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FXUS21 KWNC 121837
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT JUNE 12 2023
SYNOPSIS: MID-LEVEL HIGH PRESSURE IS PREDICTED TO PERSIST FROM WEEK-1 INTO MUCH
OF WEEK-2 ACROSS THE SOUTH-CENTRAL CONTIGUOUS U.S. (CONUS), SUPPORTING
CONTINUED INCREASED CHANCES FOR EXCESSIVE HEAT ACROSS PARTS OF THE REGION
THROUGHOUT MUCH OF THE PERIOD. THERE IS A POTENTIAL FOR SOME AREAS TO
EXPERIENCE NEAR RECORD TEMPERATURES IN THE TRIPLE DIGITS, ESPECIALLY AT THE
BEGINNING OF WEEK-2, ACROSS THE SOUTHERN PLAINS AND LOWER MISSISSIPPI VALLEY.
FURTHER NORTH, MID-LEVEL HIGH PRESSURE IS FORECAST TO BUILD ACROSS THE UPPER
MIDWEST, GRADUALLY EXPANDING TO THE NORTHEAST, FAVORING ABOVE NORMAL
TEMPERATURES ACROSS PARTS OF THE MIDWEST. DUE TO SIGNIFICANT MODEL AND TOOL
UNCERTAINTY REGARDING THE POTENTIAL FOR HEAT AND TEMPERATURES BEING MARGINAL
FOR REACHING EXCESSIVE HEAT CRITERIA, AN ADDITIONAL HEAT RISK IS NOT POSTED FOR
THIS AREA AT THIS TIME. 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, TUE-THU, JUN 20-22.
SLIGHT RISK OF EXCESSIVE HEAT ACROSS PARTS OF THE SOUTH-CENTRAL CONUS AND LOWER
MISSISSIPPI VALLEY, TUE-SAT, JUN 20-24.
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 THURSDAY JUNE 15 - MONDAY JUNE 19:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR TUESDAY JUNE 20 - MONDAY JUNE 26: THE PRIMARY HAZARDS CONCERN IS THE
CONTINUED INCREASED RISK FOR EXCESSIVE HEAT ACROSS THE SOUTH-CENTRAL CONUS AND
LOWER MISSISSIPPI VALLEY DURING WEEK-2. THERE IS GOOD AGREEMENT AMONG THE MODEL
ENSEMBLE MEANS INDICATING MID-LEVEL RIDGING ACROSS THE SOUTH-CENTRAL CONUS
CONTINUING FROM WEEK-1 THROUGH MUCH OF WEEK-2. THIS TRANSLATES INTO THE
TEMPERATURE AND HEAT TOOLS HAVING GOOD CONSENSUS SUPPORTING INCREASED CHANCES
FOR EXCESSIVE HEAT ACROSS THE REGION. BOTH THE GEFS AND ECMWF PROBABILISTIC
EXTREMES TOOL (PET) INDICATE AT LEAST A 40% CHANCE OF MAXIMUM TEMPERATURES
EXCEEDING THE 85TH PERCENTILE CLIMATOLOGICALLY OVER TEXAS ON DAY 8 (JUN 20).
THE ECMWF MAINTAINS AREAS OF GREATER THAN 40% CHANCES FOR EXCEEDING THIS
THRESHOLD DAYS 9 AND 10 (JUN 21-22), WHILE THE GEFS DECREASES TO GREATER THAN
30%. DESPITE THESE MINOR DIFFERENCES IN TOOL PROBABILITIES, A MODERATE RISK IS
DESIGNATED FOR PARTS OF THE SOUTHERN PLAINS AND LOWER MISSISSIPPI VALLEY JUN
20-22 BASED ON MULTIPLE HEAT TOOLS AND THE NATIONAL BLEND OF MODELS (NBM)
INDICATING THE POTENTIAL FOR NEAR RECORD BREAKING TEMPERATURES IN THE TRIPLE
DIGITS. A BROADER SLIGHT RISK AREA IS HIGHLIGHTED ACROSS PARTS OF THE
SOUTH-CENTRAL CONUS AND LOWER MISSISSIPPI VALLEY, JUN 20-24, WHERE MULTIPLE
TOOLS SHOW AT LEAST A 20% CHANCE OF HEAT INDEX VALUES EXCEEDING THE 90TH
PERCENTILE.
MID-LEVEL RIDGING IS ALSO FORECAST TO BUILD ACROSS THE UPPER MIDWEST,
INCREASING THE LIKELIHOOD FOR ABOVE NORMAL TEMPERATURES DURING WEEK-2. THE GEFS
AND ECMWF PET SHOWS AT LEAST A 20% CHANCE OF TEMPERATURES EXCEEDING THE 85TH
PERCENTILE, WITH THE ECMWF INDICATING AT LEAST A 40% CHANCE OF EXCEEDING THIS
THRESHOLD ACROSS THE NORTHERN PLAINS AND UPPER MISSISSIPPI VALLEY AT THE
BEGINNING OF THE PERIOD. THE GEFS, AND CANADIAN PET GENERALLY INDICATE THE
POTENTIAL FOR EXCEEDING 90 DEG F BEING LIMITED TO THE CENTRAL PLAINS AND MIDDLE
MISSISSIPPI AND OHIO VALLEYS, WHEREAS THE ECMWF EXTENDS THIS SIGNAL FURTHER
NORTH TO PARTS OF THE NORTHERN PLAINS. DUE TO SIGNIFICANT DIFFERENCES IN THE
DYNAMICAL MODELS AND TEMPERATURE TOOLS IN ADDITION TO TEMPERATURES NOT
ANTICIPATED TO REACH HAZARDOUS THRESHOLDS, AN ASSOCIATED HEAT RISK IS NOT
DESIGNATED FOR THIS REGION AT THIS TIME.
RECENT DETERMINISTIC AND ENSEMBLE MODEL GUIDANCE HAS BEEN SHOWING SOME
POTENTIAL OF A SURFACE LOW FORMING NEAR OR ALONG THE COAST OF THE CAROLINAS
FROM THE BEGINNING TO MIDDLE OF WEEK-2, WHICH COULD BRING ENHANCED
PRECIPITATION TO PARTS OF THE MID-ATLANTIC AND SOUTHEAST. THE GEFS, ECMWF, AND
CANADIAN PET SHOW AT LEAST A 20% CHANCE OF 3-DAY RAINFALL EXCEEDING THE 85TH
PERCENTILE AND ONE INCH, ALTHOUGH WITH VARYING SPATIAL COVERAGE. THERE IS TOO
MUCH UNCERTAINTY AT THIS TIME REGARDING THE DETAILS OF THIS FEATURE TO
DESIGNATE A RELATED HEAVY PRECIPITATION HAZARD AT THIS TIME.
GIVEN THE EXCESSIVE HEAT FORECAST ALONG WITH ANTECEDENT DRY CONDITIONS, RAPID
ONSET DROUGHT (ROD) RISK REMAINS ELEVATED ACROSS PORTIONS OF THE LOWER
MISSISSIPPI VALLEY WHERE SOIL MOISTURE VALUES HAVE DROPPED BELOW THE 30TH
CLIMATOLOGICAL PERCENTILE IN SOME AREAS. THE NORTHERN PERIPHERY OF LAST WEEK'S
ROD RISK AREA HAS BEEN REMOVED IN TODAY'S OUTLOOK WHERE THE WEATHER PREDICTION
CENTER'S (WPC) 7-DAY ACCUMULATED POTENTIAL RAINFALL DURING WEEK-1 EXCEEDS 1.5
INCHES. THIS ROD AREA CONTINUES TO HAVE CONSIDERABLE UNCERTAINTY DUE TO THE
DIFFICULTY OF PINPOINTING WHERE LOCALIZED THUNDERSTORMS COULD OCCUR.
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.
POSITIVE MID-LEVEL HEIGHT DEPARTURES ARE FAVORED ACROSS ALASKA, SUPPORTING NEAR
TO SLIGHTLY ABOVE NORMAL TEMPERATURES ACROSS MUCH OF THE CENTRAL AND EASTERN
MAINLAND AND SOUTHEAST ALASKA, WITH BELOW NORMAL TEMPERATURES FORECAST ACROSS
THE WESTERN MAINLAND. A RELATIVELY INACTIVE STORM PATTERN IS ANTICIPATED FOR
ALASKA PRECLUDING ANY HAZARDS DESIGNATED FOR THE STATE.
FORECASTER: MELISSA OU
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