Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 347 AM EST Sat Nov 09 2024 Valid 12Z Sat Nov 09 2024 - 12Z Mon Nov 11 2024 ...Widespread, potentially significant flash flooding possible in central and southwestern Louisiana today... ...Showers and thunderstorms will bring heavy rain and the risk for flash flooding to the Lower Mississippi and Tennessee/Ohio Valleys this weekend... ...Atmospheric river to arrive across the Pacific Northwest on Sunday with heavy coastal rains and high elevation snowfall... ...Above average temperatures continue for much of the country this weekend... A significant flash flooding event is anticipated today ahead of a low pressure system/cold front moving eastward towards the Mississippi Valley this morning that will slow and eventually stall as ridging builds northward over the eastern U.S. Strong southerly flow ahead of the front will continue to bring a fetch of deep, very moist air associated with Tropical Storm Rafael northward over the region. Numerous showers and thunderstorms producing very heavy downpours (rain rates 1-2"+ per hour) are expected along and ahead of the front from the Lower Tennessee Valley/Mid-South southwestward into the Lower Mississippi Valley and the western Gulf Coast. A concentrated risk of locally significant heavy rainfall totals of 3-6", locally 10", and widespread instances of flash flooding is expected ahead of the front closer to the Gulf over central/southwestern Louisiana, where a High Risk of Excessive Rainfall (level 4/4) is in effect. A broader Slight Risk (level 2/4) covers the rest of the region for more scattered instances of flash flooding. The front will make some progress eastward Sunday, especially with northern extent, bringing the heavy rainfall threat further eastward across the Ohio and Tennessee Valleys while lingering through the Lower Mississippi Valley. However, the more progressive nature of the front/storm movement as well as a decreasing fetch of moisture should limit the flash flood threat to a few isolated instances. While this moisture streaming northward from Rafael will influence the threat for heavy rain, the storm is located far offshore over the Gulf of Mexico and forecast by the National Hurricane Center to remain offshore and dissipate over the next few days. Outside of this heavy rainfall threat, an expanding area of showers and thunderstorms is forecast ahead of the low pressure system and an arcing occluded/cold front lifting northeastward across the northern Plains, Midwest, and Mississippi Valley on Saturday with some moderate amounts possible. Some moderate snow may linger over portions of the central Rockies in Colorado after a historic snowstorm the past couple days, though most snow will have tapered off this morning as the low moves away. The low pressure system/front will continue eastward on Sunday, bringing a broad area of beneficial rainfall to the Northeast after weeks of little to no precipitation. Showers and thunderstorms are also expected in vicinity of a wavy frontal boundary along the coastal Southeast/Florida this weekend. Elsewhere, an initial system pushing inland over the Pacific Northwest will continue to bring moderate to heavy showers for lower elevations with some very high elevation snow Saturday, and a wintry mix and higher elevation snow spreading into the northern Rockies by Sunday morning. Then, during the day Sunday, a stronger system and accompanying Atmospheric River will begin to bring heavier rain with an isolated chance of flooding to the Pacific Northwest, expected to last over the next several days. Most of the country will continue to see above average temperatures this weekend outside of portions of the central/southern Rockies and High Plains on Saturday, though temperatures will begin to recover here as well by Sunday. Forecast highs will generally be in the 50s from the Pacific Northwest east through the northern Rockies/Plains, Great Lakes, and into New England; the 50s and 60s in the Great Basin, central Plains, Midwest, and Mid-Atlantic; and the 70s and 80s in the Southwest, Texas, and the Southeast. Aforementioned cooler temperatures in the 40s and 50s over the central/southern Rockies and High Plains will moderate by 10 degrees or so for most locations by Sunday. Putnam Graphics available at https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php