928
FXUS02 KWBC 160659
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
258 AM EDT MON OCT 16 2023
VALID 12Z THU OCT 19 2023 - 12Z MON OCT 23 2023
..OVERVIEW
GUIDANCE CONTINUES TO SUGGEST THAT A STRONG UPPER RIDGE OVER THE
WEST AT THE START OF THE FORECAST PERIOD EARLY THURSDAY WILL
SUPPORT EASTERN U.S. TROUGH AMPLIFICATION AND POTENTIAL FOR
DEEPENING LOW PRESSURE NEAR THE EAST COAST BY THE WEEKEND.
HOWEVER IMPORTANT DETAILS OF THIS DEVELOPMENT WILL RELY ON SMALLER
SCALE AND THUS LOWER PREDICTABILITY SHORTWAVES FEEDING INTO THE
OVERALL MEAN TROUGH, SO IT WILL TAKE ADDITIONAL TIME TO DETERMINE
WITH SOME PRECISION WHAT THE ASSOCIATED PRECIPITATION AND WIND
EFFECTS WILL BE. BEHIND THIS SYSTEM EXPECT THE WESTERN U.S. RIDGE
TO WEAKEN SOME AND PROGRESS INTO THE PLAINS/MISSISSIPPI VALLEY BY
THE START OF NEXT WEEK WHILE A PACIFIC TROUGH OF MODERATE DEPTH
MOVES INTO THE WEST AND BRINGS PRECIPITATION INTO THE PACIFIC
NORTHWEST AND NORTHERN ROCKIES. THE FORECAST PATTERN WILL FAVOR A
BROAD AREA OF ABOVE NORMAL TEMPERATURES OVER THE WEST AND INTO THE
PLAINS LATE THIS WEEK, FOLLOWED BY A COOLER TREND OVER THE WEST AS
THE UPPER TROUGH ARRIVES. WITH THE EXCEPTION OF ABOVE NORMAL
READINGS OVER NEW ENGLAND LATE THIS WEEK, MOST OF THE EAST SHOULD
SEE NEAR TO BELOW AVERAGE HIGHS FOR MOST OF THE PERIOD.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
WHILE MODELS AND ENSEMBLES HAVE BEEN REFLECTING THE AMPLIFIED
WESTERN RIDGE/EASTERN TROUGH THEME, THERE ARE STILL SIGNIFICANT
UNCERTAINTIES WITH HOW THE EASTERN TROUGH ENERGY WILL EVOLVE AND
AFFECT THE SURFACE EVOLUTION. ALREADY AT THE START OF THE PERIOD,
THE LATEST GFS/GEFS MEAN RUNS SHOW MORE SOUTHWESTWARD AMPLITUDE OF
THE INITIAL TROUGH CROSSING THE MISSISSIPPI VALLEY/SOUTHERN PLAINS
VERSUS OTHER GUIDANCE (LEADING TO GREATER SOUTHWESTWARD EXTENT OF
QPF ON THURSDAY). CONSENSUS SHOWS THE INITIAL COMPACT UPPER LOW
CROSSING THE MIDWEST EJECTING QUICKLY AS UPSTREAM ENERGY ROUNDING
THE WESTERN RIDGE DIVES INTO THE MEAN TROUGH. THE PRECISE
EVOLUTION OF THIS ENERGY AS IT REACHES THE EAST COAST, ALONG WITH
WHAT INFLUENCE THERE MAY BE BY ANOTHER UPSTREAM SHORTWAVE (WHICH
COULD PRODUCE A SEPARATE SURFACE WAVE/FRONT), WILL DETERMINE THE
STRENGTH/TRACK/TIMING OF EAST COAST LOW PRESSURE. ASIDE FROM THE
PROGRESSIVE 00Z/15 ECMWF RUN, RECENT GFS/ECMWF RUNS HAVE BEEN THE
MOST CONSISTENT WITH THE GENERAL IDEA OF A MID-ATLANTIC WAVE
BECOMING DEEPER AS IT REACHES NEW ENGLAND OR VICINITY BY SUNDAY
(WHEN AN UPPER LOW SHOULD BE OVER OR NEAR THE REGION). ECMWF MEAN
RUNS HAVE BEEN HINTING AT THIS THEME TOO, WHILE GEFS MEANS HAVE
TENDED TO MAINTAIN GREATER DEFINITION OF THE INITIAL INLAND
SURFACE LOW. THE NEW 00Z GEFS MEAN IS GIVING EQUAL WEIGHT TO A
COASTAL WAVE THOUGH. EARLIER/SOUTHWARD UPPER LOW FORMATION IN THE
00Z UKMET LEADS TO STRONGER MID-ATLANTIC LOW PRESSURE, WHILE IN
CONTRAST THE 00Z CMC OPENS UP ITS SYSTEM TO YIELD A WEAKER AND
PROGRESSIVE SURFACE LOW. PRIOR CMC RUNS WERE CLOSER TO THE
GFS-GEFS/ECMWF-ECENS CLUSTER BUT FASTER. FOR THE FAVORED
DETERMINISTIC FORECAST BASED ON 12Z/18Z GUIDANCE, A COMPROMISE
AMONG THE 12Z/18Z GFS, 12Z ECMWF, AND 18Z GEFS/12Z ECENS MEANS
SEEMED TO OFFER THE BEST STARTING POINT. CONFIDENCE REMAINS
SOMEWHAT BELOW AVERAGE GIVEN THE LOW PREDICTABILITY OF IMPORTANT
SHORTWAVE DETAILS. FOR THE MOST PART THE UPPER TROUGH ENTERING
THE WEST LATE IN THE PERIOD HAS BEEN MUCH BETTER BEHAVED THAN THE
EASTERN SYSTEM. THE MAIN CONSIDERATION WAS TO EXCLUDE THE CMC AS
ITS LATEST RUNS HAVE BEEN STRAYING TO THE AMPLIFIED SIDE OF THE
GUIDANCE SPREAD. AN AVERAGE OF REMAINING MODEL AND ENSEMBLE
GUIDANCE REPRESENTS THIS FEATURE WELL.
..WEATHER/HAZARDS HIGHLIGHTS
CURRENTLY THERE ARE NO RISK AREAS DEPICTED IN THE DAYS 4-5
EXCESSIVE RAINFALL OUTLOOKS THAT COVER THE THURSDAY THROUGH FRIDAY
NIGHT TIME FRAME. THE FRONT EXTENDING SOUTH/SOUTHWEST FROM GREAT
LAKES LOW PRESSURE LATE THIS WEEK WILL PRODUCE AREAS OF RAINFALL
OF VARYING INTENSITY, WITH SOME CONTINUED UNCERTAINTY OVER PRECISE
COVERAGE AND AMOUNTS. AS OF THURSDAY, MOISTURE AND INSTABILITY DO
NOT APPEAR SUFFICIENT TO YIELD A MEANINGFUL POTENTIAL FOR INTENSE
RAIN RATES. BY FRIDAY-FRIDAY NIGHT MOISTURE/INSTABILITY COULD
INCREASE SOMEWHAT OVER PARTS OF THE MID-ATLANTIC INTO SOUTHERN NEW
ENGLAND JUST AHEAD OF DEVELOPING LOW PRESSURE, WITH SOME GUIDANCE
SIGNALS FOR LOCALLY HEAVIER RAINFALL. CONFIDENCE IN SPECIFICS IS
TOO LOW AT THIS TIME TO DEFINE ANY RISK AREA THOUGH. GOING INTO
SATURDAY, THE MOST LIKELY FORECAST SCENARIO WOULD HAVE INCREASING
RAINFALL AND STRENGTHENING WINDS OVER THE NORTHEAST WITH BRISK TO
STRONG WINDS CONTINUING THROUGH AT LEAST SUNDAY. DEPENDING ON
SYSTEM EVOLUTION/TRACK, HIGHEST ELEVATIONS COULD SEE A LITTLE
SNOW. LOWER PREDICTABILITY OF IMPORTANT DETAILS OF UPPER DYNAMICS
SUPPORTING THIS SYSTEM SUGGEST MORE TIME WILL BE REQUIRED TO
RESOLVE PRECIPITATION AND WIND EFFECTS. MUCH OF THE WEST WILL BE
DRY THROUGH LATE THIS WEEK. THE UPPER TROUGH/LEADING SURFACE
FRONT MOVING INTO THE REGION SHOULD BRING LIGHT TO PERHAPS
ISOLATED MODERATE RAINFALL TO THE PACIFIC NORTHWEST BY THE
WEEKEND, WITH THIS MOISTURE CONTINUING INTO THE NORTHERN ROCKIES
BY SUNDAY-MONDAY. SOME OF THE PRECIPITATION COULD FALL AS SNOW AT
HIGH ELEVATIONS OF THE NORTHERN ROCKIES.
A BROAD AREA OF VERY WARM TEMPERATURES WILL EXTEND ACROSS THE WEST
INTO THE PLAINS LATE THIS WEEK, FOLLOWED BY A STEADY COOLING TREND
OVER THE WEST LEADING TO MODESTLY BELOW NORMAL HIGHS BY
SUNDAY-MONDAY AS THE UPPER TROUGH MOVES IN. THE WARMTH OVER THE
CENTRAL U.S. WILL ALSO DECREASE IN COVERAGE BY THE START OF NEXT
WEEK WITH THE NORTHERN PLAINS COOLING TOWARD NORMAL FOR HIGHS.
WITHIN THE AREA OF ABOVE NORMAL TEMPERATURES, EXPECT MANY
LOCATIONS TO SEE ONE OR MORE DAYS WITH PLUS 10F OR GREATER
ANOMALIES, AND BEST POTENTIAL FOR SOME PLUS 15-20F ANOMALIES
SHOULD BE OVER THE NORTHERN ROCKIES/HIGH PLAINS LATE THIS WEEK.
SOME DAILY RECORDS FOR HIGHS/WARM LOWS WILL BE POSSIBLE OVER THE
WEST LATE THIS WEEK AND TEMPERATURES COULD CHALLENGE RECORD HIGHS
OVER PARTS OF SOUTHERN TEXAS FRIDAY INTO THE WEEKEND. MEANWHILE
OVER THE EAST, NEW ENGLAND WILL SEE ABOVE NORMAL TEMPERATURES
THURSDAY INTO SATURDAY BUT THE REST OF THE EASTERN U.S. SHOULD SEE
A RETURN OF COOLER THAN NORMAL HIGHS FRIDAY ONWARD WITH THE
AMPLIFIED UPPER TROUGH CROSSING THE REGION.
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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