178
FXUS02 KWBC 171859
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
158 PM EST FRI NOV 17 2023
VALID 12Z MON NOV 20 2023 - 12Z FRI NOV 24 2023
..PATTERN OVERVIEW
THE DOMINANT FOCUS OF NEXT WEEK'S FORECAST WILL BE A DEEPENING
STORM SYSTEM FORECAST TO TRACK FROM THE SOUTH-CENTRAL PLAINS
THROUGH THE GREAT LAKES AND INTO EAST-CENTRAL CANADA, IN RESPONSE
TO DIGGING WESTERN CANADA ENERGY THAT COULD PHASE WITH AN INITIAL
PLAINS UPPER LOW/TROUGH. THIS SHOULD YIELD A DEEP UPPER LOW
SOMEWHERE BETWEEN THE UPPER MIDWEST/GREAT LAKES AND SOUTHERN
CANADA BY WEDNESDAY. THE UPPER LOW AND TROUGH TO THE SOUTH SHOULD
GRADUALLY LIFT NORTHWARD LATE IN THE WEEK WHILE A SHORTWAVE TROUGH
MOVES INTO THE WEST. THIS EVOLUTION WOULD BRING A WINDY STORM
SYSTEM WITH POTENTIAL FOR SIGNIFICANT PRECIPITATION OVER THE
EASTERN HALF OF THE COUNTRY DURING THE FIRST HALF OF THE WEEK,
FOLLOWED BY AN EXPANDING AREA OF BELOW NORMAL TEMPERATURES OVER
MANY AREAS EAST OF THE ROCKIES WITH VERY UNCERTAIN HEAVY LAKE
EFFECT SNOW POTENTIAL TO THE LEE OF THE GREAT LAKES. THE WEST WILL
BE FAIRLY DRY BUT NORTHERN AREAS MAY SEE SOME PRECIPITATION AS THE
LATE WEEK TROUGH MOVES IN.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THERE REMAINS A SIGNIFICANT AMOUNT OF UNCERTAINTY SURROUNDING THE
EVOLUTION OF THE FORECAST IN THE CENTRAL-EASTERN PART OF THE
NATION NEXT WEEK. BASED ON THE 00Z/06Z GUIDANCE, THERE WAS
SUFFICIENT AGREEMENT ON EVENTUAL PHASING OF NORTHERN STREAM ENERGY
THROUGH CENTRAL CANADA AND A SOUTHERN STREAM LOW/TROUGH IN THE
PLAINS RESULTING IN A DEEP LOW OVER THE GREAT LAKES AROUND MID TO
LATER NEXT WEEK. THIS KIND OF EVOLUTION WOULD SUPPORT SIGNIFICANT
EASTERN U.S. PRECIPITATION POTENTIAL EARLY NEXT WEEK, FOLLOWED BY
HEAVY LAKE EFFECT SNOWS DOWNWIND OF LAKES ERIE AND ONTARIO NEXT
THURSDAY/THANKSGIVING. THE 06Z GFS WAS AN OUTLIER SHOWING SLIGHTLY
LESS PHASING AND A MORE NEGATIVE TILT TO THE SOUTHERN STREAM
SYSTEM INTO THE MID-ATLANTIC AND DEVELOPMENT OF A DEEPENING
SURFACE LOW OFF THE NORTHEAST COAST. THE WPC FORECAST FROM THIS
MORNING WAS BASED ON THE 00Z/06Z GUIDANCE, UTILIZING GOOD
AGREEMENT THE FIRST HALF OF THE WEEK FOR A PURELY DETERMINISTIC
BLEND AND INCREASING USAGE OF THE ENSEMBLE MEANS AMIDST INCREASING
UNCERTAINTY IN THE DETAILS OF THE UPPER LOW/PHASING AND ALSO
ADDITIONAL SHORT WAVE ENERGY INTO THE WEST. THIS HELPED MAINTAIN
GOOD CONTINUITY WITH THE PREVIOUS WPC FORECAST AS WELL.
THE NEW 12Z GUIDANCE (AVAILABLE AFTER FORECAST GENERATION TIME)
HAS TRENDED MUCH LESS PHASED NOW WITH THIS SYSTEM AND THE SPEED OF
THE NORTHERN STREAM TROUGH IN THE 12Z GFS AND CMC HAS SPED UP
SIGNIFICANTLY, POSSIBLY NOT EVEN ALLOWING THE SOUTHERN STREAM
PORTION TO CATCH UP. THIS BRINGS A FLATTER PATTERN ACROSS THE
NORTHEAST LATE WEEK AND DECREASES POTENTIAL FOR SIGNIFICANT LAKE
EFFECT SNOWFALL ACROSS THE GREAT LAKES NEXT WEEK. HOWEVER, THE 12Z
ECMWF CONTINUES TO SUPPORT A MORE PHASED SOLUTION BUT MAY BE MORE
IN THE MINORITY NOW. NEEDLESS TO SAY, THE OVERALL PATTERN ACROSS
THE CENTRAL AND EASTERN U.S. DURING THE UPCOMING HOLIDAY WEEK
REMAINS VERY UNCERTAIN BUT THERE REMAINS SOME POTENTIAL FOR RATHER
IMPACTFUL WEATHER TO AFFECT TRAVEL LEADING UP TO AND INCLUDING THE
THANKSGIVING HOLIDAY ACROSS THE EASTERN U.S. AND GREAT LAKES
REGIONS.
..WEATHER/HAZARDS HIGHLIGHTS
HEAVY RAINFALL POTENTIAL WILL INCREASE ACROSS THE SOUTH-CENTRAL TO
EASTERN U.S. FOR THE UPCOMING HOLIDAY WEEK AS A DEEPENING LOW
PRESSURE SYSTEM TRACKS FROM THE SOUTH-CENTRAL PLAINS THROUGH THE
GREAT LAKES. ALSO THE TIGHTENING PRESSURE GRADIENT BEHIND THE LOW
SHOULD PRODUCE A PERIOD OF HIGH WINDS ACROSS THE HIGH PLAINS EARLY
NEXT WEEK, WITH LESS EXTREME BUT STILL BRISK TO STRONG WINDS
ACROSS THE PLAINS AND INTO THE GREAT LAKES. INSTABILITY AHEAD OF
THE SYSTEM COULD BRING SEVERE WEATHER POTENTIAL TO THE CENTRAL
GULF COAST AROUND MONDAY, AS HIGHLIGHTED BY STORM PREDICTION
CENTER OUTLOOKS. WITH THE SOUTHERN TIER CONVECTIVE POTENTIAL, THE
DAY 4 EXCESSIVE RAINFALL OUTLOOK COVERING MONDAY-MONDAY NIGHT
MAINTAINS A MARGINAL RISK AREA TO REFLECT THE ONGOING SIGNAL FOR
ORGANIZED AND POSSIBLY HEAVY RAINFALL, DESPITE FAIRLY DRY
ANTECEDENT CONDITIONS. FOR THE DAY 5 ERO (TUESDAY-TUESDAY NIGHT),
A MARGINAL RISK AREA HAS BEEN MAINTAINED FROM THE PREVIOUS
ISSUANCE FROM THE MID-ATLANTIC SOUTHWEST INTO ALABAMA AS ABUNDANT
MOISTURE SHOULD STREAM INTO THE SOUTHERN AND EASTERN U.S. AHEAD OF
THE MISSISSIPPI VALLEY-GREAT LAKES STORM/FRONTAL SYSTEM. WHILE
ACTIVITY WILL BE FAIRLY PROGRESSIVE AND GROUND CONDITIONS WILL
START OUT ON THE DRY SIDE, LOCALIZED RUNOFF ISSUES WILL BE
POSSIBLE. WITHIN THIS OVERALL AREA, THE MID-ATLANTIC MAY BE A
LITTLE MORE SENSITIVE GIVEN THE COMBINATION OF HIGHEST QPF SIGNALS
IN MODEL/ENSEMBLE GUIDANCE AND POTENTIAL FOR IMPAIRED DRAINAGE DUE
TO LEAVES/URBANIZATION/ETC. PRECIPITATION WILL CONTINUE THROUGH
NEW ENGLAND BY MIDWEEK. SNOW WILL BE POSSIBLE ON THE FAR NORTHWEST
PERIPHERY OF THE MOISTURE SHIELD, AND POTENTIALLY IN NEW ENGLAND
AT THE START OF THE EVENT. A PERIOD OF LAKE EFFECT SNOW WILL BE
POSSIBLE AFTER SYSTEM PASSAGE, WITH DURATION AND TOTALS DEPENDENT
ON HOW QUICKLY THE SYSTEMS LIFTS AWAY. A MORE PHASED SYSTEM AS
DESCRIBED ABOVE, WOULD RESULT IN POSSIBLY SIGNIFICANT SNOWFALL
TOTALS ESPECIALLY DOWNWIND OF LAKES ERIE AND ONTARIO FOR
THANKSGIVING, BUT THIS REMAINS HIGHLY UNCERTAIN THOUGH COULD BE
PARTICULARLY IMPACTFUL GIVEN THE UPCOMING HOLIDAY. THE ROCKIES MAY
SEE LINGERING PRECIPITATION EARLY IN THE WEEK. OTHERWISE THE WEST
SHOULD BE DRY EARLY-MID WEEK. A SYSTEM MOVING INTO THE REGION LATE
IN THE WEEK MAY BRING MOSTLY LIGHT TOTALS ACROSS NORTHERN AREAS,
POSSIBLY EXTENDING INTO THE PLAINS FRIDAY. SOME OF THE LATEST
GUIDANCE SUGGESTS SOME HEAVY SNOWFALL POTENTIAL FOR PARTS OF THE
NORTHERN ROCKIES AROUND THANKSGIVING, BUT STILL WITH A LOT OF
UNCERTAINTY IN THE DETAILS.
THE MAIN STORY FOR TEMPERATURES WILL BE THE INCREASING COVERAGE OF
BELOW NORMAL READINGS FROM THE NORTHERN-CENTRAL HIGH PLAINS
EASTWARD MID-LATE WEEK. BY THAT TIME EXPECT LOCATIONS FROM THE
HIGH PLAINS INTO GREAT LAKES TO SEE ONE OR MORE DAYS WITH HIGHS
10-20F BELOW NORMAL. THE WEST WILL TREND FROM NEAR OR SLIGHTLY
BELOW NORMAL EARLY IN THE WEEK TO MODERATELY ABOVE NORMAL
WEDNESDAY, AND THEN DRIFT BACK TO NEAR OR SLIGHTLY BELOW NORMAL
TOWARD THE END OF THE WEEK.
SANTORELLI/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 FORECAST, EXCESSIVE RAINFALL OUTLOOK,
WINTER WEATHER OUTLOOK PROBABILITIES, HEAT INDICES AND KEY
MESSAGES 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
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=OVW
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