Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 449 AM EDT Sat Oct 31 2015 Valid 12Z Sat Oct 31 2015 - 12Z Mon Nov 02 2015 ...Severe thunderstorms possible for portions of eastern Texas and lower Mississippi valley today... ...Flash flooding possible for the Gulf Coastal Plains and for the southern Appalachian and Piedmont ranges Sunday... ...Heavy rain possible for the Mid-Atlantic on Monday... ...Heavy rain possible across portions of the Pacific Northwest... The Gulf states will continue to have wet and unsettled conditions over the next couple of days. An upper-level trough and associated surface low pressure system is forecast to track slowly to the East, reaching central Alabama by early Monday morning. A rather strong upper-level jet will align itself nearly parallel with the surface front, which will likely result in multiple rounds of slow moving convection. Moisture advecting in from the Gulf of Mexico ahead of the low pressure system will be on the order of 2+ standard deviations above normal for early November. This setup will be favorable for high rainfall rates and/or long durations of rain. The axis of the higher amounts will span from the Mississippi Delta to northwest South Carolina, where 3-day totals of 2 to 7 inches are forecast. The risk for flash flooding will be elevated through the weekend as rapid runoff and ponding is expected. Some of the storms today across the Southern Plains may become severe. Please refer to Convective Outlook products issued by the Storm Prediction Center for further details on the severe weather threat. Moisture from the system crossing the southern plains and the Southeast will also stream farther north, bringing showers to portions of the central plains and Midwest today, and into the Northwest by Sunday. Snow may mix with rain showers across portions of northern New England on Sunday. Moisture amounts are expected to be less than 1 inch through Monday morning. A series of upper-level disturbances along with a constant plume of moisture will continue to impact parts of the Pacific Northwest through the weekend. Significant rainfall will impact a vast area from southwest British Columbia down to northern California. Snow will be possible at the higher elevations. Total moisture will be dependent on elevation. Most areas along the coast and in the valleys will have amounts less than 3 inches. The higher elevations of the Coast Ranges and the Cascades could see 3 to 7 inches, with isolated higher amounts. Rain and high elevation snow showers will also occur over the northern Intermountain West as the plume of moisture crosses this area-- 1 to 2 inches will be common, with 2 to 4 in the northern Rockies. The long duration of the rain, in addition to runoff from steep terrain, will likely result in heavy rainfall amounts and increased risk of flooding through the weekend. Campbell Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_wbg.php