707
FXUS21 KWNC 051756
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT JULY 05 2024
SYNOPSIS: MID-LEVEL HIGH PRESSURE IS FORECAST TO AMPLIFY ACROSS THE WESTERN
CONTIGUOUS U.S. (CONUS) FAVORING INCREASING CHANCES OF EXCESSIVE HEAT
CONDITIONS, WITH THE GREATEST CHANCES ANTICIPATED FOR THE GREAT BASIN AND
NORTHERN ROCKIES. SOUTHERLY MOIST FLOW INTO THE SOUTHWEST RESULTS IN INCREASED
CHANCES FOR LOCALIZED HEAVY PRECIPITATION IN THE REGION. INTERACTIONS BETWEEN A
DISSIPATING FRONTAL ZONE AND MOIST TROPICAL AIR LEAD TO THE POTENTIAL FOR HEAVY
PRECIPITATION FOR PORTIONS OF THE MID-ATLANTIC REGION EARLY IN WEEK-2. PERIODS
OF POTENTIALLY HIGH WINDS COMBINED WITH HOT,DRY CONDITIONS ACROSS THE CASCADES
AND ADJACENT LEESIDE AREA, SOUTHWESTERN OREGON, AND CENTRAL AND NORTHERN
CALIFORNIA MAY INCREASE THE RISK FOR WILDFIRES IN THE AREA.
HAZARDS
HIGH RISK OF EXCESSIVE HEAT ACROSS PARTS OF THE NORTHERN ROCKIES AND GREAT
BASIN, SAT, JUL 13.
MODERATE RISK OF EXCESSIVE HEAT ACROSS THE GREAT BASIN, NORTHERN AND CENTRAL
ROCKIES, AND NORTHERN PLAINS, SAT-SUN, JUL 13-14.
SLIGHT RISK OF EXCESSIVE HEAT ACROSS MUCH OF THE WESTERN CONUS AND NORTHERN AND
CENTRAL PLAINS, SAT-MON, JUL 13-15.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE MID-ATLANTIC AND
SOUTHEAST U.S., SAT-MON, JUL 13-15.
SLIGHT RISK OF PERIODS OF HEAVY PRECIPITATION FOR PORTIONS OF THE SOUTHERN
ROCKIES AND ARIZONA, MON-FRI, JUL 15-19.
SLIGHT RISK OF EPISODIC HIGH WINDS FOR PORTIONS OF CASCADES AND ADJACENT
LEESIDE AREA, SOUTHWESTERN OREGON, AND CENTRAL AND NORTHERN CALIFORNIA,
SAT-MON, JUL 13-15.
RAPID ONSET DROUGHT RISK FOR PORTIONS OF THE SOUTHEAST U.S., OHIO AND TENNESSEE
VALLEYS, AND NORTHERN PLAINS.
DETAILED SUMMARY
FOR MONDAY JULY 08 - FRIDAY JULY 12:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR SATURDAY JULY 13 - FRIDAY JULY 19: AN AMPLIFIED MID-LEVEL RIDGE IS FORECAST
TO BE CENTERED OVER THE INTERIOR WEST BY THE BEGINNING OF WEEK-2, EXPANDING
EASTWARD AND GRADUALLY WEAKENING OVER TIME. MULTIPLE MODEL ENSEMBLE MEANS
INDICATE WIDESPREAD POSITIVE 500 HPA HEIGHT DEPARTURES OVER THE NORTHERN
ROCKIES, NORTHERN PLAINS, AND GREAT LAKES AT THE START OF THE PERIOD, SIMILAR
TO YESTERDAY, RESULTING IN CONTINUED CHANCES FOR EXCESSIVE HEAT ACROSS THESE
AREAS. THE LIKELIHOOD OF EXCESSIVE HEAT IS HIGHEST OVER THE GREAT BASIN, WHERE
THE PROBABILISTIC EXTREMES TOOLS (PETS) INDICATE AT LEAST A 60% CHANCE OF
MAXIMUM TEMPERATURES EXCEEDING THE 85TH CLIMATOLOGICAL PERCENTILE, WITH AREAS
AS FAR NORTH AS NORTHERN IDAHO EXCEEDING TRIPLE DIGITS. THE HIGH RISK OF
EXCESSIVE HEAT (AT LEAST A 60% CHANCE) REMAINS ISSUED, BUT IS DECREASED IN
SPATIAL COVERAGE COMPARED TO YESTERDAY DUE TO THE EASTWARD SHIFTING RIDGE,
DESIGNATED FOR THE NORTHERN ROCKIES AND GREAT BASIN, JUL 13. A MODERATE RISK
(40-60% CHANCE) REMAINS IN PLACE FOR THE GREAT BASIN, NORTHERN AND CENTRAL
ROCKIES, AND NORTHERN PLAINS, JUL 13-14, WITH A SLIGHT RISK (20-40% CHANCE)
HIGHLIGHTED ACROSS MUCH OF THE WESTERN CONUS AND NORTHERN AND CENTRAL PLAINS,
JUL 13-15.
POSSIBLE SURFACE LOW FORMATION OVER THE GREAT BASIN WITH ADJACENT SURFACE HIGH
PRESSURE OVER THE NORTHERN PACIFIC MAY SUPPORT TIGHT PRESSURE GRADIENTS ACROSS
THE NORTHWEST AND CALIFORNIA. THE SLIGHT RISK (20-40% CHANCE) OF EPISODIC HIGH
WINDS OVER THE CASCADES, SOUTHWESTERN OREGON, AND CENTRAL AND NORTHERN
CALIFORNIA HAS BEEN EXTENDED NORTHEASTWARD TO INCLUDE EASTERN WASHINGTON, JUL
13-15, GIVEN THE ANTICIPATED SYNOPTIC PATTERN AND CURRENT LARGE ACTIVE
WILDFIRES IN THE AREA. THE GEFS AND ECENS PETS SHOW AT LEAST A 20% CHANCE OF
WIND SPEEDS ACROSS PARTS OF COASTAL CALIFORNIA EXCEEDING THE 85TH PERCENTILE.
IN GENERAL, HOT, DRY, AND WINDY CONDITIONS MAY LEAD TO ENHANCED RISK OF
WILDFIRES ACROSS WEST COAST STATES, ESPECIALLY LOCATIONS ALREADY UNDER RED FLAG
WARNINGS.
MID-LEVEL TROUGHING PREDICTED OVER THE GREAT LAKES AND OHIO VALLEY MAY SUPPORT
A LINGERING STATIONARY FRONT OVER THE EASTERN SEABOARD FROM THE END OF WEEK-1
INTO WEEK-2. A SLIGHT RISK FOR HEAVY PRECIPITATION IS POSTED FOR PARTS OF THE
MID-ATLANTIC AND SOUTHEAST U.S., JUL 13-15, WHERE THE ECENS, GEFS, AND CANADIAN
PETS SHOW AT LEAST A 20% CHANCE OF 3-DAY RAINFALL TOTALS EXCEEDING ONE INCH.
THE INITIAL POSITION OF THE RIDGE AXIS NEAR THE DESERT SOUTHWEST FAVORS A
DIMINISHING MONSOON SIGNAL EARLY IN WEEK-2. HOWEVER, THE RIDGE IS FORECAST TO
WEAKEN AND SHIFT MORE TO THE EAST LATER IN THE PERIOD TOWARD THE FOUR CORNERS,
WHICH IS MORE FAVORABLE FOR SOUTHERLY MOISTURE FLOW INTO PARTS OF THE
SOUTHWEST. THE PETS INDICATE A GROWING SIGNAL FOR HEAVY PRECIPITATION LATER IN
WEEK-2, THUS A SLIGHT RISK OF PERIODIC HEAVY PRECIPITATION IS POSTED ACROSS
PORTIONS OF THE SOUTHERN ROCKIES AND ARIZONA, JUL 15-19 WHERE THESE TOOLS SHOW
PROBABILITIES ABOVE 20 PERCENT FOR 3-DAY PRECIPITATION TOTALS EXCEEDING THE
85TH CLIMATOLOGICAL PERCENTILE AND 0.5 INCHES. LOCALIZED FLOODING IS POSSIBLE
ACROSS THIS AREA, ALTHOUGH THERE IS TOO MUCH UNCERTAINTY AT THIS TIME TO
DESIGNATE A CORRESPONDING FLOOD HAZARD ON THE MAP.
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 SOUTHEAST U.S.
THE RECENT HEAT WAVES ACROSS THE EASTERN U.S. HAVE EXACERBATED THE ONGOING
DRYNESS ACROSS THIS AREA, AND LED TO MODERATE DROUGHT (D1) FOR MANY AREAS IN
THE EAST. MUCH 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. THERE IS ADDITIONAL RISK FOR
HIGH EVAPOTRANSPIRATION RATES WITH ABOVE-NORMAL TEMPERATURES FORECAST ACROSS
MUCH OF THE EASTERN CONUS. 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: MELISSA OU
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