375
FXUS21 KWNC 111813
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT JULY 11 2024
SYNOPSIS: MID-LEVEL HIGH PRESSURE IS FORECAST OVER MUCH OF THE WESTERN AND
CENTRAL CONTIGUOUS U.S. (CONUS) FAVORING CONTINUED CHANCES OF EXCESSIVE HEAT
CONDITIONS, PARTICULARLY ACROSS PORTIONS OF THE WEST. 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
MODERATE RISK OF EXCESSIVE HEAT ACROSS PORTIONS OF THE GREAT BASIN AND NORTHERN
HIGH PLAINS, FRI-SUN, JUL 19-21.
SLIGHT RISK OF EXCESSIVE HEAT ACROSS PORTIONS OF THE WEST, FRI-THU, JUL 19-25.
MODERATE RISK OF HEAVY PRECIPITATION ACROSS SOUTHEASTERN VIRGINIA AND THE
CAROLINAS, FRI-SUN, JUL 19-21.
SLIGHT RISK OF HEAVY PRECIPITATION ACROSS PORTIONS OF THE SOUTHERN
MID-ATLANTIC, SOUTHERN APPALACHIANS, SOUTHEAST, AND TENNESSEE VALLEY, FRI-TUE,
JUL 19-23.
SLIGHT RISK OF PERIODS OF HEAVY PRECIPITATION FOR PORTIONS OF THE SOUTHWEST AND
CENTRAL AND SOUTHERN ROCKIES, FRI-THU, JUL 19-25.
SLIGHT RISK OF EPISODIC HIGH WINDS FOR PORTIONS OF CALIFORNIA AND THE PACIFIC
NORTHWEST, FRI-MON, JUL 19-22.
RAPID ONSET DROUGHT RISK FOR PORTIONS OF THE OHIO, TENNESSEE, AND LOWER
MISSISSIPPI VALLEYS, AND NORTHERN PLAINS.
DETAILED SUMMARY
FOR SUNDAY JULY 14 - THURSDAY JULY 18:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR FRIDAY JULY 19 - THURSDAY JULY 25: AT THE OUTSET OF THE PERIOD, AN
AMPLIFIED MID-LEVEL RIDGE IS FORECAST TO BE CENTERED ACROSS THE FOUR CORNERS.
THIS FAVORS ANOMALOUSLY WARM TEMPERATURES ALONG WITH EXCESSIVE HEAT CONDITIONS
ACROSS MUCH OF THE WEST. THE ECENS AND GEFS PROBABILISTIC EXTREMES TOOLS (PETS)
INDICATE AT LEAST A 40 PERCENT CHANCE OF MAXIMUM TEMPERATURES EXCEEDING THE
85TH CLIMATOLOGICAL PERCENTILE OVER PARTS OF THE NORTHERN GREAT BASIN INTO THE
NORTHERN HIGH PLAINS, WITH THE CALIBRATED ECENS/GEFS SKILL WEIGHTED HEAT
GUIDANCE ALSO SHOWING THE STRONGEST SIGNAL FOR EXCESSIVE HEAT IN THIS REGION.
THEREFORE, MODERATE RISKS (40-60 PERCENT CHANCE) FOR EXCESSIVE HEAT ARE POSTED
JUL 19-21 ACROSS THE SNAKE RIVER VALLEY SOUTHWARD INTO NORTHEASTERN NEVADA AND
WESTERN UTAH, AND ALSO ACROSS PARTS OF EASTERN MONTANA, NORTHERN WYOMING, AND
THE FAR WESTERN DAKOTAS. IN THESE AREAS, TEMPERATURES ARE LIKELY TO BE NEAR OR
EXCEEDING 100 DEG F BASED ON UNCALIBRATED GUIDANCE FROM THE 0Z GEFS AND ECENS.
WHILE LOW DEWPOINTS MAY DECREASE THE HEAT INDEX BY A FEW DEGREES RELATIVE TO
THE ACTUAL TEMPERATURE, EXCESSIVE HEAT THRESHOLDS ARE STILL FAVORED TO BE
REACHED. TO THE SOUTH, THE SIGNALS IN THE PETS ARE WEAKER, BUT THERE IS AN
UPTICK IN TEMPERATURES THROUGHOUT THE PERIOD, WITH THE 0Z GEFS AND ECENS
DEPICTING MAXIMUM TEMPERATURES EXCEEDING 105 (110) DEG F OVER THE CALIFORNIA
CENTRAL VALLEY (DESERT SOUTHWEST), WITH THE NATIONAL BLEND OF MODELS INDICATING
NEAR RECORD HIGH DAILY TEMPERATURES ACROSS PARTS OF SOUTHERN CALIFORNIA AND
NEVADA. THEREFORE, THE SLIGHT RISK (20-40 PERCENT CHANCE) FOR EXCESSIVE HEAT
HAS BEEN EXTENDED INTO THESE AREAS, 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 (20-40 PERCENT CHANCE) OF EPISODIC
HIGH WINDS IS MAINTAINED FOR THE CASCADES AND NORTHERN AND CENTRAL CALIFORNIA,
JUL 19-22. 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 (20-40 PERCENT CHANCE)
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 HAVING LESS COVERAGE. HOWEVER, THE UNCALIBRATED GEFS AND
ECENS GUIDANCE INDICATES 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 PET
DEPICTS 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, INCREASING TO ABOVE 30 PERCENT IN THE ECENS
PET. THE UNCALIBRATED GUIDANCE FROM THE 0Z ECENS, GEFS, AND CMCE ALL DEPICT
UPWARDS OF 2 INCHES OF PRECIPITATION DURING WEEK-2, WITH MOST OCCURRING IN THE
FIRST HALF OF THE PERIOD. GIVEN THESE INCREASING SIGNALS, A MODERATE RISK
(40-60 PERCENT CHANCE) OF HEAVY PRECIPITATION IS HIGHLIGHTED ACROSS
SOUTHEASTERN VIRGINIA AND THE CAROLINAS JUL 19-21, WITH A SLIGHT RISK (20-40
PERCENT CHANCE) CONTINUING TO JUL 23 AND EXTENDING FARTHER INTO PARTS OF THE
TENNESSEE VALLEY, SOUTHEAST, AND SOUTHERN APPALACHIANS. THE NATIONAL HURRICANE
CENTER IS ALSO MONITORING THE POTENTIAL FOR TROPICAL CYCLONE DEVELOPMENT ALONG
THIS FRONT, ALTHOUGH CHANCES ARE MINIMAL (10 PERCENT).
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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