582
FXUS02 KWBC 141853
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
152 PM EST TUE NOV 14 2023
VALID 12Z FRI NOV 17 2023 - 12Z TUE NOV 21 2023
...PATTERN OVERVIEW AND GUIDANCE EVALUATION/PREDICTABILITY
ASSESSMENT...
A SPLIT FLOW PATTERN IS FORECAST OVER MUCH OF NORTH AMERICA
THROUGH THIS WEEKEND AND INTO NEXT WEEK. A COUPLE UPPER LEVEL
TROUGHS WILL SWING ACROSS THE CONTINENTAL U.S. THROUGH THE PERIOD
WITH EMBEDDED SYSTEMS IN THE NORTHERN AND SOUTHERN STREAM FLOWS,
AND TIMING AND STRENGTH OF THESE FEATURES WILL BE DEPENDENT ON THE
DEGREE OF UPSTREAM AMPLIFICATION. MODEL GUIDANCE HAS BEEN
CONSISTENTLY SHOWING A HIGHLY AMPLIFIED WAVE, WHICH WOULD RESULT
IN SLOWER SYSTEM PROGRESSION.
MODEL SOLUTIONS ARE FAIRLY SIMILAR FOR DAYS 3-5 (FRIDAY THROUGH
SUNDAY), BUT SOLUTIONS DIVERGE SIGNIFICANTLY ON DAYS 6 AND 7
(MONDAY AND TUESDAY). FOR THIS FORECAST PACKAGE, WPCS MODEL BLEND
FAVORS THE 06Z GFS AND 00Z ECMWF, WHICH HAVE SHOWN CONSISTENT
AMPLIFICATION AND RELATIVELY SLOWER PROGRESSION OF FEATURES
THROUGH THE PERIOD. THE 00Z CMC WAS THE FASTEST OUT OF THE
AVAILABLE GUIDANCE, THOUGH NOT UNREASONABLE, AND WAS GIVEN LESS
WEIGHT IN THE BLEND FOR THIS REASON. THE GEFS AND EC MEANS WERE
FACTORED IN HEAVILY FOR DAYS 6 AND 7 TO PRODUCE A MIDDLE OF THE
ROAD SOLUTION. THE 12Z GFS AND CMC RUNS BECAME AVAILABLE AFTER THE
FORECAST WAS MADE, BUT BOTH ARE TRENDING TOWARDS WPCS MIDDLE OF
THE ROAD SOLUTION WITH THE GFS SPEEDING UP SLIGHTLY AND THE CMC
SLOWING DOWN.
..WEATHER/HAZARDS HIGHLIGHTS
THE SLOW AND STEADY MARCH OF AN AMPLIFIED AND DYNAMIC UPPER TROUGH
AND ASSOCIATED WAVY FRONTAL SYSTEM ACROSS THE GREAT LAKES/MIDWEST
AND NORTHEAST SHOULD FAVOR INCREASING PRECIPITATION CHANCES ACROSS
THE REGION LATE THIS WEEK INTO THIS WEEKEND. THE CURRENT FORECAST
HAS MOISTURE INCREASING SUBSTANTIALLY OVER THE FAR NORTHEAST AS A
COASTAL LOW LIFTS NORTHWARD OFF THE EAST COAST. THIS MAY FOCUS
SEVERAL INCHES OF RAIN IN EASTERN NEW ENGLAND WITH BEST LIKELIHOOD
IN DOWNEAST MAINE, BUT MODEST INSTABILITY AND RAIN RATES IN
COMBINATION WITH THE EXISTING ANTECEDENT CONDITIONS DOES NOT SEEM
TO SUPPORT ISSUANCE OF ANY EXCESSIVE RAINFALL OUTLOOK THREAT AREAS
AT THIS TIME.
FOR THE WEST/SOUTHWEST, THE SLOW APPROACH OF THE CLOSED SOUTHERN
STREAM UPPER LOW WILL ONLY GRADUALLY BRING IN BOUTS OF LIGHT TO
MODERATE TERRAIN ENHANCED RAIN AND MOUNTAIN SNOW THAT EXPAND
EASTWARD IN TIME. THE DELAY IN THE HEIGHT FALLS LIKELY LESSENS THE
STRONGER MOISTURE FLUX INTO THE AREA AS THE SYSTEM FILLS BEFORE
MOVING ASHORE, BUT MOST AREAS OF CALIFORNIA INTO THE SOUTHWEST
WILL SEE AT LEAST MEASURABLE RAINFALL (ESPECIALLY COASTAL AREAS)
OUTSIDE SOME OF THE SHADOWED DESERTS. GIVEN THE CONSISTENT SLOW
TREND IN THE GUIDANCE, NO EXCESSIVE RAINFALL RISK AREAS ARE IN
PLACE. AS THE AMPLIFIED UPPER SYSTEM FINALLY CROSSES THE DIVIDE,
RETURN FLOW OUT OF THE GULF OF MEXICO WILL HELP INCREASE MOISTURE
OVER THE PLAINS AND MISSISSIPPI VALLEY, WITH RAIN CHANCES
EXPANDING IN COVERAGE LATE WEEKEND INTO EARLY NEXT WEEK. LEAD
CYCLOGENESIS AND FRONTOGENESIS MAY INCREASINGLY SUPPORT A RENEWED
HEAVY RAINFALL PATTERN WITH FOCUS OVER THE LOWER MISSISSIPPI
VALLEY IN ABOUT A WEEK TO MONITOR. IN THE WAKE OF THIS SYSTEM,
RENEWED PACIFIC SYSTEM ENERGY WITHIN NORTHERN STREAM FLOW IS
EXPECTED TO DIG MORE SHARPLY SOUTHEASTWARD FROM THE NORTHWEST
THROUGH THE ROCKIES THIS WEEKEND INTO EARLY NEXT WEEK AND FOCUS A
SWATH OF RAIN AND TERRAIN ENHANCED MOUNTAIN SNOW GIVEN UPPER
DYNAMIC SUPPORT.
DOLAN/SCHICHTEL
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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