192
FXUS02 KWBC 091911
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
210 PM EST FRI DEC 09 2022
VALID 12Z MON DEC 12 2022 - 12Z FRI DEC 16 2022
..MOUNTAIN HEAVY SNOW/WIND THREAT INTO THE ROCKIES ON MONDAY
...MAJOR STORM SYSTEM TO BRING HEAVY SNOW/BLIZZARD CONDITIONS TO
NORTHERN-CENTRAL PLAINS WITH A HEAVY RAIN/SEVERE WEATHER THREAT
FOR SOUTHERN AREAS NEXT WEEK...
..OVERVIEW
A MAJOR STORM SYSTEM IS EXPECTED TO CROSS MUCH OF THE U.S. NEXT
WEEK. AS THE PERIOD BEGINS MONDAY, A DEEP UPPER TROUGH AND
EMBEDDED UPPER LOW WILL BE CROSSING THE INTERMOUNTAIN WEST,
PRODUCING WIDESPREAD AND POTENTIALLY SIGNIFICANT MOUNTAIN SNOWS
ACROSS THE HIGHER ELEVATIONS INCLUDING THE ROCKIES. BY TUESDAY AND
BEYOND, INTENSE CYCLOGENESIS IS EXPECTED TO OCCUR AND CONFIDENCE
REMAINS HIGH FOR A DEEP LOW PRESSURE SYSTEM EMERGING INTO THE
PLAINS. THIS SYSTEM SHOULD BRING A WIDE ARRAY OF HAZARDS INCLUDING
HEAVY RAIN/SEVERE WEATHER TO THE SOUTH AND HEAVY SNOW WITH HIGH
WINDS CREATING POTENTIAL BLIZZARD CONDITIONS ACROSS PARTS OF THE
NORTH-CENTRAL PLAINS AND INTO THE UPPER MIDWEST AROUND MIDWEEK
WITH SOME CHANCE OF FREEZING RAIN IN THE TRANSITION ZONE. THIS
STORM SYSTEM SHOULD TRACK STEADILY EASTWARD BRINGING A HEAVY RAIN
THREAT TO PARTS OF THE SOUTHEAST AND MID-ATLANTIC (WITH SOME MORE
UNCERTAIN SNOW POTENTIAL FARTHER NORTH) LATER NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THROUGH AROUND MIDWEEK, MODEL GUIDANCE HAS BEEN AND CONTINUES TO
BE WELL CLUSTERED FOR THE OVERALL PATTERN SETUP INCLUDING AN UPPER
LOW CLOSING OFF AS IT MOVES FROM THE WEST INTO THE PLAINS, WITH A
VIGOROUS SURFACE LOW CONSOLIDATING IN THE CENTRAL PLAINS AND
SHIFTING TOWARD THE MIDWEST. THERE REMAIN SOME WIGGLES IN THE
TIMING OF THE SURFACE LOW TRACK AND ITS ASSOCIATED FRONTS, WITH
RECENT CMC RUNS ON THE FASTER SIDE AND UKMET RUNS A LITTLE SLOWER.
BUT A MULTI-MODEL DETERMINISTIC BLEND WEIGHTED TOWARD THE GFS AND
ECMWF WORKED WELL FOR A COMPROMISE SOLUTION ON TIMING, WHICH WAS A
BIT FASTER THAN THE PREVIOUS FORECAST.
MODEL DIFFERENCES INCREASE LATER INTO THE WEEK WITH HOW THE
CENTRAL U.S. UPPER LOW EVOLVES, WHICH ARE DUE IN PART TO SYSTEMS
TO THE EAST AND WEST. TO THE EAST, A DEEP COMPACT UPPER LOW OVER
THE CANADIAN MARITIMES (WITH A SHORTWAVE EXTENDING INTO THE
NORTHEAST EARLY MONDAY) IS LIKELY TO DRIFT GRADUALLY SOUTHWARD
THROUGH MIDWEEK, BUT THEN THE TIMING OF ITS EJECTION EAST
(GENERALLY FASTER IN THE NEW 12Z GUIDANCE) PLAYS A ROLE IN HOW
MUCH THE CENTRAL U.S. UPPER LOW CAN MOVE EASTWARD OR STALL. THEN
TO THE WEST, AMPLE MODEL DIFFERENCES HAVE BEEN SEEN OVER THE PAST
FEW DAYS IN THE EVOLUTION/PLACEMENT OF A CLOSED UPPER LOW FORMING
ACROSS THE PACIFIC AND THEN POTENTIALLY ADDITIONAL ENERGY SPILLING
INTO THE WEST BY THE LATTER HALF OF THE WEEK DEPENDENT ON MANY
FACTORS INCLUDING THE FIRST UPPER LOW. WITH THESE DIFFERENCES
AMONG OTHERS, GFS RUNS INCLUDING THE NEW 12Z HAVE TRENDED TOWARD
FASTER WEAKENING OF THE CENTRAL U.S. UPPER LOW AND A QUICKER SHUNT
EASTWARD COMPARED TO OTHER GUIDANCE THAT MAINTAINS IT LONGER.
THESE DIFFERENCES AFFECT THE POTENTIAL FOR A DEVELOPING SURFACE
LOW THAT COULD TURN INTO A NOR'EASTER LATE NEXT WEEK (ECMWF/CMC
SOLUTIONS) OR GET SHUNTED EASTWARD OVER THE ATLANTIC (GFS
DETERMINISTIC RUN WITH SUPPORT FROM MANY GEFS MEMBERS). WITH THESE
DIFFERENCES, CONFIDENCE IN THE PATTERN DIPS BY THE LATER PART OF
THE PERIOD ESPECIALLY ACROSS THE EAST. THE LATTER PART OF THE
MEDIUM RANGE FORECAST BLEND FAVORED INCREASING PROPORTIONS OF THE
EC AND GEFS ENSEMBLE MEANS GIVEN THIS INCREASING UNCERTAINTY.
..WEATHER/HAZARD HIGHLIGHTS
AS THE MAIN UPPER TROUGH DIGS ACROSS THE WEST ON MONDAY AND SHIFTS
EASTWARD THE REMAINDER OF THE WEEK, A WIDE VARIETY OF HAZARDS ARE
LIKELY ACROSS THE COUNTRY. HEAVY PRECIPITATION IS IMMINENT ACROSS
THE WEST THROUGH MONDAY, WITH HEAVY SNOW ESPECIALLY INTO HIGHER
ELEVATIONS OF THE GREAT BASIN AND ROCKIES. THEN AS THE UPPER
TROUGH/LOW APPROACHES THE PLAINS AND A SURFACE LOW CONSOLIDATES
AND DEEPENS, AMPLE MOISTURE WILL SPREAD AHEAD OF A COLD FRONT TO
PRODUCE SIGNIFICANT RAINFALL ACROSS THE LOWER/MIDDLE MISSISSIPPI
VALLEY AND VICINITY BEGINNING MONDAY BUT WITH HIGHER AMOUNTS BY
TUESDAY, WHICH SHOULD SHIFT EAST WITH TIME. THE STORM PREDICTION
CENTER CONTINUES TO MONITOR AND HIGHLIGHT THE POTENTIAL FOR STRONG
TO SEVERE CONVECTION ACROSS THIS REGION AS WELL. ON THE BACKSIDE
OF THE LOW, COLD TEMPERATURES AND WRAP-BACK MOISTURE WILL SUPPORT
SIGNIFICANT SNOW/WINDS IN THE NORTHERN PLAINS/UPPER MIDWEST AS
SHOWN BY STEADILY INCREASING WPC WINTER WEATHER OUTLOOK
PROBABILITIES AS WELL AS AREAS OF ICE/FREEZING RAIN WITHIN THE
TRANSITION ZONE. BY THE LATTER HALF OF THE WEEK, CURRENT FORECASTS
SHOW PRECIPITATION IS LIKELY TO SPREAD ACROSS THE EAST COAST ALONG
AND AHEAD OF THE FRONTAL SYSTEM, WITH POTENTIAL FOR WINTRY WEATHER
SPREADING ACROSS THE GREAT LAKES REGION AND NORTHEAST WHILE HEAVY
RAIN COULD BE A THREAT IN THE SOUTHEAST. BUT PRECIPITATION TYPES
AND AREAS OF HEAVIEST PRECIPITATION HAVE A GREAT DEAL OF
UNCERTAINTY ESPECIALLY CONSIDERING POSSIBLE COASTAL LOW
DEVELOPMENT OFF THE MID-ATLANTIC COAST.
THE WEST SHOULD SEE BELOW NORMAL CONDITIONS THROUGH THE PERIOD,
WITH THE MOST WIDESPREAD READINGS OF AT LEAST 10-15F BELOW NORMAL
FOR HIGH TEMPERATURES AS THE DEEP UPPER TROUGH CROSSES THE REGION
FOR THE FIRST HALF OF NEXT WEEK. SOME OF THIS COLDER AIR SHOULD
SPILL INTO THE HIGH PLAINS BY NEXT TUESDAY-THURSDAY BEHIND THE
EXPECTED PLAINS STORM. ON THE OTHER HAND, SOUTHERN/EASTERN AREAS
WILL BE NEAR TO ABOVE NORMAL FOR TEMPERATURES. ANOMALIES WILL BE
GREATEST FOR MORNING LOWS, WITH SOME PLUS 15-25F ANOMALIES ACROSS
THE SOUTHERN TIER THROUGH MUCH OF THE PERIOD EXPANDING NORTHWARD
AT TIMES ACROSS THE MISSISSIPPI VALLEY. HIGHS ARE FORECAST TO BE
AROUND 10-15F ABOVE NORMAL FOR THE CENTRAL AND THEN EAST-CENTRAL
U.S., LOCALLY HIGHER AHEAD OF THE STORM SYSTEM. MUCH OF THE
COUNTRY LOOKS TO BE NEAR OR BELOW NORMAL BY NEXT FRIDAY AFTER THE
COLD FRONTAL PASSAGE.
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, EXPERIMENTAL EXCESSIVE RAINFALL
OUTLOOK, WINTER WEATHER OUTLOOK PROBABILITIES AND HEAT INDICES ARE
AT:
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
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