648
FXUS21 KWNC 161850
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT MAY 16 2023
SYNOPSIS: A BROAD AREA OF MID-LEVEL HIGH PRESSURE ACROSS MUCH OF THE NORTHERN
CONTIGUOUS UNITED STATES (CONUS) FAVORS GENERALLY ABOVE-NORMAL TEMPERATURES BUT
WITH LIMITED CHANCES FOR REACHING HAZARDS THRESHOLDS. HOWEVER, WARM
TEMPERATURES COULD ENHANCE THE SNOWMELT RATE WHERE DEEP SNOWPACK REMAINS IN
PLACE ACROSS THE HIGHER ELEVATIONS, INCREASING THE POTENTIAL FOR FLOODING ALONG
SOME RIVERS. HEAVY PRECIPITATION IS POSSIBLE IN PARTS OF THE GREAT PLAINS WHERE
MOIST, SOUTHERLY FLOW MAY INTERACT WITH A WEAK LOW-PRESSURE SYSTEM, AND ACROSS
THE SOUTHEAST COAST AND FLORIDA, DUE TO A POTENTIAL CUT-OFF SYSTEM. IN ALASKA,
RIVER-ICE BREAK-UP COULD LEAD TO FLOODING AND ICE JAMS IN THE INTERIOR ALONG
MAJOR RIVERS.
HAZARDS
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF FLORIDA AND THE COASTAL
CAROLINAS, WED-SUN, MAY 24-28.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE SOUTHERN AND CENTRAL
PLAINS, WED-FRI, MAY 24-26.
POSSIBLE FLOODING FOR PORTIONS OF CALIFORNIA, NEVADA, UTAH, WYOMING, WESTERN
MONTANA, IDAHO, OREGON, AND WASHINGTON.
POSSIBLE FLOODING ALONG PORTIONS OF THE JAMES RIVER AND THE MISSISSIPPI RIVER.
POSSIBLE FLOODING IN PARTS OF INTERIOR ALASKA ALONG THE TANANA, YUKON,
KUSKOKWIM, KOYUKUK, AND KOBUK RIVERS.
DETAILED SUMMARY
FOR FRIDAY MAY 19 - TUESDAY MAY 23:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR WEDNESDAY MAY 24 - TUESDAY MAY 30: THERE IS FAIR AGREEMENT IN THE MEAN
WEEK-2 500-HPA HEIGHT HEIGHT FORECASTS ACROSS THE DYNAMICAL MODELS TODAY.
POSITIVE 500-HPA HEIGHT ANOMALIES ARE FORECAST ACROSS MUCH OF THE CONUS
EXCLUDING THE SOUTHEAST WHERE NEAR TO SLIGHTLY BELOW-NORMAL HEIGHTS ARE
FORECAST, AND ALONG THE IMMEDIATE WEST COAST WHERE THE EUROPEAN AND GEFS ARE IN
BETTER AGREEMENT ON NEAR-NORMAL 500-HPA HEIGHTS. IN ALASKA, POSITIVE 500-HPA
HEIGHT ANOMALIES ACROSS THE WESTERN THIRD OF THE STATE ARE FORECAST, WITH NEAR
TO SLIGHTLY BELOW-NORMAL HEIGHTS IN THE EAST.
ABOVE-NORMAL TEMPERATURES ARE FAVORED ACROSS MUCH OF THE CONUS DURING WEEK-2.
THE ECMWF AND GEFS BOTH FORECAST TEMPERATURES EXCEEDING THE 85TH CLIMATOLOGICAL
PERCENTILE IN PORTIONS OF NORTHERN CONUS FROM THE PACIFIC NORTHWEST TO THE
GREAT LAKES DURING THE PERIOD. HOWEVER, THERE IS LIMITED SUPPORT FOR THESE
TEMPERATURES EXCEEDING 85 DEGF. THEREFORE, NO CORRESPONDING HAZARD SHAPES ARE
POSTED. WARM TEMPERATURES ARE ANTICIPATED TO ENHANCE THE SNOWMELT RATE ACROSS
THE WESTERN CONUS, INDUCING RIVER FLOODING ESPECIALLY ACROSS HIGHER ELEVATIONS
IN THE WEST AND THE SOUTHERN CANADIAN ROCKIES, WHERE A FEW SITES STILL REPORT
OVER 50 INCHES OF SNOW WATER CONTENT. THE ABOVE-NORMAL TEMPERATURES MAY CAUSE
RAPID SNOWMELT IN PARTS OF THE SIERRA NEVADA, GREAT BASIN, NORTHERN ROCKIES,
AND PACIFIC NORTHWEST, RESULTING IN AREAS AT HIGH RISK OF FLOODING AND
MUDSLIDES ALONG MANY RIVERS, AND IN AREAS ADJACENT TO THE HIGHER ELEVATIONS;
HOWEVER, EXPANSIVE, MULTI-STATE FLOODING IS NOT EXPECTED TO ENVELOP LARGE AREAS
OF THE INTERIOR WEST. FLOODING CONTINUES TO BE POSSIBLE ALONG SOME RIVERS IN
THE NORTH-CENTRAL CONUS DUE TO PREVIOUS SNOWMELT.
AT THE BEGINNING OF THE PERIOD, MULTIPLE MODELS INDICATE THE POTENTIAL FOR A
SURFACE LOW OVER THE WESTERN PORTIONS OF THE FOUR CORNERS, SOUTHERN NEVADA AND
SOUTHERN CALIFORNIA. THIS PATTERN MAY SUPPORT ENHANCED MOIST SOUTHERLY FLOW
OVER PARTS OF THE FOUR CORNERS, RESULTING IN ENHANCED PRECIPITATION IN THE
REGION. BOTH REFORECAST TOOLS INDICATE A BROAD AREA WITH AT LEAST A 20% CHANCE
OF 3-DAY RAINFALL EXCEEDING THE 85TH CLIMATOLOGICAL PERCENTILE, PRIMARILY
DURING DAYS 8 TO 10, BUT LIMITED SUPPORT FOR PRECIPITATION EXCEEDING HALF AN
INCH. THE ECMWF TOOLS SHOW THE HIGHEST CHANCES (>40%) OF EXCEEDING THESE
THRESHOLDS ACROSS NORTHERN ARIZONA, SOUTHERN UTAH AND SOUTHERN NEVADA. DUE TO
THIS BEING THE DRIEST TIME OF THE YEAR IN A RELATIVELY ARID REGION OF THE
COUNTRY, ONLY A FEW TENTHS OF AN INCH FOR A ONE-WEEK PERIOD IS CONSIDERABLY
ABOVE NORMAL. IN ALMOST 130 YEARS OF RECORD, MAY MONTHLY TOTALS AT PHOENIX, AZ
HAVE ONLY EXCEEDED AN INCH FOUR TIMES, AND ONLY THE EUROPEAN REFORECAST SHOWS A
NON-TRIVIAL CHANCE FOR PRECIPITATION TOTALS TO EXCEED A HALF AN INCH. THE
UNCALIBRATED ENSEMBLE MEANS HAVE LESS AGREEMENT COMPARED TO THE REFORECAST
TOOLS, WITH THE GEFS HAVING A GREATER SIGNAL FOR ENHANCED PRECIPITATION THAN
THE ECMWF. BASED ON SIGNIFICANT UNCERTAINTY REGARDING HEAVY PRECIPITATION
POTENTIAL AND CONSIDERING CLIMATOLOGY AT THIS TIME OF THE YEAR, NO HAZARD IS
POSTED AT THIS TIME.
BENEATH AN AREA OF BELOW-NORMAL 500-HPA HEIGHTS ALONG THE EASTERN GULF COAST AN
AREA OF LOW-PRESSURE MAY DEVELOP AND REMAIN NEARLY STATIONARY DURING THE WEEK-2
PERIOD. THE EUROPEAN REFORECAST TOOL HAS STRONG CHANCES (>60%) FOR 3-DAY TOTAL
PRECIPITATION TOTALS IN FLORIDA TO EXCEED THE 85TH CLIMATOLOGICAL PERCENTILE.
THE GEFS AND CANADIAN REFORECAST TOOLS LIKEWISE SUPPORT 3-DAY TOTAL
PRECIPITATION EXCEEDING THE 85TH PERCENTILE WITH LOWER PROBABILITIES. THE
UNCALIBRATED GUIDANCE FROM THE ECMWF AND GEFS SIMILARLY SUPPORT A CHANCE FOR
HEAVY PRECIPITATION. THEREFORE, A SLIGHT RISK OF HEAVY PRECIPITATION IS POSTED
FOR WED-SUN, MAY 24-28, FOR MUCH OF FLORIDA AND THE COASTAL REGIONS OF NORTH
AND SOUTH CAROLINA.
REFORECAST AND UNCALIBRATED GUIDANCE FROM MULTIPLE MODEL RUNS INDICATE ELEVATED
CHANCES FOR PRECIPITATION TO EXCEED THE 85TH CLIMATOLOGICAL PERCENTILE ACROSS
PARTS OF THE CENTRAL AND SOUTHERN PLAINS DURING THE WEEK-1 PERIOD. MOIST
SOUTHERLY SURFACE FLOW FROM THE GULF OF MEXICO MAY INTERACT WITH A WEAK LOW
PRESSURE SYSTEM BRINGING CHANCES FOR THUNDERSTORMS TO THE REGION. THEREFORE, A
SLIGHT RISK OF HEAVY PRECIPITATION IS POSTED FOR WED-FRI, MAY 24-26, FOR
PORTIONS OF THE CENTRAL AND SOUTHERN PLAINS.
IN INTERIOR ALASKA, WARMER TEMPERATURES DURING THE PAST WEEK HAVE LED TO RISES
IN MANY OF THE RIVERS IN THE REGION. THERE ARE CURRENTLY SEVERAL FLOOD WATCHES
AND ADVISORIES POSTED THROUGHOUT INTERIOR ALASKA. MUCH OF THE TANANA RIVER NOW
HAS OPEN WATER AS RIVER ICE CONTINUES TO MELT BUT THERE ARE LINGERING CONCERNS
FOR SNOWMELT FLOODING INTO THE WEEK-2 PERIOD. THE ICE FRONT ALONG THE YUKON
RIVER IS PROGRESSING DOWNRIVER AND MAY BRING FLOODING CONCERNS TO AREAS
DOWNRIVER OF FAIRBANKS BY WEEK-2. OTHER RIVERS OF CONCERN FOR RIVER ICE BREAK
UP LEADING TO THE POTENTIAL FOR POSSIBLE FLOODING AND ICE JAMS ARE THE
KUSKOKWIM, KOYUKUK, AND KOBUK RIVERS.
FORECASTER: RYAN BOLT
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page