841
FXUS02 KWBC 201900
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 PM EST SUN NOV 20 2022
VALID 12Z WED NOV 23 2022 - 12Z SUN NOV 27 2022
...A COUPLE OF LOW PRESSURE SYSTEMS INCLUDING A POSSIBLE
NOR'EASTER COULD CAUSE MEANINGFUL PRECIPITATION ACROSS EASTERN
PARTS OF THE U.S. LATE THIS WEEK...
..OVERVIEW
A QUASI-ZONAL UPPER PATTERN WITH EMBEDDED SHORTWAVES EXPECTED TO
BE IN PLACE ACROSS THE LOWER 48 AS THE MEDIUM RANGE PERIOD STARTS
EARLY WEDNESDAY SHOULD QUICKLY AMPLIFY THEREAFTER. THIS TRANSITION
WILL INVOLVE AN EASTERN PACIFIC TROUGH HELPING TO BUILD AN UPPER
RIDGE INTO THE WEST AND DIGGING OF DOWNSTREAM ENERGY INTO A
CENTRAL/EASTERN U.S. TROUGH BY THE LATTER HALF OF THE WEEK.
HOWEVER THERE HAS BEEN A DISCONCERTING LEVEL OF GUIDANCE SPREAD
AND RUN-TO-RUN VARIABILITY FOR THE ULTIMATE EVOLUTION OF INITIAL
PACIFIC TROUGH ENERGY, HOW QUICKLY THE WESTERN U.S. RIDGE ERODES,
AND WHAT BECOMES OF THE AMPLIFYING CENTRAL/EASTERN U.S. TROUGH. A
FAIR MAJORITY OF MODEL GUIDANCE CONTINUES TO ADVERTISE A
LARGE-SCALE UPPER TROUGH TRACKING EAST/NORTHEAST THROUGH THE
WEEKEND, SUPPORTING A CENTRAL-EASTERN U.S. FRONTAL SYSTEM
(ANCHORED BY LOW PRESSURE THAT COULD BE ANYWHERE BETWEEN CANADA
AND THE GREAT LAKES/OHIO VALLEY) AND A SEPARATE EAST COAST SYSTEM
LIFTING NORTHWARD. THIS PATTERN WOULD LEAD TO INCREASING CHANCES
FOR PRECIPITATION LATE THIS WEEK FOR THE EAST AND A POTENTIALLY
STRONG STORM AFFECTING NEW ENGLAND DURING THE WEEKEND. ON THE
OTHER HAND, THERE IS A PERSISTENT MINORITY SCENARIO THAT WOULD
HAVE AN UPPER LOW CLOSE OFF OVER NORTHERN MEXICO OR THE SOUTHERN
PLAINS, LEADING TO A SLOWER/SOUTHERN AREA OF SIGNIFICANT RAINFALL
AND LESS PRECIPITATION/SURFACE DEVELOPMENT OVER THE NORTHEAST.
MEANWHILE THE DIFFERENCES/ADJUSTMENTS WITH PACIFIC TROUGH ENERGY
HAVE BEEN LEADING TO SIGNIFICANT UNCERTAINTY OVER THE COVERAGE,
INTENSITY, AND DURATION FOR PACIFIC NORTHWEST PRECIPITATION AS
WELL.
..GUIDANCE AND PREDICTABILITY ASSESSMENT
IF ANYTHING, LATEST GUIDANCE HAS ADDED MORE UNCERTAINTY TO THE
FORECAST. THERE HAS BEEN A NOTICEABLE TREND TOWARD MORE CLUSTERING
FOR SOME DEGREE OF SEPARATION FOR INITIAL PACIFIC TROUGH ENERGY,
WITH THE NORTHERN STREAM PORTION OF THIS FLOW ULTIMATELY SERVING
TO FLATTEN THE WESTERN RIDGE MORE QUICKLY BY THE WEEKEND VERSUS
PRIOR CONSENSUS--YIELDING NEARLY ZONAL MEAN FLOW ONCE AGAIN BY
LATE IN THE WEEKEND INSTEAD OF MORE PERSISTENT RIDGING OVER THE
WEST-CENTRAL STATES. AT THE SAME TIME THERE IS STILL A LOT OF
SPREAD AND VARIABILITY FOR HOW THE LOWER 48 TROUGH WILL EVOLVE
FROM MIDWEEK ONWARD. 00Z/06Z GFS RUNS CONTINUED THE THEME BACK TO
THE 12Z/19 RUN OF PULLING AN UPPER LOW DOWN THROUGH THE
ROCKIES/NORTHERN MEXICO/SOUTHERN PLAINS REGION BUT THE 12Z RUN HAS
REVERTED TO A MORE PROGRESSIVE TROUGH WITH AN UPPER LOW TRACKING
ACROSS THE MID-LATITUDES OF THE EAST AND THEN THE SOUTHEAST CORNER
OF NEW ENGLAND (ESSENTIALLY A SLOWER VERSION OF THE 12Z CMC).
SHORTWAVE DIFFERENCES WITH THE GFS IN PARTICULAR ACTUALLY TRACE
BACK TO THE PACIFIC IN THE SHORT RANGE. ECMWF/CMC RUNS THAT HAVE
BEEN PART OF THE MAJORITY CLUSTER WITH THE MEANS HAVE TRENDED
NORTHWARD WITH THE SURFACE LOW ANCHORING THE INITIAL CENTRAL U.S.
FRONT (BUT THE 12Z ECMWF HAS COME BACK TO THE SOUTH) WHILE
MAINTAINING THE IDEA OF A LEADING EAST COAST DEVELOPMENT THAT
COULD ULTIMATELY BECOME FAIRLY STRONG BY THE TIME IT REACHES NEW
ENGLAND. ENSEMBLE MEMBERS OVER THE CENTRAL U.S. BY THE LATTER HALF
OF THE WEEK HAVE ACTUALLY DIVERGED OVER THE PAST DAY. A HIGHER
PERCENTAGE OF GEFS MEMBERS DEPICTED SOME VARIATION OF THE 00Z/06Z
GFS IDEA VERSUS 24 HOURS AGO, WHILE THE MINORITY OF ECENS MEMBERS
PULLING THE UPPER TROUGH FARTHER WEST/SOUTHWEST YESTERDAY HAS
DWINDLED TO ONLY ONE MEMBER (AND THAT ONE ONLY MATCHING WITH THE
UKMET VERSUS THE FARTHER SOUTHWEST 00Z/06Z GFS).
BASED ON THE GUIDANCE AVAILABLE FROM THE 00Z/06Z CYCLES, THE
UPDATED FORECAST REPRESENTED VARIOUS IDEAS FROM CONTINUITY AND
SIGNIFICANT CHANGES INTRODUCED BY A MAJORITY OF GUIDANCE. AN
OPERATIONAL GUIDANCE BLEND EARLY (QUICKLY SPLITTING GFS INPUT WITH
THE 06Z GEFS MEAN) FOLLOWED BY A TRANSITION TO THE GEFS/ECMWF
MEANS AND 00Z ECMWF/CMC ALLOWED FOR RELATIVE CONSISTENCY FOR THE
POTENTIAL SYSTEM ALONG THE EAST COAST, THOUGH REFLECTING THE
MAJORITY CLUSTER THAT TRENDED NORTHWARD FOR THE SURFACE LOW
ANCHORING THE INITIAL CENTRAL U.S. FRONTAL SYSTEM. GEFS MEAN
INCLUSION PROVIDED A MODEST NUDGE TOWARD THE POSSIBILITY OF SOME
ENERGY HANGING BACK IN THE SOUTHERN STREAM (WHICH COULD BE FROM A
COMBINATION OF INITIAL ENERGY NEAR BAJA CALIFORNIA AND ANY FLOW
FROM THE NORTHERN STREAM). MEANWHILE THE BLEND REFLECTS CONSENSUS
TRENDS TOWARD FLATTER MEAN FLOW BY NEXT WEEKEND, WITH MORE
PRECIPITATION REACHING THE NORTHWEST U.S.
..WEATHER/HAZARD HIGHLIGHTS
WEDNESDAY IS LIKELY TO BE FAIRLY DRY ACROSS THE LOWER 48, THOUGH
WITH PERHAPS SOME SHOWERS ACROSS FLORIDA AND THE SOUTHEASTERN
ATLANTIC COAST AS WELL AS PARTS OF THE SOUTHERN PLAINS, PLUS A FEW
RAIN AND SNOW SHOWERS IN NORTHERN PARTS OF THE ROCKIES AND PLAINS.
THEN AS THE UPPER TROUGH AMPLIFIES EAST OF THE ROCKIES BY
THANKSGIVING DAY AND BEYOND, GULF MOISTURE SHOULD STREAM INTO THE
EASTERN HALF OF THE U.S. AHEAD OF THE TROUGH. THE SOUTHEASTERN
QUADRANT OF THE U.S. NORTHWARD INTO THE OHIO VALLEY AND GREAT
LAKES MAY SEE SOME PRECIPITATION AROUND THANKSGIVING, WHILE
HEAVIER PRECIPITATION LOOKS MORE LIKELY ACROSS THE NORTHEASTERN
U.S. ON FRIDAY. CURRENT FORECASTS CONTINUE TO INDICATE THAT WINTRY
PRECIPITATION IS A BETTER POSSIBILITY FOR THE INTERIOR NORTHEAST
WHILE THE METROPOLITAN AREAS ALONG THE I-95 CORRIDOR ARE MORE
LIKELY TO GET RAIN. BUT STAY TUNED TO FUTURE FORECASTS AS THESE
UNCERTAIN DETAILS LIKE PRECIPITATION TYPES IN PARTICULAR AREAS
COULD CHANGE AS MODEL GUIDANCE EVENTUALLY COMES INTO BETTER
CONSENSUS WITH LOW TRACKS AND TEMPERATURES. DEPENDING ON THE
STRENGTH OF ONE OR MORE LOW PRESSURE CENTERS, WINDS COULD BECOME
BRISK TO STRONG FOR A TIME. ALSO NOTE THAT THERE IS STILL A
MINORITY POTENTIAL FOR SIGNIFICANTLY DIFFERENT PRECIPITATION
COVERAGE AND AMOUNTS, WHICH COULD INVOLVE MORE RAINFALL ACROSS THE
SOUTHERN TIER AND LOWER TOTALS (WITH WEAKER/MORE OFFSHORE LOW
PRESSURE) FARTHER NORTH. THEN BY NEXT WEEKEND, LAKE EFFECT SNOW IS
ONCE AGAIN A POSSIBILITY BEHIND THE UPPER TROUGH. THE NORTHWEST
MAY SEE A BRIEF PERIOD OF DRY WEATHER BUT MOISTURE COULD RETURN
INTO WESTERN WASHINGTON AS SOON AS THANKSGIVING DAY, WITH A SERIES
OF FRONTAL SYSTEMS SPREADING RAIN AND HIGH ELEVATION SNOW ACROSS
MORE OF THE NORTHWEST AND EVENTUALLY NORTHERN CALIFORNIA THROUGH
THE END OF THE WEEK AND NEXT WEEKEND.
TEMPERATURES IN THE MEDIUM RANGE PERIOD SHOULD BE OVERALL MORE
SEASONABLE COMPARED TO THOSE OF LAST WEEK. TEMPERATURES ARE LIKELY
TO TREND ABOVE AVERAGE ALONG THE WEST COAST BY MIDWEEK WITH PLUS
5-15F ANOMALIES EXPANDING INTO THE ROCKIES AND CENTRAL U.S. LATER
IN THE WEEK AS THE UPPER RIDGE BUILDS IN. WESTERN U.S.
TEMPERATURES SHOULD TREND BACK TOWARD NORMAL BY NEXT SUNDAY GIVEN
THE LATEST FORECAST OF UPPER FLOW BECOMING MORE ZONAL. CONVERSELY,
POST-FRONTAL COOLER TEMPERATURES ESPECIALLY IN TERMS OF HIGHS
SHOULD EXTEND FROM THE MISSISSIPPI VALLEY TOWARD THE EAST COAST
FRIDAY-SUNDAY AS THE UPPER TROUGH IS LIKELY TO MOVE THROUGH.
ANOMALIES WILL DEPEND UPON THE DETAILS OF THE EASTERN U.S. UPPER
TROUGH AND POTENTIAL EAST COAST SYSTEM, WHICH ARE STILL QUITE
UNCERTAIN.
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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