569
FXUS02 KWBC 180700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 AM EDT WED OCT 18 2023
VALID 12Z SAT OCT 21 2023 - 12Z WED OCT 25 2023
..OVERVIEW
LATEST GUIDANCE CONTINUES TO ADVERTISE A SIGNIFICANT PATTERN
CHANGE OVER THE LOWER 48 DURING THE PERIOD. A VIGOROUS EASTERN
U.S. UPPER TROUGH WILL SUPPORT STRENGTHENING LOW PRESSURE THAT MAY
BRING LOCALLY HEAVY RAIN AND GUSTY WINDS TO THE NORTHEAST THIS
WEEKEND. SOME DEGREE OF UPPER TROUGHING WILL LINGER NEAR THE EAST
COAST INTO EARLY NEXT WEEK BEFORE A RIDGE BUILDS INTO THE EAST. ON
THE OTHER HAND, EXPECT MEAN TROUGHING TO REPLACE THE INITIAL RIDGE
OVER THE WEST. A LEADING SHORTWAVE WITH POSSIBLE EMBEDDED LOW
SHOULD MOVE INTO THE REGION AROUND SUNDAY WHILE STRONGER UPSTREAM
ENERGY SHOULD FEED INTO THE DEVELOPING MEAN TROUGH BY
TUESDAY-WEDNESDAY, BUT WITH INCREASING UNCERTAINTY FOR DETAILS.
THIS PATTERN TRANSITION WOULD BRING COOLER AND WETTER WEATHER TO
THE WEST, WITH THE PLAINS TRENDING WETTER AS WELL BY MIDWEEK,
WHILE THE EAST WILL TREND DRIER AFTER THE WEEKEND WITH COOL
TEMPERATURES EVENTUALLY MODERATING.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
FOR THE SYSTEM AFFECTING THE NORTHEAST THIS WEEKEND, LATEST
OPERATIONAL MODELS ARE STILL SHOWING FINER-SCALE DETAIL
DIFFERENCES THAT HAVE ONLY MEDIUM TO LOWER PREDICTABILITY 3-4 DAYS
OUT IN TIME AND WILL BE IMPORTANT FOR RESOLVING PRECIPITATION
SPECIFICS IN PARTICULAR. OVER THE PAST DAY AN AVERAGE OF THE
GFS/ECMWF RUNS AND THEIR ENSEMBLE MEANS HAS HELD UP THE BEST FOR
THE OVERALL EVOLUTION, WITH THE DEVELOPING COASTAL WAVE OVER OR A
LITTLE SOUTH OF SOUTHERN NEW ENGLAND AS OF EARLY SATURDAY AND
REACHING OVER OR A LITTLE BEYOND NORTHERN/EASTERN MAINE BY EARLY
SUNDAY. SOME RECENT GFS RUNS HAVE BEEN ON THE SOUTH SIDE OF THE
SPREAD BUT ARE TRENDING CLOSER TO THE MAJORITY. UKMET/CMC RUNS
STILL DIFFER WITH SOME DETAILS, AS THE NEW 00Z RUNS STRAY FASTER
WITH THE SUPPORTING UPPER LOW WHICH OTHER GUIDANCE SAYS WILL STILL
BE CLOSER TO MAINE AS OF EARLY SUNDAY. LATEST GFS RUNS ARE
SOMEWHAT SLOWER THAN THE MAJORITY FOR THE WEAK TRAILING SYSTEM
REACHING THE MIDWEST EARLY SATURDAY.
FORECAST DETAILS HAVE BECOME MORE UNCERTAIN OVER THE WESTERN AND
EVENTUALLY CENTRAL U.S. AFTER MOST GUIDANCE HAD BEEN SHOWING A
FAIRLY DIFFUSE LEADING UPPER TROUGH MOVING INTO THE WEST SUNDAY
ONWARD OVER RECENT RUNS, THE PAST DAY HAS TRENDED TOWARD A BETTER
DEFINED EMBEDDED LOW THAT MAY REACH THE SOUTHWEST BY EARLY NEXT
WEEK. BEYOND THIS TREND, INDIVIDUAL MODELS AND ENSEMBLES ARE
SUGGESTING THAT PATTERN COMPLEXITIES NEAR AND SOUTH OF ALASKA FROM
THE WEEKEND INTO NEXT WEEK ARE LEADING TO HIGH SENSITIVITY FOR THE
ULTIMATE DETAILS OF NORTHERN STREAM ENERGY EXPECTED TO DROP INTO
THE WESTERN U.S. BY TUESDAY-WEDNESDAY. DIFFERENCES OVER THAT
UPSTREAM AREA OF SENSITIVITY LEAD TO THE RECENT CMC RUNS BEING THE
MOST AGGRESSIVE WITH DIGGING ENERGY BY MIDWEEK VERSUS THE NEW 00Z
GFS BEING AT LEAST A DAY LATER TO BRING ITS ENERGY INTO THE
NORTHWEST. ENSEMBLE MEMBERS ARE EXPECTEDLY DIVERSE BUT THE MEANS
AVERAGE OUT FAIRLY CLOSE TO THE INTERMEDIATE 12Z ECMWF.
CORRESPONDING TO THESE UPSTREAM ISSUES, A WIDE SPREAD DEVELOPS FOR
HOW QUICKLY THE LEADING TROUGH/LOW MAY EJECT NORTHEASTWARD--WITH
MINIMAL CONFIDENCE IN A SPECIFIC SOLUTION (THOUGH TRENDS LEAN AWAY
FROM FAST TIMING LIKE THE 12Z CMC). FINALLY, THE GUIDANCE STILL
SIGNALS THAT THE OVERALL TROUGH MAY INCORPORATE MOISTURE FROM
TROPICAL STORM NORA WHICH NATIONAL HURRICANE CENTER ADVISORIES
EXPECT TO STRENGTHEN TO HURRICANE STATUS AS IT TRACKS NORTHWARD
OFFSHORE THE WESTERN MEXICO COAST.
PREFERENCES BASED ON THE 12Z/18Z ARRAY OF GUIDANCE LED TO STARTING
THE EARLY PART OF THE FORECAST WITH A BLEND OF THE 12Z/18Z GFS AND
12Z ECMWF AND THEN SLOWING INCORPORATING MORE 18Z GEFS/12Z ECENS
MEANS SO THAT THE MEANS HAD HALF WEIGHT BY LATE IN THE PERIOD.
..WEATHER/HAZARDS HIGHLIGHTS
DURING THE DAY 4 EXCESSIVE RAINFALL OUTLOOK THAT COVERS
SATURDAY-SATURDAY, GUIDANCE CONTINUES TO SHOW THE POTENTIAL FOR
SOME AREAS OF SIGNIFICANT RAINFALL OVER PARTS OF THE NORTHEAST AS
NORTHWARD MOVING LOW PRESSURE DEEPENS. SPECIFICS ARE STILL
UNCERTAIN AND DEPEND ON FINE-SCALE DETAILS AND EXACT TIMING THAT
WOULD AFFECT HOW LONG THE SYSTEM COULD BRING IN MOIST INFLOW FROM
THE ATLANTIC TO ENHANCE RAINFALL AMOUNTS. THE NEW DAY 4 ERO STAYS
UNCHANGED FROM THE PRIOR DAY 5 ISSUANCE, DEPICTING A MARGINAL RISK
AREA FROM CENTRAL/NORTHERN PARTS OF EASTERN NEW YORK STATE THROUGH
CENTRAL AND NORTHERN NEW ENGLAND. LATEST GUIDANCE TRENDS HAVE
BECOME A LITTLE MORE MIXED IN THE FAR SOUTHWESTERN PART OF THIS
AREA BUT ARE NOT EMPHATIC ENOUGH TO FAVOR ANY CHANGE YET. SURFACE
LOW INTENSIFICATION WILL ALSO SUPPORT THE POTENTIAL FOR A PERIOD
OF BRISK TO STRONG WINDS AT LEAST THROUGH SUNDAY. DEPENDING ON
SYSTEM STRENGTH/TRACK, HIGHEST ELEVATIONS COULD SEE A LITTLE SNOW.
NEXT WEEK WILL BRING A DRIER TREND OVER THE EAST AS THIS SYSTEM
DEPARTS.
THE WEST WILL SEE EXPANDING COVERAGE OF PRECIPITATION FROM THE
WEEKEND INTO NEXT WEEK. A LEADING SYSTEM SHOULD BRING LIGHT TO
MODERATE TOTALS TO NORTHERN AND CENTRAL LATITUDES AFTER DAYTIME
SATURDAY, WITH THIS MOISTURE SHIFTING ACROSS THE INTERMOUNTAIN
WEST ON MONDAY. ADDITIONAL TROUGH ENERGY SHOULD BRING MORE
PRECIPITATION INTO THE NORTHWEST NEXT WEEK BUT DETAILS ARE
BECOMING MORE UNCERTAIN. LEADING MOISTURE SHOULD SPREAD ACROSS THE
ROCKIES AND REACH THE CENTRAL U.S. BY TUESDAY-WEDNESDAY. GUIDANCE
CONTINUES TO SUGGEST THAT RAINFALL OVER THE PLAINS COULD BE
ENHANCED BY MOISTURE ORIGINATING FROM NORA IN THE EAST PACIFIC.
SOME OF THE PRECIPITATION OVER THE WEST SHOULD FALL AS SNOW IN THE
HIGHER NORTHERN ROCKIES, WITH SNOW LEVELS GRADUALLY DECLINING WITH
TIME.
A BROAD AREA OF TEMPERATURES 10-20F ABOVE NORMAL WILL EXTEND FROM
THE INTERIOR WEST INTO THE PLAINS ON SATURDAY. WITH TIME THIS
WARMTH WILL MODERATE AND SHRINK IN COVERAGE AS IT REACHES PORTIONS
OF THE PLAINS AND MISSISSIPPI VALLEY BY TUESDAY. ABOVE NORMAL
HIGHS MAY EXPAND INTO THE OHIO VALLEY/GREAT LAKES BY WEDNESDAY BUT
MOST ANOMALIES AS OF MIDWEEK SHOULD BE WITHIN 10 DEGREES OF
AVERAGE. POTENTIAL FOR SOME RECORD WARM LOWS MAY EXTEND INTO
SATURDAY ESPECIALLY OVER CALIFORNIA, WHILE A FEW RECORD HIGHS MAY
BE POSSIBLE FROM ARIZONA INTO TEXAS DURING THE WEEKEND. STILL
EXPECT THE WEST TO SEE BELOW NORMAL HIGHS EXPAND IN COVERAGE FROM
WEST TO EAST, THOUGH LATEST TRENDS HAVE SLIGHTLY DELAYED THE
ARRIVAL OF COLDER AIR (WEDNESDAY INSTEAD OF TUESDAY) THAT WOULD
BRING HIGHS AT SOME LOCATIONS DOWN TO 10-20F BELOW NORMAL. THE
NORTHEAST SHOULD SEE ABOVE NORMAL TEMPERATURES (ESPECIALLY FOR
MORNING LOWS) INTO THE WEEKEND. OTHERWISE THE AMPLIFIED UPPER
TROUGH CROSSING THE EAST WILL SUPPORT HIGHS UP TO 5-10F BELOW
NORMAL FROM SATURDAY INTO EARLY NEXT WEEK. THE TROUGH'S DEPARTURE
WILL PROMOTE A REBOUND CLOSER TO OR SLIGHTLY ABOVE NORMAL BY
MIDWEEK.
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 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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