Quantitative Precipitation Forecast Discussion NWS Weather Prediction Center College Park MD 458 PM EDT Mon Apr 16 2018 Prelim Day 1, Day 2 and Day 3 QPF Discussion Valid Apr 17/0000 UTC thru Apr 20/0000 UTC Reference AWIPS Graphics under...Precip Accum - 24hr Day 1 ...Mid Atlantic into the Northeast and Great Lakes... A negatively tilted mid/upper level trough supports strong upper level divergence, strong low-level inflow, and ample moisture which moves through New England today and tonight. CAPE should be harder and to come by rain translates northeast, instability slowly fades, and the moisture feed slowly winnows, though it should be enough to allow for continued embedded heavier convective cores within the rain shield. Localized rates peaking in the 0.5"-0.75" in an hour range early on will slowly fade with time. Further northwest under the closed mid/upper level low, will continue to see precipitation into the Great Lakes region. Overall, a compromise of continuity, the 12z ARW, the 14z National Blend of Models, the 12z GFS, and the 00z ECMWF were used for the precipitation pattern, with a strong lean towards the National Blend of Models near the Great Lakes themselves where global guidance can underestimate lake effect. ...West... A trough will continue moving east into the Great Basin and northern Rockies with associated low- to mid-level frontogenesis supporting modest precipitation over much of the area. WPC QPF used a compromise of continuity, the 12z ARW, the 14z National Blend of Models, the 12z GFS, and the 00z ECMWF were used for precipitation amounts. Days 2/3 ...West Coast/Intermountain West... Upper-level low off the West Coast will move southeastward to the Great Basin/Southwest by Thursday evening. Onshore flow over the Pacific Northwest will end and become offshore by Wednesday morning. The precipitable water values along the coast are 0.50 inches that will drop off to near 0.25 inches by Thursday morning. The qpf will be generally light with maximum qpf amounts over the Northern Cascades and the Olympic Peninsula with maximum qpf amounts ranging from 0.25 to 0.30 inches from Tuesday evening into Wednesday evening. The Upper-level low will move onshore over California moving into parts of the Great Basin Wednesday evening into Thursday evening. A week plume of moisture will pass along the Southern California Coast with precipitable water values of 0.50 inches with the low-level flow of 20 knots from early Thursday morning through late Thursday morning when the plume moves into Northwestern Mexico. The qpf will be modest with maximum qpf amounts ranging from 0.25 to 0.35 inches over parts of the Great Basin on Wednesday evening into Thursday evening. WPC used a blend of the GFS and the ECMWF as the starting point of the manual graphics. ...Northern/Central Plains eastward to the Northeast/Northern Mid-Atlantic... A baroclinic zone over the Middle Mississippi Valley and the Central/Southern Plains will move northeastward off the East Coast by Thursday evening. A plume of moisture from the Western Gulf of Mexico will intersect the boundary with precipitable water values of 0.75 inches that will pool along the boundary until the front and the moisture plume move off the East Coast by Thursday morning. The low-level flow will increase from 15 to 20 knots to 35 to 40 knots on Wednesday morning over the Middle Mississippi Valley. The storm will produce a maximum qpf over parts of the Upper/Middle Mississippi Valley with maximum qpf amounts from 1.00 to 1.20 inches on Tuesday evening into Wednesday evening. A secondary maximum will develop over parts of the Lower Great Lakes/Northern Appalachians under a deep upper-level low over the Northeast with maximum qpf amounts ranging from 0.25 to 0.45 inches also from Tuesday evening into Wednesday evening. As the upper-level energy associated with the baroclinic zone moves eastward the energy forms a new upper-level low over the Northeast by Thursday evening. The boundary will aid in producing a broad region of qpf from the Lower Great Lakes to New England Coast with maximum qpf amounts ranging from 0.25 to 0.50 inches from Wednesday evening to Thursday evening. WPC used a blend of the GFS and the ECMWF as the starting point for the manual qpf. ...Southern High Plains into the Rio Grande Valley... As the aforementioned upper-level low over the West Coast moves inland, circulation around the upper-level low will pull moisture from the Western Gulf of Mexico westward into the Southern High Plains Wednesday evening into Thursday evening. Precipitable water values will increase from below 0.25 inches to 1.00 inches by Thursday evening. The system will produce some qpf over parts of Northeastern Mexico that will drain into the Rio Grande. The heaviest qpf during the period will occur late on Thursday afternoon into Thursday evening over parts of the Southern High Plains with maximum qpf amounts ranging from 0.25 to 0.40 inches. Roth/Ziegenfelder Graphics available at www.wpc.ncep.noaa.gov/qpf/qpf2.shtml