Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 229 PM EST Thu Dec 21 2017 Valid 00Z Fri Dec 22 2017 - 00Z Sun Dec 24 2017 ...There is a moderate risk of flash flooding across portions of the South... ...Icy conditions along with snow may occur along the Great Lakes and New England... ..Bitterly cold temperatures expected across the northern Plains and northern Rockies... A frontal system moving into the Plains is expected to move across the southern Plains and into the Mississippi Valley by Friday morning. Showers and thunderstorms ahead of the front along southeast Texas can be expected later tonight and into early hours of Friday as deep southerly flow transports moisture from the Gulf of Mexico ahead of this front cold front. However, by Friday, a flash flooding event could unfold from parts of the lower Mississippi Valley to the Tennessee Valley by Friday afternoon. Heavy rainfall will set up along the front in the lower Mississippi Valley by early afternoon. These thunderstorms will be very slow moving--allowing for an increasing potential of flash flooding. The axis of heavy rainfall will shift to the western portions of the Tennessee Valley by early hours of Saturday morning. A moderate risk of flash flooding is in place from the lower Mississippi Valley to the Tennessee Valley on Friday as a result. By Saturday afternoon, the cold front quickly moves toward the East Coast. Rainfall will still occur along and ahead of the front by Saturday afternoon albeit not nearly as heavy. Ahead of the system that will give way to flash flooding in the southern portions of the U.S., it will also bring winter precipitation north of it. Snow is expected along the northern portions of the Great Lakes on Friday morning--with icy conditions possible near the rain/snow line. Freezing rain along with snow will spread northward across the Northeast throughout Friday and into Saturday morning as the frontal boundary lifts north. The icy conditions can be expected especially in New England. Please see WPC's winter weather products and discussion for more information pertaining to the winter weather hazards associated with this system. As an Arctic high pressure dives across the northern Plains and northern Rockies on Friday, bitter cold temperatures will follow. Expect high temperatures to be in the teens on Saturday--which is about 20 degrees below average for this time of year. Ahead of the cold front pressing eastward from the Plains to the East Coast--high temperatures will be about 15 degrees above normal. Reinhart Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php