Quantitative Precipitation Forecast Discussion NWS Weather Prediction Center College Park MD 502 AM EDT Sun May 06 2018 Final Day 1, Day 2 and Day 3 QPF Discussion Valid May 06/1200 UTC thru May 09/1200 UTC Reference AWIPS Graphics under...Precip Accum - 24hr Day 1 ...Outer Banks of NC... The heavy rains blossoming along the NC coast early this morning will persist through the morning hours of Sunday as the very anomalous to near record pw values continue to affect this region. Very favorable right entrance region jet dynamics from the jet across the northeast will continue to enhance lift along the NC coast in this anomalous pw axis. Additional 1"+ totals possible over the Outer Banks this morning before the heavy rains push offshore late morning into early afternoon. The 0000 UTC NAM conest was a western outlier with heavy precip over eastern NC this morning---with a farther northwestward heavy precip axis. The 0600 UTC NAM conest trended back to the southeast with the qpf axis---now more similar to the remainder of the model guidance. ...Central Appalachians---Northern Mid Atlantic into the Northeast... The upper trof moving through the TN Valley into the Central Appalachians early Sunday morning will be pushing across the Mid-Atlantic Sunday and then shearing across southern New England Sunday night-early Monday. An area of moderate to heavy precip expected to the northeast to this trof from the Central Appalachians into the Northern Mid-Atlantic----eastern NY state and central to southern New England in pw values 1 to 1.5 standard deviations above the mean. WPC day 1 qpf followed the href mean for details to mitigate the model to model and run to run variability across these areas. ...Lower Great Lakes---OH Valley---TN Valley into the Lower MS Valley... A west to east oriented surface front will be dropping southward day 1 from the Lower Great Lakes into the OH Valley--TN Valley and Lower MS Valley. Not a lot of confidence with qpf details in what will be a scattered convective pattern along and ahead of this front with the latest model guidance showing a lot of spread with their respective qpfs. Given the uncertainties with details---areal average totals were kept on the light to moderate side with potential for locally heavier totals where convection does maximize. ...Florida... The surface cold front across the Southeast early this morning will be pressing south through northern to central Florida day 1. With much above average pw values already in place from the recent northwest surge of tropical pws across the peninsula---moderate to heavy rains possible from expected enhancing convection Sunday afternoon ahead of this front over central to south Florida. With the low level winds out of the west and southwest ahead of this front---convection that does form will likely maximize along the east central to southeast coastal areas. ...Pacific Northwest---Northern Great Basin into the Northern Rockies... Northeast Pacific trof moving into Northern California this morning is expected to track northeastward across the Pacific Northwest---Northern Great Basin into the Northern Rockies day 1. Strong upper difluence ahead of these height falls will support increasing shower activity this afternoon over northeast Oregon/southeast Washington---central to northern ID---spreading into northwest Montana Sunday night/early Monday. The strong dynamics in a region of much above average pw values---2 to 3+ standard deviations above the mean---will support moderate to heavy precip totals. This rainfall potential along with melting snows will result in rising stream flows. No changes are planned to the marginal risk area on the excessive rainfall potential outlook for the 12 UTC Sunday to 12 UTC Monday time period over northern ID into northwest MT. Days 2/3... ...Carolinas to Mid-Atlantic... A broad scale trough will persist east from the Southern Appalachians through Monday. Diurnally drives wrap around precip will affect western VA/NC and along the Delmarva/New Jersey coast. Up to a half inch QPF is possible on an areal average. WPC QPF reflects a model blend that gave significant weight to the GFS and less so for the ECMWF/NAM/UKMET. ...Northern Rockies to the Northern Plains... A shortwave trough interacting with anomalous moisture is expected to produce moderate to locally heavy amounts as it moves from the northern Rockies to the northern Plains Monday into Tuesday. Gulf sourced moisture ahead of this trough draws PW of 1 to 1.25 inches (2-2.5 standard deviations above normal) across the northern Plains. WPC QPF is a blend of the 00Z GFS/ECMWF/NAM/UKMET through the period. ...Central Plains... The shortwave trough spills across the northern Plains Tuesday with 1.25 inch PW spreading across MO/IA (1.5 to 2 standard deviations above normal) Tuesday night. Lift from the trough and a few hundred joules of CAPE trigger at least locally heavy showers and thunderstorms with organized convective activity possible. Areal averages of one inch QPF warrants a marginal risk for excessive rainfall for Day 3 (12Z Tuesday-12Z Wednesday). WPC QPF is a blend of the 00Z GFS/ECMWF/NAM/UKMET through the period. ...Pacific Northwest... A closed low opens as it approaches Vancouver Island Tuesday night. The associated precip shield reaches the WA/OR coast Tuesday afternoon. One inch PW in southwesterly flow ahead of the low results in moderate to locally heavy rainfall, particularly for preferred slopes of the Coast Ranges and Cascades in Day 3. Followed a blend of the 00Z GFS/ECMWF with the NAM much more amplified than any other guidance and the UKMET more progressive. Oravec/Jackson Graphics available at www.wpc.ncep.noaa.gov/qpf/qpf2.shtml