923
FXUS21 KWNC 051753
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT MAY 05 2023
SYNOPSIS: A BROAD AREA OF MID-LEVEL HIGH PRESSURE SHOULD FAVOR PREDOMINANTLY
ABOVE-NORMAL TEMPERATURES ACROSS MOST OF THE CONTIGUOUS U.S. (CONUS) DURING
WEEK-2. IN PARTS OF THE NORTH-CENTRAL AND WESTERN CONUS, THIS IS EXPECTED TO
INCREASE THE RATE OF SNOWMELT, ELEVATING THE POTENTIAL FOR RIVER FLOODING. THIS
IS PARTICULARLY TRUE IN THE NORTHWEST QUARTER OF THE CONUS, WHERE TEMPERATURES
WILL BE WELL ABOVE NORMAL AND WHERE DEEP SNOW IS STILL IN PLACE ACROSS THE
HIGHER ELEVATIONS. IN CONTRAST, DEPLETED SNOW COVER SHOULD HAVE FLOODING ON THE
WANE IN THE NORTH-CENTRAL CONUS. MEANWHILE, MID-LEVEL LOW PRESSURE ALONG WITH
ENHANCED LOW-LEVEL MOISTURE FROM THE GULF OF MEXICO SUPPORTS AN INCREASED RISK
FOR HEAVY PRECIPITATION ACROSS THE SOUTH-CENTRAL CONUS.
HAZARDS
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE GREAT PLAINS, THE
SOUTHEAST, THE MISSISSIPPI VALLEY, AND ADJACENT AREAS, SAT-SUN, MAY 13-14.
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 MONDAY MAY 08 - FRIDAY MAY 12:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR SATURDAY MAY 13 - FRIDAY MAY 19: THERE IS GOOD AGREEMENT IN THE MEAN WEEK-2
500-HPA HEIGHT ANOMALY FORECASTS BETWEEN THE DYNAMICAL MODELS, WITH THE
LESS-AMPLIFIED GEFS SHIFTING TOWARD THE MORE AMPLIFIED EUROPEAN AND CANADIAN
MODEL ENSEMBLE MEANS. IN THE WEST, BELOW-NORMAL TEMPERATURES DURING WEEK-1 WILL
HAVE BEEN SCOURED OUT QUICKLY AS ANOMALOUS MID-LEVEL RIDGING ENVELOPS MUCH OF
THE CONUS FOR MOST OF WEEK-2. THIS SHOULD LEAD TO GENERALLY ABOVE-NORMAL
TEMPERATURES FOR MUCH OF THE COUNTRY, BUT READINGS ARE EXPECTED TO REMAIN BELOW
HAZARDS THRESHOLDS, SO NO TEMPERATURE HAZARDS ARE POSTED. STILL, A FEW DAYS
COULD BE WELL ABOVE NORMAL IN THE NORTHWEST DURING THE EARLIER PART OF WEEK-2,
WITH NONTRIVIAL CHANCES FOR TEMPERATURES TOPPING OUT IN THE MID-80S TO LOW 90S
DEF. F IN SOME VALLEYS EAST OF THE CASCADES AND WEST OF THE SIERRA NEVADA. THE
TOOLS IN GENERAL ARE CONSIDERABLY WARMER IN THIS REGION THAN YESTERDAY. THE
WARM WEATHER WILL ACCELERATE SNOW MELT, WHICH WOULD INCREASE THE POTENTIAL FOR
FLOODING ALONG SOME RIVERS IN THE NORTH-CENTRAL STATES AND SOME LOWER
ELEVATIONS IN THE WESTERN CONUS. DECLINING SNOWPACK IS EXPECTED TO REDUCE THE
CHANCES FOR SIGNIFICANT FLOODING IN THE NORTH-CENTRAL STATES NEAR THE RED RIVER
(OF THE NORTH), JAMES RIVER, AND MISSISSIPPI RIVER LATER WEEK-2. IN CONTRAST,
THE SNOWPACK REMAINS VERY DEEP IN SOME HIGHER ELEVATIONS IN THE WEST AND THE
SOUTHERN CANADIAN ROCKIES, WITH A FEW SITES THERE STILL REPORTING OVER 100
INCHES OF SNOW WATER CONTENT. AS A RESULT, THE ABOVE-NORMAL TEMPERATURES CREATE
AN INCREASED RISK OF FLOODING AND MUDSLIDES IN PARTS OF THE SIERRA NEVADA,
GREAT BASIN, NORTHERN ROCKIES, AND PACIFIC NORTHWEST. EXPANSIVE, MULTI-STATE
FLOODING IS NOT EXPECTED TO ENVELOP THE INTERIOR WEST, BUT AREAS NEAR RIVERS
AND ADJACENT TO THE HIGHER ELEVATIONS WITH DEEPER SNOWPACK WILL BE AT RISK
THROUGH THE PERIOD.
WEEK-2 IS EXPECTED TO START WITH A WEAK MID-LEVEL TROUGH AXIS APPROXIMATELY
OVER THE SOUTHERN ROCKIES, SOUTH OF A LARGE ANOMALOUS MID-LEVEL RIDGE CENTERED
OVER INTERIOR WESTERN CANADA. AT THE SAME TIME, A DECENT FETCH OF MOIST
SUBTROPICAL AIR FROM THE GULF OF MEXICO INTO PARTS OF THE CENTRAL AND WESTERN
GULF COAST REGION, THE SOUTHERN HALVES OF THE MISSISSIPPI VALLEY AND GREAT
PLAINS, AND PARTS OF THE SOUTHERN HIGH PLAINS. THE CYCLONICALLY-CURVED
MID-LEVEL FLOW ALONG WITH THE SURFACE INFLUX OF MILD AND MOIST AIR INCREASES
THE CHANCES FOR HEAVY PRECIPITATION IN THESE AREAS EARLY WEEK-2. CONDITIONS ARE
EXPECTED TO IMPROVE TOWARD THE MIDDLE OF THE PERIOD, BUT SOME OF THE REFORECAST
TOOLS ARE SHOWING A CHANCE FOR HEAVY PRECIPITATION TO PERSIST LATER INTO
WEEK-2, BUT THIS IS NOT CURRENTLY THE FAVORED SOLUTION GIVEN ONLY ONE SET OF
MODEL RUNS HAS HIGHLIGHTED THIS POSSIBILITY. EVEN EARLY IN THE PERIOD,
INCONSISTENCIES AMONG THE TOOLS REGARDING THE PLACEMENT AND AMOUNT OF HEAVY
PRECIPITATION - IF ANY - KEEPS THE RISK ONLY SLIGHTLY ELEVATED. TOOLS DERIVED
FROM THE GEFS ARE A LITTLE MORE ROBUST THAN YESTERDAY, BUT CONTINUE TO KEEP
PRECIPITATION TOTALS BELOW HAZARDS THRESHOLDS.
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. GIVEN THE ANTICIPATED
ABOVE-NORMAL TEMPERATURES, THIS RAISES THE POSSIBILITY OF RAPID-ONSET DROUGHT;
HOWEVER, AT LEAST ONE-HALF INCH OF PRECIPITATION IS ANTICIPATED ACROSS THIS
REGION DURING WEEK-1, AND WEEK-2 TEMPERATURES ARE NOT EXPECTED TO BE HIGH
ENOUGH TO SUBSTANTIALLY INCREASE SURFACE MOISTURE LOSS. IN ADDITION, WINDS ARE
NOT FORECAST TO BE PARTICULARLY HIGH, AND RELATIVE HUMIDITY IS UNLIKELY TO BE
SIGNIFICANTLY BELOW-NORMAL, AND FOR THESE REASONS, THE RISK OF RAPID-ONSET
DROUGHT DOES NOT SEEM PARTICULARLY HIGH AT THIS TIME.
ACROSS ALASKA, THE DEEP MID-LEVEL TROUGH IN PLACE EARLY WEEK-2 IS EXPECTED TO
INDUCE CYCLOGENESIS OVER OR NEAR THE GULF OF ALASKA. THE GEFS IS MORE AMPLIFIED
THAN YESTERDAY, MOVING TOWARD THE STRONGER SOLUTIONS OF THE EUROPEAN AND
CANADIAN ENSEMBLE MEANS; HOWEVER, MOST TOOLS SHOW THE FAIRLY STRONG MID-LEVEL
TROUGH FARTHER SOUTH THAN YESTERDAY, WELL REMOVED FROM THE ALASKAN GULF COAST.
WHILE ABOVE-NORMAL PRECIPITATION AND GUSTY WINDS ARE POSSIBLE ACROSS
SOUTH-CENTRAL AND SOUTHEAST ALASKA, MOST TOOLS KEEP CONDITIONS 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; ENSEMBLE REFORECAST TOOLS ARE
CONSIDERABLY WARMER THAN THE CALIBRATED TOOLS. BUT IN ANY CASE, 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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