Quantitative Precipitation Forecast Discussion NWS Weather Prediction Center College Park MD 448 AM EDT Sat Mar 31 2018 Prelim Day 1, Day 2 and Day 3 QPF Discussion Valid Mar 31/1200 UTC thru Apr 03/1200 UTC Reference AWIPS Graphics under...Precip Accum - 24hr Day 1 Upper MS Valley---Upper Great Lakes into southeast Canada Overall good agreement in the latest guidance with the east northeast push of a well defined surface low from the Upper MS Valley into the Upper Great Lakes on Saturday---across southeast Ontario into southern QB Saturday night into early Sunday. Strong isentropic lift ahead of this low will continue to support heavy snow potential day 1 from northeast WI...across most of the U.P. of MI into the northern portion of the L.P. of MI...northeast across southeast portions of Ontario into southern QB. See the latest QPFHSD for additional winter weather information across this region. Northeast...lower Great Lakes...central Appalachians--OH Valley...lower AR/lower MS Valleys The trailing cold front from the Upper MS Valley-Upper Great Lakes low pressure will be moving quickly south through the Central to Southern Plains...southeastward from the Upper MS Valley...into the mid MS Valley...through the lower Great Lakes...OH Valley and into the northeast. Precip along and ahead of this front should increase with time as pw values rise in the vicinity of the front during the day 1 period. The fast movement of the front will remain the greatest detriment to any heavy totals---with generally moderate totals depicted from the Northeast...lower Great Lakes...central Appalachians...OH Valley into the lower AR/lower MS Valley region. Model consensus for the greatest precip potential along the front is over portions of the lower AR/lower MS river valleys from eastern OK into northern to central AR where areal average .25-50" totals are possible. Lee of the Central Rockies into the Central Plains Shortwave energy moving east southeastward across the Northern to Central Rockies into the central Plains will enhance isentropic lift over the arctic air entrenched over the plains. This will support an area of accumulating snows pushing eastward Saturday afternoon/evening from the lee of the Northern to Central Rockies into the Central Plains. Model consensus is for moderate to heavy snow potential from southeast WY/far northeast CO into southwest Nebraska. See the latest QPFHSD for additional winter weather information across this region. Days 2 & 3 ...Pacific Northwest... A potent shortwave trough over southern British Columbia Sunday morning shifts south to Washington 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 Washington/Oregon coast with locally moderate Coast Range and Cascade enhanced precip. Good agreement among the models warranted a 00Z GFS/ECMWF/NAM blend for the QPF. ...Northern and Central Rockies Eastward Across the Northern and Central Plains... A fairly strong shortwave trough pushes southeast from Washington 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 from the High Plains adjacent to the Central and Northern Rockies eastward to Wisconsin through Monday. The NAM remained an outlier with this second wave bring stronger and more progressive, so the QPF was weighted toward the 00Z GFS/ECMWF. ...Northeast... Any lingering precipitation over New England and New York associated with a surface low moving along and north of the Lawrence Valley will be tapering off on Sunday. Any additional precipitation amounts early on day 2 should be a quarter of an inch or less before enough dry air sweeps into the region and shuts down the precipitation. ...Mid-Mississippi Valley/TN and OH Valleys/Mid-Atlantic... A trend north with low pressure that began early on Friday morning continued this morning. A ontinued in the 12Z guidance. A swath of half to one inch qpf is expected from the southern portion of the Ohio Valley/northern portion of the Tennessee Valley across the Mid-Atlantic. The model agreement was fairly good on day 2...with the exception of the GFS which got to be on the fast side of the guidance. As a result, a non-GFS model compromise was used here. A second wave embedded within fast northwest flow aloft will sweep over many portions of the mid-Mississippi Valley and Ohio/Tennessee Valleys where a quasi-stationary front will be in place at the surface. The model agreement with respect to QPF was not as good as it was on Day 2. It seemed as though the GFS had a better handle on the flow pattern than the ECMWF and the GFS had the support of other global models. Oravec/Bann Graphics available at www.wpc.ncep.noaa.gov/qpf/qpf2.shtml