RISKS ASSOCIATED WITH THE
REMNANTS OF THE TYPHOON AT THIS TIME.
FORECASTER: RICH TINKER
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page