Quantitative Precipitation Forecast Discussion NWS Weather Prediction Center College Park MD 354 PM EST Sun Mar 04 2018 Prelim Day 1, Day 2 and Day 3 QPF Discussion Valid Mar 05/0000 UTC thru Mar 08/0000 UTC Reference AWIPS Graphics under...Precip Accum - 24hr Day 1 ...Rockies and Central U.S... Locally terrain enhanced snows will linger over the northern Rockies into tonight as a dynamic mid-upper level trough and associated height falls/jet punch works through. System progression meanwhile spawns plains cyclogenesis with surface system deepening coincident tomorrow with development of a closed low aloft over the north central plains and upper Midwest. Moisture feed will deepen with precipitable water values expected to rise in excess of 2.5 standard deviations above normal wrapping on the eastern periphery of the system. Precipitation will increasingly expand/organize in a region of favorable upper diffluence mainly along/ahead of a lead frontal system/boundaries over the MS valley and back into the snowy comma head over the colder and windy Dakotas and Upper Midwest. Please see local WFO and WPC winter weather desk products for more information on this disrupting March storm that could produce local blizzard conditions. The return flow of moisture farther south near the surface from the Gulf of Mexico, with a continued connection aloft from offshore Baja California, will meanwhile generate showers and thunderstorms across the lower and mid MS valley with some moderate rainfall potential. Overall, the WPC day1 qpf for this period was primarily derived from WPC continuity as locally adjusted to latest trends from reasonably compatible 12 UTC GFS and a ARW/NNMB meso-model and NBM guidance. ...Northeast... Guidance generally now agrees that compact closed trough energy will slide southeastward across New England underneath higher latitude blocky flow today. The unsettling flow could be dynamic enough to squeeze out a swath of light-modest snows today/tonight with a potential focus over southeast New England, but moisture will be quite limited. Schichtel Days 2/3... An occluded low over SD/MN/IA Monday evening will shift east to Chicago through Tuesday. Meanwhile two systems will interact with this low. The first is a shortwave trough from Alberta that wraps around the south side and the second is an upper low from James Bay that will retrograde southwest across Ontario and merge with the system Tuesday night. This keeps the upper levels of the low over the western Great Lakes with surface low pressure developing around the eastern extent over eastern NC Tuesday night and up the Mid-Atlantic coast Wednesday. WPC QPF was based on a blend of the 12Z GFS/ECMWF with some 12Z NAM consideration. ...Northern Great Plains across the Great Lakes... Frontogenetical convergence persists Monday night both along the occluded front east of the low (from MI to the MN/WI) and along an inverted surface trough extending up the central Dakotas from the Alberta shortwave trough. However, occlusion processes/cyclolysis causes decreasing precip rates Monday night through Tuesday. The presence of the upper low spinning over the Great Lakes Tuesday night/Wednesday allows light precip across the eastern half of the lakes. Precip type and SLR is of concern with this system...please refer to WPC's Heavy Snow Discussion (QPFHSD) for more details on winter weather...especially from the Dakotas into parts of Minnesota. ...Ohio and Tennessee Valleys... No Flooding risk for Day 2 over this area that has had a very wet past few weeks. Light rainfall is expected across the OH/TN valleys with the cold front advancing well east of the occluding low initially over SD/IA. Amounts should be kept in check given the progressive nature of the front and the fact that the precipitable water ahead of the front will be below an inch. ...Gulf Coast and Deep South... The cold front from the upper Plains low pivots to an east-west orientation from east TX to GA/SC Monday night. Precipitable water around 1.50 inches on the south side of this front is two standard deviations above normal which should allow a narrow swath of areally averaged one to two inches of rainfall near the gulf coast of Tuesday. A trend slightly inland across GA up to Atlanta continued in the 12Z guidance suite. However, there is not a flood risk here, just relief from low end drought conditions. ...Carolinas to Mid-Atlantic... The upper low over the Great Lakes is revived by a merger with the James Bay low and energy wrapping around the south side from the Alberta shortwave trough. This will allow coastal low development from the eastern Carolinas Tuesday night and up the Mid-Atlantic coast Wednesday. The surface/coastal low is expected to develop a narrow deformation zone as it lifts up the Mid-Atlantic coast per the 12Z global guidance suite. The 12Z GFS is farthest west while the 12Z ECMWF is farthest east and keeps much of the heavy precip east of the northern Mid-Atlantic coast. The 12Z UKMET is in between these solutions suggesting a narrow, but too early to determine uncertainty swath for the low center. As snow is the main precip type...please see the QPFHSD (along with future forecasts) for further information. Schichtel/Jackson Graphics available at www.wpc.ncep.noaa.gov/qpf/qpf2.shtml