709
FXUS02 KWBC 231900
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 PM EST MON DEC 23 2024
VALID 12Z THU DEC 26 2024 - 12Z MON DEC 30 2024
...UNSETTLED WEATHER FOR THE WEST COAST WITH PERIODS OF HEAVY RAIN
AND MOUNTAIN SNOW...
..GENERAL OVERVIEW
THE GENERAL FLOW PATTERN WILL DEAMPLIFY/BECOME MORE ZONAL WITH
TIME AS RIDGING IN THE EAST MOVES INTO THE WESTERN ATLANTIC AS A
RELENTLESS SERIES OF PACIFIC SYSTEMS SHOVES THE DOWNSTREAM RIDGE
ALONG. THIS WILL ALLOW PROGRESSIVE SYSTEMS TO MOVE FAIRLY QUICKLY
FOR THE MOST PART, WITH THE MAIN EXCEPTION BEING A LOW PRESSURE
SYSTEM MOVING NORTH FROM TX INTO THE UPPER MIDWEST AHEAD OF A BROAD
BUT NEGATIVELY TILTED UPPER TROUGH. FOR THE MOST PART, THIS SHOULD
BE A MILD PATTERN FOR THE LOWER 48 WITH MUCH OF THE COUNTRY
EXPERIENCING ABOVE NORMAL TEMPERATURES.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE LATEST GUIDANCE CONTINUES TO SHOW FAIRLY GOOD AGREEMENT ON THE
LARGE SCALE PATTERN, BUT PLENTY OF UNCERTAINTY IN THE DETAILS OF
INDIVIDUAL SYSTEMS. THE INITIAL SYSTEM LIFTING OUT OF THE SOUTHERN
PLAINS INTO THE MIDWEST LATER THIS WEEK HAS SOME TIMING
UNCERTAINTY, BUT SHOULD WEAKEN PRETTY QUICKLY AS IT HEADS INTO THE
MEAN RIDGE. THE NEXT SYSTEM INTO THE WEST SHOULD RESULT IN BROAD
TROUGHING ACROSS THE CENTRAL U.S. BY THE WEEKEND, BUT INDIVIDUAL
PIECES OF ENERGY ROTATING THROUGH THE MAIN TROUGH LEADS TO STILL
VERY UNCERTAIN DETAILS ESPECIALLY AS IT PERTAINS TO SURFACE
FEATURES. THIS SYSTEM SHOULD PROGRESS EASTWARD, KICKING THE EASTERN
RIDGE AWAY, BUT STILL CONSIDERABLE QUESTIONS ON TIMING OF THIS AND
HOW SHARP/AMPLIFIED THAT TROUGH BECOMES. YET ANOTHER SHORTWAVE
WILL MOVE ACROSS THE WEST COAST SUNDAY-MONDAY, AND THE GUIDANCE
RIGHT NOW HAS A GOOD HANDLE ON THIS FEATURE.
THE WPC FORECAST FOR TODAY USED A BLEND OF THE DETERMINISTIC
GUIDANCE THROUGH DAY 5. FOR DAYS 6 AND 7, BLENDED IN SOME OF THE
ENSEMBLE MEANS WITH THE GFS AND ECMWF TO HELP SMOOTH OUT THE
DETAILS DIFFERENCES. OVERALL, THIS MAINTAINED GOOD CONTINUITY WITH
THE PREVIOUS WPC FORECAST AS WELL.
..WEATHER/HAZARDS HIGHLIGHTS
MULTIPLE ROUNDS OF MODERATE TO HEAVY RAINFALL ARE EXPECTED TO
IMPACT THE WEST COAST LATER THIS WEEK AS MULTIPLE FRONTAL SYSTEMS
APPROACH THE COAST, WITH THE SIGNAL FOR HEAVY RAINFALL BECOMING
STRONGER BY THE DAY BETWEEN THURSDAY AND NEXT SUNDAY AND EVENTUALLY
CONCENTRATING NEAR THE CALIFORNIA/OREGON BORDER. FLOODING WILL BE
POSSIBLE, ESPECIALLY WHERE BURN SCARS EXIST AND POSSIBLY NEAR THE
STEEP TERRAIN OF THE OLYMPICS AND COASTAL MOUNTAIN RANGES AND INTO
THE FOOTHILLS OF THE CASCADES. A MARGINAL RISK OF EXCESSIVE
RAINFALL IS IN EFFECT FOR COASTAL WASHINGTON, OREGON, AND NORTHERN
CALIFORNIA ON THURSDAY AND FRIDAY.
MOISTURE SPREADING INLAND IN THE WEST WILL LIKELY PRODUCE HEAVY
SNOW OVER THE HIGHER/HIGHEST TERRAIN OF THE CASCADES AND ROCKY
MOUNTAINS, AND PORTIONS OF THE SIERRA NEVADA. HEAVY SNOW WILL FOCUS
OVER THE NORTHWEST ON CHRISTMAS AND EXPAND THROUGH THE
INTERMOUNTAIN WEST/ROCKIES LATER THIS WEEK. TIGHT PRESSURE
GRADIENTS MAY RESULT IN SOME PERIODICALLY GUSTY WINDS FOR SOME
LOCATIONS AS WELL.
DOWNSTREAM, MULTIPLE FRONTAL SYSTEMS WILL BRING RAIN AND
THUNDERSTORM CHANCES TO THE PLAINS, MISSISSIPPI VALLEY, AND
SOUTHEAST. SOUTHERLY FLOW WILL BRING MOISTURE UP FROM THE GULF OF
MEXICO INTO THE ARK-LA-TEX REGION WHERE MULTIPLE ROUNDS OF RAIN ARE
EXPECTED. A MARGINAL RISK OF EXCESSIVE RAINFALL EXISTS FOR THAT
AREA ON THURSDAY/THURSDAY NIGHT. RAINFALL SHOULD EVENTUALLY SPREAD
INTO THE EAST AS WELL.
WIDESPREAD ABOVE NORMAL/MILD TEMPERATURES BY LATE DECEMBER
STANDARDS ARE EXPECTED ACROSS MUCH OF THE CONUS. THE GREATEST
POSITIVE ANOMALIES ARE LIKELY ACROSS PORTIONS OF THE PLAINS-UPPER
MIDWEST AND EXTENDING INTO THE OHIO VALLEY BY SATURDAY. READINGS
CLOSER TO CLIMATOLOGY ARE EXPECTED NEAR THE WEST COAST.
TEMPERATURES ACROSS THE SOUTHERN PLAINS WILL TREND WARMER WITH
TIME, WITH DAYTIME HIGHS 20-25 DEGREES ABOVE NORMAL BY EARLY NEXT
WEEK AS UPPER RIDGING SLIDES OVER THE REGION.
SANTORELLI/ROTH
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 FORECAST (QPF), EXCESSIVE RAINFALL
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:
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
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=OVW
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