Quantitative Precipitation Forecast Discussion NWS Weather Prediction Center College Park MD 522 PM EDT Tue May 29 2018 Final Day 1, Day 2 and Day 3 QPF Discussion Valid May 30/0000 UTC thru Jun 02/0000 UTC Reference AWIPS Graphics under...Precip Accum - 24hr Day 1 For the 00z QPF issuance: no major changes were made to the 29/18z QPF issuance. Some tweaks were made over western TN/western KY in conjunction with Alberto, as well as a few over the southern Appalachians. Both tweaks were made based on radar trends, as well as the time lagged HRRR. ...Alberto / Southeast U.S. / Ohio and Tennessee valleys/ southern Appalachians... Based on the consensus of the 12z hi-res models, made an eastward adjustment to the anticipated axis of heavier amounts near the track of the center. There remains a good signal for 1-2 inch, with locally heavier amounts near the track of the center, especially early in the period as the system moves across western Tennessee into the lower Ohio valley this evening. Further to the south, there is still a good indication as well for additional locally heavy amounts along the trailing inflow axis across Alabama, as well as into the upslope regions of the southern Appalachians extending from northern Georgia to southwest Virginia. The HREF Mean was utilized as a starting point for WPC QPF across much of the region. ...Eastern Kansas and central to eastern Oklahoma... Still a good model signal for convective development to produce moderate to heavy rain totals as a progressive shortwave trough moves into the central Plains this afternoon. Based on the consensus of the hi-res models, adjusted the axis of heavier amounts further to the south across central into southeastern Oklahoma this afternoon-evening. Here also, WPC QPF utilized the HREF Mean as a starting point. ...Northern Plains and upper Midwest... A negatively-tilted trough comprised of an upper low lifting out of the northern High Plains and shortwave energy emanating from the central Plains is expected to pivot across the Dakotas and Nebraska into the upper Mississippi valley on Wed. Deep southwesterly flow ahead of the trough is expected to tap some of the deep moisture associated with Alberto, supporting the development of moderate to heavy rains across the upper Mississippi valley during the afternoon/evening hours, with lighter amounts further to the west in a developing deformation zone back across the Dakotas. Days 2/3... ...Great Lakes... Remains from Alberto will advance northeastward from the Great Lakes into Ontario overnight Wednesday into Thursday. Tropical air mass associated with Alberto will have precipitable water values of 2.00 inches that will wane to 1.25 inches by Thursday afternoon. The maximum rainfall associated with Alberto will range between 1.00 and 1.50 inches over parts of the Upper Peninsula of Michigan on Wednesday evening into Thursday evening. Thursday evening into Friday evening, the qpf over the Great Lakes will be with maximum qpf amounts ranging between 0.10 and 0.25 inches. With a lack of a strong low-level focusing mechanism (other than Alberto's center), the Excessive Rainfall Outlook for Day 2 shows a broad Slight Risk for most of the region. Although rain may be focused more along the track of the low, flash flood guidance is higher in those areas suggesting that antecedent conditions may prevent more widespread flooding. WPC is issuing the latest advisories on Alberto. ...Ohio Valley/Mid-Atlantic southward to the Southeast... In the wake of the remains of Alberto, deep tropical moisture will extend from the Mid-Atlantic Coast southward to Florida with precipitable water values of 2.00 inches that will begin to move off the coast overnight Thursday. The precipitable water values will decrease to near 1.75 inches by Friday evening. The moisture will interact with short wave over the Southeast that will aid in producing maximum qpf amounts ranging between 1.00 and 1.40 inches on Wednesday evening into Thursday evening. A secondary maximum will be over parts of the Northern Mid-Atlantic into the Eastern Ohio Valley with maximum qpf amounts ranging 0.50 to 0.85 inches. On Thursday evening into Friday evening, precipitable water values over Florida will remain at or near 2.00 inches. Diurnal heating will interact with the moisture to produce maximum qpf amounts ranging from 0.50 to 0.60 inches over the central portion of the Florida peninsula. ...Central Plains into the Ohio Valley and Northeast... Disorganized short wave energy over the Southern Rockies will move eastward into the Ohio Valley by Thursday evening. A baroclinic zone over Central Canada on Thursday morning will move southeastward to into the Ohio Valley into the Northeast. Precipitable water values will be relatively high over the region ranging from 1.75 to 1.50 inches. The energy will aid in producing a maximum qpf amounts over parts of the Middle Mississippi Valley/Central Plains ranging from 0.75 to 1.10 inches on Wednesday evening into Thursday evening. As the baroclinic zone and upper-level energy move in on Friday, maximum qpf amounts will range from 0.50 to 1.10 inches over parts of the Ohio and Tennessee Valleys from Thursday evening into Friday evening. Models show an expanding low-mid level thermal ridge into the southern Plains over the next several days, with sporadic QPF along the periphery of the elevated mixed layer from eastern Colorado, through Kansas, and into the Ozarks and Mid Mississippi Valley regions. From a pattern recognition standpoint, this seems reasonable and also provides greater than normal uncertainty in the QPF. Models can struggle with the timing of MCSs as they roll in a generally easterly direction around the periphery of a ridge, and also struggle with how much latitude they can lose as they mature and propagate further into the higher theta e air mass. Generally followed a compromise of the ECMWF and GFS in terms of timing and position of QPF maxima in this region, with a marked increase in nocturnal QPF relative to the NBM. ...Northern Rockies into Northern Plains... An amplified trough pushing into the Northwest and eventually into the Rockies should lead to increasingly widespread convection, on Wednesday evening into Thursday evening over Montana and from Thursday evening into Friday evening over Montana into North Dakota. Maximum qpf amounts will range from 1.40 to 1.00 inches over parts of Montana on Wednesday evening into Thursday evening. On Thursday evening into Friday evening, the maximum qpf amounts will range between 1.60 to 1.00 inches over North Dakota with a secondary maximum ranging from 1.20 to 0.90 inches over Western Montana. Pereira/Ziegenfelder Graphics available at www.wpc.ncep.noaa.gov/qpf/qpf2.shtml