232
FXUS21 KWNC 121825
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT JULY 12 2024
SYNOPSIS: MODELS CONTINUE TO TREND TOWARD A GREATER AMPLIFICATION OF MID-LEVEL
HIGH PRESSURE ACROSS THE WESTERN CONTIGUOUS U.S. DURING THE WEEK-2 PERIOD. THIS
FAVORS INCREASING CHANCES OF ANOTHER PROLONGED STRETCH OF EXCESSIVE HEAT
COINCIDING WITH THE CLIMATOLOGICAL PEAK IN TEMPERATURES. WHILE EXCESSIVE HEAT
CHANCES ARE FORECAST TO DIMINISH IN THE EAST, A STALLED FRONT IS LIKELY TO
BRING PERIODS OF HEAVY PRECIPITATION TO PARTS OF THE SOUTHERN MID-ATLANTIC AND
SOUTHEAST. SOUTHERLY MOIST FLOW INTO THE SOUTHWEST RESULTS IN INCREASED CHANCES
FOR LOCALIZED PERIODS OF HEAVY PRECIPITATION ACROSS THE SOUTHWEST AND CENTRAL
AND SOUTHERN ROCKIES. PERIODS OF POTENTIALLY HIGH WINDS ACROSS THE CASCADES,
SOUTHWESTERN OREGON, AND CENTRAL AND NORTHERN CALIFORNIA MAY INCREASE THE RISK
FOR WILDFIRES IN THE AREA.
HAZARDS
HIGH RISK OF EXCESSIVE HEAT ACROSS PORTIONS OF THE GREAT BASIN, NORTHERN
ROCKIES, AND NORTHERN HIGH PLAINS, SAT-MON, JUL 20-22.
MODERATE RISK OF EXCESSIVE HEAT ACROSS PORTIONS OF THE INTERIOR PACIFIC
NORTHWEST, GREAT BASIN, CALIFORNIA, DESERT SOUTHWEST, ROCKIES, AND NORTHERN AND
CENTRAL HIGH PLAINS, SAT-WED, JUL 20-24.
SLIGHT RISK OF EXCESSIVE HEAT ACROSS MUCH OF THE WESTERN CONUS AND HIGH PLAINS,
SAT-FRI, JUL 20-26.
MODERATE RISK OF HEAVY PRECIPITATION ACROSS SOUTHEASTERN VIRGINIA AND THE
CAROLINAS, SAT-SUN, JUL 20-21.
SLIGHT RISK OF HEAVY PRECIPITATION ACROSS PORTIONS OF THE SOUTHERN
MID-ATLANTIC, SOUTHERN APPALACHIANS, SOUTHEAST, AND TENNESSEE VALLEY, SAT-TUE,
JUL 20-23.
SLIGHT RISK OF PERIODS OF HEAVY PRECIPITATION FOR PORTIONS OF THE SOUTHWEST AND
CENTRAL AND SOUTHERN ROCKIES, SAT-FRI, JUL 20-26.
SLIGHT RISK OF EPISODIC HIGH WINDS FOR PORTIONS OF CALIFORNIA AND THE PACIFIC
NORTHWEST, SAT-MON, JUL 20-22.
RAPID ONSET DROUGHT RISK FOR PORTIONS OF THE OHIO, TENNESSEE, AND LOWER
MISSISSIPPI VALLEYS, AND NORTHERN PLAINS.
DETAILED SUMMARY
FOR MONDAY JULY 15 - FRIDAY JULY 19:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR SATURDAY JULY 20 - FRIDAY JULY 26: AT THE OUTSET OF THE PERIOD, AN
AMPLIFIED MID-LEVEL RIDGE IS FORECAST TO BE CENTERED ACROSS THE FOUR CORNERS
WITH RECENT DETERMINISTIC GFS AND ECMWF RUNS INDICATING A 597-600 DM HEIGHT
MAXIMA. THIS FAVORS ANOMALOUSLY WARM TEMPERATURES ALONG WITH EXCESSIVE HEAT
CONDITIONS ACROSS MUCH OF THE WEST. FOR NORTHERN AREAS, PROBABILITIES FOR
MAXIMUM TEMPERATURES EXCEEDING THE 85TH CLIMATOLOGICAL PERCENTILE RANGE FROM
40-60 PERCENT IN THE GEFS PROBABILISTIC EXTREMES TOOL (PET) AND 30-50 PERCENT
IN THE ECENS PET, WITH DIMINISHING PROBABILITIES FURTHER SOUTH ACROSS
CALIFORNIA AND THE SOUTHWEST. HOWEVER, THE SYNOPTIC PATTERN, COMBINED WITH THE
CLIMATOLOGICAL HOTTEST TIME OF YEAR IS CONCERNING. UNCALIBRATED TEMPERATURES IN
THE 0Z GEFS AND ECENS ARE CLOSE TO OR EXCEED 100 DEG F ACROSS NORTHERN PORTIONS
OF THE INTERMOUNTAIN REGION AND HIGH PLAINS. ADDITIONALLY, THE CALIBRATED
ECENS/GEFS SKILL WEIGHTED HEAT RISK TOOL DEPICTS 60 PERCENT OR GREATER
PROBABILITIES FOR HEAT TO EXCEED THE 95TH CLIMATOLOGICAL PERCENTILE DURING
WEEK-2. THEREFORE, A HIGH RISK FOR EXCESSIVE HEAT IS POSTED ACROSS PORTIONS OF
THE GREAT BASIN, NORTHERN ROCKIES, AND NORTHERN HIGH PLAINS, JUL 20-22. A
MODERATE RISK FOR EXCESSIVE HEAT CONTINUES THROUGH JUL 24 AND EXTENDS FURTHER
SOUTH INTO CALIFORNIA AND INTO PARTS OF THE DESERT SOUTHWEST IN THE UPDATED
OUTLOOK. THE 0Z GEFS AND ECENS DEPICT TEMPERATURES EXCEEDING 105 DEG F ACROSS
PORTIONS OF THE CALIFORNIA CENTRAL VALLEY AND 110 DEG F IN THE DESERT
SOUTHWEST, AND THE NATIONAL BLEND OF MODELS INDICATES THE POTENTIAL FOR DAILY
RECORD HIGH TEMPERATURES OVER SOME AREAS. THE SLIGHT RISK FOR EXCESSIVE HEAT
COVERS MUCH OF THE WESTERN CONUS AND NORTHERN AND CENTRAL HIGH PLAINS, AND IS
VALID FOR ALL OF WEEK-2.
POSSIBLE SURFACE LOW FORMATION WITH ADJACENT SURFACE HIGH PRESSURE OVER THE
NORTHERN PACIFIC MAY SUPPORT TIGHT PRESSURE GRADIENTS ACROSS THE PACIFIC
NORTHWEST AND CALIFORNIA, THUS A SLIGHT RISK OF EPISODIC HIGH WINDS IS
MAINTAINED FOR THE CASCADES AND IS EXPANDED INTO SOUTHERN CALIFORNIA, JUL
20-22, BASED ON THE ECENS PET. HOT, DRY, AND WINDY CONDITIONS ARE LIKELY TO
LEAD TO ENHANCED RISK OF WILDFIRES ACROSS WEST COAST STATES AND INHIBIT EFFORTS
TO CONTAIN ANY ACTIVE WILDFIRES.
THE INITIAL POSITION OF THE RIDGE AXIS NEAR THE FOUR CORNERS FAVORS A MORE
ACTIVE MONSOON DURING WEEK-2. THEREFORE, A SLIGHT RISK FOR PERIODS OF HEAVY
PRECIPITATION IS POSTED ACROSS PORTIONS OF THE SOUTHWEST AND CENTRAL AND
SOUTHERN ROCKIES FOR ALL OF WEEK-2. THE GEFS PET DEPICTS AT LEAST A 20 PERCENT
CHANCE 3-DAY PRECIPITATION TOTALS EXCEED THE 85TH CLIMATOLOGICAL PERCENTILE AND
0.5 INCHES OVER PARTS OF THE HIGHLIGHTED AREA, WITH THE ECENS PET INCREASING
THE SIGNAL COMPARED TO YESTERDAY. THE UNCALIBRATED GEFS AND ECENS GUIDANCE
INDICATE AREAS OF SPORADIC CONVECTION THROUGHOUT THE PERIOD WHICH COULD RESULT
IN LOCALIZED AREAS OF FLOODING, ALTHOUGH THERE IS TOO MUCH UNCERTAINTY
REGARDING THE EXACT PLACEMENT TO DESIGNATE A FLOOD RISK.
LATE IN WEEK-1, A MID-LEVEL TROUGH IS FORECAST TO MOVE ACROSS THE GREAT LAKES
AND NORTHEAST, WITH AN ASSOCIATED FRONT PROGRESSING SOUTHEASTWARD THROUGH THE
EASTERN CONUS. WHILE THIS FEATURE IS LIKELY TO RESULT IN A MODERATION OF
TEMPERATURES AND SOME MUCH-NEEDED PRECIPITATION, THERE ARE GROWING INDICATIONS
THAT THE FRONT WILL STALL ACROSS THE SOUTHERN MID-ATLANTIC EARLY IN WEEK-2 AND
BECOME A FOCUS AREA FOR MULTIPLE ROUNDS OF HEAVY PRECIPITATION. THE GEFS AND
ECENS PETS DEPICT AT LEAST A 20 PERCENT CHANCE OF 3-DAY PRECIPITATION TOTALS
EXCEEDING THE 85TH CLIMATOLOGICAL PERCENTILE AND 1-INCH ACROSS THE CAROLINAS
AND ADJACENT AREAS THROUGH THE MIDDLE OF WEEK-2. THE UNCALIBRATED GUIDANCE FROM
THE 0Z ECENS, GEFS, AND CMCE ALL DEPICT SOME AREAS WITH UPWARDS OF 2 INCHES OF
PRECIPITATION DURING WEEK-2, WITH MOST OCCURRING IN THE EARLY IN THE PERIOD. A
MODERATE RISK OF HEAVY PRECIPITATION REMAINS HIGHLIGHTED ACROSS SOUTHEASTERN
VIRGINIA AND THE CAROLINAS FOR JUL 20-21, WITH A SLIGHT RISK CONTINUING TO JUL
23 AND EXTENDING FARTHER INTO PARTS OF THE TENNESSEE VALLEY, SOUTHEAST, AND
SOUTHERN APPALACHIANS.
THE PERSISTENT WARMER AND DRIER THAN NORMAL CONDITIONS OVER AT LEAST THE PAST
MONTH HAVE LED TO A RISK FOR RAPID ONSET DROUGHT FOR PARTS OF THE NORTHERN
PLAINS, OHIO VALLEY (EASTERN CORN BELT), TENNESSEE VALLEY, AND LOWER
MISSISSIPPI VALLEY. THE RISK AREA HAS BEEN PULLED OUT OF THE SOUTHEAST DUE TO
INCREASING CHANCES FOR PRECIPITATION RELATED TO THE AFOREMENTIONED STALLED
FRONTAL BOUNDARY. THE RECENT HEAT WAVES ACROSS THE EASTERN U.S. HAVE
EXACERBATED THE ONGOING DRYNESS ACROSS THIS AREA, AND HAS LED TO MODERATE
DROUGHT (D1) FOR MANY AREAS IN THE EAST. MANY OF THE AREAS HIGHLIGHTED FOR RISK
OF RAPID ONSET DROUGHT HAVE SEEN LARGE PRECIPITATION DEFICITS OVER THE PAST TWO
WEEKS TO A MONTH AND HAVE SEEN LARGE REDUCTIONS IN AVAILABLE SOIL MOISTURE.
PERIODIC, LOCALIZED HEAVY PRECIPITATION CANNOT BE RULED OUT DUE TO FRONTAL
AND/OR DAYTIME THUNDERSTORM ACTIVITY, BUT THIS IS UNLIKELY TO RESULT IN ANY
MEANINGFUL CHANGE IN THE POTENTIAL FOR CONTINUED DEVELOPMENT OF DROUGHT
CONDITIONS. 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.
FORECASTER: THOMAS COLLOW
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