458
FXUS02 KWBC 020715
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
315 AM EDT SAT NOV 2 2024
VALID 12Z TUE NOV 05 2024 - 12Z SAT NOV 09 2024
..OVERVIEW
THE MAJORITY OF GUIDANCE SHOWS STRONG UPPER RIDGING OVER PARTS OF
THE SOUTHEASTERN U.S. AND WESTERN ATLANTIC WHILE STRONGLY DIGGING
WESTERN U.S. TROUGH ENERGY LIKELY CLOSES OFF A LOW THAT DRIFTS OVER
THE FOUR CORNERS BEFORE EMERGING INTO THE PLAINS BY LATE WEEK OR
EARLY WEEKEND. THE UPPER LOW SHOULD PRODUCE AN AREA OF POTENTIALLY
SIGNIFICANT SNOWFALL OVER PARTS OF THE ROCKIES AROUND MIDWEEK AND
THEN SPREAD RAIN OVER THE PLAINS LATER IN THE WEEK. TO THE SOUTH OF
THE UPPER RIDGE, GUIDANCE CONTINUES TO SHOW POSSIBLE CARIBBEAN INTO
GULF OF MEXICO TROPICAL DEVELOPMENT (BEING MONITORED BY THE
NATIONAL HURRICANE CENTER) WITH A LOT OF GUIDANCE SPREAD FOR WHERE
THE SURFACE SYSTEM ITSELF MAY TRACK, AS WELL AS FOR THE PATH OF
MOISTURE TO ITS NORTH/EAST. A WAVY FRONT PUSHING INTO THE
MISSISSIPPI VALLEY BY TUESDAY MAY PRODUCE SOME ENHANCED RAINFALL
OVER THAT REGION. NORTHERN STREAM FLOW WILL SEE MODERATE
PROGRESSION, WITH A RIDGE BUILDING INTO WESTERN CANADA AND MEAN
TROUGHING SETTING UP FARTHER EAST. A PACIFIC TROUGH MAY APPROACH
THE NORTHWEST BY NEXT SATURDAY.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THIS FORECAST UPDATE INCORPORATED AN AVERAGE AMONG THE 12Z/18Z GFS
AND 12Z ECMWF/UKMET FOR THE FIRST HALF OF THE PERIOD, FOLLOWED BY
SOME INCLUSION OF THE 18Z GEFS/12Z ECENS MEANS ALONG WITH CONTINUED
INPUT OF THE 12Z ECMWF AND EVENTUAL TRANSITION OF GFS INPUT TO ONLY
THE 12Z RUN.
THE LARGEST SCALE CONSIDERATION THIS CYCLE WAS TO DISCOUNT THE 12Z
CMC/CMCENS WHICH WERE NOTABLY FASTER AND MORE OPEN WITH THE EARLY-
PERIOD WESTERN UPPER TROUGH, PLUS QUITE PROGRESSIVE TO LIFT THE
POSSIBLE CARIBBEAN/GULF SYSTEM INTO THE EAST. WHILE SIGNALS ARE
SOMEWHAT MORE MIXED FOR THE TROPICAL FEATURE, OTHER DYNAMICAL
GUIDANCE PLUS ALL OF THE 12Z MACHINE LEARNING (ML) MODELS FAVOR
SOME VARIATION OF THE FOUR CORNERS UPPER LOW. HOWEVER THE ML MODELS
OVER THE PAST COUPLE DAYS HAVE BEEN UP TO A FEW DEGREES OF
LONGITUDE EASTWARD WITH THE UPPER LOW POSITION. THE NEW 00Z CMC HAS
IMPROVED CONSIDERABLY IN TERMS OF ADJUSTING TOWARD THE CONSENSUS
FOR THE FOUR CORNERS LOW. BY SATURDAY THE 18Z/00Z GFS RUNS STRAY
FARTHER NORTH/NORTHEAST OF MOST OTHER GUIDANCE INCLUDING THE ML
MODELS, FAVORING THE AFOREMENTIONED SWITCH TO JUST THE 12Z RUN FOR
THAT COMPONENT OF THE BLEND. UPSTREAM, THERE ARE TYPICAL
DETAIL/TIMING DIFFERENCES FOR THE PACIFIC TROUGH APPROACHING THE
NORTHWEST BY SATURDAY BUT DECENT CLUSTERING OVERALL FOR A DAY 7
FORECAST. ML MODELS SHOW SIMILAR IDEAS TO THE DYNAMICAL GUIDANCE.
MEANWHILE, MODELS ARE STRUGGLING TO RESOLVE THE COMBINATION OF
POSSIBLE CARIBBEAN/GULF OF MEXICO DEVELOPMENT AS WELL AS DETAILS OF
UPPER RIDGING WHOSE EVOLUTION WILL DETERMINE HOW MUCH
MOISTURE/SHORTWAVE ENERGY COULD REACH THE SOUTHEAST/FLORIDA. THE
12Z ECMWF SHOWED HOW THESE TWO COULD BE SEPARATE CONSIDERATIONS,
AND LATEST GUIDANCE STILL SHOWS A LOT OF SPREAD. ECMWF AIFS RUNS
CONTINUE TO LEAN ON THE NORTHERN/NORTHEASTERN SIDE OF THE ML SPREAD
OVER THE GULF, WHILE A COUPLE ML MODELS SUGGEST A STRONGER DRYING
INFLUENCE OF UPPER RIDGING ALONG AND JUST INLAND FROM THE SOUTHEAST
COAST (CLOSEST TO THE UKMET) VERSUS SOME OTHER GUIDANCE. THE MANUAL
FORECAST STAYS VERY CLOSE TO CONTINUITY IN REFLECTING YESTERDAY'S
WPC/NHC COORDINATED DEPICTION OF THE POSSIBLE TROPICAL SYSTEM AND
EXTRAPOLATION INTO THE NEW DAY 7.
..WEATHER/HAZARDS HIGHLIGHTS
A SLOW WAVY FRONT SHOULD APPROACH/REACH THE MISSISSIPPI VALLEY AND
WESTERN GULF COAST BY TUESDAY-TUESDAY NIGHT, WITH CONTINUED
POTENTIAL FOR SOME TRAINING OF MODERATE TO HEAVY RAINFALL BUT
LIKELY TO A LESS PRONOUNCED DEGREE THAN EXPECTED JUST TO THE WEST
IN THE SHORT RANGE. THE DAY 4 EXCESSIVE RAINFALL OUTLOOK MAINTAINS
A MARGINAL RISK AREA FROM THE LOWER OHIO VALLEY SOUTHWESTWARD, NOW
EXTENDING TO THE NORTHERN HALF OF THE TEXAS COAST. THERE HAS BEEN
SOME IMPROVEMENT FOR GUIDANCE CLUSTERING REGARDING WHERE THE
RELATIVE MAXIMUM OF RAINFALL SHOULD BE WITHIN THIS REGION (ALONG
AND JUST EAST OF AN AREA FROM EASTERN ARKANSAS INTO FAR SOUTHERN
ILLINOIS). HOWEVER GROUND CONDITIONS ARE GENERALLY NEUTRAL TO DRY
AND THE GFS/ECMWF DO NOT SUGGEST TOO MUCH INSTABILITY REACHING THAT
FAR NORTH. THUS FOR NOW WILL MAINTAIN JUST THE MARGINAL RISK AREA
WHILE MONITORING FOR SIGNALS OF ANY HEAVIER BANDS THAT COULD FAVOR
AN UPGRADE.
ESPECIALLY BY WEDNESDAY, GUIDANCE DIVERGES CONSIDERABLY REGARDING
THE DETAILS OF ANOMALOUS MOISTURE/HEAVIER RAINFALL THAT MAY
OVERSPREAD PARTS OF THE SOUTHEAST/FLORIDA TO THE NORTH OF THE
POSSIBLE CARIBBEAN INTO GULF TROPICAL DEVELOPMENT. THIS WILL DEPEND
ON FINER SCALE DETAILS OF UPPER RIDGING WHOSE WESTERN SIDE WILL
DETERMINE HOW MUCH MOISTURE/SHORTWAVE ENERGY MAY LIFT NORTHWARD. THE
MOST COMMON THEME IS FOR SIGNIFICANT PRECIPITABLE WATER ANOMALIES
TO REACH PORTIONS OF THE FLORIDA PENINSULA AT THE VERY LEAST, SO
THE DAY 5 ERO STARTS OUT WITH A MARGINAL RISK AREA OVER THE
SOUTHERN TWO-THIRDS OF FLORIDA. OTHER PARTS OF THE SOUTHEAST MAY
ULTIMATELY BE INCLUDED DEPENDING ON GUIDANCE TRENDS. GUIDANCE
SPREAD FOR WHAT HAPPENS WITH THIS MOISTURE AND THE POSSIBLE GULF
FEATURE AFTER THURSDAY IS STILL VERY WIDE, KEEPING CONFIDENCE LOW.
UPPER TROUGH DYNAMICS LIKELY CLOSING OFF AN UPPER LOW AROUND THE
FOUR CORNERS SHOULD PUSH AN AREA OF MOUNTAIN SNOW SOUTHWARD
THROUGH THE ROCKIES, WITH HIGHEST TOTALS LIKELY TO BE OVER SOUTHERN
COLORADO/NORTHERN NEW MEXICO BASED ON THE CURRENT FORECAST PATH OF
THE UPPER LOW. SOME SNOW COULD EXTEND INTO PARTS OF THE HIGH
PLAINS. EXPECT RAINFALL OVER THE PLAINS TO INCREASE IN COVERAGE AND
INTENSITY AFTER MIDWEEK AS THE FOUR CORNERS UPPER LOW BEGINS TO
DRIFT EASTWARD. THERE IS STILL UNCERTAINTY FOR THE DETAILS, BUT
GRADUALLY INCREASING CONFIDENCE IN SOME AREAS OF HEAVIER RAINFALL.
A LARGE PORTION OF THE EASTERN U.S. WILL SEE WELL ABOVE NORMAL
TEMPERATURES, ESPECIALLY FROM TUESDAY INTO THURSDAY MORNING WHEN
SOME AREAS WILL SEE PLUS 20F OR GREATER ANOMALIES (MORE FOR MORNING
LOWS VERSUS DAYTIME HIGHS) ALONG WITH POTENTIAL FOR DAILY RECORDS
FOR HIGHS/WARM LOWS. FRONTAL PROGRESSION WILL TEMPER THE MOST
EXTREME ANOMALIES BUT PERSISTENT SOUTHEAST UPPER RIDGING SHOULD
KEEP THE SOUTHERN TWO-THIRDS OF THE EAST ABOVE NORMAL THROUGH
FRIDAY-SATURDAY. IN CONTRAST, THE UPPER TROUGH/LOW LIKELY AFFECTING
THE WEST/ROCKIES FOR MULTIPLE DAYS SHOULD PRODUCE CHILLY
TEMPERATURES FOR MOST OF NEXT WEEK WITH HIGHS OF 10-20F BELOW
NORMAL MOST COMMON WEDNESDAY-FRIDAY.
RAUSCH
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.PHPSCHICHTEL/HAMRICK
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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page