Quantitative Precipitation Forecast Discussion NWS Weather Prediction Center College Park MD 528 PM EDT Wed Apr 04 2018 Prelim Day 1, Day 2 and Day 3 QPF Discussion Valid Apr 05/0000 UTC thru Apr 08/0000 UTC Reference AWIPS Graphics under...Precip Accum - 24hr Day 1 ...Pacific Northwest into the northern Rockies... Warm front will bring light rain/snow to Washington overnight before a much more impressive surge of moisture pushes into coastal Oregon/Washington by Thursday morning ahead of a cold front. Precipitable water values of 0.75-1.00" (+2 to +2.5 standard deviations) will support widespread light to modest amounts, generally 0.25" to 0.50" but a bit lighter in the valleys and about 2-3 times that in the Olympics/Cascades. 110kt jet streak should push into southwestern Oregon late Thursday morning coinciding with larger PW anomalies (southward to NorCal) of about +2 to +3 standard deviations. HREF mean (or blended means) provided a good starting point for the Pac Northwest. Over northern ID into MT/WY, also followed the 12Z HREF mean which expanded the precip eastward along rising PW values, a ~120kt jet out of SW Canada, and the surface front along/east of the Divide with modest upslope potential on Thursday. ...Florida... Cold front will push into south Florida early Thursday with isolated showers and embedded convection. Hi-res models target extreme southern portion of the peninsula tomorrow afternoon along a convergence zone between northeast winds behind the front (sinking into the Florida Straits) and sea breeze development. Isolated local maxima may be .5-1" with healthier convection. Days 2/3 ...Pacific Northwest/California... A plume of moisture will stream into Northern/Central California that will slowly move southward to the California/Mexican border by Saturday evening. The moisture plume will stream air with precipitable water values ranging from 1.00 to 1.25 inches on Thursday evening that will increase 1.50 to 1.75 inches by Friday evening. Likewise, the low-level flow will increase from 15 knots to 30 to 35 knots by early Saturday morning. On Saturday, the precipitable water values over Northern/Central California will drop below 0.50 inches. By Friday evening, the low-level flow over the Pacific Northwest will become parallel to the coast and by Saturday afternoon the flow will again become onshore with precipitable water values of 0.50 inches with the low-level flow 50 to 55 knots. On Thursday evening into Friday evening, the maximum qpf will fall over the Central Californian Coast with maximum qpf amounts ranging from 1.75 to 1.80 inches with a secondary maximum over the Sierras with maximum qpf amounts ranging from 1.25 to 1.40 inches. A tertiary maximum of qpf will develop over the Northern Cascades with maximum qpf amounts ranging from 0.50 to 0.60 inches on Thursday evening into Friday evening. As the precipitable water values are maximized on Saturday, the maximum qpf amounts will be over the Sierras with maximum qpf amounts ranging from 2.50 to 3.00 inches on Friday evening into Saturday evening. Also on Friday evening into Saturday evening, secondary maximum will develop over the Olympic Peninsula with return of onshore flow over the Pacific Northwest with maximum qpf amounts ranging from 2.25 to 2.50 inches. A tertiary maximum will develop over the Northern/Central California Coast with maximum qpf amounts ranging from 2.25 to 2.35 inches on Friday evening into Saturday evening. WPC used a blend of the NAM, GFS, and ECMWF for the manual graphics on Thursday evening into Friday evening. WPC used a blend of the GFS and the ECMWF on Friday evening into Saturday evening for the manual guidance. ...Northern Rockies into the Middle/Lower Mississippi Valley... A cold front sagging southward from Canada will become quasi-stationary as the cold air dams up against the Rockies, while the southern portion of the front makes its way into the Southern Plains/Lower Mississippi Valley. Upslope flow will aid in producing maximum qpf amounts over Bitterroot range, Wind River Mountains, and Medicine Bow Mountains with maximum qpf amounts ranging from 0.50 to 0.70 inches on Thursday evening into Friday evening. As the front sags south into the Southern Plains/Lower Mississippi Valley, the boundary will intersect moisture with precipitable water values ranging from 1.00 to 1.50 inches. The maximum qpf will develop over Eastern Oklahoma/Western Arkansas with maximum qpf amounts ranging from 0.75 to 1.10 inches, likewise, on Thursday evening into Friday evening. ...Southern Plains/Tennessee Valley into the Mid Atlantic/Southern New England... The eastern half of the baroclinic zone over the Lower Mississippi Valley into the Mid-Atlantic will have moisture pooling along the boundary with precipitable water values ranging from 1.00 to 1.25 inches on Friday evening into Saturday evening. The qpf will develop along a broad path from the Lower Mississippi Valley to the Mid-Atlantic with the maximum qpf amounts ranging from 1.50 to 1.75 inches over parts of the Tennessee Valley. A secondary maximum will develop over other parts of the region with maximum qpf amounts ranging from 1.00 to 1.25 inches on Friday evening into Saturday evening. Fracasso/Ziegenfelder Graphics available at www.wpc.ncep.noaa.gov/qpf/qpf2.shtml