322
FXUS21 KWNC 221911
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT JUNE 22 2023
SYNOPSIS: MID-LEVEL HIGH PRESSURE IS ANTICIPATED TO PERSIST OVER THE SOUTHERN
CONTIGUOUS U.S. (CONUS) DURING WEEK-2, LEADING TO THE INCREASED POTENTIAL FOR
EXCESSIVE HEAT FOR MUCH OF THE SOUTH. MID-LEVEL LOW PRESSURE FAVORED OVER THE
EAST COMBINED WITH ABUNDANT MOISTURE SUPPORTS AN INCREASED RISK FOR HEAVY
PRECIPITATION TO PORTIONS OF THE MID-ATLANTIC. SNOWMELT SEASON CONTINUES FOR
PORTIONS OF THE WEST AFTER EXCEPTIONAL WINTER ACCUMULATIONS, LEADING TO THE
CONTINUED POTENTIAL FOR FLOODING, WHILE ABNORMALLY DRY CONDITIONS OVER
LOUISIANA AND TEXAS RESULT IN THE POTENTIAL FOR RAPID ONSET DROUGHT (ROD).
HAZARDS
HIGH RISK OF EXCESSIVE HEAT FOR PORTIONS OF EASTERN TEXAS, SOUTHEASTERN
OKLAHOMA, AND WESTERN LOWER MISSISSIPPI VALLEY, FRI, JUN 30.
MODERATE RISK OF EXCESSIVE HEAT FOR PORTIONS OF THE SOUTHWEST, SOUTHERN PLAINS,
AND LOWER AND MIDDLE MISSISSIPPI VALLEY, FRI-SUN, JUN 30-JUL 2.
SLIGHT RISK FOR EXCESSIVE HEAT FOR PORTIONS OF THE CENTRAL AND SOUTHERN PLAINS,
LOWER AND MIDDLE MISSISSIPPI VALLEY, OHIO AND TENNESSEE VALLEYS, SOUTHEASTERN
U.S., SOUTHERN ROCKIES AND SOUTHWEST, FRI-THU, JUN 30-JUL 6.
SLIGHT RISK FOR HEAVY PRECIPITATION FOR PORTIONS OF THE MID-ATLANTIC, SAT-SUN,
JUL 1-2.
POSSIBLE FLOODING FOR PORTIONS OF CALIFORNIA, NEVADA, UTAH, WYOMING, AND IDAHO.
POSSIBLE FLOODING ALONG PORTIONS OF THE JAMES RIVER IN SOUTH DAKOTA.
RAPID ONSET DROUGHT RISK ACROSS PORTIONS OF LOUISIANA AND SOUTHEASTERN TEXAS.
DETAILED SUMMARY
FOR SUNDAY JUNE 25 - THURSDAY JUNE 29:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR FRIDAY JUNE 30 - THURSDAY JULY 06: ENSEMBLE MODEL SOLUTIONS FROM THE GEFS,
ECMWF, AND CMCE ALL CONTINUE TO DEPICT POSITIVE 500-HPA HEIGHT ANOMALIES
PERSISTING OVER THE SOUTHERN CONUS THROUGHOUT THE FORECAST PERIOD. MODEL
GUIDANCE DEPICTS MID-LEVEL HEIGHTS NEARING 600 DM, THOUGH THIS FEATURE APPEARS
GENERALLY WEAKER COMPARED TO YESTERDAY AND THE RIDGE AXIS SHIFTED SLIGHTLY
WESTWARD. THE ECMWF MID-LEVEL HEIGHT DEPARTURES ARE GREATER THAN THE GEFS,
WHICH TRANSLATES TO STRONGER HEAT SIGNALS IN THE HEAT TOOLS COMPARED TO THE
GEFS. FOR DAYS 8 AND 9 (JUN 30-JUL 1) THERE ARE INCREASED PROBABILITIES (>40%
CHANCE) OF MAXIMUM TEMPERATURES EXCEEDING THE 85TH PERCENTILE,
CLIMATOLOGICALLY, IN THE GEFS PROBABILISTIC EXTREMES TOOL (PET) ACROSS OKLAHOMA
AND THE LOWER MISSISSIPPI VALLEY COMPARED TO YESTERDAY. MEANWHILE THE ECMWF
COUNTERPART GENERALLY SHOWS A STRONGER HEAT SIGNAL (HIGHER PROBABILITIES ARE
SLIGHTLY MORE EXPANSIVE) THAN YESTERDAY, INDICATING AT LEAST A 70% CHANCE OF
EXCEEDING THE AFOREMENTIONED THRESHOLD OVER NORTHEASTERN TEXAS AND WESTERN
PORTIONS OF THE LOWER MISSISSIPPI VALLEY FOR THE BEGINNING OF WEEK-2.
BASED ON TODAY'S MODEL GUIDANCE AND TOOLS, THE HIGH RISK (>60% CHANCE) OF
EXCESSIVE HEAT HAS BEEN EXPANDED SLIGHTLY FURTHER NORTHEAST INTO PORTIONS OF
OKLAHOMA AND WESTERN PORTIONS OF THE LOWER MISSISSIPPI VALLEY FOR JUN 30. THE
NATIONAL BLEND OF MODELS (NBM) INDICATES AN AREA OF POTENTIAL RECORD BREAKING
MAXIMUM TEMPERATURES ACROSS PARTS OF TEXAS AND LOUISIANA, JUN 30 TO JUL 1. THE
MODERATE RISK (>40% CHANCE) IS POSTED FOR THE SOUTHWEST, SOUTHERN PLAINS, AND
LOWER AND MIDDLE MISSISSIPPI VALLEY, WHICH HAS BEEN EXPANDED INTO ARIZONA, JUN
30 TO JUL 2. THE BROADER AREA OF SLIGHT RISK (>20% CHANCE) IS HIGHLIGHTED FOR
PORTIONS OF THE CENTRAL AND SOUTHERN PLAINS, LOWER AND MIDDLE MISSISSIPPI
VALLEY, OHIO AND TENNESSEE VALLEYS, SOUTHEASTERN U.S., SOUTHERN ROCKIES AND
SOUTHWEST. IOWA IS NO LONGER INCLUDED IN THIS SLIGHT RISK AREA DUE TO
UNCERTAINTY REGARDING POTENTIAL MID-LEVEL TROUGHING DURING WEEK-2 POTENTIALLY
DECREASING CHANCES FOR TEMPERATURES REACHING EXCESSIVE HEAT CRITERIA. HOT AND
DRY CONDITIONS ACROSS THE SOUTH MAY ENHANCE WILDFIRE RISK ACROSS THE
HIGHLIGHTED EXCESSIVE HEAT AREAS. THE NATIONAL INTERAGENCY FIRE CENTER (NIFC)
INDICATES HIGH RISK TRIGGERS BY THE END OF WEEK-1 ACROSS MUCH OF THE AREA WHERE
EXCESSIVE HEAT IS PREDICTED.
FURTHER NORTH, WITH THE WESTWARD SHIFT OF THE MID-LEVEL RIDGE MAY ALSO BE
ACCOMPANIED BY MORE AMPLIFIED RIDGING ACROSS THE NORTHWESTERN CONUS AT THE
BEGINNING OF THE PERIOD. THIS PATTERN MAY SUPPORT ANOMALOUS WARMTH ACROSS PARTS
OF THE NORTHWEST. THERE IS A GREATER SIGNAL IN THE HEAT INDEX TOOLS AND PET
SHOWING TEMPERATURES EXCEEDING THE 85TH PERCENTILE IN THIS REGION COMPARED TO
YESTERDAY. THERE IS MULTI-MODEL DEPICTION IN THE PET SHOWING MAXIMUM
TEMPERATURES POSSIBLY EXCEEDING 95 DEG F, PRIMARILY ON DAY 9 (JUL 1). DUE TO
HIGH UNCERTAINTY REGARDING WHETHER TEMPERATURES WILL REACH HAZARDOUS CRITERIA
AND THE DURATION, A RELATED HEAT RISK IS NOT POSTED FOR THE NORTHWEST AT THIS
TIME BUT WILL BE MONITORED IN THE UPCOMING DAYS.
MID-LEVEL TROUGHING IS PREDICTED OVER THE EAST THROUGHOUT MUCH OF WEEK-2, WHICH
MAY SUPPORT SURFACE LOW FORMATION OVER THE REGION. DYNAMICAL MODEL GUIDANCE AND
CALIBRATED TOOLS INDICATE THE POTENTIAL FOR HEAVY PRECIPITATION SHIFTED FURTHER
SOUTH COMPARED TO YESTERDAY. A SLIGHT RISK OF HEAVY PRECIPITATION IS DESIGNATED
ACROSS PARTS OF THE MID-ATLANTIC WHERE THE PETS SHOW AT LEAST A 20% CHANCE OF
3-DAY RAINFALL (JUN 30-JUL 2) EXCEEDING THE 85TH PERCENTILE. THE ECMWF AND
CANADIAN INDICATE 3-DAY RAINFALL TOTALS EXCEEDING ONE INCH, WHEREAS THE GEFS
REMAINS BELOW THE ONE INCH THRESHOLD (BUT EXCEEDS 0.75 INCHES), SIMILAR TO
YESTERDAY. ADDITIONALLY, THE ECMWF AND CANADIAN PET CONTINUES TO INDICATE A
BROAD AREA OF AT LEAST A 20% CHANCE OF EXCEEDING THE 85TH PERCENTILE FOR
PORTIONS OF THE CENTRAL AND SOUTHERN PLAINS, WHILE THE GEFS ONLY INDICATES A
SMALL AREA OVER NORTHERN TEXAS AND OKLAHOMA REACHING THESE THRESHOLDS. DUE TO
SIGNIFICANT UNCERTAINTY AN ADDITIONAL HEAVY PRECIPITATION HAZARD IS NOT
INCLUDED OVER THESE REGIONS.
ANTICIPATED HOT, DRY CONDITIONS ACROSS THE SOUTH DURING WEEK-1 AND WEEK-2
INCREASES CHANCES FOR RAPID ONSET DROUGHT (ROD). THE ROD RISK AREA HAS BEEN
EXPANDED TO PARTS OF SOUTHEASTERN TEXAS, PRIMARILY ALONG THE COAST, AND TO
SOUTHERN LOUISIANA COMPARED TO YESTERDAY. THIS REGION HAS RECEIVED AT LEAST A
25% DEFICIT OF PRECIPITATION COMPARED TO NORMAL OVER THE LAST 30 DAYS. THE ROD
AREA OVER WISCONSIN IN YESTERDAY'S OUTLOOK HAS BEEN REMOVED TODAY SINCE THE
REGION IS ALREADY EXPERIENCING DROUGHT.
SNOWMELT SEASON CONTINUES ACROSS THE WESTERN CONUS AFTER ACCUMULATING A VERY
LARGE AND IN SOME CASES RECORD-BREAKING SNOWPACK, INDUCING RIVER FLOODING
ESPECIALLY ACROSS HIGHER ELEVATIONS FOR SOME AREAS IN THE WEST, WHERE A FEW
SITES STILL REPORT OVER 40 INCHES OF SNOW WATER CONTENT. AS SNOWMELT CONTINUES
IN PARTS OF THE SIERRA NEVADA, GREAT BASIN, AND NORTHERN ROCKIES, FLOODING MAY
CONTINUE TO OCCUR ALONG SOME RIVERS, AND IN AREAS ADJACENT TO THE HIGHER
ELEVATIONS. FLOODING IS ALSO EXPECTED TO CONTINUE ALONG THE JAMES RIVER IN
SOUTH DAKOTA AS RIVER LEVELS HAVE BEEN VERY SLOW TO RECEDE DUE TO SATURATED
GROUND CONDITIONS AND RELATIVELY FLAT TOPOGRAPHY.
FORECASTER: MELISSA OU
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