678
FXUS02 KWBC 151855
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
254 PM EDT SAT OCT 15 2022
VALID 12Z TUE OCT 18 2022 - 12Z SAT OCT 22 2022
..OVERVIEW
THE MEDIUM RANGE PERIOD BEGINS TUESDAY WITH AN AMPLIFIED/BLOCKY
UPPER LEVEL FLOW PATTERN CONSISTING OF AN ANOMALOUSLY STRONG UPPER
LOW CENTERED NEAR THE LOWER GREAT LAKES WITH TROUGHING EXTENDING
THROUGH THE EASTERN HALF OF THE U.S. AND AN UPPER RIDGE/HIGH OVER
MUCH OF THE WEST. THIS PATTERN SHOULD PERSIST THROUGH
WEDNESDAY-THURSDAY WHILE STRONG SHORTWAVES MOVE THROUGH THE
EASTERN TROUGH AND A SOUTHERN STREAM UPPER LOW SLOWLY EDGES
EASTWARD ACROSS THE PACIFIC TOWARD SOUTHERN CALIFORNIA. LAKE
EFFECT/ENHANCED PRECIPITATION (INCLUDING SOME SNOW) WILL BE COMMON
THROUGH MIDWEEK ACROSS THE GREAT LAKES WITH LIGHTER AMOUNTS LATER
IN THE WEEK. THROUGH THURSDAY TEMPERATURES WILL BE MUCH BELOW
AVERAGE IN THE EASTERN HALF OF THE COUNTRY BUT WARMER THAN AVERAGE
IN THE NORTHWEST UNDER THE RIDGE. THEN BY FRIDAY-SATURDAY THERE IS
A LIKELY TREND TOWARD OVERALL DEAMPLIFICATION OF THE UPPER FLOW
AND POSSIBLY EVEN SOME NORTHWEST TROUGHING, WHICH SHOULD FOCUS THE
WARMTH OVER THE PLAINS WITH A TREND TOWARD MORE NORMAL
TEMPERATURES ELSEWHERE.
..MODEL AND PREDICTABILITY ASSESSMENT
THE FORECAST DURING THE FIRST HALF OF THE PERIOD CONTINUES TO SHOW
BETTER THAN AVERAGE AGREEMENT AND CONTINUITY OVERALL,
REPRESENTATIVE OF THE TYPICALLY GOOD PREDICTABILITY OF A HIGHLY
AMPLIFIED LARGE SCALE PATTERN. THERE ARE STILL SMALLER SCALE
DIFFERENCES INVOLVING THE WAVY FRONT AND SUPPORTING SHORTWAVE
ENERGY CROSSING NEW ENGLAND EARLY IN THE PERIOD. SPECIFICS WILL BE
IMPORTANT FOR ASSOCIATED RAINFALL BUT WILL TAKE INTO THE SHORT
RANGE TIME FRAME TO RESOLVE. MEANWHILE THE MODELS/MEANS CONTINUE
TO DEVELOP SOME SPREAD FOR THE UPPER LOW OFFSHORE SOUTHERN
CALIFORNIA. OVER RECENT RUNS THE GFS/GEFS AND CMC HAVE TENDED TO
BE ON THE FASTER SIDE (THOUGH WITH THE 12Z GFS SLOWING DOWN
SLIGHTLY) WHILE RECENT ECMWF RUNS HAVE BEEN SLOWER THAN EARLIER
ONES (WITH THE 00Z ECMWF MEAN BETWEEN THE TWO EXTREMES). SOME OF
THESE DIFFERENCES EXTEND THROUGH THE REST OF THE PERIOD THOUGH THE
12Z ECMWF DOES SHOW SOME ACCELERATION LATE.
THE FRIDAY-SATURDAY PERIOD HAS FEATURED CONSIDERABLE SPREAD WITH
RESPECT TO HOW QUICKLY INCOMING PACIFIC FLOW BREAKS DOWN THE UPPER
RIDGE OVER THE WEST. OVER THE PAST DAY THE GFS/GEFS HAVE MADE
PRONOUNCED TRENDS TOWARD THE ECMWF/ECMWF MEAN IDEA OF LOWER
HEIGHTS AND AN EVENTUAL TROUGH REACHING THE WEST, LEADING TO MUCH
BETTER AGREEMENT AMONG THOSE SOLUTIONS. HOWEVER THE 00Z CMC AND
THE 00Z UKMET (THROUGH THE END OF ITS RUN) SUGGESTED A LINGERING
POSSIBILITY THAT THE PATTERN CHANGE COULD STILL TAKE A LITTLE
LONGER TO DEVELOP. THE NEW 12Z CMC IS NOT AS AMPLIFIED WITH THE
SHORTWAVE WHICH THE 12Z GFS/00Z ECMWF BRING TO THE NORTHWEST BY
EARLY NEXT SATURDAY BUT IS MUCH CLOSER TO THE OVERALL SCENARIO
NOW. AS UPPER HEIGHTS OVER THE EAST RISE IN RESPONSE TO THE
EVOLUTION UPSTREAM, LATEST MODEL RUNS HAVE BEEN SHOWING POTENTIAL
FOR SOME SHORTWAVE ENERGY REACHING THE SOUTHEAST TO SEPARATE FROM
THE WESTERLIES AND FORM A SEPARATE SMALLER SCALE TROUGH/UPPER LOW.
SUCH A FEATURE WOULD HAVE LOWER PREDICTABILITY AND THUS FAR THE
MODELS HAVE BEEN INCONSISTENT WITH WHERE SUCH A FEATURE WOULD
FORM/TRACK, THOUGH THE 12Z GFS/ECMWF ARE NOT TOO FAR FROM THE 06Z
GFS/00Z ECMWF. PREFER A CONSERVATIVE APPROACH AT THIS TIME.
A BLEND OF THE 00Z/06Z OPERATIONAL MODELS PROVIDED A GOOD STARTING
POINT TO RESOLVE LINGERING DETAIL QUESTIONS DURING THE FIRST HALF
OF THE PERIOD, WITH MINIMAL CONTINUITY CHANGES. THE FORECAST
INCORPORATED AN INCREASING PROPORTION OF ENSEMBLE MEANS LATER IN
THE PERIOD (06Z GEFS/00Z ECENS, AS WELL AS 00Z CMCENS WHICH WAS A
TAD FLATTER), REACHING 60 PERCENT BY DAY 7 SATURDAY WHILE THE 06Z
GFS/00Z ECMWF PROVIDED THE REMAINING INPUT. THIS PROVIDED A MODEST
NUDGE TOWARD THE DEVELOPING MAJORITY SCENARIO.
..SENSIBLE WEATHER AND POTENTIAL HAZARDS
BY TUESDAY, A FRONTAL SYSTEM WILL HAVE PASSED ACROSS MUCH OF THE
EAST WITH A DRYING HIGH PRESSURE SYSTEM BEHIND IT. HOWEVER, THE
FRONT COULD CONTINUE TO CAUSE SHOWERS AND THUNDERSTORMS ACROSS
MAINE, THE FLORIDA PENINSULA, AND SOUTHERN TEXAS AHEAD OF THE
FRONTAL PASSAGE IN THOSE AREAS. THE FORECAST FOR MAINE CONTINUES
TO BE PARTICULARLY CHALLENGING, WITH MODEL RUNS VARYING FOR EXACT
TIMING AND WAVE DETAILS. MOST OF THE MODELS HAVE BEEN ADVERTISING
JUST FAST ENOUGH PROGRESSION TO PUSH A SWATH OF MODERATE TO HEAVY
RAINFALL, SUPPORTED BY CONSIDERABLE MOISTURE TRANSPORT, MOSTLY
EAST INTO CANADA BUT A MINORITY HAS BEEN DEPICTING THIS BAND
FARTHER WEST OVER MAINE. NOW THE AVERAGE OF LATEST 12Z GUIDANCE
SEEMS TO BE NUDGING BACK A LITTLE MORE TO THE WEST, AT LEAST
INCREASING THE RAINFALL POTENTIAL OVER EASTERN MAINE. IT MAY TAKE
UNTIL WELL INTO THE SHORT RANGE PERIOD TO RESOLVE THIS PART OF THE
FORECAST SATISFACTORILY. MEANWHILE UPPER LEVEL ENERGY AND THE
WESTERLY FLOW ACROSS THE RELATIVELY WARM GREAT LAKES COMPARED TO
THE COLD AIR TEMPERATURES WILL PRODUCE CONSIDERABLE LAKE EFFECT
PRECIPITATION DOWNWIND OF THE LAKES. SUPPORT IS HIGHEST FOR
NOTABLE AMOUNTS OF RAIN AND/OR SNOW ON TUESDAY WITH A SURFACE LOW
PRESSURE SYSTEM NEARBY, BUT AT LEAST THE FLOW ALOFT WILL BE
FAVORABLE FOR ADDITIONAL LAKE EFFECT PRECIPITATION THROUGH
THURSDAY. OTHER THAN THOSE AREAS, MUCH OF THE CONTIGUOUS U.S.
SHOULD BE DRY THROUGH THE END OF THE WEEK. EXCEPTIONS BY
FRIDAY-SATURDAY WILL LIKELY BE WITH AN EXPANDING AREA OF
PRECIPITATION OVER THE PACIFIC NORTHWEST INTO NORTHERN ROCKIES
WITH UPPER LEVEL ENERGY AND A SURFACE FRONT, AND SOME SHOWERS
REACHING SOUTHERN CALIFORNIA AND THE SOUTHWEST WITH THE SOUTHERN
STREAM UPPER LOW/TROUGH.
THE AMPLIFIED WESTERN RIDGE IN PLACE FOR MOST OF THE WEEK WILL
CAUSE WARMER THAN AVERAGE TEMPERATURES ACROSS THE NORTHWEST IN
PARTICULAR, WITH HIGHS COMMONLY 10-20F ABOVE AVERAGE, POTENTIALLY
LEADING TO SOME DAILY RECORD HIGHS THROUGH THURSDAY. CONVERSELY,
THE ANOMALOUS UPPER LOW/TROUGH IN THE EAST SHOULD PRODUCE RATHER
COLD TEMPERATURES MORE COMMON TO NOVEMBER AND DECEMBER FROM THE
PLAINS EASTWARD. BELOW NORMAL TEMPERATURES BY 10-25F WILL BE
WIDESPREAD AND TRANSLATE INTO LOWS IN THE TEENS IN PORTIONS OF THE
NORTH-CENTRAL U.S. TUESDAY AND 30S SPREADING SOUTH POSSIBLY ALL
THE WAY TO THE GULF COAST (MOBILE, ALABAMA FOR EXAMPLE) BY
WEDNESDAY-THURSDAY. THE SOUTHEAST COULD ALSO SEE HIGHS IN THE 50S
AND 60S, AND RECORD LOW MAXIMUM AND MINIMUM TEMPERATURES ARE
LIKELY TO BE SET IN THE EAST-CENTRAL U.S. AS THE UPPER LEVEL
PATTERN RELAXES TOWARDS THE END OF THE WEEK, TEMPERATURE ANOMALIES
SHOULD LESSEN OVER BOTH THE WEST AND EAST WHILE HIGHS REACH 10-15F
ABOVE NORMAL OVER THE NORTHERN/CENTRAL PLAINS BY FRIDAY-SATURDAY.
RAUSCH/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, EXPERIMENTAL EXCESSIVE RAINFALL
OUTLOOK, WINTER WEATHER OUTLOOK PROBABILITIES AND HEAT INDICES 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
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