Extended Forecast Discussion NWS Weather Prediction Center College Park MD 113 AM EDT Wed Apr 10 2019 Valid 12Z Sat Apr 13 2019 - 12Z Wed Apr 17 2019 ...Heavy rainfall threat from eastern Texas/Lower Mississippi Valley during the weekend... ...Overview and Guidance Assessment/Preferences... A system will exit the Southwest/Southern Rockies on to the Plains and MS Valley this weekend, bringing widespread rain to much of eastern Texas, Lower Mississippi and western Tennessee Valley with the potential for excessive rainfall and flash flooding. A surface low is expected to form along the boundary and aid in the progressive track toward the Ohio Valley. Model guidance suggests that this system will occlude, with a new low forming near the mid Atlantic coast and proceeding northeast near or off the New England coast early next week. The GEFS and ECMWF ensemble means cluster well with the cyclone track, with timing differences persistent as the operational ECMWF lags a few hours behind the ensemble timing, and the 18z GFS a few hours ahead of the ensemble means. Consequently, greater weighting continues to be placed on the respective 18z GEFS/12z ECMWF ensemble means. The models/ensembles show a couple of shortwaves moving onshore the Pacific Northwest and into the northern Rockies and high pains over the weekend into early next week. Guidance is clustering better than on prior days so a models/ensemble mean blend sufficed for this region. The waves will bring precipitation to the Pacific northwest and northern Rockies with valley rain showers and mountain snows. e Northern High Plains. The models show the southern portion of the upper trough moving onshore CA Sunday night and crossing into the Great Basin Monday and the Rockies to the Plains on Tuesday. This trough is expected to induce a frontal wave on the Plains Tue into Wed, with the stronger 18z gfs inducing the wave further north than the ensemble means/ECMWF. ...Weather Highlights/Hazards... The low pressure developing over southeast TX and moving into the lower MS Valley will lead to a heavy rainfall threat from eastern Texas and the Lower Mississippi Valley region into the Appalachians, Mid-Atlantic and southern New England, and possibly including the Ohio Valley. The highest forecast rainfall amounts are centered over the lower MS Valley. The next system developing over the Plains in the middle of next week will lead to an increase in rainfall amounts and coverage, including more rain expected in the lower MS Valley. The Pacific Northwest and Northern Rockies should see additional precipitation after the late week system in association with frontal systems moving onshore and inland. Early to mid week, snow focuses on the ranges of the Great Basin to the Co/WY Rockies. The cold temperature anomalies will be over the Rockies/Plains Saturday, peaking 20-25 degrees below normal in the Plains states. Also during Saturday expect above normal temperatures over the East, especially for morning lows which may be 10-20F above normal in the mid Atlantic to New York and much of the Appalachians on Saturday. Expect readings to moderate over much of the Lower 48 early next week. As the trough progresses across the west mid week, below normal temps will redevelop across the Great Basin to the Rockies Tue Apr 16 and Wed Apr 17. In the return southerly flow ahead of the trough on the Plains, a warmup is expected to result in above normal minimum temperatures mid week. Petersen Additional 3-7 Day Hazards information can be found on the WPC medium range hazards chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indices are at: https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml