Quantitative Precipitation Forecast Discussion NWS Weather Prediction Center College Park MD 317 PM EDT Sun May 20 2018 Prelim Day 1 QPF Discussion Valid May 21/0000 UTC thru May 22/0000 UTC Reference AWIPS Graphics under...Precip Accum - 24hr Day 1... ...Central-Northern Intermountain West... The highly-amplified, initially negatively tilted upper trough along the west coast early will evolve toward a deepening/closed upper low over southern CA-NV on Monday as an upper level jet streak moves through the trough base. During this time, shortwave ridging builds across southwest Canada, thus putting the northern Great Basin within a 'col' region both aloft and at lower levels. Given the broadly difluent upper flow, along with the departing area of confluent upper flow (toward south-central Canada), the models continue to depict focused areas of upper level divergence during the day 1 period from the Sierra Nevada northeast to the northern Rockies to include the intermountain region. Modest deep-layer instability (MUCAPES 1000-1500 j/kg) along with the moist environment (PW anomalies ~2 standard deviations above normal) will generate widespread additional areal-average totals between 0.25-0.50" this afternoon through Monday, with locally higher totals between 1-1.5" per the high res CAMs. ...Texas... The models, including the high-res CAMs, continue to play catch-up with the overnight MCS activity and airmass modification, with renewed convection forming across central and south-central TX along outflow boundaries (south of the main front). Quite a bit of adjustments were made to the QPF this afternoon through evening -- mainly to account for the convective trends -- thus early on the forecast was initialized with the more recent HRRR/experimental HRRR guidance and NBM. Confidence in the QPF details lowers considerably after 06Z Mon, however departing MCV energy and ensuing shortwave ridging would favor less convective coverage on Monday (mainly confined along the Gulf coast where the axis of higher PWs will linger). ...Lower-Mid Mississippi Valley into the Tennessee and Ohio Valleys and Mid Atlantic... Another region where the model guidance continues to lag the observational/mesoanalysis trends. Leaned more toward the experimental HRRR early in the period (through the overnight) with the QPF ahead of the mesoscale-convective aided vort centers across western NE and eastern OK-KS early this afternoon. WPC focused the highest areal-average totals where the airmass was able to destabilize Sun afternoon (following the thinning/dissipation of nocturnal debris from last night's convection) Moderate to high instability will develop, and will generally be uncapped given the broad troughing remaining over the area. PWATs, while not extreme, will continue to run above normal. Multi-cellular convection will be most organized downstream of the aforementioned shortwaves, with the modest deep-layer instability in place. The activity farther north will likely become better organized given the 30-40 kt 0-6km bulk shear; however, slower cell motions (Corfidi vectors 5kts or less) would support locally heavy rainfall into central and southern MO-IL where bulk shear values are 20-25 kts or less. ...Florida... Will be another wet period across Florida, with moisture remaining high. As usual, low confidence with the details today. The potential will certainly be there for heavy rates and some flooding concerns, just a question as to if/where we see enough instability and localized convergence to generate more intense convection. Some signs another weak mid level shortwave wave may be approaching the state again on Monday, as the southeasterly 850mb flow will remains strong enough to support the persistence of organized convection shall it develop. Hurley