836
FXUS02 KWBC 260653
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
153 AM EST TUE NOV 26 2024
VALID 12Z FRI NOV 29 2024 - 12Z TUE DEC 03 2024
...ARCTIC COLD WILL SPREAD ACROSS THE NORTHERN PLAINS WITH BELOW
NORMAL TEMPERATURES REACHING MOST AREAS EAST OF THE ROCKIES...
...MULTIPLE DAYS OF POTENTIALLY HEAVY LAKE EFFECT SNOW LATE THIS
WEEK INTO EARLY NEXT WEEK...
..OVERVIEW
BY LATE WEEK, A LARGE SCALE UPPER TROUGH WILL BE SET UP ATOP MUCH
OF THE CENTRAL TO EASTERN UNITED STATES. A SURFACE LOW IS FORECAST
TO PULL AWAY FROM NEW ENGLAND AS THE PERIOD BEGINS FRIDAY, BEHIND
WHICH BREEZY WESTERLY WINDS (SHIFTING A BIT TO NORTHWESTERLY BY
EARLY NEXT WEEK) ATOP THE GREAT LAKES WILL PROVIDE A FAVORABLE
PATTERN FOR LAKE EFFECT SNOW. HEAVY SNOW MAY ACCUMULATE IN
TYPICALLY FAVORED LOCATIONS DOWNWIND. THE TROUGH ALOFT AND COLD
SURFACE HIGH PRESSURE STEMMING FROM THE ARCTIC WILL CAUSE
TEMPERATURES TO DROP WELL BELOW AVERAGE IN THE NORTHERN PLAINS
SOUTHEASTWARD ACROSS THE MISSISSIPPI VALLEY, OHIO/TENNESSEE
VALLEYS, AND TOWARD THE APPALACHIANS AND EASTERN SEABOARD. THIS
WILL BE THE COLDEST AIR OF THE SEASON SO FAR, WITH TEMPERATURES
FALLING INTO THE NEGATIVE TEENS AND WIND CHILLS IN THE -20S IN
NORTH DAKOTA. MEANWHILE QUIETER WEATHER AND MORE MODERATE
TEMPERATURES ARE FORECAST FOR THE WEST.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE LARGE SCALE PATTERN DURING THE LATE WEEK INTO EARLY NEXT WEEK
MEDIUM RANGE PERIOD IS FORTUNATELY REASONABLY PREDICTABLE WITH THE
BROAD TROUGHING ENCOMPASSING MUCH OF THE CENTRAL AND EASTERN UNITED
STATES. SMALLER SCALE FEATURES EMBEDDED WITHIN THE MEAN FLOW COULD
HAVE SENSIBLE WEATHER IMPACTS THOUGH. ONE EXAMPLE IS WITH A
SHORTWAVE TRACKING THROUGH THE NORTH-CENTRAL U.S. ON THE WESTERN
SIDE OF THE TROUGH FRIDAY-SATURDAY THAT LOOKS TO BRING A STREAK OF
LIGHT TO MODERATE SNOW GENERALLY FROM THE NORTH-CENTRAL PLAINS INTO
THE MID-MISSISSIPPI VALLEY. THE DEPTH OF THE SHORTWAVE WILL HELP
DETERMINE THE AXIS OF THE SNOW, WITH SOME MODEL SPREAD THAT IS
REASONABLE FOR A SUBTLE FEATURE. THE GENERAL TREND IN THIS CYCLE
WAS FOR THE SHORTWAVE TO DIG A BIT MORE, LEADING TO A FARTHER SOUTH
SNOW AXIS, BUT WITH LOW CONFIDENCE.
SPLIT FLOW WILL PREVAIL ACROSS THE EASTERN PACIFIC TO WESTERN
U.S., AS NORTHERN STREAM RIDGING COMES ACROSS THE PACIFIC
NORTHWEST, WHILE SOUTHERN STREAM TROUGHING NUDGES TOWARD
CALIFORNIA. MODELS ARE PRETTY AGREEABLE ON THE NORTHERN STREAM
RIDGE OTHER THAN CMC RUNS THAT HAVE BEEN AGGRESSIVE IN BRINGING A
SHORTWAVE INTO THE NORTHWEST SUNDAY-MONDAY AND BECOMING OUT OF
PHASE. THE 12Z CMC WAS ALSO THE ONLY MODEL TO DIG CANADIAN ENERGY
SO DEEP THAT IT COMES INTO THE NORTHERN PLAINS BY TUESDAY, SO THIS
WAS NOT FAVORED. FARTHER SOUTH, MODELS SHOW REASONABLE TIMING WITH
DRIFTING TROUGHING EASTWARD TOWARD CALIFORNIA THROUGH THE WEEKEND,
WITH A BIT MORE SPREAD INTO MONDAY-TUESDAY AS AN UPSTREAM ROUND OF
ENERGY MAY INTERACT, BUT THE VARIABILITY WAS WITHIN REASON FOR A
LATE PERIOD FORECAST.
THE WPC FORECAST WAS BASED ON A BLEND OF THE DETERMINISTIC MODELS
EARLY IN THE PERIOD, GRADUALLY RAMPING UP THE ENSEMBLE MEANS TO
HALF BY DAYS 6-7. THIS MAINTAINED GOOD CONTINUITY FROM THE PREVIOUS
FORECAST (DAYS 3-6).
..WEATHER/HAZARDS HIGHLIGHTS
AS A PRONOUNCED UPPER TROUGH SETTLES OVER THE CENTRAL AND EASTERN
U.S., A SIGNIFICANT ARCTIC AIR INTRUSION IN THE FORM OF A COLD
SURFACE HIGH WILL SPREAD FROM THE NORTHERN PLAINS SOUTHEASTWARD
INTO THE WEEKEND. THIS EVENT DOES NOT LOOK TO BREAK MANY
TEMPERATURE RECORDS NOR IS IT PARTICULARLY EARLY IN THE SEASON FOR
THE FIRST ARCTIC AIRMASS. HOWEVER, THE COLD COULD STILL BE A SHOCK
TO THE SYSTEM AS THE COLDEST AIR SINCE MID-FEBRUARY. THE VERY COLD
TEMPERATURES IN THE SINGLE DIGITS TO TEENS AND OVERNIGHT LOWS WELL
BELOW ZERO COMBINED WITH WINDY CONDITIONS WILL BRING DANGEROUSLY
COLD WIND CHILLS TO PARTS OF THE NORTHERN PLAINS AND UPPER MIDWEST,
BELOW -20F IN NORTH DAKOTA. THIS WILL POSE AN INCREASED RISK OF
HYPOTHERMIA AND FROSTBITE ON EXPOSED SKIN, SO TAKE APPROPRIATE
PREPAREDNESS ACTIONS. A HANDFUL OF RECORD LOW MAX AND MIN
TEMPERATURES ARE MORE LIKELY FARTHER SOUTH 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. TEMPERATURES ARE LIKELY TO MODERATE ACROSS THE NORTH-CENTRAL
U.S. INTO EARLY NEXT WEEK, WHILE THE GREATEST BELOW NORMAL
TEMPERATURE ANOMALIES ARE FORECAST TO MIGRATE OVER THE EAST IN
MODERATED FORM.
HEAVY LAKE-EFFECT SNOW IS EXPECTED THROUGH MUCH OF THE PERIOD, AS
WESTERLY FLOW DEVELOPS SNOW EAST OF THE LAKES FRIDAY-SATURDAY, AND
WINDS MAY SHIFT TO A MORE NORTHWESTERLY DIRECTION INTO EARLY NEXT
WEEK FOR A SNOW FOCUS SOUTHEAST OF THE LAKES SUNDAY-MONDAY.
SIGNIFICANT ACCUMULATIONS ARE POSSIBLE FOR SOME OF THE FAVORED LAKE
EFFECT LOCATIONS. WHILE SPECIFIC ACCUMULATIONS WILL BECOME CLEARER
OVER THE NEXT FEW DAYS, PEAK AMOUNTS ARE LIKELY DOWNWIND OF LAKE
ERIE AND LAKE ONTARIO. TRAVEL DISRUPTIONS ARE LIKELY ESPECIALLY ON
I-90 BETWEEN CLEVELAND AND BUFFALO AND I-81 NORTH OF SYRACUSE.
ELSEWHERE, A QUIETER PERIOD IS LIKELY FOR THE WEST PRECIPITATION-
WISE. LIGHT TO LOCALLY MODEST PRECIPITATION IS POSSIBLE AT TIMES IN
THE PACIFIC NORTHWEST INTO THE NORTHERN ROCKIES. EXPECT
TEMPERATURES IN THE ROCKIES WESTWARD TO BE NEAR AVERAGE LATE THIS
WEEK AND WARM TO A FEW DEGREES ABOVE NORMAL INTO EARLY NEXT WEEK.
MODELS CONTINUE TO SHOW A GENERAL SIGNAL FOR A ROUND OF LIGHT TO
MODERATE SNOW ACROSS PARTS OF THE NORTH-CENTRAL PLAINS ON FRIDAY
INTO THE MID-MISSISSIPPI AND OHIO VALLEYS SATURDAY, THOUGH THE AXIS
IS UNCERTAIN DEPENDING ON A SHORTWAVE ALOFT. MEANWHILE, SOME RAIN
SHOWERS ARE POSSIBLE IN FLORIDA ON FRIDAY WITH A COLD FRONT. OVER
THE WEEKEND AND EARLY NEXT WEEK, RETURN FLOW OF MOISTURE COULD
START TO COME INTO THE WESTERN GULF COAST REGION FOR SOME SHOWER
ACTIVITY.
TATE/TAYLOR
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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