244
FXUS21 KWNC 041927
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT JULY 04 2024
SYNOPSIS: MID-LEVEL HIGH PRESSURE IS FORECAST TO AMPLIFY ACROSS THE WESTERN
CONTIGUOUS U.S. (CONUS) FAVORING INCREASING CHANCES OF EXCESSIVE HEAT
CONDITIONS, PARTICULARLY OVER PORTIONS OF THE GREAT BASIN WHERE THE HOTTEST
TEMPERATURES ARE FORECAST. 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 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 MUCH OF THE GREAT BASIN, FRI, JUL 12.
MODERATE RISK OF EXCESSIVE HEAT ACROSS THE GREAT BASIN AND NORTHERN ROCKIES, AS
WELL AS PORTIONS OF THE CENTRAL ROCKIES AND NORTHERN PLAINS, FRI-SAT, JUL 12-13.
SLIGHT RISK OF EXCESSIVE HEAT ACROSS MUCH OF THE WESTERN CONUS AND NORTHERN
PLAINS, FRI-MON, JUL 12-15.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE MID-ATLANTIC AND
SOUTHEAST U.S., FRI-SUN, JUL 12-14.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE DESERT SOUTHWEST,
SUN-THU, JUL 14-18.
SLIGHT RISK OF HIGH WINDS FOR PORTIONS OF CALIFORNIA AND THE PACIFIC NORTHWEST,
FRI-SUN, JUL 12-14.
RAPID ONSET DROUGHT RISK FOR PORTIONS OF THE SOUTHEAST U.S., OHIO AND TENNESSEE
VALLEYS, AND NORTHERN PLAINS.
DETAILED SUMMARY
FOR SUNDAY JULY 07 - THURSDAY JULY 11:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR FRIDAY JULY 12 - THURSDAY JULY 18: 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 AND NORTHERN PLAINS AT THE START OF THE PERIOD, SIMILAR TO YESTERDAY,
RESULTING IN CONTINUED CHANCES FOR EXCESSIVE HEAT ACROSS THESE AREAS. THE RISKS
OF EXCESSIVE HEAT ARE 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. A HIGH RISK (AT LEAST A 60% CHANCE) OF
EXCESSIVE HEAT IS DESIGNATED FOR THE GREAT BASIN, CALIFORNIA, SOUTHWEST, AND
NORTHERN ROCKIES FOR JUL 12, WITH MODERATE RISK (40-60% CHANCE) FOR JUL 12-13
ACROSS A BROADER AREA OF THE WESTERN THIRD OF THE CONUS INCLUDING PORTIONS OF
THE NORTHERN AND CENTRAL PLAINS. A BROADER AREA OF SLIGHT RISK IS HIGHLIGHTED
FOR JUL 12-15 FOR MUCH OF THE WEST AND PORTIONS OF THE NORTHERN PLAINS.
POSSIBLE SURFACE LOW FORMATION WITH ADJACENT SURFACE HIGH PRESSURE OVER THE
NORTHERN PACIFIC MAY SUPPORT TIGHT PRESSURE GRADIENTS ACROSS THE NORTHWEST AND
CALIFORNIA, THUS A SLIGHT RISK OF EPISODIC HIGH WINDS IS MAINTAINED FOR THE
CASCADES AND NORTHERN AND CENTRAL CALIFORNIA, JUL 12-14. THE GEFS (ECENS) PET
SHOWS AT LEAST A 20% (30%) CHANCE OF WIND SPEEDS OVER SOUTHWESTERN OREGON AND
NORTHERN AND CENTRAL CALIFORNIA EXCEEDING THE 85TH PERCENTILE. 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. THE ECENS PET CONTINUES TO BE MORE FAVORABLE OF HEAVY RAINFALL
ACROSS PARTS OF THE EAST COAST, INDICATING PARTS OF THIS REGION HAVING AT LEAST
A 20% CHANCE OF 3-DAY RAINFALL EXCEEDING THE 85TH PERCENTILE AND ONE INCH JUL
12-14, WITH THE GEFS MAINTAINING THE HEAVIEST PRECIPITATION OFFSHORE BUT NOW
HIGHLIGHTING THE CAROLINAS WITH A 20% CHANCE OF 3-DAY RAINFALL EXCEEDING THE
85TH PERCENTILE AS WELL. WITH TODAY’S MODEL SOLUTIONS COMING INTO BETTER
AGREEMENT, A SLIGHT RISK FOR HEAVY PRECIPITATION IS POSTED FOR PORTIONS OF THE
MID-ATLANTIC AND SOUTHEAST U.S. FOR JUL 12-14.
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, WITH PROBABILITIES ABOVE 20 PERCENT FOR 3-DAY PRECIPITATION TOTALS
EXCEEDING THE 85TH CLIMATOLOGICAL PERCENTILE AND 0.5 INCHES DURING THE LATTER
HALF OF THE PERIOD. THEREFORE, A SLIGHT RISK OF PERIODIC HEAVY PRECIPITATION IS
POSTED ACROSS PORTIONS OF ARIZONA AND WESTERN NEW MEXICO, JUL 14-18. LOCALIZED
FLOODING IS POSSIBLE ACROSS THIS AREA, ALTHOUGH THERE IS TOO MUCH UNCERTAINTY
AT THIS TIME TO DESIGNATE A FLOOD RISK.
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 HAS 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: DANNY BARANDIARAN
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