258
FXUS21 KWNC 271842
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT JUNE 27 2024
SYNOPSIS: MID-LEVEL HIGH PRESSURE PREDOMINANTLY FAVORED OVER SOUTHEASTERN AND
WESTERN CONUS IS EXPECTED TO INCREASE CHANCES FOR EXCESSIVE HEAT CONDITIONS
DURING WEEK-2. MUCH OF THE ANOMALOUS WARM SUMMERTIME TEMPERATURES AND DRIER
THAN NORMAL CONDITIONS ARE ANTICIPATED TO SUSTAIN THE RISK FOR RAPID ONSET
DROUGHT (ROD) OVER PARTS OF THE PLAINS, CORN BELT AND LOWER HALF OF THE EASTERN
SEABOARD DURING WEEK-2. POSSIBLE MID-LEVEL LOW PRESSURE AND CONTINUED RAINFALL
OVER THE NORTH-CENTRAL CONUS EARLY IN WEEK-2 SUPPORTS POSSIBLE FLOODING ACROSS
MANY PARTS OF THE MIDWEST. AN ACTIVE NORTH AMERICAN MONSOON CIRCULATION AND
POSSIBLE MOISTURE SURGES INTO THE DESERT SOUTHWEST FAVOR AN INCREASED RISK OF
LOCALLY HEAVY PRECIPITATION AND POSSIBLE FLOODING OVER THE LOWER FOUR CORNERS.
HAZARDS
MODERATE RISK FOR EXCESSIVE HEAT FOR PORTIONS OF THE SOUTHEAST, LOWER
MISSISSIPPI AND TENNESSEE VALLEYS, AND SOUTHERN MID-ATLANTIC, FRI-SAT, JUL 5-6.
SLIGHT RISK OF EXCESSIVE HEAT FROM THE SOUTHERN PLAINS EASTWARD TO THE LOWER
EASTERN SEABOARD, FRI-THU, JUL 5-11.
SLIGHT RISK OF EXCESSIVE HEAT FOR PORTIONS OF CALIFORNIA, PACIFIC NORTHWEST,
AND THE INTERIOR WEST, FRI-TUE, JUL 5-9.
SLIGHT RISK OF PERIODS OF HEAVY PRECIPITATION FOR PARTS OF THE DESERT SOUTHWEST
AND SOUTHERN ROCKIES, FRI-TUE, JUL 5-9.
POSSIBLE FLOODING FOR PORTIONS OF SOUTHERN ARIZONA AND NEW MEXICO.
POSSIBLE FLOODING FOR PORTIONS OF THE NORTHERN AND CENTRAL PLAINS AND UPPER AND
MIDDLE MISSISSIPPI VALLEY.
RAPID ONSET DROUGHT RISK FOR PARTS OF GREAT PLAINS, MISSISSIPPI VALLEY,
TENNESSEE AND OHIO VALLEYS, APPALACHIANS, SOUTHEAST AND MID-ATLANTIC.
DETAILED SUMMARY
FOR SUNDAY JUNE 30 - THURSDAY JULY 04:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR FRIDAY JULY 05 - THURSDAY JULY 11: DYNAMICAL MODELS CONTINUE TO ADVERTISE
PREDOMINATELY ABOVE-NORMAL 500-HPA HEIGHT DEPARTURES IN THE WEEK-2 MEAN
THROUGHOUT MUCH OF THE CONUS. THE ACCOMPANYING ABOVE-NORMAL JULY TEMPERATURES
ARE EXPECTED TO MAINTAIN AN ELEVATED RISK OF EXCESSIVE HEAT CONDITIONS
PARTICULARLY FOR THE SOUTHERN TIER OF THE CONUS DURING THE PERIOD. BY LATE NEXT
WEEK, THE LATEST RUNS OF THE ECMWF ENSEMBLE ARE BEGINNING TO FEATURE MORE OF A
WEAKNESS IN THE MID-LEVEL RIDGE PATTERN OVER THE CENTRAL CONUS, WHICH APPEARS
TO BE TIED TO ADDITIONAL, AND POSSIBLY DEEPER SHORTWAVE ENERGY PROPAGATING
ALONG THE LONGWAVE TROUGH AXIS SITUATED OVER CENTRAL CANADA. THE 0Z AND 6Z GEFS
ARE LESS PRONOUNCED WITH THIS TREND, BUT NONETHELESS FAVOR MEAN ZONAL FLOW AND
COOLER CONDITIONS OVER THE NORTHERN TIER OF THE CONUS BY NEXT WEEKEND THAN
PREVIOUSLY FORECAST. A KEY QUESTION CONCERNS HOW FAR SOUTH ANY POTENTIALLY
COOLER AIR REACHES TO PROVIDE RELIEF TO ANOMALOUSLY HOT SUMMERTIME TEMPERATURES
LEADING INTO THE PERIOD ACROSS THE PLAINS, MISSISSIPPI VALLEY AND THE
SOUTHEAST. TEMPERATURE TOOLS FROM THE GEFS AND ECMWF INDICATE THE COOLING TREND
IS STRONGEST OVER MANY PARTS OF THE PLAINS AND MISSISSIPPI VALLEY EARLY IN THE
PERIOD, BUT MAINTAIN FAIRLY STRONG POSITIVE TEMPERATURE ANOMALIES OVER PARTS OF
THE TENNESSEE AND OHIO VALLEYS, SOUTHEAST AND MID-ATLANTIC EARLY IN THE PERIOD.
THEREFORE, A MODERATE RISK FOR EXCESSIVE HEAT REMAINS POSTED WITH ITS COVERAGE
NOW FOCUSED OVER THE SOUTHEASTERN CONUS FOR JUL 5-6. GIVEN THE PERSISTENCE OF
ANOMALOUS MID-LEVEL RIDGING FAVORED OVER THE SOUTHERN TIER OF THE U.S, THE
SLIGHT RISK OF EXCESSIVE HEAT REMAINS POSTED FOR THE ENTIRETY OF WEEK-2, BUT
WITH LESSER COVERAGE OVER THE PLAINS AND MISSISSIPPI VALLEY DUE TO POTENTIAL
FOR MORE NORTHWESTERLY FLOW IN DURING THE PERIOD.
GIVEN THE POTENTIAL FOR CONTINUED SHORTWAVE ENERGY FAVORED OVER THE
NORTH-CENTRAL CONUS, UNCALIBRATED PRECIPITATION TOOLS CONTINUE TO SHOW THE
POTENTIAL FOR INCREASED PRECIPITATION AMOUNTS LATE IN WEEK-1 AND INTO EARLY
WEEK-2. WHILE THESE TOOLS ARE LARGELY UNSUPPORTIVE OF A HEAVY PRECIPITATION
RISK, A FLOODING POSSIBLE HAZARD IS CONTINUED FOR MANY PARTS OF THE MIDWEST.
ANY CONTINUED RAINFALL HEADING INTO WEEK-2 MAY WORSEN ONGOING FLOODING ALONG
THE MISSOURI AND MISSISSIPPI RIVERS WHERE POTENTIALLY EXCESSIVE PRECIPITATION
IS FORECAST DURING WEEK-1.
UPSTREAM, MORE AMPLIFIED RIDGING IS FEATURED OVER THE EASTERN PACIFIC AND
WESTERN CONUS. LATE IN WEEK-1, DOUBLE-DIGIT POSITIVE TEMPERATURE DEPARTURES ARE
FAVORED IN THE CENTRAL CALIFORNIA VALLEY (BASED ON WPCS DAY 6 AND DAY 7
FORECASTS), AS THESE TEMPERATURES ARE FAVORED TO PERSIST TIED TO THE BUILDING
MID-LEVEL RIDGE LEADING INTO WEEK-2. THEREFORE, A BROAD SLIGHT RISK AREA OF
EXCESSIVE HEAT IS POSTED FOR JUL 5-9 BEFORE MUCH OF THE ANOMALOUS RIDGING
BEGINS TO WEAKEN LATER IN THE PERIOD. UNCALIBRATED GEFS AND ECMWF GUIDANCE
SHOW ELEVATED CHANCES FOR MAXIMUM DAYTIME TEMPERATURES EXCEEDING 110 DEGREES F
ACROSS PARTS OF THE CALIFORNIA CENTRAL VALLEY AND THE SONORAN DESERT.
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 OHIO VALLEY
(EASTERN CORN BELT), MID-ATLANTIC, SOUTHEAST, SOUTHERN PLAINS, AND SOUTHERN
CENTRAL PLAINS. THE RECENT HEAT WAVES ACROSS THE EASTERN U.S. HAVE EXACERBATED
THE ONGOING DRYNESS ACROSS THESE AREAS, AND HAVE 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. ALTHOUGH PERIODIC,
LOCALIZED HEAVY PRECIPITATION CANNOT BE RULED OUT DUE TO FRONTAL AND/OR DAYTIME
THUNDERSTORM ACTIVITY. 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.
UNDERNEATH THE ANOMALOUS MID-LEVEL RIDGING FAVORED OVER THE SOUTHERN TIER OF
THE CONUS, EASTERLY FLOW FROM THE GULF OF MEXICO CONSISTENT WITH THE NORTH
AMERICAN MONSOON CIRCULATION IS EXPECTED TO PROMOTE INCREASED PRECIPITATION
AMOUNTS OVER NORTHERN MEXICO AND THE SOUTHWESTERN U.S. ALTHOUGH THE GREATEST
THREAT FOR HEAVY PRECIPITATION APPEARS TO HAVE TIMED OFF PROMPTING THE REMOVAL
OF A MODERATE RISK OF HEAVY PRECIPITATION IN THE UPDATED OUTLOOK, ABOVE-NORMAL
PRECIPITATION REMAINS FAVORED ACROSS THE LOWER FOUR CORNERS REGION DURING
WEEK-2. THE THERMAL LOW LOOKS TO BE FIRMLY ESTABLISHED OVER THE SONORAN DESERT,
AND WITH SOME MODEL SOLUTIONS DEPICTING SHARP UPTICKS IN DEWPOINT TEMPERATURES,
THERE REMAINS THE POTENTIAL FOR GULF OF CALIFORNIA MOISTURE SURGES TO SUPPORT
THE CONTINUATION OF A SLIGHT RISK OF HEAVY PRECIPITATION FOR JUL 5-9. A
FLOODING POSSIBLE RISK IS ALSO DESIGNATED FOR SOUTHERN PARTS OF ARIZONA AND NEW
MEXICO WHERE STRONGER PRECIPITATION SIGNALS ARE DEPICTED IN MULTIPLE MODELS.
PRECIPITATION IS EXPECTED TO BE ISOLATED AND NOT ALL LOCATIONS WILL EXPERIENCE
HEAVY RAINFALL. HOWEVER, FLASH FLOODING IS POSSIBLE BOTH WHERE PRECIPITATION
OCCURS AND IN DOWNSTREAM VALLEYS, PARTICULARLY IN AND AROUND BURN SCARS WHERE
DEBRIS FLOWS CAN BE TRIGGERED BY HEAVY RAINFALL.
IN THE TROPICS, THE MADDEN-JULIAN OSCILLATION (MJO) HAS BEEN LARGELY
DISORGANIZED FOR MUCH OF JUNE. HOWEVER, THERE IS GOOD CONTINUITY IN THE MODEL
GUIDANCE FAVORING A MORE COHERENT MJO SIGNAL EMERGING OVER THE INDIAN OCEAN AND
PROPAGATING EASTWARD INTO THE MARITIME CONTINENT DURING THE NEXT TWO WEEKS.
HISTORICALLY, THIS EVOLVING SIGNAL IS SUPPORTIVE FOR TROPICAL CYCLOGENESIS IN
THE WESTERN HEMISPHERE BASED ON MJO COMPOSITES DURING JUN-AUG, AND THE NATIONAL
HURRICANE CENTER (NHC) IS MONITORING THE POTENTIAL FOR TROPICAL CYCLONE (TC)
DEVELOPMENT ASSOCIATED WITH TWO TROPICAL WAVES IN THE ATLANTIC. WHILE THE ODDS
FOR FORMATION CURRENTLY REMAIN LOW (<20%) FOR A WAVE LOCATED IN THE
WEST-CENTRAL CARIBBEAN, CHANCES FOR DEVELOPMENT HAVE RAPIDLY RISEN (70% DURING
THE NEXT 7 DAYS) TIED TO AN EASTERLY WAVE IN THE MAIN DEVELOPMENT REGION (MDR).
NO CORRESPONDING HAZARDS ARE POSTED GIVEN LARGE UNCERTAINTY WITH EVENTUAL
STRENGTH AND TRACK OF THE ASSOCIATED LOW, BUT IT BEARS MONITORING DURING THE
NEXT SEVERAL DAYS, AS THE SHEARING ENVIRONMENT LOOKS FAVORABLE FOR FURTHER
DEVELOPMENT AS IT APPROACHES THE CARIBBEAN.
FORECASTER: NICK NOVELLA
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