937
FXUS02 KWBC 280657
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
157 AM EST THU NOV 28 2024
VALID 12Z SUN DEC 01 2024 - 12Z THU DEC 05 2024
..ARCTIC COLD GRADUALLY MODERATING AS IT PUSHES EAST NEXT WEEK
..LAKE EFFECT SNOW LIKELY TO CONTINUE INTO NEXT WEEK
..OVERVIEW
A LARGE SCALE UPPER TROUGH IS EXPECTED TO ENCOMPASS MUCH OF THE
CENTRAL TO EASTERN UNITED STATES AT THE START OF THE PERIOD SUNDAY,
WITH SOME VERY GRADUAL SHIFT EAST AND WEAKENING AS NEXT WEEK
PROGRESSES. THIS PATTERN WITH WEST/NORTHWEST WINDS WILL BE
FAVORABLE FOR CONTINUED LONG DURATION LAKE EFFECT SNOW. SOME OF THE
SNOWFALL ACCUMULATIONS COULD BE SIGNIFICANT IN FAVORED LOCATIONS.
THE TROUGH ALOFT AND COLD SURFACE HIGH PRESSURE ORIGINALLY STEMMING
FROM THE ARCTIC WILL CAUSE CONTINUED COLDER THAN AVERAGE
TEMPERATURES MIGRATING ACROSS CENTRAL AND EASTERN PARTS OF THE
COUNTRY. MEANWHILE BENIGN WEATHER AND GRADUALLY WARMING
TEMPERATURES ARE FORECAST FOR THE WEST.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE IS RATHER AGREEABLE WITH THE LARGE SCALE PATTERN
NEXT WEEK, INCLUDING THE BROAD UPPER TROUGH ATOP THE
CENTRAL/EASTERN U.S. AND SPLIT FLOW ACROSS THE WEST WITH NORTHERN
STREAM RIDGING AND ROUNDS OF SOUTHERN STREAM TROUGHING IN THE
EASTERN PACIFIC TOWARD CALIFORNIA AND THE SOUTHWEST. THERE IS A
GENERAL SIGNAL FOR THE EASTERN TROUGH TO START LIFTING OUT OF THE
SOUTHEAST AND FOR THE TROUGH TO DRIFT EAST AS THE WEEK PROGRESSES.
HOWEVER, THE EASTWARD SHIFT IS MADE MORE COMPLEX BY SHORTWAVES
MOVING THROUGH THE TROUGH THAT ARE MORE UNCERTAIN IN TIMING AND
DEPTH. THERE WERE NOT PARTICULAR MODEL OUTLIERS WITH THESE
FEATURES, ASIDE FROM THE 12Z CMC THAT BECAME A BIT STRONG WITH A
WESTERN ATLANTIC SHORTWAVE AND DISPLACED WITH A HUDSON BAY UPPER
LOW BY DAY 7/THURSDAY. SURFACE FRONTS FORCED BY THESE SHORTWAVES
ARE UNCERTAIN IN PLACEMENT. EXPECT THIS TO BE THE ASPECT OF THE
FORECAST THAT CHANGES THE MOST IN FUTURE DAYS AS THESE CLIPPER
SYSTEMS ARE NOT VERY PREDICTABLE.
ACROSS THE WEST, MODELS APPEAR REASONABLE WITH INITIAL ENERGY
COMING INTO SOUTHERN CALIFORNIA SUNDAY. THEN 12/18Z MODELS VARIED A
BIT MORE WITH TIMING OF A MORE NOTABLE SOUTHERN STREAM TROUGH
APPROACHING; NAMELY, THE 12Z ECMWF WAS ON THE SLOWER SIDE IN
BRINGING THIS POSITIVELY TILTED TROUGH/POTENTIAL CLOSED LOW TOWARD
THE SOUTHWEST AND NORTHERN MEXICO TUESDAY-WEDNESDAY. THE NEWER 00Z
MODEL SUITE SEEMS TO BE COMING IN WITH BETTER ALIGNMENT UNTIL DAY
7/THURSDAY WHEN THERE ARE TIMING DIFFERENCES WITH THAT TROUGH/LOW
DRIFTING EASTWARD THAT COULD DEPEND IN PART ON A POSSIBLE NORTHERN
STREAM SHORTWAVE DISRUPTING THE RIDGE AXIS.
THE WPC FORECAST USED A BLEND OF THE DETERMINISTIC MODELS EARLY IN
THE FORECAST PERIOD, AND GRADUALLY REDUCED THE DETERMINISTIC
GUIDANCE WHILE INCREASING THE PROPORTION OF ENSEMBLE MEANS TO HALF
BY DAYS 6-7 TO SMOOTH OUT DIFFERENCES FROM THE INDIVIDUAL MODELS.
..WEATHER/HAZARDS HIGHLIGHTS
THE PRONOUNCED UPPER TROUGH AND A COLD SURFACE HIGH WILL REMAIN IN
PLACE INTO EARLY 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 SUNDAY-MONDAY IN THE NORTHERN
PLAINS AS LOWS WILL BE IN THE NEGATIVE SINGLE DIGITS WITH HIGHS IN
THE LOW 10S. MEANWHILE THE COLD WILL SPREAD FARTHER SOUTHEAST IN
MODERATED FORM, REACHING MOST AREAS EAST OF THE ROCKIES 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
SUNDAY-TUESDAY. BY MIDWEEK THE COLD SHOULD BE GRADUALLY LESSENING
IN SCOPE AND MAGNITUDE, BECOMING MORE LIMITED TO THE EAST WEDNESDAY
AND NORTHEAST THURSDAY WITH TEMPERATURES THAT ARE BELOW NORMAL BY
AROUND 5-10 DEGREES. MEANWHILE ABOVE AVERAGE TEMPERATURES ARE
FORECAST TO SPREAD ACROSS THE WEST AND REACH THE PLAINS BY
WEDNESDAY-THURSDAY.
A FAVORABLE PATTERN FOR LAKE EFFECT SNOW WILL PERSIST INTO EARLY
NEXT WEEK. EXACT SNOW AXES WILL DEPEND ON WIND DIRECTIONS THAT
COULD VARY FROM NORTHWEST TO WEST DAY TO DAY, BUT SOME AREAS
DOWNWIND OF THE LAKES COULD SEE SIGNIFICANT ACCUMULATIONS DURING
LATE THIS WEEK TO EARLY NEXT WEEK, LIKELY CAUSING TRAVEL
DISRUPTIONS ON I-90 BETWEEN CLEVELAND AND BUFFALO AND I-81 NORTH OF
SYRACUSE. CLOSER TO MIDWEEK, SHORTWAVES AND FRONTAL SYSTEMS MAY
COME THROUGH THE GREAT LAKES REGION FOR SOME ADDITIONAL LIGHT SNOW
THAT COULD COVER A BROADER AREA.
MUCH OF THE REST OF THE COUNTRY CAN EXPECT GENERALLY DRY
CONDITIONS NEXT WEEK. RETURN FLOW OF MOISTURE COULD START TO COME
INTO THE WESTERN GULF COAST REGION BY EARLY NEXT WEEK FOR SOME
SHOWER ACTIVITY, WHICH LOOKS TO SPREAD ACROSS THE SOUTH-CENTRAL
U.S. MONDAY-WEDNESDAY. INITIAL NORTHERN STREAM RIDGING WILL KEEP
THE WEST DRY FOR THE MOST PART, BUT PRECIPITATION CHANCES SHOULD
GRADUALLY INCREASE IN THE PACIFIC NORTHWEST AS NEXT WEEK
PROGRESSES.
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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page