072
FXUS02 KWBC 160657
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
257 AM EDT WED OCT 16 2024
VALID 12Z SAT OCT 19 2024 - 12Z WED OCT 23 2024
..OVERVIEW
A CLOSED UPPER LOW NEAR THE FOUR CORNERS THIS WEEKEND WILL LEAD TO
A COOL AND WET PATTERN THERE, INCLUDING HIGHER ELEVATION SNOW AND
FROST/FREEZE CONCERNS IN SOME OF THE VALLEYS. HEAVY RAIN IS
POSSIBLE JUST AHEAD OF THIS UPPER LOW IN THE SOUTH-CENTRAL HIGH
PLAINS, PUSHING EASTWARD BUT LESSENING IN AMOUNTS WITH TIME.
MEANWHILE AN ATMOSPHERIC RIVER COMING INTO THE PACIFIC NORTHWEST
COULD LEAD TO LOCALLY HEAVY PRECIPITATION. AS THE FOUR CORNERS
UPPER LOW TRACKS NORTHEAST NEXT WEEK, QUASI-ZONAL FLOW SHOULD SET
UP OVER THE LOWER 48, SPREADING THE COVERAGE OF ABOVE NORMAL
TEMPERATURES FROM THE NORTH-CENTRAL TO NORTHEASTERN TIER THIS
WEEKEND FARTHER SOUTH ACROSS MUCH OF THE U.S. INTO NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MOST GUIDANCE STILL AGREES WITH THE LARGE SCALE PATTERN THIS
WEEKEND, AS AN UPPER LOW SLOWLY MOVES ACROSS THE FOUR CORNERS WITH
RIDGING AHEAD OF IT. MORE UNCERTAIN SHORTWAVES OVER THE SOUTHEAST
OR SO COULD AFFECT THE MEAN RIDGE PATTERN OVER THE EAST, BUT LOOK
TO HAVE FAIRLY MINIMAL WEATHER IMPACT. FOR THE EARLY PART OF THE
PERIOD, THE WPC FORECAST CONSISTED OF A MULTI-MODEL DETERMINISTIC
BLEND OF THE 18Z GFS AND 12Z ECMWF/CMC/UKMET.
MODEL SPREAD INCREASES SOMEWHAT AS THE UPPER LOW EJECTS NORTHEAST,
WITH THE TRACK AND TIMING PARTLY DEPENDENT ON UPSTREAM SHORTWAVE
ENERGY. GFS RUNS REMAIN THE FASTEST FOR THE FEATURE TO MOVE EAST
AND GET ABSORBED INTO THE NORTHERN STREAM. THE ECMWF AND THE CMC
ARE SLOWER, THOUGH MANY OF THE 12Z EC-BASED AI/ML MODELS ARE A BIT
FASTER THAN THE OPERATIONAL EC. FOR THE NEWER 00Z CYCLE OF
DETERMINISTIC RUNS, MOST MODELS TRENDED SLOWER BUT STILL HAVE THE
GFS ON THE FASTER SIDE AND EC/CMC SLOWER. AN INTERMEDIATE SOLUTION
STILL SEEMS LIKE THE BEST COURSE OF ACTION. THERE IS GOOD AGREEMENT
FOR AN UPPER RIDGE TO SET UP IN THE SOUTHERN STREAM. UPSTREAM,
MODELS VARY CONSIDERABLY WITH THE ENERGY DISTRIBUTION WITHIN A
WESTERN CANADA TO EASTERN PACIFIC MEAN TROUGH ESPECIALLY INTO
TUESDAY-WEDNESDAY. MODELS SHOW THE POTENTIAL FOR AN UPPER LOW TO
PINCH OFF IN THE PACIFIC BUT WITH VARYING PLACEMENT. THIS SPREAD
BEGINS TO INFLUENCE SENSIBLE WEATHER OVER THE NORTHWEST BY TUESDAY
BUT HAS THE POTENTIAL TO PRODUCE MORE SIGNIFICANT SPREAD AND RUN-
TO-RUN VARIABILITY OVER MORE OF THE LOWER 48 THEREAFTER. THUS FOR
THE LATTER PART OF THE PERIOD, THE FORECAST USED THE 18Z GEFS/12Z
EC ENSEMBLE MEANS IN THE BLEND AND INCREASED THEIR PROPORTION TO
HALF BY THE END OF THE PERIOD AMID INCREASING SPREAD.
..WEATHER/HAZARDS HIGHLIGHTS
THE CLOSED UPPER LOW OVER THE SOUTHWEST THIS WEEKEND WILL HELP
FOCUS PRECIPITATION IN THE FOUR CORNERS STATES, ROCKIES, AND HIGH
PLAINS. EXPECT ENHANCED PRECIPITATION TOTALS IN TERRAIN WITH HIGHER
ELEVATION SNOW, WHICH WILL BE THE FIRST SNOW OF THE SEASON IN SOME
LOCATIONS GIVEN THE WARM FALL IN THE WEST THUS FAR. THE CENTRAL
ROCKIES/SAN JUANS CAN EXPECT NOTABLE SNOW SATURDAY WITH SOME
PERHAPS LASTING INTO SUNDAY. FARTHER EAST INTO THE HIGH PLAINS,
HEAVY RAIN WILL BE A CONCERN IN A MOIST ENVIRONMENT (PWS OVER THE
90TH IF NOT 95TH PERCENTILE) WITH SOME INSTABILITY. A MARGINAL RISK
IS MAINTAINED FOR DAY 4/SATURDAY FOR THE SOUTH-CENTRAL HIGH PLAINS
ALSO CONSIDERING THE SLOW MOVEMENT OF THE UPPER LOW AND THUS THE
RAIN AND THUNDERSTORMS. HEAVY RAIN WOULD BE MOST CONCERNING ATOP
SENSITIVE BURN SCAR AREAS. INTO SUNDAY, THE UPPER LOW IS FORECAST
TO MOVE SOMEWHAT MORE QUICKLY NORTHEASTWARD AND SPREAD MODERATE TO
HEAVY RAIN WITH IT, LIKELY FOCUSED IN THE TEXAS/OKLAHOMA PANHANDLES
INTO THE WESTERN HALF OF KANSAS. THIS RAIN GENERALLY LOOKS TO BE
BENEFICIAL RATHER THAN CAUSE A NOTABLE FLOODING THREAT, AS
SHOWERS/STORMS ARE FORECAST TO MOVE MORE QUICKLY, BUT RAIN RATES
MAY BE HIGH ENOUGH FOR PERHAPS A NONZERO FLOOD RISK. SOME SHOWERS
WILL SHIFT INTO THE CENTRAL PLAINS/MID-MISSISSIPPI VALLEY BY
MONDAY, THOUGH WITH DECREASING INTENSITY.
MEANWHILE, THE PACIFIC NORTHWEST WILL LIKELY SEE MORE
PRECIPITATION OVER THE WEEKEND AS AN ATMOSPHERIC RIVER COINCIDES
WITH THE SOUTHERN PERIPHERY OF A STRONG JET PUSHING INTO BRITISH
COLUMBIA. SOME LOCALLY HEAVY RAIN (AND HIGHER ELEVATION SNOW) ARE
POSSIBLE IN THE OLYMPICS/CASCADES SATURDAY, AREAS THAT ARE NOT
TYPICALLY SENSITIVE TO FLOODING FROM THE EXPECTED 2-4 INCHES OF
RAIN. WITH TIME, EXPECT UPSTREAM SHORTWAVE ENERGY TO EXPAND THE
PRECIPITATION SHIELD SOUTHWARD AND EASTWARD BUT WITH GRADUALLY
LESSER MAX AMOUNTS. UNCERTAINTY ABOUT SPECIFICS OF EASTERN
PACIFIC/WEST COAST FLOW ALOFT DECREASES CONFIDENCE IN PRECIPITATION
DETAILS OVER THE NORTHWEST BY TUESDAY-WEDNESDAY.
THE EASTERN U.S. IS FORECAST TO BE GENERALLY DRY THIS WEEKEND INTO
EARLY NEXT WEEK, WITH THE EXCEPTION OF PARTS OF THE FLORIDA
PENINSULA. THERE, RETURN FLOW OF MOISTURE NEAR A MEANDERING FRONT
COULD INCREASE RAIN AND THUNDERSTORM CHANCES ESPECIALLY FOR SOUTH
FLORIDA ON SATURDAY. RAIN AMOUNTS AND RAIN RATES DO NOT LOOK TO BE
HEAVY ENOUGH TO CAUSE FLOODING CONCERNS AT THIS POINT, EVEN IN THE
SENSITIVE URBAN CORRIDOR. EASTERLY FLOW COULD SPREAD SOME LIGHT
SHOWERS ACROSS THE PENINSULA INTO EARLY NEXT WEEK.
COOLER THAN AVERAGE TEMPERATURES WILL BE IN PLACE OVER THE FOUR
CORNERS/GREAT BASIN THIS WEEKEND UNDERNEATH THE UPPER LOW. HIGHS
AROUND 15-20 DEGREES BELOW NORMAL ARE LIKELY SATURDAY, WITH SOME
GRADUAL MODERATION SUNDAY AND ESPECIALLY INTO THE WORKWEEK.
MEANWHILE, UPPER RIDGING AHEAD OF THE UPPER LOW WILL HELP CAUSE
ABOVE NORMAL TEMPERATURES ACROSS THE NORTHERN PLAINS TO UPPER
MIDWEST/GREAT LAKES AND NORTHEAST. THE MIDWEST CAN EXPECT THE
GREATEST ANOMALIES OF 15-25 DEGREES ABOVE AVERAGE ON SUNDAY AS
HIGHS REACH THE 70S. THE UPPER PATTERN IS FORECAST TO RELAX
SOMEWHAT INTO NEXT WEEK FOR DEVELOPING QUASI-ZONAL FLOW, THOUGH A
SUBTROPICAL UPPER HIGH ACROSS THE GULF/NORTHERN MEXICO/TEXAS WILL
ALLOW FOR WARMER TEMPERATURES TO EXPAND SOUTHWARD THROUGH MUCH OF
THE LOWER 48 INTO TUESDAY-WEDNESDAY, THOUGH COOLING ACROSS THE
NORTHERN TIER BEHIND A COLD FRONT.
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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