877
FXUS02 KWBC 161859
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
258 PM EDT SUN OCT 16 2022
VALID 12Z WED OCT 19 2022 - 12Z SUN OCT 23 2022
..OVERVIEW
THE MEDIUM RANGE PERIOD BEGINS WEDNESDAY WITH AN AMPLIFIED/BLOCKY
UPPER LEVEL FLOW PATTERN CONSISTING OF POTENT TROUGHING ACROSS THE
EASTERN HALF OF THE U.S. EXTENDING SOUTH FROM AN ANOMALOUSLY
STRONG UPPER LOW IN EASTERN CANADA AND AN UPPER RIDGE/HIGH OVER
MUCH OF THE WEST. THIS INITIAL PATTERN WILL PROMOTE RELATIVELY DRY
WEATHER OVER MUCH OF THE LOWER 48, ASIDE FROM LAKE EFFECT/ENHANCED
PRECIPITATION (INCLUDING SOME SNOW), ALONG WITH UNSEASONABLY
CHILLY TEMPERATURES OVER THE EASTERN HALF OF THE COUNTRY AND VERY
WARM WEATHER OVER THE NORTHERN HALF OF THE WEST. THEN LATEST
GUIDANCE STILL ADVERTISES A PRONOUNCED PATTERN CHANGE HEADING INTO
NEXT WEEKEND, WITH AN AMPLIFYING UPPER TROUGH BRINGING COOLER AND
WETTER WEATHER TO THE WEST WHILE AREAS EAST OF THE ROCKIES TREND
WARMER WITH THE GREATEST ANOMALIES OVER THE PLAINS. MEANWHILE A
SOUTHERN STREAM PACIFIC UPPER LOW SHOULD EVENTUALLY TRACK TOWARD
THE WESTERN U.S.-MEXICO BORDER AND MAY INCREASE RAINFALL CHANCES
OVER THE SOUTHWEST TO SOME DEGREE BY NEXT WEEKEND.
..MODEL AND PREDICTABILITY ASSESSMENT
THE FIRST COUPLE DAYS OF THE FORECAST SHOW GOOD AGREEMENT AND
STABILITY OVERALL, AS MIGHT BE EXPECTED GIVEN THE TYPICALLY GOOD
PREDICTABILITY OF AMPLIFIED FLOW. THERE ARE ONLY MINOR DIFFERENCES
WITH EMBEDDED SHORTWAVES AND ASIDE FROM ANY INFLUENCE ON LAKE
EFFECT PRECIPITATION, IMPACTS ON SENSIBLE WEATHER SHOULD BE
MINIMAL GIVEN THE OTHERWISE DRY PATTERN.
INTO DAY 6 SATURDAY THE GUIDANCE IS GRADUALLY CONVERGING WITH
RESPECT TO DETAILS OF THE PATTERN CHANGE AS AN UPPER TROUGH
REACHES THE NORTHWEST. THERE WERE SEVERAL 00Z GEFS MEMBERS THAT
DEPICTED A RIDGE AT THAT TIME BUT ONLY ONE CMC ENSEMBLE MEMBER
(SHIFTED A BIT EASTWARD) AND NO ECMWF MEMBERS. THE 12Z GEFS
MEMBERS SHOW A GREATER MEMBER PROPORTION SIDING WITH THE MAJORITY
TROUGH SCENARIO PER OTHER OPERATIONAL MODELS AND ENSEMBLE MEANS,
AS ONLY ONE MEMBER NOW SHOWS A RIDGE. BY SUNDAY THERE ARE MORE
DIFFERENCES WITH TROUGH SHAPE/TIMING AND UPSTREAM FLOW. THE 12Z
GFS HAS GONE TO A CLOSED LOW IN CONTRAST TO AN OPEN TROUGH IN
PRIOR RUNS (AND OTHER MODELS) WHILE LATEST CMC RUNS ARE SHIFTED A
BIT EAST WITH THE OVERALL PACIFIC/WESTERN U.S. PATTERN.
ELSEWHERE, GUIDANCE CONTINUES TO WAFFLE FOR THE SOUTHERN STREAM
PACIFIC UPPER LOW. GENERAL TREND OVER THE PAST DAY HAS BEEN SLOWER
(DELAYING ANY MOISTURE REACHING THE SOUTHWEST) BUT THE 06Z GFS
TOOK THIS TO AN APPARENT EXTREME. IN CONTRAST THE 12Z GFS JUMPS TO
THE FAST SIDE OF THE SPREAD BY SATURDAY. FINALLY, MODELS/ENSEMBLES
REMAIN INDECISIVE ABOUT WEAK SOUTHEAST U.S. ENERGY THAT MAY
SEPARATE FROM THE WESTERLIES AROUND THE END OF THE WEEK. THE WEAK
AND FAIRLY SMALL SCALE NATURE OF THIS ENERGY LEADS TO LOW
PREDICTABILITY IN THE MEDIUM RANGE TIME FRAME. OVERALL THE ECMWF
HAS BEEN THE MOST CONSISTENT WITH ITS FORECAST UPPER LOW AND TRACK
BUT STILL SHOWS SOME RUN-TO-RUN OSCILLATIONS (12Z RUN BACK TO THE
WEST). AMONG ENSEMBLE GUIDANCE, ECMWF MEMBERS HAVE A GREATER
PERCENTAGE DEPICTING SUCH A TROUGH/LOW RELATIVE TO THE
GEFS/CMCENS. THE RELATIVE LACK OF AGREEMENT AND LOW PREDICTABILITY
ULTIMATELY FAVOR MAINTAINING A CONSERVATIVE APPROACH TO THE
DEPICTION OF THIS FEATURE AND ITS POTENTIAL EFFECT ON THE WAVY
FRONT OFF THE SOUTHEAST.
THE WPC FORECAST FOR FRONTS/PRESSURES WAS BASED ON A BLEND OF THE
DETERMINISTIC 00Z/06Z MODELS TO RESOLVE LINGERING DETAIL QUESTIONS
DURING THE FIRST PART OF THE PERIOD, AND THEN INCORPORATED GEFS
AND EC ENSEMBLE MEANS AFTER EARLY FRIDAY AS OPERATIONAL MODELS
DIVERGED WITH VARIOUS DETAILS. THIS APPROACH MAINTAINED GOOD
CONTINUITY WITH THE PREVIOUS FORECAST ASIDE FROM TYPICAL NUDGES
REFLECTING LATEST TRENDS.
..SENSIBLE WEATHER AND POTENTIAL HAZARDS
THE CONTIGUOUS U.S. SHOULD OVERALL BE RATHER DRY ON
WEDNESDAY-THURSDAY, WITH THE EXCEPTION OF LAKE EFFECT RAIN/SNOW
DUE TO UPPER LEVEL ENERGY AND THE WESTERLY FLOW ACROSS THE
RELATIVELY WARM GREAT LAKES COMPARED TO THE COLD AIR TEMPERATURES.
PRECIPITATION AMOUNTS ARE LIKELY TO BE HIGHER THROUGH WEDNESDAY
DOWNWIND OF THE LOWER GREAT LAKES IN PARTICULAR BUT WITH SOME
LINGERING SHOWERS POSSIBLE INTO THURSDAY. SOUTH FLORIDA MAY SEE A
FEW RAIN SHOWERS AS WELL. BY LATE IN THE WEEK THROUGH NEXT
WEEKEND, THE UPPER TROUGH ARRIVAL/AMPLIFICATION ACROSS THE WEST
AND AN ASSOCIATED SURFACE FRONT PUSHING ACROSS THE REGION SHOULD
PRODUCE A NOTABLE INCREASE IN PRECIPITATION COVERAGE AND
INTENSITY. BEST FOCUS WILL BE OVER FAVORED WINDWARD TERRAIN OVER
THE PACIFIC NORTHWEST AND THEN EXTENDING INTO THE NORTHERN-CENTRAL
ROCKIES, WITH HIGHER ELEVATION SNOW AND LOWER ELEVATION RAIN.
CONFIDENCE IN A MEANINGFUL PRECIPITATION EVENT IS INCREASING BUT
IT WILL TAKE MORE TIME TO REFINE IMPORTANT DETAILS THAT WILL
INFLUENCE PRECISE TIMING AND TOTALS AT ANY PARTICULAR LOCATION.
THE SOUTHERN STREAM PACIFIC UPPER LOW MAY REACH FAR ENOUGH EAST BY
THIS WEEKEND TO PRODUCE SOME RAINFALL OVER THE SOUTHWEST.
MEANWHILE SOME RAIN MAY BE POSSIBLE ALONG OR NEAR THE EAST COAST
THIS WEEKEND, BUT WITH LOW CONFIDENCE ON HOW MUCH RAIN COULD FALL
ONSHORE.
THE AMPLIFIED WESTERN RIDGE IN PLACE FOR THE EARLY PART OF THE
PERIOD 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 30S
SPREADING SOUTH POSSIBLY ALL THE WAY TO THE GULF COAST (MOBILE,
ALABAMA FOR EXAMPLE) FOR 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 AROUND FRIDAY AND THEN
TRANSITIONS TO A WESTERN TROUGH/EASTERN RIDGE PATTERN, ABOVE
NORMAL TEMPERATURES SHOULD GET PUSHED INTO THE CENTRAL U.S., WITH
THE NORTH-CENTRAL PLAINS SEEING HIGHS OF 10-20F ABOVE AVERAGE.
EXPECT TEMPERATURES TO REBOUND OVER THE EAST, REACHING NEAR NORMAL
OVER THE SOUTHEAST AFTER A CHILLY MORNING ON SATURDAY WHILE
TRENDING ABOVE NORMAL OVER THE NORTHEAST. MUCH OF THE WEST SHOULD
SEE MODERATELY BELOW NORMAL HIGHS BY NEXT SUNDAY.
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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