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WPC Medium Range Archive
Medium Range Products Valid On:
12/22/2024
(Day 7 PMDEPD: Valid 12/18/2024 to 12/22/2024)
Extended Forecast Discussion
NWS Weather Prediction Center College Park MD 201 PM EST Sun Dec 15 2024 Valid 12Z Wed Dec 18 2024 - 12Z Sun Dec 22 2024 ...Overview... The pattern should be turning much more amplified during the medium range period as mean troughing becomes established over the East, and strong ridging builds over the West. A couple of shortwaves will help reinforce the Eastern trough during the period, including an initial one late this week which should allow a low pressure system to lift from the Mid-South to the Northeast with potential snow on the north side of the track. The next shortwave digging down the west side of the trough should bring with it a fresh blast of arctic air to the East by next weekend, while the West turns progressively warmer. An atmospheric river may bring a period of heavy rain/mountain snows to parts of the West Coast by next weekend as well. ...Guidance/Predictability Assessment... Models are in good agreement about the overall synoptic pattern across the lower 48 during the medium range. The GFS trended more progressive with the Central U.S. trough for this Wednesday compared to earlier runs; bringing itself in-step with the rest of the guidance. The 06z GFS continues the more progressive trend with a faster/negatively tilted trough pattern off the East Coast by Thursday, while the rest of the models still have mid-level energy moving through interior portions of the East. A general model blend consisting of the 00z EC/CMC/UKMET and 06 GFS were utilized through day 5. The 06z GFS had reduced weighting on day 4 to account for it's more progressive solution in the East. The 00z ECE and 06z GEFS were introduced to the blend on day 5 and continued through the end fo the period. The 00z CMCE was introduced to the blend on day 6 and favored through day 7 alongside the 00z ECE due to less spread between their respective members regarding a deep EPAC cyclone and downstream ridging over the Central U.S. ...Weather/Hazards Highlights... A cold front shifting through the East mid week will be accompanied by modest precipitation. Moderate to heavy rainfall is possible across portions of the Tennessee/Ohio Valley into the central Appalachians but low rainfall rates and the overall progressive nature of the front should limit any sort of excessive rainfall/flash flood threat. Some wintry weather is possible on the northwestern side of the surface low which tracks near the Northeast Coast, with highest probabilities in the higher terrain. Behind this system, westerly flow across the still relatively warm lakes should allow for some lake effect snows, reinforced by the next shortwave through the region late week/next weekend. Meanwhile, out West, conditions should dry out by the medium range period, except for some increased precipitation associated with weak shortwaves into the Northwest. Increasing precipitation looks likely by next weekend with the next Atmospheric River into the region. After a warmer day on Wednesday, the Eastern U.S. should trend much colder through the period as an arctic high pressure expands across the Midwest and East. By next weekend, temperatures across much of this region could be 10 to 15 degrees below normal. Meanwhile, from the Rockies and westward, temperatures should trend warmer with time with some spots 10-15+ degrees above normal. Kebede/Santorelli 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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