717
FXUS21 KWNC 201829
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT JUNE 20 2023
SYNOPSIS: MID-LEVEL HIGH PRESSURE PERSISTS OVER THE SOUTHERN CONTIGUOUS U.S.
(CONUS) DURING WEEK-2, LEADING TO THE POTENTIAL FOR EXCESSIVE HEAT FOR THE
SOUTHERN AND CENTRAL PLAINS. MID-LEVEL LOW PRESSURE OVER THE NORTHERN ROCKY
MOUNTAINS BRINGS A CHANCE FOR HEAVY PRECIP FOR PORTIONS OF THE NORTHERN CONUS,
WHILE A CUT–OFF LOW OVER THE GREAT LAKES COMBINED WITH ABUNDANT TROPICAL
MOISTURE BRINGS THE RISK FOR HEAVY PRECIPITATION FOR PORTIONS OF THE
NORTHEASTERN CONUS. SNOWMELT SEASON CONTINUES FOR PORTIONS OF THE WEST AFTER
EXCEPTIONAL WINTER ACCUMULATIONS, LEADING TO THE CONTINUED POTENTIAL FOR
FLOODING, WHILE ABNORMALLY DRY CONDITIONS OVER PORTIONS OF WISCONSIN AND
LOUISIANA RESULT IN THE POTENTIAL FOR RAPID ONSET DROUGHT (ROD).
HAZARDS
HIGH RISK OF EXCESSIVE HEAT FOR PORTIONS OF EASTERN TEXAS, WED-THU, JUN 28-29
MODERATE RISK FOR EXCESSIVE HEAT FOR PORTIONS OF THE SOUTHERN AND CENTRAL
PLAINS AND LOWER AND MIDDLE MISSISSIPPI VALLEY, WED-SAT, JUN 28-JUL 1.
SLIGHT RISK FOR EXCESSIVE HEAT FOR THE CENTRAL AND SOUTHERN PLAINS, LOWER AND
MIDDLE MISSISSIPPI VALLEY, AND PORTIONS OF THE OHIO AND TENNESSEE VALLEYS,
SOUTHEASTERN U.S., SOUTHERN ROCKIES, WED-MON, JUN 28-JUL 3.
SLIGHT RISK OF EXCESSIVE HEAT FOR PORTIONS OF THE FOUR CORNERS AND DESERT
SOUTHWEST, SAT-TUE, JUL 1-4
SLIGHT RISK FOR HEAVY PRECIPITATION FOR PORTIONS OF THE NORTHERN GREAT BASIN,
NORTHERN ROCKIES, AND NORTHERN PLAINS, WED-FRI, JUN 28-30.
SLIGHT RISK FOR HEAVY PRECIPITATION FOR PORTIONS OF THE MID-ATLANTIC AND
NORTHEASTERN U.S., WED-SUN, JUN 28-JUL 2.
POSSIBLE FLOODING FOR PORTIONS OF CALIFORNIA, NEVADA, UTAH, WYOMING, AND IDAHO.
POSSIBLE FLOODING ALONG PORTIONS OF THE JAMES RIVER IN SOUTH DAKOTA.
RAPID ONSET DROUGHT RISK ACROSS PORTIONS OF NORTHERN WISCONSIN AND CENTRAL
LOUISIANA.
DETAILED SUMMARY
FOR FRIDAY JUNE 23 - TUESDAY JUNE 27:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR WEDNESDAY JUNE 28 - TUESDAY JULY 04: ENSEMBLE MODEL SOLUTIONS FROM THE
GEFS, ECMWF, AND CMCE ALL DEPICT POSITIVE 500-HPA HEIGHT ANOMALIES PERSISTING
OVER THE SOUTHERN CONUS THROUGHOUT THE FORECAST PERIOD. THIS FAVORS INCREASED
TEMPERATURES ACROSS THE SOUTHERN AND CENTRAL CONUS, LEADING TO THE POTENTIAL
FOR EXCESSIVE HEAT. THE REFORECAST-BASED EXTREME FORECAST TOOLS FROM THE GEFS
AND ECMWF ENSEMBLES FORECAST AREAS OF GREATER THAN 60% PROBABILITY FOR MAXIMUM
TEMPERATURES TO EXCEED THE 85TH CLIMATOLOGICAL PERCENTILE AND 100 DEGF IN PARTS
OF EASTERN TEXAS. THE NATIONAL BLEND OF MODELS IS ALSO INDICATING A BROAD AREA
OF POTENTIAL RECORD BREAKING HEAT IN TEXAS EARLY IN THE WEEK-2 PERIOD.
THEREFORE, A HIGH RISK OF EXCESSIVE HEAT IS POSTED FOR JUN 28-29 FOR PARTS OF
EASTERN TEXAS. THE REFORECAST-BASED EXTREMES FORECAST TOOLS FROM THE GEFS,
ECMWF, AND CMCE ALSO INDICATE AT LEAST A 40% PROBABILITY OF MAXIMUM
TEMPERATURES EXCEEDING THE 85TH PERCENTILE AND AT LEAST 95 DEGF FOR MUCH OF THE
SOUTHERN AND CENTRAL PLAINS, AND THE MIDDLE AND LOWER MISSISSIPPI VALLEY, WITH
HIGH TEMPERATURES OVER 100 DEGF FOR MUCH OF TEXAS AND OKLAHOMA. THIS RISK
EXTENDS FROM JUN 28-JUL 1 FOR THE SOUTHERN AND CENTRAL PLAINS AS FAR NORTH AS
KANSAS CITY. BY DAY 11, THE STRONGEST SIGNALS FOR CONTINUED HEAT LOOK LIKELY TO
PERSIST IN THE SOUTHERN PLAINS, WITH LOWER CHANCES IN THE CENTRAL PLAINS
ALTHOUGH THE GEFS REFORECAST TOOL MAINTAINS HIGHER PROBABILITIES FURTHER NORTH.
THEREFORE A MODERATE RISK FOR EXCESSIVE HEAT IS MAINTAINED FOR JUN 28-JUL 1.
ADDITIONALLY, THE REFORECAST TOOLS INDICATE A BROAD AREA OF AT 20% PROBABILITY
OF EXCEEDING THE 85TH PERCENTILE FOR PORTIONS OF THE CENTRAL AND SOUTHERN
PLAINS, LOWER AND MIDDLE MISSISSIPPI VALLEY, AND PORTIONS OF THE OHIO AND
TENNESSEE VALLEYS, SOUTHEASTERN U.S., SOUTHERN ROCKIES, AND DESERT SOUTHWEST,
THEREFORE A SLIGHT RISK FOR EXCESSIVE HEAT IS POSTED FOR THESE REGIONS FOR JUN
28-JUL 3. BY THE MIDDLE AND THROUGH THE END OF THE PERIOD, THERE IS A GROWING
SIGNAL FOR EXCESSIVE HEAT TO BUILD INTO THE DESERT SOUTHWEST WITH THE
PROBABILISTIC REFORECAST TOOLS SHOWING INCREASED CHANCES FOR EXCEEDING THE 85TH
PERCENTILE AND 110 DEGF. THEREFORE, A SLIGHT RISK OF EXCESSIVE HEAT IS POSTED
FOR JUL 1-4 FOR THESE REGIONS.
AT THE BEGINNING OF WEEK-2 MODEL SOLUTIONS CONTINUE TO DEPICT NEGATIVE 500-HPA
HEIGHT ANOMALIES OVER THE NORTHWEST AND THE GREAT LAKES, LEADING TO ENHANCED
PRECIPITATION FOR THE NORTHEAST AND NORTHWEST CONUS. REFORECAST TOOLS FROM THE
GEFS AND ECMWF BOTH INDICATE AT LEAST A 20% PROBABILITY OF 3-DAY PRECIPITATION
ACCUMULATIONS TO EXCEED THE 85TH PERCENTILE AND AT LEAST A HALF INCH FOR
PORTIONS OF THE NORTHERN GREAT BASIN, NORTHERN ROCKIES, AND NORTHERN PLAINS FOR
JUN 28-30. AS THE FORECAST PERIOD PROGRESSES THIS TROUGH IS FAVORED TO DECREASE
IN AMPLITUDE, REDUCING THE POTENTIAL FOR HEAVY PRECIPITATION FOR THE NORTHERN
CONUS. MEANWHILE, CONTINUED WEAK TROUGHING AND ABUNDANT MOISTURE FROM THE
TROPICAL ATLANTIC FAVORS THE POTENTIAL FOR PERIODS OF HEAVY PRECIPITATION FOR A
LONGER PERIOD IN THE NORTHEASTERN CONUS, WITH THE REFORECAST TOOLS INDICATING A
20% PROBABILITY OF 3-DAY PRECIPITATION ACCUMULATIONS TO EXCEED THE 85TH
PERCENTILE AND AT LEAST A HALF INCH FOR PORTIONS OF THE MID-ATLANTIC AND
NORTHEAST FOR JUN 28-JUL 2. THEREFORE, A SLIGHT RISK FOR HEAVY PRECIPITATION IS
POSTED FOR THE REGIONS AND TIME PERIODS INDICATED.
DROUGHT CONCERNS ARE FORECAST TO INCREASE ACROSS PARTS OF THE MIDWEST AS THE
HEAT OF SUMMER BUILDS AND A PERSISTENCE OF BELOW-NORMAL PRECIPITATION FORECAST
FOR THE REGION. THE POTENTIAL FOR ROD CONTINUES FOR MUCH OF NORTHERN WISCONSIN
IN TODAY’S OUTLOOK. SIGNIFICANT PRECIPITATION DEFICITS HAVE BROUGHT THE
POTENTIAL FOR ROD TO CENTRAL LOUISIANA AS WELL, AND WAS INITIALLY HIGHLIGHTED
LAST THURSDAY. THERE HAS BEEN SOME RECENT HEAVY RAINFALL ALONG THE NORTHERN
LOUISIANA BORDER, SO TODAY’S OUTLOOK INCLUDES A SLIGHT RETREAT FOR THE NORTHERN
EXTENT OF THIS AREA AT RISK FOR ROD.
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 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
FORECASTER: RYAN BOLT
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