045
FXUS02 KWBC 070736
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
236 AM EST TUE NOV 07 2023
VALID 12Z FRI NOV 10 2023 - 12Z TUE NOV 14 2023
..OVERVIEW
THE UPPER FLOW PATTERN ACROSS THE CONTIGUOUS U.S. LATE WEEK INTO
THE WEEKEND LOOKS TO BE PROGRESSIVE WITH MULTIPLE EMBEDDED
SHORTWAVES THAT WILL BE IMPACTFUL IN SPINNING UP LOW
PRESSURE/FRONTAL SYSTEMS. THE FIRST SYSTEM OF CONCERN IS A
POSITIVELY TILTED SHORTWAVE OVER THE NORTH-CENTRAL U.S. FRIDAY
COMBINING WITH CANADIAN FLOW TO PRODUCE TROUGHING ACROSS PARTS OF
THE CENTRAL AND EASTERN U.S. LATE WEEK. EASTWARD PROGRESSION OF
THE UPPER TROUGH AND AN ASSOCIATED WAVY FRONT WILL GRADUALLY
SUPPRESS AN AREA OF ABOVE AVERAGE TEMPERATURES ACROSS THE
SOUTHEAST LATE WEEK, WHILE SPREADING RAIN ACROSS THE SOUTHERN AND
EASTERN U.S. THAT COULD LINGER INTO EARLY NEXT WEEK. UPSTREAM, A
QUICKLY MOVING SHORTWAVE AND FRONTAL SYSTEM OR TWO COMING THROUGH
THE NORTHWEST SHOULD INCREASE RAIN/SNOW CHANCES THERE, FOLLOWED BY
A LARGER SCALE EASTERN PACIFIC UPPER TROUGH THAT MAY GENERATE
ADDITIONAL PRECIPITATION OVER THE PACIFIC NORTHWEST DURING THE
WEEKEND AND BEYOND. THIS EASTERN PACIFIC TROUGH WILL PROMOTE UPPER
RIDGING FARTHER EAST INTO THE NORTH-CENTRAL U.S. WITH WARMER
TEMPERATURES, AND OVERALL A MORE LONGWAVE-DOMINATED PATTERN INTO
NEXT WEEK.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
AT THE START OF THE PERIOD FRIDAY, THERE ARE SOME MODEL
DIFFERENCES REGARDING THE SOUTHEASTERN CANADA UPPER LOW AND A
POSITIVELY TILTED SHORTWAVE BACK INTO THE GREAT LAKES/MIDWEST, BUT
NOTHING THAT A MULTI-MODEL BLEND COULD NOT HANDLE. BUT MORE
DIFFICULT IS THE SHORTWAVE TROUGH COMING INTO THE NORTHWEST FRIDAY
AND TRACKING EAST THROUGH THE WEEKEND. WHILE A SMALL FEATURE, THE
TIMING DIFFERENCES IN THE SHORTWAVE CREATE COMPLICATIONS FOR THE
MODEL DIAGNOSTICS BECAUSE THE MODELS GO OUT OF PHASE WITH EACH
OTHER, MAKING IT DIFFICULT TO BLEND GUIDANCE. THE ECMWF AND EC
MEAN, AND MANY EC ENSEMBLE MEMBERS, ARE SLOWER WITH THE TROUGH
THAN THE REST OF THE GUIDANCE AND PRODUCE RIDGING AHEAD OF THE
FEATURE ON TOP OF WHERE OTHER MODELS HAVE THE FASTER TROUGH.
INTERESTINGLY, THE ECMWF MACHINE LEARNING MODELS ARE FASTER WITH
THE TROUGH, CLUSTERING BETTER WITH THE GFS SUITE. FOR THIS
FORECAST FOR THIS FEATURE, SINCE TOO MUCH BLENDING OF MODELS WAS
NOT A GOOD OPTION, LEANED HEAVILY TOWARD THE 18Z GFS AND GEFS MEAN
THAT SEEMED TO BE A GOOD MIDDLE GROUND POSITION BETWEEN THE SLOWER
EC RUNS AND THE FASTER CMC. THIS LED TO A FASTER TREND IN PUSHING
FRONTS THROUGH THE NORTHERN TIER COMPARED TO THE PREVIOUS
FORECAST, BUT THE TIMING OF THIS SHORTWAVE AND THE DOWNSTREAM
EFFECTS ACROSS THE NORTHEASTERN U.S. EARLY NEXT WEEK ARE STILL
UNCERTAIN, SO MORE CHANGES TO THE FORECAST MAY BE NECESSARY IN
FUTURE CYCLES. THE NEWER 00Z ECMWF TRENDED FASTER THAN ITS
PREVIOUS RUN WITH THIS SHORTWAVE THOUGH, BETTER CLUSTERED WITH THE
OTHER GUIDANCE, HOPEFULLY A GOOD SIGN.
FARTHER UPSTREAM, MODELS ARE INDICATING A SPLIT FLOW UPPER PATTERN
WHERE A SOUTHERN STREAM LOW SITS OVER NORTHERN MEXICO EARLY NEXT
WEEK, WHILE THE NORTHERN STREAM SHOWS RIDGING OVER THE
WEST-CENTRAL U.S. POSSIBLY SHIFTING EASTWARD WITH TIME. THIS IS IN
RESPONSE TO A STRONG TROUGH DIGGING OVER THE EASTERN PACIFIC THAT
MODELS AGREE SHOULD EXIST EARLY NEXT WEEK, BUT WITH CONSIDERABLE
DIFFERENCES IN THE AXIS OF THE TROUGH AND POSSIBLY AN EMBEDDED
UPPER LOW. THE 18Z AND NEWER 00Z GFS CUT OFF AN UPPER LOW OVER THE
PACIFIC WELL WEST OF THE CONUS (AROUND 140W), WHILE THE 12Z ECMWF
INDICATES A PHASED TROUGH PUSHING INTO THE WEST COAST BY TUESDAY
(AHEAD OF OTHER GUIDANCE AND ALMOST ALL ENSEMBLE MEMBERS). THE NEW
00Z ECMWF STAYED QUITE FAST IN BRINGING THE TROUGH EAST COMPARED
TO CONSENSUS, THOUGH A TAD SLOWER THAN THE 12Z RUN. THE EC
ENSEMBLE MEAN AND THE GEFS MEAN BOTH FOLLOW THEIR DETERMINISTIC
MODELS WITH THE EC MEAN FASTER AND THE GEFS MEAN SLOWER, BUT
NEITHER TO THE SAME EXTREME AS THE OPERATIONAL MODELS. THUS A
BLEND FAVORING THE GEFS AND EC MEAN (TO 75 PERCENT BY DAY 7)
SEEMED TO WORK BEST FOR THE LATTER PART OF THE FORECAST PERIOD.
..WEATHER/HAZARDS HIGHLIGHTS
MOISTURE OVERRUNNING THE COLD FRONT THAT IS LIKELY TO PUSH THROUGH
THE SOUTHEAST AND THEN STALL OVER THE NORTHERN GULF WILL LEAD TO
SOME RAIN ACROSS THE SOUTH-CENTRAL TO SOUTHEASTERN QUADRANT OF THE
U.S. FOR LATE WEEK INTO EARLY NEXT WEEK. THE HIGHEST RAINFALL
TOTALS ARE LIKELY TO BE OVER SOUTHERN TEXAS NEAR A MEANDERING
SURFACE LOW ALONG THE FRONT, WITH EASTERN PACIFIC AND GULF
MOISTURE COMBINING. ON FRIDAY, SOME INSTABILITY COULD BE IN PLACE
ESPECIALLY EARLY IN THE DAY BEFORE THE FRONT PUSHES THROUGH. THIS
COULD LEAD TO LOCALLY HEAVY RAINFALL RATES, BUT ARE LIKELY TO STAY
BELOW ANY FLASH FLOODING THRESHOLDS, SO IN CONJUNCTION WITH THE
REMOVAL OF THE DAY 3 MARGINAL RISK IN THE EXCESSIVE RAINFALL
OUTLOOK, REMOVED THE DAY 4/FRIDAY MARGINAL RISK AS WELL. BY
SATURDAY SINCE THE FRONT IS LIKELY TO HAVE PASSED, LACK OF
INSTABILITY SHOULD MEAN RAIN RATES WILL NOT BE TOO HIGH, SO NO
RISK AREA IS PLANNED FOR THE DAY 5/SATURDAY ERO EITHER. INTO NEXT
WEEK THOUGH, THERE MAY BE MORE SUPPORT FOR CONVECTION AS MID-UPPER
LEVEL ENERGY APPROACHES, SO THIS WILL CONTINUE TO BE MONITORED.
FARTHER NORTH, LAKE EFFECT PRECIPITATION IS LIKELY WITH TROUGHING
AND WESTERLY FLOW OVER THE GREAT LAKES, LIKELY MAXIMIZED FRIDAY.
ADDITIONAL UPPER-LEVEL ENERGY COULD SPREAD LIGHT PRECIPITATION TO
THE NORTHEAST EARLY NEXT WEEK. ROUNDS OF FRONTAL SYSTEMS AND
SHORTWAVES PUSHING THROUGH THE NORTHWEST WILL MAINTAIN
PRECIPITATION CHANCES ACROSS THE PACIFIC NORTHWEST AND THE
NORTHERN ROCKIES. MODERATE TO HEAVY AMOUNTS ARE LIKELY TO BE
DIRECTED INTO THE NORTHERN PARTS OF THE OLYMPICS AND CASCADES,
WITH LOWER ELEVATION RAIN AND HIGHER ELEVATION SNOW.
SOUTHEASTERN PORTIONS OF THE COUNTRY WILL REMAIN WARMER THAN
AVERAGE AHEAD OF THE FRONTAL BOUNDARY ON FRIDAY, WITH A CORRIDOR
OF LOWS THAT ARE 10-20F ABOVE NORMAL EXTENDING FROM THE LOWER
MISSISSIPPI VALLEY INTO THE SOUTHEAST TO THE MID-ATLANTIC FRIDAY
MORNING BEFORE THE COLD FRONT PASSES AND LIMITS ABOVE NORMAL HIGHS
TO THE SOUTHEAST/FLORIDA. THE FLORIDA PENINSULA SHOULD BE THE MAIN
AREA ABOVE AVERAGE BY SATURDAY, WITH HIGHS WELL INTO THE 80S
ACTUALLY CLOSE TO DAILY RECORD HIGHS. ELSEWHERE, TEMPERATURES
SHOULD BE NEAR AVERAGE TO COOLER THAN AVERAGE THROUGH LATE WEEK IN
THE POST-FRONTAL COOL HIGH PRESSURE. BUT AS UPPER RIDGING BUILDS
ACROSS THE NORTH-CENTRAL U.S. EARLY NEXT WEEK, ABOVE NORMAL
TEMPERATURES BY AROUND 10-15F WILL OVERSPREAD THE CENTRAL AND
NORTHERN PLAINS INTO THE MIDWEST. MEANWHILE BELOW NORMAL HIGHS
SHOULD LINGER IN THE SOUTH-CENTRAL U.S. WITH LOWER HEIGHTS
OVERHEAD AND CLOUDS AND RAIN POSSIBLE, AND INTERESTINGLY LEAD TO
SIMILAR HIGHS FROM TEXAS ALL THE WAY NORTH TO SOUTH DAKOTA OR SO
(IN THE UPPER 50S AND 60S). NEAR TO COOLER THAN NORMAL OVER THE
EASTERN SEABOARD THIS WEEKEND SHOULD GRADUALLY MODERATE THROUGH
THE EARLY PART OF NEXT WEEK.
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, 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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