031
FXUS21 KWNC 181822
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT JULY 18 2024
SYNOPSIS: AN EASTWARD SHIFTING AREA OF MID-LEVEL HIGH PRESSURE DURING WEEK-2 IS
EXPECTED TO SUSTAIN AN INCREASED RISK FOR EXCESSIVE HEAT OVER MANY PARTS OF THE
WESTERN CONTIGUOUS U.S. (CONUS) EARLY IN THE PERIOD, WITH INCREASING CHANCES
FOR HEAT ACROSS THE NORTHERN GREAT PLAINS AND EXPANDING OVER THE NORTHERN TIER
OF THE CONUS LATER IN JULY. MID-LEVEL LOW PRESSURE FOCUSED OVER THE LOWER
PLAINS AND MISSISSIPPI VALLEY IS LIKELY TO PROMOTE COOLER AND WETTER CONDITIONS
EARLY IN WEEK-2, WITH INCREASED CHANCES FOR HEAVY PRECIPITATION IN THE SOUTHERN
PLAINS AND LOWER MISSISSIPPI VALLEY. WITH HOTTER AND DRIER THAN NORMAL
CONDITIONS PREDOMINATELY FAVORED, AN EXPANDED RAPID ONSET DROUGHT (ROD) RISK
AREA IS ISSUED FOR PARTS OF THE NORTHERN AND CENTRAL PLAINS.
HAZARDS
MODERATE RISK OF EXCESSIVE HEAT FOR PARTS OF THE NORTHERN PLAINS AND UPPER
MISSISSIPPI VALLEY, FRI-SUN, JUL 26-28.
SLIGHT RISK OF EXCESSIVE HEAT FOR PARTS OF CALIFORNIA, DESERT SOUTHWEST, GREAT
BASIN, ROCKIES AND NORTHERN INTERMOUNTAIN, FRI, JUL 26.
SLIGHT RISK OF EXCESSIVE HEAT FOR PARTS OF THE NORTHERN ROCKIES, NORTHERN AND
CENTRAL PLAINS, UPPER MISSISSIPPI VALLEY, GREAT LAKES, AND THE NORTHEAST,
FRI-THU, JUL 26-AUG 1.
SLIGHT RISK OF EPISODIC HIGH WINDS FOR MUCH OF THE WESTERN CONUS, FRI-SUN, JUL
26-28.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PARTS OF THE SOUTHERN PLAINS, LOWER
MISSISSIPPI AND TENNESSEE VALLEYS, AND THE SOUTHEAST, FRI-SAT, JUL 26-27.
RAPID ONSET DROUGHT RISK FOR PORTIONS OF THE NORTHERN AND CENTRAL PLAINS.
DETAILED SUMMARY
FOR SUNDAY JULY 21 - THURSDAY JULY 25:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR FRIDAY JULY 26 - THURSDAY AUGUST 01: DYNAMICAL MODEL GUIDANCE APPEARS TO
REMAIN ON TRACK OVER THE PAST FEW DAYS. BOTH THE GEFS AND ECMWF CONTINUE TO
FAVOR A WEAKENING 500-HPA RIDGE OVER THE WESTERN CONUS WITH COOLING
TEMPERATURES TO ALLEVIATE THE EXCESSIVE HEAT RISK OVER MANY PARTS OF WEST FOR
LATE NEXT WEEK. ANOMALOUS MID-LEVEL TROUGHING DEVELOPING OVER WESTERN CANADA
AND INTO THE WEST COAST IS EXPECTED TO LEAD TO EASTWARD PROGRESSION OF THE
AMPLIFIED RIDGE CENTER TO THE SOUTH OF HUDSON BAY WHERE THERE IS BETTER
AGREEMENT BETWEEN THE GEFS AND ECMWF ENSEMBLES IN THE TIMING, LOCATION, AND
STRENGTH OF THIS MID-LEVEL FEATURE. AS A RESULT, THERE IS ADDED CONFIDENCE FOR
ABOVE-NORMAL TEMPERATURES TO OVERSPREAD THE NORTHERN TIER, AND INTO PARTS OF
THE EASTERN CONUS LATER IN JULY, WITH A RENEWED RISK OF EXCESSIVE HEAT FOR
PARTS OF THE GREAT PLAINS AND UPPER MIDWEST. ACROSS THE SOUTHERN TIER OF THE
U.S., MUCH OF THE TROUGHING THAT IS FAVORED TO LINGER OVER THE LOWER PLAINS AND
MISSISSIPPI VALLEY DURING WEEK-1 LOOKS TO BE FINALLY LIFTING OUT LATE NEXT
WEEK, BUT NOT BEFORE ANOTHER ROUND OF POTENTIALLY HEAVY PRECIPITATION COULD BE
FELT OVER PARTS OF THE PLAINS, MISSISSIPPI AND TENNESSEE VALLEYS EARLY IN THE
PERIOD.
A SLIGHT RISK OF EXCESSIVE HEAT REMAINS POSTED FOR PARTS OF CALIFORNIA AND THE
INTERIOR WEST FOR DAY 8 (JUL 26), WHERE THERE ARE RESIDUAL HEAT SIGNALS IN THE
PROBABILISTIC EXTREMES TOOLS (PETS) TIED TO THE WEAKENING RIDGE ALOFT. MUCH OF
THE SLIGHT RISK COVERAGE HAS BEEN WITHDRAWN OVER THE NORTHERN INTERMOUNTAIN
REGION IN THE UPDATED OUTLOOK DUE TO THE ENCROACHING MID-LEVEL TROUGH FAVORED
OVER THE NORTHWESTERN CONUS. ACROSS THE NORTHERN TIER OF THE CONUS, THERE IS
BETTER AGREEMENT BETWEEN THE GEFS AND ECMWF PETS DEPICTING AN EXPANSIVE AREA
WITH AT LEAST 20% CHANCES OF MAXIMUM TEMPERATURES EXCEEDING THE 85TH
PERCENTILE. HIGHER PROBABILITIES (30-40%) ARE INDICATED ACROSS NORTHERN PARTS
OF EASTERN MONTANA, NORTH DAKOTA, AND MINNESOTA AND WHILE CHANCES FOR ACTUAL
TEMPERATURES EXCEEDING 95 DEG F APPEAR RATHER WEAK IN THE PETS, RAW TEMPERATURE
TOOLS ARE MORE ROBUST IN EXCEEDING THIS THRESHOLD, WITH THE POTENTIAL FOR
ENHANCED HEAT INDEX VALUES. THEREFORE, A MODERATE RISK OF EXCESSIVE HEAT IS
ADDED FOR THE REGION (JUL 26-28) AND A BROADER SLIGHT RISK AREA FOR EXCESSIVE
HEAT IS CONTINUED FOR JUL 27-AUG 1. THE SLIGHT RISK AREA IS EXPANDED EASTWARD
TO INCLUDE NORTHERN PORTIONS OF THE GREAT LAKES, AND THE NORTHEAST, WHERE PETS
SHOW BUILDING WARM SIGNALS LATER IN THE PERIOD IN PROXIMITY TO THE AMPLIFIED
RIDGING OVER SOUTHERN CANADA. 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, THOUGH THE ECMWF PET
AS WELL AS RAW TEMPERATURE TOOLS ARE MUCH LESS SUPPORTIVE OF THIS REALIZATION,
AS MUCH OF THE COLDER AIR ESTABLISHED OVER THE CENTRAL U.S. EARLY IN WEEK-2 MAY
TAKE SOME TIME TO MIX OUT.
THE COMBINATION OF CONTINUED ABOVE-NORMAL TEMPERATURES AND BELOW-NORMAL
PRECIPITATION SUPPORTS THE CONTINUATION OF A RAPID ONSET DROUGHT (ROD) RISK
OVER PARTS OF EASTERN MONTANA, WYOMING AND THE DAKOTAS. BASED ON SOIL MOISTURE
TRENDS, RAINFALL REGISTERED DURING THE PAST MONTH AND IN THE NEXT TWO WEEKS,
THE ROD RISK HAS BEEN EXPANDED TO INCLUDE PARTS OF THE WESTERN DAKOTAS,
NEBRASKA, NORTHEASTERN COLORADO AND KANSAS IN THE UPDATED OUTLOOK. 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.
AT THE BASE OF THE TROUGHING ALOFT OVER THE NORTHWESTERN CONUS, LEE SIDE
SURFACE TROUGHING IS 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 26-28
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.
WITH MUCH OF THE TROUGHING FAVORED TO LIFT OUT OVER THE LOWER PLAINS AND
MISSISSIPPI VALLEY, RAW TOOLS HAVE BEGUN TO BACK OFF ON THE CONTINUED
ENHANCEMENT OF DAILY PRECIPITATION AMOUNTS. NOTWITHSTANDING, RETURN FLOW FROM
THE GULF OF MEXICO AND A STALLED FRONTAL BOUNDARY THAT IS EXPECTED TO LINGER
LATE NEXT WEEK SUSTAINS A HEAVY PRECIPITATION RISK EARLY IN WEEK-2. THERE
REMAINS GOOD AGREEMENT IN THE PETS SHOWING INCREASED CHANCES FOR 3-DAY AMOUNTS
EXCEEDING THE 85TH PERCENTILE, AND A CORRESPONDING SLIGHT RISK REMAINS POSTED
FOR JUL 26-27. A KEY CHANGE IN THE PETS IS THE REDUCTION OF THE WET SIGNALS
OVER THE EASTERN U.S., AND THE SLIGHT RISK COVERAGE IS REMOVED OVER THIS PART
OF THE COUNTRY. AS A RESULT OF THE REDUCED POTENTIAL FOR HEAVY PRECIPITATION
FURTHER EAST, AS WELL AS A LOWERED RISK IN OWPS LATEST EXPERIMENTAL FLOOD
HAZARD OUTLOOK, THE POSSIBLE FLOODING IS LIKEWISE REMOVED OVER THE EASTERN
CAROLINAS AND SOUTHEASTERN VIRGINIA IN THE UPDATED OUTLOOK. IT SHOULD BE NOTED
HOWEVER, THAT ABOVE-NORMAL PRECIPITATION PREDOMINATELY FAVORED DURING WEEK-2
MAY STILL LEAD TO LOCALIZED FLOODING IN THE REGION.
FORECASTER: NICK NOVELLA
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page