116
FXUS02 KWBC 171847
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
247 PM EDT TUE OCT 17 2023
VALID 12Z FRI OCT 20 2023 - 12Z TUE OCT 24 2023
..OVERVIEW
A DEEP UPPER LEVEL TROUGH WILL BE POSITIONED OVER THE EASTERN U.S.
LATE THIS WEEK INTO THIS WEEKEND, WHICH WILL SUPPORT PRECIPITATION
CHANCES EAST OF THE MISSISSIPPI FRIDAY THROUGH SUNDAY. A STRONG
COASTAL LOW IS FORECAST TO DEVELOP OFF THE MID-ATLANTIC ON FRIDAY
AND TRACK NORTH ALONG THE EAST COAST OVER THE WEEKEND, WHICH MAY
CAUSE LOCALLY HEAVY RAINFALL AND GUSTY WINDS FOR PARTS OF THE
NORTHEAST. THE UPPER TROUGH AND SURFACE LOW PRESSURE SYSTEM WILL
PUSH OFFSHORE EARLY NEXT WEEK, AND UPPER LEVEL TROUGHING WILL MOVE
OVER THE WEST. THE WEATHER PATTERN WILL TREND COOLER AND WETTER
FOR THE WEST NEXT WEEK. PRECIPITATION CHANCES WILL INCREASE ACROSS
THE PACIFIC NORTHWEST AND ALONG THE WEST COAST ON SUNDAY, THEN
EXPAND EAST INTO THE PLAINS AND UPPER MIDWEST THROUGH TUESDAY.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE IS IN GENERALLY GOOD AGREEMENT ON THE TIMING,
STRENGTH, AND POSITION OF THE EASTERN U.S. TROUGH THROUGH THE
WEEKEND, BUT THERE ARE SOME MINOR DIFFERENCES IN HOW THE
DETERMINISTIC MODELS HANDLE SHORTWAVES MOVING AROUND THE BASE OF
THE TROUGH. THE LATEST RUNS OF THE GFS/ECMWF/CMC/UKMET ALL SHOW A
WAVE DEVELOPING OFF THE MID-ATLANTIC COAST ON FRIDAY AND MOVING
NORTH UP THE EAST COAST ON SATURDAY ACCOMPANIED BY A STRONG
COASTAL LOW AT THE SURFACE. THERE ARE SLIGHT DIFFERENCES IN THE
TIMING/SPEED OF THE COASTAL LOW, WHICH WILL AFFECT THE FORECAST
RAINFALL. A MAINLY DETERMINISTIC MODEL BLEND WAS USED FOR THE WPC
FORECAST FOR FRIDAY THROUGH SUNDAY WITH SMALL AMOUNTS OF THE GEFS
MEAN AND EC MEAN. SLIGHTLY LESS WEIGHT WAS GIVEN TO THE CMC, WHICH
CONTINUES TO DIFFER FROM THE MAJORITY THIS AFTERNOON WITH HOW IT
HANDLES THE WAVES OF ENERGY IN THE EASTERN TROUGH.
THERE IS QUITE A BIT MORE UNCERTAINTY SURROUNDING THE TROUGHING
OVER THE WEST NEXT WEEK. TWO SUCCESSIVE TROUGHS WILL LIKELY MOVE
INTO THE WEST THROUGH MID-NEXT WEEK, BUT THE CMC/ECMWF/GFS
DISAGREE ON THE SPEED OF THE SECOND TROUGH. THE ECMWF STRENGTHENS
THE SECOND TROUGH SIGNIFICANTLY MORE THAN THE OTHER MODELS AND
BRINGS IT INTO THE WEST THE SLOWEST, KEEPING BOTH TROUGHS
SEPARATE. THE GFS IS ON THE OTHER END OF THE SPECTRUM, KEEPING THE
SECOND FEATURE WEAKER AND BRINGING IT INTO THE WEST FASTER,
ALLOWING THE TWO TROUGHS TO COMBINE QUICKLY. THE CMC SEEMS TO FALL
BETWEEN THE GFS AND ECMWF. ADDITIONAL UNCERTAINTY IS INTRODUCED
FROM THE POTENTIAL TROPICAL SYSTEM IN THE EASTERN PACIFIC, WHICH
MAY AFFECT THE EVOLUTION OF THE UPPER LEVEL PATTERN AS THE UPPER
LEVEL ENERGY MOVES INTO THE MID-LATITUDES. FOR THE FORECAST BLEND,
ENSEMBLE MEANS WERE ASSIGNED THE HEAVIEST WEIGHT WITH SMALLER
AMOUNTS GIVEN TO THE DETERMINISTIC MODELS TO PRODUCE A MIDDLE OF
THE ROAD SOLUTION.
..WEATHER/HAZARDS HIGHLIGHTS
THE FRONT CROSSING THE EASTERN U.S. ON FRIDAY WILL PRODUCE
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 COAST WILL LIKELY PRODUCE ANOTHER RELATIVE FOCUS FOR RAINFALL
IN THE COASTAL MID-ATLANTIC. 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. THE POTENTIAL FOR SIGNIFICANT RAINFALL SEEMS
TO BE SLIGHTLY HIGHER ON DAY 5 (SATURDAY-SATURDAY NIGHT) AS THE
COASTAL LOW MOVES UP THE NORTHEAST COAST. THERE IS STILL
UNCERTAINTY IN THE LOCATION OF THE HEAVIEST RAINFALL AMOUNTS,
WHICH WILL DEPEND ON THE TRACK, INTENSITY, AND SPEED OF THE
COASTAL LOW. MODELS DO INDICATE THAT THERE WILL BE AT LEAST SOME
MOIST INFLOW FROM THE ATLANTIC AHEAD OF THE SYSTEM, WHICH MAY
ENHANCE RAINFALL 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
ON 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 AND UPPER MIDWEST BY 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 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 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. THE NORTHEAST SHOULD SEE ABOVE NORMAL
TEMPERATURES (ESPECIALLY FOR MORNING LOWS) LATE THIS 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 THE START OF NEXT
WEEK, FOLLOWED BY A RETURN TOWARD NORMAL.
RAUSCH/DOLAN
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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