Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 357 AM EDT Sat Mar 21 2015 Valid 12Z Sat Mar 21 2015 - 12Z Mon Mar 23 2015 ...Heavy rain and flash flooding possible across south Texas and the lower Mississippi Valley this weekend... Showers and thunderstorms will continue today and tonight across south Texas---along a frontal boundary extending from south central Texas eastward to the southeast coast of Georgia. This weekend---low pressure forming along this boundary will migrate eastward along the I-10 corridor and be a focus for additional heavy precipitation along the Gulf Coast, the Southeast and portions of the Florida peninsula. Very heavy rainfall and possibility of flash flooding---are greatest today and tonight over a large portion of southern Texas and northwest Louisiana---where an additional 1 to 2 1/2 inches of rain---may fall during the next 12 to 24 hours. Please refer to the latest WPC discussions---QPFERD, QPFPFD and FFGMPD---for the latest information concerning this heavy rainfall threat. Across the Northeast and Great Lakes---a persistent trough over eastern Canada will allow cold Canadian air to spread over the region. Low pressure developing off the New England coast and intensifying across the Canadian Maritimes will produce light snow and snow showers for northern New England and Maine. An active weather pattern in the northeast Pacific---will gradually migrate a series of Pacific systems and their cold fronts inland across Washington, Oregon, northern California and the northern Great Basin---with precipitation developing downstream across the northern Rockies, northern High Plains and Missouri Valley on Sunday and Sunday night. An inch or two of rainfall is possible along the Oregon and northwest California coast and the adjacent coastal ranges between late Sunday morning and early Monday morning. Vojtesak Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_wbg.php