121
FXUS21 KWNC 201915
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT JUNE 20 2024
SYNOPSIS: EARLY IN WEEK-2, AREAS OF MID-LEVEL LOW PRESSURE ARE FORECAST ACROSS
THE NORTHEASTERN AND WESTERN CONTIGUOUS U.S. (CONUS). BOTH OF THESE FEATURES
ARE PREDICTED TO WEAKEN, WITH BROAD MID-LEVEL HIGH PRESSURE EXPANDING ACROSS
THE CONUS LATER IN THE PERIOD. THE RISK OF EXCESSIVE HEAT IS LIKELY TO REMAIN
ELEVATED FOR MANY AREAS OF THE LOWER 48 STATES THROUGH THE BEGINNING OF JULY.
FREQUENT PERIODS OF THUNDERSTORMS WITH LOCALLY HEAVY RAINFALL AND AN INCREASED
RISK OF FLASH FLOODING ARE EXPECTED TO PERSIST FOR THE UPPER MISSISSIPPI
VALLEY. THE SOUTHWEST MONSOON IS FORECAST TO BECOME MORE ACTIVE, LEADING TO
INCREASING CHANCES OF LOCALLY HEAVY RAINFALL AND FLOODING ACROSS PARTS OF THE
SOUTHWESTERN U.S.
HAZARDS
SLIGHT RISK OF EXCESSIVE HEAT FOR PORTIONS OF THE EASTERN AND CENTRAL U.S.,
FRI-THU, JUN 28-JUL 4.
SLIGHT RISK OF EXCESSIVE HEAT FOR PORTIONS OF THE GREAT BASIN, ROCKIES,
SOUTHWEST, AND CALIFORNIA CENTRAL VALLEY, MON-THU, JUL 1-4.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE NORTHERN PLAINS, UPPER
MISSISSIPPI VALLEY, AND GREAT LAKES, FRI-THU, JUN 28-JUL 4.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PARTS OF THE SOUTHWEST AND SOUTHERN
ROCKIES, FRI-THU, JUN 28-JUL 4.
FLOODING POSSIBLE FOR PORTIONS OF THE NORTHERN PLAINS AND UPPER MISSISSIPPI
VALLEY.
FLOODING POSSIBLE FOR PORTIONS OF SOUTHERN ARIZONA AND NEW MEXICO.
RAPID ONSET DROUGHT RISK EXTENDING FROM NEW JERSEY AND PENNSYLVANIA SOUTHWARD
THROUGH NORTHERN GEORGIA.
RAPID ONSET DROUGHT RISK ACROSS THE EASTERN CORN BELT.
RAPID ONSET DROUGHT RISK ACROSS NORTHERN OKLAHOMA AND ADJACENT AREAS.
DETAILED SUMMARY
FOR SUNDAY JUNE 23 - THURSDAY JUNE 27:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR FRIDAY JUNE 28 - THURSDAY JULY 04: LATE IN WEEK-1 AND INTO THE OUTSET OF
WEEK-2, MID-LEVEL TROUGHING IS FORECAST TO MOVE ACROSS THE GREAT LAKES AND
NORTHEAST USHERING IN A REPRIEVE FROM THE ONGOING EXCESSIVE HEAT. HOWEVER, THIS
BREAK IS PREDICTED TO BE SHORT-LIVED AS THE 0Z GEFS, ECENS, AND CMCE QUICKLY
REBUILD RIDGING ACROSS MUCH OF THE CENTRAL AND EASTERN CONUS BY THE MIDDLE OF
THE PERIOD. MAXIMUM TEMPERATURES IN THE UNCALIBRATED 0Z GEFS ARE GENERALLY ON
THE COOLER SIDE ACROSS THE OHIO VALLEY AND MID-ATLANTIC AT THE START OF THE
PERIOD, TIED TO THE AFOREMENTIONED TROUGHING, WITH MANY AREAS REMAINING IN THE
80S DEG F. THE 0Z ECENS IS NOTABLY A FEW DEGREES WARMER, AND THE CORRESPONDING
PROBABILISTIC EXTREMES TOOL (PET) DEPICTS AT LEAST A 40 PERCENT CHANCE MAXIMUM
TEMPERATURES EXCEED THE 85TH CLIMATOLOGICAL PERCENTILE AND 90 DEG F ACROSS
PARTS OF THE MIDWEST ON DAYS 9 AND 10 (JUN 29-30). BY THE END OF THE PERIOD,
THE 0Z ECENS AND CMCE HAVE AN EXPANSIVE 595-DAM RIDGE CENTERED OVER THE
SOUTHERN CONUS WITH POSITIVE 500-HPA HEIGHT ANOMALIES ACROSS THE ENTIRE CONUS,
WHICH IS AN IDEAL SYNOPTIC SET-UP FOR WIDESPREAD EXCESSIVE HEAT IN EARLY JULY.
A SLIGHT RISK FOR EXCESSIVE HEAT IS POSTED ACROSS PORTIONS OF THE EASTERN AND
CENTRAL CONUS FOR ALL OF WEEK-2. INCREASING HEAT LATER IN WEEK-2 MAY
NECESSITATE THE NEED FOR A MODERATE RISK, PARTICULARLY OVER THE MIDDLE
MISSISSIPPI AND OHIO VALLEYS AND MID-ATLANTIC WHERE HEAT INDICES MAY EXCEED 105
DEG F, BUT WOULD LIKE TO SEE BETTER MODEL AGREEMENT GIVEN THE RELATIVELY COOLER
TEMPERATURES IN THE GEFS. HEAT IS ALSO FORECAST TO INCREASE ACROSS THE INTERIOR
WEST AND CALIFORNIA CENTRAL VALLEY AS THE RIDGE BROADENS LATER IN WEEK-2 AND
TROUGHING EARLY IN THE PERIOD LIFTS OUT ACROSS CENTRAL CANADA. THE GEFS AND
ECENS PETS DEPICT EXPANDING COVERAGE OF PROBABILITIES OF AT LEAST 20 PERCENT
FOR MAXIMUM TEMPERATURES EXCEEDING THE 85TH CLIMATOLOGICAL PERCENTILES ACROSS
THESE REGIONS BEGINNING AROUND THE MIDDLE OF THE PERIOD RESULTING IN A SLIGHT
RISK FOR EXCESSIVE HEAT JUL 1-4. ACTUAL TEMPERATURES RANGE FROM THE 90S DEG F
ACROSS THE NORTHERN GREAT BASIN AND ROCKIES TO TRIPLE DIGITS OVER THE
CALIFORNIA CENTRAL VALLEY AND SOUTHWEST. INCREASING MONSOON MOISTURE MAY HELP
LIMIT TEMPERATURES ACROSS PARTS OF THE SOUTHWEST AND FOUR CORNERS.
THE GEFS AND ECMWF ENSEMBLES DEPICT MULTIPLE SHORTWAVE 500-HPA TROUGHS
PROGRESSING EAST FROM THE WESTERN TO THE NORTH-CENTRAL CONUS OVERTOP THE
EXPANDING MID-LEVEL RIDGE. THIS LONGWAVE PATTERN ALONG WITH UNCALIBRATED
24-HOUR PRECIPITATION AMOUNTS FROM THE GEFS AND ECENS SUPPORT A SLIGHT RISK OF
HEAVY PRECIPITATION ACROSS THE NORTHERN PLAINS, UPPER MISSISSIPPI VALLEY, AND
GREAT LAKES THROUGH THE END OF WEEK-2. THUNDERSTORMS COULD TRIGGER FLASH
FLOODING. IN ADDITION, MINOR TO MODERATE RIVER FLOODING IS EXPECTED TO PERSIST
INTO THE BEGINNING OF JULY, ESPECIALLY ACROSS SOUTHERN MINNESOTA.
THE WESTWARD-EXPANDING RIDGE FAVORS THE START OF THE SOUTHWEST MONSOON, WITH
DEWPOINTS INCREASING INTO THE 60S DEG F ACROSS THE REGION IN SEVERAL RECENT
RUNS OF THE DETERMINISTIC GFS. THIS IS ALSO AIDED BY INCREASING SOUTHEASTERLY
MOIST FLOW RELATED TO TROPICAL STORM ALBERTO AND POTENTIALLY ANOTHER TROPICAL
DISTURBANCE LATER IN WEEK-1. BOTH THE ECENS AND GEFS PETS DEPICT AT LEAST A 20
PERCENT CHANCE THAT 3-DAY RAINFALL TOTALS EXCEED A HALF-INCH ACROSS PARTS OF
THE SOUTHWEST AND SOUTHERN ROCKIES, WITH THE ECENS BEING THE MOST ROBUST,
BRINGING THESE INCREASED CHANCES THROUGH MUCH OF ARIZONA LATER IN THE PERIOD,
AND ALSO HAVING AT LEAST A 20 PERCENT CHANCE 3-DAY RAINFALL EXCEEDS 1-INCH
ACROSS EXTREME SOUTHERN ARIZONA. THIS IS ALSO SUPPORTED BY THE UNCALIBRATED
TOOLS WHICH DEPICT EXPANDING COVERAGE OF WEEK-2 RAINFALL TOTALS OF GREATER THAN
A HALF-INCH INTO PARTS OF ARIZONA AND NEW MEXICO. GIVEN THIS SUPPORT, A SLIGHT
RISK FOR HEAVY PRECIPITATION IS HIGHLIGHTED ACROSS PORTIONS OF THE SOUTHWEST
AND SOUTHERN ROCKIES FOR ALL OF WEEK-2, WITH A FLOODING POSSIBLE AREA COVERING
SOUTHERN PARTS OF ARIZONA AND NEW MEXICO WHERE THE STRONGER PRECIPITATION
SIGNALS ARE DEPICTED. PRECIPITATION IS EXPECTED TO BE ISOLATED AND NOT ALL
LOCATIONS WILL EXPERIENCE HEAVY RAINFALL. HOWEVER, FLASH FLOODING IS POSSIBLE
BOTH WHERE PRECIPITATION OCCURS AND IN DOWNSTREAM VALLEYS, PARTICULARLY IN AND
AROUND BURN SCARS WHERE DEBRIS FLOWS CAN BE TRIGGERED BY HEAVY RAINFALL.
RAPID ONSET DROUGHT (ROD) RISK EXTENDS FROM A REGION INCLUDING NEW JERSEY AND
PENNSYLVANIA SOUTHWARD THROUGH NORTHERN GEORGIA, AS WELL AS PORTIONS OF THE
EASTERN CORN BELT AND NORTHERN OKLAHOMA. THESE AREAS ARE MOST VULNERABLE TO THE
RAPID ONSET OF DROUGHT DUE TO: 30-DAY PRECIPITATION DEFICITS OF 2 TO 4 INCHES,
LOW SOIL MOISTURE, AND ABOVE-NORMAL TEMPERATURES WITH HIGH EVAPOTRANSPIRATION
RATES FORECAST DURING THE NEXT TWO WEEKS.
FORECASTER: THOMAS COLLOW
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