831
FXUS21 KWNC 011830
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT JUNE 01 2023
SYNOPSIS: MID-LEVEL HIGH PRESSURE FAVORED LATE NEXT WEEK IS EXPECTED TO SUSTAIN
THE RISK OF EXCESSIVE HEAT FOR PORTIONS OF THE NORTHWESTERN CONTIGUOUS U.S.
(CONUS) EARLY IN WEEK-2. POTENTIALLY DEEPENING SURFACE LOW PRESSURE SUPPORTS
INCREASED CHANCES FOR HEAVY PRECIPITATION OVER THE SOUTH-CENTRAL CONUS AS WELL
AS OVER PORTIONS OF FLORIDA. ANTECEDENT ANOMALOUS DRYNESS COMBINED WITH
INCREASED CHANCES FOR BELOW-NORMAL PRECIPITATION CONTINUING THROUGH MID-JUNE
INCREASES THE RISK FOR RAPID ONSET DROUGHT OVER PORTIONS OF THE MIDWEST AND
EXTENDING EASTWARD TOWARDS THE CENTRAL APPALACHIANS. LOCALIZED FLOODING RELATED
TO THE SPRING THAW REMAINS POSSIBLE FOR PORTIONS OF THE WESTERN CONUS, AND
ALONG PORTIONS OF THE JAMES RIVER IN SOUTH DAKOTA.
HAZARDS
SLIGHT RISK OF EXCESSIVE HEAT FOR PARTS OF THE NORTHWEST, FRI, JUN 9.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE SOUTHERN AND CENTRAL
PLAINS AND LOWER AND MIDDLE MISSISSIPPI VALLEY, FRI-SUN, JUN 9-11.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF FLORIDA, FRI-SUN, JUN 9-11.
SLIGHT RISK OF HIGH WINDS FOR PARTS OF SOUTHWEST ALASKA AND ALEUTIAN ISLANDS,
FRI, JUN 9.
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 THE MIDDLE AND UPPER MISSISSIPPI
VALLEYS, THE OHIO VALLEY, AND GREAT LAKES.
DETAILED SUMMARY
FOR SUNDAY JUNE 04 - THURSDAY JUNE 08:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR FRIDAY JUNE 09 - THURSDAY JUNE 15: BY LATE NEXT WEEK, DYNAMICAL MODEL
500-HPA HEIGHT FORECASTS CONTINUE TO ADVERTISE A SPLIT FLOW PATTERN PREVAILING
OVER THE WESTERN CONUS WITH MORE AMPLIFIED TROUGHING DOWNSTREAM FORECAST
THROUGHOUT MUCH OF THE EASTERN CONUS. MUCH OF THE AMPLIFIED MID-LEVEL RIDGING
FAVORED OVER WESTERN CANADA IS STILL EXPECTED TO EASE EARLY IN WEEK-2, LEADING
TO A MODERATION OF TEMPERATURES AND A LOWERED RISK OF EXCESSIVE HEAT PERSISTING
OVER THE PACIFIC NORTHWEST AND NORTHERN INTERMOUNTAIN REGIONS. THE GEFS AND
ECMWF ENSEMBLES DIFFER SOMEWHAT ON THE TIMING OF THE DEAMPLIFICATION OF THIS
FEATURE . HOWEVER, THIS COOLING TREND IS REFLECTED IN THE REFORECAST TOOLS
WHICH GENERALLY DEPICT LOWER CHANCES FOR MAXIMUM TEMPERATURES EXCEEDING THE
85TH PERCENTILE COMPARED TO PREVIOUS GUIDANCE. A SLIGHT RISK OF EXCESSIVE HEAT
REMAINS ISSUED FOR DAY 8 (JUN 9) WHERE THERE IS STILL A 20% CHANCE OF DAYTIME
TEMPERATURES EXCEEDING 90 DEGREES F, AS THIS HEAT SIGNAL IS EXPECTED TO
DISSIPATE BY NEXT WEEKEND TIED TO THE WEAKENING AND NORTHWESTWARD SHIFTING
POSITIVE HEIGHT DEPARTURES.
AS THE NEGATIVE MID-LEVEL HEIGHT DEPARTURES OVER THE SOUTHWESTERN CONUS ARE
FAVORED TO SHIFT EASTWARD OVER THE INTERIOR WEST LATER IN THE PERIOD, BOTH THE
GEFS AND ECMWF ENSEMBLES SHOW MORE OF A SOUTHERLY FLOW COMPONENT AHEAD OF THE
TROUGH AXIS TO PROMOTE WARMING TEMPERATURES OVER PORTIONS OF THE GREAT PLAINS
AND MISSISSIPPI VALLEY. SINCE EARLIER THIS WEEK, REFORECAST TOOLS HAVE BEEN
FAIRLY CONSISTENT IN REGARDS TO THE ONSET OF THE INCREASING WARM SIGNAL OVER
SOUTHERN TEXAS BY NEXT WEEKEND, WITH INCREASED CHANCES OF DAYTIME TEMPERATURES
EXCEEDING THE 85TH PERCENTILE AND 100 DEGREES F ALONG AND NEAR THE RIO GRANDE
VALLEY. WHILE THE CALIBRATED HEAT TOOLS ALSO SUPPORT THIS GROWING WARM SIGNAL,
UNCALIBRATED TEMPERATURE GUIDANCE FROM THE GEFS AND ECMWF APPEAR RATHER TEPID,
DEPICTING A LIMITED COVERAGE OF WEAK, POSITIVE TEMPERATURE ANOMALIES OVER
SOUTHERN AND EASTERN TEXAS THROUGH THE MIDDLE OF THE PERIOD. AS A RESULT, NO
TEMPERATURE RELATED HAZARDS ARE ISSUED AT THIS TIME, BUT WILL CONTINUE TO BE
MONITORED IN SUBSEQUENT OUTLOOKS.
IN THE MIDWEST, THE ECMWF AND CANADIAN REFORECAST TOOLS INDICATE AT LEAST A 40%
CHANCE OF TEMPERATURES EXCEEDING THE 85TH CLIMATOLOGICAL PERCENTILE AND 90 DEG
F. HOWEVER, DUE TO THESE TOOLS NOT SHOWING ENHANCED RISK OF REACHING 95 DEG F
AND THE LACK OF SUPPORT FROM THE GEFS, A CORRESPONDING HEAT HAZARD IS NOT
POSTED. THIS HEAT EVENT WOULD LIKELY BE DRIVEN BY ABSOLUTE TEMPERATURES RATHER
THAN BEING MOISTURE DRIVEN, THUS REACHING HAZARDOUS THRESHOLDS WOULD BE LESS
LIKELY.
FOR PRECIPITATION, THERE IS FAIR AGREEMENT IN THE ENSEMBLES FEATURING SURFACE
LOW FORMATION IN THE LEE OF THE ROCKIES BY THE OUTSET OF WEEK-2. UNCALIBRATED
DAILY PRECIP AMOUNTS ARE ON THE LOW SIDE; HOWEVER REFORECAST TOOLS CONTINUE TO
INDICATE INCREASED CHANCES FOR 3-DAY AMOUNTS EXCEEDING THE 85TH PERCENTILE AND
1 INCH TO SUPPORT A SLIGHT RISK OF HEAVY PRECIPITATION OVER THE SOUTH-CENTRAL
CONUS DURING THE FIRST SEVERAL DAYS OF THE PERIOD. THE MOIST, LOW-LEVEL RETURN
FLOW FAVORED ALSO INCREASES THE POTENTIAL FOR THUNDERSTORM ACTIVITY IN THIS
HIGHLIGHTED REGION. FARTHER EAST, RAW PRECIPITATION TOOLS CONTINUE TO POINT TO
A STRONG UPTICK IN RAINFALL AND TROPICAL MOISTURE OVER FLORIDA AND THE
CARIBBEAN TIED TO A WEAKNESS IN THE SUBTROPICAL RIDGE AND A BROAD AREA OF LOW
PRESSURE EARLY IN THE PERIOD. A SLIGHT RISK OF HEAVY PRECIPITATION IS ADDED
OVER THE FLORIDA PENINSULA WHERE THERE IS BETTER AGREEMENT IN THE REFORECAST
TOOLS INDICATING AT LEAST A 20% CHANCE OF 3-DAY AMOUNTS EXCEEDING THE 85TH
PERCENTILE, AND THE UNCALIBRATED ECMWF DEPICTING >40% CHANCES FOR 3-DAY TOTALS
EXCEEDING AN INCH EARLY IN THE PERIOD.
DEVELOPING DROUGHT CONCERNS PERSIST ACROSS PARTS OF THE CENTRAL AND EASTERN
CORN BELT AND ADJACENT AREAS DURING WEEK-2. ANTECEDENT CONDITIONS ARE QUITE DRY
(2-4 INCHES BELOW NORMAL PRECIPITATION SINCE EARLY MAY) FROM THE MISSISSIPPI
VALLEY TO THE CENTRAL APPALACHIANS. ALTHOUGH TEMPERATURES AREN'T EXPECTED TO BE
VERY EXCEPTIONALLY WARM TO INCREASE EVAPOTRANSPIRATION RATES, MANY AREAS IN THE
MIDWEST AND THE MID-ATLANTIC ARE NOW EXPERIENCING ABNORMAL DRYNESS BASED ON THE
LATEST DROUGHT MONITOR, WITH LITTLE INDICATIONS FOR IMPROVEMENT GIVEN THE
NORMAL TO BELOW-NORMAL PRECIPITATION FAVORED THROUGH MID-JUNE. THEREFORE, THE
RAPID ONSET DROUGHT RISK REMAINS HIGHLIGHTED AND IS EXPANDED TO INCLUDE
ADDITIONAL AREAS IN THE MISSISSIPPI AND OHIO VALLEYS, GREAT LAKES, AND EASTWARD
TO THE CENTRAL APPALICHIANS.
SNOWMELT 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. 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. WITH INCREASED CHANCES FOR ABOVE NORMAL PRECIPITATION PREDICTED FOR
MUCH OF THE WESTERN CONUS DURING WEEK-2, POSSIBLE FLOODING CONTINUES TO BE
HIGHLIGHTED. DUE TO DECREASING SNOW WATER EQUIVALENT LEVELS ACROSS PORTIONS OF
SOUTH-CENTRAL AND NORTHEASTERN IDAHO, THE CORRESPONDING FLOOD HAZARD IS REMOVED
IN THE UPDATED OUTLOOK, AS WELL AS OVER PORTIONS OF SOUTHERN UTAH, WHERE
FLOODING ISSUES ARE EXPECTED TO EASE PRIOR TO THE WEEK-2 PERIOD. 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.
IN THE WESTERN PACIFIC, TROPICAL CYCLONE MAWAR IS FORECAST TO UNDERGO
EXTRATROPICAL TRANSITION AND BECOME ABSORBED IN THE WESTERLIES, WHERE AN
AMPLIFICATION OF THE MID-LEVEL PATTERN REMAINS FAVORED OVER THE BERING SEA AND
THE ALEUTIANS LATE IN WEEK-1. WHILE THE STRENGTH OF TROUGHING ALOFT AND SURFACE
LOW IS EXPECTED TO WEAKEN BY THE ONSET OF WEEK-2, THERE IS CONTINUED SUPPORT OF
STRENGTHENING PRESSURE GRADIENTS ASSOCIATED WITH THIS PATTERN AND SLIGHT RISK
OF HIGH WINDS REMAINS ISSUED (JUN 9) ACROSS THE ALEUTIAN ISLANDS AND PORTIONS
OF SOUTHWEST MAINLAND ALASKA.
FORECASTER: NICK NOVELLA
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