262
FXUS02 KWBC 220700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
159 AM EST FRI DEC 22 2023
VALID 12Z MON DEC 25 2023 - 12Z FRI DEC 29 2023
...HEAVY SNOW THREAT OVER THE NORTH-CENTRAL PLAINS ON CHRISTMAS
DAY...
...HEAVY RAIN THREAT FROM THE SOUTHEAST CHRISTMAS DAY THEN INTO
THE MID-ATLANTIC BY TUESDAY...
..OVERVIEW
MOST GUIDANCE SUGGESTS THAT AN INITIAL CENTRAL PLAINS UPPER LOW
WILL DRIFT NORTHEASTWARD EARLY NEXT WEEK AND THEN NORTHERN STREAM
ENERGY MAY DIG INTO WHAT SHOULD REMAIN A FAIRLY AMPLIFIED UPPER
TROUGH REACHING THE EASTERN U.S. BY LATE WEEK. THE SYSTEM
ASSOCIATED WITH THE PLAINS UPPER LOW WILL SPREAD A BROAD AREA OF
RAINFALL OVER THE EAST WITH SOME LOCALLY HEAVY, AND PORTIONS OF
THE NORTH-CENTRAL PLAINS COULD SEE SIGNIFICANT SNOWFALL ON THE
BACK SIDE OF THE SYSTEM. PACIFIC SHORTWAVES PUSHING INTO A
PERSISTENT WESTERN U.S. MEAN RIDGE ALOFT WILL BRING SOME EPISODES
OF PRECIPITATION TO THE CENTRAL AND NORTHERN WEST COAST.
..GUIDANCE/PREDICTABILITY ASSESSMENT
AS SUPPORTED BY RECENT DEEPER TRENDS IN THE ENSEMBLE MEANS,
GUIDANCE IS CLUSTERING TOWARD BETTER DEFINITION OF THE INITIAL
PLAINS/MIDWEST UPPER LOW AND SURFACE SYSTEM EARLY IN THE WEEK.
THE FORECAST RAPIDLY BECOMES MORE UNCERTAIN FOR DETAILS BY
MID-LATE WEEK AS SOLUTIONS DIVERGE FOR HOW DIGGING NORTHERN STREAM
ENERGY MAY INTERACT WITH THE INITIAL LOW (SHEAR IT OUT OR EJECT
IT) OR ALTERNATIVELY NOT AFFECT THE LOW AND ALLOW THE ORIGINAL LOW
TO PERSIST. BY LATE IN THE WEEK THE ENSEMBLE MEANS PROVIDE DECENT
CONFIDENCE IN AN EASTERN U.S. UPPER TROUGH BUT THE FULL ARRAY OF
GUIDANCE OFFERS LITTLE AGREEMENT ON HOW ENERGY MAY BE DISTRIBUTED
WITHIN THE TROUGH. FARTHER WEST, THERE IS REASONABLE AGREEMENT ON
A SHALLOW PACIFIC SHORTWAVE BRUSHING THE PACIFIC NORTHWEST BY
EARLY TUESDAY AND THEN A SOMEWHAT MORE AMPLIFIED ONE CROSSING THE
WEST COAST BY THURSDAY. THERE IS A LOT MORE SPREAD BY FRIDAY,
WITH CMC RUNS TRYING TO BRING ANOTHER TROUGH INTO THE WEST (VERSUS
THE CONSENSUS RIDGE) AND THE 12Z ECMWF SOMEWHAT FASTER THAN THE
GFS/GEFS WITH THE MORE AGREEABLE TROUGH OVER THE EASTERN PACIFIC
AT THAT TIME. OVERALL PREFERENCES WERE TO FOLLOW AN OPERATIONAL
MODEL COMPOSITE WITH MORE 18Z GFS/12Z ECMWF WEIGHT VERSUS THE 12Z
UKMET/CMC EARLY IN THE PERIOD AND THEN TRANSITION TOWARD 60
PERCENT 18Z GEFS/12Z ECENS MEANS AND LINGERING GFS/ECMWF INPUT BY
DAY 7 FRIDAY.
..WEATHER/HAZARDS HIGHLIGHTS
THE SYSTEM AFFECTING THE CENTRAL AND EASTERN U.S. EARLY-MID WEEK
WILL SPREAD PRECIPITATION ACROSS THE NORTH-CENTRAL PLAINS AND MOST
LOCATIONS FROM THE MISSISSIPPI VALLEY TO EAST COAST. THE
NORTH-CENTRAL PLAINS WILL BE ON THE COLD SIDE OF THE SYSTEM AND
WPC WINTER WEATHER OUTLOOK PROBABILITIES SHOW SOME POTENTIAL
(ALBEIT CURRENTLY UNDER 50 PERCENT) FOR AT LEAST 0.25" IN LIQUID
EQUIVALENT OF SNOW FOR CHRISTMAS DAY. SOME AREAS ACROSS THE FAR
NORTHERN TIER MAY ALSO SEE SOME WINTRY WEATHER BUT WITH
UNCERTAINTY IN SPECIFICS. MEANWHILE EXPECT THE POTENTIAL FOR
LOCALLY HEAVY RAINFALL AHEAD OF THE LOW PRESSURE/FRONTAL SYSTEM
THAT SHOULD DRAW UPON MOISTURE FROM THE GULF AND THEN THE
ATLANTIC. THE DAY 4 EXCESSIVE RAINFALL OUTLOOK VALID
MONDAY/CHRISTMAS DAY MAINTAINS A MARGINAL RISK AREA OVER THE
SOUTHEAST WITH AN EMBEDDED SLIGHT RISK AREA CENTERED OVER AND NEAR
THE FLORIDA PANHANDLE WHERE THE BEST COMBINATION OF MOISTURE AND
INSTABILITY SHOULD EXIST. THE DAY 5 OUTLOOK VALID ON TUESDAY
INTRODUCES A MARGINAL RISK AREA OVER THE MID-ATLANTIC AS THE
MOISTURE AXIS PROGRESSES NORTHEASTWARD. ON BOTH DAYS,
SOUTHEASTERLY LOW LEVEL FLOW MAY HELP TO ENHANCE TOTALS OVER
FAVORED TERRAIN ALONG THE APPALACHIANS. PRECIPITATION WILL
CONTINUE INTO THE NORTHEAST BY MIDWEEK. SOME LAKE EFFECT
PRECIPITATION WILL BE POSSIBLE AFTER SYSTEM PASSAGE.
ALONG THE WEST COAST, THE DAY 4 MONDAY/CHRISTMAS DAY EXCESSIVE
RAINFALL OUTLOOK MAINTAINS A MARGINAL RISK AREA OVER THE NORTHERN
PACIFIC NORTHWEST COAST WITH A CONSISTENT SIGNAL FOR A DEFINED
ATMOSPHERIC RIVER, ALBEIT WITH SOME CONTINUED SPREAD FOR EXACT
RAINFALL TOTALS. THERE IS MORE GUIDANCE SPREAD BY TUESDAY SO NO
AREA IS DEPICTED IN THE DAY 5 OUTLOOK AT THIS TIME. A SOMEWHAT
MORE AMPLIFIED SHORTWAVE APPROACHING/REACHING THE WEST COAST
SHOULD HELP TO FOCUS MODERATE TO HEAVY PRECIPITATION ALONG THE
CENTRAL WEST COAST BY WEDNESDAY. THEN CONFIDENCE DECREASES
REGARDING COVERAGE/AMOUNTS OF ANY ADDITIONAL PRECIPITATION AROUND
THE END OF THE WEEK AS GUIDANCE SOLUTIONS DIVERGE FOR FLOW ALOFT.
TEMPERATURES WILL BE QUITE WARM AHEAD OF THE SYSTEM AFFECTING THE
CENTRAL/EASTERN U.S. WITH THE GREATEST ANOMALIES FROM THE MIDWEST
INTO THE NORTHEAST. MORNING LOWS SHOULD BE UP TO 20-30F OR SO
ABOVE NORMAL WHILE HIGHS WILL TEND TO BE 10-25F ABOVE NORMAL.
MOST DAILY RECORDS WILL LIKELY BE FOR WARM LOWS OVER THE
MISSISSIPPI VALLEY INTO GREAT LAKES/OHIO VALLEY EARLY IN THE WEEK,
WITH A FEW STILL POSSIBLE FARTHER TO THE EAST THEREAFTER. COOLER
AIR BEHIND THE SYSTEM WILL STILL BE ON THE MILD SIDE, WITH ONLY
SLIGHTLY BELOW NORMAL READINGS OVER THE CENTRAL-SOUTHERN
ROCKIES/HIGH PLAINS ON MONDAY AND THEN THE GULF COAST/FLORIDA BY
LATER IN THE WEEK AS THE WEST AND HIGH PLAINS TREND GRADUALLY
WARMER.
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
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,
QUANTITATIVE PRECIPITATION FORECAST, EXCESSIVE RAINFALL OUTLOOK,
WINTER WEATHER OUTLOOK PROBABILITIES, HEAT INDICES AND KEY
MESSAGES 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
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=OVW
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