433
FXUS21 KWNC 021818
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT JUNE 02 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. DEVELOPING 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, SAT-SUN, JUN 10-11.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE SOUTHERN AND CENTRAL
PLAINS AND LOWER AND MIDDLE MISSISSIPPI VALLEY, TENNESSEE VALLEY AND SOUTHEAST,
SAT-TUE, JUN 10-13.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF FLORIDA, SAT-SUN, JUN 10-11.
SLIGHT RISK OF HIGH WINDS FOR PARTS OF SOUTHWEST ALASKA AND THE ALEUTIAN
ISLANDS, SAT, JUN 10.
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 MONDAY JUNE 05 - FRIDAY JUNE 09:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR SATURDAY JUNE 10 - FRIDAY JUNE 16: RELATIVE TO YESTERDAY, THERE IS LITTLE
CHANGE TO THE HAZARDS PERSPECTIVE DURING WEEK-2. BY THE START OF THE PERIOD,
DYNAMICAL MODELS CONTINUE TO FAVOR A SPLIT FLOW PATTERN OVER THE WESTERN CONUS,
WITH FAIRLY AMPLIFIED TROUGHING DOWNSTREAM FORECAST THROUGHOUT MUCH OF THE
EASTERN CONUS. MUCH OF THE MID-LEVEL RIDGING FAVORED OVER WESTERN CANADA
REMAINS FAVORED TO WEAKEN AND SHIFT WESTWARD WITH TIME, HOWEVER BOTH THE GEFS
AND ECMWF MEAN ENSEMBLES HAVE BECOME MORE SLUGGISH WITH THIS EVOLUTION, AND THE
LATTER MEAN SOLUTION FEATURES A STRONGER AND MORE EXPANSIVE RIDGE COMPARED TO
YESTERDAY'S GUIDANCE. AS A RESULT, ANOMALOUSLY WARM TEMPERATURES AND EXCESSIVE
HEAT ARE FAVORED TO LINGER A BIT LONGER THAN PREVIOUSLY FORECAST OVER THE
NORTHWESTERN CONUS. WITH THE ECMWF FAVORING THE STRONGER RIDGE ALOFT, ITS
REFORECAST GUIDANCE SHOWS A GREATER AND MORE PERSISTENT COVERAGE OF INCREASED
CHANCES FOR MAXIMUM TEMPERATURES EXCEEDING HAZARDS CRITERIA COMPARED TO THE
GEFS AND CANADIAN COUNTERPART. TO RECONCILE THESE DIFFERENCES, A SLIGHT RISK
OF EXCESSIVE HEAT REMAINS ISSUED WHERE THE REFORECAST TOOLS ARE IN MOST
AGREEMENT (JUN 10-11) BEFORE THE HEAT SIGNALS BEGIN TO DISSIPATE LATER IN THE
PERIOD.
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 THE SOUTH-CENTRAL CONUS.
ALTHOUGH THE GEFS CONTINUES TO SUPPORT A GROWING POTENTIAL FOR EXCESSIVE HEAT
ACROSS THE RIO GRANDE VALLEY DURING THE PERIOD, THERE IS LESSER SUPPORT FOR
THIS REALIZATION IN THE LATEST ECMWF REFORECAST TOOL, AND UNCALIBRATED
TEMPERATURE GUIDANCE CONTINUES TO DEPICT WEAKLY POSITIVE TEMPERATURE ANOMALIES
ACROSS THE REGION. THEREFORE, NO CORRESPONDING TEMPERATURE HAZARDS ARE POSTED.
TIED TO POTENTIAL SHORTWAVE ENERGY SHIFTING EASTWARD OVER THE ROCKIES, THERE
ARE CONTINUED INDICATIONS OF SURFACE LOW FORMATION OVER THE GREAT PLAINS EARLY
IN THE PERIOD. SOME UNCERTAINTY EXISTS WITH THE DEGREE OF RETURN FLOW TO
INCREASE LOWER-LEVEL MOISTURE, HOWEVER THERE IS GOOD AGREEMENT IN THE
REFORECAST TOOLS DEPICTING AT LEAST A 20% CHANCE OF 3-DAY AMOUNTS EXCEEDING THE
85TH PERCENTILE AND 1 INCH OVER PORTIONS OF THE GREAT PLAINS AND MISSISSIPPI
VALLEY THAT SUPPORTS THE CONTINUATION OF A SLIGHT RISK OF HEAVY PRECIPITATION
EARLY IN THE PERIOD. RELATIVE TO YESTERDAY, THERE ARE INCREASED SIGNALS IN THE
REFORECAST TOOLS FOR THIS HEAVY PRECIPITATION RISK SHIFTING EASTWARD INTO PARTS
OF THE TENNESSEE VALLEY AND SOUTHEAST LATER IN THE PERIOD. THIS IS ALSO
REFLECTED IN THE RAW GUIDANCE FAVORING INCREASED PRECIPITATION AMOUNTS MAINLY
OVER THE GULF STATES BY DAY 10 (JUN 12), AND THE SLIGHT RISK AREA IS EXPANDED
AND EXTENDED THROUGH JUN 13 TO ACCOUNT FOR THIS POTENTIAL. FARTHER EAST, RAW
PRECIPITATION TOOLS CONTINUE TO POINT TO A STRONG UPTICK IN RAINFALL AND
TROPICAL MOISTURE OVER PARTS OF FLORIDA AND THE CARIBBEAN TIED TO A WEAKNESS IN
THE SUBTROPICAL RIDGE AND A BROAD AREA OF LOW PRESSURE EARLY IN THE PERIOD.
SIGNALS FOR HEAVY PRECIPITATION HAVE BACKED OFF AND SHIFTED SOUTHWARD COMPARED
TO YESTERDAY, AS SOME OF THIS POTENTIAL IS STARTING TO TIME-OFF BASED ON RAW
PRECIPITATION GUIDANCE LATE IN WEEK-1. HOWEVER, A SLIGHT RISK OF HEAVY
PRECIPITATION REMAINS ISSUED FOR PORTIONS OF FLORIDA WHERE THE RAW ECMWF
INDICATES 20-30% CHANCES FOR 3-DAY AMOUNTS 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
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 INDICATION FOR IMPROVEMENT GIVEN THE NORMAL
TO BELOW-NORMAL PRECIPITATION FAVORED THROUGH MID-JUNE. THEREFORE, THE RAPID
ONSET DROUGHT RISK REMAINS HIGHLIGHTED FOR PORTIONS OF THE MIDDLE AND UPPER
MISSISSIPPI VALLEYS, THE OHIO VALLEY, AND GREAT LAKES.
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. 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 THE
SURFACE LOW IS EXPECTED TO WEAKEN BY EARLY WEEK-2, STRONG PRESSURE GRADIENTS
ARE STILL POSSIBLE ASSOCIATED WITH THIS PATTERN AND A SLIGHT RISK OF HIGH WINDS
REMAINS POSTED (JUN 10) ACROSS THE ALEUTIAN ISLANDS AND PORTIONS OF
SOUTHWESTERN MAINLAND ALASKA.
FORECASTER: NICK NOVELLA
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