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FXUS21 KWNC 191841
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT JULY 19 2024
SYNOPSIS: AN EASTWARD SHIFTING AREA OF STRONG MID-LEVEL HIGH PRESSURE DURING
WEEK-2 LEADS TO AN INCREASED RISK FOR EXCESSIVE HEAT OVER PARTS OF THE
NORTH-CENTRAL AND NORTHEASTERN CONTIGUOUS U.S. (CONUS) LATER IN JULY. WITH
HOTTER AND DRIER THAN NORMAL CONDITIONS PREDOMINATELY FAVORED OVER THE INTERIOR
WEST AND GREAT PLAINS, AN EXPANDED RAPID ONSET DROUGHT (ROD) RISK AREA IS
ISSUED FOR PARTS OF THE NORTHERN AND CENTRAL PLAINS WHERE POOR SOIL MOISTURES
AND BELOW-NORMAL RAINFALL AMOUNTS HAVE BEEN REGISTERED.
HAZARDS
MODERATE RISK OF EXCESSIVE HEAT FOR PARTS OF THE NORTHERN PLAINS AND UPPER
MISSISSIPPI VALLEY, SAT-SUN, JUL 27-28.
MODERATE RISK OF EXCESSIVE HEAT FOR PARTS OF THE NORTHERN GREAT LAKES AND THE
NORTHEAST, SUN-TUE, JUL 28-30.
SLIGHT RISK OF EXCESSIVE HEAT FOR PARTS OF THE NORTHERN ROCKIES, NORTHERN AND
CENTRAL PLAINS, UPPER MISSISSIPPI VALLEY, GREAT LAKES, OHIO VALLEY,
MID-ATLANTIC, AND THE NORTHEAST, SAT-FRI, JUL 27-AUG 2.
SLIGHT RISK OF EPISODIC HIGH WINDS FOR MUCH OF THE WESTERN CONUS, SAT-MON, JUL
27-29.
RAPID ONSET DROUGHT RISK FOR PORTIONS OF THE NORTHERN AND CENTRAL PLAINS.
DETAILED SUMMARY
FOR MONDAY JULY 22 - FRIDAY JULY 26:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR SATURDAY JULY 27 - FRIDAY AUGUST 02: BY LATE NEXT WEEK AND INTO THE
FOLLOWING WEEKEND, 500-HPA HEIGHT FORECASTS FROM THE GEFS AND ECMWF ENSEMBLES
CONTINUE TO FEATURE AN AMPLIFYING TROUGH OVER WESTERN CANADA AND THE WEST
COAST, AND AN EASTWARD PROGRESSION OF A STRONG RIDGE CENTER WITH POSITIVE
HEIGHT DEPARTURES OVERSPREADING MUCH OF SOUTHERN CANADA AND THE NORTHEASTERN
CONUS. LATER IN WEEK-2, DYNAMICAL MODELS GENERALLY AGREE ON THE MID-LEVEL
PATTERN EVOLUTION OVER EASTERN NORTH AMERICA, FAVORING THE CONTINUATION OF THE
ANOMALOUS RIDGING (ALBEIT SOME DIFFERENCES IN STRENGTH) OVER THE CANADIAN
MARITIMES WITH MORE SUBTROPICAL RIDGING DEVELOPING IN THE SOUTHEAST, BUT
DIVERGE IN REGARDS TO THE EVOLUTION OF TROUGHING UPSTREAM OVER THE WEST. THE
GEFS MAINTAINS A MORE PERSISTENT SOLUTION OF THE TROUGH, WHEREAS THE ECMWF IS
QUICK TO BUILD MORE RIDGING BACK IN OVER THE FOUR CORNERS. GIVEN THIS, OUTLOOK
CONFIDENCE IS HIGHER EAST OF THE ROCKIES, FAVORING WARMING TEMPERATURES AND THE
POTENTIAL FOR EXCESSIVE HEAT ACROSS THE NORTHERN TIER OF THE CONUS, WITH THE
HAZARDS PICTURE BECOMING LESS CLEAR OUT WEST THROUGH THE END OF JULY AND
HEADING INTO AUGUST.
TIED TO THE AMPLIFYING TROUGH AND THE ASSOCIATED NORTHWESTERLY FLOW TO BRING
COOLER TEMPERATURES OVER PARTS OF THE WESTERN CONUS LATE NEXT WEEK, THE SLIGHT
RISK OF EXCESSIVE HEAT IS DISCONTINUED IN TODAY'S OUTLOOK AS THE PREDICTED HEAT
EVENT OVER THE WEST NOW APPEARS TO BE LARGELY WITHIN THE WEEK-1 TIMEFRAME. BUT
IN RESPONSE TO THE ENHANCED SOUTHWESTERLY FLOW UPSTREAM OF THE AMPLIFIED RIDGE
CENTER TO THE SOUTH OF HUDSON BAY, THERE CONTINUES TO BE INCREASED ODDS FOR
ABOVE-NORMAL TEMPERATURES MAINLY OVER THE NORTH-CENTRAL CONUS EARLY IN THE
PERIOD. GOOD AGREEMENT EXISTS BETWEEN THE GEFS AND ECMWF PROBABILISTIC EXTREMES
TOOLS (PETS) SHOWING ELEVATED CHANCES (30-40%) FOR MAXIMUM TEMPERATURES
EXCEEDING THE 85TH PERCENTILE TO SUPPORT THE CONTINUATION OF THE MODERATE RISK
OF EXCESSIVE HEAT OVER THE NORTHERN HIGH PLAINS AND UPPER MISSISSIPPI VALLEY
THROUGH DAY 9 (JUL 28).
AS THE TROUGHING OVER THE NORTHWESTERN CONUS WEAKENS, AND THE ANOMALOUS RIDGE
CENTER SHIFTS EASTWARD INTO SOUTHEASTERN CANADA TOWARDS THE MIDDLE OF WEEK-2,
PETS SHOW AN EXPANSION OF THE HEAT SIGNALS INTO PORTIONS OF THE GREAT LAKES,
OHIO VALLEY, MID-ATLANTIC AND THE NORTHEAST. GIVEN INCREASED SUPPORT IN THE RAW
TEMPERATURE TOOLS AND THE BETTER AGREEMENT IN THE PETS DEPICTING 30-50% CHANCES
FOR MAXIMUM TEMPERATURES EXCEEDING THE 85TH PERCENTILE, A MODERATE RISK OF
EXCESSIVE HEAT IS ISSUED FOR THE REGION FROM JUL 28-30. A BROAD SLIGHT RISK OF
EXCESSIVE HEAT REMAINS ISSUED ALONG THE NORTHERN TIER OF THE CONUS, EAST OF THE
ROCKIES, IN PROXIMITY TO THE PREVAILING POSITIVE HEIGHT ANOMALIES OVER SOUTHERN
CANADA AND REMAINS VALID FOR ALL OF WEEK-2. OF NOTE, THE GEFS PET CONTINUES TO
FAVOR INCREASED CHANCES FOR EXCESSIVE HEAT FURTHER SOUTH INTO THE MIDDLE
MISSISSIPPI, OHIO AND TENNESSEE VALLEYS TOWARDS THE MIDDLE OF WEEK-2, HOWEVER
THE ECMWF PET, AS WELL AS RAW TEMPERATURE TOOLS ARE LESS SUPPORTIVE OF THIS
REALIZATION. EXCESSIVE HEAT CONDITIONS MAY BE FELT ACROSS PARTS OF THE CORN
BELT AND LOWER GREAT LAKES AS THE HEAT SIGNALS BEGIN TO SHIFT SOUTH, BUT THERE
REMAINS UNCERTAINTY AS TO HOW LONG THE COLDER AIR ESTABLISHED OVER THE CENTRAL
U.S. EARLY IN WEEK-2 TAKES TO MODERATE. THERE ARE ALSO QUESTIONS AS TO
RELIABILITY AND BIAS OF THE GEFS PET IN THIS PART OF THE COUNTRY DURING THE
WARM SEASON.
THE COMBINATION OF CONTINUED ABOVE-NORMAL TEMPERATURES AND BELOW-NORMAL
PRECIPITATION SUPPORTS THE CONTINUATION OF A RAPID ONSET DROUGHT (ROD) RISK
OVER MANY PARTS OF THE NORTHERN AND CENTRAL HIGH PLAINS. DRY SOILS, STRESSED
VEGETATION, AND REDUCED WATER AVAILABILITY DUE TO LOW PONDS AND STREAMS MAY
LEAD TO INCREASED IMPACTS TO AGRICULTURE AND LIVESTOCK, WITH SEVERAL LOCATIONS
ALREADY EXPERIENCING IMPACTS.
LEE SIDE SURFACE TROUGHING REMAINS FAVORED OVER THE NORTHERN AND CENTRAL PLAINS
WHERE ENSEMBLES CONTINUE TO SHOW PERIODS OF STRENGTHENING PRESSURE GRADIENTS IN
THE REGION, AS WELL AS FURTHER SOUTH IN THE DESERT SOUTHWEST. BASED ON
CONTINUED SUPPORT FROM THE ECMWF PET FAVORING INCREASED CHANCES FOR WIND SPEEDS
EXCEEDING THE 85TH PERCENTILE, A SLIGHT RISK OF HIGH WINDS REMAINS ISSUED FOR
JUL 27-29 BEFORE THE PATTERN DEAMPLIFIES OVER THE WESTERN CONUS. HOT, DRY AND
WINDY CONDITIONS ARE LIKELY TO LEAD TO ENHANCED RISK OF WILDFIRES IN THE
HIGHLIGHTED REGION, AND INHIBIT EFFORTS TO CONTAIN ANY ACTIVE WILDFIRES.
FOR PRECIPITATION, THE THREAT OF HEAVY RAINFALL LOOKS TO HAVE TIMED OFF OVER
THE LOWER PLAINS AND MISSISSIPPI VALLEY, WITH MUCH OF THE TROUGHING FAVORED TO
LIFT OUT LATE NEXT WEEK, AND MORE SUBTROPICAL RIDGING OVERSPREADING THE
SOUTHEAST FROM THE WESTERN ATLANTIC. WHILE THERE CONTINUES TO BE MODEST SUPPORT
IN THE PETS FOR 3-DAY AMOUNTS EXCEEDING THE 85TH PERCENTILE EARLY IN WEEK-2,
RAW PRECIPITATION AMOUNTS FROM THE ENSEMBLES HAVE BECOME TENUOUS, AND THE
SLIGHT RISK OF HEAVY PRECIPITATION IS REMOVED IN THE UPDATED OUTLOOK. IT SHOULD
BE NOTED HOWEVER, THAT ABOVE-NORMAL PRECIPITATION PREDOMINATELY FAVORED IN THE
NEXT TWO WEEKS OVER PORTIONS OF SOUTHERN TEXAS AND THE EASTERN CAROLINAS MAY
LEAD TO LOCALIZED FLOODING IN THESE REGIONS DURING THE PERIOD.
OVER ALASKA, A HIGHLY AMPLIFIED TROUGH/RIDGE COUPLET IS FAVORED OVER THE BERING
SEA AND NORTHERN PACIFIC DURING WEEK-2. THE RESULTANT ENHANCED ONSHORE FLOW IS
EXPECTED TO LEAD TO PERIODS OF ELEVATED WIND SPEEDS AND ENHANCED PRECIPITATION
OVER PARTS OF THE MAINLAND, HOWEVER, PETS SHOW NEITHER WIND NOR PRECIPITATION
AMOUNTS EXCEEDING HAZARD THRESHOLDS, AND NO CORRESPONDING HAZARDS ARE ISSUED.
LOCALIZED FLOODING MAY BE A CONCERN ASSOCIATED WITH THE GLACIAL OUTBURST FLOOD
FOR THE MENDENHALL RIVER.
FORECASTER: NICK NOVELLA
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