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FXUS21 KWNC 291828
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT MAY 29 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 ALONG THE EAST COAST OF
NORTH AMERICA. THIS RESULTS IN WARMER AND RELATIVELY QUIET WEATHER FOR MOST OF
THE CONUS. AS THE ANOMALOUS MID-LEVEL RIDGE IN CANADA DRIFTS WEST AND BUILDS
ACROSS THE NORTHWEST CONUS, THERE WILL BE SLIGHTLY ENHANCED CHANCES FOR A
PERIOD OF EXCESSIVE HEAT IN THE NORTHWEST. A FAVORABLE ENVIRONMENT FOR
THUNDERSTORMS AND HEAVY RAINFALL IN THE SOUTHERN PLAINS AND LOWER MISSISSIPPI
VALLEY REMAINS POSSIBLE THROUGH 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 SOUTHERN PLAINS AND
SOUTHEAST, TUE-FRI, JUN 6-9.
SLIGHT RISK FOR EXCESSIVE HEAT FOR PARTS OF THE NORTHWEST TUE-SUN, JUN 6-11.
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 THURSDAY JUNE 01 - MONDAY JUNE 05:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR TUESDAY JUNE 06 - MONDAY JUNE 12: THE MEAN WEEK-2 MID-LEVEL, 500-HPA,
HEIGHT PATTERN HAS RETROGRADED SLIGHTLY RELATIVE TO LAST WEEK 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
TOUGHING IS FORECAST ACROSS THE ALEUTIAN ISLANDS. HOWEVER, AT ONSET OF THE
PERIOD, THE PATTERN REMAINS SIMILAR TO PREVIOUS FORECASTS WITH RIDGING ACROSS
MUCH OF THE NORTHERN CONUS AND CANADA AND SLIGHTLY BELOW-NORMAL 500-HPA HEIGHT
ANOMALIES ACROSS THE SOUTHERN TIER. BY THE MIDDLE OF THE PERIOD, TYPHOON MAWAR
LOOKS LIKELY TO HAVE DISRUPTED THE MID-LEVEL FLOW PATTERN WITH A MORE AMPLIFIED
PATTERN DEVELOPING ACROSS THE CONUS WITH TROUGHING IN THE EAST AND RIDGING IN
THE WEST.
WITH RIDGING PERSISTING THROUGHOUT MUCH OF THE PERIOD IN THE NORTHWEST, DESPITE
THE EVOLUTION OF THE MID-LEVEL PATTERN, REFORECAST TOOLS ARE INDICATING
INCREASED CHANCES FOR TEMPERATURES TO EXCEED THE 85TH CLIMATOLOGICAL PERCENTILE
DURING MUCH OF THE PERIOD. THE HIGHEST PROBABILITIES ARE IN THE ECMWF
REFORECAST WITH CHANCES GREATER THAN 60% ACROSS A WIDE REGION. RELATIVE TO LAST
WEEK, THE HIGHEST CHANCES IN ALL THE TOOLS HAVE SHIFTED SLIGHTLY WEST TO
INCLUDE HIGHER CHANCES WEST OF THE CASCADES. THE BIGGEST CONCERN REGARDING A
HEAT HAZARD IS THE CHANCES FOR TEMPERATURES TO REACH HAZARDOUS THRESHOLDS.
RECENT HEAT WAVES IN THE REGION HAVE REACHED RECORD TEMPERATURES IN THE LOW
90’S DEGF EAST OF THE CASCADES WITHOUT A CORRESPONDING HEAT HAZARD BEING
ISSUED. THIS EVENT LOOKS LIKELY TO REACH SIMILAR TEMPERATURES IN THE LOW-90’S
DEGF BUT REFORECAST TOOLS HAVE LIMITED SUPPORT FOR EXCEEDING 95 DEGF.
THEREFORE, DESPITE THE HIGH PROBABILITIES SHOWN IN THE REFORECAST TOOLS AND
SKILL WEIGHTED CALIBRATED EXCESSIVE HEAT TOOLS ONLY A SLIGHT RISK OF EXCESSIVE
HEAT IS POSTED FOR JUNE 6-11.
LOW-LEVEL RETURN FLOW OFF THE GULF OF MEXICO LEADS TO INCREASED CHANCES FOR
HEAVY PRECIPITATION INTO PARTS OF THE SOUTHERN PLAINS AND LOWER MISSISSIPPI
VALLEY. REFORECAST TOOLS ALL SUGGEST CHANCES FOR THREE DAY PRECIPITATION TOTALS
TO EXCEED THE 85TH CLIMATOLOGICAL PERCENTILE AND 1 INCH OF PRECIPITATION IN
THESE AREAS. FURTHER, SOME PARTS OF THE SOUTHERN PLAINS HAVE SEEN OVER 200% OF
NORMAL PRECIPITATION IN THE PAST 30 DAYS, MUCH OF THAT COMING IN THE LAST WEEK.
THEREFORE, A SLIGHT RISK OF HEAVY PRECIPITATION IS POSTED FOR JUN 6-9.
FURTHER NORTH, 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.
SOUTHERLY MID-LEVEL FLOW ACROSS ALASKA FAVORS ABOVE NORMAL TEMPERATURES ACROSS
PARTS OF NORTHERN AND CENTRAL ALASKA DURING THE WEEK-2 PERIOD. 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 TYPHOON MAWAR, CURRENTLY NORTHEAST OF THE PHILIPPINES IN THE
PACIFIC OCEAN WITH WINDS NEAR 115 MPH. THE TYPHOON IS EXPECTED TO RECURVE IN
THE NEXT FEW DAYS, 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. SOME TOOLS BRING THE
REMNANTS OF MAWAR CLOSE TO ALASKA DURING WEEK-2, WHICH COULD IMPACT SOME PARTS
OF THE STATE WITH STRONG WINDS AND ABOVE-NORMAL PRECIPITATION. HOWEVER,
REFORECAST TOOLS HAVE LIMITED SUPPORT FOR ANY WIND OR PRECIPITATION HAZARDS
NEAR ALASKA. THEREFORE, NO CORRESPONDING HAZARDS ARE CURRENTLY POSTED.
FORECASTER: RYAN BOLT
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