Quantitative Precipitation Forecast Discussion NWS Weather Prediction Center College Park MD 440 PM EDT Sun Apr 22 2018 Prelim Day 1, Day 2 and Day 3 QPF Discussion Valid Apr 23/0000 UTC thru Apr 26/0000 UTC Reference AWIPS Graphics under...Precip Accum - 24hr Day 1 ...Lower Ohio Valley---TN Valley--Southern Appalachians into the Southeast... There are no significant model differences with the evolution of the strong closed low moving slowly from the Lower MS Valley into the TN Valley this period. A stream of much above average pw values will continue to be entrained into this circulation---supporting widespread heavy precipitation potential in a region of well defined upper difluence ahead of this circulation. There is good model qpf agreement with the overall heavy precip distribution. One max region expected in the comma head/deformation precip area to the north of the closed low track from the TN Valley to the OH Valley---with 1 to 1.5"+ areal average totals depicted. A more convective precip max expected farther to the southeast from eastern Gulf coast into the Southeast. Max values across this region likely across the southern Appalachians from northeast GA----the Upstate of SC into western NC where strong southeasterly upslope flow will persist for most of this period. Rainfall totals in excess of 5" likely across the southern Appalachians. While one max precip area is likely over the southern Appalachians---another precip max possible along the southeast coast in the vicinity of the upper GA/SC coast where strong onshore in an axis of greater instability extending north from FL will persist. Here 2-3"+ totals possible. ...Northern Rockies into the northern High Plains... Shortwave energy moving through the Pacific Northwest Sunday afternoon expected to amplify across the Northern Rockies-northern High Plains region Sunday. Strengthening upper difluence and low level upslope north northeasterly flow will support increasing precipitation coverage early Monday across portions of the Northern Rockies into the northern High Plains. Model consensus is for moderate to heavy precip totals from far northeast ID---far northwest to northern WY and across the southern portions of MT. Early spring heavy snows likely across the northern Rockies of northwest WY into southern MT. See the latest QPFHSD for additional winter weather information. Days 2/3... ...Mid-Atlantic and Ohio Valley to the Northeast... Widespread rainfall is expected over portions of the Ohio Valley and Mid-Atlantic states Monday night into Tuesday as a compact closed low lifts northeastward out of the Tennessee Valley. The slow progression of the system, combined with strong inflow off the Atlantic and divergence aloft should allow for areas of heavy and potentially excessive rainfall. There is some spread with the timing of the upper low lifting out of the Tennessee Valley, but overall, models have become better defined with highlighting two separate areas for rainfall amounts to exceed flash flood guidance values. First, along coastal regions of the Carolinas and a second area farther west into the southern Appalachians. The Day 2 Slight Risk of Excessive Rainfall was maintained across these areas. The upper low will continue to lift northeastward Tuesday night into Monday, shifting the chance for precipitation into the northern Mid-Atlantic states and Northeast. However, the threat for heavy and excessive rainfall should diminish as the upper low weakens and gets absorbed into a northern stream trough amplifying over the Great Lakes Region. Model spread and confidence in the exactly how fast the onshore flow and upper forcing weakens increases beyond 00Z Wednesday, so adjustments were made to the broad Day 3 Marginal Risk of Excessive Rainfall extending from coastal North Carolina and Virginia to the Delmarva and southern New Jersey. ...Great Plains... Model guidance has come into much better agreement with the timing and amplitude of a shortwave trough dropping southeastward from the northern Rockies to the central Plains Monday night into Tuesday. The fast progression of this system should initially limit any widespread excessive rainfall concerns, but there is a growing consensus for areas of moderate to heavy rainfall to develop with the associated cold front while it presses through the southern Plains Tuesday night into Wednesday. Oravec/Gerhardt Graphics available at www.wpc.ncep.noaa.gov/qpf/qpf2.shtml