853
FXUS02 KWBC 291850
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
150 PM EST FRI NOV 29 2024
VALID 12Z MON DEC 02 2024 - 12Z FRI DEC 06 2024
..CENTRAL/EAST ARCTIC COLD MAY MODERATE THEN RENEW NEXT WEEK
..SIGNIFICANT GREAT LAKE EFFECT SNOWS CONTINUE INTO NEXT WEEK
..OVERVIEW
A LARGE SCALE UPPER TROUGH IS EXPECTED TO ENCOMPASS MUCH OF THE
CENTRAL TO EASTERN UNITED STATES NEXT WEEK, WITH ONLY A VERY
GRADUAL SHIFT EAST AND WEAKENING OVER TIME. THIS PATTERN WITH
WEST/NORTHWEST WINDS WILL BE FAVORABLE FOR CONTINUED LONG DURATION
LAKE EFFECT FOCUSING SNOWS. SOME OF THE SNOWFALL ACCUMULATIONS
COULD BE SIGNIFICANT IN FAVORED TO THE LEE LOCATIONS. THE
PERIODICALLY REINFORCED TROUGH ALOFT AND COLD SURFACE HIGH PRESSURE
ORIGINALLY STEMMING FROM THE ARCTIC WILL CAUSE CONTINUED COLDER
THAN AVERAGE TEMPERATURES MIGRATING FAR SOUTHWARD ACROSS CENTRAL
AND EASTERN PARTS OF THE COUNTRY, ALBEIT LIKELY TO OFFER SOME
MODERATION OVER TIME AS RETURN INFLOW FROM THE GULF OF MEXICO ALSO
BRINGS SOME ENHANCED RAINFALL CHANCES TO TEXAS AND LOUISIANA WITH
SYSTEM GENESIS. MEANWHILE, BENIGN WEATHER AND GRADUALLY WARMING
TEMPERATURES ARE FORECAST FOR THE WEST.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODELS AND ENSEMBLE GUIDANCE CONTINUES TO SHOW FAIRLY GOOD
AGREEMENT AND AS A RESULT HIGHER CONFIDENCE IN THE OVERALL LARGE
SCALE PATTERN THROUGH NEXT WEEK. ESPECIALLY MID TO LATE PERIOD
THOUGH, THERE ARE SOME SMALLER SCALE DIFFERENCES PARTICULARLY WITH
SHORTWAVES WORKING TO REINFORCE EASTERN U.S. TROUGHING AND THE
SPECIFICS/FRONTAL TIMING OF A MORE DEFINED SURFACE LOW/SYSTEM
THROUGH THE GREAT LAKES MID NEXT WEEK. THERE IS ALSO SOME
UNCERTAINTY WITH THE TIMING/ORIENTATION OF A VERY SLOW MOVING
SOUTHERN STREAM ELONGATED TROUGH/CLOSED LOW NEAR THE SOUTHWEST U.S.
WHICH HAS IMPLICATIONS FOR RAINFALL AMOUNTS ACROSS SOUTH-SOUTHEAST
TEXAS MUCH OF THE WEEK. WPC PROGS FOR TODAY USED A GENERAL MODEL
BLEND FOR THE FIRST HALF OF THE PERIOD, TRENDING TOWARDS HALF OF
THE ENSEMBLE MEANS LATER IN THE PERIOD. THIS MAINTAINED GOOD
CONTINUITY WITH THE PREVIOUS WPC FORECAST AS WELL.
..WEATHER/HAZARDS HIGHLIGHTS
IT GENERALLY REMAINS THE CASE THAT A PRONOUNCED UPPER TROUGH AND A
COLD SURFACE HIGH WILL REMAIN IN PLACE INTO NEXT WEEK AND PRODUCE
SOME CONTINUED COLD WEATHER THAT COULD BE DANGEROUS IN THE NORTHERN
PLAINS. THE COLD IS FORECAST TO GRADUALLY MODERATE COMPARED TO THE
SHORT RANGE PERIOD, BUT REMAIN BELOW NORMAL BY 15-20F MONDAY IN
THE NORTHERN PLAINS AS LOWS WILL BE IN THE NEGATIVE SINGLE DIGITS
WITH HIGHS IN THE LOW 10S. MEANWHILE THE COLD AIR MASS WILL SPREAD
FARTHER SOUTHEAST IN MODERATED FORM, ACROSS THE MISSISSIPPI VALLEY,
OHIO/TENNESSEE VALLEYS, AND INTO THE APPALACHIANS AND EASTERN
SEABOARD. A HANDFUL OF RECORD LOW MAX AND MIN TEMPERATURES ARE
POSSIBLE ACROSS THE OHIO VALLEY INTO THE APPALACHIANS, WHERE
TEMPERATURES ARE FORECAST TO BE AROUND 15-20F BELOW AVERAGE AND
STAY BELOW FREEZING FOR HIGHS IN MANY AREAS MONDAY-TUESDAY. BY
MIDWEEK, THE COLD SHOULD BE GRADUALLY LESSENING IN SCOPE AND
MAGNITUDE, BECOMING MORE LIMITED TO THE EAST WEDNESDAY, BUT
ADDITIONAL COLD AIR MAY SURGE IN FROM CANADA INTO LATER NEXT WEEK.
MEANWHILE ABOVE AVERAGE TEMPERATURES ARE FORECAST TO SPREAD ACROSS
THE WEST AND REACH THE PLAINS INTO MID-LATER NEXT WEEK.
A FAVORABLE PATTERN FOR GREAT LAKE EFFECT SNOW WILL PERSIST INTO
NEXT WEEK. EXACT SNOW AXES AND LOCAL INTENSITIES WILL DEPEND ON
REINFORCING SYSTEM PASSAGES WITH WIND DIRECTIONS THAT COULD VARY
FROM NORTHWEST TO WEST DAY TO DAY, BUT SOME AREAS DOWNWIND OF THE
LAKES COULD SEE SIGNIFICANT ACCUMULATIONS, LIKELY CAUSING TRAVEL
DISRUPTIONS ON I-90 BETWEEN CLEVELAND AND BUFFALO AND I-81 NORTH OF
SYRACUSE. LATER, SHORTWAVES AND FRONTAL SYSTEMS MAY COME THROUGH
THE GREAT LAKES REGION FOR SOME ADDITIONAL LIGHT SNOW THAT COULD
COVER A BROADER AREA WITH LAKE ENHANCED SNOW POSSIBLE AGAIN ON THE
BACKSIDE.
MUCH OF THE REST OF THE COUNTRY CAN EXPECT MAINLY DRY CONDITIONS
NEXT WEEK. RETURN FLOW OF MOISTURE COULD START TO COME INTO THE
WESTERN GULF COAST REGION BY EARLY NEXT WEEK TO FUEL SOME ENHANCED
RAINFALL, WHICH LOOKS TO BE SLOW TO SPREAD ACROSS THE LOWER
MISSISSIPPI VALLEY AND VICINITY INTO MID-LATER NEXT WEEK. AT THIS
POINT, RAINFALL AMOUNTS ARE NOT HIGH ENOUGH TO WARRANT EVEN A
MARGINAL RISK ON THE DAYS 4 AND 5 EXCESSIVE RAINFALL OUTLOOKS, BUT
THIS CAN CONTINUED TO BE MONITORED GIVEN ANOMALOUS MOISTURE AND
MODEST INSTABILITY. INITIAL UPPER RIDGING WILL KEEP THE WEST MAINLY
DRY, BUT PRECIPITATION CHANCES MAY GRADUALLY INCREASE INTO THE
PACIFIC NORTHWEST LATER NEXT WEEK.
SANTORELLI/SCHICHTEL
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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