Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 355 AM EDT Thu Sep 20 2018 Valid 12Z Thu Sep 20 2018 - 12Z Sat Sep 22 2018 ...Severe weather and a threat for flash flooding across the Upper Midwest today... ...Moderate Risk for flash flooding in place over central Oklahoma on Friday into the overnight hours... ...Substantial temperature contrast on the order of 40-50 degrees F from the Dakotas into the central U.S... ...Wet conditions likely across sections of western Washington up into British Columbia... As an upper trough accelerates from the Central Great Basin toward the Dakotas, a surface cyclone will deepen while racing into the Upper Midwest this evening. While all severe threats are possible over northern Iowa into southern Minnesota and western Wisconsin, there remains a notable threat for tornadoes given considerable turning of the winds with height. The Storm Prediction Center has this region outlined in an Enhanced Risk as the wave of low pressure sweeps northeastward toward the Upper Great Lakes. Given substantial moisture transport intercepting this frontal system, some heavy rainfall capable of producing flash floods are possible over the Upper Great Lakes back toward western Iowa. The entire system should remain progressive with marked deepening anticipated as it crosses the international border with Canada. A considerable pressure gradient will ensue leading to gusty winds across the Great Lakes into the northeastern U.S. for Friday and Saturday. The combination of energetics from northern Mexico lifting toward the Southern Rockies/Great Plains and enhanced moisture from the remains of Tropical Depression Nineteen-E will lead to a heavy rainfall event across the south-central U.S. There should be a particular focus across central Oklahoma where a wavy frontal zone is forecast to stall. Several inches of rain are possible on Friday into Saturday morning which led to an upgrade of the flash flood potential to a Moderate Risk which includes the city of Oklahoma City. The footprint of heavier rainfall should surround this region extending into western Arkansas and southward across the Red River into north Texas. Amidst the active weather across the middle of the country, an impressive temperature gradient will set up from the northern tier states down into the nation's mid-section. The wavy stationary frontal zone will demarcate this temperature contrast with today's highs only in the mid 40s across North Dakotas while upper 80s to lower 90s encompass southern Nebraska and Iowa southward. Relative to climatology, anomalies will be quite impressive, particularly north of the boundary with departures in the 20 to 25 degree F range. The air mass within the cold sector should modify a bit by the following day as highs stay in the mid to upper 50s across the Northern Plains into the Upper Midwest. A compact upper low dropping down from the Gulf of Alaska will take aim at the Pacific Northwest. Energetics from this upper trough passage coupled with ample onshore flow orographics will spark widespread precipitation across western Washington up into British Columbia. As usual, much of the precipitation will focus against the upslope terrain with the highest amounts expected over the Olympic Mountains. Rubin-Oster Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php