588
FXUS02 KWBC 280701
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 AM EDT SUN MAY 28 2023
VALID 12Z WED MAY 31 2023 - 12Z SUN JUN 04 2023
...WELL ABOVE NORMAL TO NEAR RECORD TEMPERATURES FROM THE UPPER
MIDWEST TO THE NORTHEAST NEXT WEEK...
...BROAD MULTI-DAY THUNDERSTORM AND LOCAL HEAVY RAIN THREAT
CONTINUES FOR THE PLAINS/NORTHERN ROCKIES...
..OVERVIEW
MODELS AND ENSEMBLES STILL ADVERTISE THE DEVELOPMENT OF A LARGE
SCALE OMEGA BLOCK PATTERN FROM MIDWEEK THROUGH NEXT WEEKEND, AS
GREAT LAKES AND HIGH PLAINS RIDGES MERGE AND AMPLIFY OVER THE
CENTRAL U.S. AND CANADA. RIDGING MAY AMPLIFY EVEN MORE INTO
NORTHWESTERN CANADA AND ALASKA NEXT WEEKEND. MULTIPLE FEATURES
WILL COMPRISE OVERALL MEAN TROUGHING OVER THE WESTERN U.S./EASTERN
PACIFIC, WITH A TENDENCY FOR WESTERN U.S. SHORTWAVES/UPPER LOWS TO
BECOME SOMEWHAT WEAKER/MORE DIFFUSE AROUND NEXT WEEKEND AS A
RELOADING NORTHEASTERN PACIFIC UPPER TROUGH/LOW BECOMES MORE
DOMINANT. TO THE EAST OF THE RIDGE, AN AMPLIFYING TROUGH OVER
EASTERN CANADA SHOULD BEGIN TO PUSH INTO THE NORTHEAST AROUND
FRIDAY AND EXTEND ITS INFLUENCE FARTHER SOUTH AND WEST THEREAFTER.
THE FORECAST PATTERN WILL SUPPORT RAINFALL OF VARYING INTENSITY
FROM THE SIERRA NEVADA THROUGH THE GREAT BASIN AND NORTHERN
ROCKIES, WHILE PORTIONS OF THE PLAINS WILL SEE POTENTIAL FOR
LOCALLY HEAVY RAINFALL OVER MULTIPLE DAYS. ONE OR MORE FRONTS
SHOULD PROVIDE ADDED FOCUS OVER THE NORTHERN PLAINS AND A
SHORTWAVE TRAVERSING THE SOUTHERN TIER, ALONG WITH ASSOCIATED
SURFACE TROUGHING/POSSIBLE EMBEDDED LOWS, COULD ENHANCE ACTIVITY
NEAR THE GULF COAST AND EVENTUALLY INTO THE FLORIDA PENINSULA.
AREAS FROM THE NORTHERN PLAINS THROUGH NORTHWEST WILL SEE WELL
ABOVE NORMAL TEMPERATURES MID-LATE WEEK WITH THE NORTHEAST UPPER
TROUGH LEADING TO A COOLING TREND OVER THAT REGION DURING THE
WEEKEND. NEAR TO MODERATELY BELOW NORMAL TEMPERATURES SHOULD
PREVAIL ACROSS THE SOUTHERN TIER.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THE LATEST GUIDANCE RUNS CONTINUE THE THEME OF DEPICTING THE LARGE
SCALE PATTERN EVOLUTION REASONABLY WELL BUT WITH EMBEDDED
DIFFERENCES AND RUN-TO-RUN VARIABILITY. ACROSS THE WESTERN
U.S./EASTERN PACIFIC, GFS RUNS HAVE TENDED TO BE ON THE FAST SIDE
WITH THE UPPER LOW TRACKING INLAND FROM CALIFORNIA MIDWEEK ONWARD.
HOWEVER A COMBINATION OF GRADUAL SLOWER NUDGES IN SUCCESSIVE GFS
RUNS AND SOME NEW 00Z RUNS TRENDING A BIT FASTER HAVE NARROWED THE
TIMING SPREAD. THERE IS DECENT CONTINUITY WITH THE SHORTWAVE
EXPECTED TO REACH THE PACIFIC NORTHWEST AROUND THURSDAY AND EJECT
NORTHEASTWARD THEREAFTER, AS WELL AS THE GENERAL IDEA FOR
ADDITIONAL ENERGY BEHIND THE CALIFORNIA LOW TO REINFORCE A DIFFUSE
NEGATIVELY TILTED TROUGH BY SATURDAY. CONSENSUS SHOWS HEIGHTS
RISING A BIT OVER THIS AREA INTO SUNDAY. THE PRIMARY ISSUE WITH
THE TROUGH AMPLIFYING OVER THE EASTERN PACIFIC IS THAT RECENT GFS
RUNS HAD STRAYED TO THE SOUTHERN EXTREME WITH THE ANCHORING UPPER
LOW. THE NEW 00Z GFS COMPARES MUCH BETTER TO OTHER GUIDANCE IN
THAT REGARD BUT MAY STILL BE OVERDONE WITH HEIGHT FALLS REACHING
CALIFORNIA BY NEXT SUNDAY. MEANWHILE GUIDANCE IS CURRENTLY
WAFFLING WITH RESPECT TO DEPTH/AMPLITUDE OF THE DEVELOPING EASTERN
CANADA INTO NORTHEASTERN U.S. TROUGH, RELATED IN PART TO THE
ULTIMATE PATH OF ANY EMBEDDED UPPER LOW. NEW 00Z RUNS SEEM TO BE
MINIMIZING THE POTENTIAL FOR A LEADING LOW OFFSHORE EASTERN CANADA
TO GET INCORPORATED INTO THE TROUGH AS DEPICTED IN THE 12Z ECMWF
AND SOME EARLIER GFS RUNS. THE 00Z GFS KEEPS ITS UPPER LOW
ASSOCIATED WITH THE DIGGING EASTERN CANADA ENERGY WELL NORTH OF
THE 12Z/18Z RUNS, NOW ALIGNING BETTER WITH THE ENSEMBLE MEANS.
THE 12Z ECMWF MAY ALSO BECOME OVERDONE WITH HOW MUCH TROUGHING
EXTENDS INTO THE GREAT LAKES BY NEXT SUNDAY. FINALLY, THE PAST
COUPLE CYCLES HAVE BECOME BETTER DEFINED WITH A SURFACE TROUGH AND
ONE OR MORE EMBEDDED LOWS CROSSING THE GULF OF MEXICO AND FLORIDA
IN ASSOCIATION WITH THE UPPER SHORTWAVE/LOW DRIFTING EASTERN OVER
THE COURSE OF THE PERIOD. RECENT UKMET RUNS HAVE BEEN A
PRONOUNCED EXTREME, DEPICTING A DEEPER UPPER LOW THAN OTHER
SOLUTIONS WITH THE NEW 00Z RUN ACTUALLY LIFTING ITS SURFACE LOW
INLAND OVER THE SOUTH VERSUS THE MORE SUPPRESSED TRACK IN OTHER
MODELS/MEANS. A 12Z/18Z OPERATIONAL MODEL COMPOSITE EARLY IN THE
PERIOD, FOLLOWED BY A TRANSITION TO A NEARLY EVEN MODEL/MEAN
WEIGHT LATE IN THE FORECAST, REPRESENTED THE MOST COMMON IDEAS OF
GUIDANCE WHILE DOWNPLAYING THE MORE QUESTIONABLE ASPECTS ON A
REGIONAL BASIS.
..WEATHER/HAZARDS HIGHLIGHTS
THE FORECAST PATTERN EVOLUTION SHOULD FAVOR MULTIPLE DAYS OF
SHOWERS AND THUNDERSTORMS FROM NEAR THE SIERRA NEVADA INTO THE
NORTHERN ROCKIES AND EXTENDING SOUTH ACROSS MUCH OF THE HIGH
PLAINS AND VICINITY. ONE OR MORE SURFACE FRONTS AS WELL AS UPPER
SHORTWAVES/LOWS MOVING INTO AND THROUGH PARTS OF THE WEST/ROCKIES
WILL HELP TO ENHANCE THE FOCUS FOR CONVECTIVE EPISODES, WITH A
GENERAL TENDENCY FOR MAXIMUM RAINFALL TOTALS TO INCREASE AFTER
MIDWEEK. THE FAR WESTERN PART OF THIS ACTIVITY COULD TAPER OFF
TOWARD THE END OF THE WEEK AND WEEKEND THOUGH. THE DAY 4
EXCESSIVE RAINFALL OUTLOOK (12Z WEDNESDAY-12Z THURSDAY) MAINTAINS
THE IDENTICAL MARGINAL RISK AREAS FROM THE PREVIOUS DAY 5
FORECAST, NAMELY FROM NEAR THE SIERRA NEVADA INTO THE NORTHERN
ROCKIES AND OVER THE SOUTHERN HIGH PLAINS. SOME GUIDANCE SIGNALS
FOR QPF OVER THE LATTER AREA HAVE BECOME LESS PRONOUNCED OVER THE
PAST DAY BUT THE UPPER PATTERN AND OTHER INGREDIENTS APPEAR TO BE
FAIRLY CONSISTENT, FAVORING NO CHANGE IN THE OUTLOOK AT THIS TIME.
THE DAY 5 OUTLOOK (12Z THURSDAY-12Z FRIDAY) INTRODUCES A SLIGHT
RISK AREA FOCUSED OVER CENTRAL MONTANA WITH A FRONTAL WAVE
CROSSING THE AREA, MOISTURE ANOMALIES SHOWING A PRONOUNCED
INCREASE OVER THE COURSE OF THE PERIOD, AND INSTABILITY SUFFICIENT
TO SUPPORT FAIRLY HIGH RAIN RATES. A SURROUNDING MARGINAL RISK
AREA ENCOMPASSES MOST AREAS INCLUDED IN THE DAY 4 OUTLOOK AS WELL
AS MOST REMAINING PORTIONS OF THE HIGH PLAINS. A WAVY FRONT
EXTENDING INTO OVER THE UPPER MIDWEST MAY STILL FOCUS SOME LOCALLY
HEAVY RAINFALL BUT GUIDANCE STILL DIFFERS ENOUGH TO DEPICT ANY
RISK AREA. MEANWHILE, THE SYSTEM TRACKING ALONG AND SOUTH OF THE
GULF COAST SHOULD PRODUCE SOME AREAS OF HEAVY RAINFALL BUT WITH
CONTINUED UNCERTAINTY IN NORTHWARD EXTENT. THE BEST GUIDANCE
CLUSTERING SUGGESTS THAT FLORIDA AND POSSIBLY NEARBY AREAS WILL
SEE THE HIGHEST POTENTIAL FOR SOME LOCALLY HEAVY RAINFALL BY THE
DAY 5 TIME FRAME, WITH A MARGINAL RISK AREA DEPICTED IN THE
EXCESSIVE RAINFALL OUTLOOK. ENHANCED RAINFALL MAY CONTINUE AT
LEAST INTO FRIDAY.
MOST NORTHERN TIER LOCATIONS EAST OF THE ROCKIES PLUS THE MIDDLE
MISSISSIPPI VALLEY WILL SEE WELL ABOVE NORMAL TEMPERATURES THROUGH
AT LEAST FRIDAY, WITH AREAS FROM THE NORTHERN PLAINS THROUGH GREAT
LAKES AND NORTHEAST MOST LIKELY TO SEE MULTIPLE DAYS OF PLUS
10-20F ANOMALIES. HIGH TEMPERATURES WILL LIKELY BE WELL INTO THE
80S TO LOW 90S WHICH COULD APPROACH OR EXCEED DAILY RECORD HIGHS.
THE UPPER TROUGH AND LEADING COLD FRONT DROPPING IN THROUGH THE
NORTHEASTERN U.S. AROUND THE END OF THE WEEK WILL BRING A
NOTICEABLE COOLING TREND TO AREAS FROM THE EASTERN GREAT
LAKES/OHIO VALLEY INTO NEW ENGLAND FOR THE WEEKEND. THE NORTHWEST
SHOULD SEE NEAR NORMAL TEMPERATURES WEDNESDAY-THURSDAY AS AN UPPER
SHORTWAVE REACHES THE REGION MID-LATE WEEK, FOLLOWED BY A WARMING
TREND THAT COULD BRING HIGHS UP TO 5-15F ABOVE NORMAL BY NEXT
WEEKEND. MUCH OF THE SOUTHERN TIER WILL TEND TO SEE NEAR TO
MODERATELY BELOW NORMAL TEMPERATURES, WITH THE BEST FOCUS FOR
HIGHS 5-10F BELOW NORMAL GRADUALLY SHIFTING FROM SOUTHERN
CALIFORNIA AND THE DESERT SOUTHWEST INTO THE SOUTHERN HALF OF THE
ROCKIES/HIGH PLAINS.
RAUSCH
ADDITIONAL 3-7 DAY HAZARD INFORMATION CAN BE FOUND ON THE WPC
MEDIUM RANGE HAZARDS OUTLOOK CHART AT:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,
QUANTITATIVE PRECIPITATION, EXPERIMENTAL EXCESSIVE RAINFALL
OUTLOOK, WINTER WEATHER OUTLOOK PROBABILITIES AND HEAT INDICES ARE
AT:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST500_WBG.GIF
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST_WBG_CONUS.GIF
HTTPS://WWW.WPC.NCEP.NOAA.GOV/5KM_GRIDS/5KM_GRIDSBODY.HTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/DAY4-7.SHTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=ERO
HTTPS://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4
HTTPS://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML
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