541
FXUS02 KWBC 031901
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 PM EDT FRI NOV 03 2023
VALID 12Z MON NOV 06 2023 - 12Z FRI NOV 10 2023
..OVERVIEW WITH GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
A SYNOPTIC-SCALE SPLIT FLOW PATTERN IS FORECAST TO PREVAIL ACROSS
THE NORTH AMERICAN CONTINENT THROUGH THE MEDIUM-RANGE PERIOD. A
WEST-SOUTHWESTERLY FLOW ACROSS THE SOUTHWESTERN U.S. AND A
NORTHWESTERLY FLOW ACROSS CENTRAL CANADA WILL TEND TO CONVERGE
NEAR THE GREAT LAKES AND TEND TO CREATE A QUASI-ZONAL UPPER FLOW
PATTERN ACROSS THE CONTIGUOUS U.S. HOWEVER, THE MERGING OF THESE
TWO AIR STREAMS HAS RESULTED IN ISSUES ON EXACTLY WHERE THE STREAM
INTERACTION WILL OCCUR OVER THE MID-SECTION OF THE COUNTRY, WHERE
A PAIR OF LOW PRESSURE WAVES ARE FORECAST TO INTERACT MIDWEEK NEXT
WEEK. THERE HAS BEEN A GENERAL TREND FOR THE MODELS TO DEVELOP A
MORE CONSOLIDATED LOW PRESSURE WAVE FARTHER AND FARTHER TO THE
NORTH OVER THE CENTRAL PLAINS TOWARD MIDWEEK NEXT WEEK WHILE
ANOTHER LOW OVER THE NORTHERN PLAINS WILL TEND TO WEAKEN AND BE
ABSORBED BY THE SOUTHERN LOW. THIS GENERAL MODEL TREND HAS ALSO
RESULTED IN (1) A SLOWER SOUTHWARD PROGRESSION OF COLDER AIR DOWN
THE WESTERN U.S., (2) A MORE AMPLIFIED UPPER TROUGH FROM THE
EASTERN PACIFIC TO REACH THE SOUTHWESTERN U.S., AND (3) MORE
UNCERTAINTIES TO THE EVOLUTION OF THE FLOW PATTERN DOWNSTREAM LATE
NEXT WEEK, PARTICULARLY FROM THE MID-ATLANTIC NORTHWARD TO NEW
ENGLAND.
DESPITE THE NOTABLE MODEL ADJUSTMENTS DISCUSSED ABOVE, MODEL
SOLUTIONS HAVE BEEN VERY AGREEABLE WITH EACH OTHER IN THE LATEST
MODEL CYCLE. THE WPC FORECAST WAS BASED ON A BLEND OF THE LATEST
DETERMINISTIC AND ENSEMBLE MEANS FROM THE 06Z GFS/GEFS, 00Z
ECMWF/EC MEAN, AND THE 00Z CMC/CMC MEAN, TRANSITIONING TO MOSTLY A
BLEND OF THE ENSEMBLE MEANS BY DAY 7. THE 06Z GFS DOWNPLAYS THE
DEVELOPMENT OF THE LOW PRESSURE OVER THE OHIO VALLEY/GREAT LAKES
ON DAY 6, WHICH IS NOT SUPPORTED BY THE GEFS MEAN AS WELL THE
ECMWF AND CMC. THEREFORE, A HIGHER PERCENTAGE OF THE 06Z GEFS WAS
GIVEN TO THIS TIME FRAME.
..WEATHER/HAZARDS HIGHLIGHTS
THE WESTERN U.S. WILL SEE ACTIVE WEATHER INTO MONDAY WITH THE
POSSIBILITY OF A WEAK ATMOSPHERIC RIVER EVENT INTO THE PACIFIC
NORTHWEST. ONSHORE FLOW WILL CONTINUE INTO THE COASTAL RANGES AND
INTO THE CASCADES IN THE PACIFIC NORTHWEST, WITH SHORTWAVE ENERGY
PROVIDING UPPER-LEVEL DYNAMICAL SUPPORT AND SOME INSTABILITY FOR
SLIGHTLY ENHANCED RAINFALL RATES. LOCALLY HEAVIER RAINFALL ON THE
WEST FACING SLOPES MAY BE ENOUGH TO CAUSE SOME MINOR FLOODING
CONCERNS, PARTICULARLY FOR URBAN AREAS AND BURN SCARS, AND
ESPECIALLY AS RAINFALL FROM THE PRIOR DAYS BRINGS WETTER
ANTECEDENT CONDITIONS. THUS A MARGINAL RISK IS PLANNED IN THE
EXCESSIVE RAINFALL OUTLOOK FOR MONDAY. PRECIPITATION SHOULD REDUCE
IN MAGNITUDE BY TUESDAY, ALLOWING FOR NO HEAVY RAINFALL OR FLASH
FLOODING RISK AREAS. BUT SOME AREAS OF HEAVIER SNOW ARE POSSIBLE
FOR HIGHER ELEVATIONS OF THE CASCADES AND INTO THE NORTHERN
ROCKIES FOR MONDAY-TUESDAY. EXPECT PRECIPITATION FROM THE PACIFIC
NORTHWEST INTO THE ROCKIES TO GENERALLY TREND LIGHTER BY THE
MIDDLE OF NEXT WEEK AS UPPER-LEVEL RIDGING BRIEFLY BUILDS BACK IN,
BEFORE PRECIPITATION CHANCES INCREASE AGAIN LATE WEEK.
FARTHER EAST, THE MIDWEST/GREAT LAKES REGION TO NORTHEAST SHOULD
SEE ROUNDS OF PRECIPITATION NEXT WEEK AS LOW PRESSURE AND FRONTAL
SYSTEMS TRACK ACROSS. AMOUNTS AND NORTH-SOUTH EXTENT OF THE
PRECIPITATION REMAINS SOMEWHAT UNCERTAIN THOUGH. LOCATIONS NEAR
THE CANADIAN BORDER AND THE HIGHER ELEVATIONS OF NORTHERN NEW
ENGLAND MAY ALSO SEE SOME SNOW OR MIXED PRECIPITATION DURING THE
PERIOD. RAIN SHOULD BE THE PREVAILING PRECIPITATION TYPE ELSEWHERE
THROUGH MIDWEEK, THOUGH SNOW LEVELS MAY LOWER BY THURSDAY FOR SOME
SNOW CHANCES IN THE INTERIOR NORTHEAST, BUT CONFIDENCE IS LOW AT
THIS POINT.
TEMPERATURES WILL BE GENERALLY ABOVE AVERAGE ACROSS THE COUNTRY AS
THE PERIOD BEGINS MONDAY, WITH THE CENTRAL U.S. SEEING THE LARGEST
ANOMALIES AT 10-20F ABOVE NORMAL. ON TUESDAY AND WEDNESDAY THE
SOUTH-CENTRAL U.S. CAN EXPECT HIGHS AROUND 15-20F ABOVE NORMAL,
POTENTIALLY SETTING SOME RECORD HIGHS AS TEMPERATURES COULD RISE
INTO THE MID-80S. COLD FRONTS TRACKING SOUTH AND EAST SHOULD
GRADUALLY LIMIT THE AREA OF ABOVE NORMAL TEMPERATURES ACROSS THE
CONUS, COOLING TEMPERATURES ACROSS THE NORTHERN TIER, THEN THE
CENTRAL U.S. TO OHIO VALLEY, AND FINALLY ACROSS THE SOUTHEAST BY
AROUND FRIDAY. AREAS BEHIND THE FRONT SHOULD SEE NEAR TO BELOW
NORMAL TEMPERATURES, SPREADING PROGRESSIVELY FROM THE WESTERN U.S.
INTO THE SOUTH-CENTRAL U.S. AND TOWARD THE OHIO VALLEY, GREAT
LAKES, AND THE NORTHEAST LATE WEEK.
KONG/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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