556
FXUS02 KWBC 300701
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 AM EDT TUE MAY 30 2023
VALID 12Z FRI JUN 02 2023 - 12Z TUE JUN 06 2023
...WELL ABOVE NORMAL TO NEAR RECORD TEMPERATURES FROM THE UPPER
MIDWEST TO THE NORTHEAST INTO LATE WEEK...
...BROAD MULTI-DAY THUNDERSTORM AND LOCAL HEAVY RAIN THREAT
CONTINUES FOR PARTS OF THE PLAINS/ROCKIES...
..OVERVIEW
LATEST GUIDANCE MAINTAINS THE IDEA OF A BLOCKY LARGE SCALE PATTERN
DOMINATED BY A GREAT LAKES-MIDWEST UPPER RIDGE/HIGH THAT GRADUALLY
RETROGRADES THROUGH THE WEEKEND AND SETTLES OVER THE NORTHERN
PLAINS INTO CENTRAL CANADA EARLY NEXT WEEK. MEANWHILE DIFFUSE
TROUGHING INITIALLY OVER THE WEST MAY CONTAIN MULTIPLE SHORTWAVE
IMPULSES, WITH LOW PREDICTABILITY FOR THE DETAILS BUT WITH
CONSENSUS SHOWING A GRADUAL WEAKENING TREND FOR THIS ENERGY WHILE
A SOUTHERN STREAM PACIFIC TROUGH/LOW APPROACHES CALIFORNIA. THE
FORECAST PATTERN SHOULD LEAD TO CONTINUED EPISODES OF LOCALLY
HEAVY SHOWERS AND THUNDERSTORMS FROM THE NORTHERN ROCKIES/HIGH
PLAINS SOUTHWARD INTO THE SOUTHERN PLAINS. WHILE THIS SYNOPTIC
THEME HAS HELD UP WELL OVER RECENT DAYS, LATEST GUIDANCE HAS
REALLY GONE ASTRAY FOR DETAILS WITHIN EASTERN NORTH AMERICA MEAN
TROUGHING THAT HAS BEEN ADVERTISED TO DEVELOP DOWNSTREAM FROM THE
UPPER RIDGE. THUS COMPARED TO PAST DAYS, CONFIDENCE HAS DECLINED
WITH RESPECT TO SOME TEMPERATURE AND PRECIPITATION SPECIFICS OVER
THE EAST AFTER FRIDAY. WELL ABOVE NORMAL TEMPERATURES WILL
PREVAIL FROM THE NORTHERN PLAINS INTO NORTHEAST ON FRIDAY, WITH
EASTERN LOCATIONS TRENDING COOLER THEREAFTER, WHILE THE NORTHWEST
SHOULD ALSO SEE MULTIPLE DAYS OF VERY WARM TO HOT WEATHER.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
OVER THE PAST 24 HOURS, THE EASTERN U.S. EVOLUTION DOWNSTREAM FROM
THE MIDWEST INTO NORTHERN PLAINS RIDGE HAS BECOME VERY PROBLEMATIC
IN TERMS OF GUIDANCE SPREAD AND RUN-TO-RUN VARIABILITY.
DIFFERENCES BEGIN TO SHOW UP ON DAY 4 SATURDAY AS LEADING
SHORTWAVE ENERGY DROPS INTO NEW ENGLAND AND THE CANADIAN
MARITIMES, WITH RAPIDLY WIDENING DIVERGENCE FOR WHERE A POSSIBLE
UPPER LOW MAY TRACK. THE 12Z ECMWF WAS THE MOST WESTWARD EXTREME,
TRACKING IT DOWN ALONG THE APPALACHIANS, WHILE THE NEW 00Z UKMET
IS ON THE OPPOSITE EXTREME WITH A TRACK ACROSS AND SOUTH/SOUTHEAST
OF NEWFOUNDLAND. SIX-HOURLY GFS RUNS HAVE BEEN QUITE ERRATIC AS
WELL, RANGING AMONG JUST OFF THE MID-ATLANTIC COAST (12Z RUN),
SOUTHEAST OF NOVA SCOTIA (18Z RUN), AND JUST OFF SOUTHERN NEW
ENGLAND. THESE VARIOUS POSSIBILITIES WERE WITHIN THE FULL 12Z
ENSEMBLE SPREAD, THOUGH ONLY SOME ECMWF ENSEMBLE MEMBERS CONTAINED
THE OPERATIONAL ECMWF SCENARIO (WHILE NO GEFS/CMCENS MEMBERS DID).
BEHIND THIS FEATURE, GUIDANCE HAS ALSO SLIPPED INTO DISARRAY
REGARDING THE NEXT POTENTIAL SHORTWAVE POTENTIALLY AMPLIFYING OVER
EASTERN CANADA INTO THE NORTHEASTERN U.S. (AFTER BRIEFLY AGREEING
IN THE DAYTIME RUNS ON SUNDAY). LATEST GFS RUNS HAVE BEEN ON THE
EXTREME SIDE IN TERMS OF THEIR WESTWARD AMPLIFICATION AND CLOSED
LOW DEPTH. THE 12Z CMC HINTED AT A VARIATION OF THE GFS SCENARIO
BUT NOW DIVERTS THE ENERGY MUCH FARTHER EAST IN THE NEW 00Z RUN.
ISSUES WITH THESE FEATURES WILL HAVE SOME INFLUENCE ON THE UPPER
TROUGH/LOW FORECAST TO REACH NEAR THE SOUTHEASTERN COAST BY THE
WEEKEND. WEAKER NORTHEAST TROUGHING COULD ALLOW THE SOUTHERN
FEATURE TO LINGER FOR A LONGER TIME (PER THE UKMET), WHILE A MORE
AMPLIFIED TROUGH COULD EJECT IT MORE QUICKLY. MINIMAL CONFIDENCE
IN ANY PARTICULAR SOLUTION AND THE DESIRE TO MAINTAIN A REASONABLE
DEGREE OF CONTINUITY LED TO FAVORING AN EARLIER THAN USUAL
INCORPORATION OF 18Z GEFS AND 12Z ECENS/CMCENS MEANS INTO THE
FORECAST AFTER DAY 3 FRIDAY AND ULTIMATELY 70-80 PERCENT WEIGHT OF
THE MEANS BY DAYS 6-7 MONDAY-TUESDAY. THIS LED TO GENERAL
NORTHERLY FLOW ALOFT OVER THE NORTHEAST DURING THE WEEKEND AND
THEN MORE EASTERN CANADA/NORTHEASTERN U.S. TROUGHING EARLY NEXT
WEEK.
WITH TYPICAL DIFFERENCES IN DETAILS, GUIDANCE GENERALLY AGREES
THAT THE DIFFUSE TROUGH OVER THE WEST LATE THIS WEEK SHOULD SLOWLY
WEAKEN WITH TIME, THOUGH WITH ONE OR MORE UPPER LOWS POSSIBLY
EXISTING THROUGH THE WEEKEND. THE ENSEMBLE MEANS HAVE BEEN FAIRLY
CONSISTENT WITH THE SOUTHERN STREAM PACIFIC ENERGY EXPECTED TO
APPROACH CALIFORNIA IN THE FORM OF A WEAK UPPER LOW EARLY NEXT
WEEK. 12Z ECMWF/CMC DETAILS DIFFERED SOMEWHAT BUT THE NEW 00Z CMC
HAS COME IN CLOSER TO THE ENSEMBLE MEAN SCENARIO. THE 18Z GFS WAS
CLOSE TO THE MEANS WHILE THE NEW 00Z GFS IS SOMEWHAT SOUTH BY DAY
7 TUESDAY. THE GUIDANCE BLEND EMPLOYED FOR THE EASTERN U.S.
PATTERN WORKED WELL FOR DEPICTING THE BEST CONSENSUS/CONTINUITY
OVER THE WEST AND VICINITY, THOUGH NEW 00Z GUIDANCE IS SUGGESTING
THAT STRONGER HEIGHT FALLS COULD BRUSH THE NORTHWEST AROUND SUNDAY
WITH THE EJECTION OF A NORTHEASTERN PACIFIC LOW.
..WEATHER/HAZARDS HIGHLIGHTS
SLOW EVOLUTION OVER THE LARGE SCALE PATTERN OVER THE CENTRAL AND
WESTERN U.S. SHOULD MAINTAIN THE THREAT FOR SHOWERS AND
THUNDERSTORMS OVER PARTS OF THE ROCKIES AND PLAINS DURING THE
PERIOD. A GRADUAL WEAKENING OF INITIAL SHORTWAVES/UPPER LOW(S)
OVER THE WEST/ROCKIES WITH TIME SHOULD LEAD TO A GRADUAL DECREASE
IN HEAVIEST RAINFALL TOTALS THOUGH. AREAS FROM THE SIERRA NEVADA
INTO GREAT BASIN MAY SEE SOME INCREASE OF SCATTERED ACTIVITY BY
THE WEEKEND OR EARLY NEXT WEEK AS THE UPPER TROUGH/LOW APPROACHES
CALIFORNIA. THE DAY 4 EXPERIMENTAL EXCESSIVE RAINFALL OUTLOOK
(12Z FRIDAY-12Z SATURDAY) REFLECTS TWO PRIMARY AREAS OF EMPHASIS
FOR FLASH FLOOD POTENTIAL. A SLIGHT RISK AREA ALREADY DEPICTED
OVER PARTS OF MONTANA INTO A SMALL PART WYOMING IN THE PREVIOUS
DAY 5 ISSUANCE WILL BE EXTENDED FARTHER SOUTH IN THIS NEW DAY 4
ISSUANCE PER GUIDANCE SIGNALS AND FAVORABLE PATTERN/ANOMALOUS
MOISTURE. IN ADDITION A SLIGHT RISK AREA WILL BE INTRODUCED OVER
A REGION CENTERED ON THE SOUTH-CENTRAL PLAINS, WITH GUIDANCE NOW
OFFERING SUFFICIENT CLUSTERING ALONG WITH UPPER DIFFLUENCE TO
RECOMMEND THIS AREA. NOTE THAT THE WESTERN HALF OF THIS AREA
SHOULD BE MORE SENSITIVE DUE TO RECENT RAINFALL. THE DAY 5
OUTLOOK (12Z SATURDAY-12Z SUNDAY) DEPICTS A MARGINAL RISK AREA
FROM THE NORTH-CENTRAL ROCKIES SOUTH-SOUTHEAST INTO THE SOUTHERN
PLAINS, WITH A GENERAL SIGNAL FOR SOME LOCALLY INTENSE RAIN RATES
BUT NO PRONOUNCED AREAS OF FOCUS AT THIS TIME. ROCKIES/PLAINS
CONVECTION SHOULD CONTINUE TO SOME DEGREE FOR THE REST OF THE
PERIOD, THOUGH HEAVY RAINFALL SHOULD BECOME MORE ISOLATED. THE
TROUGH/UPPER LOW NEARING CALIFORNIA MAY PROMOTE SOME INCREASE IN
SHOWERS/THUNDERSTORMS OVER THE SIERRA NEVADA/GREAT BASIN BY THE
WEEKEND OR EARLY NEXT WEEK. OVER THE EAST, ISSUES WITH THE UPPER
PATTERN SIGNIFICANTLY REDUCE CONFIDENCE IN RAINFALL SPECIFICS,
THOUGH IN GENERAL EXPECT THE POTENTIAL FOR SOME SHOWERS/STORMS
WITH A COUPLE COLD FRONTS DROPPING SOUTH DURING THE PERIOD. THERE
WILL ALSO BE POTENTIAL FOR RAINFALL NEAR THE SOUTHEASTERN COAST,
DEPENDING ON THE EVOLUTION OF A SOUTHERN STREAM LOW/TROUGH.
WELL ABOVE AVERAGE TEMPERATURES WILL BE COMMON ACROSS THE NORTHERN
PLAINS, UPPER/MIDDLE MISSISSIPPI VALLEY, AND THE GREAT LAKES/OHIO
VALLEY REGIONS LATE THIS WEEK INTO EARLY NEXT WEEK UNDER THE
RIDGE/HIGH ALOFT. HIGH TEMPERATURES IN THE 80S TO LOW 90S COULD
APPROACH OR EXCEED A FEW DAILY RECORD HIGHS LATE THIS WEEK INTO
THE WEEKEND, WITH SLIGHT MODERATION POSSIBLE EARLY NEXT WEEK.
ANOMALOUS WARMTH WILL ALSO EXTEND ACROSS THE NORTHEAST INTO FRIDAY
WITH TEMPERATURES OF 15-20F ABOVE NORMAL LIKELY TO SET SOME RECORD
HIGHS BEFORE A COOLING TREND FOR THE WEEKEND WITH SOME UPPER-LEVEL
ENERGY AND A BACKDOOR COLD FRONT. EXPECT THE NORTHWEST TO SEE A
WARMING TREND THAT COULD BRING HIGHS 5-10F ABOVE NORMAL ON FRIDAY
AND AT LEAST 10-20F ABOVE NORMAL THROUGH NEXT TUESDAY. EJECTION
OF A NORTHEASTERN PACIFIC UPPER LOW COULD DENT THE HEAT BRIEFLY
DURING THE WEEKEND. MEANWHILE, MUCH OF THE SOUTHERN TIER WILL
TEND TO SEE NEAR TO MODERATELY BELOW NORMAL TEMPERATURES, WITH THE
BEST FOCUS FOR HIGHS 5-15F BELOW NORMAL SETTLING INTO THE
CENTRAL-SOUTHERN ROCKIES/HIGH PLAINS BY THE WEEKEND AND EARLY NEXT
WEEK.
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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page