Quantitative Precipitation Forecast Discussion NWS Weather Prediction Center College Park MD 150 AM EST Tue Feb 27 2018 Prelim Day 1 QPF Discussion Valid Feb 27/1200 UTC thru Feb 28/1200 UTC Reference AWIPS Graphics under...Precip Accum - 24hr Day 1 Southern Plains---lower MS Valley---lower TN Valley The low level southerly to south southwesterly flow is expected to strengthen Tuesday across the Southern Plains and into the lower MS valley/lower TN valley by Tuesday night/early Wednesday. This will raise pw values to 2 to 2.5+ standard deviations above the mean and support increasing overrunning precipitation along and to the north of the northeastward moving warm frontal boundary across these areas. There is some model spread with axis of the heaviest precip---leading to below average confidence as the first wave of heavy precip breaks out---followed by a second potentially heavier event day 2. The day 1 qpf leaned toward the href mean which was closest to the more southern max axes of the hi res guidance and south of the EC...NAM and GFS axes. The heaviest precip potential likely late afternoon Tuesday into Tuesday night/early Wednesday corresponding to the strengthening of the low level inflow into the boundary. There will be potential for a period of training of cells to the north of the warm front with localized hourly precip totals in the .50-1"+ range. With stream flow anomalies much above average from recent heavy rains--additional runoff issues possible. The marginal and slight risk areas on the previous excessive rainfall potential outlook for this period were expanded slightly across northeast TX---southeast OK into central AR and southwest TN to cover some of the model spread with respect to the max axis. Lower MO Valley into the lower OH Valley Model consensus is for a secondary precip max farther to the north across portions of the lower MO river valley toward the lower OH valley ahead of a northern stream cold front pressing southeastward. With pw values also rising to much above average levels ahead of this boundary---moderate to isolated heavy precip amounts possible---although believe the most organized activity will be farther to the south along and to the north of the warm front where the strongest isentropic lift is expected. Southern California...southern Great Basin into the Southwest The well defined closed low over northern California early this morning will continue to press southeastward through central to southern California and into the Southwest this period. Strong westerly onshore flow into the peninsular range of southern California will support moderate to locally heavy totals. Elsewhere--the model consensus is for light to moderate totals from the southern Sierra into the southern Great Basin and Southwest as this system will continue to not have an anomalous pw tap with values near seasonal norms. Pacific Northwest into the Northern Rockies Weak onshore flow expected day 1 across the Pacific Northwest into the northern Rockies as shortwave energy passes southeast across southwest Canada. The day 1 qpf did not deviate from the model consensus of light to moderate totals from the northern Rockies of northern ID/northwest MT and through the Washington-northern Oregon Cascades west to the northern Oregon Coast range and the Olympic Range. Oravec