766
FXUS02 KWBC 131946
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
246 PM EST FRI DEC 13 2024
VALID 12Z MON DEC 16 2024 - 12Z FRI DEC 20 2024
..OVERVIEW
THE PATTERN DURING EARLY NEXT WEEK WILL BE CHARACTERIZED BY
PROGRESSIVE SHORTWAVES CARRYING A COUPLE OF COLD FRONTS MARCHING
EASTWARD FROM THE CENTRAL U.S. TO THE EAST COAST, WITH MODERATE TO
POTENTIALLY LOCALLY HEAVY RAIN. ANOTHER SHORTWAVE WILL AFFECT THE
WEST COAST/NORTHWEST WITH A ROUND OF PRECIPITATION MONDAY-TUESDAY.
BY THE LATTER HALF OF THE WEEK, A SIGNIFICANT PATTERN SHIFT IS
LIKELY, WITH AMPLIFYING MEAN TROUGHING COVERING THE CENTRAL-EASTERN
STATES WHILE RIDGING DEVELOPS UPSTREAM OVER THE WEST. THIS SHOULD
PROMOTE WARMER AND DRIER CONDITIONS IN THE WEST AND COOLING
TEMPERATURES IN THE EAST, AND THERE MAY BE AN EMERGING NOR'EASTER
THREAT BY LATE NEXT WEEK BUT WITH LOW CONFIDENCE.
..GUIDANCE/PREDICTABILITY ASSESSMENT
BESIDES SOME RELATIVELY MINOR TIMING/SURFACE DETAIL DIFFERENCES,
THE MODELS ARE STILL IN GOOD AGREEMENT THE FIRST PART OF NEXT WEEK
AS A SHORTWAVE MOVES THROUGH THE MIDWEST INTO THE NORTHEAST, AND
ANOTHER SHORTWAVE ENTERS THE WEST. BY MIDWEEK UPPER RIDGING IS
FORECAST TO FORM OVER THE WEST COAST STATES, BUT A SHORTWAVE AND
SURFACE LOW WEST OF THE RIDGE IN THE EASTERN PACIFIC IS UNCERTAIN
IN PLACEMENT AND COULD BE RELATIVELY STRONG. AT FIRST GLANCE THE
ECMWF RUNS ARE QUITE AGGRESSIVE AND FARTHER EAST THAN OTHER MODELS
LIKE THE GFS, BUT MOST AI MODELS CLUSTER WELL WITH IT. PREFERRED
SOMETHING LIKE THE EC MEAN FOR THIS FEATURE, WEAKER THAN THE
CONTROL RUN OF THE EC BUT WITH SIMILAR POSITIONING. THIS SHORTWAVE
IS ONE CONTRIBUTING FACTOR TO MAINTAINING THE CENTRAL-EASTERN
TROUGH INTO LATER WEEK.
MEANWHILE, DETAILS OF THE CENTRAL-EASTERN TROUGH DIVERGE EVEN
BEFORE THIS FEATURE ARRIVES. MOST NOTABLY, THE 00Z ECMWF FORMED A
CLOSED LOW IN THE SOUTHERN STREAM, CAUSING AN ASSOCIATED SURFACE
LOW TO SLOW CONSIDERABLY AND TRACK FARTHER INLAND COMPARED TO THE
PHASED TROUGH AND QUICKLY MOVING SURFACE LOW OF THE GFS RUNS. THE
CMC DID SHOW SOME AMPLIFICATION OF THE SOUTHERN STREAM AS WELL, BUT
NOT TO THE DEGREE OF THE ECMWF. INCOMING NEWER 12Z MODELS MAY BE
REACHING SOME COMPROMISE ON A SOUTHERN STREAM CLOSED LOW DEVELOPING
AT SOME POINT NOT AS FAR SOUTH AS THE 00Z ECMWF, THOUGH THERE IS
STILL SOME SPREAD, AND THE LACK OF RUN-TO-RUN CONSISTENCY IN MODELS
KEEPS CONFIDENCE LOW. THE FORECAST DID TREND TOWARD MORE
PRECIPITATION ALONG THE EASTERN SEABOARD THAN THE PREVIOUS FORECAST
HAD, GIVEN THE SLOWING LOW TRACK THROUGH THE WESTERN ATLANTIC.
THE WPC FORECAST WAS BASED ON A 00/06Z MODEL/MEAN BLEND THROUGH
THE PERIOD, WITH MORE DETERMINISTIC MODELS THAN MEANS DAYS 3-4,
EVEN WEIGHTING OF MODELS AND MEANS DAY 5, AND MORE MEANS THAN
MODELS DAYS 6-7 GIVEN THE SPREAD.
..WEATHER/HAZARDS HIGHLIGHTS
A COLD FRONT MOVING ACROSS THE CENTRAL AND EASTERN U.S. MONDAY-
TUESDAY SHOULD BE ACCOMPANIED BY SOME MODEST PRECIPITATION. AREAS
FROM THE LOWER TO MIDDLE MISSISSIPPI VALLEY INTO THE OHIO VALLEY
ARE LIKELY TO SEE THE HEAVIEST RAIN SINCE RAIN AMOUNTS SHOULD
DECREASE IN THE EAST TUESDAY. AREAS RIGHT NEAR THE OHIO VALLEY LIKE
SOUTHERN ILLINOIS/INDIANA AND NORTHERN KENTUCKY APPEAR TO HAVE THE
BEST CHANCE FOR RAIN TOTALS OVER AN INCH MONDAY, BUT LACK OF
INSTABILITY MAY LIMIT RAIN RATES. MEANWHILE FARTHER SOUTHWEST,
INSTABILITY SHOULD BE HIGHER, BUT ANY HEAVY RAIN AMOUNTS SHOULD BE
MORE SCATTERED AND THERE ARE AMPLE PLACEMENT DIFFERENCES IN THE
MODELS, AS WELL AS SOME TIMING DIFFERENCES THAT INCLUDE HEAVIER
AMOUNTS TAKING PLACE ON SUNDAY RATHER THAN MONDAY. THESE AREAS
GENERALLY HAVE DRY ANTECEDENT CONDITIONS IN TERMS OF SOIL MOISTURE
AND STREAMFLOWS, THOUGH SOME RAINFALL EXPECTED IN THE SHORT TERM
MAY TEMPER THE INITIAL DRYNESS. SO THERE ARE SOME POSITIVES AND
NEGATIVES IN TERMS OF FLASH FLOODING INGREDIENTS AND WILL HOLD OFF
INTRODUCING AN ERO RISK AREA FOR MONDAY.
DETAILS OF THE SURFACE PATTERN AND CORRESPONDING PRECIPITATION
COVERAGE, AMOUNTS, AND TIMING OVER THE CENTRAL/EASTERN U.S. BECOME
INCREASINGLY UNCERTAIN BY MID NEXT WEEK, BUT MODELS DO CONTINUE TO
INDICATE ANOTHER ROUND OF MODERATE TO HEAVY RAINFALL EMERGING IN
THE SOUTH-CENTRAL U.S. TO MID-SOUTH. PRECIPITATION MAY SPREAD
ACROSS THE EASTERN SEABOARD ON THURSDAY-FRIDAY, WITH SOME WINTRY
WEATHER POSSIBLE ON THE NORTHWESTERN SIDE OF THE LOW TRACK. THIS
FORECAST INDICATES SOME 10-30 PERCENT PROBABILITIES OF 0.25" QPF
IN THE FORM OF SNOW IN THE INTERIOR NORTHEAST ESPECIALLY IN HIGHER
ELEVATIONS, BUT CONTINUE TO MONITOR FORECASTS BECAUSE SNOW AMOUNTS
AND PLACEMENT WILL BE QUITE SENSITIVE TO THE UNCERTAIN EVENTUAL LOW
TRACK.
THE NORTHERN HALF OF THE WEST COAST AND INTO THE NORTHWEST SHOULD
SEE ANOTHER EPISODE OF RAIN AND HIGHER ELEVATION SNOW ON MONDAY
LASTING INTO TUESDAY. AFTER THAT, THE WEST SHOULD SEE DRIER
CONDITIONS UNDERNEATH RIDGING, OTHER THAN PERHAPS SOME MOISTURE
INTO WESTERN WASHINGTON ROUNDING THE RIDGE.
WITHIN AN INITIAL GENERALLY MILD PATTERN ACROSS THE LOWER 48,
WARMEST ANOMALIES SHOULD EXTEND FROM THE EASTERN SLOPES OF THE
ROCKIES TO THE EAST. EXPECT A DECENT AREA OF HIGHS 10-15 DEGREES
ABOVE NORMAL AND ANOMALIES UP TO PLUS 15-25 DEGREES IN PLACES FOR
MORNING LOWS. AFTER WEDNESDAY, TEMPERATURES SHOULD TREND BACK TO
NORMAL ACROSS THE CENTRAL-EASTERN U.S. WITH SOME BELOW NORMAL
READINGS POSSIBLE ACROSS THE NORTHERN PLAINS AS ARCTIC HIGH
PRESSURE NUDGES INTO THE REGION. OUT WEST, EXPECT TEMPERATURES TO
TREND WARMER UNDERNEATH PERSISTENT AMPLIFIED RIDGING.
TATE/SANTORELLI
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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page