787
FXUS02 KWBC 220729
PMDEPD
EXTENDED FORECAST DISCUSSION...AMENDED
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
228 AM EST THU DEC 22 2022
VALID 12Z SUN DEC 25 2022 - 12Z THU DEC 29 2022
***UNSETTLED CONDITIONS FOR THE WEST COAST WITH HEAVY RAIN AND
HEAVY MOUNTAIN SNOW WITH AN ATMOSPHERIC RIVER EVENT EARLY NEXT
WEEK***
..SYNOPTIC OVERVIEW
THE OVERALL WEATHER PATTERN IMPROVES GOING INTO CHRISTMAS WEEKEND
ACROSS THE EASTERN HALF OF THE NATION AS THE CORE OF THE INTENSE
LOW LIFTS FARTHER NORTHWARD ACROSS CENTRAL CANADA AND WEAKENS WITH
TIME. HOWEVER, THERE WILL STILL BE SOME LINGERING LAKE EFFECT
SNOW, MAINLY DOWNWIND OF LAKES ERIE AND ONTARIO. THE IMPRESSIVELY
COLD AIRMASS WILL BEGIN MODIFYING AS THE SURFACE HIGH SETTLES
ACROSS THE SOUTHERN TIER STATES. LOOKING AHEAD TO EARLY NEXT
WEEK, AN ALBERTA CLIPPER SYSTEM TRACKS ACROSS THE CENTRAL/NORTHERN
PLAINS, AND A SOUTHERN STREAM DISTURBANCE TRACKS EASTWARD NEAR THE
GULF COAST. MULTIPLE SHORTWAVE PASSAGES NEAR THE PACIFIC
NORTHWEST WILL KEEP THINGS UNSETTLED FROM NORTHERN CALIFORNIA TO
WASHINGTON STATE WITH AN ATMOSPHERIC RIVER EVENT LIKELY DURING THE
MONDAY-TUESDAY NIGHT TIME PERIOD.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE LATEST 00Z MODEL GUIDANCE SUITE INDICATES VERY GOOD SYNOPTIC
SCALE AGREEMENT ON SUNDAY ON THE OVERALL UPPER LEVEL PATTERN THAT
FEATURES A WEST COAST RIDGE AND A GRADUALLY WEAKENING EASTERN U.S.
TROUGH. HOWEVER, MODEL DIFFERENCES INCREASE AS EARLY AS MONDAY
WITH THE SHORTWAVE DROPPING SOUTH ACROSS THE PLAINS, WITH THE GFS
INDICATING A MUCH FASTER SOLUTION, AND THE GFS SHOWS A STRONGER
UPPER TROUGH IN THE VICINITY OF THE SOUTHEAST COAST BY EARLY
TUESDAY, WHEREAS THE ENSEMBLE MEANS FARTHER INLAND AND WEAKER, AND
THE ECMWF IS ON THE SLOWER SIDE OF THE GUIDANCE. THERE IS STILL
NOT MUCH PHASING BETWEEN THIS AND THE NORTHERN STREAM SHORTWAVE,
SO THIS SHOULD LIMIT THE EXTENT OF ANY SURFACE CYCLOGENESIS. OUT
WEST, MODEL AGREEMENT HAS IMPROVED ACROSS THE EASTERN PACIFIC.
THE LARGER SCALE TROUGH EXPECTED TO MOVE INTO THE WEST BY DAY 6
WEDNESDAY, ALONG WITH THE FAIRLY STRONG PACIFIC SURFACE LOW
EARLIER, HAVE SOME DETAIL/TIMING SPREAD BUT WITH A REASONABLY
CONSISTENT SIGNAL OVERALL. THE WPC FRONTS/PRESSURES FORECAST
RELIED MAINLY ON A ECMWF/CMC/WPC CONTINUITY BLEND ALONG WITH A
LESSER PERCENTAGE OF THE GFS THROUGH DAY 4, AND THEN INCREASED USE
OF THE ENSEMBLE MEANS GOING FORWARD INTO THE MIDDLE OF THE WEEK.
..WEATHER/HAZARD HIGHLIGHTS
SATURDAY WILL FEATURE WIDESPREAD TEMPERATURE ANOMALIES OF 20-30
DEGREES BELOW AVERAGE FOR MORNING LOWS AND DAYTIME HIGHS ACROSS
MUCH OF THE CENTRAL AND EASTERN U.S. SUNDAY WILL STILL BE QUITE
COLD OVER THE EASTERN HALF OF THE COUNTRY WITH A BROAD AREA OF
READINGS 15-25 DEGREES BELOW NORMAL. THE THEME FOR NEXT WEEK WILL
BE A STEADY WARMING TREND AS THE UPPER PATTERN BECOMES LESS
AMPLIFIED. MODERATELY ABOVE NORMAL TEMPERATURES WILL BECOME
ESTABLISHED OVER THE WEST (LOWS TENDING TO BE A LITTLE MORE ABOVE
NORMAL THAN DAYTIME HIGHS) AND THEN SPREAD INTO THE HIGH PLAINS BY
NEXT TUESDAY-WEDNESDAY WITH SOME AREAS REACHING 10-20F ABOVE
NORMAL. THE EASTERN HALF OF THE COUNTRY WILL CONTINUE TO
MODERATE, LEADING TO MOSTLY SINGLE-DIGIT NEGATIVE ANOMALIES BY
NEXT WEDNESDAY.
A SERIES OF NORTHEASTERN PACIFIC SYSTEMS SHOULD BRING A MULTI-DAY
PERIOD OF ATMOSPHERIC RIVER EVENTS TO THE WEST COAST, LEADING TO
SIGNIFICANT TOTALS OF RAIN AND HIGHER ELEVATION SNOW. SOME OF
THIS MOISTURE WILL LIKELY EXTEND EASTWARD TO THE ROCKIES. THE
PRIMARY FOCUS DURING THE WEEKEND IS FORECAST TO BE OVER THE
PACIFIC NORTHWEST AND FAR NORTHERN ROCKIES. THERE IS STILL SOME
UNCERTAINTY OVER THE PRECISE INTENSITY AND SOUTHWARD EXTENT OF
PRECIPITATION AT ANY PARTICULAR TIME, THOUGH AT THE MOMENT THE
BEST SIGNAL FOR HIGHEST AMOUNTS IS OVER THE OLYMPICS AND
WASHINGTON CASCADES. THEN THE PRECIPITATION SHIELD WILL LIKELY
PUSH SOUTHEASTWARD DURING THE FIRST HALF OF THE WEEK AS A MORE
AMPLIFIED UPPER TROUGH AND LEADING SURFACE FRONT MOVE IN. AS THIS
OCCURS, THE HEAVIEST RAIN/MOUNTAIN SNOW SHOULD FOCUS ALONG THE
CENTRAL WEST COAST INTO THE SIERRA NEVADA WHILE SOME MOISTURE
EXTENDS FARTHER SOUTH OVER CALIFORNIA AND EAST INTO THE GREAT
BASIN/ROCKIES, AND NOTEWORTHY PRECIPITATION PERSISTS OVER THE
NORTHWEST. THESE SYSTEMS MAY BRING PERIODS OF HIGH WINDS TO SOME
AREAS NEAR THE WEST COAST. ELSEWHERE, A WEAK ALBERTA CLIPPER MAY
BRING AN AREA OF LIGHT SNOW FROM THE NORTHERN PLAINS INTO THE
MIDWEST DURING SUNDAY-MONDAY. GULF COAST SHORTWAVE ENERGY AND
ASSOCIATED STATIONARY FRONT SHOULD SPREAD SOME MOISTURE ACROSS THE
GULF OF MEXICO AND WESTERN ATLANTIC EARLY-MID WEEK, WITH FLORIDA
POSSIBLY SEEING SOME RAINFALL DURING THAT TIME. IT REMAINS
UNCERTAIN ABOUT HOW MUCH, IF ANY, OF THIS MOISTURE REACHES THE
GULF/SOUTHEAST COAST AREAS THOUGH.
HAMRICK
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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