Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 255 PM EST Wed Feb 21 2018 Valid 00Z Thu Feb 22 2018 - 00Z Sat Feb 24 2018 ...Cold and unsettled weather is expected over the West including some heavy snow over the Rockies... ...Additional heavy rainfall and widespread concerns for flooding will persist across parts of the southern Plains, lower Mississippi Valley and the Ohio Valley... ...Warm temperatures are generally expected to continue across a large portion of the East... The Western U.S. will mainly be cold, but also unsettled through the end of the week, as a series of impulses dropping south across western North America help to reinforce a broad upper level trough of low pressure. This will maintain below normal temperatures with most of the West seeing high temperatures about 10 to 20 degrees below normal. This energy will also bring the threat for heavy snow across parts of northern California, the Great Basin and the central Rockies as the energy traverses the interior of the West. Unfortunately, these impulses of energy ejecting down across the West and then out into the Plains will be the primary drivers of multiple rounds of heavy rainfall farther off to the east. This will include portions of the southern Plains, lower Mississippi Valley and Ohio Valley as multiple waves of low pressure eject northeast up along a frontal zone draped across the region. This additional rainfall will be largely falling on saturated ground from recent heavy rain over the last several days and going back to last week in some cases. Therefore, the threat for additional flash flooding and main stem river flooding will become enhanced through the remainder of the week. Aside from the focus for heavy rainfall, the same aforementioned front is marking the difference from an abnormally warm airmass in place across much of the East where temperatures are reaching as high as the 70s and 80s, and a very cold airmass that has nosed south down across much of the Plains where temperatures are locally below freezing as much as 10 to 20 degrees below normal. Over the next couple of days, some of the warm air across especially the Northeast and parts of the Mid-Atlantic region will be tempered by a modestly colder airmass behind a frontal passage later tonight, but this boundary will stall out from the lower Mississippi Valley to across the Tennessee Valley and into the Mid-Atlantic region on Thursday before then gradually beginning to lift back north as a warm front by Friday as a new area of low pressure lifts up across the Midwest. This will keep the Southeast U.S. in particular quite warm with much above normal temperatures through the end of the week. Regarding the threat of winter weather, there will be the approach of a wave of low pressure from the Tennessee Valley on Thursday that will actually interact with sufficient cold air over parts of the upper Ohio Valley, far northern Mid-Atlantic and interior of the Northeast for a stripe of some accumulating snow and ice. Meanwhile, there will also be a swath of accumulating snow and ice across portions of especially the central Plains, Midwest and Great Lakes for Thursday and Friday as low pressure rides northeast up across the region. Orrison Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php