473
FXUS02 KWBC 181858
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
258 PM EDT FRI OCT 18 2024
VALID 12Z MON OCT 21 2024 - 12Z FRI OCT 25 2024
..OVERVIEW
A CLOSED UPPER LOW TRACKING ACROSS THE GREAT PLAINS WILL PRODUCE
SOME SCATTERED SHOWER AND THUNDERSTORM ACTIVITY ACROSS THE REGION
ON MONDAY, BEFORE OPENING UP AND PHASING WITH A NORTHERN STREAM
TROUGH THAT WILL AMPLIFY AND SHARPEN OVER THE EAST BY MIDWEEK. THIS
LATTER TROUGH WILL PUSH A COLD FRONT THROUGH THE EASTERN HALF OF
THE COUNTRY WITH MOST ASSOCIATED RAINFALL LIKELY TO BE OVER THE
GREAT LAKES/NORTHEAST. A TRAILING UPPER RIDGE WILL PREVAIL ACROSS
THE WESTERN AND EVENTUALLY CENTRAL CONUS THROUGH NEXT WEEK. AN
ELONGATED TROUGH EXTENDING INTO THE PACIFIC INTO THE START OF NEXT
WEEK WILL CONTRIBUTE TO A WEAKENING ATMOSPHERIC RIVER EVENT ACROSS
THE PACIFIC NORTHWEST NEXT MONDAY, FOLLOWED BY AN UPPER LOW CLOSING
OFF OVER THE EASTERN PACIFIC. PROGRESSION OF THIS SYSTEM SHOULD
RENEW POTENTIAL FOR RAINFALL AND PERHAPS HIGH ELEVATION SNOW OVER
THE PACIFIC NORTHWEST TOWARD THE END OF NEXT WEEK. AN ANOMALOUSLY
WARM AIRMASS OVER THE NORTHERN TIER WILL SHIFT INTO THE NORTHEAST
THROUGH MIDWEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
WITH GUIDANCE FINALLY COMING INTO GOOD ALIGNMENT FOR THE UPPER
SYSTEM TRACKING THROUGH THE PLAINS/MIDWEST EARLY IN THE WEEK, THE
PRIMARY FOCUS OF THE FORECAST WILL BE ON THE SPLITTING OF INITIAL
WESTERN CANADA INTO EASTERN PACIFIC TROUGHING AND THEN TRACKING THE
EVOLUTION OF SEPARATE RESULTING FEATURES--IN PARTICULAR A MEAN
TROUGH REACHING INTO EASTERN NORTH AMERICA AND AN UPPER LOW THAT
CLOSES OFF OVER THE EASTERN PACIFIC. BETWEEN THESE, UPPER RIDGING
THAT BUILDS OVER THE WEST SHOULD APPROACH OR REACH THE CENTRAL
U.S. BY LATE WEEK.
MODELS/ENSEMBLES ARE STILL AT LEAST MORE SIMILAR IN PRINCIPLE THAN
THEY CAN BE SOMETIMES IN SUCH FLOW SEPARATION SCENARIOS, THOUGH
MEANINGFUL DIFFERENCES/TRENDS REMAIN. NORTHERN STREAM UPPER TROUGH
ENERGY PROGRESSING THROUGH CENTRAL/EASTERN NORTH AMERICA HAS
EXHIBITED BETTER CLUSTERING IN LATEST RUNS WITH A TREND TOWARD A
SHARPER AND MORE NEUTRALLY TILTED FEATURE BY THE TIME IT REACHES
THE GREAT LAKES AND NEW ENGLAND, LEADING TO A MORE PRONOUNCED
SURFACE FRONT. MEANWHILE, DIFFERENCES STILL EXIST FOR THE
STRENGTH/LOCATION OF WESTERN U.S. UPPER RIDGING AND IN TURN FOR THE
TIMING OF THE EASTERN PACIFIC UPPER LOW/ASSOCIATED SURFACE SYSTEM.
UPSTREAM FLOW DIVING SOUTHEAST FROM THE ALEUTIANS/BERING SEA MAY
BEGIN TO HAVE SOME INFLUENCE ON THIS SYSTEM BY THE END OF THE WEEK
AS WELL. LATEST MACHINE LEARNING (ML) MODELS HAVE TRENDED TOWARD
THE UPPER RIDGE BEING MORE OVER THE INTERIOR WEST/WEST BY MIDWEEK
OR SO VERSUS BEING FARTHER WESTWARD 24-36 HOURS AGO, WHILE
REMAINING GUIDANCE LEANS AWAY FROM THE STRONGER SIDE FOR RESIDUAL
SHORTWAVE ENERGY THAT COULD BE OVER THE NORTHWEST FOR A TIME (PER
UKMET RUNS AND THE 00Z ECMWF).
RELATIVE TO 6-7 DAY FORECASTS, SPREAD FOR EASTERN PACIFIC SYSTEM
TIMING LATE NEXT WEEK LOOKS FAIRLY TYPICAL. HOWEVER THE 12Z
ECMWF/ICON HAVE TRENDED TO THE SLOW SIDE OF THE SPREAD WHILE THE
12Z CMC IS ON THE FASTER SIDE AND 06Z/12Z GFS RUNS HAVE ADJUSTED TO
AN INTERMEDIATE TIMING AFTER BEING SOMEWHAT FASTER IN THE 00Z RUN.
AS FOR SURFACE LOW TRACK, THE AVERAGE OF ML MODELS WOULD SUGGEST A
PATH TOWARD VANCOUVER ISLAND, VERSUS 06Z/12Z GFS RUNS THAT ARE
SOUTH OR THE 00Z ECMWF THAT IS DEEP AND FARTHER NORTHWEST. LATEST
GEFS MEAN RUNS HAVE BEEN SUSPICIOUSLY WEAK AND THUS COULD NOT BE
USED IN THE FORECAST.
THE UPDATED FORECAST STARTED WITH A BLEND OF THE 06Z GFS, 00Z AND
12Z/17 ECMWF RUNS, AND SOME 00Z CMC/UKMET FOR THE FIRST HALF OF THE
PERIOD AND THEN ADDED ONLY SLIGHT WEIGHT OF THE 00Z ECENS/CMCENS
MEANS LATE IN THE PERIOD (REPLACING THE UKMET AND A FRACTION OF THE
GFS). THIS BLEND WAS STILL CLOSE TO THE MEANS IN PRINCIPLE OVER
THE EAST WHILE MAINTAINING REASONABLE DEFINITION WITH A FAVORED
TRACK FOR THE SYSTEM EXPECTED TO AFFECT THE NORTHWEST BY NEXT
FRIDAY.
..WEATHER/HAZARDS HIGHLIGHTS
THIS WEEKEND'S FOUR CORNERS UPPER LOW WILL SHIFT INTO THE CENTRAL
PLAINS BY MONDAY, MARKING THE END OF AN ACTIVE PERIOD ACROSS THE
FOUR CORNERS/HIGH PLAINS. SOME LINGERING SHOWERS AND THUNDERSTORMS
WILL IMPACT PARTS OF THE CENTRAL/SOUTHERN PLAINS AND TO A LESSER
DEGREE MIDDLE MISSISSIPPI VALLEY ON MONDAY. THE UPPER LOW WILL
TRACK FAR ENOUGH NORTH THAT IT WILL AVOID TAPPING MOISTURE FROM
THE GULF OF MEXICO, WHICH WILL KEEP RAINFALL TOTALS IN THE LIGHT TO
MODERATE RANGE. ANY RAIN THAT DOES FALL WILL BE BENEFICIAL GIVEN
THE DRY GROUND CONDITIONS ACROSS MUCH OF THE CENTRAL U.S. THEN A
NORTHERN STREAM COLD FRONT MAY PRODUCE SOME LIGHT RAIN ACROSS THE
NORTHERN TIER, POSSIBLY BECOMING BETTER ORGANIZED OVER THE GREAT
LAKES AND NORTHEAST WEDNESDAY-THURSDAY AS SUPPORTING UPPER
DYNAMICS SHARPEN. HIGHEST ELEVATIONS IN NEW ENGLAND COULD SEE A
LITTLE SNOW BEHIND THE FRONT BEFORE ANY REMAINING MOISTURE DEPARTS.
THE ONE OTHER PRECIPITATION FOCUS WILL BE OVER THE NORTHWEST.
LEADING SHORTWAVE ENERGY AND ASSOCIATED SURFACE FRONT WILL PRODUCE
SOME RAIN AND HIGH ELEVATION SNOW FROM THE PACIFIC NORTHWEST INTO
FAR NORTHERN ROCKIES ON MONDAY. THEN THE APPROACH/ARRIVAL OF AN
EASTERN PACIFIC SYSTEM MAY BRING ANOTHER PLUME OF MOISTURE INTO THE
PACIFIC NORTHWEST/NORTHERN CALIFORNIA BY AROUND NEXT FRIDAY. THERE
IS STILL SIGNIFICANT SPREAD FOR THE TIMING, TRACK, AND STRENGTH OF
THIS SYSTEM SO IT WILL TAKE SOME TIME TO RESOLVE MORE PRECISE
DETAILS OF WHEN THE PRECIPITATION ARRIVES AND ITS INTENSITY. EXPECT
MOST OF THIS ACTIVITY TO BE RAIN, WITH A LITTLE SNOW POTENTIAL IN
THE HIGHEST ELEVATIONS OF THE NORTHERN CASCADES.
DURING EARLY-MID WEEK, THE WARM SECTOR AHEAD OF AN ADVANCING COLD
FRONT WILL FEATURE WELL ABOVE NORMAL TEMPERATURES OVER THE
CENTRAL/EASTERN U.S. THE GREATEST ANOMALIES SHOULD BE IN THE PLUS
20-25F RANGE OVER THE NORTHERN PLAINS/UPPER MIDWEST ON MONDAY BUT
THERE WILL ALSO BE BROAD COVERAGE OF PLUS 10-20F ANOMALIES FARTHER
SOUTH THROUGH THE PLAINS AND ALSO EXTENDING AS FAR AS THE
NORTHEAST. TEMPERATURES COULD CHALLENGE DAILY RECORDS OVER PARTS OF
TEXAS ON WEDNESDAY. NEAR TO SLIGHTLY BELOW NORMAL READINGS WILL
PROGRESS FROM THE NORTHERN HALF OF THE PLAINS INTO THE EAST MID-
LATE WEEK WHILE TEMPERATURES REBOUND FROM THE INTERIOR WEST THROUGH
THE PLAINS, WITH HIGH PLAINS LOCATIONS LIKELY SEEING THE WARMEST
ANOMALIES (UP TO PLUS 15-20F) BY NEXT FRIDAY. THE FAR SOUTHERN TIER
SHOULD STAY ABOVE NORMAL THROUGH FRIDAY. THE WEST COAST STATES WILL
TEND TO BE NEAR/ABOVE NORMAL TUESDAY-THURSDAY, SANDWICHED BY
SLIGHTLY COOLER HIGHS EARLY AND LATE IN THE WEEK.
RAUSCH/KEBEDE
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 (QPF), EXCESSIVE RAINFALL
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:
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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