Quantitative Precipitation Forecast Discussion NWS Weather Prediction Center College Park MD 436 PM EDT Wed Mar 14 2018 Prelim Day 1, Day 2 and Day 3 QPF Discussion Valid Mar 15/0000 UTC thru Mar 18/0000 UTC Reference AWIPS Graphics under...Precip Accum - 24hr Day 1 Northeast The strong low currently over the Canadian Maritimes will be slow moving for the upcoming day 1...lingering over New Brunswick- Gulf of St Lawrence area. Snowfall intensities in the comma head/deformation precip band affecting portions of the northeast are expected to decrease as per latest hi res simulated radars---but with cyclonic low to mid level flow persisting through day 1---snow showers will persist. Additional moderate to heavy snowfall likely from northern to central NY to the east of lake Ontario---east northeastward into the favored terrain of northern New England. Across the Great Lakes---a reinforcing shot of cold air expected to sink southeastward across the lakes region tonight into Thursday. This should support increasing lake effect snow showers developing from northwest to southeast downwind of all the lakes. Model consensus is for light to moderate precip/snowfall totals. Rockies---Great Basin---central to southern California The elongated full latitude mid to upper level trof will be pushing inland from California---into the Great Basin---Southwest and through the Rockies day 1. Above average pw values ahead of these height falls and the associated surface frontal boundary will support widespread moderate to locally heavy precip totals through the central to northern Rockies into eastern portions of the Great Basin and across central to southern California. Northern California into the coastal Pacific Northwest Stronger height falls associated with a closed low off the B.C. coast will be dropping southeastward along the Pacific Northwest coast during Thursday. This will help strengthen the low level southerly to south southwesterly flow from northwest California into the coastal Pacific Northwest. This will support increased shower activity Thursday across these areas with the greatest precip potential from the northern Sierra into the northwest California coast range and the far southwest Oregon coast range where the upslope component to the strengthening low level flow will be the greatest. Northward into the coastal Pacific Northwest the low level southerly flow will have a primarily terrain parallel trajectory--with less precip amounts expected. Elsewhere---light precip amounts possible over south TX as the low level southerly flow strengthens off the western Gulf of Mexico. Scattered showers also possible across southwest TX ahead of shortwave energy moving east northeastward across northern Mexico into southwest TX. Days 2/3... WPC QPF was based on a blend of the ECMWF/UKMET. ...West Coast to the Rockies... A deep upper-level low near the Pacific Northwest Coast will slowly weaken as some short wave energy ejects eastward from Thursday evening to Saturday evening. Circulation around the upper-level low will stream moisture into Central California with precipitable water values of 0.50 inches with the low-level flow of 35 to 40 knots on Thursday evening that will slowly move southward to Southern California by Friday afternoon with the flow slowing to 15 to 20 knots. The moisture plume will continue to move southward into Northwest Mexico by Saturday evening. The system will produce maximum qpf amounts ranging between 2.00 to 2.30 inches over the Sierras on Thursday evening into Friday evening. As the moisture plume moves south, the qpf over the Sierras will decrease with maximum qpf amounts ranging from 0.50 to 0.90 inches on Friday evening into Saturday evening with a secondary maximum over the Wasatch mountains ranging between 0.25 and 0.55 inches. ...Central/Northern High Plains to the Ohio/Tennessee Valleys and Central Appalachians to the Southeast... Short wave energy ejected from West Coast upper-level low will coalesce over the Central Plains by Friday morning moving to the Ohio Valley/Mid-Atlantic by Saturday evening. The associated baroclinic zone over the Southern High Plains will, likewise, move eastward to the Southern Mid-Atlantic by Saturday evening. The storm will draw moisture from the Western Gulf of Mexico into the Central Plains with precipitable water values as high as 0.75 inches on a low-level flow of 45 to 50 knots on Thursday evening. The precipitable water values will weaken to mostly 0.50 inches with the low-level flow of 30 to 20 knots by Friday evening. The maximum qpf amounts will range from 1.25 to 1.50 inches over the Central Plains from Thursday evening to Friday evening. A secondary maximum will develop over parts of the Lower Mississippi Valley with maximum qpf amounts ranging from 0.40 to 0.50 inches. As the system moves eastward, moisture will move into the Ohio/Tennessee Valleys with precipitable water values of 0.75 inches. The system will produce maximum qpf amounts ranging from 0.35 to 0.50 inches on Friday evening into Saturday evening over parts of the Ohio/Tennessee Valleys. WPC used a blend of the ECMWF/UKMET as a starting point for the manual guidance with the GFS being faster with the system and the ECMWF/UKMET being more consistent with the qpf placement. Oravec/Ziegenfelder Graphics available at www.wpc.ncep.noaa.gov/qpf/qpf2.shtml