Extended Forecast Discussion NWS Weather Prediction Center College Park MD 353 PM EST Thu Feb 28 2019 Valid 12Z Sun Mar 03 2019 - 12Z Thu Mar 07 2019 ...Low pressure system likely to bring threat of heavy snow/ice from portions of the Mid-Mississippi/Ohio Valleys to the Mid-Atlantic and Northeast Sun-Mon... ...Pattern Overview... The forecast of large scale flow has maintained good continuity over the past day. Downstream from persistent mean ridging/positive height anomalies over northwestern North America, a trough will amplify into the eastern U.S. with greatest depth around midweek before the trough axis continues into the western Atlantic. At the same time a mean ridge will build into the west-central U.S. as a mean trough settles near the West Coast. ...Guidance Evaluation/Preferences... Agreement among models/ensembles has improved significantly over the past 24 hours with respect to many of the forecast details during the medium range. A blend of the latest deterministic solutions (ECMWF/GFS/CMC/UKMET) was used as a starting point for the forecast during days 3-5 (Sun-Tue). Solutions are now relatively well clustered around the ensemble means with the wave of low pressure expected to move from the lower Mississippi Valley to off the New England coast Sun-Mon, with confidence increasing in the potential for significant winter weather north/west of the low track. Farther west, models also show improved consensus with respect to an energetic shortwave/low pressure system expected to reach the West Coast Tue night into Wed. Solutions show spread on both timing and amplitude of this feature, however the ensemble means are reasonably well-centered within the spread. This makes the means suitable to comprise a significant component of the forecast for days 6-7 (Wed-Thu). Overall, the forecast remained close to continuity with only minor adjustments. ...Weather Highlights/Hazards... A broad area of precipitation will accompany the vigorous wave tracking northeast over parts of the eastern states and into the Canadian Maritimes Sun-Mon. Northwest trends in the past day have pushed the most likely area for significant wintry weather to an axis extending from the Mid-Mississippi Valley/Ohio Valley into portions of the Mid-Atlantic and Northeast. At this time, the specifics remain a bit murky with respect to p-type in the major cities along the East Coast, but the greatest potential for heavy snows should be across interior areas from Ohio/Pennsylvania to interior New England. A more consistent theme from yesterday is the potential for heavy rainfall over parts of the Lower Mississippi Valley and Tennessee Valley/interior Southeast. Rain and higher elevation snow in progress over the central/south-central parts of the West late in the weekend will taper off from west to east. Then from Tue onward the next system in the series will spread a broad area of moisture across the West, with greater northward extent than with the previous system. Favored terrain over northern and central California should once again see the highest precipitation totals with this system. Moisture reaching northern portions of the West may bring wintry weather to low elevations over some areas given the cold temperatures in place from early in the week. Continue to expect coldest temperatures relative to normal during Sun-Mon with some central U.S. locations seeing anomalies of 30-45F below normal and a widespread area over the Plains/Midwest with readings that will approach or break daily records--more likely a greater number for cold highs. Interior Northwest locations may also see some temperatures at least 20F below normal with local challenges to daily records. The area of potential daily records will likely shift more into the eastern half of the country (Midwest/Great Lakes/Ohio Valley) by Tue. Ryan/Rausch Hazards: - Heavy rain across portions of California, the Central Great Basin, the Pacific Northwest, and the Southwest, Tue-Wed, Mar 5-Mar 6. - Heavy rain across portions of the Mid-Atlantic, the Northeast, the Tennessee Valley, the Lower Mississippi Valley, the Southern Appalachians, the Southeast, and the Ohio Valley, Sun-Mon, Mar 3-Mar 4. - Heavy snow across portions of the Central Great Basin, the Northern Plains, the Northern Rockies, the Central Rockies, California, the Northern Great Basin, the Pacific Northwest, and the Southwest, Wed-Thu, Mar 6-Mar 7. - Heavy snow across portions of the Central Rockies, the Northeast, the Central Great Basin, the Southern Rockies, the Middle Mississippi Valley, the Mid-Atlantic, the Southern Appalachians, the Central Appalachians, the Great Lakes, the Ohio Valley, and the Southwest, Sun-Mon, Mar 3-Mar 4. - Heavy snow across portions of the Central Rockies, Thu, Mar 7. - Severe weather across portions of the Southeast, the Lower Mississippi Valley, the Southern Appalachians, and the Tennessee Valley, Sun, Mar 3. - Flooding possible across portions of the Mid-Atlantic. - Flooding occurring or imminent across portions of the Lower Mississippi Valley, the Tennessee Valley, the Great Lakes, the Middle Mississippi Valley, the Mid-Atlantic, California, the Upper Mississippi Valley, the Southeast, the Pacific Northwest, and the Ohio Valley. - Flooding likely across portions of the Southeast. - Much below normal temperatures for much of the eastern two-thirds of the country, including the interior sections of the Pacific Northwest, Sun-Thu, Mar 3-Mar 7. Additional 3-7 Day Hazards information can be found on the WPC medium range hazards chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, 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/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml