269
FXUS02 KWBC 060658
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
158 AM EST WED MAR 06 2024
VALID 12Z SAT MAR 09 2024 - 12Z WED MAR 13 2024
...WET PATTERN OVER THE EASTERN U.S. THIS WEEKEND WITH PARTS OF
THE INTERIOR NORTHEAST POSSIBLY SEEING SOME SNOW EXTEND INTO EARLY
NEXT WEEK...
...MULTI-DAY UNSETTLED PERIOD ALONG THE NORTHERN-CENTRAL WEST
COAST STARTING LATE THIS WEEK...
..OVERVIEW
GUIDANCE CONTINUES TO SHOW STRONG SURFACE LOW PRESSURE DEVELOPMENT
OVER THE EASTERN U.S. THIS WEEKEND IN RESPONSE TO THE LIKELY
CLOSING OF AN UPPER LOW WITHIN THE TROUGH PROGRESSING INTO/THROUGH
THE EAST. THIS SYSTEM WILL SPREAD A BROAD AREA OF MOISTURE ACROSS
THE EASTERN STATES THROUGH THE WEEKEND WITH SOME AREAS SEEING
HEAVY RAINFALL AND PARTS OF NEW ENGLAND LIKELY TO RECEIVE SOME
SNOW. A BROADENING DRIER TREND WILL EXTEND FROM THE CENTRAL INTO
EASTERN U.S. BEHIND THIS STORM. MEANWHILE A SERIES OF SHORTWAVES
AND SURFACE FRONTS WILL PUSH INTO THE WEST, SUPPORTING MULTIPLE
DAYS OF RAIN AND HIGHER ELEVATION SNOW OVER THE PACIFIC NORTHWEST
AND NORTHERN CALIFORNIA ALONG WITH INCREASING SNOWFALL OVER THE
NORTHERN ROCKIES BY EARLY NEXT WEEK. A MEAN RIDGE ALOFT SETTING
UP OVER THE CENTRAL U.S. WILL SUPPORT AN EXPANDING AREA OF WELL
ABOVE NORMAL TEMPERATURES FROM PORTIONS OF THE PLAINS INTO THE
GREAT LAKES DURING THE FIRST HALF OF NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
SUCCESSIVE GUIDANCE RUNS HAVE BEEN GRADUALLY IMPROVING THEIR
CLUSTERING FOR THE SYSTEM DEVELOPING OVER THE EASTERN U.S. MOST
DYNAMICAL AND MACHINE LEARNING MODELS HAVE GENERALLY BEEN LEANING
TOWARD MAINTAINING TWO DEFINED SURFACE LOW CENTERS FROM SATURDAY
INTO SUNDAY, ALBEIT WITH SOME DIFFERENCES IN EMPHASIS, BEFORE
SOLUTIONS CONVERGE TOWARD THE DOMINANT SURFACE LOW BEING NEAR THE
COAST OF MAINE AS OF EARLY MONDAY. LATEST UKMET RUNS HAVE BEEN A
BIT ON THE SLOW SIDE FOR THE UPPER LOW FORECAST TO FORM OVER THE
GREAT LAKES AND THEN TRACK EASTWARD. RECENT ECMWF RUNS WERE ALSO
A BIT ON THE SLOWER SIDE BUT THE NEW 00Z RUN HAS SHIFTED A LITTLE
EAST (WHICH ALSO HAS BETTER SUPPORT FROM THE MACHINE LEARNING
MODELS). AN OPERATIONAL BLEND INCORPORATING MORE 18Z GFS/12Z
ECMWF ALONG WITH SOME 12Z CMC AND LEAST WEIGHT FROM THE 12Z UKMET
REFLECTED THE BEST CONSENSUS AND REASONABLE CONTINUITY FOR THIS
FORECAST UPDATE.
ALONG THE WEST COAST, THERE IS GOOD AGREEMENT FOR THE FIRST
SHORTWAVE OF THE SERIES ARRIVING ON SATURDAY AND THEN MODERATE
CLUSTERING FOR THE NEXT ONE ARRIVING AROUND SUNDAY. THE NEW 00Z
UKMET STRAYS TO THE SLOW SIDE WHILE REMAINING GUIDANCE SHOWS
TYPICAL SPREAD FOR AMPLITUDE AND TIMING. CONFIDENCE STEADILY
DECREASES WITH TIME AS THESE FEATURES CONTINUE EASTWARD THROUGH
THE LARGER SCALE MEAN RIDGE COVERING THE CENTRAL U.S. BY
TUESDAY-WEDNESDAY RECENT GUIDANCE HAS BEEN CONSISTENTLY IN
CONFLICT REGARDING HOW MUCH TROUGHING WILL MOVE FROM THE EAST
PACIFIC INTO WESTERN U.S., WITH GFS/GEFS RUNS GENERALLY LEANING
TOWARD FLATTER FLOW AND THE ECMWF/CMC AND THEIR MEANS (PLUS THE
ICON) ADVERTISING MORE AMPLIFIED TROUGHING. THE MAJORITY OF
LATEST MACHINE LEARNING MODELS WOULD FAVOR TILTING MORE TOWARD THE
ECMWF CLUSTER, THOUGH THE ML MODELS ALONG WITH TELECONNECTIONS
RELATIVE TO THE EAST PACIFIC UPPER RIDGE'S POSITIVE HEIGHT ANOMALY
CENTER OFFER POTENTIAL FOR THE WESTERN U.S. UPPER TROUGH THAT
DEVELOPS BY WEDNESDAY TO BE A LITTLE EAST OF THE ECMWF. NOTE THAT
WHILE THE NEW 00Z GFS STILL SHOWS FLATTER FLOW OVER THE WEST AS OF
EARLY WEDNESDAY, IT DOES TREND MORE STRONGLY TOWARD THE ECMWF IDEA
A DAY LATER. THE 00Z GEFS MEAN ALSO SHOWS A TREND TOWARD THE
ECMWF MEAN. THESE CONSIDERATIONS THROUGH THE 12Z/18Z GUIDANCE
RUNS LED TO TILTING THE FORECAST ABOUT 70 PERCENT TOWARD THE
ECMWF/CMC/ECENS SCENARIO BY LATE IN THE PERIOD.
..WEATHER/HAZARDS HIGHLIGHTS
GUIDANCE CONTINUES TO SHOW AN ACTIVE WEATHER PATTERN FOR THIS
WEEKEND OVER THE EAST, WITH AN ELONGATED AXIS OF SURFACE LOW
PRESSURE OVER THE EAST-CENTRAL U.S. AS OF EARLY SATURDAY LIKELY
DEEPENING AND CONSOLIDATING INTO A STRONG SYSTEM NEAR THE MAINE
COAST BY EARLY MONDAY. THIS STORM SHOULD THEN TRACK OFF TO THE
EAST. DURING THE SATURDAY-SATURDAY NIGHT PERIOD COVERED BY THE
DAY 4 EXCESSIVE RAINFALL OUTLOOK, GUIDANCE CONTINUES TO EMPHASIZE
TWO GENERAL AREAS OF ENHANCED RAINFALL AS THE STORM SYSTEM
DEVELOPS. ONE IS OVER THE SOUTHEAST, REFLECTING EASTWARD
CONTINUATION OF HEAVIER CONVECTION EXPECTED FRIDAY (NOW IN THE
SHORT RANGE TIME FRAME). THE ONGOING MARGINAL RISK AREA CONTINUES
TO REFLECT FAVORABLE SIGNALS FOR AT LEAST ONE AXIS OF HEAVY
RAINFALL BUT SO FAR GUIDANCE HAS BEEN RELUCTANT TO IMPROVE ITS
CLUSTERING FOR TIMING/LOCATION DETAILS. THEREFORE CONTINUE TO
HOLD OFF WITH AN EMBEDDED SLIGHT RISK AREA BUT WITH THE
EXPECTATION THAT IMPROVED GUIDANCE AGREEMENT SHOULD EVENTUALLY
SUPPORT THIS REFINEMENT. THE OTHER AREA OF ENHANCED RAINFALL
POTENTIAL EXTENDS ACROSS PARTS OF THE OHIO VALLEY/LOWER GREAT
LAKES/NORTHERN MID-ATLANTIC, BUT WITH LESS INSTABILITY SUGGESTED.
A MARGINAL RISK AREA OVER THIS REGION ACCOUNTS FOR A COMBINATION
OF MODEL QPF SIGNALS, AND OVER THE MID-ATLANTIC WET GROUND
CONDITIONS FROM SHORTER-TERM RAINFALL, WITH NEW GUIDANCE NOT
REALLY PROVIDING A COMPELLING NEED TO CHANGE THIS RISK AREA FOR
NOW. GOING INTO DAY 5 (SUNDAY-SUNDAY NIGHT), AREAS ALONG AND A
LITTLE INLAND FROM THE NEW ENGLAND COAST MAY SEE A PERIOD OF
STRONG ONSHORE FLOW THAT WOULD SUPPORT A PERIOD OF HEAVY RAINFALL.
THUS THE DAY 5 ERO HAS INTRODUCED A MARGINAL RISK AREA FOR THIS
ACTIVITY. EXPECT GREATER POTENTIAL FOR SNOW FARTHER INLAND OVER
NEW ENGLAND, WITH SOME LOCATIONS POSSIBLY COLD ENOUGH FOR SOME
SNOW ALREADY AS THE SYSTEM REACHES THE GREAT LAKES/MID-ATLANTIC,
FOLLOWED BY THE PATTERN BECOMING INCREASINGLY FAVORABLE FOR SNOW
AS LOW PRESSURE EMPHASIS SHIFTS TO ALONG/OFFSHORE THE COAST BY
MONDAY. THE WINTER WEATHER OUTLOOK PROBABILITIES FOR AT LEAST
0.25 INCH LIQUID IN THE FORM OF SNOW STILL EXCEED 50 PERCENT
ACROSS PORTIONS OF INTERIOR NEW ENGLAND FOR THE SUNDAY-SUNDAY
NIGHT PERIOD. EXPECT SOME LAKE EFFECT/TERRAIN-ENHANCED SNOW TO
THE LEE OF THE EASTERN GREAT LAKES, WHILE PARTS OF NORTHERN NEW
ENGLAND MAY SEE SOME SNOW EXTEND THROUGH MONDAY. THIS SYSTEM WILL
LIKELY PRODUCE A PERIOD OF BRISK WINDS, ESPECIALLY OVER THE
NORTHEAST.
A RAPID SUCCESSION OF FRONTAL SYSTEMS WILL BRING MULTIPLE DAYS OF
RAIN AND MOUNTAIN SNOW TO THE PACIFIC NORTHWEST AND NORTHERN
CALIFORNIA FROM THE WEEKEND THROUGH THE FIRST HALF OF NEXT WEEK
WITH SNOW STEADILY INCREASING OVER THE NORTHERN ROCKIES AS WELL.
IN THE SATURDAY-SATURDAY NIGHT PERIOD COVERED BY THE DAY 4 ERO,
THE LOWER ELEVATIONS OF THE OLYMPICS ARE THE MAIN REGION OF
INTEREST FOR POTENTIAL RAINFALL ENHANCEMENT WITH LIGHTER TOTALS
EXTENDING FARTHER SOUTH. GUIDANCE IS STILL OFFERING MIXED
MESSAGES FOR MOISTURE/INSTABILITY/QPF (GFS GENERALLY HIGHER) SO
WILL MAINTAIN NO RISK AREA FOR NOW. BY DAY 5 (SUNDAY-SUNDAY
NIGHT) THERE IS A SOMEWHAT BETTER, THOUGH NOT EXCEPTIONAL,
MOISTURE SIGNAL TOWARD THE CALIFORNIA/OREGON BORDER WHILE RAINFALL
FROM THE PRIOR DAY MAY PROVIDE A LITTLE MORE SENSITIVITY FROM
ONGOING ACTIVITY TO THE NORTH. THUS THE PLAN IS TO INTRODUCE A
MARGINAL RISK AREA ALONG THE PACIFIC NORTHWEST COAST INTO NORTHERN
CALIFORNIA. CURRENTLY EXPECT SOME LOCALLY MODERATE TO HEAVY
ACTIVITY TO PERSIST INTO TUESDAY, LIKELY TRENDING LIGHTER BY
WEDNESDAY AS A BUILDING EAST PACIFIC UPPER RIDGE NEARS THE COAST.
AT THE SAME TIME MOISTURE MAY START TO EXTEND A LITTLE FARTHER
SOUTH INLAND FROM THE COAST.
SUPPORTED BY MEAN RIDGING ALOFT, THE MOST PRONOUNCED TEMPERATURE
ANOMALIES DURING THE PERIOD WILL BE ON THE WARM SIDE OF NORMAL AND
DEVELOPING OVER THE CENTRAL U.S. AROUND SUNDAY-MONDAY, THEN
EXPANDING TO INCLUDE THE GREAT LAKES AND VICINITY BY MIDWEEK.
SOME LOCATIONS FROM THE NORTHERN PLAINS INTO THE CENTRAL GREAT
LAKES MAY SEE ONE OR MORE DAYS WITH DAYTIME HIGHS AT LEAST 20-25F
ABOVE NORMAL, WITH SOMEWHAT LESS COVERAGE OF SIMILAR ANOMALIES FOR
MORNING LOWS. TO A LESS EXTREME DEGREE, MOST OF THE COUNTRY EAST
OF THE ROCKIES SHOULD SEE ABOVE AVERAGE TEMPERATURES BY NEXT
WEDNESDAY WITH THE SOUTHEAST BEING CLOSEST TO NORMAL. OTHERWISE,
THE SYSTEM AFFECTING THE EAST DURING THE WEEKEND WILL LEAVE A COOL
DAY IN ITS WAKE OVER THE SOUTHERN PLAINS ON SATURDAY AND THE
SOUTHERN TIER ON SUNDAY WITH SOME NEAR TO SLIGHTLY BELOW NORMAL
READINGS OVER THE EAST ON SUNDAY-MONDAY. THE WEST/SNOWY PATTERN
OVER NORTHERN-CENTRAL WEST COAST AND EVENTUALLY INTO THE ROCKIES
WILL MAINTAIN MODERATELY BELOW AVERAGE HIGHS AND NEAR/ABOVE
AVERAGE LOWS OVER THE WEST.
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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page