853
FXUS02 KWBC 290701
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 AM 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 EXTEND WELL NORTHWESTWARD BY THE
WEEKEND. MODEL/ENSEMBLE RUNS OVER THE PAST DAY HAVE ALTERED SOME
DETAILS THOUGH. 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. THIS
PATTERN SHOULD SUPPORT MULTIPLE DAYS OF POTENTIALLY HEAVY SHOWERS
AND THUNDERSTORMS FROM THE NORTHERN ROCKIES INTO THE SOUTHERN
PLAINS. TO THE EAST OF THE UPPER RIDGE/HIGH, SOME TROUGHING MAY
BRUSH THE NORTHEAST AROUND THE END OF THE WEEK AND INTO THE
WEEKEND, WITH A LARGER SCALE TROUGH POSSIBLY DEVELOPING OVER THE
EASTERN HALF OF CANADA AND APPROACHING THE GREAT LAKES/NEW ENGLAND
BY EARLY NEXT WEEK. MEANWHILE, A GULF COAST UPPER TROUGH/LOW MAY
SETTLE NEAR THE SOUTHEASTERN COAST BY THE WEEKEND AND EARLY NEXT
WEEK, BRINGING THE POTENTIAL FOR AREAS OF HEAVY RAINFALL TO PARTS
OF THE SOUTHEAST. 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 SOME COOLING OVER THAT REGION DURING THE WEEKEND. THE
NORTHWEST WILL ALSO SEE ABOVE NORMAL TEMPERATURES FROM FRIDAY
ONWARD. NEAR TO MODERATELY BELOW NORMAL TEMPERATURES WILL TEND TO
PREVAIL ACROSS PORTIONS OF THE SOUTHERN TIER.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
FIRST LOOKING AT THE WESTERN U.S. AND EASTERN PACIFIC, THE GFS
CONTINUES TO BE A BIT ON THE FAST SIDE WITH THE LEADING UPPER LOW
FORECAST TO REACH THE FOUR CORNERS REGION BY THE START OF THE
PERIOD EARLY THURSDAY. RECENT TRENDS HAVE NUDGED A BIT FASTER,
ALLOWING FOR A COMPROMISE AT LEAST EARLY IN THE PERIOD. THE NEW
00Z GFS HAS ADJUSTED A TAD SLOWER INITIALLY, THOUGH BY DAY 5
SATURDAY IT IS A DEEP EXTREME AS THE REMAINING ENERGY REACHES THE
NORTHERN HIGH PLAINS. ADDITIONAL SOUTHERN STREAM ENERGY SHOULD
COME INTO THE WEST RIGHT BEHIND THE UPPER LOW, WITH GUIDANCE
SHOWING VARIOUS IDEAS FOR A RESULTING DIFFUSE UPPER TROUGH/LOW
THAT COULD LINGER OVER THE WEST INTO THE WEEKEND. THE NEW 00Z GFS
IS FAIRLY EXTREME, EVEN COMPARED TO THE GEFS MEAN, IN PUSHING MOST
OF THIS ENERGY INTO THE HIGH PLAINS VERSUS KEEPING IT FARTHER
WEST. MEANWHILE A SHORTWAVE REACHING THE PACIFIC NORTHWEST BY
THURSDAY SHOULD LIFT NORTHEASTWARD THEREAFTER (WITHOUT THE
SOUTHERN PART PULLING OFF AS DEPICTED IN THE 00Z CMC), FOLLOWED BY
RISING HEIGHTS IF NOT A SMALL-SCALE RIDGE OVER THE NORTHWEST AS A
NORTHEASTERN TROUGH/UPPER LOW EVENTUALLY LIFTS OUT. SOUTHERN
STREAM SHORTWAVE ENERGY OVER THE PACIFIC MAY CLOSE OFF AN UPPER
LOW AS IT APPROACHES SOUTHERN CALIFORNIA BY DAY 7 MONDAY. FOR THE
TIME BEING, GUIDANCE SHOWS BETTER THAN AVERAGE AGREEMENT GIVEN THE
SCALE OF THE FEATURE AND BEING THAT FAR OUT IN TIME.
OVER THE EASTERN HALF OF NORTH AMERICA, ONE NOTABLE TREND OVER THE
PAST DAY HAS BEEN TOWARD GREATER DOMINANCE OF THE INITIAL GREAT
LAKES UPPER RIDGE FORECAST TO RETROGRADE SLOWLY WITH TIME,
RELATIVE TO NORTHEAST TROUGHING. AS A RESULT CONSENSUS NOW
SUGGESTS MERELY A PROGRESSIVE PASSAGE OF SHORTWAVE ENERGY ACROSS
THE NORTHEAST AROUND FRIDAY-SATURDAY INSTEAD OF THE DEEPER AND
MORE PERSISTENT TROUGH SEEN IN EARLIER RUNS. THE 00Z ECMWF HAS
REVERSED THIS TREND SOMEWHAT. FOR THE START OF NEXT WEEK THE
12Z-18Z MODELS/MEANS AGREED FAIRLY WELL ON A LARGER SCALE TROUGH
DEVELOPING OVER THE EASTERN HALF OF CANADA AND BEGINNING TO REACH
INTO THE GREAT LAKES AND NORTHEAST. HOWEVER THE 00Z GFS DELAYS
THE EVOLUTION OF THIS TROUGH BY AT LEAST A DAY. FARTHER SOUTH,
12Z/18Z GUIDANCE WAS TRENDING TOWARD A SOMEWHAT SLOWER AND DEEPER
GULF COAST UPPER TROUGH/LOW ULTIMATELY EXPECTED TO REACH AROUND
THE SOUTHEASTERN COAST. COMPLICATING THE FORECAST, SOME MODELS
NOW SUGGEST THAT WEAK ENERGY LINGERING OVER THE MID-ATLANTIC COULD
FEED INTO THE OVERALL FEATURE. HIGHLIGHTING THE UNCERTAINTY/LOW
PREDICTABILITY, THE 00Z GFS/ECMWF HAVE SWITCHED TO A FASTER AND
MORE OPEN SOLUTION COMPARED TO THE 18Z GFS AND 12Z ECMWF.
THE UPDATED FORECAST EMPLOYED AN OPERATIONAL MODEL COMPOSITE FOR
THE FIRST HALF OF THE PERIOD TO YIELD THE BEST COMPROMISE OR
CONSENSUS DEPENDING ON THE FEATURE, FOLLOWED BY A TREND TOWARD 60
PERCENT TOTAL ENSEMBLE MEANS (18Z GEFS AND 12Z ECENS/CMCENS) WITH
LINGERING OPERATIONAL MODEL INPUT TO ADD SOME DETAIL TO THE MEANS
WHERE REASONABLE. LATEST MODEL TRENDS MAY FAVOR SOME ADJUSTMENTS
TO THIS BLEND.
..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. PARTS OF THE GREAT BASIN MAY SEE SOME ACTIVITY AS WELL
LATE IN THE WEEK, FOLLOWED BY LIGHTER AND MORE SCATTERED RAINFALL.
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. 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. PARTS OF THE GREAT BASIN
COULD ALSO SEE LOCALLY HEAVY RAINFALL IN THE DAY 4 PERIOD WHEN A
MARGINAL RISK IS DEPICTED THERE AS WELL. 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 TRIMMING THE POTENTIAL NORTHWARD EXTENT OF
HEAVIEST RAIN THOUGH. ESPECIALLY WITH THE TRENDS IN THE NEW 00Z
GUIDANCE, 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.
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.
A COLD FRONT DROPPING IN THROUGH THE NORTHEASTERN QUADRANT OF THE
U.S. AROUND THE END OF THE WEEK WILL BRING A COOLING TREND
PRIMARILY TO AREAS FROM THE EASTERN GREAT LAKES/OHIO VALLEY INTO
NEW ENGLAND FOR THE WEEKEND, BUT ONLY NEW ENGLAND HIGHS MAY DROP
AS LOW AS AROUND NORMAL WITH SUPPORTING DYNAMICS TRENDING WEAKER.
THE NORTHWEST SHOULD SEE NEAR NORMAL TEMPERATURES THURSDAY WITH A
SHORTWAVE PASSING OVERHEAD. THEN THE REGION WILL LIKELY SEE A
WARMING TREND THAT COULD BRING HIGHS UP TO 5-15F OR SO ABOVE
NORMAL FROM FRIDAY ONWARD, PEAKING BY SUNDAY-MONDAY. 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.
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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