Powerful low pressure system to produce gusty winds, heavy rain, andthe potential for severe thunderstorms across parts of the Great Lakes,Ohio Valley, and eastern United States through Friday......Lower elevation rain and mountain snow to enter California onSaturday......Well above average temperatures forecast to surge into thenorthern/central Plains this weekend...A large, deepening low pressure system currently over the Ohio/Tennesseevalleys this afternoon will be the driving force behind active weatherthroughout the eastern United States until early this weekend. Widespreadshower and thunderstorm activity is forecast to continue through tonightacross the lower Great Lakes, Ohio Valley, Appalachians, Mid-Atlantic, andNortheast. Rainfall could be heavy enough at times to create instances offlash flooding over the Ohio Valley and central Appalachians, where aSlight Risk (level 2/4) of Excessive Rainfall is in effect. Additionally,severe thunderstorms are possible throughout a similar region and couldcontain a few tornadoes, scattered damaging winds, and isolated severehail. This severe threat also includes the central Florida Peninsula intothis evening, but thunderstorm activity should drastically diminish acrossthe eastern U.S. by Friday. Heavy rain will continue to be a hazard onFriday throughout northern New England due to the combination of rainfalland recent snowmelt. Flood Watches remain in effect between northern NewHampshire and central Maine as antecedent conditions support the threat offlash and river flooding. Wind will be another aspect of this storm worthmonitoring as the large low pressure system develops a strong pressuregradient. The East Coast can expect strong southerly flow ahead of thesystem through early Friday and the potential for coastal flood hazards.Meanwhile, on the backside of the system gusty northwesterly winds areexpected to impact the Great Lakes and Appalachians on Friday and Saturday.Unsettled weather will enter California on Saturday as low pressure churnsjust off the coast and an associated frontal boundary pushes inland.Locally heavy rain is possible along coastal regions, with moderate toheavy snow in the high terrain of the Sierra Nevada. Rainfall is alsoexpected to expand northward into parts of southern Oregon, but isanticipated to be mostly beneficial.After a cooler Thursday throughout the Great Plains underneath highpressure, much warmer weather is on the way by Saturday. Highs areexpected to surge upwards of 20 to 30 degrees above average through thenorth-central United States. This equates to widespread highs into the 70sand 80s from the Great Plains and Upper Midwest to the northern GreatBasin.