115
FXUS02 KWBC 271835
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
135 PM EST WED NOV 27 2024
VALID 12Z SAT NOV 30 2024 - 12Z WED DEC 04 2024
...ARCTIC COLD WILL SPREAD ACROSS THE NORTHERN PLAINS WITH BELOW
NORMAL TEMPERATURES REACHING MOST AREAS EAST OF THE ROCKIES...
...MULTIPLE DAYS OF HEAVY LAKE EFFECT SNOW THIS WEEKEND INTO NEXT
WEEK...
..OVERVIEW
A LARGE SCALE UPPER TROUGH IS EXPECTED TO ENCOMPASS MUCH OF THE
CENTRAL TO EASTERN UNITED STATES OVER THE WEEKEND, WITH SOME VERY
GRADUAL SHIFT EAST AS NEXT WEEK PROGRESSES. THIS PATTERN WITH
WEST/NORTHWEST WINDS WILL BECOME FAVORABLE FOR LONG DURATION LAKE
EFFECT SNOW. SOME OF THE SNOWFALL ACCUMULATIONS COULD BE
SIGNIFICANT IN FAVORED LOCATIONS. THE TROUGH ALOFT AND COLD SURFACE
HIGH PRESSURE STEMMING FROM THE ARCTIC WILL CAUSE TEMPERATURES TO
DROP WELL BELOW AVERAGE ACROSS MUCH OF THE COUNTRY EAST OF THE
ROCKIES. 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 SATURDAY MORNING. MEANWHILE BENIGN WEATHERAND
MORE MODERATE TEMPERATURES ARE FORECAST FOR THE WEST.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE GUIDANCE CONTINUES TO SHOW GOOD AGREEMENT ON THE LARGE SCALE
PATTERN ACROSS THE CONUS INTO NEXT WEEK. SOME SMALLER SCALE
FEATURES EMBEDDED WITHIN THE MEAN FLOW COULD HAVE IMPACTS ON
SENSIBLE WEATHER, BUT ARE ALSO MUCH LESS PREDICTABLE AT LATER TIME
SCALES. THIS INCLUDES MULTIPLE SHORTWAVES TRACKING THROUGH THE
WESTERN AND SOUTHERN SIDES OF THE TROUGH THAT COULD PROVIDE FORCING
FOR LIGHT SNOW EVENTS, LAKE EFFECT SNOW ENHANCEMENT, OR JUST HELP
DETERMINE WHERE THE FRONTAL POSITION WILL BE. BY TUESDAY-WEDNESDAY
THE MODELS DIFFER WITH THE STRENGTH OF A SHORTWAVE EXITING INTO THE
WESTERN ATLANTIC AND ALSO WITH HOW MUCH ENERGY COMES SOUTH FROM
CENTRAL CANADA. ELSEWHERE, SPLIT FLOW WILL PREVAIL ACROSS THE
EASTERN PACIFIC TO WESTERN U.S., AS NORTHERN STREAM RIDGING COMES
ACROSS THE PACIFIC NORTHWEST, WHILE A COUPLE ROUNDS OF SOUTHERN
STREAM TROUGHING NUDGES TOWARD CALIFORNIA. ACROSS THE ENTIRE CONUS
THOUGH, A GENERAL MODEL BLEND SEEMS TO SUFFICE TO HELP SMOOTH SOME
OF THE LESS PREDICTABLE DETAILS. WAS ABLE TO BLEND THE OPERATIONAL
GUIDANCE THE FIRST HALF OF THE PERIOD, BRINGING IN UP TO HALF
ENSEMBLE MEANS BY DAY 7. OVERALL, MAINTAINED VERY GOOD AGREEMENT
WITH THE PREVIOUS WPC FORECAST.
..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 WILL BE A NOTICEABLE
CHANGE IN MANY AREAS, AND FOR SOME ACROSS THE NORTHERN PLAINS,
POTENTIALLY DANGEROUS COLD TEMPERATURES ARE EXPECTED. OVERNIGHT
LOWS IN THE NEGATIVE TEENS COULD COMBINE WITH WIND TO BRING WIND
CHILLS DOWN INTO THE -20S, APPROACHING -30F, IN NORTH DAKOTA IN
PARTICULAR FOR THE WEEKEND. THIS WILL POSE AN INCREASED RISK OF
HYPOTHERMIA AND FROSTBITE ON EXPOSED SKIN, SO TAKE APPROPRIATE
PREPAREDNESS ACTIONS. HIGHS ARE FORECAST TO REMAIN IN THE SINGLE
DIGITS AND TEENS. TEMPERATURES ARE LIKELY TO GRADUALLY MODERATE
ACROSS THE NORTH-CENTRAL U.S. AND REACH AVERAGE VALUES BY MIDWEEK.
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 TOWARD 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. BY
TUESDAY-WEDNESDAY THE COLDEST AIR WILL MIGRATE OVER THE EAST WITH
TEMPERATURES GENERALLY 10-15 DEGREES BELOW NORMAL AS THE UPPER
TROUGH AXIS SLOWLY SHIFTS EAST.
HEAVY LAKE-EFFECT SNOW IS EXPECTED THROUGH MUCH OF THE PERIOD, AS
WESTERLY FLOW DEVELOPS SNOW EAST OF THE LAKES THROUGH SATURDAY, AND
WINDS MAY SHIFT TO A MORE NORTHWESTERLY DIRECTION INTO EARLY NEXT
WEEK FOR A SNOW FOCUS SOUTHEAST OF THE LAKES SUNDAY-TUESDAY.
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 TO MID-
MISSISSIPPI AND OHIO VALLEYS SATURDAY, THOUGH THE AXIS AND TIMING
ARE SOMEWHAT UNCERTAIN DEPENDING ON A SHORTWAVE ALOFT. RETURN FLOW
OF MOISTURE COULD START TO COME INTO THE WESTERN GULF COAST REGION
OVER THE WEEKEND FOR SOME SHOWER ACTIVITY, WHICH MAY SPREAD INLAND
INTO THE SOUTH-CENTRAL U.S. BY MONDAY AND TUESDAY.
SANTORELLI/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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