Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 203 AM EDT Wed Mar 18 2015 Valid 12Z Wed Mar 18 2015 - 12Z Fri Mar 20 2015 ...Cool and relatively dry across the Great Lakes and Northeast... ...Wet weather constrained mostly to the West and South... The general flow pattern is mainly a zonal (or west-to-east oriented) one, which brings Pacific moisture into the Pacific Northwest with higher elevation snows as a disturbance aloft moved through. Once the system crosses the northern Rockies, precipitation becomes harder to come by due to a dry downsloped flow off the higher terrain, with precipitation areas decreasing in coverage as they enter the northern Plains by Thursday morning. Across the Northeast, northwesterly flow in the wake of a storm moving by Atlantic Canada should keep conditions cooler than average over the next couple of days. Across the Southern tier of the country, a developing upper level low across northwest Mexico brings its strengthening pocket of cold air aloft and resultant increasing atmospheric instability across the Mojave Desert and the Southwest, causing afternoon and evening thunderstorms late Thursday, particularly in the proximity of mountains. The system draws Pacific moisture aloft across Mexico into the southern Plains, with a return flow off the Gulf of Mexico closer to the surface invading the Gulf coast. This pattern leads to a broadening area of thunderstorms stretching nearly from coast to coast from southern California across the Red River of the South through the Southeast by late Thursday. Thunderstorms across Texas and the Southeast are capable of producing locally heavy rains over the next couple of days. Roth Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_wbg.php