Quantitative Precipitation Forecast Discussion NWS Weather Prediction Center College Park MD 312 AM EDT Mon Mar 26 2018 Prelim Day 1 QPF Discussion Valid Mar 26/1200 UTC thru Mar 27/1200 UTC Reference AWIPS Graphics under...Precip Accum - 24hr Day 1 ...Southern Plains northeast into the Mid Mississippi Valley and Upper Midwest... An amplified split flow upper trough will move slowly through the West over the next day, as the digging southern stream trough eventually leads to a closed mid-upper low across the Southwest while the leading edge of upper height falls and upper disturbances along the subtropical jet emerge into the central portion of the country. This will be the start of a multi-day active convection and heavy to excessive rainfall event, as the amplification of the upper trough west/ridge pattern retards the w-e progression of frontal features and convection ahead of the trough until at least mid-week before the next northern stream shortwave diving se across the northern-central Rockies can finally kick the longwave trough eastward. For the upcoming day 1 period (12Z Mon-12Z Tue), broadening upper divergence downstream of the amplifying trough will be accompanied by deepening sw flow and an uptick in warm/moisture/theta-e advection through the column -- with the spike in PW values (1.5-1.75") owing to the moisture transport aloft (via the subtropical connection off Baja) as well as within the lower-mid layers (trajectories off the western GOMEX). The latest ESRL atmospheric river detection tool (ARDT) in fact depicts a bona-fide AR toward Monday evening (by 00Z Tue) from the southern Plains into the mid MS Valley, with integrated water vapor transport (IVT) anomalies climbing to near 2 standard deviations above normal. At the same time, both the SREF and GEFS show PW and 850-700 mn moisture flux anomalies reaching +3-3.5 over the MO/KS/AR/OK four state region. In terms of the QPF, the spring-like nature of the system is exemplified by the latitudinal spread among the global and high-res guidance, at least in terms of axis of heaviest rainfall. The global QPFs remain on the northern edges of the guidance spread, while the high-res CAMs make up the majority of middle to southern solutions. WPC opted to lean toward the southern members, including the 00Z WRF-ARW, while also giving some weight to the HREF mean given the spread. The attempt was to align the max QPF axis where the rather broad, favorable sw-ne low-level frontogenesis would more likely intercept a more unstable thermodynamic profile, as both the GFS-ECMWF show the northern periphery of the instability axis (MUCAPES up to 500 j/kg) lifting into northeast OK, northwest AR, and southern-central MO overnight. In addition, southwesterly 850 mb flow increasing to ~50kts Monday night will veer and align nearly parallel to the mean 850-300 mb flow by 08-12Z Tue over the aforementioned area, favoring increased upwind propagation (weak Corfidi vectors) and thus an enhanced potential for back-building and cell training. ...Pacific Northwest... A rather impressive short wave trough moving rapidly across the nern Pacific towards British Columbia will yield zonal moist onshore flow into WA and extending south into OR over the next 24 hrs. This upper disturbance and lower heights will not dig much at all, due to the mammoth upper ridge over the eastern Pacific and extending into the northwest quad of the country. However, an anomalous long fetch of Pacific moisture flux over-top the upper ridge will persist through Monday night across the Pacific Northwest. Overall WPC followed a blend of the GFS/ECMWF along with the 00z high-res package, which yielded areal avg totals of 1 to 2+ inches with locally higher values in the coastal ranges, Olympics and Cascades. Hurley