887
FXUS02 KWBC 251901
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
201 PM EST SUN DEC 25 2022
VALID 12Z WED DEC 28 2022 - 12Z SUN JAN 01 2023
...MULTIPLE ROUNDS OF MODERATE TO HEAVY PRECIPITATION ARE LIKELY
ACROSS THE WEST THIS WEEK...
...RAINFALL COULD BE HEAVY ACROSS THE SOUTHEASTERN QUADRANT OF THE
COUNTRY LATE THIS WEEK...
..OVERVIEW
MANY PARTS OF THE LOWER 48 SHOULD SEE AN ACTIVE WEATHER PATTERN
FROM MIDWEEK THROUGH NEXT WEEKEND. A RAPID SEQUENCE OF PACIFIC
SYSTEMS WILL BRING MULTIPLE EPISODES OF PRECIPITATION TO MUCH OF
THE WEST, WITH SOME AREAS OF POTENTIALLY HEAVY RAIN/SNOW DEPENDING
ON ELEVATION. THERE WILL LIKELY BE A TENDENCY FOR GREATER MOISTURE
FOCUS OVER SOUTHERN PARTS OF THE REGION BY THE START OF THE
WEEKEND. THE ENERGY FROM THESE SYSTEMS WILL FEED INTO A LONG-TERM
UPPER LEVEL MEAN TROUGH BECOMING ESTABLISHED OVER THE
ROCKIES/PLAINS WHILE AN UPPER RIDGE BUILDS OVER THE EAST
COAST/WESTERN ATLANTIC. THE FLOW BETWEEN THE TROUGH AND DOWNSTREAM
RIDGE ALOFT, AND BETWEEN ONE OR MORE CENTRAL U.S. SYSTEMS AND HIGH
PRESSURE TO THE EAST AT THE SURFACE, WILL SPREAD PRECIPITATION
ACROSS AN INCREASING PORTION OF THE EASTERN HALF OF THE COUNTRY
WHILE PROMOTING UNSEASONABLY WARM TEMPERATURES THAT SHOULD LEAD TO
A MAJORITY OF THIS PRECIPITATION FALLING AS RAIN. THE BEST
POTENTIAL FOR HIGHEST RAINFALL TOTALS SHOULD EXTEND FROM THE GULF
COAST NORTHWARD THROUGH THE SOUTHERN HALF OF THE MISSISSIPPI
VALLEY AND EASTWARD INTO THE FAR SOUTHERN APPALACHIANS.
..GUIDANCE/PREDICTABILITY ASSESSMENT
IN A CONTINUATION FROM RECENT MODEL CYCLES, THERE IS A CONSISTENT
AND AGREEABLE DEPICTION OF THE OVERALL MEAN PATTERN BUT WITH SOME
SPREAD FOR INDIVIDUAL FEATURES. GUIDANCE FROM THE 00Z/06Z RUNS
USED FOR THE UPDATED FORECAST, COMBINED WITH NEW 12Z RUNS, SUGGEST
SOME DETAILS MAY BE STARTING TO COME INTO BETTER FOCUS BUT OF
COURSE WITH RECENT GUIDANCE BEHAVIOR STILL TEMPERING CONFIDENCE
SOMEWHAT.
REGARDING THE SEQUENCE OF PACIFIC SYSTEMS, CONSENSUS LOOKS GOOD
FOR THE INITIAL UPPER TROUGH MOVING INTO THE WEST. THE MAJORITY OF
GUIDANCE SHOWS THE NEXT FEATURE AS A FRONTAL SYSTEM THAT COULD
HAVE SOME EMBEDDED WAVINESS BUT WITH MODEST DEFINITION AND A TRACK
NEAR OR NORTH OF VANCOUVER ISLAND IF THERE IS ONE. THERE IS STILL
MODERATE SPREAD FOR THE NEXT SYSTEM FORECAST TO ARRIVE FRIDAY,
WITH THE NEW 12Z UKMET JOINING LATEST GFS/ECMWF RUNS IN SHOWING A
FAIRLY VIGOROUS SYSTEM REACHING THE PACIFIC NORTHWEST WHILE CMC
RUNS AND THE ENSEMBLE MEANS SHOW OR IMPLY ANY SURFACE LOW WOULD
TRACK WELL TO THE NORTH. FINALLY, THERE HAS ACTUALLY A LITTLE
BETTER CLUSTERING FOR THE TRAILING SYSTEM THAT IS MOST LIKELY TO
TRACK FARTHER SOUTH INTO CALIFORNIA AND BEYOND DURING THE WEEKEND.
HOWEVER THE NEW 12Z ECMWF HAS SHIFTED SOMEWHAT NORTH OF THE
MAJORITY, BUT SUPPORTING DYNAMICS ARE STILL WELL WITHIN TYPICAL
DETAIL VARIABILITY FOR THAT TIME FRAME.
MEANWHILE AHEAD OF THE DEVELOPING MEAN TROUGH, GUIDANCE HAS BEEN
WAFFLING OVER THE LAST FEW DAYS WITH RESPECT TO WHETHER NORTHERN
TIER ENERGY COULD SUPPORT LOW PRESSURE THAT WOULD LIFT
NORTHEASTWARD INTO SOUTHERN CANADA LATE THIS WEEK. IN THE ONGOING
MULTI-DAY OSCILLATION, LATEST TRENDS HAVE SHIFTED TOWARD BETTER
POTENTIAL OF SUCH A FEATURE IN CONTRAST TO MORE PERSISTENT EASTERN
CANADA HIGH PRESSURE. THE NEW 12Z ECMWF HAS STRAYED ON THE FAST
SIDE OF GUIDANCE. THERE HAS BEEN A LITTLE MORE CONSISTENCY WITH
THE IDEA FOR A WELL-DEFINED LOW TO EMERGE FROM THE PLAINS AND THEN
TRACK OVER THE MISSISSIPPI VALLEY INTO THE GREAT LAKES BY THE
WEEKEND. THERE IS SPREAD/VARIABILITY FOR TIMING AND TRACK BUT THE
ENSEMBLE MEANS DEPICT THIS SYSTEM WELL IN PRINCIPLE.
THE UPDATED FORECAST STARTED WITH A 00Z/06Z MODEL COMPOSITE EARLY
AND THEN TRANSITIONED TO A BLEND OF THE 06Z GFS/00Z ECMWF AND
THEIR RESPECTIVE ENSEMBLE MEANS. THE 00Z CMC STRAYED FROM THE
PRIMARY CLUSTER OVER THE EASTERN HALF OF NORTH AMERICA BY THE
LATTER HALF OF THE PERIOD SO IT WAS PHASED OUT OF THE BLEND THEN.
..WEATHER/HAZARD HIGHLIGHTS
A SERIES OF PACIFIC FRONTS/SYSTEMS SHOULD BRING A MULTI-DAY PERIOD
OF NOTABLE PRECIPITATION TO MUCH OF THE WEST. WHILE THE STRONGEST
ATMOSPHERIC RIVER EXPECTED HAS NOW SHIFTED INTO THE SHORT RANGE
PERIOD, ADDITIONAL ROUNDS OF HEAVY RAINFALL ALONG COASTAL AREAS
MAY CAUSE FLOODING PROBLEMS IN AREAS THAT WILL BE HYDROLOGICALLY
SENSITIVE BY THAT TIME. A SLIGHT RISK AREA WAS MAINTAINED IN THE
EXPERIMENTAL DAY 5 EXCESSIVE RAINFALL OUTLOOK FOR SOUTHWESTERN
OREGON/COASTAL CALIFORNIA AS MOST MODEL GUIDANCE SHOWS ANOTHER
BOUT OF HEAVY RAIN MOVING IN BY THEN, THOUGH THERE REMAINS SOME
UNCERTAINTY WITH THE TIMING. ADDITIONALLY, SIGNIFICANT SNOW
AMOUNTS ARE LIKELY IN HIGHER ELEVATIONS OF THE WEST THROUGH MUCH
OF THE WEEK. EXACT TIMING AND PLACEMENT DETAILS OF THE HEAVIEST
PRECIPITATION THROUGH LATE WEEK AND THE WEEKEND STILL SHOW SOME
DIFFERENCES, SO CONTINUE TO MONITOR FORECASTS FOR SPECIFICS AS THE
DETAILS COME INTO BETTER FOCUS OVER COMING DAYS. HOWEVER FOR NEXT
WEEKEND THE LATEST GUIDANCE DOES SHOW A GENERAL THEME OF
PRECIPITATION TRENDING LIGHTER OVER NORTHERN AREAS, WITH GREATER
FOCUS FROM CALIFORNIA THROUGH THE SOUTHERN GREAT BASIN AND
SOUTHWEST U.S.
EAST OF THE ROCKIES, A WEAK LEADING WAVE LIFTING NORTHEASTWARD MAY
PRODUCE SOME PRECIPITATION (LIKELY AT LEAST SOME OF IT SNOW)
ACROSS THE NORTHERN PLAINS AROUND WEDNESDAY-THURSDAY. BY THE
LATTER HALF OF THE WEEK, DEVELOPING MOISTURE INFLOW FROM THE GULF
OF MEXICO INTO THE MISSISSIPPI VALLEY AND VICINITY AHEAD OF ONE OR
MORE PLAINS LOW PRESSURE/FRONTAL SYSTEMS AND SUPPORTING UPPER
TROUGH WILL LEAD TO INCREASING COVERAGE AND INTENSITY OF
PRECIPITATION, MOST OF IT RAIN. WITHIN THIS EXPANDING MOISTURE
SHIELD, RAINFALL COULD BECOME LOCALLY MODERATE TO HEAVY BY
FRIDAY-SATURDAY WITH HIGHEST RAINFALL TOTALS CURRENTLY EXPECTED TO
BE APPROXIMATELY FROM THE GULF COAST THROUGH THE LOWER MISSISSIPPI
VALLEY AND INTO THE TENNESSEE VALLEY AND SOUTHEAST. LATEST
GUIDANCE IS STARTING TO CLUSTER AROUND THE POTENTIAL FOR A BAND OF
ENHANCED RAINFALL OVER AND NEAR ARKANSAS THURSDAY-THURSDAY NIGHT,
LEADING TO THE INTRODUCTION OF A SLIGHT RISK AREA IN THE
EXPERIMENTAL DAY 5 EXCESSIVE RAINFALL OUTLOOK. A BROADER AREA OF
HEAVY RAINFALL WILL BE POSSIBLE ACROSS THE SOUTH SHORTLY
THEREAFTER. PROGRESSION OF A POTENTIAL PLAINS INTO GREAT LAKES
SYSTEM NEXT WEEKEND SHOULD SPREAD MOISTURE THROUGH THE REST OF THE
EAST BUT WITH MAXIMUM RAINFALL TOTALS LIKELY TO TREND LOWER AS
MOISTURE STREAMS NORTHWARD. EXPECT MOST WINTRY WEATHER FROM THIS
SYSTEM TO BE CONFINED TO THE NORTHERN PLAINS/UPPER MIDWEST.
AFTER THE RECENT COLD SPELL, THE TEMPERATURE PATTERN IN THE MEDIUM
RANGE PERIOD WILL SIGNIFICANTLY CHANGE ACROSS MUCH OF THE NATION.
THOUGH THE SOUTHEAST MAY STILL HAVE SOME BELOW NORMAL READINGS FOR
MIDWEEK, A WIDESPREAD AREA OF ABOVE NORMAL TEMPERATURES IN THE
CENTRAL U.S. WILL BE EXPANDING EASTWARD THROUGH THE LATTER PART OF
THE WEEK. LOW TEMPERATURES LOOK TO BE 15-30F ABOVE AVERAGE OVER
THE HIGH PLAINS WEDNESDAY WITH HIGHS AROUND 10-20F ABOVE AVERAGE,
AND TEMPERATURES OF THIS MAGNITUDE SHOULD SHIFT EAST UNDERNEATH
THE UPPER RIDGE INTO THE EAST-CENTRAL U.S. LATE WEEK AND THE EAST
BY NEXT SUNDAY. SOME DAILY RECORDS FOR WARM LOWS MAY BE POSSIBLE
AS THE WARMEST AIR REACHES THE EAST, WHILE A FEW ISOLATED DAILY
RECORD HIGHS CANNOT BE RULED OUT. THOUGH MEANWHILE IN THE WEST,
THE WET/SNOWY PATTERN WILL TEND TO KEEP DAYTIME TEMPERATURES
WITHIN A FEW DEGREES OF NORMAL, THOUGH LOWS SHOULD GENERALLY BE A
BIT ABOVE AVERAGE.
RAUSCH/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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