762
FXUS02 KWBC 020658
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
156 AM EST SAT MAR 02 2024
VALID 12Z TUE MAR 05 2024 - 12Z SAT MAR 09 2024
...WET PATTERN FOR PARTS OF THE EASTERN U.S., ESPECIALLY ACROSS
THE SOUTH...
..OVERVIEW
MODELS AND ENSEMBLES ADVERTISE A MEAN TROUGH ALOFT CROSSING THE
WEST AND THEN EMERGING INTO THE CENTRAL U.S., WHILE A LEADING
DIFFUSE SHORTWAVE TROUGH POSSIBLY HELPS TO ENHANCE EAST COAST LOW
PRESSURE. THE COMBINATION OF THESE FEATURES WILL FAVOR A COUPLE
EPISODES OF SIGNIFICANT PRECIPITATION OVER THE EASTERN HALF OF THE
COUNTRY WITH RELATIVELY MORE CONFIDENCE IN HIGHEST TOTALS BEING
OVER THE SOUTH, WHILE TEMPERATURES STAY ABOVE NORMAL. THE WEST
WILL BE ON THE COOL SIDE WITH SOME AREAS OF RAIN AND HIGHER
ELEVATION SNOW.
..GUIDANCE/PREDICTABILITY ASSESSMENT
GUIDANCE CONTINUES TO EXHIBIT SIMILARITIES FOR SOME ASPECTS OF THE
LARGE SCALE PATTERN EVOLUTION BUT SIGNIFICANT DIFFERENCES FOR SOME
EMBEDDED DETAILS. ONE AREA OF CONTENTION IS WITH THE DIFFUSE
UPPER TROUGH WHICH MOST GUIDANCE DEVELOPS OVER THE EAST IN ONE WAY
OR ANOTHER MID-LATE WEEK, WITH EFFECTS ON SURFACE LOW PRESSURE
NEAR THE EAST COAST. ECMWF RUNS HAVE TENDED TO BE ON THE SLOW
SIDE WITH THIS FEATURE AND THE GFS SOMEWHAT FAST (PLUS NORTHWEST
FOR THE SURFACE LOW). CMC RUNS AND THE GEFS/ECENS MEANS DEPICT A
SURFACE LOW TRACK A LITTLE FARTHER EAST, AS DOES THE NEW 00Z
UKMET. 12Z ECMWF-INITIALIZED MACHINE LEARNING MODELS FAVOR THE
EASTERN SIDE OF THE SURFACE LOW ENVELOPE. FARTHER WEST THE
GUIDANCE HAS BEEN HAVING DIFFICULTY IN RESOLVING SHORTWAVE DETAILS
ACROSS THE NORTHWEST/NORTHERN PLAINS INTO SOUTHERN CANADA. THE
18Z GFS ACTUALLY COMPARES BETTER IN PRINCIPLE TO OTHER GUIDANCE
THAN THE NEW 00Z RUN WHICH SEEMS TO BECOME TOO SLOW AND SHARP
ALOFT BY WEDNESDAY. AFTER MIDWEEK THERE IS SOME CONTINUITY IN THE
CONCEPT OF MULTIPLE PIECES OF ENERGY COMPRISING AN OVERALL UPPER
TROUGH CROSSING THE WEST AND REACHING THE PLAINS. HOWEVER BY NEXT
SATURDAY THERE IS STILL SPREAD FOR TIMING OF THIS TROUGH AND AN
UPSTREAM EASTERN PACIFIC TROUGH. THE BEST CLUSTERING OF GUIDANCE
SUGGESTS THAT THE GFS MAY STRAY A LITTLE FAST WITH BOTH.
GUIDANCE COMPARISONS AMONG 12Z/18Z SOLUTIONS LED TO UPDATING THE
FORECAST WITH AN OPERATIONAL MODEL COMPOSITE EARLY IN THE PERIOD
(TUESDAY-WEDNESDAY), FOLLOWED BY INCORPORATING SOME 18Z GEFS/12Z
ECENS MEANS BY THURSDAY AND THEN 50-60 PERCENT TOTAL WEIGHT OF THE
MEANS BY FRIDAY-SATURDAY. THIS TRANSITION HELPED TO NAVIGATE THE
INCREASING DETAIL SPREAD WITHIN THE MORE AGREEABLE LARGE SCALE
PATTERN.
..WEATHER/HAZARDS HIGHLIGHTS
THE LARGE SCALE PATTERN EVOLUTION WILL FAVOR A WET PERIOD OVER
PORTIONS OF THE EASTERN HALF OF THE LOWER 48, WITH HIGHEST
RAINFALL TOTALS LIKELY TO BE OVER THE SOUTHERN TIER FROM ONE EVENT
AROUND TUESDAY AND ANOTHER LATE IN THE WEEK. THE FIRST EPISODE
WILL FEATURE A WEAKENING FRONT NEAR THE GULF/SOUTHEAST COASTS AND
A STRONGER FRONT APPROACHING FROM THE NORTHWEST, WITH AN AXIS OF
ENHANCED DEEP MOISTURE PASSING THROUGH. MODELS DISAGREE ON THE
NORTHWARD EXTENT OF INSTABILITY AND THE FULL MODEL/ENSEMBLE RANGE
VARIES CONSIDERABLY FOR WHERE HEAVIEST RAINFALL MAY OCCUR.
HOWEVER LATEST GFS/ECMWF RUNS AND THEIR ENSEMBLES ROUGHLY FAVOR
MAINTAINING THE MARGINAL RISK AREA OVER THE SOUTHEAST IN THE NEW
DAY 4/TUESDAY EXCESSIVE RAINFALL OUTLOOK CLOSE TO WHERE DEPICTED
IN THE PRIOR DAY 5 OUTLOOK, SO WILL MAINTAIN CONTINUITY UNTIL MORE
CONFIDENT CHANGES CAN BE MADE. BY DAY 5/WEDNESDAY THE GUIDANCE
DIVERGES CONSIDERABLY FOR EVOLUTION OF DIFFUSE EASTERN U.S. UPPER
TROUGHING AND ASSOCIATED FRONTAL WAVINESS/RAINFALL DISTRIBUTION.
SOME SOLUTIONS OFFER POTENTIAL FOR SIGNIFICANT RAINFALL BETWEEN
THE CENTRAL APPALACHIANS/MID-ATLANTIC INTO PARTS OF THE NORTHEAST,
WHILE THERE IS AN ALTERNATE SIDE OF THE ENVELOPE THAT IS MORE
SUPPRESSED WITH THE MOISTURE. FOR NOW THE SIGNAL FOR DETAILS IS
NOT YET COHERENT ENOUGH TO REACH THE POINT OF DEPICTING A RISK
AREA. SOME OF THIS ACTIVITY MAY EXTEND INTO THURSDAY. BEHIND
THIS SYSTEM, STRONGER DYNAMICS EMERGING FROM THE WEST SHOULD
GENERATE A CENTRAL-EASTERN U.S. LOW PRESSURE AND FRONTAL SYSTEM
LATE IN THE WEEK WITH ANOTHER POTENTIAL EPISODE OF HEAVY RAINFALL
FROM THE LOWER MISSISSIPPI VALLEY INTO THE SOUTHEAST AND LESS
EXTREME PRECIPITATION EXTENDING FARTHER NORTH. DEPENDING ON
SYSTEM DETAILS, SOME PRECIPITATION OVER THE CENTRAL PLAINS COULD
BE IN THE FORM OF SNOW. NORTHERN NEW ENGLAND MAY ALSO SEE SOME
SNOW WITH MOISTURE FROM THE LEADING EAST COAST SYSTEM.
OVER THE WEST, A FRONTAL SYSTEM MAY FOCUS A NARROW AXIS OF
ENHANCED PRECIPITATION OVER NORTHERN CALIFORNIA ON TUESDAY. THERE
IS STILL SPREAD IN THE GUIDANCE FOR EXACT DETAILS INCLUDING HOW
MUCH MOISTURE THIS SYSTEM WILL INCORPORATE. FOR NOW THE DAY 4 ERO
DOES NOT DEPICT ANY RISK AREA FOR EXCESSIVE RAINFALL WHILE
AWAITING BETTER CLUSTERING. AT THE SAME TIME, AN UPPER TROUGH TO
THE NORTH WILL BRING AN EPISODE OF ORGANIZED SNOW TO THE NORTHERN
ROCKIES. WHAT IS LEFT OF THIS MOISTURE SHOULD SINK SOUTHEASTWARD
OVER THE WEST THROUGH MIDWEEK OR SO, WITH SOME SNOW LINGERING OVER
THE SOUTHERN HALF OF THE ROCKIES INTO LATE WEEK. MODEST AMOUNTS
OF PRECIPITATION MAY REACH THE PACIFIC NORTHWEST LATER IN THE WEEK
AS AN UPPER TROUGH/LEADING FRONT APPROACH.
UPPER TROUGHING MOVING THROUGH THE WEST WILL PROMOTE BELOW NORMAL
TEMPERATURES ACROSS MOST OF THE REGION, WITH SOME COOL READINGS
EXTENDING INTO THE HIGH PLAINS AT TIMES. HIGHS WILL TEND TO BE
5-15F BELOW NORMAL WHILE NEGATIVE ANOMALIES FOR MORNING LOWS
SHOULD BE CONFINED MORE TO THE NORTHWEST/GREAT BASIN.
TEMPERATURES MAY BEGIN TO MODERATE TOWARD THE END OF NEXT WEEK
FROM WEST TO EAST AS AN UPPER RIDGE BUILDS IN. MEANWHILE THE
EASTERN HALF OF THE COUNTRY SHOULD STAY ON THE WARM SIDE OF NORMAL
THROUGH THE PERIOD. THE MOST ANOMALOUS READINGS OF UP TO PLUS
20-30F SHOULD BE FROM TUESDAY INTO EARLY WEDNESDAY, WITH BEST
POTENTIAL FOR SOME DAILY RECORDS LIKELY TO BE OVER THE NORTHEAST.
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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