Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 429 AM EDT Mon Apr 21 2014 Valid 12Z Mon Apr 21 2014 - 12Z Wed Apr 23 2014 ...Severe weather will be possible today from Central to Northeast Texas... ...Heavy snow is expected across the Oregon Cascades and over the Tetons... A definitive pattern change will be underway as a strong upper trof sets up across the Western U.S. by Tuesday. This will lead to quite a sinusoidal pattern with unsettled weather across the Western/Eastern U.S. while ridging across the middle of the nation keeps conditions more tranquil. To begin the forecast period, a slow moving cold front was seen moving toward the Middle Mississippi Valley and Central Plains. Mid-level energy associated with a weakening trof should help ignite showers and thunderstorms ahead of the advancing cold front. Much of the convection should spawn along a north-south oriented trof across Texas/Oklahoma where low-level convergence will be maximized. Sufficient daytime heating is expected leading to large amounts of instability in the atmosphere. The Storm Prediction Center outlook suggests a threat for severe thunderstorm development anywhere from Central Texas toward the Arkansas/Louisiana border through tonight. As an upper trof in the northern stream begins to dig through the Upper Great Lakes early Tuesday, the cold front is forecast to accelerate reaching the Eastern Seaboard by late Tuesday night. Showers and thunderstorms will break out along and ahead of the boundary with any wintry precipitation remaining north of the U.S./Canadian border. Ahead of this advancing cold front the temperatures should be quite mild with highs well into the 70s along the I-95 corridor on Tuesday. The change in the pattern bringing the large upper trof to the West will allow cooler and wetter conditions to affect the region. The combination of onshore flow with frontal and orographic lift will help spread an expansive region of precipitation to the Western U.S. Snow levels should fall sufficiently to bring decent accumulations to the Oregon Cascades and across the Tetons. Both of these mountain ranges can expect snow totals through early Wednesday of 6 to 10 inches while localized heavier amounts will be possible. The other aspect of this system will be dry and gusty winds expected as the pressure gradient tightens across the Intermountain West. An enhanced risk for wildfire development is in place for the Desert Southwest on Tuesday with locations further east being affected by mid-week. Rubin-Oster Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_wbg.php