668
FXUS02 KWBC 040700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 AM EDT WED OCT 04 2023
VALID 12Z SAT OCT 07 2023 - 12Z WED OCT 11 2023
...HEAVY RAIN AND FLASH FLOODING THREATS LIKELY IN THE NORTHEAST
SATURDAY DUE IN PART TO PHILIPPE...
..OVERVIEW
AN UPPER TROUGH AND LIKELY AN EMBEDDED UPPER LOW ARE FORECAST TO
SWING SLOWLY THROUGH THE GREAT LAKES REGION AND SOUTH THIS
WEEKEND. AT THE SURFACE A COLD FRONT WILL SWEEP THROUGH THE
EASTERN U.S., WHILE AMPLE MOISTURE STREAMS IN AHEAD OF IT, AND THE
LOW CIRCULATION ASSOCIATED WITH PHILIPPE (WHICH SHOULD BE
POST-TROPICAL BY THEN) COULD TRACK NEAR OR INTO MAINE. THIS
COMBINATION WILL LEAD TO HEAVY RAIN AND FLOODING CONCERNS IN THE
NORTHEAST ON SATURDAY. THEN SOME RAIN COULD LINGER INTO EARLY NEXT
WEEK UNDERNEATH THE UPPER LOW, WITH LAKE EFFECT ENHANCEMENT
LIKELY. MEANWHILE AN UPPER RIDGE SHOULD OVERTAKE THE WESTERN U.S.
FOR WARMER THAN AVERAGE TEMPERATURES AND GENERALLY DRY CONDITIONS
THROUGH SATURDAY, THOUGH EARLY NEXT WEEK A TROUGH AND FRONTAL
SYSTEM LOOKS TO PUSH INTO THE PACIFIC NORTHWEST AND FARTHER INTO
THE INTERIOR WEST AS NEXT WEEK PROGRESSES.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE HAS BEEN PERSISTENT IN SHOWING AN UPPER-LEVEL
TROUGH AXIS ACROSS THE EAST-CENTRAL U.S. AT THE START OF THE
PERIOD SATURDAY, AND THE ENERGY WITHIN THE TROUGH LOOKS TO FORM A
CLOSED LOW WITHIN IT ATOP THE GREAT LAKES OVER THE WEEKEND AND
ALSO HELP THE TROUGH TO BECOME NEGATIVELY TILTED (WHICH CAN HELP
THE SYSTEM PULL IN MORE ATLANTIC MOISTURE). THE 12Z CMC CLOSED OFF
THE LOW FARTHER NORTH COMPARED TO THE BULK OF OTHER GUIDANCE. SOME
SMALL DIFFERENCES ARE NOTED WITH THE POSITIONS OF THE ASSOCIATED
SURFACE COLD FRONT, WHICH AFFECTS THE AXIS OF HEAVY QPF. ONE
CHANGE OVER THE PAST DAY IS THAT MODELS HAVE SHOWN A MARKED TREND
TOWARD A FARTHER WEST TRACK FOR CURRENT TROPICAL STORM PHILIPPE.
THE NATIONAL HURRICANE CENTER AS WELL AS MUCH OF THE DETERMINISTIC
AND ENSEMBLE GUIDANCE INDICATE THAT PHILIPPE SHOULD BECOME
POST-TROPICAL BUT ITS EXTRATROPICAL LOW COULD TRACK INTO NEW
ENGLAND OR ATLANTIC CANADA. THE MEAN POSITION LOOKS TO BE INTO
MAINE. THIS WOULD PROVIDE ANOTHER SWATH OF HEAVY RAIN TO THE
NORTHEAST. THE LOW AND ENERGY ARE LIKELY TO GET ABSORBED INTO THE
SOUTHEASTERN CANADA/NORTHEASTERN U.S. SYSTEM ON SUNDAY. MODELS
SHOW THE CORE OF THE UPPER LOW COULD DRIFT SLOWLY NORTH THROUGH
THE FIRST HALF OF NEXT WEEK, WITH SOME VARIATIONS IN THE CENTROID
POSITION, BUT THE ENSEMBLE MEANS SHOWED GOOD AGREEMENT SO
PREFERRED THEIR PLACEMENT IN GENERAL. THE 12Z CMC RETROGRADED THE
UPPER LOW TO THE WEST BY DAY 7/WEDNESDAY, WHICH WAS NOT PREFERRED
AS IT WAS NOT SUPPORTED BY OTHER GUIDANCE, BUT THE 00Z CMC LOOKS
MORE REASONABLE.
FARTHER WEST, MODELS AGREE ON THE GENERAL IDEA OF AN UPPER RIDGE
ATOP THE WEST TRACKING TOWARD THE ROCKIES EARLY NEXT WEEK. GFS
RUNS HAVE BEEN MORE SUPPORTIVE OF A SHORTWAVE OVER THE GREAT BASIN
OVER THE WEEKEND, BUT THESE DIFFERENCES DO NOT SEEM TO HAVE MUCH
SENSIBLE WEATHER IMPACT. THE RIDGING WILL GET COMPRESSED BY ENERGY
AND TROUGHING COMING ACROSS THE EASTERN PACIFIC INTO THE WEST
EARLY NEXT WEEK, AND THIS TROUGH HAS SOME VARIATIONS IN THE MODEL
GUIDANCE. GFS RUNS REMAIN ON THE LESS AMPLIFIED SIDE WITH THE
TROUGHING, SO MORE SHORTWAVE ENERGY OVERSPREADS THE NORTHWEST
EARLIER, IN CONTRAST TO THE INCREDIBLY AMPLIFIED 12Z ECMWF WHICH
WAS SLOWER. THE NEWER 00Z ECMWF BACKED OFF SOME ON THIS
AMPLIFICATION AND NOW IS MORE CONSISTENT WITH OTHER GUIDANCE ON
THE TIMING OF THE TROUGH AND FRONTAL SYSTEM.
THE WPC FORECAST BEGAN WITH A MULTI-MODEL DETERMINISTIC BLEND
FAVORING THE 12/18Z GFS AND 12Z ECMWF. INCORPORATED THE GEFS AND
EC ENSEMBLE MEANS IN THE BLEND BY DAY 5/MONDAY AND INCREASED THEIR
PROPORTIONS FAIRLY QUICKLY THROUGH DAYS 6-7 GIVEN THE INCREASING
DETERMINISTIC MODEL SPREAD IN CONTRAST WITH THEIR STEADIER
SOLUTIONS.
..WEATHER/HAZARDS HIGHLIGHTS
AS THE UPPER TROUGH AND FORMING EMBEDDED LOW TRACK ACROSS THE
GREAT LAKES LATE WEEK, ATLANTIC MOISTURE IS LIKELY TO FLOW INTO
THE NORTHEASTERN U.S., LEADING TO INCREASING RAIN TOTALS
ESPECIALLY BY SATURDAY ALONG AND AHEAD OF THE COLD FRONT.
INSTABILITY MAY BE SOMEWHAT LIMITED, BUT THE FORCING FOR ASCENT
WILL BE STRONG WITH THE RIGHT ENTRANCE REGION OF THE JET OVERHEAD,
AND PRECIPITABLE WATER ANOMALIES ARE FORECAST TO BE AT LEAST ABOVE
THE 75TH IF NOT THE 90TH PERCENTILE. ADDITIONALLY, THE LOW
PRESSURE SYSTEM THAT IS CURRENTLY TROPICAL STORM PHILIPPE, BUT IS
FORECAST TO BE POST-TROPICAL BY THAT TIME PER THE NATIONAL
HURRICANE CENTER, HAS SHOWN A WESTWARD TREND OVER THE PAST DAY AND
IS CURRENTLY EXPECTED TO TRACK INTO MAINE OR SURROUNDING AREAS.
GIVEN ALL THIS, A SLIGHT RISK REMAINS IN PLACE FOR NORTHEASTERN
NEW YORK INTO PARTS OF NEW ENGLAND FOR DAY 4/SATURDAY. UPSLOPE
FLOW/TERRAIN ENHANCEMENT COULD PLAY A CONTRIBUTING ROLE IN
PRODUCING LOCALLY HEAVIER TOTALS IN SOME TERRAIN AREAS. THE HEAVY
RAIN THREAT WILL LIKELY BE OVER BY SUNDAY, THOUGH THERE IS A SMALL
CHANCE IT COULD PERSIST IN MAINE, BUT SHOWERS WILL LINGER FOR
PORTIONS OF NORTHERN NEW ENGLAND ALONG WITH LAKE EFFECT/ENHANCED
SHOWERS FOR THE LOWER GREAT LAKES UNDERNEATH THE DEEP UPPER LOW.
ELSEWHERE, MUCH OF THE COUNTRY SHOULD BE DRY THROUGH THE WEEKEND,
ASIDE FROM SOME LINGERING LIGHT RAIN POSSIBLE IN SOUTH TEXAS AND
SOME LIMITED SHOWERS IN THE SOUTHWEST. BUT THE PACIFIC NORTHWEST
SHOULD START TO SEE INCREASING PRECIPITATION CHANCES EARLY NEXT
WEEK AS A FRONT AND UPPER TROUGH APPROACH, AND PRECIPITATION IS
FORECAST TO SPREAD EAST WITH TIME INTO THE INTERIOR WEST. SOME
SNOW IS POSSIBLE IN THE HIGHER ELEVATIONS OF THE CASCADES AND
NORTHERN ROCKIES.
COOLER THAN NORMAL TEMPERATURES WILL BE IN PLACE ACROSS THE
CENTRAL U.S. ON SATURDAY, WITH THE NORTHERN HALF OF THE PLAINS AT
RISK OF ITS FIRST FROST OR FREEZE OF THE SEASON. THESE BELOW
AVERAGE TEMPERATURES ARE FORECAST TO SHIFT EAST EARLY NEXT WEEK
UNDER THE UPPER TROUGH/LOW BEHIND THE COLD FRONT. LOWS AROUND
10-15F BELOW NORMAL AND HIGHS OF 10-20F BELOW NORMAL ARE LIKELY
ACROSS THE EAST-CENTRAL U.S. AND REACHING THE EASTERN SEABOARD.
THESE LOOK TO GRADUALLY MODERATE TOWARDS MIDWEEK. MEANWHILE, THE
INITIAL UPPER RIDGE ACROSS THE WEST WILL RAISE TEMPERATURES ALONG
THE WEST COAST TO 10-15F ABOVE NORMAL ON SATURDAY, WITH SOME
RECORD WARM LOWS POSSIBLE. THE SHIFT/EXPANSION OF THE RIDGE
FARTHER EAST SHOULD LEAD TO WARMER THAN AVERAGE TEMPERATURES
ACROSS THE NORTHERN ROCKIES AND INTO THE HIGH PLAINS EARLY NEXT
WEEK. BUT THE WEST COAST IS EXPECTED TO FLIP TO BELOW AVERAGE
ESPECIALLY IN TERMS OF HIGHS BY TUESDAY-WEDNESDAY AS THE NEXT
TROUGH AND LOW APPROACH.
TATE
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 FORECAST, EXCESSIVE RAINFALL OUTLOOK,
WINTER WEATHER OUTLOOK PROBABILITIES, HEAT INDICES AND KEY
MESSAGES 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
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=OVW
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