Quantitative Precipitation Forecast Discussion NWS Weather Prediction Center College Park MD 213 PM EST Wed Feb 28 2018 Prelim Day 1 QPF Discussion Valid Mar 01/0000 UTC thru Mar 02/0000 UTC Reference AWIPS Graphics under...Precip Accum - 24hr Day 1 ...Eastern U.S... ...High Risk of Excessive Rainfall parts of OK/TX/AR/LA/TN/MS... Southern and northern stream troughs will phase during this period along the length of the Mississippi River. The southern stream component will pull height falls across the central corridor of Gulf return moisture, driving a pronounced heavy rain and flash flooding risk from east Texas toward Tennessee. Low levels were nearly saturated and topped by dry mid levels / steep lapse rates to produce sizable CAPE which will contribute to strong convection and enhanced short term rain rates. Owing to extraordinarily wet antecedent conditions, expect a high percentage of surface runoff and associated hazards. See Excessive Rainfall Discussion and Mesoscale Precipitation Discussion for details. The phasing troughs will also lead to cyclogenesis across the Ohio Valley, wrapping in some of the Gulf return moisture, with PW values rising to around 0.75 inches as far north as the lower Great Lakes. This will yield a secondary axis of heavier QPF. Whereas areas in the southern states will see a swath of areal average 2 to 5 inches (locally greater), the northern Ohio Valley and lower Great Lakes should see average amounts 1 to 2 inches. The system may pivot around southeast lower Michigan and northeast Ohio as it assumes a negative tilt, meaning somewhat heavier precipitation may be found there. WPC QPF was influenced by our in-house ensemble, given an increasingly strong consensus, along with some hi-res influence, the WRF-ARW and WRF-ARW2. This approach kept good continuity while increasing QPF over southern Arkansas where the greatest overlap of CAPE and low level moisture transport is expected, as well as increasing it over the lower Lakes area where models had come into better agreement as to the strength and placement of the developing cyclone. ...Maine... A clipper type system seen over Quebec at midday will spread snow over primarily the state of Maine tonight and early Thursday, affecting especially northern Maine. This well defined wave should be well handled in the models, and the coverage of half inch liquid amounts has increased via a QPF consensus approach. ...Western U.S... Strong amplification expected to the mid to upper level trof dropping along the West Coast. This developing closed low will have a better tap of above average PW values than the previous systems that have amplified into the mean western trof over the past several days. Strengthening southwesterly onshore flow will support widespread heavy precip totals this period from the northern Sierra/northwest and Central California coastal ranges, northward along the Oregon coastal range and into the Olympic range. Heavy precip values are likely inland through the Oregon Cascades while moderate to heavy totals are expected northward into the Washington Cascades. Compared to new global guidance the inherited WPC grids better preserve some of the terrain details, without maxing out the values at higher elevations as some of the hi-res models do. Trends in our in-house, bias-corrected, ensemble are essentially flat over several runs, meaning the system seems locked in from a model standpoint. Therefore, we went with nearly 100 percent the previous WPC forecast, making no change. Expect this system to drive some excessive rain risk along the California Coast, especially burn scars, and also heavy snows in the mountains...per the QPFHSD product. Burke/Oravec