Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 111 AM EST Sat Dec 16 2017 Valid 12Z Sat Dec 16 2017 - 12Z Mon Dec 18 2017 ...Pattern change expected over the weekend... The persistent western ridge and eastern U.S. trough over the past week is now in the process of changing as a strong upper level trough and shortwave disturbance over the West breaks down the ridge and flattens the eastern trough. This trough is expected to amplify over the Rocky Mountains during the weekend and increase the chance of snow for this region through Monday. After an extended period of dry weather, accumulating snow is likely for parts of the Rockies over the next few days in response to a developing surface low over the Four-Corners region and shortwave energy aloft. There will likely be a decrease in the amount of lake effect snow with less cold air advection over the Great Lakes. Warm and dry conditions are expected for Florida and the lower elevations of the Desert Southwest and into central and southern California this weekend. Fire weather concerns will still exist across parts of California owing to the dry conditions and gusty winds. Above normal temperatures are expected across the central Plains on Saturday before colder weather arrives on Sunday behind a cold front. On the other end of the temperature spectrum will be the northern Rockies and northern New England, where readings will remain quite chilly with sub-freezing high temperatures expected. After a thunderstorm drought across the nation, some lightning and thunder will be possible from southern Texas to the central Gulf Coast this weekend. Deeper moisture returning northward from the Gulf of Mexico ahead of a front could fuel the development of some scattered storms, along with locally heavy rainfall at times. D. Hamrick Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php