401
FXUS02 KWBC 081905
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
204 PM EST THU DEC 08 2022
VALID 12Z SUN DEC 11 2022 - 12Z THU DEC 15 2022
...HEAVY COASTAL RAINS AND WIDESPREAD MOUNTAIN/INLAND HEAVY
SNOW/WIND THREAT ACROSS THE WEST/ROCKIES INTO SUNDAY/MONDAY...
...DEEP STORM GENESIS/BLIZZARD THREAT WITH HEAVY SNOW AND
TRANSITION AREAS OF ICE/FREEZING RAIN FOR THE NORTH-CENTRAL U.S.
MONDAY PAST MIDWEEK...
...EXCESSIVE RAINFALL AND SEVERE WEATHER THREAT TO SPREAD EASTWARD
FROM THE SOUTH-CENTRAL U.S. MONDAY PAST MIDWEEK...
..OVERVIEW
RAIN SHOWERS AND THUNDERSTORMS ARE POSSIBLE ACROSS THE
SOUTHEASTERN U.S. WITH A WAVY FRONT IN THE VICINITY THIS WEEKEND,
WHILE FARTHER NORTH A POTENT SHORTWAVE WILL SPREAD RAIN/SNOW FROM
THE GREAT LAKES REGION INTO THE NORTHERN MID-ATLANTIC AND
NORTHEAST BEFORE TRACKING OFFSHORE TO DEVELOP A DEEP ATLANTIC
STORM THREAT OFF THE NORTHEAST TOWARD THE CANADIAN MARITIMES NEXT
WEEK.
HOWEVER, THE MAIN STORY DURING THE MEDIUM RANGE PERIOD WILL BE
UPSTREAM WHERE WELL CLUSTERED GUIDANCE HAVE NOW LOCKED IN ON
DEPICTION OF AN AMPLIFIED TROUGH TO WORK INLAND FROM THE WEST
COAST THROUGH THE WEEKEND, WITH THE DEEPEST REINFORCING ENERGY
ARRIVING SUNDAY INTO MONDAY LEADING TO CLOSED LOW/TROUGH FORMATION
OVER THE INTERMOUNTAIN WEST. THE DYNAMIC SYSTEM WILL LIFT
VIGOROUSLY OVER THE CENTRAL U.S. TUESDAY-THURSDAY. THIS PATTERN
WOULD SUPPORT A PERIOD OF WIDESPREAD AND SIGNIFICANT
TERRAIN-ENHANCED RAIN AND MOUNTAIN SNOW OVER THE WEST THROUGH THE
WEEKEND INTO EARLY NEXT WEEK. THIS IS INCREASINGLY EXPECTED TO BE
FOLLOWED BY EXPANDING/INTENSIFYING RAINFALL OVER THE MISSISSIPPI
VALLEY/VICINITY EASTWARD ACROSS THE EAST-CENTRAL U.S. ALONG WITH
SIGNIFICANT WRAP-BACK SNOW OVER THE NORTH-CENTRAL U.S. EARLY-MID
NEXT WEEK IN ASSOCIATION WITH DEEP STORM/POSSIBLE BLIZZARD GENESIS
AND CORRESPONDING FRONTS. THIS SYSTEM SHOULD ALSO CAUSE BELOW
NORMAL HIGH TEMPERATURES OVER THE WEST AND NEAR TO ABOVE NORMAL
PRE-FRONTAL READINGS OVER MUCH OF THE EASTERN HALF OF THE COUNTRY.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL AND ENSEMBLE FORECASTS CONTINUE TO BE WELL CLUSTERED FOR THE
MAIN SURFACE/UPPER LOW CONSIDERING THE MEDIUM RANGE TIMESCALE,
BOLSTERING FORECAST CONFIDENCE. THE STORM SYSTEM KEEPS TRENDING A
LITTLE SLOWER IN THE 00Z/06Z RUNS AND NEW 12Z RUNS COMPARED TO
PREVIOUS FORECASTS, LEADING TO AN UPWARD TREND IN PRECIPITATION ON
THE WRAPAROUND NORTHWEST SIDE OF THE LOW AS WELL AS A SLOWER
ARRIVAL OF PRECIPITATION. FARTHER UPSTREAM, DIFFERENCES IN THE
OVERALL FLOW BECOME CONSIDERABLE BY TUESDAY AND BEYOND OVER THE
PACIFIC--AFTER WHAT LOOKS TO BE A NARROW RIDGE BEHIND THE CENTRAL
U.S. UPPER LOW, PLACEMENT DIFFERENCES ABOUND WITH A PACIFIC UPPER
LOW WITH THE GFS SUITE GENERALLY FARTHER WEST WITH THE LOW
COMPARED TO THE FARTHER EAST EC/CMC. THIS LEADS TO DIFFERENCES IN
THE PATTERN ACROSS THE WESTERN U.S. BY DAY 7/THURSDAY AND COULD
CAUSE FORECAST ISSUES IN THE UPCOMING DAYS AS THE LOW MAY DRIFT
TOWARD THE CONUS. THE WPC FORECAST WAS BASED ON A MULTI-MODEL
00/06Z DETERMINISTIC BLEND EARLY WITH INCREASING AMOUNTS OF THE
GEFS AND EC ENSEMBLE MEANS FOR DAYS 5-7 GIVEN INCREASING MODEL
SPREAD ESPECIALLY IN THE PACIFIC/WEST.
..WEATHER/HAZARD HIGHLIGHTS
FOR THE WEEKEND, GULF OF MEXICO MOISTURE INFLOW COMBINED WITH A
WAVY SURFACE FRONT AND WEAK UPPER ENERGY MAY SUPPORT MODERATE TO
HEAVY RAINFALL ACROSS THE SOUTHEASTERN PART OF THE COUNTRY.
FARTHER NORTH, PRECIPITATION WILL LIKELY INCLUDE SOME PLOWABLE
SNOW TO SPREAD FROM THE GREAT LAKES THROUGH THE NORTHERN
MID-ATLANTIC AND THE NORTHEAST SUNDAY, WITH HIGHEST WWO
PROBABILITIES NOW OVER THE BEAUTIFUL CATSKILLS.
AS THE MAIN UPPER TROUGH DIGS ACROSS THE WEST THIS WEEKEND AND
SHIFTS EASTWARD THROUGH THE FIRST HALF OF NEXT WEEK, MULTIPLE
HAZARDS ARE LIKELY ACROSS THE COUNTRY. HEAVY PRECIPITATION IS
IMMINENT ACROSS THE WEST THIS WEEKEND/MONDAY, ESPECIALLY INCLUDING
HEAVY TERRAIN-ENHANCED SNOWS ACROSS THE SIERRA NEVADA AND FARTHER
EAST INTO HIGHER ELEVATIONS OF THE GREAT BASIN AND ROCKIES. LOWER
ELEVATION HEAVY RAIN IS ALSO POSSIBLE THIS WEEKEND PARTICULARLY
ACROSS COASTAL AND INTERIOR PARTS OF CALIFORNIA IN CONJUNCTION
WITH A WEAK-MODERATE ATMOSPHERIC RIVER. 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 AND ESPECIALLY BY TUESDAY AND
SHIFTING EAST WITH TIME. SOME STRONG TO SEVERE CONVECTION IS ALSO
POSSIBLE, WITH THE STORM PREDICTION CENTER ALREADY MONITORING THIS
POTENTIAL. 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 IN A TRANSITION ZONE. THIS ALSO SHOWS SOME
WINTRY WEATHER POTENTIAL SPREADING ACROSS THE GREAT LAKES REGION
AND NORTHEAST IN FAVORABLE DOWNSTREAM THETA-E ADVECTION OVER A
PRE-COOLED AIRMASS.
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.
SCHICHTEL/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, 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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