Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 406 PM EDT Fri Jun 16 2017 Valid 00Z Sat Jun 17 2017 - 00Z Mon Jun 19 2017 ...Heavy thunderstorms will move eastward from the Plains into the Appalachians during the weekend... ...Heat getting more intense over California into the Desert Southwest... ...Tropical moisture could bring some heavy downpours into southern Florida on Sunday... An energetic onshore flow, which is currently bringing cool and unsettled weather over the Pacific Northwest into the northern Rockies, will move rapidly toward the northern and central Plains during the weekend. This will invigorate the somewhat stagnant weather pattern currently over the central and eastern U.S. Before the Pacific energy reaches the Appalachians later on Sunday though, much of the eastern U.S. will continue to be under summer heat and humidity with scattered showers and thunderstorms. Over the central and southern Plains, a stationary front has been the focus of strong to severe thunderstorms in the past couple of days. As the Pacific energy reaches the northern Plains and begins to interact and merge with the stationary front over the weekend, showers and thunderstorms are expected to form ahead of a fast-moving strong cold front. Some of the thunderstorms could become quite intense as they are expected to spread rapidly from west to east across the Midwest into the Appalachians on Sunday. By Sunday night, the front will lose some momentum as showers and thunderstorms will continue to be near and along the Appalachians as the main low pressure system moves north of the Great Lakes into Canada. Cool air will pour into the northern and central Plains behind the low from Sunday into Monday. Meanwhile, much of the southwestern U.S. continues to be under the influence of a strong high pressure cell aloft. In fact, the high is forecast to strengthen further during the weekend. Temperatures are forecast to soar into triple digits in the afternoons over the interior valleys of California, and into the 110s over much of the Desert Southwest. In fact, some locations could see temperatures reaching 120 degrees Sunday afternoon, where some daily record highs could be tied or broken! Elsewhere, tropical moisture from the Caribbean Sea could reach southern Florida with some heavy downpours possible on Sunday. Kong Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php