366
FXUS02 KWBC 271859
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
159 PM EST FRI DEC 27 2024
VALID 12Z MON DEC 30 2024 - 12Z FRI JAN 03 2025
..OVERVIEW
PROGRESSIVE FLOW WITH MULTIPLE SHORTWAVES ROTATING AROUND THE
SOUTHERN SIDE OF A SOUTH-CENTRAL CANADA UPPER LOW WILL BE IN PLACE
EARLY NEXT WEEK, PRODUCING MANY LOW PRESSURE/FRONTAL SYSTEMS ACROSS
THE LOWER 48. ONE SYSTEM WILL EXIT THE NORTHEAST BY TUESDAY AFTER
PRODUCING SOME PRECIPITATION THERE. ANOTHER LOW PRESSURE SYSTEM
WILL BE DEEPENING OVER THE CENTRAL PLAINS MONDAY, WITH WINDY
CONDITIONS BEHIND IT AND CAUSING PRECIPITATION IN THE VICINITY OF
THE LOW TRACK, INCLUDING POSSIBLE SNOW IN THE NORTH-CENTRAL
PLAINS. THIS LOW SHOULD PUSH INTO THE EAST-CENTRAL AND EASTERN U.S.
TUESDAY-WEDNESDAY FOR ANOTHER ROUND OF PRECIPITATION THAT SHOULD
OVERALL BE LIGHTER THAN THIS WEEKEND'S EVENT. EXPECT A TREND
TOWARD A LARGER SCALE WESTERN RIDGE/EASTERN TROUGH PATTERN BY MID-
LATE WEEK. WARMER THAN NORMAL TEMPERATURES FOR MOST OF THE LOWER 48
EARLY NEXT WEEK WILL MODERATE CLOSER TO NORMAL, AND EVEN SLIGHTLY
BELOW IN SOME SPOTS, FROM WEST TO EAST DURING THE PERIOD. THE WEST
MAY SEE A MODEST WARMING TREND LATE IN THE WEEK UNDERNEATH THE
STRONGER UPPER RIDGE.
..GUIDANCE/PREDICTABILITY ASSESSMENT
LATEST GUIDANCE MAINTAINS GOOD AGREEMENT WITH THE LARGE SCALE
PATTERN EVOLUTION WHILE SPREAD IS GRADUALLY NARROWING SOME FOR
EMBEDDED SHORTWAVES/SYSTEMS. FOR THE LEADING SYSTEM AFFECTING THE
NORTHEAST U.S. AND SOUTHEASTERN CANADA AS OF MONDAY, GUIDANCE
TRENDS HAVE BEEN IN FAVOR OF THE SLOWER SIDE OF THE SPREAD PER
RECENT ECMWF RUNS AND MOST MACHINE LEARNING (ML) GUIDANCE. LATEST
GFS/CMC/UKMET RUNS HAVE BEEN CLOSING IN ON THIS SCENARIO AND IN
FACT THE 12Z CMC/ECMWF HAVE NUDGED A BIT SLOWER WITH THE SURFACE
LOW AND/OR TRAILING COLD FRONT. BEHIND THIS SYSTEM, DYNAMICAL AND
ML GUIDANCE IS CONVERGING ON TRACKING MONDAY LOW PRESSURE OVER THE
PLAINS INTO THE OHIO VALLEY BY TUESDAY, FOLLOWED BY A CONTINUED
SPLIT OVER LOW PRESSURE EMPHASIS BETWEEN THE EASTERN GREAT LAKES
AND NORTHERN MID-ATLANTIC/SOUTHERN NEW ENGLAND COAST AS OF EARLY
WEDNESDAY. LATEST ECMWF RUNS HAVE NUDGED TOWARD A CONSOLIDATED
INLAND SYSTEM OVER SOUTHERN NEW ENGLAND WHILE OTHER GUIDANCE
REMAINS MIXED, THOUGH WITH A COASTAL TENDENCY TOWARD NORTHERN NEW
ENGLAND. DYNAMICAL/ML MODELS MAINTAIN GOOD CONTINUITY IN SHOWING A
PATH OVER OR NORTHEAST OF MAINE BY THURSDAY. DEEPER TRENDS BY ML
MODELS OVER THE PAST COUPLE DAYS AND TRIMMING FROM THE DEEP SIDE OF
THE SPREAD IN THE DYNAMICAL GUIDANCE HAVE LED TO BETTER CONSENSUS
FOR STORM DEPTH. THE 06Z GFS LOOKED TOO WEAK NEAR MAINE THOUGH.
FARTHER WEST, GFS/GEFS RUNS HAVE STILL BEEN ON THE STRONG SIDE WITH
SHORTWAVE ENERGY REACHING THE WEST AROUND TUESDAY. THE 06Z GFS WAS
MOST PROMINENTLY OVERDONE, WHILE THE 00Z GFS/06Z GEFS MEAN WERE AT
LEAST TEMPERED ENOUGH TO INCLUDE A SMALL WEIGHT IN THE FORECAST.
THE NEW 12Z GFS HAS DAMPENED THIS WAVE AND IS NOW CLOSER TO
REMAINING GUIDANCE THAN MOST PRIOR RUNS. MEANWHILE GUIDANCE AGREES
ON AN EASTERN PACIFIC PATTERN THAT WILL HAVE MULTIPLE FEATURES
BRUSH THE PACIFIC NORTHWEST BUT WITH A DECENT AMOUNT OF SPREAD FOR
INDIVIDUAL WAVE/FRONTAL SPECIFICS DURING WEDNESDAY-THURSDAY. AN
APPROACHING LARGER SCALE UPPER TROUGH SHOULD IMPROVE PREDICTABILITY
SOME BY FRIDAY, ASIDE FROM TIMING DIFFERENCES. MODEL/ENSEMBLE
CONSENSUS SUGGESTS THE 06Z GFS MAY BE TOO FAST WITH THE FRIDAY
SYSTEM (00Z AND 12Z GFS COMPARING BETTER TO OTHER SOLUTIONS),
THOUGH THE ML MODEL SPREAD IS WIDE ENOUGH TO INCLUDE THE FASTER
SCENARIO. THE AMPLIFYING NATURE OF THE PATTERN SEEMS TO FAVOR
LEANING AWAY FROM FAST SOLUTIONS THOUGH.
BASED ON 00Z/06Z GUIDANCE, THE FIRST HALF OF THE FORECAST STARTED
WITH HALF 00Z ECMWF AND THE REST COMPRISING THE 00Z GFS/CMC/UKMET
IN ORDER OF MORE TO LESS WEIGHT. THEREAFTER THE FORECAST
INCORPORATED 35-45 PERCENT ENSEMBLE MEANS (06Z GEFS AND 00Z
ECENS/CMCENS) ALONG WITH MORE 00Z ECMWF INPUT RELATIVE TO THE 00Z
GFS AND CMC.
..WEATHER/HAZARDS HIGHLIGHTS
A LOW PRESSURE SYSTEM WILL MOVE ACROSS SOUTHEASTERN ONTARIO/WESTERN
QUEBEC BY MONDAY WITH ITS FRONTS PROVIDING A FOCUS FOR
PRECIPITATION OVER THE NORTHEAST. RECENTLY ABOVE AVERAGE MODEL
SPREAD WITH THE EXACT EVOLUTION OF THE SETUP AND ASSOCIATED
PRECIPITATION PLACEMENT, AMOUNTS, AND TYPE HAS SHOWN SOME NARROWING
TODAY. GENERALLY IT SEEMS THAT A WARMING ATMOSPHERE BY MONDAY WILL
ALLOW FOR THIS TO BE MOSTLY RAIN AFTER SOME FREEZING RAIN
SUNDAY/SUNDAY NIGHT, PERHAPS EVEN IN HIGHER ELEVATIONS LIKE THE
WHITE MOUNTAINS. STRONG SOUTHERLY FLOW AND ANOMALOUS MOISTURE AHEAD
OF THE COLD FRONT MAY PROMOTE A BAND OF BRIEFLY HEAVY RAIN PASSING
THROUGH NORTHERN NEW ENGLAND. THIS RAIN FALLING ON COLD HARD
GROUND OR SNOW COVERED AREAS MAY LEAD TO A NONZERO CHANCE OF FLASH
FLOODING OR AT LEAST SOME NUISANCE ISSUES IN AREAS THAT HAVE POOR
DRAINAGE. HOWEVER PER WFO COORDINATION THIS POTENTIAL STILL SEEMS
TO BE BELOW THE MARGINAL RISK THRESHOLD, SO THE DAY 4/MONDAY
EXCESSIVE RAINFALL OUTLOOK CONTINUES TO DEPICT NO RISK AREA.
A LOW PRESSURE SYSTEM WILL DEVELOP IN THE PLAINS BY MONDAY WITH A
SHORTWAVE EJECTING FROM THE WEST. STRONG AND GUSTY WINDS ARE LIKELY
BEHIND THIS LOW ACROSS PARTS OF THE ROCKIES AND HIGH PLAINS.
MEANWHILE NORTH OF THE LOW TRACK, SNOW IS POSSIBLE ACROSS THE
NORTH-CENTRAL PLAINS MONDAY WITH PROBABILITIES FOR AT LEAST 0.25
INCH LIQUID IN THE FORM OF SNOW MAXIMIZING AT 30-50 PERCENT OVER
SOUTHERN SOUTH DAKOTA AND INTO NORTHERN NEBRASKA. ACCUMULATIONS
COULD REACH HEAVY CRITERIA WITHIN A NARROW BAND, BUT THE SMALL
SCALE NATURE OF SUCH A BAND YIELDS HIGH SENSITIVITY WITH RESPECT TO
EXACT TOTALS AT ANY SPECIFIC LOCATION. CONTINUE TO MONITOR
FORECASTS AS FINER SCALE DETAILS BECOME BETTER RESOLVED.
PRECIPITATION WILL THEN SPREAD THROUGH THE MIDWEST/OHIO
VALLEY/LOWER GREAT LAKES, MOSTLY IN THE FORM OF RAIN ASIDE FROM
PERHAPS SOME SNOW ON THE NORTHWEST PERIPHERY OF THE MOISTURE
SHIELD. PRECIPITATION WILL LIKELY REACH THE MID-ATLANTIC AND
NORTHEAST BY TUESDAY-WEDNESDAY. THE DAY 5/TUESDAY ERO DEPICTS NO
RISK AREAS SINCE RAIN SHOULD MOSTLY BE UNDER EXCESSIVE THRESHOLDS,
BUT WILL KEEP AN EYE ON IT IN FUTURE FORECASTS IF AMOUNTS TREND
UPWARD. FARTHER EAST, WINTRY WEATHER SHOULD REMAIN CONFINED FAIRLY
FAR NORTHWARD AS WITH THE PRIOR SYSTEM, WITH WHAT SNOW OCCURRING IN
THE GREAT LAKES ON TUESDAY EXTENDING INTO THE INTERIOR NORTHEAST BY
MIDWEEK. HIGHEST PROBABILITIES FOR SNOW (CURRENTLY 30-60 PERCENT
PROBABILITY FOR 0.25 INCH OR MORE IN LIQUID) WILL BE IN HIGHER
ELEVATION AREAS LIKE THE ADIRONDACKS AND THE GREEN AND WHITE
MOUNTAINS. COLD CYCLONIC FLOW BEHIND THE STORM SYSTEM WILL LIKELY
PRODUCE A PERIOD OF LAKE EFFECT SNOW INTO THURSDAY AND FRIDAY.
THE PACIFIC NORTHWEST TO NORTHERN ROCKIES CAN EXPECT LINGERING
MODERATE PRECIPITATION AMOUNTS ON MONDAY WITH LOWER ELEVATION RAIN
AND HIGHER ELEVATION SNOW. PRECIPITATION CHANCES WILL TREND DOWN
TUESDAY, BUT BY TUESDAY NIGHT MOIST INFLOW MAY GET RENEWED IN THE
PACIFIC NORTHWEST AND RAIN/SNOW CHANCES COULD INCREASE THERE ONCE
AGAIN. EXPECT PRECIPITATION TO CONTINUE FOR THE LATTER HALF OF THE
WEEK IN THE PACIFIC NORTHWEST AND AT TIMES FARTHER EAST INTO THE
NORTHERN ROCKIES. OVERALL AMOUNTS ARE LIKELY TO BE SOMEWHAT LOWER
THAN WITH THE WEEKEND SYSTEM, THOUGH SOME LOCALIZED AREAS OF
ENHANCED RAIN/MOUNTAIN SNOW ARE POSSIBLE. THERE IS A FAIR AMOUNT OF
SPREAD FOR SYSTEM/FRONTAL SPECIFICS BEFORE A BETTER DEFINED FEATURE
ARRIVES AROUND FRIDAY--ALBEIT WITH SOME TIMING DIFFERENCES. HIGHEST
TOTALS SHOULD BE OVER WASHINGTON WITH MEANINGFUL PRECIPITATION
POSSIBLY REACHING SOUTH INTO OREGON AT TIMES.
MUCH OF THE COUNTRY ASIDE FROM THE NORTHWESTERN QUADRANT WILL BE
WELL ABOVE AVERAGE TEMPERATURE-WISE INTO MONDAY. THE MOST ANOMALOUS
TEMPERATURES ARE FORECAST IN THE SOUTHERN PLAINS, WITH HIGHS IN
THE 70S AND 80S ACROSS TEXAS THAT COULD BREAK DAILY RECORD HIGHS
ESPECIALLY IN SOUTHERN PARTS OF THE STATE. THE SECOND MOST
ANOMALOUS TEMPERATURES SHOULD BE OVER THE NORTHEAST, WITH LOWS
20-30 DEGREES ABOVE AVERAGE AND HIGHS 15-20F ABOVE AVERAGE ON
MONDAY. AS MULTIPLE COLD FRONTS TRACK ACROSS THE NATION, MORE
SEASONABLE COOL AIR SHOULD GRADUALLY TAKE OVER AS THE WEEK
PROGRESSES. EXPECT THE NORTHWESTERN TO CENTRAL U.S. TO SEE NEAR
NORMAL TEMPERATURES MONDAY-TUESDAY, AND COOLER TEMPERATURES WILL
SPREAD ACROSS THE EASTERN U.S. WEDNESDAY-THURSDAY. BY LATER WEEK,
THE AMPLIFYING UPPER LEVEL PATTERN WITH RIDGING OVER THE WEST WILL
PROMOTE TEMPERATURES OF 5-10F OR SO ABOVE NORMAL ESPECIALLY OVER
THE SOUTHWEST, WHILE CONVERSELY UPPER TROUGHING ALOFT WILL SPREAD
COOLER THAN NORMAL TEMPERATURES ACROSS THE NORTH-CENTRAL TO EAST-
CENTRAL AND EASTERN U.S. THURSDAY AND FRIDAY.
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 FORECAST (QPF), EXCESSIVE RAINFALL
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:
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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