Quantitative Precipitation Forecast Discussion NWS Weather Prediction Center College Park MD 519 PM EDT Fri Mar 30 2018 Final Day 1, Day 2 and Day 3 QPF Discussion Valid Mar 31/0000 UTC thru Apr 03/0000 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. A few tweaks were made across FL based on radar trends, and a few changes were made across ND to account for timing before 31/06z. ...Northern Plains into the Upper MS Valley and Upper Great Lakes... An area of low pressure will move across the Northern Plains and into the Upper MS Valley tonight into Saturday. Will see strong isentropic lift ahead of this low...with an axis of strong frontogenesis and steeper lapse rates north of the low likely supporting a band of heavy snow. Some disagreement exists with the exact corridor of these higher QPF amounts. In general have noted a southward trend over the past few model cycles. WPC thus trended in this direction as well...although still some uncertainty on where the heaviest banding sets up. The 12z GFS and GEM Regional are the furthest south solutions, with the 12z HRW ARW and 0z ECMWF furthest north. Overall went for a consensus between these two solutions...weighted a bit more towards the further south GFS/GEM Regional given trends. Looks like a nice swath of 0.5"+...and while not in our deterministic forecast given model spread...would anticipate some 0.75"+ amounts to occur where banding ends up maximized...likely somewhere from east central MN into north central WI. ...Northern Rockies... In the wake of the area of low pressure moving eastward from the Northern Plains into the Upper MS Valley---the arctic front will push southward Friday and become banked up against the Northern Rockies. Post frontal upslope flow will support continued snows into portions of the Northern Rockies. Days 2 & 3 ...Pacific Northwest... A potent shortwave trough along the central BC coast Saturday evening shifts south to western WA by Sunday evening then to the northern Rockies Monday. Continued onshore flow south and southwest of this system as it passes will bring half inch PW into the WA/OR coast with locally moderate Coast Range and Cascade enhanced precip. Good agreement among the models warranted a 12Z GFS/ECMWF/NAM blend for the QPF. ...Northern and Central Rockies/Northern and Central Plains... Weak short wave energy tracking across the northern Rockies Saturday night will provide synoptic scale lift over an arctic front stretching from western MT into northeastern CO that spreads across NE Sunday. Only minor timing differences were apparent in Day 2 guidance, so the QPF was based on the 12Z GFS/ECMWF/NAM. A stronger shortwave trough pushes southeast from WA Sunday night to the northern Rockies through Monday. Broad surface low development over the high central plains with zonal jet support will bring a broad swath of precip across the northern plains from MT to WI Sunday night through Monday. The NAM was more of an outlier with this second wave bring stronger and more progressive, so the Day 3 blend leaned more toward the 12Z GFS/ECMWF. ...Mid-South... A cold front stalling over the ArkTexOma will allow convergence of gulf moisture from the Red River of the south across AR. Utilized 12Z ARW2 output to focus the heavy QPF axis. Maintained a marginal risk for excessive rainfall across this area for Day 2 (12Z Sat-12Z Sun). ...Upper Great Lakes/Northeast... A surface low will track north of the St. Lawrence Valley Saturday night through Sunday. Precip ahead and south of this low track will stretch across the eastern Great Lakes across the northeast. Up to a quarter inch QPF can be expected along this swath in Day 2 (00Z Sun-00Z Mon). ...TN/OH Valley/Mid-Atlantic... A trend north with low pressure that began at 00Z continued in the 12Z guidance. A swath of half to one inch qpf is expected south of OH Valley to across the Mid-Atlantic. A blend of the 12Z GFS/ECMWF with some 12Z NAM was used for Day 3 QPF. A decent baroclinic zone along this swath will allow for snow on the north side. Please see QPFHSD for further info on snow. Chenard/Jackson Graphics available at www.wpc.ncep.noaa.gov/qpf/qpf2.shtml