Extended Forecast Discussion NWS Weather Prediction Center College Park MD 211 AM EST Mon Feb 17 2025 Valid 12Z Thu Feb 20 2025 - 12Z Mon Feb 24 2025 ...Intense Central to Eastern U.S. Arctic Blast this week... ...Guidance/Predictability Assessment... The WPC medium range product suite was primarily derived from composite of reasonably clustered medium to larger scale guidance of the 18 UTC GFS and the 12 UTC ECMWF/UKMET/Canadian models valid for Thursday and Friday. Opted to switch to a composite of best clustered guidance of the 18 UTC GEFS mean and the 12 UTC ECMWF/Canadian ensemble means by next weekend amid growing forecast spread. The blend process tends to smooth the increasingly numerous smaller scale system differences over time as consistent with individual predictability. This solution maintains good WPC product continuity and seems mainly in line with latest 00 UTC guidance. ...Weather/Hazards Highlights... An exiting coastal storm with lift robustly offshore the East Coast Thursday as mainly a maritime threat, but high winds and surf will impact eastern New England along with a threat of wrap- back snow. In the wake of this storm, quite an impressive Arctic airmass is taking hold over the central and eastern U.S. this week with advent of strong Canadian high pressure. Entrenched cold air will maintain some lake effect snows and offer a widespread Extreme Cold threat. Numerous record temperatures are likely from the South- Central Plains through the Mid-Lower Mississippi Valley and The South. Temperatures anomalies into Thursday will range from 30 to 40 degrees below normal over the Central Plains/Mid-Mississippi Valley, with widespread values 10-20 degrees below normal over much of the central and eastern U.S. The airmass will slowly moderate late week through next weekend. While no strongly organized storm system is evident Thursday through next Monday, the approach of several uncertain impulses may produce some light and unheralded but locally disruptive wintry weather in the Arctic airmass. Periodic moderate rainfall is more likely over the Gulf in closer proximity to a persistent and slow moving/wavy frontal zone through this forecast period, but will with more uncertainty also try to work onshore into the cooled Gulf Coast states. Upstream, several organized shortwaves/frontal systems will dig through the West later this week. A main lead system in this period will bring a swath of terrain/Mountain enhanced snow Thursday over the north-central Intermountain West/Rockies. The pattern becomes increasingly favorable for longer fetch moisture feed to fuel rounds of moderate to heavy low elevation rain and mountain snow primarily into the Pacific Northwest, but also inland to the northern Rockies next weekend into early next week. Schichtel 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