Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 500 AM EDT Wed Aug 12 2015 Valid 12Z Wed Aug 12 2015 - 12Z Fri Aug 14 2015 ...Heavy rain and flash flooding possible for portions of the southwestern U.S through Thursday morning... ...Heavy rain and flash flooding possible for north-central Washington Friday... ...Above average temperatures expected from the Pacific Northwest to the northern plains and across the Southwest... With an upper ridge in place over much of the southern and western U.S, temperatures will remain above seasonal average for a vast area. Afternoon high temperatures will be 10 to 15 degrees above average in many areas. An upper-level trough over the Pacific Ocean will push onshore through the end of week. Moist air will stream into the Desert Southwest and Great Basin region during this time; scattered showers and thunderstorms are expected to develop. Widespread coverage will be likely for areas of higher terrain during the afternoon and evening. With ample moisture available, an increase risk for heavy rain and flash flooding is anticipated. A cold front, associated with the incoming Pacific trough, will develop and move through the Pacific Northwest and Canadian Prairies over the next few days. Shower activity is expected to initiate along and ahead of the front; primarily for the British Columbia Coast today, then spanning from northern Saskatchewan to the Oregon Coast by Friday morning. A cold front will continue to advance through the eastern and southern U.S. late today before pushing offshore on Thursday. Widespread shower and thunderstorms will develop along and ahead of the front. A majority of the eastern third of the U.S. will observe slightly cooler temperatures through the end of the week. Afternoon high temperatures are expected to range 5 to 10 degrees below average. The frontal boundary will slow its forward speed along the Gulf Coast and become nearly stationary at by Friday. Campbell Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_wbg.php