Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 237 AM EST Thu Dec 22 2016 Valid 12Z Thu Dec 22 2016 - 12Z Sat Dec 24 2016 ...Heavy to excessive rainfall possible on Thursday for portions of the Southwest... ...Heavy to excessive rainfall possible along the California coast on Friday... ...Heavy snowfall possible across the higher terrain of the Sierras and into the Intermountain West... An upper level system just off the Southwest U.S. coast this morning will continue to spread heavy rainfall and higher elevation snow as it moves inland on Thursday over much of the Southwest and southern Rockies. Excessive rainfall and flash flooding is possible across portions of central Arizona into far western New Mexico. As the upper system slides eastward into the Southern High Plains by Friday, it should tap into Gulf of Mexico moisture and spread precipitation as it moves eastward from the Plains to the Northeast Friday and Saturday. The best chance for organized rainfall will be to the north of a warm front from the Lower Mississippi Valley into the Tennessee Valley on Friday. In the northern portion of the precipitation shield, it should be cold enough for snow from the Upper Mississippi Valley to the Great Lakes. Generally light accumulations are expected in these areas on Friday. Meanwhile, another system pushing eastward through the eastern Pacific will bring precipitation into the Western states by Thursday night. On Friday, a steady stream of moisture focused into California could bring very heavy rainfall and the potential for flash flooding along the coast, with heavy snowfall expected in the higher terrain of the Sierras. As the system pushes eastward across the West, conditions should begin to dry out by the weekend along the coast, but another round of rain and mountain snow will spread eastward into the Intermountain West and the Southwest Friday night and into Saturday. Elsewhere, a departing system out of the Northeast on Thursday may spread some light snowfall across the lower Great Lakes and New England. At the same time, a lingering frontal boundary will keep mainly light rain in the forecast along coastal Florida as well as the western Gulf coast. Santorelli Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php