188
FXUS02 KWBC 170700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 AM EDT TUE OCT 17 2023
VALID 12Z FRI OCT 20 2023 - 12Z TUE OCT 24 2023
..OVERVIEW
FROM LATE THIS WEEK INTO THE WEEKEND, EXPECT INITIALLY STRONG
WESTERN U.S. UPPER RIDGING TO WEAKEN SOMEWHAT AND DRIFT EASTWARD
WHILE A VIGOROUS EASTERN U.S. TROUGH WITH POTENTIAL EMBEDDED LOW
LIKELY SUPPORTS STRENGTHENING LOW PRESSURE ALONG THE EAST COAST
AND POSSIBLY INTO THE CANADIAN MARITIMES. THERE ARE STILL
IMPORTANT DETAILS TO BE RESOLVED FOR THIS SYSTEM BUT THERE IS A
FAIR CLUSTERING OF GUIDANCE INDICATING SOME POTENTIAL FOR
SIGNIFICANT RAINFALL AND A PERIOD OF BRISK TO STRONG WINDS OVER
THE NORTHEAST. THEN AS THIS SYSTEM AND SUPPORTING UPPER TROUGH
LIFT AWAY FROM THE EASTERN STATES, THE WEST SHOULD SEE A
SIGNIFICANT PATTERN CHANGE TOWARD MORE TROUGHING. A PACIFIC
TROUGH OF MODERATE STRENGTH ARRIVING AROUND SUNDAY WILL START THIS
EVOLUTION, FOLLOWED BY DEEPER ENERGY EXPECTED TO DROP DOWN FROM
NORTHWESTERN NORTH AMERICA AND THE FAR NORTHEASTERN PACIFIC. THE
OVERALL MEAN TROUGH WILL SUPPORT EXPANDING PRECIPITATION COVERAGE
AND A PRONOUNCED COOLER TREND ACROSS THE WESTERN HALF OF THE
COUNTRY.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
FOR THE EASTERN U.S. UPPER TROUGH AND SURFACE SYSTEM, THE FORECAST
DEPENDS UPON SOME STILL LOWER PREDICTABILITY DETAILS FOR SHORTWAVE
ENERGY DIGGING INTO THE EAST AS OF FRIDAY AND UPSTREAM ENERGY
LIKELY TO FEED INTO THE OVERALL TROUGH. AMONG LATEST/RECENT
CYCLES, THERE HAS BEEN SOME LOOSE CLUSTERING AMONG RECENT GFS
RUNS, GEFS/EC MEANS, AND 00Z/16 ECMWF RUN THAT WOULD SUPPORT A
DEVELOPING COASTAL WAVE NEAR THE NORTHERN MID-ATLANTIC BY SATURDAY
AND REACHING THE VICINITY OF MAINE BY SUNDAY (THE MEANS BEING
FASTER, GFS SLOWER, 00Z/16 ECMWF IN THE MIDDLE). THIS OCCURS
WHILE GUIDANCE GENERALLY HINTS AT AN EMBEDDED UPPER LOW TRACKING
SOMEWHERE OVER THE GREAT LAKES/NORTHERN MID-ATLANTIC/NEW
ENGLAND/SOUTHERN CANADA. CMC RUNS HAVE DIFFERED FROM THE MAJORITY
LATELY, WHILE THE 12Z/16 ECMWF SHOWED MORE DIGGING OF ENERGY IN
THE BASE OF THE EASTERN TROUGH THAN OTHER GUIDANCE. THE NEW 00Z
ECMWF HAS RETURNED TO A SOLUTION SOMEWHAT CLOSER TO THE MAJORITY.
PREFERENCE WAS FOR A COMPROMISE AMONG THE MEANS/GFS/OLD 00Z ECMWF
WHICH ALSO MAINTAINED REASONABLE CONTINUITY.
ACROSS THE WEST, THE LEADING TROUGH ARRIVING BY SUNDAY CONTINUES
TO BE FAIRLY WELL BEHAVED VIA MODEL/ENSEMBLE BLEND THOUGH THE NEW
00Z CMC HAS RETURNED TO A SOMEWHAT MORE AMPLIFIED DEPICTION AS HAD
BEEN ITS TENDENCY BEFORE THE 12Z/16 RUNS. TO THE SOUTH OF THIS
TROUGH, A SIGNIFICANT WILD CARD WILL BE A TROPICAL SYSTEM EXPECTED
TO DEVELOP OVER THE EASTERN PACIFIC AND LIFT NORTHWARD OFFSHORE
THE WESTERN MEXICO COAST. THE COMBINATION OF FASTER NORTHWARD
PROGRESSION AND MORE AMPLIFIED TROUGH IN THE CMC HAS LED THAT
MODEL TO BE ON THE FAST SIDE OF INCORPORATING THE SYSTEM AND ITS
MOISTURE. THERE IS MORE SPREAD FOR UPSTREAM TROUGHING THAT MAY
REACH THE NORTHWEST BY NEXT TUESDAY, ALONG WITH THE CORRESPONDING
SURFACE PATTERN. THE ENSEMBLE MEANS PROVIDE THE MOST CONSISTENT
STARTING POINT HERE, WITH SOME ASPECTS OF GFS/CMC RUNS AND 00Z/16
ECMWF ALSO VALID CONTRIBUTORS TO A BLEND. THE DEEPER/OFFSHORE
DEPICTION OF THE 12Z ECMWF (ALONG WITH A STRONG SURFACE SYSTEM)
APPEAR LESS PROBABLE.
PREFERENCES ACROSS THE ABOVE REGIONS LED TO STARTING THE FORECAST
WITH A 12Z/18Z MODEL BLEND EARLY IN THE PERIOD, BUT WITH THE
00Z/16 ECMWF PROVIDING THE ECMWF COMPONENT INSTEAD OF THE 12Z RUN.
THE LATTER HALF OF THE FORECAST INCORPORATED SOME 18Z GEFS/12Z
ECENS MEANS, REACHING A TOTAL OF HALF WEIGHT BY THE END OF THE
PERIOD.
..WEATHER/HAZARDS HIGHLIGHTS
THE FRONT CROSSING THE EASTERN U.S. ON FRIDAY MAY PRODUCE SOME
RAINFALL OF VARYING INTENSITY FROM THE EASTERN GREAT LAKES
SOUTHWARD INTO THE SOUTHEAST, WITH SOME LINGERING UNCERTAINTY OVER
BEST EMPHASIS WITHIN THIS BROAD AREA. LOW PRESSURE DEVELOPING
NEAR THE EAST COAST MAY PRODUCE ANOTHER RELATIVE FOCUS FOR
RAINFALL. IN BOTH CASES THE INGREDIENTS STILL DO NOT YET APPEAR
SUFFICIENTLY FAVORABLE FOR DEPICTING ANY RISK AREAS IN THE CURRENT
DAY 4 EXCESSIVE RAINFALL OUTLOOK THAT COVERS FRIDAY-FRIDAY NIGHT.
DEPENDING ON THE TRACK AND TIMING OF STRENGTHENING LOW PRESSURE
DURING THE DAY 5 PERIOD (SATURDAY-SATURDAY NIGHT), THERE IS
SOMEWHAT MORE POTENTIAL FOR SIGNIFICANT RAINFALL OVER PARTS OF THE
NORTHEAST AS SOME DURATION OF MOIST ATLANTIC INFLOW MAY HELP TO
ENHANCE AMOUNTS. THE DAY 5 OUTLOOK DEPICTS A MARGINAL RISK AREA
FROM CENTRAL/NORTHERN PARTS OF EASTERN NEW YORK STATE THROUGH
CENTRAL AND NORTHERN NEW ENGLAND, WHICH REPRESENTS THE BEST
OVERLAP OF HEAVIEST RAINFALL POTENTIAL (BETWEEN THE SLOW GFS AND
FASTER ENSEMBLE MEANS). SURFACE LOW INTENSIFICATION WILL ALSO
SUPPORT THE POTENTIAL FOR A PERIOD OF BRISK TO STRONG WINDS AT
LEAST THROUGH SUNDAY. DEPENDING ON SYSTEM EVOLUTION/TRACK,
HIGHEST ELEVATIONS COULD SEE A LITTLE SNOW. NEXT WEEK WILL BRING
A DRIER TREND OVER THE EAST AS THIS SYSTEM DEPARTS.
IN CONTRAST, MUCH OF THE WEST START OUT DRY LATE THIS WEEK AND
THEN SEE EXPANDING COVERAGE OF PRECIPITATION FROM THE WEEKEND INTO
NEXT WEEK. A LEADING UPPER TROUGH/SURFACE FRONT SHOULD BRING
MOSTLY LIGHT RAINFALL TO THE PACIFIC NORTHWEST AROUND SATURDAY
NIGHT, WITH THIS MOISTURE SHIFTING ACROSS THE INTERMOUNTAIN WEST
INTO MONDAY. ADDITIONAL TROUGH ENERGY SHOULD BRING MORE
PRECIPITATION INTO THE NORTHWEST EARLY NEXT WEEK WHILE LEADING
MOISTURE SPREADS ACROSS THE ROCKIES AND POSSIBLY REACHING THE
PLAINS BY NEXT TUESDAY. AT THAT TIME IT WILL BE WORTH MONITORING
HOW MUCH EAST PACIFIC TROPICAL MOISTURE MAY GET INCORPORATED INTO
THE MEAN FLOW. SOME OF THE PRECIPITATION 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
THROUGH THE WEST AND INTO THE PLAINS ON FRIDAY. WITH TIME THIS
WARMTH WILL MODERATE AND SHRINK IN COVERAGE AS IT REACHES PORTIONS
OF THE PLAINS/MISSISSIPPI VALLEY BY NEXT TUESDAY, AT WHICH TIME
THE HIGH TEMPERATURE ANOMALIES SHOULD BE ONLY IN THE PLUS 5-12F
RANGE. LATE THIS WEEK A SCATTERING OF DAILY RECORD HIGHS WILL BE
POSSIBLE ACROSS THE WEST, WITH RECORD WARM LOWS TENDING TO BE A
LITTLE MORE NUMEROUS AND CONCENTRATED MORE OVER CALIFORNIA.
DURING THE WEEKEND THE POTENTIAL FOR RECORD HIGHS SHOULD SHIFT
INTO THE SOUTHERN ROCKIES AND TEXAS. WITH THE WEST TRANSITIONING
TO MORE MEAN TROUGHING ALOFT FROM SUNDAY ONWARD, EXPECT THE REGION
TO SEE A PRONOUNCED COOLING TREND, WITH HIGHS LIKELY DROPPING TO
5-15F BELOW NORMAL BY EARLY NEXT WEEK. OVER THE EAST, THE
NORTHEAST SHOULD SEE ABOVE NORMAL TEMPERATURES (ESPECIALLY FOR
MORNING LOWS) LATE WEEK INTO THE WEEKEND. OTHERWISE THE AMPLIFIED
UPPER TROUGH CROSSING AREAS EAST OF THE MISSISSIPPI RIVER WILL
SUPPORT MULTIPLE DAYS WITH HIGHS MODERATELY BELOW NORMAL FROM LATE
THIS WEEK INTO START OF NEXT WEEK, FOLLOWED BY A RETURN TOWARD
NORMAL.
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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