603
FXUS02 KWBC 070655
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
154 AM EST THU DEC 07 2023
VALID 12Z SUN DEC 10 2023 - 12Z THU DEC 14 2023
..PATTERN OVERVIEW
BROAD CYCLONIC MEAN FLOW ALOFT IS FORECAST ACROSS THE EASTERN
TWO-THIRDS OF THE LOWER 48 THROUGH MID-NEXT WEEK, THEN THE UPPER
TROUGH WILL GRADUALLY SHIFT OFFSHORE. A VIGOROUS SHORTWAVE MOVING
FROM THE SOUTHERN PLAINS TO THE NORTHEAST OVER THE WEEKEND WILL
SUPPORT A STRONG SURFACE LOW PRESSURE SYSTEM THAT WILL BRING
SIGNIFICANT PRECIPITATION FROM THE GULF COAST TO THE GREAT LAKES
AND NORTHEAST. ON MONDAY, THE EASTERN SYSTEM WILL PUSH OFFSHORE,
AND AN AMPLIFYING PACIFIC RIDGE WILL REINFORCE THE MEAN TROUGH
OVER THE EAST BUT GIVE IT A POSITIVE TILT. A FEW RELATIVELY WEAKER
FRONTAL SYSTEMS WILL SWING ACROSS THE CENTRAL AND EASTERN U.S.
NEXT WEEK, AND MODELS ARE STARTING TO AGREE ON AN UPPER LOW
FORMING OVER THE SOUTHWEST WEDNESDAY AND THURSDAY.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
MODELS ARE IN FAIRLY GOOD AGREEMENT ON THE GENERAL UPPER LEVEL
PATTERN, BUT THERE IS STILL SOME UNCERTAINTY SURROUNDING THE
SYSTEM THAT WILL IMPACT THE EASTERN U.S. THIS WEEKEND. LATEST
MODEL GUIDANCE HAS BEEN SHOWING A LEADING LOW PRESSURE CENTER
TRACKING FROM THE SOUTHERN PLAINS TO THE GREAT LAKES AND A SECOND
WAVE OF LOW PRESSURE FORMING IN THE VICINITY OF THE MID-SOUTH AND
TRACKING ACROSS THE NORTHEAST. EVEN WITH CHANGES IN HOW MODELS ARE
DEPICTING THE STRUCTURE OF THIS SYSTEM, THERE IS STILL A CONSENSUS
THAT THERE WILL BE WIDESPREAD MODERATE TO HEAVY RAINFALL IN THE
EAST. THROUGH THE REST OF THE PERIOD, THERE ARE SOME EXPECTED
DIFFERENCES IN TIMING OF SHORTWAVES, WHICH WILL AFFECT TIMING OF
SURFACE FEATURES. MODEL AGREEMENT HAS BEEN INCREASING OVERNIGHT TO
SHOW A CLOSED UPPER LOW FORMING OVER THE SOUTHWEST AROUND
WEDNESDAY, WHICH MAY HELP ENHANCE PRECIPITATION MID-TO-LATE NEXT
WEEK.
FOR THIS FORECAST PACKAGE, THE DAY 3-4 WPC MODEL BLEND IS
COMPRISED OF DETERMINISTIC MODEL SOLUTIONS WITH MORE WEIGHT ON THE
ECMWF/GFS THAN THE UKMET/CMC. THE CMC CONTINUES TO STRAY THE
FARTHEST FROM THE CONSENSUS, SO IT HAS THE LEAST WEIGHT IN THE
BLEND. FROM DAY 5 ONWARD, ENSEMBLE MEANS WERE ADDED IN INCREASING
AMOUNTS TO HELP SMOOTH DIFFERENCES BETWEEN THE DETERMINISTIC RUNS.
..WEATHER/HAZARDS HIGHLIGHTS
PRECIPITATION WILL BE WINDING DOWN IN THE PACIFIC NORTHWEST ON
SUNDAY, AND PRECIPITATION TOTALS ARE NOT EXPECTED TO BE HIGH
ENOUGH TO BE HAZARDOUS. THE CMC CONTINUES TO SHOW HIGHER
PRECIPITATION AMOUNTS THAN THE OTHER GUIDANCE, AND IF THIS
SOLUTION COMES TO FRUITION, THERE COULD BE ISOLATED FLOODING IN
WESTERN OREGON AND WASHINGTON. FOR NOW, NO RISK AREA WAS ADDED TO
THE PACIFIC NORTHWEST IN THE DAY 4 EXCESSIVE RAINFALL OUTLOOK, BUT
WE WILL CONTINUE TO MONITOR MODEL TRENDS AS NEW GUIDANCE BECOMES
AVAILABLE.
IN THE EAST, A BROAD AREA OF SIGNIFICANT PRECIPITATION WILL
STRETCH FROM THE FLORIDA PANHANDLE THROUGH THE MID-ATLANTIC TO THE
NORTHEAST ON SUNDAY AS A STRONG FRONTAL SYSTEM PASSES THROUGH. A
MARGINAL RISK OF EXCESSIVE RAINFALL WAS MAINTAINED FOR THIS AREA
IN THE DAY 4 OUTLOOK. THE PROGRESSIVE NATURE OF THIS SYSTEM WILL
HELP TO LIMIT RAINFALL TOTALS. HOWEVER, ANOMALOUS MOISTURE AND
SUFFICIENT INSTABILITY SHOULD STILL SUPPORT RAIN RATES HIGH ENOUGH
TO PRODUCE SOME FLOODING CONCERNS, AND THERE MAY ALSO BE
THUNDERSTORM POTENTIAL IN THE WARM SECTOR OVER THE SOUTHEAST.
MIXED PRECIPITATION AND SNOW ARE FORECAST ON THE NORTHWESTERN SIDE
OF THE SYSTEM, WHICH WILL LIKELY IMPACT HIGHER ELEVATIONS OF THE
APPALACHIANS AND INTERIOR NORTHEAST. IN ADDITION TO POTENTIAL
PRECIPITATION HAZARDS, ELEVATED WINDS ARE FORECAST ALONG THE EAST
COAST.
THE FORECAST TRENDS DRIER FOR MOST OF THE NATION THROUGH THE REST
OF THE MEDIUM RANGE PERIOD, BUT A LINGERING FRONTAL BOUNDARY WILL
LIKELY ENHANCE PRECIPITATION CHANCES IN FLORIDA AND PARTS OF THE
SOUTHERN PLAINS AND SOUTHWEST. LIGHT PRECIPITATION WILL ALSO
RETURN TO THE PACIFIC NORTHWEST AS A PACIFIC FRONTAL SYSTEM
APPROACHES MID-NEXT WEEK.
IN TERMS OF TEMPERATURES, THE FORECAST CALLS FOR WELL ABOVE
AVERAGE TEMPERATURES IN THE WARM SECTOR OF THE EASTERN FRONTAL
SYSTEM SUNDAY AND MONDAY. HIGH TEMPERATURES WILL BE 10-20 DEGREES
ABOVE NORMAL FROM SOUTH CAROLINA TO THE NORTHEAST. HIGHS IN A FEW
LOCATIONS IN THE MID-ATLANTIC MAY CHALLENGE DAILY RECORDS.
TEMPERATURES WILL HOVER NEAR FOR THE REST OF THE NATION THROUGH
TUESDAY, THEN ABOVE NORMAL TEMPERATURES MAY DEVELOP OVER THE
NORTHERN PLAINS AND UPPER MIDWEST AS A WARM FRONT LIFTS ACROSS THE
REGION.
DOLAN
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, EXCESSIVE RAINFALL OUTLOOK,
WINTER WEATHER OUTLOOK PROBABILITIES, HEAT INDICES AND KEY
MESSAGES ARE AT:
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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