Quantitative Precipitation Forecast Discussion NWS Weather Prediction Center College Park MD 353 PM EST Tue Mar 06 2018 Final Day 1, Day 2 and Day 3 QPF Discussion Valid Mar 07/0000 UTC thru Mar 10/0000 UTC Reference AWIPS Graphics under...Precip Accum - 24hr Day 1... For the 00z QPF issuance: no significant changes were made to the 18z qpf issuance. ...Great Lakes/Ohio Valley to East Coast... The focus for the rest of Tuesday and all of Wednesday will shift from the Upper Midwest to the East Coast. The powerful cyclone over the Midwest will gradually shift downstream and decay/fill over the Great Lakes before partially reforming over the region, while upper dynamics from this system round the base of the upper trough to induce a coastal low near the DelMarVa. This surface low will deepen rapidly by 5-10 mb, while moving up the coast toward Long Island. This will set the stage for back to back late season winter storms to impact portions of the Northeast. Most of the qpf is anticipated in association with this developing Nor'easter, as an increase of Atlantic moisture streams in from the east and flourishes on the north and west sides of the intensifying system. WPC followed a 5 way blend for qpf, 12z gfs, nam conest, nbm and href mean with the 00z/06 ecmwf. This blend focuses 1 to 2 inch areal avg qpf amounts with locally higher values from DE/nern MD through eastern PA/all of NJ into NYC/southern Hudson Valley/Long Island and perhaps into southern New England. Meanwhile, other qpf highlights include possible focus from the coastal low to the 500mb circulation over MI along an inverted trough axis and possible scattered showers/storms from the southeast through FL this evening through midday tomorrow. The difficulty with the forecast is ptype from the Mid-Atlantic up into the Northeast or where the rain/snow line will set up. The surface low track is absolutely critical and the latest trend with the 12z guidance is a little left, closer to the coast, which may shift the rain/snow line over the major metro cities from PHL to NYC to BOS or north and west or the metro areas and I95. For more on this difficult wet snow forecast, please refer to the latest qpfhsd. Days 2/3... ...Pacific Northwest and Northern/Central California into Northern Rockies... A weakening closed middle-level low approaching the Pacific Northwest Coast will eject multiple short waves into the Northwest diminishing the upper-level ridge over the region. The system will produce onshore flow into the Northwest/California through Friday evening. The low-level flow will range between 35 and 60 knots into the Pacific Northwest that increase from Wednesday evening into Thursday evening with precipitable water values of 0.50 inches. The low-level flow will decrease from 40 to 35 knots to 15 to 10 knots by Thursday evening over Northern/Central California with the precipitable water values or 0.50 inches, too. The storm will produce maximum qpf ranging from 1.00 to 1.35 inches over the coastal ranges of Oregon and Northern California on Wednesday evening into Thursday evening. The onshore flow steadily decreases while becoming more directly onshore from 55 to 10 knots over the Northwest by Friday evening while the precipitable water values decrease below 0.50 inches. The low-level flow will continue between 15 and 10 knots over Northern/Central California with the precipitable water values continuing at 0.50 inches through Friday evening. The maximum qpf will develop over parts of the Northern Rockies with maximum qpf amounts ranging between 0.75 to 1.00 inches with a secondary maximum over the Shasta/Trinity Mountains into the Cascades with maximum qpf amounts ranging between 0.50 to 0.85 inches. WPC used a blend of the GFS/ECMWF with a bit of the NAM on Thursday evening into Friday evening. ...Great Lakes into the Central/Southern Appalachians into the Northeast... Deep upper-level low over the Great Lakes into the Northeast with the center moving from the Great Lakes to the Northeast by Friday evening. Circulation around the upper-low will stream moisture into Northern New England with low-level flow ranging from 50 to 60 knots with precipitable water values of 0.50 inches that will slowly lift northward into the Canadian Maritimes by Thursday evening. On Wednesday evening into Thursday evening, the maximum qpf amounts will range from 2.00 to 2.40 inches over Northern New England with a secondary maximum over the Great Lakes with maximum qpf amounts ranging from 0.25 to 0.50 inches. On Thursday evening into Friday evening, additional short wave energy flows from the Upper Mississippi Valley/Upper Great Lakes into the base of the upper-level trough over the Northern Mid-Atlantic by Friday evening. The energy will aid in producing a maximum qpf amounts ranging from 0.25 to 0.45 inches over the Lower Great Lakes. WPC used a blend of the GFS/ECMWF with a bit of the NAM on Thursday evening into Friday evening. ...Western Gulf Coast/Southern Plains... Return flow off the Western Gulf of Mexico will begin to flow northward over the Plains on Thursday morning with precipitable water values of 0.75 inches that will increase to 1.25 to 1.50 inches over the Western Gulf Coast with moisture moving into the Middle Mississippi Valley by Friday evening. In addition by Friday evening, very light amounts of qpf will develop over the Western Gulf Coast/Southern Plains with qpf amounts being very modest around 0.01 inches. Musher/Ziegenfelder Graphics available at www.wpc.ncep.noaa.gov/qpf/qpf2.shtml