247
FXUS02 KWBC 192025
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
424 PM EDT THU OCT 19 2023
VALID 12Z SUN OCT 22 2023 - 12Z THU OCT 26 2023
..RAIN CHANCES INCREASE FOR THE SOUTH-CENTRAL U.S. NEXT WEEK
..OVERVIEW
THE MEDIUM RANGE PERIOD BEGINS SUNDAY WITH A STRONG CANADIAN
MARITIMES LOW PRODUCING GUSTY WINDS AND SOME LINGERING
PRECIPITATION OVER THE NORTHEAST, FOLLOWED BY A COOL AND DRIER
PATTERN AS THE SUPPORTING UPPER TROUGH DEPARTS IN FAVOR OF RIDGING
AT THE SURFACE AND ALOFT. MEANWHILE, AN UPPER LOW IS LIKELY TO
DIVE SOUTHEAST ACROSS THE WEST EARLY IN THE WEEK, PRODUCING SOME
PRECIPITATION INCLUDING SNOW IN THE NORTHERN ROCKIES. BY TUESDAY
OR SO, ADDITIONAL ENERGY COULD TRACK INITIALLY SOUTH ACROSS THE
NORTHEASTERN PACIFIC AND THEN POTENTIALLY PIVOT EAST INTO THE
NORTHWEST. BUT MODEL GUIDANCE SHOWS SOME CONSIDERABLE DIFFERENCES
IN THE STRENGTH, TRACK, AND EVEN THE EXISTENCE OF THIS ENERGY, AS
WELL AS ITS POTENTIAL INTERACTION WITH THE UPPER LOW OVER THE
SOUTHWEST AT THAT POINT. REGARDLESS IT SEEMS LIKELY THAT EASTERN
PACIFIC MOISTURE (POSSIBLY LINGERING FROM WHAT IS CURRENTLY
HURRICANE NORMA) AND GULF MOISTURE COULD COMBINE AHEAD OF THE
UPPER-LEVEL SYSTEMS AND SURFACE FRONTS TO SPREAD POTENTIALLY HEAVY
RAINFALL INTO PARTS OF THE CENTRAL U.S., WHILE SNOW CHANCES
INCREASE ONCE AGAIN IN THE NORTHERN ROCKIES AND PERHAPS INTO THE
NORTHERN HIGH PLAINS, BUT THE MODEL DIFFERENCES KEEP CONFIDENCE
LOW IN THE DETAILS FOR NOW.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE IS IN REASONABLE AGREEMENT FOR THE EARLY PART OF
THE PERIOD, AND A MODEL BLEND FAVORING THE 00Z ECMWF, 06Z GFS, AND
00Z CMC WAS FAVORED. BUT MODEL SPREAD QUICKLY INCREASES WITH THE
TWO FEATURES MENTIONED ABOVE. BY DAY 5/TUESDAY THERE ARE MINOR
VARIATIONS WITH THE PLACEMENT OF THE UPPER LOW IN THE SOUTHWEST
U.S./NORTHWESTERN MEXICO, INCLUDING THE 00Z UKMET SLIGHTLY FARTHER
WEST OF CONSENSUS. BUT GREATER DIFFERENCES ARE ALREADY PRESENT
WITH THE ENERGY/POTENTIAL UPPER LOW COMING THROUGH THE
NORTHEASTERN PACIFIC TOWARD NORTH AMERICA, WITH VARIATIONS FROM
MODEL TO MODEL AND CYCLE TO CYCLE. IN TERMS OF THE 00/06Z MODEL
CYCLE, THE ECMWF WAS MOST AGGRESSIVE WITH BRITISH COLUMBIA/U.S.
NORTHWEST ENERGY IN THE FORM OF A STRONG CLOSED LOW COMPARED TO
OTHER GUIDANCE. THE 00Z GFS HAD BACKED OFF CONSIDERABLY FROM THIS
TYPE OF PATTERN IN A CHANGE FROM YESTERDAY'S SOLUTIONS, BUT THE
06Z GFS RUN AT LEAST HAD SOME ENERGY MAKING ITS WAY INTO THE
NORTHWEST. THE 12Z ECMWF AND GFS RUNS FORTUNATELY HAVE CONVERGED
SOMEWHAT, WITH THE GFS STRENGTHENING WHILE THE ECMWF WEAKENED
SOMEWHAT. BUT MEANWHILE THE 00Z AND NEWER 12Z CMC HAVE HARDLY ANY
ENERGY IN THE NORTHWEST MIDWEEK. ENSEMBLE MEMBERS SHOW
CONSIDERABLE SPREAD. GIVEN THAT THE PIECES OF ENERGY STEM FROM THE
UNCERTAIN ARCTIC, ADDITIONAL MODEL CHANGES ARE LIKELY, AND THIS IS
A RATHER LOW CONFIDENCE ASPECT OF THE FORECAST.
THESE NORTHERN STREAM DIFFERENCES ALSO HAVE EFFECTS ON THE
EVOLUTION OF THE SOUTHERN STREAM UPPER LOW ATOP THE SOUTHWEST
MIDWEEK. RECENT DETERMINISTIC MODELS HAVE BEEN MAINTAINING THE
SOUTHERN LOW AS A SEPARATE FEATURE (NOT TRACKING NORTHEAST AND
GETTING ABSORBED INTO THE NORTHERN STREAM TROUGHING) FOR LONGER.
SO THE WPC FORECAST DID TREND IN THIS DIRECTION, A CHANGE FROM THE
PREVIOUS FORECAST. ANOTHER BIG QUESTION IS THE POSSIBILITY OF
RIDGING COMING INTO THE WEST BY WEDNESDAY-THURSDAY. THIS WAS MOST
EVIDENT IN CMC AND OLDER GFS RUNS THAT WERE WEAKER WITH THE
NORTHWEST ENERGY. THIS STILL SEEMS LIKE A LOWER PROBABILITY
SOLUTION BUT WOULD YIELD VERY DIFFERENT SENSIBLE WEATHER IN THE
WEST, SO WILL CONTINUE TO MONITOR. REGARDLESS, TROUGHING IN THE
WEST BY MIDWEEK AND BEYOND HAS BEEN TRENDING WEAKER IN GENERAL, AS
EVEN SOLUTIONS LIKE THE ECMWF THAT HAVE STRONG ENERGY IN THE
NORTHWEST HAVE IT TRACKING MORE EASTWARD THAN DIGGING AS MUCH AS
MODEL RUNS FROM A DAY AGO.
THUS BY THE LATTER HALF OF THE MEDIUM RANGE PERIOD, THE WPC
FORECAST QUICKLY RAMPED UP THE PERCENTAGES OF THE GEFS AND EC
ENSEMBLE MEANS AND INCLUDED A BIT OF THE PREVIOUS FORECAST, WITH
THE DETERMINISTIC RUNS BECOMING SO QUESTIONABLE. THIS ALLOWED FOR
AN INTERMEDIATE SOLUTION. EXPECT THE DETAILS TO CHANGE WITH TIME.
..WEATHER/HAZARDS HIGHLIGHTS
THE DAYS 4-5 EXCESSIVE RAINFALL OUTLOOKS THAT COVER SUNDAY THROUGH
MONDAY NIGHT DEPICT NO RISK AREAS AT THIS TIME. ON SUNDAY GUIDANCE
SHOWS SIGNALS OF SOME LINGERING NORTHEAST PRECIPITATION THAT COULD
PRODUCE LOCALIZED ENHANCED TOTALS, BUT LACK OF INSTABILITY AND
FAIRLY RAPID DEPARTURE OF ANOMALOUS MOISTURE SHOULD TEMPER
SHORT-TERM RAINFALL RATES. GFS RUNS HAVE BEEN PERSISTENT IN
DEPICTING THE ONSET OF LOCALLY HEAVY RAINFALL OVER THE SOUTHERN
PLAINS SUNDAY-MONDAY DUE TO ITS FAST PROGRESSION OF NORMA, BUT THE
GFS IS ON ITS OWN WITH OTHER MODELS MUCH DRIER. OTHERWISE MOISTURE
WILL SPREAD ACROSS THE WEST WITH THE CENTRAL WEST COAST AND
NORTHERN ROCKIES LIKELY SEEING RELATIVELY HIGHER BUT NOT
EXCEPTIONALLY HEAVY TOTALS. PROBABILITIES FOR MEANINGFUL SNOW AT
HIGH ELEVATIONS OF THE ROCKIES SHOULD START INCREASING EARLY IN
THE WEEK. BY LATE MONDAY INTO MONDAY NIGHT, SOME INSTABILITY COULD
COME INTO ARIZONA/NEW MEXICO WITH MOISTURE INCREASING AS WELL
AHEAD OF THE UPPER LOW, SO THERE MAY BE SOME CONVECTION IN THE
SOUTHWEST TO CONSIDER, BUT PROBABILITIES FOR FLASH FLOODING STILL
REMAIN LOW FOR NOW.
THE WESTERN AND CENTRAL U.S. FORECAST DURING TUESDAY-THURSDAY WILL
DEPEND IN PART ON THE UNCERTAIN PATTERN ALOFT. A GENERAL WEAKENING
TREND FOR TROUGHING IN THE WEST HAS LED TO A LATER ARRIVAL OF/LESS
ANOMALOUSLY COOL TEMPERATURES THAN THE PREVIOUS FORECAST SHOWED.
BUT THERE IS ROOM FOR THESE TEMPERATURES TO DECREASE AGAIN
CONFIDENCE BUILDS. NORTHERN HIGH PLAINS LOCATIONS COULD SEE HIGHS
AT LEAST 15F BELOW NORMAL THOUGH BY WEDNESDAY-THURSDAY, WITH
INCREASING SNOW COVERAGE IN THE ROCKIES AND SOME HIGHER ELEVATION
SNOW IN THE CASCADES AS WELL. MORE QUESTIONABLE IS HOW MUCH SNOW
COULD SPREAD INTO LOWER ELEVATIONS OF AREAS LIKE MONTANA, SO
CONTINUE TO MONITOR UPCOMING FORECASTS. MEANWHILE THE PATTERN
SHOULD BECOME FAVORABLE FOR INCREASING COVERAGE AND INTENSITY OF
RAINFALL OVER THE CENTRAL U.S. BY TUESDAY OR SO, WITH LINGERING
MOISTURE FROM HURRICANE NORMA LIKELY CONTRIBUTING TO THIS
ACTIVITY. THE CURRENT MOST LIKELY PATTERN WOULD PRODUCE A FAIRLY
BROAD AREA OF MODERATE TO HEAVY RAINFALL IN THE SOUTHERN HALF OF
THE PLAINS, WITH UNCERTAINTY IN HOW MUCH STRETCHES INTO THE
MIDWEST.
EXPECT THE NORTHEAST TO SEE GUSTY WINDS ON SUNDAY BEHIND THE
DEPARTING CANADIAN MARITIMES SYSTEM. COOL TEMPERATURES OVER THE
EAST SUNDAY-MONDAY SHOULD MODERATE TO NEAR OR ABOVE NORMAL BY
MIDWEEK. THE EARLY WEEK COOL SPELL MAY BRING THE FIRST FROST OR
FREEZE OF THE SEASON TO SOME LOCATIONS FROM THE GREAT LAKES INTO
THE APPALACHIANS. WARM TEMPERATURES OVER THE ROCKIES AND THEN
PLAINS EARLY IN THE WEEK, WITH SOME HIGHS AT LEAST 10-15F ABOVE
AVERAGE, SHOULD MODERATE THEREAFTER BUT MORNING LOWS WILL REMAIN
QUITE WARM (10-20F ABOVE NORMAL) ACROSS THE PLAINS INTO THE GREAT
LAKES THROUGH THURSDAY IN THE MOIST FLOW AROUND THE WESTERN SIDE
OF EAST COAST/ATLANTIC HIGH PRESSURE.
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
HAZARDS:
- HEAVY RAIN ACROSS PORTIONS OF THE CENTRAL/SOUTHERN PLAINS AND
THE MISSISSIPPI VALLEY, TUE-WED,
OCT 24-OCT 25.
- HEAVY SNOW ACROSS PORTIONS OF THE NORTHERN PLAINS AND THE
NORTHERN ROCKIES, TUE-WED, OCT 24-OCT
25.
- FLOODING POSSIBLE ACROSS PORTIONS OF THE SOUTHEAST.
- FROST/FREEZE ACROSS PORTIONS OF THE NORTHEAST, THE APPALACHIANS,
THE TENNESSEE/OHIO VALLEY, THE
MID-ATLANTIC, THE SOUTHEAST AND THE GREAT LAKES, MON-TUE, OCT
23-OCT 24.
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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