583
FXUS02 KWBC 281821
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
220 PM 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 WED-FRI...
...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
LATER THIS WEEK. AREAS FROM THE NORTHERN PLAINS EASTWARD THROUGH
THE GREAT LAKES TO THE NORTHEAST 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 AND ESPECIALLY AROUND THE SOUTHWEST EARLY IN THE
PERIOD.
..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.
ASIDE FROM THE APPARENT ERRANT 06Z GFS RUN, THE 00Z MODELS WERE IN
GOOD AGREEMENT AND A BLENDED SOLUTIONS SUFFICED TO START. 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. UPSTREAM, ENSEMBLES DIFFER ON THE SHAPE
AND SOUTHEASTWARD EXTENT OF LOWER HEIGHTS INTO/TOWARD COASTAL
CALIFORNIA STEMMING FROM UNCERTAINTY IN THE NORTH PACIFIC SYSTEM
NEARING THE GULF OF ALASKA. WITH NO OBVIOUS TRENDS AND A SPLIT IN
THE MID-LATITUDE SPREAD MAXIMA, OPTED TO RELY ON A BROAD CONSENSUS
UNTIL A CLEARER PICTURE EMERGES.
MEANWHILE GUIDANCE IS STILL 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. AGAIN THE 00-06Z GFS/GEFS WERE SOUTHWEST OF THE 00Z
ECMWF/ECENS AND CANADIAN/CMCE MEAN OVER THE MARITIMES, SO RELIED
MOSTLY ON THE BETTER ECMWF-LED CONSENSUS THERE BUT WITH CONTINUED
CHANGES IN THE FRONTAL PROGRESSION. FINALLY, IN THE GULF OF
MEXICO, CONSENSUS REMAINS ON A DEVELOPING AREA OF LOW PRESSURE (OR
TWO) MOVING EASTWARD IN TANDEM WITH THE UPPER TROUGH INTO/ACROSS
FLORIDA LATER THIS WEEK. ASIDE FROM THE STILL LIKELY OVERDONE 00Z
UKMET, A GENERAL CONSENSUS WAS PREFERRED THOUGH THE CANADIAN AND
ECMWF WERE ON THE DEEPER SIDE COMPARED TO THE GFS. OVERALL A
PREFERENCE AMONG THE 00Z MODELS/ENSEMBLES WAS USED AS A STARTING
POINT WHICH 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
EXPERIMENTAL EXCESSIVE RAINFALL OUTLOOK (12Z WEDNESDAY-12Z
THURSDAY) HIGHLIGHTS THE AREAS 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) CONTINUES 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, WHICH MAY BE CONTINGENT ON ANY DAY
3 RAINFALL. 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 AS TEMPERATURES
FALL BACK TO NEAR NORMAL EARLY JUNE VALUES. 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.
FRACASSO/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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