Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 317 AM EDT Sat May 18 2013 Valid 12Z Sat May 18 2013 - 12Z Mon May 20 2013 ***Stormy weather for the Northern Plains and Upper Midwest*** ***Warm and humid for the southern tier states*** ***Showers and scattered storms for the Northern Rockies*** An active weather pattern is forecast to continue over the Dakotas and into Minnesota and the western Great Lakes region as a strong spring storm system moves slowly eastward across the Great Plains. Multiple rounds of organized thunderstorm activity are likely through Sunday, and numerous strong and severe thunderstorms are expected from northern Texas northward to the Upper Midwest. Much of this activity should fire up along and east of a dryline and slowly approaching cold front, in an environment of high instability and wind shear. Over the eastern U.S., a stalled frontal boundary situated from North Carolina westward to Illinois will serve as the delineation between very warm temperatures over the south central states and Southeast, and 60s and 70s to the north. Moisture convergence along this boundary will result in periods of rain for the southeastern quadrant of the country, coupled with support from a mid-level shortwave passing slowly overhead. A warming trend is expected to commence by Monday for much of the Ohio Valley and Mid-Atlantic region as the front lifts northward and washes out. Elsewhere, scattered showers and storms remain in the forecast for much of the Inter-Mountain West and extending into the Pacific Northwest for the weekend. A large scale trough in the atmosphere will allow for enough instability for convection over this region, and some onshore flow from the Pacific will generate some showers for the coastal areas of Oregon and Washington state. Hot and dry weather is expected for the Desert Southwest, along with gusty winds. Hamrick Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_wbg.php