895
FXUS21 KWNC 081808
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT MAY 08 2023
SYNOPSIS: A BROAD AREA OF MID-LEVEL HIGH PRESSURE SHOULD FAVOR PREDOMINANTLY
ABOVE-NORMAL TEMPERATURES ACROSS THE NORTH-CENTRAL STATES AND IN MOST AREAS
FROM THE ROCKIES WESTWARD TO THE PACIFIC COAST. THIS SHOULD ENHANCE THE
SNOWMELT RATE IN THESE AREAS, ELEVATING THE POTENTIAL FOR FLOODING ALONG SOME
RIVERS AND NEAR THE HIGHER ELEVATIONS. THE NORTHWEST QUARTER OF THE CONTIGUOUS
U.S. (CONUS), WHERE TEMPERATURES WILL BE WELL ABOVE NORMAL AND WHERE A DEEP
SNOWPACK IS STILL IN PLACE ACROSS THE HIGHER ELEVATIONS. N CONTRAST, DECLINING
SNOW COVER SHOULD HAVE FLOODING ON THE WANE IN THE NORTH-CENTRAL CONUS.
ELSEWHERE, SUBSTANTIAL PRECIPITATION COULD IMPACT AREAS FROM THE LOWER
MISSISSIPPI VALLEY THROUGH THE SOUTH ATLANTIC STATES, AND PERIODS OF WET AND
WINDY WEATHER ARE POSSIBLE ALONG THE GULF OF ALASKA COASTLINE, BUT CONDITIONS
ARE NOT EXPECTED TO RISE TO HAZARD THRESHOLDS.
HAZARDS
POSSIBLE FLOODING FOR PORTIONS OF CALIFORNIA, NEVADA, UTAH, WYOMING, WESTERN
MONTANA, IDAHO, OREGON, AND WASHINGTON.
POSSIBLE FLOODING ALONG PORTIONS OF THE RED RIVER OF THE NORTH, THE JAMES
RIVER, AND THE MISSISSIPPI RIVER.
DETAILED SUMMARY
FOR THURSDAY MAY 11 - MONDAY MAY 15:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR TUESDAY MAY 16 - MONDAY MAY 22: THERE IS GOOD AGREEMENT IN THE MEAN WEEK-2
500-HPA HEIGHT ANOMALY FORECASTS BETWEEN THE DYNAMICAL MODELS. ANOMALOUS
MID-LEVEL RIDGING IS FORECAST TO COVER THE NORTH-CENTRAL STATES AND AREAS FROM
THE ROCKIES WESTWARD, WITH MEAN HEIGHTS NEAR OR BELOW NORMAL IN SOUTHERN AND
EASTERN PARTS OF THE CONUS. THIS SHOULD LEAD TO CONSIDERABLY WARMER THAN NORMAL
WEATHER THERE, BUT TEMPERATURES ARE EXPECTED TO REMAIN BELOW HAZARDS
THRESHOLDS, SO NO TEMPERATURE HAZARDS ARE POSTED; HOWEVER, AT LEAST A FEW DAYS
COULD BE UNSEASONABLY WARM IN THE NORTHWEST DURING THE FIRST HALF OF WEEK-2,
WITH NONTRIVIAL CHANCES FOR TEMPERATURES TOPPING OUT IN THE MID-80S TO LOW 90S
DEG F IN SOME VALLEYS EAST OF THE CASCADES AND WEST OF THE SIERRA NEVADA. THE
WARM WEATHER SHOULD ENHANCE THE SNOWMELT RATE THROUGHOUT THESE AREAS. THIS WILL
LIKELY INDUCE RIVER FLOODING ALONG SOME RIVERS IN THE NORTH-CENTRAL STATES, BUT
SNOW COVER IS BECOMING DEPLETED IN THIS AREA AND ADJACENT CANADA, WHICH SHOULD
HAVE ANY RIVER FLOODING ON THE WANE THERE. IN CONTRAST, THE SNOWPACK REMAINS
VERY DEEP IN MANY HIGHER ELEVATIONS IN THE WEST AND THE SOUTHERN CANADIAN
ROCKIES, WITH A FEW SITES THERE STILL REPORTING OVER 100 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 IS ONGOING
OR ANTICIPATED ALONG PARTS OF THE PORTNEUF, BEAR, HUMBOLDT, NACHES, AND
OKANOGAN RIVER, AMONG OTHERS.
LATER WEEK-1, A MID-LEVEL TROUGH AXIS CENTERED APPROXIMATELY OVER THE SOUTHERN
ROCKIES IS EXPECTED TO COINCIDE WITH A FETCH OF MOIST SUBTROPICAL AIR FROM THE
GULF OF MEXICO INTO PARTS OF THE SOUTHERN GREAT PLAINS AND ADJACENT LOWER
MISSISSIPPI VALLEY. HEAVY RAIN IS EXPECTED TO RESULT LATER WEEK-1, WITH 3 TO
LOCALLY 8 INCHES ANTICIPATED OVER MUCH OF TEXAS AND PART OF OKLAHOMA. BY
WEEK-2, CONDITIONS SHOULD BE IMPROVING AS THE WET SET-UP DRIFTS EASTWARD AND
WEAKENS. TOOLS ARE INCONSISTENT IN THE MAGNITUDE, TIMING, AND LOCATION OF ANY
HEAVY PRECIPITATION OCCURRING EARLY WEEK-2, AND MOST KEEP AMOUNTS BELOW HAZARDS
THRESHOLDS, SO NO HEAVY PRECIPITATION RISK HAS BEEN POSTED.
MODELS ARE IN GOOD AGREEMENT BRINGING UNSEASONABLY HEAVY PRECIPITATION INTO THE
SOUTHWESTERN CONUS DURING THE FIRST HALF OF WEEK-2, LARGELY FUELED BY
ANOMALOUSLY STRONG EASTERLY WINDS PULLING MOISTURE FROM THE GULF OF MEXICO INTO
THE REGION. THE VARIOUS TOOLS, HOWEVER, ARE LESS CONSISTENT IN SHOWING HOW HIGH
ODDS ARE FOR HEAVY PRECIPITATION, AND IN HOW MUCH PRECIPITATION IS FORECAST.
THE EUROPEAN ENSEMBLE REFORECAST IS THE MOST ROBUST TOOL, CENTERING THE BEST
CHANCES FOR HEAVY PRECIPITATION OVER ARIZONA, INDICATING A 70 TO 90 PERCENT
CHANCE FOR PRECIPITATION AMONG THE TOP 15 PERCENT OF THE HISTORICAL
DISTRIBUTION. THE GEFS IS LESS EXTREME, BUT STILL SHOWS A 40 TO 60 PERCENT
CHANCE FOR SUCH TOTALS CENTERED OVER THE SAME AREA. MEANWHILE, THE CANADIAN
ENSEMBLE REFORECAST IS MUCH DRIER, SHOWING LITTLE IF ANY ENHANCED CHANCES FOR
HEAVY PRECIPITATION. BUT THIS IS THE DRIEST TIME OF THE YEAR FOR THIS
RELATIVELY DRY SECTION OF THE COUNTRY, AND 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 ONE-HALF INCH. BASED ON THE PREPONDERANCE OF TOOLS AND
CONSIDERING CLIMATOLOGY, IT IS UNLIKELY THAT TOTALS WILL REACH HAZARDS
THRESHOLDS, NO HAZARD IS POSTED AT THIS TIME.
OVER THE PAST SEVERAL WEEKS, BELOW-NORMAL PRECIPITATION HAS FALLEN OVER MUCH OF
THE MIDWEST, INCLUDING PART OF THE CORN BELT. TOTALS OVER THE LAST 60 DAYS WERE
BELOW HALF OF NORMAL FROM THE CENTRAL GREAT PLAINS THROUGH PORTIONS OF THE
MIDDLE MISSISSIPPI VALLEY, AND 30-DAY SHORTFALLS EXCEED 3 INCHES OVER A
SIGNIFICANT PORTION OF MISSOURI AND SOME ADJACENT AREAS. BUT MODERATE TO HEAVY
PRECIPITATION IS EXPECTED DURING WEEK-1 AND TEMPERATURES WILL NOT BE FAR
REMOVED FROM NORMAL WEEK-2, REDUCING THE THREAT FOR RAPID-ONSET DROUGHT.
ACROSS ALASKA, THE MID-LEVEL TROUGH IN PLACE EARLY WEEK-2 IS EXPECTED TO
PRODUCE SURFACE CYCLOGENESIS OVER OR WEST OF THE GULF OF ALASKA. MOST TOOLS
SHOW THE SURFACE STORM DEVELOPMENT CONSIDERABLY REMOVED FROM THE SOUTHERN
ALASKAN COASTLINE, AND SOUTH OF THE ALEUTIANS. ABOVE-NORMAL PRECIPITATION AND
GUSTY WINDS COULD AFFECT THE SOUTHERN TIER OF THE STATE FOR THE FIRST HALF OF
WEEK-2, BUT MOST TOOLS SHOW CONDITIONS REMAINING BELOW HAZARDS THRESHOLDS AT
THIS TIME. THE MID-LEVEL TROUGH DISSIPATES QUICKLY BY THE MIDDLE OF THE PERIOD,
WHICH SHOULD END ANY STORMY WEATHER. ALSO, WEEK-2 TEMPERATURE TOOLS ARE NOT
CONSISTENT WITH EACH OTHER, BUT MOST INDICATORS KEEP TEMPERATURES BETWEEN THE
THRESHOLDS FOR COLD AND WARM HAZARDS, SO NO TEMPERATURE HAZARDS ARE POSTED.
MID-MAY IS NEAR THE PEAK TIME OF YEAR WHEN RAPID SNOW- AND ICE-MELT CAN
ENGENDER FLOODING IF TEMPERATURES ARE SIGNIFICANTLY ABOVE NORMAL. CHANCES FOR
SUCH FLOODING WILL NEED TO BE MONITORED CLOSELY, BUT AT THIS TIME THE POTENTIAL
APPEARS LOW DURING THE FORECAST PERIOD.
FORECASTER: RICH TINKER
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