Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 211 PM EST Wed Dec 25 2024 Valid 00Z Thu Dec 26 2024 - 00Z Sat Dec 28 2024 ...Continued rounds of heavy rain and mountain snow for the Pacific Northwest and northern Great Basin/Rockies... ...Heavy rain and severe thunderstorms return for eastern Texas and the ArkLaTex on Thursday... ...Relatively mild conditions across the majority of the country through Friday... Active storm tracks over the northwestern as well as south-central U.S. will keep unsettled, impactful weather in the forecast over the next couple of days. In the Northwest, multiple upper-level waves/Pacific systems will pass over the region bringing rounds of moderate to heavy lower elevation/coastal rain, an inland lower elevation rain/snow mix, and very heavy snow to the area mountain ranges. One wave will pass through the Pacific Northwest overnight Christmas and into the Great Basin and northern/central Rockies Thursday followed quickly by a second wave into the Pacific Northwest by Friday morning. A flow of plentiful moisture from the Pacific/Atmospheric River will lead to several inches of rain along favorable upslope regions of the coastal ranges of the Pacific Northwest and northern California through Friday with the potential for some isolated flooding. In the mountains, storm total snowfall of at least 8-12" will be common, with locally higher amounts of 2+ feet possible, especially for the Cascades and ranges of the northern Great Basin/Rockies. In addition, strong, gusty winds are also expected, and will lead to blowing snow and very dangerous travel conditions in the mountains. Scattered showers and thunderstorms will taper off through Christmas evening for portions of the Middle/Lower Mississippi Valley and western Gulf Coast along a lingering frontal boundary following the passage of an upper-level wave. Another wave approaching from the west will lead to lee cyclogenesis over the southern Plains, helping to reinforce the frontal boundary and encourage very moist Gulf return flow northward over eastern Texas and the ArkLaTex overnight. Storms will increase in coverage and intensity through Thursday morning and into Thursday afternoon, with sufficient CAPE and wind shear for some severe thunderstorms. The Storm Prediction Center has included a Slight Risk (level 2/5) of severe weather for the threat of large hail, damaging winds, and a few tornadoes. In addition, the plentiful moisture and intense storms will lead to some locally heavy downpours, with a Slight Risk of Excessive Rainfall (level 2/4) also in place for the threat of some scattered instances of flash flooding. The system will continue northeastward Friday, bringing an expanding area of showers and thunderstorms across the Mississippi and Lower Ohio/Tennessee Valleys. A few isolated severe thunderstorms and instances of flash flooding will remain possible, particularly from the Lower Mississippi Valley into the Lower Tennessee Valley. Elsewhere, conditions will be mostly dry except for some isolated storm chances over Florida. Most of the country will continue to see relatively mild conditions temperature-wise through Friday, with the greatest anomalies of 10-15 degrees focused over the Plains and Mississippi Valley. Forecast highs generally range from the 30s and 40s for the northern Plains and Great Lakes; the 40s and 50s for the Pacific Northwest, Great Basin, northern/central Rockies, central Plains, and Ohio Valley; the 50s and 60s for California and the southern Rockies/Plains; and the 60s and 70s for the Desert Southwest, Texas, the Lower Mississippi Valley, and Florida. One region that will see some cooler, more seasonable conditions Thursday will be along the East Coast, with temperatures in the 20s and 30s in New England, the 30s and 40s in the Mid-Atlantic, and 50s and 60s into the Southeast. Temperatures will begin to warm above average for many locations here as well on Friday, with highs generally 5-10 degrees warmer. Putnam Graphics available at https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php