Quantitative Precipitation Forecast Discussion NWS Weather Prediction Center College Park MD 358 AM EST Sat Mar 03 2018 Prelim Day 1, Day 2 and Day 3 QPF Discussion Valid Mar 03/1200 UTC thru Mar 06/1200 UTC Reference AWIPS Graphics under...Precip Accum - 24hr Day 1 ...Western U.S... The combination of onshore flow and shortwaves moving around the southern and eastern side of a slow-moving deep layer cyclone will urge precipitation -- which could be heavy -- slowly through southern California, with overlapping 850-650 hPA frontogenesis across the Great Basin causing moderate to heavy precipitation with time. WPC QPF trended upward across southeast Montana to better fit the current model consensus, but remains close to continuity elsewhere. In many spots, the WPC QPF best resembles the 00z UKMET. For the precipitation in southern CA, went towards a blend of the deterministic and mesoscale guidance to try to pick a reasonable middle ground due to the existing spread and to account for SGX/San Diego's impressions that the mesoscale guidance has been high biased in their county warning area as of late. Elsewhere, hydrologically significant precipitation is not expected. Days 2/3... ...West... Decent height falls and difluent upper level flow will make its way eastward from the Intermountain West, eventually crossing the Rockies front range. While the system will not have nearly the amount of moisture it did when it came onshore, there will still be enough forcing to produce a quarter to a half inch of liquid precipitation on Sunday and Sunday night. In addition to that area...an inverted trough extending north from UT to MT will enable moderate wintry precip to develop and spread onto the high plains of MT late in Day 2. ...along with locally higher amounts where the flow is perpendicular to the terrain. Please refer to WPC's Heavy Snow Discussion (QPFHSD) for more details on winter weather. WPC QPF for Day 2 was based on a blend of the 00Z GFS/ECMWF/NAM. ...Northern Plains into the Midwest... Low pressure shifts east from the north-central Rockies tot he central plains Sunday with a low level jet advecting gulf moisture to the northern plains - to the north side of the developing surface low. A deformation zone is expected to develop on the north side of the low Sunday night with locally moderate to heavy wintry precip. Please refer to WPC's Heavy Snow Discussion (QPFHSD) for more details on winter weather. Inflow east of the system will bring rain into the upper Midwest Sunday night through Monday. However...limited instability and PW generally only two standard deviations above normal does not warrant an excessive rainfall outlook as of this time. The Day 3 WPC QPF forecast was weighted more closely to the 03/00Z GFS, with little consideration given to the NAM. The ECMWF continued to be slower than other guidance and seemed to be showing its dry bias on day 3. Felt that the ECMWF was still close enough that it was included as a component to the WPC manual QPF. ...Southern Plains/Lower MS Valley... A low level jet ahead of low pressure shifting east from the north-central Rockies will bring PW around 1.5 inches over east TX into the lower MS Valley Sunday through Monday. This anomalously moist airmass should be in place as a cold front crosses the southern plains Day 3. The result should be some locally heavy rainfall...although the maximum areal average rainfall around 1.5 inches does not warrant an excessive outlook at this time. In addition, there was pretty good agreement among the models that the precipitation should fall south of the area that got soaked over the past two weeks or so. Roth/Bann Graphics available at www.wpc.ncep.noaa.gov/qpf/qpf2.shtml