299
FXUS02 KWBC 010704
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
304 AM EDT SUN OCT 01 2023
VALID 12Z WED OCT 04 2023 - 12Z SUN OCT 08 2023
...HEAVY RAIN WILL CAUSE FLASH FLOODING CONCERNS IN THE
SOUTH-CENTRAL U.S. AROUND MIDWEEK...
..OVERVIEW
AS THE MEDIUM RANGE PERIOD BEGINS WEDNESDAY, AN AMPLIFIED UPPER
TROUGH WILL BE IN PLACE WITH ITS AXIS OVER THE HIGH PLAINS OR SO.
MOIST AND UNSTABLE INFLOW AHEAD OF THE TROUGH AND AN ASSOCIATED
WAVY COLD FRONT SHOULD LEAD TO WIDESPREAD HEAVY RAIN AND FLASH
FLOODING ACROSS THE SOUTHERN PLAINS AND PERHAPS INTO THE LOWER
MISSISSIPPI VALLEY PARTICULARLY ON WEDNESDAY, WITH SOME HEAVY RAIN
POSSIBLY LASTING LATER IN THE WEEK ON A MORE LIMITED SCALE.
FARTHER NORTH, THE COLD FRONT MARCHING EASTWARD SHOULD HELP CAUSE
SOME RAIN TO PUSH ACROSS THE EAST-CENTRAL AND EASTERN U.S. THROUGH
THE LATTER HALF OF THE WEEK, AS WELL AS SPREAD COOLER THAN NORMAL
TEMPERATURES BEHIND IT AFTER A WARM SPELL IN THE GREAT LAKES/OHIO
VALLEY INTO THE NORTHEAST AROUND MIDWEEK.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
OPERATIONAL MODELS AND ENSEMBLE MEANS AGREE ON THE GENERAL IDEA OF
GRADUAL EASTWARD PROGRESSION OF THE AMPLIFIED RIDGE-TROUGH-RIDGE
CONFIGURATION BUT THERE ARE NOTABLE DETAIL UNCERTAINTIES THAT
COMPLICATE THE FORECAST OF SENSIBLE WEATHER OVER SOME REGIONS. ONE
ASPECT NOW PHASING INTO THE SHORT RANGE PERIOD TUESDAY BUT ALSO
AFFECTING WEDNESDAY IS A FASTER SURFACE LOW TRACK INTO
SOUTH-CENTRAL CANADA, WHICH HAS REDUCED THE QPF COMPARED TO A DAY
AGO. AT LEAST MODEL GUIDANCE HAS CONVERGED BETTER WITH THAT AT
THIS POINT.
ANOTHER THORN IN THE SIDE OF THE FORECAST THE PAST COUPLE DAYS HAS
BEEN THE POTENTIAL FOR SOME ENERGY TO HANG BACK IN THE
SOUTHWESTERN U.S. BY AROUND THURSDAY. THE 12Z CMC AND UKMET AND
THEIR NEWER 00Z RUNS HAVE BEEN CONSISTENT IN SHOWING THAT, WHILE
THE 18Z GFS DID SO IN WEAKER FORM. ECMWF RUNS HAD NOT FAVORED
THIS...UP UNTIL THE CURRENTLY INCOMING 00Z RUN THAT INDICATED THIS
POSSIBILITY. FORTUNATELY THOUGH, EVEN THOUGH RECENT 00Z MODELS
STILL HAVE SOME DIFFERENCES WITH THIS ENERGY, AT LEAST THE
SHORTWAVE DOES NOT LOOK TO BE TERRIBLY STRONG, AND THE TRACK OF
THE MAIN TROUGH AXIS IS NOT AS AFFECTED. THE 12Z CMC AND UKMET DID
END UP WITH A FASTER MAIN TROUGH TRACK COMPARED TO THE MORE
AGREEABLE ECMWF/GFS AND THEIR MEANS. THAT 12Z CMC/UKMET AT LEAST
SEEMED LIKE A MINORITY SOLUTION TO LEAN AGAINST FOR THIS ASPECT OF
THE FORECAST. BUT WILL CONTINUE TO MONITOR THIS POTENTIAL FOR THE
SOUTHWESTERN SHORTWAVE THAT REMAINS UNCERTAIN.
MEANWHILE, RECENT MODELS HAVE STABILIZED A LITTLE BETTER WITH THE
EVOLUTION OF HOW ENERGY OVER AND UPSTREAM FROM THE GULF OF ALASKA
FEEDS INTO THE MEAN TROUGH BASED ON THE CHARACTER OF THE EASTERN
PACIFIC RIDGE DRIFTING TOWARD THE WEST COAST. BUT MODELS WITH
STRONGER SHORTWAVES LIKE THE 18Z GFS SHOW SOME BRIEF DAMPENING OF
THE NORTHERN PERIPHERY OF THE RIDGE LEADING TO SOMEWHAT BROADER
DOWNSTREAM TROUGHING. THE 00Z GUIDANCE SEEMS TO BE SOMEWHAT MORE
AGREEABLE BUT WITH SOME VARIATIONS REMAINING, ESPECIALLY WITH THE
CMC. THESE DIFFERENCES AFFECT THE POSITIONS OF THE LEADING COLD
FRONT REACHING THE EAST COAST AND A SECONDARY COLD FRONT
TRAVERSING THE CENTRAL U.S. THROUGH LATE WEEK.
OVERALL THE WPC MODEL PREFERENCE WAS FOR AN OPERATIONAL MODEL
BLEND FOR DAY 3/WEDNESDAY, BUT QUICKLY TOOK OUT THE 12Z CMC AND
UKMET AND REPLACED THEM WITH THE 18Z GEFS AND 12Z ECENS MEANS.
INCREASED THE PERCENTAGE OF THE MEANS TO JUST OVER HALF BY DAYS
6-7 TO LIMIT TOO MUCH INDIVIDUAL MODEL INFLUENCE WITH THEIR
CONTINUED VARIATIONS IN THE DETAILS OF THE FLOW.
..WEATHER/HAZARDS HIGHLIGHTS
THE SOUTH-CENTRAL U.S. WILL BE AN AREA OF FOCUS FOR WIDESPREAD
HEAVY RAIN ESPECIALLY ON WEDNESDAY, AS THE RIGHT ENTRANCE REGION
OF THE JET WILL PROVIDE AMPLE LIFT, AND PLENTY OF INSTABILITY IS
IN PLACE JUST AHEAD OF THE COLD FRONT. A SLIGHT RISK REMAINS IN
PLACE THERE IN THE DAY 4/WEDNESDAY EXCESSIVE RAINFALL OUTLOOK, AS
DESPITE THE DROUGHT CONDITIONS, HIGH RAIN RATES THAT COULD
OVERCOME THE DRYNESS ARE LIKELY. GENERALLY MINOR ADJUSTMENTS WERE
NEEDED COMPARED TO THE PREVIOUS ISSUANCES OF THE SLIGHT RISK, AND
A MARGINAL RISK CONTINUES TO COVER SOME OF THE SEEMINGLY
LOWER-PROBABILITY UKMET/CMC SOLUTIONS THAT INDICATE HEAVY RAIN
FARTHER NORTHWEST. BY THURSDAY, THE COLD FRONT WILL PUSH SOUTHEAST
AND CLEAR OUT RAIN POTENTIAL ON ITS BACKSIDE, BUT COULD STILL
PROVIDE FORCING FOR CONVECTION ALONG AND AHEAD OF IT INTO SOUTHERN
AND EASTERN PARTS OF TEXAS AND INTO THE LOWER MISSISSIPPI VALLEY.
MODEL GUIDANCE IS QUITE VARIABLE WITH RAIN AMOUNTS AND PLACEMENT
OF ANY HEAVY AMOUNTS, SO HAVE A MARGINAL RISK FOR THE ERO TO COVER
ANY THREAT WHILE AWAITING BETTER MODEL AGREEMENT. SOME LINGERING
RAIN MAY BE POSSIBLE IN SOUTH TEXAS LATE WEEK.
FARTHER NORTH, THE COLD FRONT SHOULD TRACK MORE PROGRESSIVELY
THROUGH THE MIDWEST/UPPER GREAT LAKES ON WEDNESDAY, ACROSS THE
OHIO/TENNESSEE VALLEYS AROUND THURSDAY, AND INTO THE EAST BY
FRIDAY, PRODUCING SHOWERS AND PERHAPS THUNDERSTORMS ALONG AND
AHEAD OF IT. THIS RAIN SHOULD OVERALL BE LIGHTER THAN FARTHER
SOUTH, BUT MAY BE ENHANCED IN THE NORTHEAST ESPECIALLY IN FAVORED
TERRAIN, AS THE FRONT COULD BEGIN TO TAP ATLANTIC MOISTURE WITHIN
SOUTHERLY FLOW TO INCREASE RAINFALL, DEPENDING ON THE SPECIFICS OF
UPPER TROUGHING BY LATE WEEK.
THE AMPLIFIED TROUGH AND THE COLD FRONT WILL LEAD TO COOLER
TEMPERATURES THAN AVERAGE WHILE THE UPPER RIDGES TO THE EAST AND
WEST WILL SUPPORT ABOVE NORMAL TEMPERATURES. THE INTERIOR WEST
SHOULD SEE COOLER TEMPERATURES THAN AVERAGE ESPECIALLY THROUGH
MIDWEEK, WITH WITH LOWS 5-10F BELOW NORMAL BUT HIGHS AROUND 10-15F
BELOW AVERAGE, BUT WARMING TO NEAR NORMAL FOR THE LATTER PART OF
THE WEEK. MEANWHILE WARMER THAN AVERAGE TEMPERATURES BY AROUND
15-20F ABOVE NORMAL ARE FORECAST FOR THE MIDWEST INTO THE GREAT
LAKES AND THE INTERIOR NORTHEAST, WITH HIGHS IN THE UPPER 70S TO
LOW 80S. SOME DAILY RECORDS FOR HIGHS/WARM LOWS MAY BE POSSIBLE
WEDNESDAY. AS THE COLD FRONT AND UPPER TROUGH MARCH EAST INTO THE
LATTER HALF OF THE WEEK, TEMPERATURES WILL COOL TO BELOW AVERAGE
ACROSS THE CENTRAL AND THEN EAST-CENTRAL U.S., LIMITING THE ABOVE
NORMAL TEMPERATURES TO THE NORTHEAST. A TRAILING FRONT MAY
REINFORCE THE COOLING TREND BY FRIDAY-SUNDAY, AND THERE COULD BE
CONCERNS FOR THE FIRST FROST OR FREEZE OF THE SEASON TO OCCUR IN
THE NORTHERN HIGH PLAINS. APPROACH/ARRIVAL OF THE EASTERN PACIFIC
UPPER RIDGE SHOULD RAISE TEMPERATURES ALONG THE WEST COAST TO
ABOVE AVERAGE, BY AS MUCH AS 5-15F, AND SOME RECORD WARM LOWS MAY
BE POSSIBLE.
TATE/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.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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