895
FXUS02 KWBC 010701
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 AM EDT THU JUN 01 2023
VALID 12Z SUN JUN 04 2023 - 12Z THU JUN 08 2023
...BROAD MULTI-DAY THUNDERSTORM AND LOCAL HEAVY RAIN THREAT
CONTINUES FROM THE NORTHERN ROCKIES TO THE SOUTHERN GREAT PLAINS...
..OVERVIEW
LATEST GUIDANCE IS CONSISTENT IN SHOWING A STRONG UPPER RIDGE/HIGH
SETTLING OVER THE NORTHERN PLAINS AND VICINITY, SUPPORTING
PROLONGED ABOVE NORMAL TEMPERATURES FROM THE NORTHERN PLAINS INTO
MIDDLE/UPPER MISSISSIPPI VALLEY THROUGH AT LEAST NEXT THURSDAY.
WEAKENING SHORTWAVE/UPPER LOW ENERGY INITIALLY OVER THE
INTERMOUNTAIN WEST THROUGH THE SOUTHERN PLAINS AS OF SUNDAY WILL
GIVE WAY TO SOUTHERN STREAM PACIFIC LOW THAT SHOULD REACH
CALIFORNIA EARLY NEXT WEEK AND NOT MOVE MUCH THEREAFTER. THESE
FEATURES WILL MAINTAIN PERIODS OF CONVECTION OVER THE ROCKIES AND
PARTS OF THE CENTRAL/SOUTHERN PLAINS, WHILE EXPANDING COVERAGE OF
RAINFALL BETWEEN THE SIERRA NEVADA AND GREAT BASIN/SOUTHERN
CASCADES. ABOVE NORMAL TEMPERATURES WILL PREVAIL OVER THE
NORTHWESTERN STATES THROUGH AT LEAST MIDWEEK, THOUGH A FRONT AHEAD
AN EJECTING PACIFIC UPPER LOW SHOULD PROVIDE A BRIEF REPRIEVE NEAR
THE PACIFIC NORTHWEST COAST DURING THE WEEKEND. DOWNSTREAM FROM
THE CENTRAL UPPER RIDGE, GUIDANCE CONTINUES TO VARY WITH THE TRACK
OF AN EARLY-WEEK UPPER LOW AND ADDITIONAL TRAILING ENERGY THAT
COULD INTERACT WITH THE FIRST LOW OR FORM ITS OWN LOW, LEADING TO
UNCERTAINTY OVER HOW ASSOCIATED LOW PRESSURE MAY AFFECT THE
REGION. AT THE VERY LEAST THE DEEPENING UPPER TROUGH SHOULD BRING
COOL AND WETTER CONDITIONS TO NEW ENGLAND AND PERHAPS THE NORTHERN
MID-ATLANTIC.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THE MOST PROMINENT GUIDANCE SPREAD CONTINUES TO BE WITHIN THE
OVERALL MEAN TROUGHING FORECAST TO DEEPEN OVER THE NORTHEASTERN
U.S. 12Z/18Z MODELS AND ENSEMBLE MEMBERS STILL EXHIBITED A VERY
WIDE ENVELOPE FOR THE TRACK OF THE UPPER LOW EXPECTED TO BE OVER
THE NORTHEAST AS OF THE START OF THE PERIOD EARLY SUNDAY. THE 12Z
UKMET TRACKED IT ALL THE WAY DOWN TO THE SOUTHERN APPALACHIANS
WHILE THE 12Z CMC'S UPPER LOW GOT ONLY AS FAR WEST AS CAPE COD
BEFORE CURVING UP INTO THE CANADIAN MARITIMES. AT LEAST INTO
MONDAY, AN AVERAGE OF THE 12Z ECMWF, 12Z GFS (A LITTLE SOUTHWEST),
AND 18Z GFS (SLIGHTLY EAST) PROVIDED THE BEST INTERMEDIATE
SOLUTION BASED ON THE SPREAD AT THAT TIME AND 24-48 HOUR TRENDS
THAT SEEMED TO BE POINTING TOWARD A SLIGHTLY FARTHER WEST TRACK
BUT NOT TO THE DEGREE OF SOME OF THE MORE WESTERN SOLUTIONS OVER
RECENT RUNS. THIS LED TO A TRACK NEAR NEW YORK CITY/LONG ISLAND
BEFORE LIFTING BACK NORTHWARD AS UPSTREAM ENERGY ARRIVES. HOWEVER
NEW 00Z RUNS (EXCEPT FOR THE GFS THAT IS SIMILAR TO THE 18Z RUN)
HAVE SHIFTED SOMEWHAT EASTWARD. MODELS CONTINUE TO VARY WITH WHAT
HAPPENS AFTER THE UPSTREAM ENERGY ARRIVES, WITH THE 18Z GFS AND
BRIEFLY THE 00Z GFS MODERATELY SOUTHWEST OF THE GENERAL MODEL/MEAN
AVERAGE FOR THE SECOND UPPER LOW. BY MIDWEEK THE MOST COMMON THEME
IS FOR AN UPPER LOW TO BE CENTERED OVER OR NEAR NORTHERN NEW
ENGLAND.
THE FORECAST FARTHER WESTWARD IS LESS CHAOTIC IN MOST RESPECTS.
THERE ARE STILL SOME LOWER-PREDICTABILITY ISSUES WITH THE UPPER
TROUGH EXTENDING SOUTH FROM AN UPPER LOW TRACKING INTO WESTERN
CANADA, WITH EFFECTS ON THE FRONT EXPECTED TO DRIFT ACROSS THE
NORTHWEST/NORTHERN ROCKIES. BOTH THE 00Z UKMET AND ECMWF SHOW MORE
SOUTHWARD ELONGATION/SLOWER TIMING THAN ESTABLISHED CONSENSUS.
MEANWHILE MOST GUIDANCE IS CONSISTENT AND SIMILAR FOR THE UPPER
LOW REACHING CALIFORNIA EARLY NEXT WEEK AND LIKELY DRIFTING VERY
SLOWLY NORTHWARD THEREAFTER.
BASED ON THE 12Z/18Z GUIDANCE AVAILABLE TO PREPARE THE UPDATED
FORECAST, THE BLEND STARTED WITH HALF 12Z ECMWF AND THE REST 12Z
GFS/18Z GFS EARLY IN THE PERIOD, FOLLOWED BY A TREND TOWARD NEARLY
HALF WEIGHT OF THE 18Z GEFS/12Z ECMWF MEANS LATE ALONG WITH
SHIFTING GFS WEIGHT MORE TOWARD THE 12Z RUN DUE TO A BETTER FIT TO
CONSENSUS FOR THE NORTHEAST UPPER LOW.
..WEATHER/HAZARDS HIGHLIGHTS
THE PATTERN KEEPS A PERSISTENT THREAT FOR SHOWERS AND
THUNDERSTORMS OVER PARTS OF THE ROCKIES AND PLAINS DURING THE
PERIOD, WITH DIURNALLY FAVORED SHOWERS/STORMS ALSO LIKELY TO
BECOME MORE COMMON WITH TIME FROM THE SIERRA NEVADA-SOUTHERN
CASCADES INTO THE GREAT BASIN AS THE SOUTHERN STREAM PACIFIC UPPER
LOW APPROACHES/REACHES SOUTHERN CALIFORNIA MONDAY. GRADUAL
WEAKENING OF UPPER IMPULSES/LOWS INITIALLY OVER THE WEST/HIGH
PLAINS SHOULD LEAD TO SOMEWHAT LOWER MAXIMUM RAINFALL TOTALS/MORE
SCATTERED HEAVY RAINFALL SUNDAY-MONDAY THAN IN THE SHORTER TERM,
BUT LOCALIZED FLASH FLOOD POTENTIAL WILL LIKELY CONTINUE GIVEN WET
GROUND CONDITIONS FROM RECENT OR SOON TO OCCUR RAINFALL. THE DAYS
4-5 EXCESSIVE RAINFALL OUTLOOKS (COVERING SUNDAY THROUGH MONDAY
NIGHT) DEPICT MARGINAL RISK AREAS ACROSS LOCATIONS FROM THE
NORTHERN ROCKIES INTO PARTS OF THE SOUTHERN PLAINS TO REFLECT THE
PERSISTENT MOISTURE/OVERALL PATTERN THAT COULD STILL PRODUCE SOME
AREAS OF LOCALLY HEAVY RAINFALL. IT WILL LIKELY TAKE INTO THE
SHORTER RANGE TIME FRAME TO RESOLVE AREAS OF MORE PRONOUNCED
FOCUS/CONFIDENCE FOR ANY EMBEDDED SLIGHT RISK AREAS. THE DAY 4
OUTLOOK INCORPORATES THE SIERRA NEVADA INTO THE OVERALL MARGINAL
RISK AREA WITH MOISTURE EXPECTED TO INCREASE ACROSS THE REGION
AHEAD OF THE UPPER LOW NEARING CALIFORNIA. THE DAY 5 OUTLOOK
ESSENTIALLY MAINTAINS THESE MARGINAL RISK AREAS AND CONNECTS THEM
ACROSS THE GREAT BASIN IN LIGHT OF INCREASING MOISTURE ACROSS THAT
REGION. OVER THE NORTHEAST, 00Z MODEL TRENDS SUGGEST LOWER
POTENTIAL FOR ANY AREAS OF HEAVY RAINFALL DURING THE FIRST HALF OF
NEXT WEEK, VERSUS WHAT WAS FORECAST BY THE 12Z ECMWF. THE FRONT
DROPPING INTO THE GREAT LAKES/UPPER MIDWEST EARLY NEXT WEEK COULD
PRODUCE SOME SHOWERS/STORMS OF VARYING INTENSITY, WITH POOR
GUIDANCE AGREEMENT ON SPECIFICS AT THIS TIME. BEYOND ANY RAINFALL
WITH THE INITIAL UPPER LOW OVER/NEAR NEW ENGLAND, THE DEEPENING
UPPER TROUGH SHOULD FAVOR DIURNALLY FAVORED POCKETS OF RAINFALL
OVER AND NEAR THE NORTHEAST THROUGH THURSDAY. THE GULF FEATURE
CURRENTLY BEING MONITORED BY THE NATIONAL HURRICANE CENTER SHOULD
REACH JUST EAST OF FLORIDA BY SUNDAY AND CONTINUE ONWARD
THEREAFTER, SO PRECIPITATION OVER FLORIDA SHOULD BE SOMEWHAT
LIGHTER DURING THE MEDIUM RANGE PERIOD.
CENTRAL U.S. RIDGING ALOFT WILL MAINTAIN AN AXIS OF ABOVE NORMAL
TEMPERATURES FROM THE NORTHERN PLAINS SOUTH-SOUTHEAST THROUGH THE
MISSISSIPPI VALLEY, WITH SOME PLUS 10-15F ANOMALIES FOR HIGHS
LIKELY EACH DAY OVER NORTHERN AREAS. INITIAL WARMTH OVER THE GREAT
LAKES SHOULD MODERATE SOME NEXT WEEK AFTER A FRONT PUSHES THROUGH
FROM THE NORTH. THE NORTHWEST WILL BE THE OTHER FOCUS FOR VERY
WARM TEMPERATURES, WITH HIGHS 10-20F OR SO ABOVE NORMAL MOST DAYS
BUT LIKELY TO BE HIGHEST MONDAY-WEDNESDAY. AREAS NEAR THE
WASHINGTON/OREGON COAST SHOULD SEE LESS EXTREME ANOMALIES ON
SUNDAY. EXPECT BELOW NORMAL TEMPERATURES OVER THE NORTHEAST AND AT
TIMES INTO THE MID-ATLANTIC AS UPPER TROUGHING BECOMES
ESTABLISHED. CLOUDS AND PERIODS OF RAINFALL SHOULD KEEP HIGHS
5-10F OR SO BELOW NORMAL OVER THE SOUTHERN HALF OF THE
ROCKIES/HIGH PLAINS FOR MOST OF THE PERIOD AND THE UPPER LOW
REACHING SOUTHERN CALIFORNIA MONDAY WILL ALSO BRING A COOLING
TREND INTO THE SOUTHWESTERN U.S. FOR THE EARLY-MIDDLE PART OF 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
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