379
FXUS02 KWBC 130657
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
257 AM EDT SUN OCT 13 2024
VALID 12Z WED OCT 16 2024 - 12Z SUN OCT 20 2024
..OVERVIEW
A PATTERN CHANGE IS FORECAST BY MIDWEEK IN THE WEST, AS UPPER
TROUGHING AND THEN REINFORCING ENERGY COME IN FROM THE EASTERN
PACIFIC, LEADING TO MUCH COOLER TEMPERATURES AND INCREASING
PRECIPITATION CHANCES, INCLUDING HIGHER ELEVATION SNOW. UPPER
RIDGING AHEAD OF THIS TROUGH WILL PROMOTE WARMER THAN AVERAGE
TEMPERATURES IN THE NORTHERN/CENTRAL PLAINS TO MIDWEST AS IT
GRADUALLY MOVES EAST, EVENTUALLY DISPLACING THE CHILLY UPPER TROUGH
AND SURFACE HIGH IN THE EAST BY LATE WEEK INTO NEXT WEEKEND.
..GUIDANCE/PREDICTABILITY ASSESSMENT
RECENT MODEL GUIDANCE REMAINS RATHER AGREEABLE IN THE AMPLIFIED
AND SOMEWHAT PROGRESSIVE PATTERN FOR THE LATTER HALF OF THIS WEEK.
MODELS ARE MORE AGREEABLE THAN A DAY AGO REGARDING THE TIMING OF
THE WESTERN U.S. TROUGH, CENTRAL U.S. RIDGE, AND EASTERN U.S.
TROUGH MOVING GRADUALLY EASTWARD WITH TIME. ADDITIONALLY, LATEST
MODELS ARE NOT AS DEEP WITH A EASTERN PACIFIC SURFACE LOW AND AS
STRONG WITH THE ATMOSPHERIC RIVER COMING INTO THE PACIFIC NORTHWEST
COMPARED TO SOME OLDER MODELS (E.G. 12Z EC FROM THE 11TH AND 00Z
EC FROM THE 12TH). WITH THOSE ASPECTS OF THE FORECAST SHOWING
BETTER CONSENSUS, THE MAIN FORECAST ISSUE ON THE LARGER SCALE IS
WITH THE EVOLUTION OF THE WESTERN TROUGH LATE WEEK INTO THE
WEEKEND. GFS AND CMC RUNS HAVE BEEN PERSISTENT NOW OVER SEVERAL
RUNS IN SHOWING AN UPPER LOW CUTTING OFF ON THE SOUTHERN SIDE OF
THE TROUGH, WITH DIFFERENCES IN POSITION FOR THE CUTOFF LOW BUT
SOMEWHERE IN THE SOUTHWESTERN TO SOUTH-CENTRAL CONUS. THE 12Z ECMWF
SPLIT SOME ENERGY INTO THE FOUR CORNERS REGION BUT DID NOT CLOSE
OFF A LOW, AND NOW THE NEWER 00Z EC JUST KEEPS A PHASED TROUGH.
HOWEVER, MOST AI/ML GUIDANCE THAT IS EC-BASED DOES INDICATE A
CLOSED LOW FORMING. THE WPC FORECAST DOES NOT EXPLICITLY DEPICT A
CLOSED LOW AT THIS POINT BUT DOES SHOW SOME SOUTHERN STREAM
TROUGHING SEPARATING FROM THE NORTHERN STREAM. WHETHER OR NOT A LOW
CLOSES OFF IN THE SOUTHERN STREAM WILL IMPACT TIMING OF TROUGHING
PROGRESSING EASTWARD (AS THE CUTOFF LOW WOULD TEND TO STALL BUT THE
NORTHERN STREAM TROUGH CAN MOVE MORE QUICKLY EAST IF THE FLOW
SPLITS).
THE WPC FORECAST WAS BASED ON A MULTI-MODEL DETERMINISTIC BLEND
FAVORING THE 12Z ECMWF AND 18Z GFS EARLY IN THE PERIOD, BUT AS
SPREAD INCREASED QUICKLY IN THE WESTERN/CENTRAL U.S. INTO THE LATER
PERIOD, USED THE GEFS AND EC ENSEMBLE MEANS AS HALF THE BLEND BY
DAY 6 AND OVER HALF BY DAY 7.
..WEATHER/HAZARDS HIGHLIGHTS
THE DEVELOPING AND RELOADING UPPER TROUGH AND MULTIPLE SURFACE
FRONTS MOVING INTO THE WEST WILL PUSH PRECIPITATION ACROSS THE
NORTHWEST WEDNESDAY, WITH ENHANCED PRECIPITATION TOTALS IN TERRAIN
LIKE THE COASTAL RANGES AND CASCADES INTO THE NORTHERN ROCKIES.
HIGHER ELEVATION SNOW IS LIKELY, WHICH WILL BE THE FIRST SNOW OF
THE SEASON IN SOME LOCATIONS GIVEN THE WARM FALL IN THE WEST THUS
FAR. PRECIPITATION IS FORECAST TO SPREAD ACROSS THE INTERMOUNTAIN
WEST AND ROCKIES THURSDAY AND FRIDAY. BY FRIDAY AND INTO THE
WEEKEND, GULF MOISTURE COULD STREAM IN JUST AHEAD OF THE UPPER
TROUGH FOR INCREASING RAIN CHANCES IN THE PLAINS TO UPPER MIDWEST.
THE FORECAST DETAILS VARY, BUT MODELS GENERALLY SHOW SOME MODERATE
TO LOCALLY HEAVY RAIN TOTALS IN THE SOUTH-CENTRAL PLAINS.
IN THE NORTHEASTERN U.S., COOL WESTERLY FLOW UNDERNEATH THE UPPER
TROUGH TO START THE PERIOD WEDNESDAY WILL LEAD TO SOME CONTINUED
LAKE-ENHANCED AND TERRAIN-ENHANCED PRECIPITATION ACROSS THE
CENTRAL/NORTHERN APPALACHIANS AND THE GREAT LAKES REGION INTO THE
INTERIOR NORTHEAST. COLDER TEMPERATURES SHOULD ALLOW FOR SNOW
ESPECIALLY IN THE HIGHER ELEVATIONS. PRECIPITATION SHOULD TAPER OFF
BY THURSDAY, AND THE EAST IS LIKELY TO BE DRY FOR LATER WEEK AS A
COOL SURFACE HIGH SETS UP BEHIND A SECONDARY COLD FRONT. THE
EXCEPTION COULD BE ACROSS SOUTH FLORIDA, WHICH IS FORECAST TO SEE
RETURN FLOW OF MOISTURE BY LATE WEEK FOR INCREASING RAIN AND
THUNDERSTORM CHANCES.
AN UPPER RIDGE ALIGNED OVER THE CENTRAL U.S. MIDWEEK AND SHIFTING
EASTWARD LATER WEEK WILL PROMOTE WELL ABOVE NORMAL TEMPERATURES IN
ITS VICINITY. THE BIGGEST ANOMALIES ARE FORECAST ACROSS THE
NORTHERN ROCKIES AND HIGH PLAINS ON WEDNESDAY, WHERE HIGHS INTO THE
70S AND 80S ARE 15-25 DEGREES ABOVE AVERAGE FOR MID-OCTOBER. THESE
WARM TEMPERATURES WILL SHIFT INTO THE CENTRAL/NORTHERN PLAINS AND
MIDWEST BY THURSDAY-FRIDAY. MEANWHILE, TEMPERATURES ARE FORECAST TO
BE BELOW AVERAGE BY 10-20 DEGREES ON WEDNESDAY IN MUCH OF THE
EASTERN U.S. UNDER COOL HIGH PRESSURE. MORNING LOWS MAY CAUSE
FROST/FREEZE CONCERNS FROM THE NORTH-CENTRAL U.S. THROUGH THE
MIDWEST/GREAT LAKES AND NORTHEAST/APPALACHIANS. SOME GRADUAL
MODERATION/WARMING IS LIKELY THERE THURSDAY-FRIDAY AND EVEN MORE SO
INTO THE WEEKEND WHEN UPPER RIDGING COMES OVERHEAD, FOR
TEMPERATURES AROUND 5-10 DEGREES ABOVE NORMAL IN THE NORTHEASTERN
TIER. ON THE OTHER HAND, THE UPPER TROUGH AND FRONTAL SURGES COMING
INTO THE WEST WILL LEAD TO BELOW NORMAL TEMPERATURES SPREADING
GRADUALLY INLAND FOR THE LATTER HALF OF THE WEEK. THESE COLDER
TEMPERATURES MAY ALSO LEAD TO ADDITIONAL FROST/FREEZE CONCERNS FOR
STILL SUSCEPTIBLE GROWING AREAS.
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 (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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