An active weather pattern for much of the Plains into the Mid to UpperMississippi Valley regions......Thunderstorms to bring heavy rains, localized flash flooding and severeweather to portions of the Plains......An elevated to critical fire weather threat across the Southern HighPlains.....Cooler than average temperatures expected from the Rockies to the Westcoast and from the Mid-Atlantic to the Northeast, while much above averagetemperatures spread from the Southern Plains to the Great Lakes...An active weather pattern expected across the mid section of the nationfrom the Plains into the Mid to Upper Mississippi Valley.  Two strongstorms expected to produce a variety of spring time weather over the nextseveral days across these regions. Thunderstorm activity occurring acrossportions of the Central Plains, Lower Arkansas and Lower Missouri ValleysThursday afternoon will be expanding northward into the NorthernPlains/Upper Mississippi Valley region and southward into the SouthernPlains as the first of two strong lows to affect these regions begins todeepen across the Central High Plains and move northeastward.  There isthe likelihood of severe weather across much of the Central to SouthernHigh Plains from Thursday afternoon into Thursday night/early Friday alongand ahead of a strengthening frontal zone.  This severe weather threatwill then push farther to the east during the day on Friday into easternportions of the Central to Southern Plains, Lower Missouri and LowerArkansas River Valleys as the strong cold front also pushes eastward.  Inaddition, heavy rains from the expected thunderstorm activity poses thethreat of localized flooding from this afternoon through Friday,especially across the eastern portions of the Central to Southern Plainsinto the into Lower Missouri and Lower Arkansas River Valleys.  In thewake of the first strong storm pushing northeastward into the NorthernPlains/Upper Mississippi Valley on Saturday, where it will producepotential for moderate to heavy rainfall amounts, a second storm willbegin to deepen across the Central High Plains.  Another round ofthunderstorms, heavy rains, flash flooding and severe weather is againpossible across the Southern Plains beginning Saturday afternoon andcontinuing into Sunday.In contrast to the wet, stormy weather across large portions of the midsection of the nation, windy and dry conditions are expected across theSouthern High Plains from southeast Colorado, the Texas-Oklahoma Panhandleregion, southward through West to Southwest Texas and eastern tosoutheastern New Mexico.  The combination of the windy conditions and lowrelative humidities will support a prolonged period of elevated tocritical fire weather conditions from Thursday through the weekend.A frontal boundary moving off the northeast Pacific into the PacificNorthwest this evening will keep conditions wet across the PacificNorthwest and Northern Rockies tonight. This wet weather and highelevation snows are then expected to spread into the Great Basin andCentral Rockies on Friday. Temperatures are expected to be below average across most areas from theRockies to the West coast over the next few days.  Much above averagetemperatures Thursday across the Central and Northern High Plains will bereplaced by much cooler temps by the beginning of the weekend.  Much aboveaverage temperatures expected from the Southern Plains, northeast theMississippi Valley, Ohio Valley and into the Great Lakes over the next twodays, while cooler,slightly below average temperatures expected from theMid-Atlantic into the Northeast.