463
FXUS02 KWBC 150706
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
306 AM 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 STAY PRETTY PERSISTENT
THROUGH WEDNESDAY-THURSDAY WHILE STRONG SHORTWAVES MOVE THROUGH
THE EASTERN TROUGH AND A SOUTHERN STREAM UPPER LOW SLOWLY EDGES
EASTWARD ACROSS THE PACIFIC TOWARD CALIFORNIA. LAKE
EFFECT/ENHANCED PRECIPITATION (INCLUDING SOME SNOW) WILL BE COMMON
THROUGH MIDWEEK ACROSS THE GREAT LAKES WITH LIGHTER AMOUNTS LATER
IN THE WEEK. TEMPERATURES ARE FORECAST TO 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, THE PATTERN
BECOMES MORE UNCERTAIN BUT WITH A LIKELY TREND TOWARD OVERALL
DEAMPLIFICATION IN THE UPPER LEVELS.
..MODEL AND PREDICTABILITY ASSESSMENT
MODEL GUIDANCE CONTINUES TO SHOW GOOD CLUSTERING FOR THE UPPER LOW
OVER THE GREAT LAKES TUESDAY AND THEN LIFTING NORTHWARD OVER
WESTERN QUEBEC, AND EVEN REASONABLE AGREEMENT FOR SHORTWAVES
EMBEDDED WITHIN THE TROUGH SUCH AS OVER THE UPPER GREAT LAKES BY
DAY 5/THURSDAY IN THE 12/18Z GUIDANCE COMPARED TO PREVIOUS RUNS.
MINOR DIFFERENCES COULD BE RESOLVED THROUGH THE BLENDING PROCESS
OF THE 18Z GFS AND 12Z ECMWF/CMC/UKMET THROUGH THE EARLY PART OF
THE PERIOD.
MODELS ALSO AGREE WELL WITH RIDGING ACROSS THE INTERMOUNTAIN WEST
THROUGH AROUND THURSDAY WHILE AN UPPER LOW IN THE EASTERN PACIFIC
TRACKS EASTWARD. THE EXACT POSITION OF THIS SOUTHERN STREAM LOW
HAS BEEN VARIABLE FROM CYCLE TO CYCLE. THE 12/18Z DETERMINISTIC
MODELS WERE FAIRLY WELL CLUSTERED WITH A WESTERN POSITION BUT WITH
THE ENSEMBLE MEANS CENTERED A BIT EAST, AND THE 00Z MODELS
GENERALLY CAME IN A BIT EASTWARD AS WELL. THIS IS WITHIN FAIRLY
TYPICAL SPREAD FOR THE MEDIUM RANGE TIMEFRAME BUT ITS TIMING WILL
CAUSE SOME SENSIBLE WEATHER DIFFERENCES WITH CLOUDS/SHOWERS COMING
INTO CALIFORNIA AND THE SOUTHWEST DEPENDENT ON WHEN THE ENERGY/LOW
TROUGH MOVES ASHORE LIKELY LATER IN THE WEEK.
THE MOST UNCERTAIN PART OF THE PERIOD ARISES BY THURSDAY-SATURDAY
AS THE PATTERN EVOLVES DEPENDENT PARTICULARLY ON ROUNDS OF
NORTHERN STREAM ENERGY ACROSS WESTERN CANADA. THE ECMWF HAS BEEN
PERSISTENT IN SHOWING THE RIDGE SHOULD START GETTING SUPPRESSED BY
WESTERN CANADA ENERGY AROUND THURSDAY, WITH OTHER GUIDANCE
INCLUDING THE GFS AND SOME GEFS ENSEMBLE MEMBERS PLAYING CATCH UP
TO THIS IDEA, THOUGH THE 12Z CMC REMAINED ON THE AMPLIFIED RIDGE
SIDE, BUT OVERALL MODELS SEEM TO BE CONVERGING SOMEWHAT AT THAT
POINT. BY FRIDAY THE 12/18Z GFS AND 12Z ECMWF AND THEIR 00Z RUNS
ALONG WITH THE 00Z CMC INDICATE SOME RETREAT OF THE MAIN UPPER LOW
BUT WITH ENERGY REMAINING WITHIN THE TROUGH FARTHER SOUTH. THE 12Z
ECMWF SEEMED PARTICULARLY AGGRESSIVE WITH CLOSING OFF A SEPARATE
LOW IN THE EAST-CENTRAL U.S. WITH A SLOWER MOVEMENT, WHILE THE GFS
IS MORE PROGRESSIVE. THERE ARE ALSO SOME DIFFERENCES WITH MODELS
FOR THE WESTERN U.S. AND HOW/WHEN THE SOUTHERN STREAM TROUGH MAY
MERGE, ALONG WITH HOW ADDITIONAL NORTHERN STREAM ENERGY MAY
SUPPRESS THE RIDGE FURTHER. THE WPC FORECAST LEANED TOWARD A
MIDDLE GROUND FOR ALL THIS BY FAVORING THE GFS/ECMWF/EC MEAN/GEFS
MEAN FOR LATE WEEK, BUT THE FORECAST LEANS TOWARD THE LOWER
PREDICTABILITY SIDE BY LATER IN THE PERIOD SO SIGNIFICANT CHANGES
TO THE FORECAST ARE POSSIBLE WITH TIME.
..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. RECENT MODEL TRENDS HAVE BEEN FOR
A SLIGHTLY FASTER SHORTWAVE AND FRONT IN NEW ENGLAND, WHICH WOULD
PUSH A SWATH OF MODERATE TO POTENTIALLY HEAVY RAINFALL DUE TO
CONSIDERABLE MOISTURE TRANSPORT EAST INTO CANADA RATHER THAN OVER
MAINE, BUT THE EXACT POSITIONING MAY NOT BE RESOLVED UNTIL THE
SHORT RANGE PERIOD. 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 MUCH OF
NEXT WEEK. OTHER THAN THOSE AREAS, MUCH OF THE CONTIGUOUS U.S. IS
FORECAST TO BE DRY DURING THE MEDIUM RANGE PERIOD, UNTIL A FEW
SHOWERS COULD COME INTO SOUTHERN CALIFORNIA AND THE SOUTHWEST WITH
THE SOUTHERN STREAM UPPER LOW/TROUGH DURING THE LATTER HALF OF THE
WEEK, AND THEN PRECIPITATION CHANCES COULD INCREASE ACROSS THE
NORTHWEST BY FRIDAY/SATURDAY WITH UPPER LEVEL ENERGY AND A SURFACE
FRONTAL SYSTEM.
THE AMPLIFIED WESTERN RIDGE WILL CAUSE WARMER THAN AVERAGE
TEMPERATURES ACROSS THE NORTHWEST IN PARTICULAR, WITH HIGHS
COMMONLY 10-20F ABOVE AVERAGE THROUGH MUCH OF NEXT WEEK,
POTENTIALLY LEADING TO SOME DAILY RECORD HIGHS. 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 AS WELL, WITH CURRENT FORECASTS SHOWING THE MOST
ANOMALOUS TEMPERATURES TO BE 10-15F ABOVE AVERAGE ACROSS THE
CENTRAL U.S. ON SATURDAY.
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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