Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 415 PM EDT Mon May 06 2013 Valid 00Z Tue May 07 2013 - 00Z Thu May 09 2013 ...A slow-moving upper low will continue to bring a threat for moderate to heavy rainfall to areas of the Eastern U.S... ...Widespread shower activity is expected across the Southwestern states in response to another closed low... The mid-level pattern affecting the country will continue to be dominated by a large-scale block. Such a regime leads to slow-moving systems which remain cut-off from the prevailing jet stream which at this time is north of the international border. Currently, a pair of closed lows are affecting the Lower Tennessee Valley and the Desert Southwest, respectively. The former disturbance has been impacting a significant portion of the Southeastern quarter of the nation the past couple of days as it remains a very slow mover. Although the intensity has diminished and is forecast to continue such a trend, the slow-moving nature of the system will keep a heavy rainfall threat in place. A well-defined moisture plume advancing inland off the Western Atlantic is still evident in water vapor imagery and will play a key role in rainfall production. As this low-level slug of moisture hits the eastern slopes of the Central Appalachians, upslope flow will kick in aiding in further support for enhanced precipitation efficiency. The Weather Prediction Center has currently highlighted this region with an increased threat for excessive rainfall given antecedent conditions and higher rainfall amounts forecasted. Further to the south within the more buoyant air, severe thunderstorms may be possible this evening. As a whole, unsettled weather is expected to be the norm through mid-week as the upper cyclone will linger over the region for days. The other key feature impacting the nation is another cut-off low which currently is swirling just offshore of the Central California coastline. The broad upper low will cool the mid-levels of the atmosphere enough to initiate numerous showers, particularly where terrain is involved. The highest elevations of the lower Sierra Nevada range can even expect light snowfall accumulations with this system. As the system advances eastward in time, precipitation should begin to break out across a larger section of the Southwestern U.S. as low-level moisture significantly increases. Snowfall is also expected across the higher peaks of Western Colorado where 3 to 6 inches of accumulations may be possible through Wednesday evening. Once this cyclone works its way into the Four Corners region, increasing coverage of showers and thunderstorms are expected across the Great Plains. The Storm Prediction Center forecast suggests the best severe threat will be from Central Texas up into Western Kansas on Wednesday. Rubin-Oster Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_wbg.php