Quantitative Precipitation Forecast Discussion NWS Weather Prediction Center College Park MD 451 AM EDT Fri Apr 27 2018 Final Day 1, Day 2 and Day 3 QPF Discussion Valid Apr 27/1200 UTC thru Apr 30/1200 UTC Reference AWIPS Graphics under...Precip Accum - 24hr Day 1 ...Northeast... The vigorous, compact mid level circulation lifting across the mid Atlantic region early this morning will continue up the northeast coast today, while another vort lobe pivots across the Great Lakes and a more expansive vort lobe drops southeast across the upper MS Valley. These 3 shortwaves will ultimately reinforce the longwave trough across the northeast CONUS into day 2 (Saturday). Strong isentropic lift within a recycling warm conveyor belt (wcb) as the first two shortwaves become phased will maintain the organized, widespread area of rainfall as it lifts northeast, though the lack of instability and anticipated swift progression will be a detractor to precip totals. Nevertheless, with moderately anomalous moisture parameters (PW and low-mid layer moisture flux), moderate areal average totals are likely per the multi-model consensus (with max amounts of 0.50+ inch along the northeast coast). ...South Florida... The axis of much above average pw values currently lying to the south of south Florida and the Keys is expected to be drawn northward ahead of a southeastward moving cold front moving across the Florida peninsula Friday. This northward push of higher PW values is related to the next area of mid to upper level height falls that are rotating through the mean eastern U.S. trof, which will pivot across the northern Gulf of Mexico Friday and across central Florida by early Saturday morning. This northward surge will enhance precip potential ahead of the aforementioned cold front -- supporting scattered convection with locally heavy rainfall over South Florida. ...Upper MS Valley---Upper Great Lakes... Strong northern stream height falls dropping from the Upper MS Valley into the upper Great Lakes will help re-amplify the northern portion of the mean eastern trof Friday into Friday night. A fast moving area of enhanced isentropic lift ahead of the associated surface low will support light-moderate precip totals from the Arrow Head of MN into the western U.P. of MI and from northern to southeast WI. Precip may change from rain to snow over the Arrow Head of MN -- supporting light snowfall accumulations. See the latest QPFHSD for additional winter weather information. ...Pacific Northwest... The well-defined closed low off the northern California coast early this morning will meander slowly east northeastward today and Friday night/early Saturday to a position just north of the coastal Oregon-California border. Model consensus is for the development of a narrow northwest to southeast oriented precip band to the north northeast of this closed low today -- affecting areas primarily across Oregon to the west of the Cascades. In the core of this precip area, moderate totals in the .25-.50"+ range possible over Oregon to the west of the Cascades, with lighter values northward into far southwest Washington and southward into northwest California. Hurley/Oravec Days 2/3... ...Northeast... Weak shortwave energy lifting up the northeastern CONUS will begin to work in tandem with an upper trough shifting east over the Great Lakes Saturday morning. The trough closes into a low as it shifts east from the Great Lakes Saturday into Saturday night. A general model blend was used for QPF with 00Z guidance continuing a trend in improved agreement. The heaviest precipitation looks to be in a swath from northern ME back to upstate NY. ...Northwest to Northern Plains... An upper low will drift eastward across the Northwest U.S. and the Northern Rockies on Saturday, eventually emerging from the mountains late Saturday/Sunday...filling as it goes and ultimately breaking down into a conglomeration of vort centers rotating around a common axis. The associated precip swath expands as the low occludes with max 24hr precip half to one inch for preferred terrain over northern from WA/ID across MT and into portions of ND and MN. As low level flow increases from the southeast...some convective precipitation should be breaking out over parts of the Northern Plains by the end of day 3. A general model blend was used for WPC QPF with decent agreement. ...Rockies into the Southern High Plains... Anticyclonic flow over the central CONUS will allow increasing moisture across central Colorado to New Mexico as it interacts with weak shortwave energy embedded within difluent flow out ahead of the western U.S. low. This activity shifts onto the high plains of CO/NM/KS/OK/TX Saturday night. A general model blend was used for WPC QPF...with the belief that the UKMET and Canadian were both too strong with shortwave energy ejecting out over the Southern High Plains. ...Florida Keys... There should still be some lingering showers along/near the southeast Florida coast and the Florida Keys early on in the day 2 period. Given high precipitable water values and potential for slow cell motion, locally heavy rain may linger over the Keys on day 2. Bann Graphics available at www.wpc.ncep.noaa.gov/qpf/qpf2.shtml