Quantitative Precipitation Forecast Discussion NWS Weather Prediction Center College Park MD 257 AM EDT Tue May 08 2018 Prelim Day 1 QPF Discussion Valid May 08/1200 UTC thru May 09/1200 UTC Reference AWIPS Graphics under...Precip Accum - 24hr Day 1 ...Eastern portions of the Northern Plains---Lower MO Valley into the Upper MS Valley... Northern stream height falls moving out of the northern High Plains will amplify Tuesday as they push eastward through the Northern to Central Plains---Lower MO river Valley and into the Upper MS Valley. Convection expected to remain fairly active through the upcoming day 1 period in a region of well defined upper difluence ahead of these height falls and in an axis of pw values 1 to 2+ standard deviations above the mean. The initial round of organized precip will be pushing into the Upper MS Valley region this morning. This will be followed by another round forming farther to the southwest in the vicinity of central to eastern SD...northeastern NE late afternoon/early evening---pushing east southeastward across IA---southern MN---southwest WI---northwest IL and into northeast MO. Widespread moderate to heavy precip totals likely across these areas along with potential for isolated runoff issues where convection maximizes. A broad marginal risk area will be depicted on the day 1 excessive rainfall potential outlook across these areas---a consolidation of the previous two marginal risk areas depicted on the prior day 2 outlook. The National Water Model stream flow anomaly is showing the greatest flow initially this period from far eastern SD---far southwest MN into central to northern IA---with much lower flow levels elsewhere across this region. ...Northern Rockies into the Northern Plains... Additional northern stream height falls will be following in the wake of the lead area---pushing southeast from the Northern Rockies into the Northern Plains. Precipitation ahead of this next area of height falls is not expected to be as organized as the lead area given the overall weaker dynamics with these height falls. Subsequently--any additional precip is expected to be scattered with light to locally moderate areal average amounts. ...Pacific Northwest toward the far Northern Rockies... The closed low off the Pacific Northwest coast centered near 44N 138W at the beginning of the day 1 period will be pressing northeastward to the west of Vancouver Island by the end of the period. Organized precipitation along the associated frontal boundary will begin to affect the coastal Pacific Northwest Tuesday afternoon---moving farther inland through the Pacific Northwest Tuesday night-early Wednesday and toward the far northern Rockies by the end of the day 1 period. Model consensus is for widespread moderate to locally heavy precipitation totals from the Washington-Oregon Cascades--west to the coast ranges and over the Blues of northeast Oregon and far southeast Washington---with the day 1 WPC qpf not deviating from this. Upper troffing from the Mid Atlantic into the Southeast will be pushing east northeastward off the coast Tuesday evening into the early hours of Wednesday. Any appreciably precip ahead of this trof will likely remain offshore---with coastal areas from eastern NC into the southern Delmarva Peninsula possibly affected by light to moderate precip totals. Scattered diurnal showers also possible through the Central to Southern Appalachians---but with instability less than the previous day---coverage and precip amounts should be less. Oravec