Quantitative Precipitation Forecast Discussion NWS Weather Prediction Center College Park MD 314 AM EDT Mon May 28 2018 Prelim Day 1 QPF Discussion Valid May 28/1200 UTC thru May 29/1200 UTC Reference AWIPS Graphics under...Precip Accum - 24hr Day 1 ...Southeast / Alberto There is a strong model consensus as to QPF along the track of Alberto. WPC trended toward our in-house ensemble and the NHC track which slid a little farther east - main core of heavy rain expected in the Florida panhandle, Alabama, and western Georgia. See Excessive Rainfall Discussion for details. Tropical moisture flanks the northern and eastern side of the storm out at a larger radius. We increased QPF somewhat in the upslope regions of the Blue Ridge / southern Appalachians over the western Carolinas. Models indicate some build of up instability just upwind, and low level flow steadily increases into the mountains later Monday. The flash flood threat will likely increase in this area from Day 1 going into Day 2. Farther east along the coast, broad upper difluence and warm advection will contribute to widespread generous rainfall. The event over the coastal plain lacks focus, however, and there is some varying model signal as to where the heaviest rain might fall. This may also be the day that convergence in the trailing moist axis sets up along the east coast of Florida, including Miami - whereas this failed to set up on Sunday. WPC QPF leaned toward the WRF-ARW2 for some of the details, and the National Blend of Models also looked reasonable, especially with respect to placement. ...Rockies / Plains... The long-lived upper low over the Great Basin will finally eject toward the Plains during this period as the northern stream becomes more active over the Pacific Northwest, providing a kicker. Instability and upslope flow will continue to favor northern Wyoming and southeast Montana for on and off rain and thunderstorms. With the synoptic system on the move, inverted low level troughing actually becomes quite focused in this area this afternoon, and may support a sharply defined MCS, one that potentially will be slow moving as it forms, feeding off deep easterly low level flow. Down at the tail end of the upper forcing there is also some concern for a slow moving MCS to form over western Kansas. The GFS has had some grid-scale feedback type 10-plus inch bulls-eyes in this area, but it has done so consistently from run to run. Very warm boundary layer will promote cold outflows, but the enhanced inflow above the surface owing to the large scale system ejecting - could support a slow moving system producing very heavy rain. Much of the hi-res guidance, while not as outlandish as the GFS, does paint heavy rain over western Kansas. Everywhere in between, from northwest Kansas to southeast Wyoming and western South Dakota, expect another active convective cycle. WPC QPF favored the WRF-ARW2 for the details, and the previous forecast had much of this handled well. ...Upper Midwest / Great Lakes... Difficult to say how much coverage of measurable rain will occur, as shortwave ridging / warm temperatures / 2.0 positive standard deviation of the 500-mb heights will act to combat convection, but warm advection rolling through from MN to MI, and strong heating along a residual frontal boundary will act to promote a few storms. We leaned toward the GFS and WRF-ARW2. ...New England... The WRF-ARW was somewhat favored for its handling of a progressive convective event that will occur ahead of a cold front this evening/overnight. The front was secondary to a frontal zone and deeper moisture draped south over the Mid Atlantic, but sufficient low level moisture and cold air aloft is forecast to support a few hundred J/Kg of CAPE over northern Maine and northern New York / New England. Brief diurnal showers/storms are also possible in Pennsylvania. Burke