Quantitative Precipitation Forecast Discussion NWS Weather Prediction Center College Park MD 643 PM EDT Sun Apr 29 2018 Final Day 1, Day 2 and Day 3 QPF Discussion Valid Apr 30/0000 UTC thru May 03/0000 UTC Reference AWIPS Graphics under...Precip Accum - 24hr Day 1 ...18Z Update... The final day 1 QPF was only slightly adjusted to blend in the later arriving 12z ECMWF and 15z SREF Mean QPF. ...Northeast... The strong mid to upper level closed low over eastern NY state this afternoon will push slowly eastward tonight across central New England and off the New England coast Monday. Precipitation is expected to remain fairly well defined in the comma head/deformation precip band to the north and northeast of this closed low tonight from northern NY state into Northern New England. The precipitation structure is forecast to become less organized during the day on Monday as drier air wraps into the circulation of this system. With overall good mass field agreement among the latest models---there is also fairly good qpf agreement. Moderate to locally heavy precip totals expected from eastern NY state and into Northern New England---with lighter totals expected southward into central to southern New England which will be influenced more by the above mentioned dry slot. Late season accumulating snows possible from the Catskills into the Adirondacks. See the latest QPFHSD for additional winter weather information. ...Pacific Northwest---Great Basin into the Northern Rockies... A broad mean upper trof will persist day 1 across the western U.S. from the Pacific Northwest---through the Great Basin and into the Rockies. Two areas of height falls expected to rotate through this mean trof. A lead area of height falls will be rotating through the base of this trof early day 1 through the Great Basin--pushing northeast across the Central to Northern Rockies during Monday. These height falls will be the primary precipitation producer day 1---support moderate to locally heavy totals form the Wasatch/Uinta into the Northern Rockies from northwest WY into southwest MT. Early spring moderate to heavy snows likely across these regions. The second area of height falls will be diving south along the Pacific Northwest coast--helping to re-anchor the mean western trof after day 1 over the Great Basin. For the day 1 time period---little if any precip is expected with these height falls. ...Southern High Plains... Broadly difluent upper flow downstream of the mean western trof will support scattered convection early in the day 1 period and again late Monday afternoon along the dry line situated across the Southern High Plains. Low confidence on any precip details in this scattered convective pattern. Light to locally moderate areal average totals depicted given this uncertainty. Days 2/3... ...California... A series of three shortwave troughs will track over CA along the positively-tilted mean western CONUS trough as it amplifies to southern CA Monday night through Tuesday night. Continental air with this interior trough will limit moisture under the forcing from the shortwave passages over the Sierra Nevada and southern CA. QPF is limited each day to around a quarter inch for preferred higher terrain. A general model blend was used for WPC QPF. ...Idaho/Wyoming/Nevada/Utah/Colorado... An amplifying positively-tilted trough over the western CONUS will wrap some Pacific-sourced moisture across the Intermountain West to the Rockies including along a stalled surface front over NV/UT/CO that sets up Tuesday. 0.5 inch PW is two standard deviations above normal for the Great Basin which enables moderate precip over preferred terrain with areal average QPF max over the Wasatch of Utah. ...Central Plains to Upper Midwest... Moderate Risk for excessive rainfall over a portion of the NE/IA border on Day 3 (12Z Tue-12Z Wed). The Gulf is open with southerly flow up the entire length of the Great Plains into the Canadian Prairies this (Sunday) afternoon west of a surface ridge axis. An amplifying trough over the western CONUS will maintain southerly moisture advection. A stationary front will set up over the central plains Tuesday night as the positively-tilted trough ejects shortwave energy over the central CONUS. This provides a convergence point for moisture and instability, both of which are above normal. Maintained a slight and marginal risk for excessive rainfall mainly over NE/IA with a slight shift northwest per 12Z guidance. An areal average of up to two inches is forecast in the Day 3 (12Z Tue-12Z Wed) time frame. Oravec/Jackson Graphics available at www.wpc.ncep.noaa.gov/qpf/qpf2.shtml