Quantitative Precipitation Forecast Discussion NWS Weather Prediction Center College Park MD 558 AM EDT Mon Apr 02 2018 Final Day 1, Day 2 and Day 3 QPF Discussion Valid Apr 02/1200 UTC thru Apr 05/1200 UTC Reference AWIPS Graphics under...Precip Accum - 24hr Day 1 Coastal northern Mid-Atlantic---Long Island---southern New England The fast moving area of height fall supporting the broad area of precipitation from the central Appalachians into the Mid Atlantic early Monday morning will continue to press quickly eastward and off the northern Mid Atlantic coast early Sunday---passing then to the south of New England by Monday afternoon. Strong isentropic lift ahead of these height falls will continue to support a concentrated region of moderate to heavy precipitation intensity across far southern New England/Long Island Monday morning. The expected fast eastward movement will keep precip values generally in the moderate range of .10-25"+. Early spring accumulating snows possible across these areas. See the latest QPFHSD for additional winter weather information. Northern Plains---Upper MS Valley---Upper Great Lakes The strong closed low moving into the Pacific Northwest this morning will be pressing east southeastward across the Northern Rockies Monday and into the northern high plains Monday night-early Tuesday. These height falls will strengthen isentropic lift to the north of the arctic frontal boundary forecast to lie from the lee of the northern Rockies into the northern Plains. This will support increasing overrunning snows developing across a fairly large region from the northern Plains into the Upper MS Valley and upper Great Lakes region day 1. The model qpf axes have come into better agreement this period---after showing some differences with the latitude of the max axis in previous model cycles. Model consensus is for .25-.50" areal average liquid equivalents with moderate to locally heavy snow potential across these regions. See the latest QPFHSD for additional winter weather information. OH Valley A second max precip area ahead of the strong height falls moving into the northern Plains is expected to develop along and north of the warm front extending east from the associated deepening low over the Central Plains. Strengthening southwesterly low level flow intersecting this front that is forecast to be moving northeastward through the Mid MS Valley-OH Valley region will support increasing overrunning rains along and to the north of the OH Valley. This strengthening inflow into the front will raise pw values to 1.5-2 standard deviations above the mean to the north of this boundary---supporting potential for widespread moderate to locally heavy precip totals. Days 2 & 3 ...Western U.S. System... Day 2 looks to have the largest break in notable precip in the next week before the next push of mouisture arrives and starts the next round of precipitation. Low pressure along the northern BC coast will direct a moisture plume into the PAC NW coast Tuesday night with precipitation breaking out first near the Coastal Range and eventually making its way into the Intermountain Region and Northern Rockies. Precipitation rates are expected to increase to moderate Wednesday in preferred western slopes of the Olympics and WA/northern OR Cascades as a plume of 0.75 inch PW comes ashore. Expect up to an inch QPF for these preferred spots in Day 3 (00Z Wed-00Z Thu) with an active and rather wet period increasing thereafter per 00Z guidance consensus. Precipitation should break out immediately east of the Northern Rockies as some of the moisture rides up and over yet another arctic airmass sliding southward. ...Eastern U.S. System... Surface low pressure initially over the Mid Mississippi Valley will head northeast and reach the eastern portion of the Great Lakes by Wednesday morning. There should be a classic precipitation pattern associated with the system--ranging from a broad precipitation shield in the isentropic lift/warm advection pattern in the warm conveyor belt east of the system to a deformation zone with the potential for banded precipitation north and west of the system and convection along and ahead of a cold front extending southward towards the Gulf of Mexico. Think that the recent runs of the GFS were depicting the system and the associated precipitation better than other models. The operational runs of the ECMWF have had a tendency to be too slow once it develops a surface low even though there were more ensemble members aligned with the GFS than the operational version of the ECMWF. This run of the NAM was probably better than others...although it too seemed to be on the dry side. Considering that there has not been a well defined front push south into the Gulf which would block the flow of Gulf moisture from coming northward, am concerned that the NAM and UKMET will end up being too light with its precipitation north and west of the surface low. The 250 mb upper jet takes on an increasingly anticyclonic curvature roughly over the Great Lakes...which all the models tended to handle comparably from Day 2 into Day 3. This would tend to give more credence to the GFS idea as well. While there was some spread in the isentropic upglide region of the low, the differences were not as big as areas near the low. And along the cold front extending southward from the low across the Ohio and Tennessee Valleys, there was some spread with respect to precipitation amounts on day 2 which appeared to be tied mainly to the speed of the front. The GFS was faster than the NAM/ECMWF/UKMET and that seemed reasonable given the strengthen of the surface system. By day 3, there was convergence among the model solutions which led to less spread in the model QPF. Opted to trim the northern and eastern portions of the marginal risk area due to the speed of the system and feedback from offices in the area that the forecast QPF could be handled without flooding. Oravec/Bann Graphics available at www.wpc.ncep.noaa.gov/qpf/qpf2.shtml