041
FXUS02 KWBC 262047
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
346 PM EST MON DEC 26 2022
VALID 12Z THU DEC 29 2022 - 12Z MON JAN 02 2023
...MULTIPLE ROUNDS OF MODERATE TO HEAVY PRECIPITATION LIKELY ALONG
THE WEST COAST, CENTRAL ROCKIES, AND THE SOUTHWEST FOR THE REST OF
THIS WEEK BEFORE POSSIBLY SPREADING INTO THE NORTHERN PLAINS TO
BEGIN 2023...
...HEAVY RAINFALL AND FLOODING POSSIBLE WEST OF THE LOWER
MISSISSIPPI VALLEY AND ACROSS THE EASTERN GULF COAST REGION TO END
2022 BEFORE THE NEXT HEAVY RAIN THREAT RE-EMERGES TO THE WEST OF
THE LOWER MISSISSIPPI VALLEY TO RING IN THE NEW YEAR...
..OVERVIEW
A TRANSITION FROM A RIDGE-TROUGH TO A TROUGH-RIDGE UPPER-LEVEL
PATTERN IS FORECAST TO OCCUR ACROSS THE MAINLAND U.S. BY THE TIME
MEDIUM-RANGE PERIOD BEGINS MIDWEEK. MULTIPLE PACIFIC SYSTEMS
PUSHING ONSHORE INTO THE WESTERN U.S. WILL ACT TO BUILD AND
MAINTAIN A SYNOPTIC SCALE TROUGH FARTHER SOUTH INTO THE
SOUTHWESTERN U.S. WITH TIME, BRINGING MULTIPLE EPISODES OF HEAVY
PRECIPITATION MAINLY ACROSS THE SOUTHWEST, THE GREAT BASIN, THEN
TOWARD THE CENTRAL ROCKIES, AND POSSIBLY REACHING INTO THE
NORTHERN PLAINS BY THE TIME 2023 BEGINS. ON THE OTHER SIDE OF THE
CONTINENT, A BUILDING RIDGE WILL KEEP MILD AIR IN PLACE FOR MUCH
OF THE EASTERN AND SOUTHERN U.S. WHILE THREE EPISODES OF HEAVY
RAIN APPEAR TO TRANSPIRE ACROSS THE SOUTH. BY EARLY NEXT WEEK,
THE NEXT PACIFIC SYSTEM APPEARS TO BRING THE NEXT SURGE OF
MOISTURE FARTHER UP THE WEST COAST FROM NORTHERN CALIFORNIA TO THE
PACIFIC NORTHWEST.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE THIS MORNING IS IN RELATIVELY GOOD AGREEMENT WITH
ONE ANOTHER WITH THE GENERAL PATTERN EVOLUTION AS DESCRIBED ABOVE.
THE LARGEST DISCREPANCY IS NOTICED ACROSS THE CENTRAL TO EASTERN
U.S. REGARDING THE SPEED OF FRONTAL WAVES AND UPPER-LEVEL
SHORTWAVES MOVING TOWARD THE GREAT LAKES, WITH THE FASTEST BEING
THE 00Z CMC. IN GENERAL, THE MODELS ARE TRENDING TOWARD A MORE
SHEAR AND POSITIVE-TILTED UPPER-LEVEL PATTERN LEADING TO A WEAKER
CYCLONE TO TRACK ACROSS THE GREAT LAKES THIS WEEKEND. AS FOR THE
WEST, MODELS ARE IN GOOD AGREEMENT ON THE TIMING AND LOCATION OF
FEATURES ASSOCIATED WITH THE LOW PRESSURE SYSTEM TO TRACK ACROSS
THE SOUTHWEST THIS WEEKEND AND REACHING INTO THE SOUTHERN PLAINS
BY EARLY NEXT WEEK.
THE WPC FORECAST WAS COMPOSED BASED ON A BLEND OF THE
DETERMINISTIC AND ENSEMBLE MEANS FROM THE 00Z ECMWF, 06Z GFS, WITH
A SMALLER CONTRIBUTION FROM THE 00Z CMC, LEADING SLIGHTLY MORE
TOWARD THE ENSEMBLE MEANS BY DAYS 6 AND 7.
..WEATHER/HAZARD HIGHLIGHTS
A SERIES OF PACIFIC FRONTS/SYSTEMS SHOULD CONTINUE TO SUSTAIN A
MULTI-DAY HEAVY PRECIPITATION EVENT ACROSS THE WESTERN U.S. WHILE
THE STRONGEST ATMOSPHERIC RIVER EXPECTED IS NOW FULLY WITHIN 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. SLIGHT RISK AREAS ARE SHOWN
IN BOTH THE DAYS 4 AND 5 EXPERIMENTAL EXCESSIVE RAINFALL OUTLOOKS
ACROSS SOUTHWESTERN OREGON/COASTAL CALIFORNIA DUE TO BOUTS OF
HEAVY RAIN MOVING IN DURING THOSE DAYS. ADDITIONALLY, SIGNIFICANT
SNOW AMOUNTS ARE LIKELY IN HIGHER ELEVATIONS OF THE WEST THROUGH
THE LATTER HALF OF THE WEEK AND INTO THE WEEKEND. EXACT TIMING AND
PLACEMENT DETAILS OF THE HEAVIEST PRECIPITATION STILL SHOW SOME
DIFFERENCES, SO CONTINUE TO MONITOR FORECASTS FOR SPECIFICS AS THE
DETAILS COME INTO BETTER FOCUS OVER COMING DAYS. HOWEVER, THERE IS
A GENERAL TREND OF PRECIPITATION LIGHTENING IN NORTHERN AREAS BY
THE WEEKEND WHILE THE BETTER FOCUS FOR PRECIPITATION BECOMES
ACROSS CALIFORNIA THROUGH THE CENTRAL/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 INTO THURSDAY. MORE NOTABLY AROUND
THURSDAY-SATURDAY, 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 HEAVY 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/SOUTHERN APPALACHIANS. SLIGHT RISKS OF EXCESSIVE
RAINFALL ARE ALSO IN PLACE FOR THESE AREAS AS INSTABILITY COULD
PRODUCE HIGH RAINFALL RATES THAT MAY CAUSE FLOODING/FLASH
FLOODING. PROGRESSION OF A POTENTIAL PLAINS INTO GREAT LAKES
SYSTEM NEXT WEEKEND SHOULD SPREAD MOISTURE THROUGH THE REST OF THE
EAST AS MOISTURE STREAMS NORTHWARD, BUT WITH MAXIMUM RAINFALL
TOTALS LIKELY TO TREND LOWER. EXPECT MOST WINTRY WEATHER FROM THIS
SYSTEM TO BE CONFINED TO THE NORTHERN PLAINS/UPPER MIDWEST THROUGH
LATE THIS WEEK. BETTER BUT STILL UNCERTAIN CHANCES FOR SNOW MAY BE
ACROSS THE CENTRAL HIGH PLAINS BY SUNDAY INTO NEXT MONDAY AS
ANOTHER UPPER TROUGH PROVIDES COLDER AIR THERE.
AFTER THE RECENT COLD SPELL, THE TEMPERATURE PATTERN IN THE MEDIUM
RANGE PERIOD WILL SIGNIFICANTLY CHANGE ACROSS MUCH OF THE NATION.
A WIDESPREAD AREA OF ABOVE NORMAL TEMPERATURES IN THE CENTRAL U.S.
WILL BE EXPANDING EASTWARD THROUGH THE LATTER PART OF THE WEEK AND
CONTINUING INTO EARLY NEXT WEEK. LOW TEMPERATURES LOOK TO BE
15-25F ABOVE AVERAGE OVER THE PLAINS/MISSISSIPPI VALLEY THURSDAY
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. DAILY
RECORDS FOR WARM LOWS MAY BE WIDESPREAD 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. LOWS
SHOULD GENERALLY BE A BIT ABOVE AVERAGE UNTIL EARLY NEXT WEEK AS
THE SECOND LARGE-SCALE UPPER TROUGH MOVES THROUGH, BRINGING HIGHS
TO AROUND 10F BELOW NORMAL AS WELL.
KONG/TATE/RAUSCH
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
HAZARDS:
- HEAVY PRECIPITATION ACROSS PORTIONS OF THE PACIFIC NORTHWEST AND
THE NORTHERN GREAT BASIN, THU,
DEC 29.
- HEAVY PRECIPITATION ACROSS PORTIONS OF CALIFORNIA, THE GREAT
BASIN, THE PACIFIC NORTHWEST, AND
THE SOUTHWEST, THU-SAT, DEC 29-DEC 31.
- HEAVY PRECIPITATION ACROSS PORTIONS OF THE SOUTHERN ROCKIES, THE
CENTRAL GREAT BASIN, AND THE
SOUTHWEST, SUN, JAN 1.
- HEAVY RAIN ACROSS PORTIONS OF THE SOUTHEAST, THE SOUTHERN
APPALACHIANS, THE MID-ATLANTIC, AND
CALIFORNIA, SAT, DEC 31.
- HEAVY RAIN ACROSS PORTIONS OF THE MIDDLE/LOWER MISSISSIPPI
VALLEY, THE TENNESSEE VALLEY, THE
SOUTHERN APPALACHIANS, THE SOUTHEAST, THE SOUTHERN PLAINS, AND THE
OHIO VALLEY, THU-SAT, DEC 29-DEC
31 AND MON, JAN 2.
- HEAVY RAIN ACROSS PORTIONS OF THE MIDDLE MISSISSIPPI VALLEY, AND
THE OHIO VALLEY, MON, JAN 2.
- HEAVY SNOW ACROSS PORTIONS OF THE NORTHERN ROCKIES AND THE
NORTHERN GREAT BASIN, THU-FRI, DEC
29-DEC 30.
- HEAVY SNOW ACROSS PORTIONS OF THE CENTRAL/SOUTHERN ROCKIES, THE
CENTRAL GREAT BASIN, THE CENTRAL
PLAINS, AND THE SOUTHWEST, SAT-SUN, DEC 31-JAN 1.
- HEAVY SNOW ACROSS PORTIONS OF THE CENTRAL/SOUTHERN ROCKIES, AND
THE NORTHERN/CENTRAL PLAINS,
SUN-MON, JAN 1-JAN 2.
- FLOODING LIKELY ACROSS PORTIONS OF THE PACIFIC NORTHWEST.
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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