Unsettled weather and severe thunderstorm chances will continue toexpand across much of the central United States over the next severaldays......Active fire weather pattern to emerge over the southern High Plains onThursday......Above average temperatures shift from the Great Basin to the Plains,while the West and East remain cool through the end of the week...An increasingly active weather pattern is beginning to unfold across themid-section of the country as an upper-level trough from the subtropicaleastern Pacific continues to head toward Baja California and theSouthwest.  This trough is expected to interact with warm and moist airreturning from the Gulf of Mexico and produce an expanding area of showersand thunderstorms gradually lifting northward of a warm front.  Theinitial stages of rain/thunderstorm formation are setting up acrossOklahoma into western Kansas this afternoon.  Combined with a southernHigh Plains dryline, a few developing thunderstorms could turn severetonight from West Texas to central Oklahoma, in addition to the chancesfor isolated flash flooding. A greater severe weather threat is expectedto expand across the central Plains on Thursday as a surface cyclonerapidly deepens in response to the approaching upper level trough. Theaforementioned warm front is expected to continue lifting northward whilethe High Plains dryline pushes east. This environment is anticipated toproduce numerous thunderstorms across the central and southern Plains,with scattered storms turning severe. The Storm Prediction Center hasissued an Enhanced Risk (level 3/5) for severe weather across parts ofsouthwest/south-central Kansas and western Oklahoma into the eastern TexasPanhandle. Very large hail, severe wind gusts, and a couple strongtornadoes will all be possible. Multiple rounds of heavy rain could alsolead to scattered flash flooding, which has prompted a Slight Risk (level2/4) of Excessive Rainfall across parts of northeast Oklahoma, easternKansas, western Missouri, and northwest Arkansas. By Friday, the lowpressure system is forecast to deepen and slide east across the centralPlains while shower and thunderstorm chances also push eastward into theupper Midwest, mid- and lower Mississippi Valley, as well as the southernPlains.  Gusty winds will also expand across the central U.S. as the lowpressure system intensifies.Behind the dryline across the southern High Plains, the combination ofvery low relative humidity and gusty winds are expected to raise firedanger to critical level on Thursday and Friday. Any fires that developwill likely spread rapidly. Outdoor burning is not recommended.Additionally, gusty winds up to 55 mph could lead to areas of blowing dust.The Pacific Northwest should be the wettest region across the West throughthe next couple of days as a Pacific low pressure system moves onshore. The Coastal Ranges as well as the Cascades could receive a couple ofinches of rainfall with heavy wet snow possible across the higherelevations.