More rounds of excessive rainfall and severe weather expected to pusheast and southeast toward the Lower Mississippi Valley through tonightinto Monday......High-elevation snow is forecast to overspread the Pacific Northwestinto the Northern Rockies Monday and Tuesday......Warmer than average temperatures spread from Midwest to Mid-Atlantic;colder weather returns to the Northern Plains and the Pacific Northwestwith warming trend across the central/southern High Plains...More active and unsettled weather is forecast to continue across themid-section of the country through the next couple of days as multipledisturbances embedded within a slow-moving upper-level trough traverse thewestern U.S. toward the Great Plains.  The low pressure system responsiblefor the latest outbreak of strong to severe thunderstorms across thecentral to southern Plains today will continue to track northeast acrossthe upper Midwest on Monday.  Another bout of strong to severethunderstorms can be expected to impact areas farther east across theArkLaTex region through tonight as the trailing cold front associated withthe low pressure system edges farther to the east.  In addition, heavydownpours associated with these storms will result in flooding concernsacross the region.  By Monday, the highest threat of severe weather andheavy rain will shift farther southeast toward to central Gulf Coastregion, mainly over Louisiana, as the front begins to weaken.  A lowerrisk of severe weather and heavy rain will extend farther northeast intothe Tennessee Valley on Monday.Meanwhile, widespread cold rain is expected to continue through tonightacross the northern Plains, upper Midwest and toward the lower Great Lakesahead of the low pressure system and the associated warm front, withembedded thunderstorms closer to the center of the low.  Temperaturescould be cold enough to support wet snow Monday morning across portions ofthe northern Plains into the upper Midwest.  The rain will then shifteastward into the western portion of New England, down across the OhioValley toward the Appalachians on Tuesday as the low center moves intosouthern Canada.On the warm side of the low pressure system, strong southerly flow willbring very warm air northward into the East Coast through the next coupleof days with high temperatures climbing well into the 80s and possiblyinto the lower 90 degrees for the interior Mid-Atlantic. Thesetemperatures will be in contrast to the cool temperatures expected for thePacific Northwest by Monday as the next upper-level trough from thePacific is forecast to push inland.  This trough will bring widespreadhigh-elevation snow and lower elevation rain across the Pacific Northwesttoward the northern Rockies on Monday with increasingly windy conditionsas a low pressure system begins to develop over the northern High Plainsinto southern Canada.  By Tuesday, the main front will move fairly quicklyacross the northern and central Plains, with rapid development of showersand thunderstorms expected across the upper Midwest in the afternoon aheadof a warm front and a low pressure wave.  Some thunderstorms may begin toerput across the central Plains into Texas east of a dry line.  Fartherwest, warm downslope winds from the southern Rockies will set a warm trendacross the southern High Plains with high temperatures reaching into the80s and lower 90s by Tuesday afternoon.