550
FXUS02 KWBC 161859
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 PM EDT WED OCT 16 2024
VALID 12Z SAT OCT 19 2024 - 12Z WED OCT 23 2024
...A FOUR CORNERS UPPER LOW WILL BRING THE FIRST SNOW OF THE SEASON
TO PARTS OF THE CENTRAL/SOUTHERN ROCKIES AND HEAVY RAIN/FLOODING
CONCERNS TO THE SOUTH-CENTRAL HIGH PLAINS THIS WEEKEND...
..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 OR BROADLY
CYCLONIC FLOW SHOULD SET UP OVER THE LOWER 48, SPREADING THE
COVERAGE OF ABOVE NORMAL TEMPERATURES FROM THE NORTH-CENTRAL TO
NORTHEASTERN TIER THIS WEEKEND WHILE GULF OF MEXICO/SOUTHERN
TEXAS/MEXICO UPPER RIDGING ALSO ASSISTS IN BRINGING WARMER
READINGS TO THE SOUTHERN STATES BY NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE PRIMARY FORECAST ISSUES IN LATEST GUIDANCE CONTINUE TO BE WITH
THE TIMING OF THE UPPER LOW EJECTING FROM THE SOUTHWEST/EVENTUAL
INFLUENCE OF INCOMING NORTHERN STREAM FLOW, AND THEN DETAILS WITHIN
NORTHEASTERN PACIFIC TROUGHING THAT THE MAJORITY OF GUIDANCE
SUGGESTS WILL SPLIT BY NEXT TUESDAY-WEDNESDAY.
SOLUTIONS CONTINUE TO VARY SOMEWHAT FOR THE EJECTING SOUTHWEST
UPPER LOW. BY SUNDAY THE 12Z UKMET BRIEFLY STRAYS A BIT EAST OF
CONSENSUS BEFORE RETURNING TO THE MIDDLE OF THE SPREAD. GFS RUNS
HAVE TENDED TO BE FASTER FROM SUDAY ONWARD, THOUGH THE 00Z AND 12Z
RUNS COMPARE BETTER TO OTHER GUIDANCE THAN THE 06Z VERSION.
ECMWF/CMC RUNS HAVE BEEN LEANING TO THE SLOWER SIDE OF THE
ENVELOPE. MOST MACHINE LEARNING (ML) MODELS FAVOR AN INTERMEDIATE
TIMING, PERHAPS WITH A SLIGHT TILT IN THE ECMWF DIRECTION. BY
AROUND TUESDAY THE UPPER LOW'S TIMING MAY ALSO DEPEND ON THE
ARRIVAL OF NORTHERN STREAM ENERGY, WHICH AGAIN SHOWS AN
INTERMEDIATE TIMING IN THE ML GUIDANCE.
REGARDING THE EASTERN PACIFIC/WESTERN NORTH AMERICA PATTERN TOWARD
NEXT TUESDAY-WEDNESDAY, THE MAJORITY OF DYANMICAL MODELS AND
ENSEMBLE MEANS HAVE RECENTLY TRENDED TOWARD THE IDEA OF FAIRLY
RAPID CLOSED LOW FORMATION OVER THE EAST-CENTRAL PACIFIC, WHILE BY
NEXT WEDNESDAY THERE WOULD BE SOME UPPER RIDGING ALONG/OFFSHORE THE
WEST COAST WITH FLAT OR NORTHWESTERLY MEAN FLOW OVER THE
NORTHWESTERN U.S. AS PART OF BROADER ZONAL TO CYCLONIC FLOW PATTERN
OVER AT LEAST THE NORTHERN HALF OF THE LOWER 48 AND SOUTHERN
CANADA. ML MODELS AND THE ECMWF AIFS MEAN SUGGEST THE UPPER RIDGE
AXIS COULD BE A BIT FARTHER OFFSHORE THE WEST COAST, WITH TYPICAL
SPREAD FOR HOW LOWER 48 SHORTWAVE ENERGY MAY LOOK. ASIDE FROM THESE
DETAILS, THE DYNAMICAL/ML MAJORITY OFFERS A COMPARABLE THEME
OVERALL AND IS PREFERRED BY THE LATTER PART OF THE FORECAST. IN
CONTRAST, LATEST ECMWF RUNS SHOW LESS FLOW SEPARATION OVER THE EAST
PACIFIC AND THUS MAINTAIN MORE RIDGING OR SOUTHWESTERLY FLOW OVER
THE WEST. REGARDLESS OF HOW AGREEABLE THE MAJORITY CLUSTER MAY BE
AT THE MOMENT, THESE FLOW SEPARATION CASES CAN STILL PRODUCE
SIGNIFICANT VARIABILITY DURING THE EXTENDED RANGE.
THE FIRST HALF OF THE UPDATED FORECAST INCORPORATED A COMPOSITE OF
00Z DYNAMICAL MODELS, GIVEN LESS FAVORABLE COMPARISONS FOR THE
SOUTHWEST UPPER LOW IN THE 06Z GFS. BY NEXT TUESDAY-WEDNESDAY THE
BLEND INCREASED 06Z GEFS/00Z ECENS INPUT (REACHING HALF TOTAL
WEIGHT BY WEDNESDAY) WHILE REDUCING ECMWF INFLUENCE AS IT STRAYED
FROM THE MAJORITY FOR THE OVERALL PACIFIC/NORTH AMERICA PATTERN.
..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. THE UPPER LOW
THAT STALLS DURING SATURDAY WILL PROVIDE STRONG FORCING AND LEAD TO
SLOW MOVEMENT OF RAIN AND STORMS. MOST MODELS SHOW 4-6 INCHES OF
RAIN CENTERED AROUND NORTHEAST NEW MEXICO, EXCEEDING THE 5-10 YEAR
ARI IF NOT HIGHER. ECENS/CMCENS PROBABILITIES ALSO HIGHLIGHT THIS
EXACT AREA, WHILE THE GFS/GEFS HAVE BEEN SKEWED A LITTLE NORTH-
NORTHEAST AND THE 12Z UKMET SHIFTS THE UPPER LOW AND RAINFALL AXIS
A BIT EAST. THE DAY 4/SATURDAY ERO MAINTAINS CONTINUITY FOR THE
SLIGHT RISK AREA DEPICTED OVER NORTHEASTERN NEW MEXICO AND VICINITY
IN ACCORDANCE WITH THE MAJORITY GUIDANCE CLUSTER, WHILE THE
SURROUNDING MARGINAL RISK AREA ACCOUNTS FOR CURRENT GUIDANCE
SPREAD/LOWER PROBABILITY SOLUTIONS. SENSITIVE BURN SCAR AREAS
WILL BE PARTICULARLY VULNERABLE DURING THIS POTENTIAL HEAVY RAIN
EVENT. BY SUNDAY THE UPPER LOW SHOULD START MOVING NORTHEASTWARD,
SPREADING MODERATE TO HEAVY RAIN WITH IT. THIS ACTIVITY WILL LIKELY
FOCUS OVER THE TEXAS/OKLAHOMA PANHANDLES INTO THE WESTERN HALF OF
KANSAS. GIVEN THE MOISTURE/INSTABILITY AND FORCING IN PLACE, HEAVY
RAIN MAY CAUSE ISOLATED FLOODING THREATS ESPECIALLY IF AREAS OF
HIGH RAIN RATES TRAIN IN THE SAME LOCATIONS. THE DAY 5/SUNDAY
MAINTAINS A MARGINAL RISK AREA DUE TO THESE FLOODING CONCERNS.
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, BUT THESE AREAS ARE
NOT TYPICALLY SENSITIVE TO FLOODING FROM THE EXPECTED 2-4 INCHES OF
RAIN AND IN PARTICULAR WITH THE LOW STREAM FLOWS OBSERVED AT THIS
EARLY POINT IN THE SEASON. WITH TIME, EXPECT UPSTREAM SHORTWAVE
ENERGY TO EXPAND THE PRECIPITATION SHIELD SOUTHWARD AND EASTWARD
BUT WITH GRADUALLY LESSER MAX AMOUNTS. THERE IS STILL UNCERTAINTY
ABOUT SPECIFICS OF EASTERN PACIFIC/WEST COAST FLOW ALOFT BY NEXT
TUESDAY-WEDNESDAY, BUT MOST GUIDANCE CURRENTLY SUGGESTS THAT THE
NORTHWEST WILL SEE A DRIER TREND BY THEN.
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 PROMOTE 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 AND TO
SOME EXTENT INTO MONDAY AS HIGHS REACH THE 70S. FORECAST
TRANSITION OF THE UPPER PATTERN TOWARD BROADLY CYCLONIC OR NEARLY
ZONAL MEAN FLOW WOULD MODERATE TEMPERATURES OVER THE NORTHERN
PLAINS AND VICINITY BY MIDWEEK, WHILE A SUBTROPICAL UPPER HIGH
ACROSS THE GULF/NORTHERN MEXICO/TEXAS WILL ALLOW FOR WARMER
TEMPERATURES TO EXPAND ACROSS THE THE SOUTHERN PLAINS INTO
SOUTHEAST.
RAUSCH/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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