599
FXUS21 KWNC 081819
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT JUNE 08 2023
SYNOPSIS: MID-LEVEL HIGH PRESSURE IS FORECAST ACROSS THE SOUTH-CENTRAL AND
SOUTHEASTERN CONTIGUOUS U.S. DURING WEEK-2 FAVORING INCREASED CHANCES OF
EXCESSIVE HEAT OVER PARTS OF THE CENTRAL AND SOUTHERN GREAT PLAINS, MIDDLE AND
LOWER MISSISSIPPI VALLEY, AND SOUTHEAST, WITH DROUGHT EXPANSION A CONCERN
ACROSS THE LOWER MISSISSIPPI VALLEY. SOME AREAS OF ENHANCED RAINFALL ARE
POSSIBLE ACROSS PORTIONS OF THE MIDWEST AND EXTENDING INTO PARTS OF THE EAST
THROUGHOUT THE PERIOD AS POTENTIAL SHORTWAVES PROPAGATE OVERTOP THE MID-LEVEL
HIGH PRESSURE TO THE SOUTH. SNOWMELT SEASON CONTINUES FOR PORTIONS OF THE WEST
AFTER EXCEPTIONAL WINTER ACCUMULATIONS, LEADING TO THE CONTINUED POTENTIAL FOR
FLOODING.
HAZARDS
MODERATE RISK OF EXCESSIVE HEAT ACROSS PARTS OF THE SOUTHERN PLAINS AND LOWER
MISSISSIPPI VALLEY, FRI-MON, JUN 16-19.
SLIGHT RISK OF EXCESSIVE HEAT ACROSS PARTS OF THE CENTRAL AND SOUTHERN PLAINS,
MIDDLE AND LOWER MISSISSIPPI AND TENNESSEE VALLEYS, AND THE SOUTHEAST, FRI-THU,
JUN 16-22.
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 THE LOWER MISSISSIPPI VALLEY.
DETAILED SUMMARY
FOR SUNDAY JUNE 11 - THURSDAY JUNE 15:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR FRIDAY JUNE 16 - THURSDAY JUNE 22: THE GEFS, ECMWF, AND CANADIAN ENSEMBLES
REMAIN IN GOOD AGREEMENT DEPICTING A LOW-AMPLITUDE RIDGE ACROSS THE
SOUTH-CENTRAL AND SOUTHEASTERN CONUS DURING WEEK-2. WHILE ABOVE-NORMAL
TEMPERATURES ARE INCREASINGLY LIKELY OVER MUCH OF THE CENTRAL AND EASTERN
CONUS, EXCESSIVE HEAT CONCERNS ARE MAINLY FOCUSED ACROSS THE SOUTHERN TIER. THE
HOTTEST ACTUAL TEMPERATURES ARE PREDICTED ACROSS TEXAS AND THE LOWER
MISSISSIPPI VALLEY WHERE THE NATIONAL BLEND OF MODELS INDICATES DAILY RECORD
HIGH TEMPERATURES (UPPER 90S TO LOW 100S DEG F). THE SKILL-WEIGHTED GEFS/ECMWF
EXCESSIVE HEAT TOOL ALSO INDICATES AT LEAST A 40 PERCENT CHANCE THAT HEAT
INDICES EXCEED 105 DEG F (110 DEG F IN SOME AREAS). THEREFORE, A MODERATE RISK
OF EXCESSIVE HEAT CONTINUES ACROSS PARTS OF THE SOUTHERN PLAINS AND LOWER
MISSISSIPPI VALLEY FOR JUN 16-19. WHILE THE GEFS AND ECMWF REFORECAST TOOLS
DEPICT AT LEAST A 20 PERCENT CHANCE MAXIMUM TEMPERATURES EXCEED 90 DEG F ACROSS
THE MIDWEST AND OHIO VALLEY, HUMIDITY LEVELS ARE FORECAST TO BE LOWER THAN
NORMAL OVER THESE AREAS, SUGGESTING HEAT INDICES WILL BE LESS LIKELY TO REACH
HAZARDS THRESHOLDS. OCCASIONAL PRECIPITATION MAY ALSO RESULT IN RELATIVELY
COOLER TEMPERATURES. THEREFORE, THE SLIGHT RISK OF EXCESSIVE HEAT IS ONLY
EXTENDED NORTHWARD THROUGH THE CENTRAL PLAINS AND MIDDLE MISSISSIPPI VALLEY
WHERE THERE IS A STRONGER SIGNAL FOR HEAT INDICES ABOVE 100 DEG F BASED ON THE
EXCESSIVE HEAT GUIDANCE, AND IS VALID FOR ALL OF WEEK-2.
GIVEN THE EXCESSIVE HEAT FORECAST ALONG WITH ANTECEDENT DRY CONDITIONS, DROUGHT
EXPANSION APPEARS POSSIBLE ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY.
THEREFORE A RAPID ONSET DROUGHT RISK HAS BEEN ADDED TO THIS REGION WHERE SOIL
MOISTURE VALUES HAVE DROPPED BELOW THE 30TH CLIMATOLOGICAL PERCENTILE IN SOME
AREAS. THE LARGEST SOURCE OF UNCERTAINTY IS THE INCREASING POTENTIAL FOR
TROPICAL MOISTURE TO MOVE ACROSS THE REGION LATER IN WEEK-2 AND INTO WEEK-3.
HOWEVER, INDIVIDUAL MODELS ARE INCONSISTENT, AND REFORECAST GUIDANCE FROM THE
GEFS AND ECMWF LEANS TOWARD NEAR TO SLIGHTLY BELOW-NORMAL PRECIPITATION FOR
WEEK-2 AS A WHOLE. THIS AREA WILL LIKELY NEED TO RE-EVALUATED EARLY NEXT WEEK
SHOULD MODELS COME INTO BETTER AGREEMENT.
THERE IS A POTENTIAL FOR WEAK SHORTWAVES TO PROPAGATE OVERTOP THE RIDGE AXIS TO
THE SOUTH, BRINGING INTERMITTENT ENHANCED PRECIPITATION CHANCES TO PORTIONS OF
THE MIDWEST THROUGH THE EASTERN CONUS. THE UNCALIBRATED GEFS, ECMWF, AND
CANADIAN ENSEMBLES GENERALLY SHOW AN ELEVATED SIGNAL FOR ENHANCED PRECIPITATION
OVER THE EASTERN CONUS STARTING LATE WEEK-1 AND PERSISTING INTO THE OUTSET OF
WEEK-2. ANOTHER SYSTEM IS INDICATED AROUND THE MIDDLE OF WEEK-2 ACROSS THE
CENTRAL CONUS. THE ECMWF REFORECAST TOOL IS PARTICULARLY ROBUST WITH THIS
SECOND FEATURE, INDICATING SOME AREAS OF THE MIDDLE MISSISSIPPI VALLEY HAVING
AT LEAST A 20 PERCENT CHANCE OF 3-DAY PRECIPITATION EXCEEDING THE 85TH
CLIMATOLOGICAL PERCENTILE AND 1-INCH DURING THE DAY 10-12 (JUN 18-20) PERIOD.
DUE TO THE MODEL UNCERTAINTY AND MARGINAL PRECIPITATION TOTALS, NO RELATED
PRECIPITATION HAZARDS ARE POSTED. HOWEVER, DUE TO THE INCREASED SIGNALS FOR
SLIGHTLY ABOVE-NORMAL PRECIPITATION FOR WEEK-2 AS A WHOLE, THE RAPID ONSET
DROUGHT RISK IS REMOVED ACROSS THE MIDWEST AND OHIO VALLEY.
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. POSSIBLE FLOODING ALSO REMAINS ACROSS NORTHERN PARTS OF THE JAMES
RIVER IN SOUTH DAKOTA AS RIVER LEVELS ARE RECEDING SLOWER DUE TO SATURATED
GROUND CONDITIONS AND RELATIVELY FLAT TOPOGRAPHY.
MID-LEVEL TROUGHING IS FAVORED FOR THE ALEUTIANS AND ALASKA MAINLAND, RESULTING
IN INCREASED CHANCES FOR NEAR TO BELOW NORMAL TEMPERATURES AND SLIGHTLY
ABOVE-NORMAL PRECIPITATION ACROSS MUCH OF THE STATE. NO AREAS OF HAZARDOUS
WEATHER ARE INDICATED ACROSS ALASKA.
FORECASTER: THOMAS COLLOW
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