558
FXUS02 KWBC 291903
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
302 PM EDT MON MAY 29 2023
VALID 12Z THU JUN 01 2023 - 12Z MON JUN 05 2023
...WELL ABOVE NORMAL TO NEAR RECORD TEMPERATURES FROM THE UPPER
MIDWEST TO THE NORTHEAST THURSDAY-FRIDAY...
...BROAD MULTI-DAY THUNDERSTORM AND LOCAL HEAVY RAIN THREAT
CONTINUES FOR THE PLAINS/NORTHERN ROCKIES...
..OVERVIEW
GUIDANCE CONTINUES TO SUGGEST THAT THE MEAN PATTERN SHOULD BEGIN
TO LOOK MORE LIKE AN OMEGA BLOCK CONFIGURATION, ANCHORED BY
CONSOLIDATING GREAT LAKES/MIDWEST UPPER RIDGING WHOSE CENTER
SHOULD ULTIMATELY RETROGRADE SLOWLY ALONG THE U.S.-CANADIAN
BORDER. THIS RIDGE SHOULD PRODUCE WARM TO HOT TEMPERATURES IN THE
NORTH-CENTRAL U.S. TO THE NORTHEAST. MEAN TROUGHING ACROSS THE
EASTERN SEABOARD IS LIKELY TO SEE EMBEDDED SYSTEMS, INCLUDING
LOWS/FRONTS THAT COULD PRODUCE HEAVY RAIN OVER FLORIDA ON THURSDAY
AND PERHAPS LASTING OVER THE SOUTHEAST. IN THE WESTERN TO CENTRAL
U.S., SOME IMPULSES COULD PRODUCE MULTIPLE DAYS OF POTENTIALLY
HEAVY SHOWERS AND THUNDERSTORMS ACROSS THE NORTHERN ROCKIES/PLAINS
AND EXTENDING SOUTHWARD ACROSS MUCH OF THE HIGH PLAINS.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE CONTINUES TO SHOW GOOD AGREEMENT WITH THE UPPER
HIGH/RIDGE TO TRACK FROM ATOP THE GREAT LAKES REGION WESTWARD
ACROSS THE MIDWEST AND PLAINS AND EXTENDING WELL NORTHWARD INTO
CANADA BY THE WEEKEND. MORE UNCERTAIN ARE THE PATTERNS OVER THE
WEST AND EAST. THE WESTERN U.S. PATTERN LOOKS COMPLEX WITH
MULTIPLE PIECES OF ENERGY/UPPER LOWS THAT COULD GET STUCK OVER THE
REGION FOR A TIME BETWEEN THE STRONG RIDGE TO THE EAST AND RISING
HEIGHTS JUST INLAND FROM THE WEST COAST (AS TROUGHING PREVAILS
OVER THE NORTHEASTERN PACIFIC LATE WEEK INTO THE WEEKEND). EARLY
IN THE PERIOD/LATE IN THE WEEK THERE HAVE BEEN SOME VARIATIONS FOR
THE TIMING OF A TROUGH TRACKING EAST BUT IN TERMS OF THE 00Z/06Z
GUIDANCE THE UKMET SEEMED LIKE A SLOW OUTLIER, WITH ITS AXIS OVER
CALIFORNIA INSTEAD OF THE SOUTHWEST LIKE OTHER GUIDANCE BY DAY
4/FRIDAY. AFTER THAT, THERE ARE SOME SMALL-SCALE DIFFERENCES IN A
PATTERN BECOMING WEAKER FORCED BETWEEN AN UPPER LOW IN THE EASTERN
PACIFIC OFF OF BRITISH COLUMBIA AND THE UPPER HIGH TO THE EAST.
SOUTHERN STREAM SHORTWAVE ENERGY OVER THE PACIFIC MAY CLOSE OFF AN
UPPER LOW AS IT APPROACHES SOUTHERN CALIFORNIA BY DAY 7 MONDAY,
AND RISING HEIGHTS IF NOT A SMALL-SCALE RIDGE OVER THE NORTHWEST
IS POSSIBLE EARLY NEXT WEEK. A BLEND OF MODELS AND ENSEMBLE MEANS
SEEMED TO WORK FINE.
ACROSS THE SOUTHEAST, AN UPPER TROUGH/LOW MAY FORM ACROSS THE
SOUTHEAST LATE WEEK ALONG WITH A SURFACE LOW PRESSURE SYSTEM. BUT
THIS WILL BE AFFECTED BY POSITIONAL AND PHASING DIFFERENCES
FARTHER NORTH ACROSS THE NORTHEAST AND EASTERN CANADA THAT HAVE
SHOWN CONSIDERABLE VARIATIONS IN THE MODEL GUIDANCE. THROUGH THE
00/06Z MODEL CYCLE, THE ECMWF (AND MANY OF ITS ENSEMBLE MEMBERS)
SHOWED A FARTHER WEST DIVING OF ENERGY SOUTH THERE BY AROUND
SUNDAY COMPARED TO THE IN-BETWEEN GFS RUNS AND THE FARTHER EAST
CMC. THE ECMWF PICKED UP THE ASSOCIATED SURFACE LOW AND BROUGHT IT
FASTER/FARTHER INTO THE ATLANTIC THAN SOME OTHER GUIDANCE THAT HAD
THE LOW STALLING. THESE POSITIONS HAVE WAFFLED FROM CYCLE TO
CYCLE, AND THE INCOMING 12Z RUNS OF THE ECMWF AND GFS ARE EVEN
FARTHER WEST. SO THIS PART OF THE FORECAST REMAINS LOW CONFIDENCE.
THE UPDATED WPC FORECAST FAVORED A BLEND OF THE 06Z GFS, 00Z
ECMWF, AND 00Z CMC ALONG WITH THE 06Z GEFS MEAN AND 00Z EC MEAN.
THE DETERMINISTIC MODELS WERE THE MAJORITY INITIALLY, WITH GRADUAL
INCREASING OF THE ENSEMBLE MEANS TO OVER HALF WITH TIME.
..WEATHER/HAZARDS HIGHLIGHTS
EXPECT THE FORECAST PATTERN TO FAVOR MULTIPLE DAYS OF SHOWERS AND
THUNDERSTORMS FROM THE NORTHERN ROCKIES SOUTHWARD 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. THE DAYS 4-5 EXPERIMENTAL EXCESSIVE RAINFALL OUTLOOKS
COVERING THE THURSDAY THROUGH FRIDAY NIGHT PERIOD HIGHLIGHT A
SLIGHT RISK AREA ON BOTH DAYS OVER PARTS OF MONTANA AND NORTHERN
WYOMING. THIS AREA HAS ALREADY SEEN SIGNIFICANT RAINFALL RECENTLY
AND THE COMBINATION OF UPPER DYNAMICS, A WAVY SURFACE SYSTEM,
SUFFICIENT INSTABILITY, AND ANOMALOUS MOISTURE SHOULD BE FAVORABLE
FOR PRODUCING LOCALLY HEAVY RAINFALL. FARTHER EAST AND SOUTH, BOTH
DAYS DEPICT A MARGINAL RISK AREA ENCOMPASSING MUCH OF THE HIGH
PLAINS AND VICINITY WITH AN EMBEDDED SLIGHT RISK BECOMING POSSIBLE
AT SOME POINT DEPENDING ON HOW WELL GUIDANCE SIGNALS CONVERGE. FOR
DAY 5/FRIDAY FOR EXAMPLE, 00Z/06Z MODELS SHOWED FAIRLY GOOD
AGREEMENT ON A SOLUTION FAVORING HEAVY RAINFALL ACROSS PARTS OF
THE TEXAS PANHANDLE INTO WESTERN OKLAHOMA, BUT WHEN THE 12Z GFS
CAME IN FARTHER EAST HELD OFF ON ANY SLIGHT RISK UPGRADES FOR NOW.
PARTS OF THE GREAT BASIN MAY SEE SOME LOCALLY HEAVY RAINFALL AS
WELL LATE IN THE WEEK, PROMPTING A DAY 4/THURSDAY MARGINAL RISK,
FOLLOWED BY LIGHTER AND MORE SCATTERED RAINFALL.
THE GULF COAST/FLORIDA SYSTEM SHOULD PRODUCE SOME AREAS OF HEAVY
RAINFALL BUT WITH CONTINUED UNCERTAINTY IN DETAILS. THE BEST
GUIDANCE CLUSTERING SUGGESTS THAT FLORIDA SHOULD SEE THE BEST
POTENTIAL FOR SOME LOCALLY HEAVY RAINFALL BY THE DAY 4 TIME FRAME,
WITH A MARGINAL RISK AREA MAINTAINED IN THE EXCESSIVE RAINFALL
OUTLOOK. RECENT TRENDS HAVE FAVORED CONTINUING TO TRIM THE
POTENTIAL NORTHWARD EXTENT OF HEAVIEST RAIN, BUT OTHER THAN THAT
IT REMAINS UNCERTAIN WHERE HEAVY RAINFALL MAY OCCUR WITHIN THIS
MOIST PATTERN. PARTICULARLY IF HEAVY RAIN LOOKS TO FOCUS OVER THE
URBAN AREAS OF SOUTHEASTERN FLORIDA, A SLIGHT RISK MAY BE NEEDED
THERE IN FUTURE ERO ISSUANCES. HEAVIEST RAINFALL MAY TREND MORE
OFFSHORE OF FLORIDA AND THE OVERALL SOUTHEAST COAST AFTER DAY 4.
COLD FRONTS DROPPING INTO THE NORTHEAST LATE THIS WEEK AND EARLY
NEXT WEEK COULD PRODUCE SOME SHOWERS AND THUNDERSTORMS.
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. PERHAPS MORE
ANOMALOUS BUT SHORTER-LIVED WARMTH WILL BE ACROSS THE NORTHEAST
THURSDAY-FRIDAY. TEMPERATURES OF 15-25F ABOVE NORMAL ARE LIKELY TO
SET SOME RECORD HIGHS ESPECIALLY ON FRIDAY BEFORE A COOLING TREND
FOR THE WEEKEND WITH SOME UPPER-LEVEL ENERGY AND A BACKDOOR COLD
FRONT. THE NORTHWEST SHOULD SEE NEAR NORMAL TEMPERATURES THURSDAY
WITH A SHORTWAVE PASSING OVERHEAD. THEN THE REGION IS LIKELY TO
SEE A WARMING TREND THAT COULD BRING HIGHS UP TO 5-15F OR SO ABOVE
NORMAL FROM FRIDAY ONWARD, PEAKING BY SUNDAY-MONDAY WITH HIGHS
POSSIBLY REACHING 20F ABOVE AVERAGE. MEANWHILE, 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 ACROSS THE FOUR CORNERS STATES INTO THE
SOUTHERN HIGH PLAINS AND POSSIBLY THE SOUTHERN CALIFORNIA COAST
NEXT MONDAY WITH THE APPROACHING PACIFIC UPPER LOW. SIMILAR
ANOMALIES ARE POSSIBLE OVER PARTS OF THE SOUTHEAST DEPENDING ON
THE COVERAGE OF CLOUDS/RAINFALL.
TATE/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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