117
FXUS21 KWNC 231944
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT MAY 23 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 MUCH OF THE WEST AND PORTIONS OF
ALASKA, AS WELL AS ALONG THE JAMES RIVER IN SOUTH DAKOTA.
HAZARDS
MODERATE RISK FOR HEAVY PRECIPITATION FOR PORTIONS OF THE SOUTHERN PLAINS,
WED-FRI, MAY 31-JUN 2.
SLIGHT RISK FOR HEAVY PRECIPITATION FOR PORTIONS OF THE SOUTHERN AND CENTRAL
PLAINS, WED-SUN, MAY 31-JUN 4.
SLIGHT RISK FOR EXCESSIVE HEAT FOR PORTIONS OF THE GREAT LAKES, AND THE OHIO,
MIDDLE AND UPPER MISSISSIPPI VALLEYS, WED-FRI, MAY 31-JUN 2.
POSSIBLE FLOODING FOR PORTIONS OF CALIFORNIA, NEVADA, UTAH, WYOMING, WESTERN
MONTANA, IDAHO, OREGON, AND WASHINGTON.
POSSIBLE FLOODING ALONG PORTIONS OF THE JAMES RIVER.
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 FRIDAY MAY 26 - TUESDAY MAY 30:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR WEDNESDAY MAY 31 - TUESDAY JUNE 06: 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 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 MAY 31-JUN 4. 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
RELATIVE TO YESTERDAY, 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 MAY 31-JUN 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% OF EXCEEDING THE 85TH PERCENTILE FOR MAXIMUM
TEMPERATURES FOR THIS REGION FROM MAY 31 THROUGH AT LEAST JUN 2, ALTHOUGH THE
SIGNAL DROPS 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 MAY 31-JUN 2.
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.
WARMING TEMPERATURES ARE ANTICIPATED TO ENHANCE THE SNOWMELT RATE ACROSS THE
WESTERN CONUS, INDUCING RIVER FLOODING ESPECIALLY ACROSS HIGHER ELEVATIONS IN
THE WEST AND THE SOUTHERN CANADIAN ROCKIES, WHERE A FEW SITES STILL REPORT OVER
50 INCHES OF SNOW WATER CONTENT. THE ABOVE-NORMAL TEMPERATURES MAY CAUSE RAPID
SNOWMELT IN PARTS OF THE SIERRA NEVADA, GREAT BASIN, NORTHERN ROCKIES, AND
PACIFIC NORTHWEST, RESULTING IN AREAS AT HIGH RISK OF FLOODING ALONG MANY
RIVERS, AND IN AREAS ADJACENT TO THE HIGHER ELEVATIONS; HOWEVER, EXPANSIVE,
MULTI-STATE FLOODING IS NOT EXPECTED TO ENVELOP LARGE AREAS OF THE INTERIOR
WEST. FLOODING CONTINUES TO BE POSSIBLE ALONG THE JAMES RIVER IN SOUTH DAKOTA
DUE TO PREVIOUS SNOWMELT SATURATING GROUND CONDITIONS.
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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