Heavy rain and heavy mountain snow in California continue throughtomorrow before subsiding.Warming trend expected to expand from the Great Plains into the Midwestthrough midweek.Critical Fire Weather day over portions of the Southern Plains onWednesday.The main area of unsettled weather through the next 24 hours remains overCalifornia as showers and thunderstorms stream inland associated with adeep upper-trough and atmospheric river. Southern California is once again"under the gun" for numerous instances of flash flooding as the main bandof atmospheric river rainfall focuses through the overnight hours there.Given the combination of saturated soils from previous rainfall andperiods of high rainfall rates approaching 1"/hour, a Moderate Risk ofExcessive Rainfall is in effect for Los Angeles and northern San Diegocounties through tomorrow morning. Outside of these areas, a broaderSlight Risk area (level 2/4) extends from Humboldt County down to SanDiego, as well as the Sacramento Valley and adjacent upslope areas of theSierra where scattered flash flooding is possible. In the mountains, anadditional 6-12 inches of snowfall are expected for the Sierra, while12-18 inches are likely over the Shasta Siskiyous today. East of theSierra, the influx of Eastern Pacific moisture combined with falling snowlevels will support moderate to heavy snow over the Intermountain Westwhere generally between 6-12 inches of snow can be expected. This snowfallis likely to continue into Wednesday and expand in coverage into theCentral Rockies.East of the Continental Divide, widespread unseasonable warmth willprevail through the work week as all of the cold Polar air remainsconfined over Canada. This warm weather combined with dry, windyconditions behind a cold front and dryline supports a Critical (level 2/3)fire weather threat over portions of the Southern Plains tomorrowaccording to the Storm Prediction Center.  By Thursday, a developing waveof low-pressure along a cold front will yield widespread showers andthunderstorms over the Ohio Valley, which could lead to isolated instancesof flash flooding.