120
FXUS21 KWNC 011915
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT MAY 01 2023
SYNOPSIS: EARLY IN WEEK-2, FORECAST MID-LEVEL LOW PRESSURE OVER THE WESTERN
CONTIGUOUS U.S. (CONUS) IS EXPECTED TO BRING ANOMALOUSLY COLD TEMPERATURES TO
PRIMARILY THE WEST COAST STATES, WHICH MAY ADVERSELY AFFECT DEVELOPING
AGRICULTURE ACROSS PARTS OF NORTHERN CALIFORNIA AND THE PACIFIC NORTHWEST.
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 MUCH BELOW-NORMAL TEMPERATURES FOR PARTS OF NORTHERN CALIFORNIA,
AND THE PACIFIC NORTHWEST, TUE-WED, MAY 9-10.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE GREAT PLAINS,
MISSISSIPPI, TENNESSEE AND OHIO VALLEYS, WED-FRI, MAY 10-12.
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 THURSDAY MAY 04 - MONDAY MAY 08:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR TUESDAY MAY 09 - MONDAY MAY 15: LEADING INTO THE WEEK-2 PERIOD, THERE HAS
BEEN GOOD RUN-TO-RUN CONTINUITY IN THE DYNAMICAL MODELS FAVORING AMPLIFIED
500-HPA RIDGING OVER CENTRAL CANADA, WITH A PAIR OF ANOMALOUS TROUGHS TO THE
EAST AND TO THE WEST OF THE RIDGE AXIS, CHARACTERISTIC OF AN OMEGA BLOCKING
PATTERN OVER NORTH AMERICA. BY EARLY TO MID-NEXT WEEK, DAILY ENSEMBLE MEAN
GUIDANCE GENERALLY FAVORS DEAMPLIFICATION IN THE PATTERN. THE 0Z GEFS OFFERS A
FAIRLY MUTED PERSPECTIVE, LIMITING THE LARGEST MID-LEVEL HEIGHT DEPARTURES TO
THE NORTHERN TIER OF THE CONUS. THE ECMWF AND CANADIAN ENSEMBLE MEAN ANOMALIES
ARE SLIGHTLY STRONGER AND MORE EXPANSIVE BY COMPARISON, INDICATING POSITIVE
HEIGHT DEPARTURES OVER THE EASTERN CONUS LATER IN THE PERIOD.
LATE IN WEEK-1, ANOMALOUS TROUGHING OVER THE NORTHEASTERN PACIFIC IS EXPECTED
TO BRING BELOW NORMAL TEMPERATURES TO MANY PARTS OF THE WEST COAST. WHILE A
MODERATION OF TEMPERATURES ARE FAVORED ASSOCIATED WITH THE RISING HEIGHTS ALOFT
EARLY NEXT WEEK, REFORECAST TOOLS SHOW AT LEAST A 20% CHANCE OF MINIMUM
TEMPERATURES FALLING BELOW THE 15TH PERCENTILE AND 40 DEGREES F EARLY IN
WEEK-2. ANY OBSERVED NEAR TO BELOW FREEZING TEMPERATURES WOULD BE CONSIDERED
CLIMATOLOGICALLY LATE WHICH MAY ADVERSELY IMPACT DEVELOPING AGRICULTURE OVER
PARTS OF NORTHERN CALIFORNIA AND THE PACIFIC NORTHWEST. THEREFORE, A SLIGHT
RISK OF MUCH BELOW NORMAL TEMPERATURES IS ISSUED (MAY 9-10) FOR THE REGION.
FOR PRECIPITATION, BOTH THE GEFS AND ECMWF ENSEMBLES FAVOR SURFACE LOW
FORMATION IN THE LEE OF THE ROCKIES TOWARDS THE MIDDLE OF NEXT WEEK. WHILE
THERE IS A GOOD DEAL OF UNCERTAINTY IN TERMS OF THE STRENGTH AND LOCATION OF
THE SURFACE LOW AT THIS LEAD, ENHANCED RETURN FLOW FROM THE GULF OF MEXICO IS
FAVORED, SUPPORTING INCREASED POTENTIAL FOR ENHANCED PRECIPITATION THROUGHOUT
THE CENTRAL CONUS, MOST LIKELY FROM THE BEGINNING TO THE MIDDLE OF THE PERIOD.
THIS POTENTIAL IS SUPPORTED BY BOTH THE GEFS AND ECMWF REFORECAST TOOLS
INDICATING AT LEAST A 20% CHANCE OF 3-DAY AMOUNTS EXCEEDING THE 85TH
PERCENTILE. THUS, A SLIGHT RISK OF HEAVY PRECIPITATION IS POSTED OVER THE
SOUTH-CENTRAL U.S. DAYS 9-11 (MAY 10-12). EVEN IF PRECIPITATION TOTALS DO NOT
REACH HAZARDOUS THRESHOLDS, THE ABOVE-NORMAL PRECIPITATION FAVORED 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.
DESPITE SOME OF THE ANOMALOUS COLD FAVORED ACROSS PARTS OF THE WEST EARLY IN
THE PERIOD, WARMER SPRINGTIME TEMPERATURES HAVE LED TO CONTINUED SNOWMELT,
ELEVATING FLOWS ALONG STREAMS AND RIVERS. AS THIS RISK IS ANTICIPATED TO
PERSIST WELL INTO MAY, A BROAD POSSIBLE FLOODING AREA REMAINS POSTED FOR MANY
PARTS OF CALIFORNIA, NEVADA, IDAHO, UTAH AND WYOMING, AND IS EXPANDED IN THE
UPDATED OUTLOOK TO INCLUDE PORTIONS OF EASTERN OREGON WHERE THERE IS AN
INCREASED RISK FOR FLOODING DURING WEEK-1, WITH ABOVE-NORMAL PRECIPITATION
FAVORED TO PERSIST INTO EARLY WEEK-2. 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.
OVER ALASKA, WARMER AND WETTER CONDITIONS ARE FAVORED FOR WEEK-2 ACROSS THE
SOUTHERN MAINLAND AND THE SOUTHEAST. WHILE THE PREDICTED TEMPERATURES AND
PRECIPITATION AMOUNTS DO NOT WARRANT ANY CORRESPONDING HAZARDS, A TRANSITION TO
A WARMER PATTERN MAY ACCELERATE SNOWMELT AND RIVER ICE BREAKUP.
FORECASTER: NICK NOVELLA
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