865
FXUS02 KWBC 171858
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
258 PM EDT THU OCT 17 2024
VALID 12Z SUN OCT 20 2024 - 12Z THU OCT 24 2024
..OVERVIEW
A CLOSED UPPER LOW ATOP THE FOUR CORNERS INTO SUNDAY COULD LEAD TO
LINGERING SNOW IN THE SOUTH-CENTRAL ROCKIES AND COOL TEMPERATURES,
WHILE MODERATE TO LOCALLY HEAVY RAIN AND SOME ISOLATED FLOODING
CONCERNS SPREAD INTO THE SOUTH-CENTRAL PLAINS. EXPECT THE UPPER
LOW TO TRACK NORTHEAST AND WEAKEN WITH TIME, PRODUCING SOME
LIGHTER RAIN. MEANWHILE, PRECIPITATION IS LIKELY IN THE PACIFIC
NORTHWEST EARLY NEXT WEEK WITH THE TAIL END OF AN ATMOSPHERIC
RIVER. BY MIDWEEK AND BEYOND, BROADLY CYCLONIC FLOW SHOULD SET UP
ACROSS THE EASTERN TWO-THIRDS OF THE CONUS WHILE UPPER RIDGING MAY
FORM OVER OR NEAR THE WEST AS SPLITTING TROUGH ENERGY YIELDS A
TROUGH/CLOSED LOW OVER THE EASTERN PACIFIC. ADDITIONALLY, RIDGING
THAT RETROGRADES FROM THE GULF OF MEXICO THROUGH SOUTHERN TEXAS
AND MEXICO WILL SPREAD WARMER THAN AVERAGE TEMPERATURES TO THE
SOUTHERN STATES, WHILE COLD FRONTS WILL GRADUALLY COOL THE
NORTHERN TIER AFTER THAT REGION SEES VERY WARM TEMPERATURES EARLY
IN THE WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
PRIMARY GUIDANCE ISSUES CONTINUE TO REVOLVE AROUND PERSISTENT MINOR
TIMING AND DETAIL DIFFERENCES FOR THE UPPER LOW EJECTING FROM THE
FOUR CORNERS REGION AND THEN PATTERN IMPLICATIONS OF THE FORECAST
SEPARATION OF FLOW WITHIN AN ELONGATED CANADA INTO EASTERN PACIFIC
UPPER TROUGH AS OF EARLY NEXT WEEK.
FOR THE FOUR CORNERS UPPER LOW, GFS TRENDS OVER THE PAST DAY HAVE
BROUGHT ITS PREVIOUS FAST SOLUTION MORE INTO LINE WITH RECENT
CONSENSUS BUT THERE IS STILL A LITTLE WAFFLING AMONG OTHER
SOLUTIONS. OF PARTICULAR NOTE, THE 12Z CMC IS A BIT ON THE SLOWER
SIDE OF THE SPREAD (WITH THAT MODEL TENDING TO BE SLOW IN RECENT
DAYS) WHILE THE NEW 12Z ECMWF HAS ALSO TRENDED SLOWER OVER THE FOUR
CORNERS AND THEN WEAKER/SOUTHWARD OVER THE PLAINS/MIDWEST (BUT
CLOSER TO THE GUIDANCE AVERAGE AT THAT POINT). THEN THIS FEATURE
SHOULD OPEN UP/SHEAR OUT AS STRONGER NORTHERN STREAM ENERGY
APPROACHES.
GUIDANCE CONTINUES TO SHOW SPLITTING OF EARLY-WEEK ELONGATED
CANADA/EASTERN PACIFIC TROUGH ENERGY, WITH SUCH FLOW SEPARATION
CASES FREQUENTLY LOWERING PREDICTABILITY AS EVIDENCED BY SOMETIMES
SIGNIFICANT MULTI-RUN GUIDANCE SPREAD AND VARIABILITY FOR THE
DOWNSTREAM PATTERN. THE MOST AGREEABLE ASPECT OF THIS EVOLUTION IS
TUESDAY-WEDNESDAY CLOSED LOW FORMATION OVER THE PACIFIC AROUND
135-145W LONGITUDE AND PROGRESSIVE CANADA/NORTHERN TIER U.S.
SHORTWAVE ENERGY REACHING EASTERN NORTH AMERICA BY THURSDAY
(SUPPORING A LEADING COLD FRONT). THE MORE CONTENTIOUS PART OF THE
FORECAST INVOLVES LOCATION/STRENGTH OF UPPER RIDGING THAT MAY SET
UP OVER THE WESTERN U.S. OR JUST OFFSHORE THE WEST COAST, AND
DETAILS OF SMALLER SCALE ENERGY THAT COULD BE LEFT BEHIND
OVER/OFFSHORE OF THE PACIFIC NORTHWEST AND SOUTHWESTERN CANADA.
LATEST DYNAMICAL MODEL RUNS HAVE BEEN LEANING TOWARD A STRONGER
UPPER RIDGE OVER THE WEST, IN CONTRAST TO SOME ECMWF/CMC ENSEMBLE
MEMBERS THAT ACTUALLY DEPICT SOME TROUGH/UPPER LOW POTENTIAL. THOSE
MEMBERS LEAD TO FLATTER FLOW OVER THE WEST IN THE RESULTING
ECENS/CMCENS MEANS. MEANWHILE THE 00Z/06Z MACHINE LEARNING MODELS
AND 00Z AIFS MEAN DEPICT UPPER RIDGING BUT ON AVERAGE WITH AN AXIS
FARTHER WEST THAN THE DYNAMICAL MODEL CLUSTER. COMPARED TO THE FULL
GUIDANCE ENVELOPE, THE NEW 12Z GFS IS FAIRLY EXTREME WITH THE
AMPLITUDE AND EASTWARD POSITION OF ITS UPPER RIDGE, AS WELL AS THE
EASTWARD POSITION OF THE PACIFIC UPPER LOW/TROUGH. THE 06Z GFS
COMPARED BETTER TO OTHER GUIDANCE.
BASED ON COMPARISONS OF 00Z/06Z MODELS AND MEANS, THE UPDATED
FORECAST INCORPORATED AN EVEN COMPROMISE OF OPERATIONAL RUNS EARLY
IN THE PERIOD AND TRANSITIONED TO AN EVEN BLEND OF 06Z GFS/00Z
ECMWF AND 00Z GEFS/ECENS MEANS TO REFLECT THE MOST COMMON IDEAS OF
GUIDANCE.
..WEATHER/HAZARDS HIGHLIGHTS
THE FOUR CORNERS UPPER LOW WILL PROVIDE FORCING FOR PRECIPITATION
ACROSS SOUTH-CENTRAL PARTS OF THE ROCKIES AND PLAINS INTO SUNDAY.
SNOW COULD LINGER IN THE HIGHER ELEVATIONS OF COLORADO IN
PARTICULAR, THOUGH LIKELY DECREASING IN MAGNITUDE COMPARED TO LATE
THIS WEEK. AHEAD OF THE UPPER LOW, MOISTURE STREAMING IN FROM THE
PACIFIC AND THE GULF WILL PROVIDE AN ENVIRONMENT WITH PWS ABOVE THE
90TH IF NOT 95TH PERCENTILE FOR POTENTIALLY HEAVY RAIN AND STORMS
ACROSS THE SOUTH-CENTRAL PLAINS. THE DAY 4 EXCESSIVE RAINFALL
OUTLOOK MAINTAINS A MARGINAL RISK AREA CENTERED OVER THE TEXAS AND
OKLAHOMA PANHANDLES INTO THE WESTERN HALF OF KANSAS, PLUS PARTS OF
NORTHEASTERN NEW MEXICO/FAR SOUTHEASTERN COLORADO AS HEAVY RAIN
MAY CAUSE ISOLATED FLOODING THREATS ESPECIALLY IF AREAS OF HIGH
RAIN RATES TRAIN IN THE SAME LOCATIONS. SOME SHOWERS WILL SHIFT
INTO THE CENTRAL PLAINS/MIDDLE MISSISSIPPI VALLEY BY MONDAY AND
PERHAPS THE OHIO VALLEY TUESDAY, THOUGH WITH DECREASING INTENSITY.
MEANWHILE, THE PACIFIC NORTHWEST WILL LIKELY SEE PRECIPITATION ON
SUNDAY AS AN ATMOSPHERIC RIVER CONTINUES TO SPREAD MOISTURE INTO
THE REGION, WITH GENERALLY LIGHT TO MODERATE RAIN AND SNOW
AMOUNTS (LESSER TOTALS THAN OVER THE OLYMPICS IN THE SHORT RANGE).
SOME PRECIPITATION MAY LINGER INTO MONDAY AND SPREAD FARTHER
INLAND BUT WITH A CONTINUED TREND TOWARD LIGHTER AMOUNTS. GUSTY
WINDS ARE POSSIBLE IN THE ROCKIES AS FRONTS PUSH THROUGH. THERE IS
STILL UNCERTAINTY ABOUT SPECIFICS OF EASTERN PACIFIC/WESTERN U.S.
FLOW ALOFT BY TUESDAY-THURSDAY, BUT MOST GUIDANCE CURRENTLY
SUGGESTS THAT MOST OF THE WEST SHOULD BE DRY WITH UPPER RIDGING
SETTING UP. THE FAST SIDE OF THE SPREAD FOR AN EASTERN PACIFIC
UPPER TROUGH/LOW WOULD LEAD TO SOME MOISTURE REACHING THE WEST
COAST BY NEXT THURSDAY OR THURSDAY NIGHT BUT THAT SCENARIO IS
SOMEWHAT IN THE MINORITY AT THE MOMENT.
MOST OF THE EASTERN U.S. SHOULD REMAIN DRY THROUGH MUCH OF THE
PERIOD. EASTERLY FLOW ACROSS THE FLORIDA PENINSULA COULD BRING
SOME LIGHT SHOWERS ONSHORE. BY TUESDAY-WEDNESDAY, LIGHT RAIN MAY
PUSH ACROSS THE NORTH-CENTRAL TO NORTHEASTERN U.S. WITH A FRONT.
COOLER THAN AVERAGE TEMPERATURES BY 5-15 DEGREES SHOULD CONTINUE
INTO SUNDAY IN THE FOUR CORNERS STATES UNDERNEATH THE UPPER LOW,
BUT GRADUALLY TREND WARMER THEREAFTER. OVERALL A MAJORITY OF THE
WEST SHOULD TREND TOWARD NEAR/ABOVE NORMAL TEMPERATURES BY MIDWEEK,
THOUGH WITH SOME UNCERTAINTY IN LIGHT OF GUIDANCE DIFFERENCES FOR
THE STRENGTH AND LOCATION OF UPPER RIDGING. MEANWHILE, ANOTHER
UPPER RIDGE INITIALLY OVER THE EAST-CENTRAL U.S. AND THEN DRIFTING
EASTWARD WILL PROMOTE WELL 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 MONDAY AS HIGHS REACH THE 70S. FORECAST
TRANSITION OF THE UPPER PATTERN TOWARD BROADLY CYCLONIC OR NEARLY
ZONAL MEAN FLOW ALONG WITH A SURFACE COLD FRONT WOULD MODERATE
TEMPERATURES OVER THE NORTHERN PLAINS AND VICINITY BY MIDWEEK AND
INTO THE GREAT LAKES/OHIO VALLEY/NORTHEAST BY NEXT THURSDAY. A
SUBTROPICAL UPPER HIGH REMAINING ACROSS THE GULF/NORTHERN
MEXICO/TEXAS INTO WEDNESDAY WILL ALLOW FOR WARMER TEMPERATURES TO
EXPAND ACROSS THE THE SOUTHERN PLAINS INTO SOUTHEAST.
RAUSCH/CAMPBELL/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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