Quantitative Precipitation Forecast Discussion NWS Weather Prediction Center College Park MD 511 PM EDT Mon Apr 09 2018 Prelim Day 1, Day 2 and Day 3 QPF Discussion Valid Apr 10/0000 UTC thru Apr 13/0000 UTC Reference AWIPS Graphics under...Precip Accum - 24hr Day 1 ...North Florida... The surface frontal boundary currently aligned west to east across north Florida is not expected to move much during the upcoming day 1 time period...remaining parallel to the west southwest mid to upper level flow. With pw values expected to remain 2+ standard deviations above the mean---favorable right entrance region jet dynamics and mu-cape values 1000-2000+ j/kg along and to the south of this front---heavy rain potential will persist through the period. Short term run to run continuity in the hi res guidance is poor---leading to low confidence with the shorter term details of the precip maxima. However---there is overall higher confidence with the heavy precip potential for the 24 hour period given the strong model signal and overall favorable synoptic set up. No changes to the thinking for potential of isolated excessive rainfall amounts in the vicinity of this front with no changes made to the previous excessive rainfall potential outlook. With little overall movement to the front expected---training of cells over the same area is possible. ...Coastal Southeast... Shortwave energy moving east from the lower MS Valley into the southeast will help expand precip to the north and northeast of the potentially heavy axis in the vicinity of the west to east oriented front over north Florida. There is a fairly large spread in amounts among the various guidance this cycle--leading to low confidence. WPC favored the somewhat lighter amounts of the HREF mean over the heavier 0000 UTC ECMWF and 1200 UTC GFS. The 1200 UTC ECMWF did trend lighter with precip across these areas---closer to the favored HREF mean. ...Mid Atlantic--NY state into central to southern New England... A separate---farther northern branch of shortwave energy is also expected to push east day 1 from the lower Great Lakes into the Mid Atlantic and into southern New England. This will support a farther north area of light to locally moderate precip values across these areas. ...South Texas...northeast Mexico The western extent of the surface front across north Florida will be pushing slowly southward from far south TX into northeast Mexico. Models are indicating a fairly strong axis of convergence into this boundary in an increasingly anomalous axis of pw values...1.5 to 2+ standard deviations above the mean. This will support increasing showers tonight into early Tuesday over far south Texas/northeast Mexico before all activity pushes south into northeast Texas late Tuesday morning into early afternoon. Model consensus is for the heaviest activity to the south of south TX with heavy precipitation potential there and mostly moderate totals over far south TX. ...Northern California---Pacific Northwest into the northern Rockies... The first in what will be a series of height falls over the next few days to rotate through the base of the northeast Pacific trof will push northeast and inland from northern California into the Pacific Northwest. An organized area of precip along and ahead of the associated frontal boundary will accompany these height falls---supporting generally moderate totals from Northern California across the Pacific Northwest and into the northern Rockies. Days 2/3 ...Pacific Northwest to the Great Lakes... A 30-50kt low level jet will direct a swath of Pacific moisture onshore the Pacific Northwest...with moisture anomalies of +1 to +2 standard deviations. The favored upslope areas will have highers amounts due to orographic enhancement. This moisture and embedded shortwave energy will translate across the Northern Rockies and into the High Plains. Downstream precipitation over the Upper Midwest/Great Lakes regions will be enhanced as well from shortwave energy moves southward from Manitoba . A more powerful shortwave swings from the Gulf of Alaska and across much of the west coast Wednesday night. PW will be less with this system, (0.5 to 0.75 inches - so QPF magnitude will be a little less while the areal coverage is much larger than the previous low passage. Models are converging on placing the highest QPF on day 3 over extreme northwest California, from the Klamoth Mountains to the near Coos Bay. The 12Z GFS/ECMWF/ECWMF ensemble means were the preferred blend in regards to placement and amounts. ...Florida... Zonal flow aloft will persist ahead of an approaching shortwave, keeping the cold front nearly stationary across the north-central portion of the FL peninsula through Tuesday. During this time showers and thunderstorms are forecast to trigger along this boundary and track over the same area. An additional areal average of 2 to 3 inches can be expected with several inches possible storm total. FFG in this area is quite high, so only the most extreme scenarios of repeating thunderstorms/upwind propagating activity would lead to life threatening issues. The inherited marginal risk for excessive rainfall was maintained over the north-central FL peninsula for Day 2 (12Z Tue-12Z Wed). ...Lower Rio Grande Valley... A cold front will push south of the Rio Grande/southern tip of TX Tuesday morning. PW of 1.75 inch (1.5 standard deviations above normal) will be present through the mid morning. Convective activity continues to be progged mainly just south/west of this lowest portion of the Rio Grande where terrain enhances the activity. Petersen/Campbell Graphics available at www.wpc.ncep.noaa.gov/qpf/qpf2.shtml