Quantitative Precipitation Forecast Discussion NWS Weather Prediction Center College Park MD 359 AM EST Tue Mar 06 2018 Prelim Day 1, Day 2 and Day 3 QPF Discussion Valid Mar 06/1200 UTC thru Mar 09/1200 UTC Reference AWIPS Graphics under...Precip Accum - 24hr Days 2/3... ...Pacific Northwest/Northern Rockies... A closed mid level low approaches the Pacific Northwest coast early on day 2 and gradually eases from the Pacific Northwest into the Northern Rockies during day 3. A Pacific moisture plume ahead of the mid level system, focused on a warm front, feeds the development of locally heavy rainfall, especially on day 3. There was generally good model agreement with the placement of the synoptic scale features, so the WPC QPF was based on a blend of the 00z ECMWF/GFS. QPF amounts are expected to be modest, ranging between 0.10 and 0.25 inches on day 2. On day 3, 40 to 50 knot low level flow ahead of the system will transport 0.50 inch precipitable water air across the Pacific Northwest from WA into northern CA and parts of the intermountain region. Given marginal instability still being shown by the model forecast soundings, saw little reason to make too many changes to the previous WPC forecast which accounted for a period of briefly enhanced precipitation rates and QPF amounts generally under an inch. Further east, as the mid level system crosses the Northern Rockies late on day 3, the combination of synoptic scale lift and upslope flow make the moisture of the paltry moisture in the column to produce local 0.35 inch qpf amounts over the higher peaks in southern and central ID. ...Great Lakes/Ohio Valley... There should be a closed mid level system over the Great Lakes...with two pieces of energy rotating around the periphery of the low. One piece of energy will head eastward while a second piece of shortwave energy drops south an reinforces the closed low. Lift and steepening mid level lapse rates associated with the mid level system will make the most of the moisture in the column to produce a broad area of 0.10 to 0.25 inches of qpf extending from eastern Michigan and into West Virginia with locally higher amounts on day 2. Another 0.10 to 0.25 inches are possible on day 3 close to the track of the mid level system and across the higher terrain of WV (where upslope flow becomes a factor). ...Mid Atlantic/Northeast... As a negatively tilted long wave trough tracks from the Great Lakes/Ohio Valley, a closed mid level low forms over NJ. Lift associated with the mid level systems induces surface cyclogenesis off the mid Atlantic coast, and the cyclone tracks north along the coast with the mid level system during day 3. The models continued to show signs of converging on a common solution, although the UKMET jumped from the eastern side of the model solutions on the 05/00Z run to being one of the western most models on the 06/00Z run tonight. We continued to favor a solution on the western side of the guidance, but given little run to run consistency we gave the UKMET little consideration. The ECMWF/GFS was used as a starting point and nudged a bit in deference to ensemble means. Day 2... Ahead of the developing mid level and surface systems, a 40/50 knot low level easterly flow transports 0.50/0.75 inch precipitable water across the northern Mid Atlantic states into southern New England, with the best mid level lifted centered on 07/18z. By the end of the period at 08/12Z, the surface low should be making its way northeast along the coast of ME, which will result in a fetch of moisture converging along the coast. The models tended to jump the placement of their 6 hourly maximum precipitation at this point. Given that the models tended to be fairly consistent with the placement of their boundary layer surface moisture flux convergence maxima, WPC tended to key on that to aid in the placement of the maximum. Day 3... The system will continue to depart of day 3 with enough upper level support and moisture transport into the region to support another half inch of precipitation or so in northern ME before the system pulls away. Heavy snowfall is possible on days 2 and 3, especially over interior portions of New England. Please refer to the most recent suite of WPC Winter Weather products for more information. ...South Florida... A cold front making its way south extending from the Southeast U.S. across the Florida peninsula will be the focus for scattered showers and thunderstorms. The deepest moisture and strongest dynamics should have moved offshore by the beginning of the day 2 period. Even so, some locally heavy rainfall is possible before the front moves far enough south and east for rain to end. Roth/Bann Graphics available at www.wpc.ncep.noaa.gov/qpf/qpf2.shtml