891
FXUS21 KWNC 201823
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT JUNE 20 2026
SYNOPSIS: ENHANCED SUBTROPICAL HIGH PRESSURE OVER THE SOUTHEASTERN CONUS BRINGS
AN INCREASED RISK OF EXTREME HEAT FROM THE FLORIDA PENINSULA NORTHWARD INTO THE
SOUTHERN AND MIDDLE ATLANTIC REGIONS THROUGHOUT WEEK-2. MID-LEVEL HIGH PRESSURE
ALSO BUILDS TOWARD THE HIGH PLAINS, INCREASING THE RISK OF EXTREME HEAT ACROSS
THE CENTRAL AND SOUTH-CENTRAL CONUS. MEANWHILE, SURFACE LOW DEVELOPMENT IN THE
LEE OF THE ROCKIES AND ENHANCED MOISTURE TRANSPORT FROM THE SOUTH SUPPORT AN
INCREASED RISK OF HEAVY PRECIPITATION ACROSS PARTS OF THE MIDDLE AND UPPER
MISSISSIPPI VALLEY AND ADJACENT AREAS EARLY IN THE PERIOD.
HAZARDS
SLIGHT RISK OF EXTREME HEAT FOR MOST OF THE SOUTHEAST AND MID-ATLANTIC REGION,
SUN-SAT, JUN 28-JUL 4.
SLIGHT RISK OF EXTREME HEAT FOR THE SOUTHERN HALF OF THE GREAT PLAINS AND
ADJACENT PORTIONS OF THE MISSISSIPPI VALLEY, SUN-SAT, JUN 28-JUL 4.
SLIGHT RISK OF HEAVY PRECIPITATION FOR THE UPPER AND MIDDLE MISSISSIPPI VALLEY,
WESTERN GREAT LAKES REGION, AND LOWER OHIO VALLEY, SUN-TUE, JUN 28-30.
DETAILED SUMMARY
FOR TUESDAY JUNE 23 - SATURDAY JUNE 27:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR SUNDAY JUNE 28 - SATURDAY JULY 04: MID-LEVEL HEIGHT ANOMALY FORECASTS FROM
THE GLOBAL ENSEMBLE FORECAST SYSTEM (GEFS), EUROPEAN ENSEMBLE (ECENS), AND
CANADIAN ENSEMBLE (CMCE) FAVOR A RIDGE OVER THE EASTERN MID-LATITUDE PACIFIC, A
TROUGH OVER THE INTERIOR WEST (ECENS HAS THE DEEPEST TROUGH, AND THE CMCE HAS
THE SHALLOWEST ONE), A RIDGE OVER THE EAST-CENTRAL CONUS, AND A WEAK TROUGH
EXITING NEW ENGLAND, EARLY IN WEEK-2. ANOTHER WEAK TROUGH IS PREDICTED NEAR
SOUTHWESTERN ALASKA. THE CIRCULATION PATTERN MODESTLY DEAMPLIFIES THEREAFTER,
ONLY TO REAMPLIFY LATE IN THE PERIOD WITH TROUGHS NEAR BOTH COASTS, A RIDGE
CENTERED OVER/NEAR THE HIGH PLAINS, AND A 594-DM HEIGHT CONTOUR FROM THE DESERT
SOUTHWEST TO THE SOUTHERN PLAINS. AS THE FLOW PATTERN EVOLVES DURING WEEK-2,
THE SUBTROPICAL RIDGING OVER THE GULF STATES BUILDS NORTHWESTWARD INTO THE
CENTRAL CONUS AND EASTERN ROCKIES WHILE A WEAK TROUGH MEANDERS NEAR THE
NORTHEAST. BY THE END OF WEEK-2, NEAR TO MOSTLY ABOVE-NORMAL 500-HPA HEIGHTS
WILL ENCOMPASS NORTH AMERICA AND ADJACENT AREAS.
FALLING 500-HPA HEIGHTS OVER THE WESTERN CONUS ON DAY 7 ARE EXPECTED TO BRING
AN END TO ANY EXTREME HEAT TO THE CENTRAL VALLEY OF CALIFORNIA AND DESERT
SOUTHWEST BY THE START OF WEEK-2. AS SUBTROPICAL RIDGING BUILDS NORTHWARD AND
NORTHWESTWARD FROM THE GENERAL VICINITY OF FLORIDA, TEMPERATURES ARE EXPECTED
TO RISE QUICKLY ALONG THE EASTERN SEABOARD, BRINGING A SLIGHT RISK OF EXTREME
HEAT AS FAR NORTH AS THE UPPER MID-ATLANTIC REGION THROUGHOUT WEEK-2. FOR
LOCATIONS LIKE THE NATION'S CAPITAL AND PHILADELPHIA, ACTUAL (I.E. DRY BULB)
AIR TEMPERATURES OF ABOUT 95 DEG F ARE PREDICTED, WITH HEAT INDEX VALUES
CLIMBING TO NEAR 105 DEG F. THIS IS SUPPORTED BY THE GEFS, ECENS, AND CMCE
PROBABILISTIC EXTREMES TOOLS (PETS) AND A SKILL-WEIGHTED, BIAS-CORRECTED
EXTREME HEAT TOOL WHICH USES THE GEFS AND ECENS. THE PETS GENERALLY KEEP AT
LEAST 20 PERCENT CHANCES FOR DAYTIME HIGHS EXCEEDING THE 85TH CLIMATOLOGICAL
PERCENTILE THROUGHOUT WEEK-2, WITH THE ECENS BRIEFLY FAVORING EVEN 30-40
PERCENT CHANCES. THE 06Z DETERMINISTIC GFS MODEL RUN DEPICTS PROLONGED
SOUTHWESTERLY SURFACE FLOW DURING THIS PERIOD AND DEW POINTS RANGING FROM THE
UPPER 60'S INTO THE LOWER 70'S FOR THE MID-ATLANTIC REGION. THEREFORE, A SLIGHT
RISK OF EXTREME HEAT IS INDICATED FOR MOST OF THE SOUTHEAST AND MID-ATLANTIC
REGION FOR THE ENTIRETY OF WEEK-2.
ACROSS THE CENTRAL AND SOUTH-CENTRAL CONUS, THE GEFS PET (WHICH IS SLIGHTLY
WARMER THAN THE ECENS PET) SHOWS A 20 PERCENT CHANCE FOR HIGH TEMPERATURES TO
EXCEED THE 85TH PERCENTILE, WHILE THE ECENS PET ONLY SHOWS A 20 PERCENT CHANCE
OVER PARTS OF THE REGION DURING THE FIRST FEW DAYS OF WEEK-2. BOTH PETS FAVOR
ACTUAL HIGHS TO REACH 100 DEG F OR SLIGHTLY HIGHER DURING THE PERIOD. THE
INTERNAL SKILL-WEIGHTED, BIAS-CORRECTED HEAT TOOL FAVORS A HEAT INDEX OF 105
DEG F, AND A 20-30 PERCENT CHANCE OF HEAT INDEX VALUES REACHING 110 DEG F OVER
NORTHERN TEXAS. THE PETS MAY BE UNDERGOING THE EXTREME HEAT, GIVEN RISING
HEIGHTS ASSOCIATED WITH THE MID-LEVEL HIGH PRESSURE AREA THAT IS PREDICTED TO
MOVE INTO THE SOUTH-CENTRAL AND CENTRAL CONUS. THEREFORE, A SLIGHT RISK OF
EXTREME HEAT IS INDICATED OVER THE SOUTHERN HALF OF THE PLAINS AND ADJACENT
PORTIONS OF THE MISSISSIPPI VALLEY DURING THE ENTIRETY OF WEEK-2.
FOR PRECIPITATION, MODELS CONTINUE TO POINT TO THE POTENTIAL DEVELOPMENT OF A
SURFACE TROUGH IN THE LEE OF THE U.S. ROCKIES AND SOUTHERN CANADIAN ROCKIES
EARLY IN WEEK-2. THE PRIMARY UNCERTAINTY INVOLVES THE LOCATION OF ANY SURFACE
LOW PRESSURE CENTER THAT DEVELOPS ALONG THIS LEE TROUGH. THE ECENS AND CMCE
PREDICT A SURFACE LOW OVER EASTERN/SOUTHEASTERN SASKATCHEWAN, WHILE THE GEFS
INDICATES THE SURFACE LOW WILL BE MUCH FARTHER SOUTH OVER WESTERN KANSAS. A
COLD FRONT TRAILING FROM LOW PRESSURE NORTH OF MAINE EXTENDS SOUTHWESTWARD
ACROSS THE OHIO VALLEY AND THEN NORTHWESTWARD (LIKELY AS A WARM FRONT OR
STATIONARY FRONT) TOWARDS THE UPPER MISSISSIPPI VALLEY AND SOUTH-CENTRAL
CANADA. THIS BAROCLINIC ZONE ROUGHLY TRACES OUT A BROAD REGION OF
PRECIPITATION. THEREFORE, IT IS REASONED THAT THE BEST CHANCE FOR A SURFACE LOW
TO DEVELOP IS AT THE END OF THIS FRONT IN SOUTH-CENTRAL CANADA. ALL THREE
ENSEMBLE MEAN SOLUTIONS PREDICT AT LEAST 0.5-INCH OF PRECIPITATION FOR MOST
AREAS EAST OF THE ROCKIES, HIGHLIGHTING A VERY BROAD REGION OF LOW-LEVEL GULF
INFLOW. HOWEVER, THE 1-INCH MINIMUM THRESHOLD USED FOR HAZARDOUS PRECIPITATION
IS REACHED WELL TO THE NORTH, NEAR THE BAROCLINIC ZONE DESCRIBED EARLIER.
THEREFORE A SLIGHT RISK OF HEAVY PRECIPITATION IS DESIGNATED FOR THE UPPER AND
MIDDLE MISSISSIPPI VALLEY, WESTERN GREAT LAKES REGION, AND PARTS OF THE LOWER
OHIO VALLEY, JUN 28-30. THIS IS ALSO CONSISTENT WITH WIDESPREAD ASCENDING
MOTION ASSOCIATED WITH AN APPROACHING MID-LEVEL TROUGH THAT WEAKENS RAPIDLY
OVER THE NEXT FEW DAYS. SCATTERED AREAS OF FLOODING ARE POSSIBLE IN THE
VICINITY OF THE FRONT IN CONJUNCTION WITH THE HEAVIER RAINFALL, BUT CHANCES ARE
NOT HIGH ENOUGH TO JUSTIFY A SPECIFIC AREA AT RISK OF BROAD-SCALE FLOODING.
ELSEWHERE, AN INCH OF PRECIPITATION IS INDICATED BY THE PET GUIDANCE ACROSS THE
FLORIDA PENINSULA, THOUGH IT IS PREDICTED TO FALL OVER A 7-DAY PERIOD, NOT A
3-DAY PERIOD AS IS REQUIRED FOR HAZARDOUS DESIGNATION.
NO HAZARDS ARE POSTED OVER ALASKA, BUT THERE IS THE POTENTIAL FOR INCREASED
THUNDERSTORM ACTIVITY AND ASSOCIATED LIGHTNING THAT COULD TRIGGER WILDFIRES.
FORECASTER: ANTHONY ARTUSA
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