Quantitative Precipitation Forecast Discussion NWS Weather Prediction Center College Park MD 448 PM EDT Thu Apr 19 2018 Prelim Day 1, Day 2 and Day 3 QPF Discussion Valid Apr 20/0000 UTC thru Apr 23/0000 UTC Reference AWIPS Graphics under...Precip Accum - 24hr Day 1 ...Great Basin into the central to southern Rockies The strong closed low moving into the western Great Basin early this afternoon will be moving steadily eastward through the Great Basin this evening/overnight and into the central to southern Rockies during the day on Friday. PW values ahead of this closed low across the Great Basin will not be anomalous with values near or slightly above the mean. This should be a limiting factor for widespread heavy precip totals with model consensus of .10-.25" areal average totals across the Great Basin and into the southern to central Rockies. Locally heavier totals likely in the favored upslope regions of the Wasatch of UT and into the central to southern Rockies from south central WY---through CO and into north central AZ. Heavy early spring snows likely through the southern Wasatch and through the southern to central Rockies. See the latest QPFHSD for additional winter weather information across this region. ...Southern to Central High Plains... PW values expected to become more anomalous day 1 to the east of the Rockies into the central to southern high plains where the low level south southeasterly flow is expected to strengthen significantly during Friday ahead of the upstream closed low. Increasing upper difluence ahead of the Great Basin/Rockies closed low in the increasingly anomalous PW axis will support increasing precip coverage Friday through large portions of the central to southern high plains. .25 to .50"+ areal average amounts possible with locally heavier totals where the north to south oriented precip bands possible train for a short period of time. ...Western to northern NY state into northern New England... Surface low pressure moving to the south of New England this afternoon will be pushing into the Canadian Maritimes tonight into Friday with the western peripheries of the associated comma head precip area possibly affecting far eastern Maine early in the day 1 period. In the wake of this low---deep layered cold cyclonic flow will persist day 1 from the eastern Great Lakes into New England. This will support scattered snow showers for portions of western to northern NY state and into northern New England. Light to locally moderate precip/snowfall totals possible across these areas. See the latest QPFHSD for additional winter weather information across this region. Days 2/3 ...Central-Southern Plains...Lower Mississippi Valley...Western Tennessee Valley... Compact, closed mid-upper level low will migrate slowly eastward through the southern Plains and lower MS Valley during days 2-3 (Friday night-Sunday). This feature is essentially cut off from the northern stream, i.e. within an otherwise broad northern stream ridge, and as such given the Rex Block characteristics, believe the eastern progression will be hindered somewhat. Exit region upper level dynamics ahead of the southern stream trough and associated upper jet streak approaching the trough base will be fairly robust, albeit focused given the compact nature of the low, owing to the stream curvature and degree of upper difluence. Moreover, this will also favor a strong southerly ageostrophic response at low levels, bolstering the deep-layer waa/theta-e advection, evidenced by the uptick in PW and 850-700 mb moisture flux/transport (albeit not overly anomalous). At the same time, limiting factors for a widespread heavy (potentially excessive) rainfall event will be the compact nature of the upper low, and the absence of upper jet forcing to the north (which would enhance low-level frontogenesis). Deep-layer instability within the warm conveyor belt (WCB) will be modest at best, with MUCAPES peaking around 1000-1500 j/kg per the GFS/ECMWF during the day on Sat-Sun. In terms of the QPF, WPC stayed fairly close to a blend of the ECMWF-GFS along with the NBM and WPC in-house bias corrected ensemble QPF, which yielded a broad area of 1-1.5+ inches across portions of the southern Plains in to the western TN Valley. In terms of the day 3 excessive rainfall outlook, WPC opted to pull the MARGINAL outlook farther south toward the TX-LA border coast, while extending the SLIGHT a little farther w-nw to encompass the pivoting/back-building WCB across northeast TX and southeast OK. Oravec/Hurley Graphics available at www.wpc.ncep.noaa.gov/qpf/qpf2.shtml