504
FXUS02 KWBC 160659
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 AM 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 PATTERN SHOULD PERSIST THROUGH 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. A PATTERN CHANGE APPEARS LIKELY LATE IN THE WEEK, WITH
OVERALL DEAMPLIFICATION OF THE UPPER FLOW FRIDAY BEFORE TROUGHING
LOOKS TO COME INTO THE WEST OVER THE WEEKEND, WHICH SHOULD FOCUS
THE WARMTH OVER THE PLAINS WITH A TREND TOWARD MORE NORMAL
TEMPERATURES ELSEWHERE BEFORE EVENTUAL COOLING IN THE WEST.
..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 EMBEDDED ENERGIES WITHIN THE UPPER
LOW/TROUGH IN THE EAST AND EXACT FRONTAL POSITIONS, BUT WITHOUT
TOO MANY IMPACTS ON THE SENSIBLE WEATHER SINCE FRONTAL PASSAGES
WILL MAINLY BE DRY BY THE MEDIUM RANGE PERIOD. 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 WITH THE ECMWF ON THE
SLOWER SIDE, WITH THE 00Z ECMWF MEAN BETWEEN THE TWO EXTREMES.
NEWER 00Z RUNS ARE ON THE WHOLE SLOWER TO BRING THE FEATURE
ONSHORE COMPARED TO THE 12/18Z GUIDANCE, SO THE DETAILS ARE YET TO
BE FIGURED OUT.
OVER THE PAST DAY OR SO, GUIDANCE HAS COME INTO BETTER AGREEMENT
ON THE LARGE SCALE WITH RESPECT TO HOW QUICKLY INCOMING PACIFIC
FLOW BREAKS DOWN THE UPPER RIDGE OVER THE WEST. THIS LOOKS TO
BEGIN ON THURSDAY WITH ENERGY OVER WESTERN CANADA WITH LOW
AMPLITUDE TROUGHING PERHAPS GETTING ESTABLISHED ATOP THE NORTHERN
ROCKIES BY FRIDAY, WHILE ADDITIONAL ENERGY UPSTREAM COMES IN TO
AMPLIFY TROUGHING OVER THE PACIFIC NORTHWEST NUDGING EASTWARD FOR
THE WEEKEND. THE INCOMING 00Z GUIDANCE HAS TENDED TO BE ON THE
SAME PAGE WITH THE TIMING AND EVOLUTION OF THE TROUGH DEVELOPMENT.
LESS CERTAIN IS THE POTENTIAL FOR THE TIMING OF THE PHASING OF
THIS DEVELOPING TROUGH WITH THE SOUTHERN STREAM, WHICH WILL TAKE
ADDITIONAL TIME TO RESOLVE.
ANOTHER POSSIBLE ISSUE FOR THE LATTER PART OF THE PERIOD IS WITH
ENERGY SEPARATING FROM THE EASTERN TROUGH INTO THE SOUTHERN STREAM
WHILE THE OVERALL NORTHERN STREAM EASTERN TROUGH RETREATS LATE
WEEK. THIS RELATIVELY SMALLER SCALE FEATURE REMAINS LESS
PREDICTABLE AS ECMWF RUNS HAVE PERSISTENTLY SHOWN A SLOW-MOVING
AND ENERGETIC FEATURE BUT GFS AND CMC RUNS HAVE WAFFLED, AND MOST
ENSEMBLE MEMBERS THAT ARE AGGRESSIVE WITH THE FEATURE ARE ECMWF
MEMBERS.
THE WPC FORECAST FOR FRONTS/PRESSURES WAS BASED ON A BLEND OF THE
DETERMINISTIC 12/18Z MODELS TO RESOLVE LINGERING DETAIL QUESTIONS
DURING THE FIRST PART OF THE PERIOD, AND THEN INCORPORATED GEFS
AND EC ENSEMBLE MEANS BY DAY 5 AND BEYOND AS OPERATIONAL MODELS
DIVERGED WITH SOME DETAILS. THIS APPROACH SEEMED TO PROVIDE GOOD
CONTINUITY WITH THE PREVIOUS FORECAST THOUGH WITH A NUDGE TOWARD
RECENT 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, ALONG WITH SOUTHERN CALIFORNIA INTO THE
SOUTHWEST WITH THE SOUTHERN STREAM LOW/TROUGH APPROACHING. BY LATE
IN THE WEEK, THE UPPER TROUGH ARRIVAL/AMPLIFICATION ACROSS THE
WEST AND AN ASSOCIATED SURFACE FRONT PUSHING ACROSS THE REGION IS
FORECAST TO SPREAD NOTABLE PRECIPITATION CHANCES INTO AND
EXPANDING ACROSS THE WEST, WITH TYPICAL TERRAIN ENHANCEMENT IN THE
PACIFIC NORTHWEST AND ROCKIES WITH HIGHER ELEVATION RAIN AND LOWER
ELEVATION SNOW. MEANWHILE SOME RAIN MAY BE POSSIBLE ALONG 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.
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
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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