508
FXUS02 KWBC 270700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 AM 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 IS FORECAST TO 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 PRECIPITATION.
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, IF
NOT SLIGHTLY BELOW IN SOME SPOTS, FROM WEST TO EAST DURING THE
PERIOD.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODELS CONTINUE TO SHOW SOME DETAIL DIFFERENCES THAT IMPACT
SENSIBLE WEATHER DESPITE GENERALLY AGREEABLE PATTERN EVOLUTION FROM
A SHORTWAVE-DOMINANT PATTERN EARLY NEXT WEEK TO A MORE AMPLIFIED
PATTERN WITH A WESTERN RIDGE AND EASTERN TROUGH LATER NEXT WEEK.
LOW PRESSURE AND UPPER TROUGH DIFFERENCES LINGER IN THE NORTHEAST
ON MONDAY, IMPACTING TIMING OF PRECIPITATION. GFS RUNS REMAIN ON
THE FASTER SIDE OF ENDING PRECIPITATION ACROSS THE REGION.
MEANWHILE A SHORTWAVE PRODUCING PLAINS LOW PRESSURE STARTS OFF IN
GOOD AGREEMENT MONDAY, WITH MODELS EVEN CONVERGING BETTER ON THE
LOW POSITION INTO THE OHIO VALLEY EARLY TUESDAY. AS THE FEATURES
MOVE EAST MIDWEEK, SPREAD INCREASES SOMEWHAT. GFS RUNS CONTINUE TO
BE FASTER THAN THE CONSENSUS OF ECMWF/ML RUNS AT PIVOTING THE
SHORTWAVE AND LOW NORTHEASTWARD, WHILE THE CMC IS EVEN SLOWER THAN
THE EC. ANOTHER CONSIDERATION WITH LOW PLACEMENT IS THE POTENTIAL
FOR COASTAL LOW DEVELOPMENT IN ADDITION TO THE INLAND LOW. WHILE
THE 12Z CYCLE OF THE ECMWF AND ML RUNS WERE PRETTY CONSISTENT IN
PRODUCING A LOW NEAR LONG ISLAND, THE NEWER 00Z ECMWF FAVORS ONE
INLAND LOW RATHER THAN THE COASTAL LOW DEVELOPING, SO THIS REMAINS
UNCERTAIN. AT LEAST BY THURSDAY MODELS ARE REASONABLY AGREEABLE IN
A LOW POSITION JUST EAST OF MAINE. THE 12Z ECMWF DID BUMP THE
SURFACE LOW BACK WEST INTO CANADA AFTER THAT (BY NEXT FRIDAY),
WHICH DID NOT HAVE MUCH SUPPORT.
GFS RUNS/GEFS ENSEMBLES CONTINUE TO BE MORE PRONOUNCED THAN OTHER
GUIDANCE WITH SHORTWAVE ENERGY THAT REACHES THE WEST BY AROUND
TUESDAY. SINCE ML MODELS STRONGLY SUPPORT THE NON- GFS/GEFS
GUIDANCE, CONTINUE NOT TO FAVOR THE GFS/GEFS AND ITS PATTERN OF
BRINGING SOUTHERN TIER PRECIPITATION INTO THE CENTRAL/EASTERN
STATES BY MID TO LATE WEEK.
MODELS ARE AGREEABLE THAT THE PATTERN WILL AMPLIFY OVERALL AS THE
WEEK PROGRESSES, WITH AN UPPER RIDGE OVER THE WEST TO ROCKIES AND
TROUGHING ATOP THE EASTERN HALF OF THE LOWER 48. THERE IS SOME
MODEL SPREAD AND RUN-TO-RUN DIFFERENCES WITH THE TIMING OF EASTERN
PACIFIC TROUGHING APPROACHING THE PACIFIC NORTHWEST BY FRIDAY,
WHICH WILL HAVE TO BE RESOLVED IN FUTURE FORECAST CYCLES.
THE WPC FORECAST CONTINUED TO FAVOR THE ECMWF IN THE FORECAST,
WITH LESSER PROPORTIONS OF OTHER GUIDANCE. GRADUALLY INCORPORATED
MORE ENSEMBLE MEANS (ESPECIALLY THE ECENS) DURING THE LATTER PART
OF THE PERIOD, REACHING HALF BY DAY 7 AS THE CONTROL RUN OF THE
ECMWF DIVERGED WESTWARD WITH THE EASTERN LOW. FOR QPF, REDUCED MOST
GFS/GEFS INFLUENCE IN THE SOUTH-CENTRAL TO SOUTHEASTERN U.S.
(KEEPING THE REGION DRIER), AND ENHANCED LAKE EFFECT PRECIPITATION
COMPARED TO THE NBM.
..WEATHER/HAZARDS HIGHLIGHTS
A LOW PRESSURE SYSTEM WILL MOVE ACROSS SOUTH-CENTRAL CANADA INTO
MONDAY WITH ITS FRONTS PROVIDING A FOCUS FOR PRECIPITATION OVER THE
NORTHEAST. THERE REMAINS ABOVE AVERAGE MODEL SPREAD WITH THE EXACT
EVOLUTION OF THE SETUP AND ASSOCIATED PRECIPITATION PLACEMENT,
AMOUNTS, AND TYPE. 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. RAIN ON COLD HARD GROUND OR SNOW COVERED AREAS
MAY LEAD TO A NONZERO CHANCE OF FLASH FLOODING, BUT GIVEN THE
UNCERTAINTIES EVEN IN THE PATTERN ITSELF, HELD OFF ON ANY ERO RISK
FOR DAY 4/MONDAY.
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. A BROADER AREA OF
PRECIPITATION WILL SPREAD A...GUIDANCE/PREDICTABILITY ASSESSMENT...
MODELS CONTINUE TO SHOW SOME DETAIL DIFFERENCES THAT IMPACT SENSIBLE WEATHER DESPITE GENERALLY AGREEABLE PATTERN EVOLUTION FROM A SHORTWAVE-DOMINANT PATTERN EARLY NEXT WEEK TO A MORE AMPLIFIED PATTERN WITH A WESTERN RIDGE AND EASTERN TROUGH LATER NEXT WEEK. LOW PRESSURE AND UPPER TROUGH DIFFERENCES LINGER IN THE NORTHEAST ON MONDAY, IMPACTING TIMING OF PRECIPITATION. GFS RUNS REMAIN ON THE FASTER SIDE OF ENDING PRECIPITATION ACROSS THE REGION. MEANWHILE A SHORTWAVE PRODUCING PLAINS LOW PRESSURE STARTS OFF IN GOOD AGREEMENT MONDAY, WITH MODELS EVEN CONVERGING BETTER ON THE LOW POSITION INTO THE OHIO VALLEY EARLY TUESDAY. AS THE FEATURES MOVE EAST MIDWEEK, SPREAD INCREASES SOMEWHAT. GFS RUNS CONTINUE TO BE FASTER THAN THE CONSENSUS OF ECMWF/ML RUNS AT PIVOTING THE SHORTWAVE AND LOW NORTHEASTWARD, WHILE THE CMC IS EVEN SLOWER THAN THE EC. ANOTHER CONSIDERATION WITH LOW PLACEMENT IS THE POTENTIAL FOR COASTAL LOW DEVELOPMENT IN ADDITION TO THE INLAND LOW. WHILE THE 12Z CYCLE OF THE ECMWF AND ML RUNS WERE PRETTY CONSISTENT IN PRODUCING A LOW NEAR LONG ISLAND, THE NEWER 00Z ECMWF FAVORS ONE INLAND LOW RATHER THAN THE COASTAL LOW DEVELOPING, SO THIS REMAINS UNCERTAIN. AT LEAST BY THURSDAY MODELS ARE REASONABLY AGREEABLE IN A LOW POSITION JUST EAST OF MAINE. THE 12Z ECMWF DID BUMP THE SURFACE LOW BACK WEST INTO CANADA AFTER THAT (BY NEXT FRIDAY), WHICH DID NOT HAVE MUCH SUPPORT.
GFS RUNS/GEFS ENSEMBLES CONTINUE TO BE MORE PRONOUNCED THAN OTHER
GUIDANCE WITH SHORTWAVE ENERGY THAT REACHES THE WEST BY AROUND
TUESDAY. SINCE ML MODELS STRONGLY SUPPORT THE NON-
GFS/GEFS GUIDANCE, CONTINUE NOT TO FAVOR THE GFS/GEFS AND ITS PATTERN OF BRINGING SOUTHERN TIER PRECIPITATION INTO THE CENTRAL/EASTERN STATES BY MID TO LATE WEEK.
MODELS ARE AGREEABLE THAT THE PATTERN WILL AMPLIFY OVERALL AS THE WEEK PROGRESSES, WITH AN UPPER RIDGE OVER THE WEST TO ROCKIES AND TROUGHING ATOP THE EASTERN HALF OF THE LOWER 48. THERE IS SOME MODEL SPREAD AND RUN-TO-RUN DIFFERENCES WITH THE TIMING OF EASTERN PACIFIC TROUGHING APPROACHING THE PACIFIC NORTHWEST BY FRIDAY, WHICH WILL HAVE TO BE RESOLVED IN FUTURE FORECAST CYCLES.
THE WPC FORECAST CONTINUED TO FAVOR THE ECMWF IN THE FORECAST, WITH
LESSER PROPORTIONS OF OTHER GUIDANCE. GRADUALLY INCORPORATED MORE
ENSEMBLE MEANS (ESPECIALLY THE ECENS) DURING THE LATTER PART OF THE
PERIOD, REACHING HALF BY DAY 7 AS THE CONTROL RUN OF THE ECMWF
DIVERGED WESTWARD WITH THE EASTERN LOW. FOR QPF, REDUCED MOST
GFS/GEFS INFLUENCE IN THE SOUTH-CENTRAL TO SOUTHEASTERN U.S.
(KEEPING THE REGION DRIER), AND ENHANCED LAKE EFFECT PRECIPITATION
COMPARED TO THE NBM.
CROSS THE EAST TUESDAY-WEDNESDAY, WITH SOME MODEST AMOUNTS BUT
OVERALL LIGHTER THAN THE PRECIPITATION THIS WEEKEND. NO AREAS ARE
CURRENTLY DELINEATED IN THE DAY 5/TUESDAY ERO SINCE RAIN SHOULD
MOSTLY BE UNDER EXCESSIVE THRESHOLDS, BUT WILL KEEP AN EYE ON IT IN
FUTURE FORECASTS IF AMOUNTS TREND UPWARD. WINTRY WEATHER SHOULD BE
CONFINED FAIRLY FAR NORTHWARD AS WITH THE PRIOR SYSTEM, WITH SNOW
POSSIBLE ACROSS PARTS OF THE GREAT LAKES REGION TUESDAY AND INTO
THE INTERIOR NORTHEAST MIDWEEK. HIGHEST PROBABILITIES FOR SNOW 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. PRECIPITATION IS FORECAST 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 LOWER THAN
THE WEEKEND SYSTEM. WHAT AREAS OF ENHANCED ACTIVITY THAT DO OCCUR
ARE MOST LIKELY TO BE OVER WESTERN WASHINGTON.
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 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.
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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