Quantitative Precipitation Forecast Discussion NWS Weather Prediction Center College Park MD 528 PM EDT Mon May 14 2018 Prelim Day 1, Day 2 and Day 3 QPF Discussion Valid May 15/0000 UTC thru May 18/0000 UTC Reference AWIPS Graphics under...Precip Accum - 24hr Day 1... ...Upper Mississippi Valley---Lower Great Lakes---Mid Atlantic---NY state into New England... Active convection expected along and ahead of the mean frontal boundary position expected to lie in a general west to east direction from portions of the Upper MS Valley---through the Lower Great Lakes---Mid-Atlantic into New England. There is expected to be very favorable right entrance region jet dynamics across these regions in an axis of pw values 1.5 to 2.5 standard deviations above the mean. Convection likely to enhance in the vicinity of this front this evening over the Upper MS Valley as moist southwest flow strengthens into the above mentioned west to east boundary--with this activity pushing downstream into the lower Great Lakes region overnight. While this activity may weaken by or prior to 1200 utc Tuesday...additional convective enhancement likely Tuesday afternoon from the eastern Great Lakes---thru NY state---New England and the Mid-Atlantic. Widespread moderate to heavy rainfall potential possible across these areas. The href mean and in house hi res mean used for the details day 1 to mitigate the large spread evident in the latest models. ...Florida into the Southeast... The mid to upper level closed low over the eastern Gulf of Mexico expected to move only slowly northward day 1 along the northwest Florida coast into the western panhandle region. There continues to be a strong model signal for widespread moderate to heavy precipitation potential across large portions of the Florida peninsula into the Southeast. Model consensus for max values are near and just north of the mid to upper level closed low over the central to eastern portions of the Florida panhandle where 2-4"+ totals are possible. A second max may align from northern Florida into the Southeast where a low level convergence axis maximizes to east northeast of the associated surface low. Outside these two max areas---confidence lowers with qpf details across the remainder of the peninsula. However---with pw values still above average---albeit not as high as in the two above max regions---locally heavy rains are possible here also. ...Southern Plains into the Lower MO Valley... Low confidence this period with qpf details from what should be active scattered convection along and ahead of the dry line over the Southern Plains and then farther northeastward along the western extent of the frontal boundary stretching from the Upper MS Valley into the Northeast. Very difluent upper flow likely downstream of the mean Great Basin closed low across these areas. This will be occurring in an axis of pw values in the 1.5-1.75"+ range---supporting locally heavy rainfall potential. Run to run and model to model spread is large---leading to the above mentioned low confidence. The href mean and in house hi res means were also used here primarily for qpf details given this spread. ...Sierra---northern California---Great Basin... The Great Basin closed low over central NV is expected to remain stationary for the first half of day 1---then lift northward Tuesday in response to upstream height falls approaching the central California coast. Models are consistent in showing a broad region of scattered convection in the vicinity of this closed low from northern California---thru the Sierra and into Great Basin. Areal average light to moderate totals possible---with the best chance of any isolated heavy totals being through the Sierra into the northwest California coastal range. ..Lee of the Central Rockies... Scattered convection possible late Monday afternoon into this evening in a region of post frontal east northeasterly upslope flow in the lee of the Central Rockies. The spread in qpf details is typically fairly large in this flow regime. Areal average moderate totals depicted with isolated heavy amounts possible where convection maximizes early Tuesday morning. Days 2/3... ...Pacific Northwest and Northern California to the Northern Rockies... Shower and thunderstorm activity will increase over portions of the Pacific Northwest, Northern California, and the northern Rockies Tuesday night into Wednesday and Thursday as a weakening upper low lifts out the central Great Basin and a second upper low edges inland over California. Sufficient moisture and instability across the region will support moderate to locally heavy precipitation, and model guidance is in general agreement that the highest totals should focus in an axis extending from Northeastern California and southwestern Oregon into northern Idaho and northwestern Montana. No major changes were made to the WPC QPF or Day 3 Marginal Risk across northeast Oregon, Idaho, and northwestern Montana. ...Northern Plains and Upper Mississippi Valley... Moisture and instability expected to funnel along a frontal boundary extending from eastern Montana into North Dakota and Minnesota should fuel convection developing across the region early Thursday. An axis extending from central North Dakota into central to northern Minnesota is the current model consensus for the highest precipitation totals. ...Southern to Central Plains... A ripple of shortwave energy ejecting out of the southern Rockies should help provide synoptic scale ascent for convection forming ahead of a weakening front/dry line extending across the western Red River Valley Tuesday evening. There is still a large amount of uncertainty with the details of developing convection, but a Marginal Risk of excessive rainfall was maintained from central Texas into Oklahoma, where some of the models suggest a decent amount of moisture and instability could result in locally heavy rainfall and overcome the relatively high flash flood guidance values across the region. ...Ohio and Tennessee Valleys to the Southeast, Mid-Atlantic States, and Northeast... An active and wet pattern is expected from the Ohio and Tennessee Valleys to the Southeast, Mid-Atlantic States, and Northeast this week as highly anomalous moisture feeds out of the tropics and begins interacting with a relatively stationary frontal boundary. A Marginal Risk of excessive rainfall was maintained for much of the region, and model guidance continues to show a strong signal for focused heavy rainfall from the central Appalachians eastward into southern Pennsylvania, the Delmarva Peninsula, and New Jersey, so a Slight Risk of excessive rainfall was maintained across these regions. Also, a weak disturbance lifting out of the eastern Gulf of Mexico should help focus heavy rainfall along the Florida Panhandle and inland into portions of eastern Alabama and northern Georgia. Oravec/Gerhardt Graphics available at www.wpc.ncep.noaa.gov/qpf/qpf2.shtml