Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 159 AM EST Tue Dec 24 2024 Valid 12Z Tue Dec 24 2024 - 12Z Thu Dec 26 2024 ...Heavy rain and mountain snow returns to the West Coast region Wednesday night... ...Showers and thunderstorms developing over portions of the south-central states... ...Relatively mild conditions across the majority of the country leading up to Christmas... An active weather pattern is expected to continue across the West Coast region as an energetic storm track across the eastern Pacific brings in multiple rounds of precipitation. The next in a series of atmospheric river events is arriving across northern California and western Oregon late tonight and continuing into Tuesday afternoon. Although the storm system will be progressive overall, there will be a deep surge of moisture ahead of the cold front that will intersect the coastal terrain and the western slopes of the northern Sierra Nevada. Rainfall totals on the order of 2-4 inches, and locally higher, are likely across this region through Tuesday evening. Snow levels will be initially high, but should fall some once the front passes. The heaviest snow from this event should affect the highest terrain of the central Sierra Nevada, with up to a foot of accumulation possible, affecting travel through the mountain passes. Winter weather advisories and winter storm warnings are currently in effect for this event. After a brief break on Christmas Day, the next round of moisture moves in towards the West Coast and brings another substantial round of rain and mountain snow, along with windy conditions as the pressure gradient tightens in response to a very intense surface low off the coast of British Columbia. A relatively weak low pressure system crossing the Northeast U.S. region on Tuesday will produce light to occasionally moderate snow from the central Appalachians to New England, increasing the odds of a White Christmas across this region, especially when combined with existing snow cover from recent snowfall. This system quickly exits offshore by Tuesday evening. Farther to the south across Texas, a separate surface low develops, and increasing southerly flow from the western Gulf of Mexico ahead of that system will fuel the development of scattered to numerous showers and some thunderstorms, mainly from eastern Texas northward across much of Arkansas and into southern Missouri through Christmas morning. Some locations may get over an inch of rainfall with this event, and thus a Marginal Risk of excessive rainfall is valid for these areas. Much of the East Coast region will have a moderation trend in the cold temperatures going into Christmas Eve, as the arctic surface high moves offshore and milder air from the Ohio Valley advects eastward across the region. The remainder of the country should enjoy generally above average temperatures by late December standards, particularly across the central and southern Plains where daytime highs could be 15-20 degrees above average. This would equate to highs well into the 60s and 70s for much of Texas. Hamrick Graphics available at https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php