Quantitative Precipitation Forecast Discussion NWS Weather Prediction Center College Park MD 352 AM EST Fri Mar 02 2018 Prelim Day 1, Day 2 and Day 3 QPF Discussion Valid Mar 02/1200 UTC thru Mar 05/1200 UTC Reference AWIPS Graphics under...Precip Accum - 24hr Day 1 ...Eastern U.S... Lows moving through the DelMarVa and offshore the NJ coast should merge and move northeast becoming a vigorous cyclone within the climatologically favored area for March off Long Island through early Saturday as an upper level low closes off overhead. Warm advection is contributing to the initial expansion of rainfall into the northern Mid-Atlantic states at this time, shifting into southern New England early on. This event will become more intensely focused as the coastal low develops which strengthens frontogenesis in the 850-650 hPa layer. These ideas fit well with the previously issued WPC forecast, which we retained. The biggest adjustment needed was to lower amounts per the recent guidance across northeast NY and northern New England. The 00z GEFS-based QPF re-forecast data, based on analog events, suggests a swath of 2-5" areal average QPF across some portion of the Northeast. Rules of thumb based on instability, moisture, and low-level inflow available across southern New England support a 4-6" range. Per information received from SAB/NESDIS, the December 11-12, 1992 nor'easter is a particularly good analog for the precipitation expected for southern New England -- 4-8" fell across southeast MA during that intense nor'easter. Other possible analogs pointed out by the BOX/Taunton MA office were the March 7, 2013 and April 1, 1997 events. Days 2/3... ...West... The active pattern across the Western U.S. will begin to abate somewhat on Saturday as part of the upper trough makes its way inland through the Great Basin. As it makes its way eastward, it'll lose connection with deep moisture. Between decent height falls and difluent upper level flow, there will still be enough forcing to produce a quarter to a half inch of liquid precipitation...along with locally higher amounts where the flow is perpendicular to the terrain. Deterministic models remained in very good agreement with 24-hr precipitation totals, although the ECMWF became slower than the GFS, NAM and UKMET on day 3. Favored the somewhat faster solutions. This resulted in a forecast that maintained good continuity with the previous WPC forecast. Please refer to WPC's Heavy Snow Discussion (QPFHSD) for more details on winter weather. ...Northern Plains... A swath of moderate precipitation should begin to develop over the Northern Plains on Sunday and Monday as an anomalous upper low/trough over the Western U.S. begins to pivot out into the Great Plains. A surface low forms and deepens to the lee of the Rockies...and there are consistent signals for a well defined deformation zone to take place over the Dakotas on Sunday and early Monday. This should lead to a fairly broad shield of snow in this region...which should also be characterized by strengthening low level winds. Refer to the WPC Heavy Snow Discussion and related graphics for more details. The models show a strengthening warm conveyor belt flow across the Central Plains but amounts are modest. The WPC QPF forecast continued to be based on a non-NAM/non-SREF consensus. ...Northeast... The deep area of low pressure which is forecast to bring heavy to excessive precipitation to parts of the Northeast U.S. will have moved out of the area by the start of the day 2 forecast. There may still be areas of light precipitation lingering over New England on Saturday...especially along the immediate coastline and to the lee of Lake Ontario. A general model compromise was used in this part of the country. Roth/Bann Graphics available at www.wpc.ncep.noaa.gov/qpf/qpf2.shtml