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FXUS21 KWNC 031743
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT MAY 03 2023
SYNOPSIS: FOLLOWING A PERIOD OF COOLER THAN NORMAL TEMPERATURES OVER THE
WESTERN CONTIGUOUS U.S. (CONUS) EARLY IN WEEK-2, BROAD SCALE MID-LEVEL HIGH
PRESSURE IS PREDOMINATELY FAVORED IN THE DYNAMICAL MODELS, WHICH IS EXPECTED TO
BRING UNSEASONABLY WARM SPRING TEMPERATURES FOR MUCH OF THE CONUS. SURFACE LOW
FORMATION ALONG WITH INCREASED RETURN FLOW FROM THE GULF OF MEXICO SUPPORTS
INCREASED CHANCES FOR HEAVY PRECIPITATION ACROSS THE SOUTH-CENTRAL CONUS.
SPRINGTIME FLOODING ASSOCIATED WITH SNOWMELT IS LIKELY TO PERSIST ACROSS PARTS
OF THE WEST, ALONG WITH THE RED RIVER OF THE NORTH, JAMES RIVER, AND UPPER TO
MIDDLE MISSISSIPPI RIVER.
HAZARDS
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE GREAT PLAINS,
MISSISSIPPI, TENNESSEE AND OHIO VALLEYS, AND SOUTHEAST, THU-SUN, MAY 11-14.
POSSIBLE FLOODING FOR PORTIONS OF CALIFORNIA, IDAHO, NEVADA, OREGON, AND UTAH.
POSSIBLE FLOODING ALONG PORTIONS OF THE RED RIVER OF THE NORTH, JAMES RIVER,
AND MISSISSIPPI RIVER.
DETAILED SUMMARY
FOR SATURDAY MAY 06 - WEDNESDAY MAY 10:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR THURSDAY MAY 11 - WEDNESDAY MAY 17: THERE IS GOOD AGREEMENT IN THE MEAN
WEEK-2 500-HPA HEIGHT ANOMALY FORECASTS BETWEEN THE DYNAMICAL MODELS. WHILE
THE GEFS FEATURES A LESS AMPLIFIED MEAN SOLUTION COMPARED TO THE ECMWF AND
CANADIAN ENSEMBLES, ANOMALOUS MID-LEVEL RIDGING IS PREDOMINATELY FAVORED
THROUGHOUT MUCH OF THE CONUS WHICH IS ANTICIPATED TO PROVIDE UNSEASONABLY WARM
SPRING TEMPERATURES, AND QUELL ANY TEMPERATURE-RELATED HAZARD POTENTIAL DURING
WEEK-2. THE ONE POSSIBLE EXCEPTION STILL CONCERNS THE WEST, AS THERE ARE
CONTINUED INDICATIONS IN THE ENSEMBLES FOR SHORTWAVE TROUGHING TO BRING A
PERIOD OF COOLER AND WETTER CONDITIONS EARLY IN THE PERIOD. WHILE THE
REFORECAST TOOLS CONTINUE TO SHOW INCREASED CHANCES FOR MINIMUM TEMPERATURES
FALLING BELOW THE 15TH PERCENTILE, THERE IS LESSER SUPPORT FOR THESE
TEMPERATURES MEETING HAZARD CRITERIA, AND THE SLIGHT RISK OF MUCH BELOW NORMAL
TEMPERATURES IS DISCONTINUED OVER NORTHERN CALIFORNIA AND THE PACIFIC
NORTHWEST. GRADUALLY RISING MID-LEVEL HEIGHTS OVER THE WEST CONTINUE TO BE
FAVORED IN THE ENSEMBLES, WHICH IS EXPECTED TO BRING WARMER THAN NORMAL
TEMPERATURES LATER IN WEEK-2.
AS SOME OF THE SHORTWAVE ENERGY PROPAGATES EASTWARD, SURFACE LOW FORMATION IN
THE LEE OF THE ROCKIES AND INCREASED RETURN FLOW FROM THE GULF OF MEXICO
REMAINS FAVORED IN THE ENSEMBLE GUIDANCE. SINCE YESTERDAY, THE RAW ECMWF HAS
BACKED OFF SOMEWHAT ON HEAVY PRECIPITATION SIGNALS, BUT STILL MAINTAINS 30-40%
CHANCES FOR 3-DAY ACCUMULATIONS EXCEEDING AN INCH OVER THE SOUTHERN PLAINS AND
LOWER MISSISSIPPI VALLEY. THE ECMWF REFORECAST TOOL ALSO DEPICTS SIMILAR
CHANCES FOR AMOUNTS EXCEEDING THE 85TH PERCENTILE IN THE REGION, BUT SHOWS
WETTER SIGNALS EXTENDING FURTHER NORTHWARD INTO THE CENTRAL PLAINS AND MIDDLE
MISSISSIPPI VALLEY. HOWEVER, BOTH THE GEFS AND CANADIAN REFORECAST TOOLS REMAIN
COMPARABLY WEAKER IN REGARDS TO THE MAGNITUDE AND SPATIAL EXTENT OF THE HEAVY
PRECIPITATION POTENTIAL, PROMPTING THE CONTINUATION OF A SLIGHT RISK OF HEAVY
PRECIPITATION OVER THE SOUTH-CENTRAL CONUS. DUE TO MODEL DIFFERENCES IN THE
TIMING AND LOCATION OF THE PREDICTED SURFACE LOW, AS WELL AS MORE PERSISTENT
WET SIGNALS EVIDENT IN THE LATEST REFORECAST GUIDANCE, THIS HAZARD IS EXTENDED
INTO THE MIDDLE OF THE WEEK-2, VALID FROM MAY 11-14. REGARDLESS OF WHETHER
PRECIPITATION EXCEEDS HAZARD THRESHOLDS, NEAR TO ABOVE-NORMAL PRECIPITATION IS
FAVORED THROUGH THE MIDDLE OF WEEK-2, WHICH IS LIKELY TO PROVIDE SOME RELIEF TO
AREAS IN THE CORN BELT AFFECTED BY ANOMALOUS DRYNESS THIS SPRING. PRECIPITATION
DEFICITS DURING THE LAST 30 DAYS CONTINUE TO RUN 2 INCHES BELOW NORMAL ACROSS
PORTIONS OF MISSOURI, SOUTHEASTERN IOWA, AND CENTRAL ILLINOIS.
WARMING SPRINGTIME TEMPERATURES HAVE LED TO CONTINUED SNOWMELT, INCREASING
FLOWS ALONG STREAMS AND RIVERS ACROSS MUCH OF THE WEST. AS THIS RISK IS
ANTICIPATED TO PERSIST WELL INTO MAY, A BROAD POSSIBLE FLOODING AREA REMAINS
POSTED FOR MANY PARTS OF CALIFORNIA, NEVADA, OREGON, IDAHO, UTAH AND WYOMING.
FARTHER EAST WHERE TEMPERATURES ARE FAVORED TO BE ABOVE-NORMAL, ACCELERATED
SPRING SNOWMELT DURING WEEK-2 IS POSSIBLE, THUS THE CORRESPONDING FLOODING
AREAS ALSO REMAIN POSTED ALONG THE RED RIVER OF THE NORTH, AND THE JAMES RIVER
OVER THE DAKOTAS, AS WELL AS ALONG THE UPPER AND MIDDLE MISSISSIPPI RIVER. MANY
RIVER GAUGES IN THE HIGHLIGHTED AREAS ARE FORECAST TO REMAIN ABOVE FLOOD STAGE.
ACROSS ALASKA, MODEST CHANCES FOR ABOVE NORMAL TEMPERATURES ARE INDICATED IN
THE REFORECAST GUIDANCE MAINLY OVER THE EASTERN MAINLAND. HOWEVER, THIS IS AT
ODDS WITH SEVERAL OF THE RAW TEMPERATURE TOOLS WHICH CONTINUE TO LEAN COLDER
OVER MUCH OF THE STATE, LEADING TO UNCERTAINTY IN THE OUTLOOK. NO TEMPERATURE
RELATED HAZARDS ARE POSTED, THOUGH SUBSEQUENT OUTLOOKS WILL CONTINUE TO MONITOR
ANY TRANSITION TO A WARMER PATTERN, AS THIS MAY ACCELERATE SNOW AND ICE MELT
DURING THE SPRING BREAKUP SEASON.
FORECASTER: NICK NOVELLA
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