Quantitative Precipitation Forecast Discussion NWS Weather Prediction Center College Park MD 448 PM EDT Fri Jun 01 2018 Final Day 1, Day 2 and Day 3 QPF Discussion Valid Jun 02/0000 UTC thru Jun 05/0000 UTC Reference AWIPS Graphics under...Precip Accum - 24hr For the 02/00z QPF issuance: not much in the way of change to the 01/18z issuance. A few tweaks were made across NE and ND, based mainly on radar trends (ND) and trends in the HRRR (NE). ...Central-Northern Plains and Upper Midwest... There remains a good model signal for two distinct areas of moderate to heavy rainfall developing this afternoon and evening across the northern and central Plains into the Mississippi valley as strong upper dynamics, deep moisture and instability converge across the region. The low level jet is expected to amplify over the central and northern Plains this afternoon-evening as a negatively-tilted upper trough translates east across the northern and central Rockies. Guidance shows PWs increasing in excess of 1.5 inches along a 40-50+ kt low level jet centered across Nebraska and the Dakotas. This moisture interacting with ample instability and the aforementioned trough is forecast to support developing storms, producing heavy rains across the Dakotas later this afternoon. As noted in the overnight discussion, with the strengthening low level jet, the hi-res models continue to show a period of slower eastward progression/cell training - raising the potential for heavy amounts flash-flooding across this region. During the overnight hours, the general model consensus showed convection moving more progressively eastward across eastern North Dakota into Minnesota with a general downward trend in rainfall rates as a developing convective complex to the south begins the interrupt the inflow of deeper moisture. WPC QPF largely utilized the HREF Mean as starting point across this region. Further to the south, there remains a strong signal for a convective complex developing and tracking southeast from central Nebraska toward the mid Mississippi and lower Missouri valleys overnight. Recent runs of the RAP show PWs increasing to around 2 inches on the nose of 50 kt southerly inflow. Upon organizing, this system should become fairly progressive, however strong southwesterly inflow may promote a period of backbuilding/training convection, further raising the threat for heavy amounts across portions of central Nebraska to northeast Kansas and northern Missouri. Convection is expected to wane as the complex continues further southeast toward the lower Ohio and Tennessee valleys during the morning hours on Saturday. However models show convection redeveloping later in the day along and ahead of cold front pushing from the Plains into the Mississippi valley. During the Fri evening into the overnight hours, WPC QPF reflects a northward shift in heavier amounts, similar to the HREF Mean. However, did not go as far north as the HRW-ARW and NSSL-WRF runs, but instead gave more weight to the more southerly HRW-NMMB and NAM CONEST solutions across Nebraska into Kansas and Missouri overnight. ...Eastern U.S.... Slow-moving, positively-tilted upper trough will nudge eastward toward the Atlantic coast by Saturday. Until then, a broad area of modest dynamical forcing east of the trough axis and surface front will favor scattered-widespread convection once again today, especially during the peak heating hours from late-afternoon into early evening. This may raise additional flash flooding concerns, particularly across portions of the central Appalachian into the Mid-Atlantic region where flash flood guidance values are quite low given the recent heavy rains impacting the region. Then on Saturday models show energy over the Great Lakes dropping southeast into the Mid-Atlantic, supporting surface low development along the Delarmva coast. Deep moisture pooling near the center will fuel an increasing threat for developing moderate to heavy rains across the Mid-Atlantic region during the afternoon into the evening hours. Days 2 ...Upper MS Valley into the Great Lakes... For day 2---models are fairly similar in taking an increasingly negatively tilted trof eastward from the Upper MS Valley through the Great Lakes. There are some timing differences that begin to develop with this trof toward the end of day 2 that have consequences with qpf timing among the models. The typically more progressive GFS is amplifying the southern portion of this negatively tilted trof more than the remainder of the guidance and is subsequently slower. Given its outlier status day 2---we trended more progressive with the qpf details. With pw values expected to be above average along and ahead of this trof and the associated frontal boundary---moderate to isolated heavy precip totals possible. The GFS besides being slow is also showing a more widespread area of heavy precip over portions of the Upper MS Valley into the Upper Lakes. Day 2 qpf leaned toward a more toned down version and more progressive---showing areal average .25-.50"+ amounts across these areas. l ...Mid to Lower MS Valley into the Southern Plains... Scattered convection likely south and southwestward along the frontal boundary extending into the Southern Plains. Dynamics are not as strong along this portion of the front but instability is much greater---especially at the beginning of day 2. Moderate areal average totals depicted with isolated heavy amounts possible where convection does become organized. ...Southern to Central Rockies.. The upper trof that moves northeastward into the Southwest day 1 will continue to move northeast day 2 into the Four Corners/Southern to Central Rockies region. This system will help draw increasing pw values northward through the Southern to Central Rockies and Southern High Plains. This will support increasing convection across these area Sunday afternoon in a region of fairly well defined upper difluence ahead of these height falls. The general model consensus is for areal average moderate totals with isolated heavy amounts possible. ..Central Appalachians into the Mid-Atlantic... The slow moving mid to upper level trof moving out of the Central Appalachians into the Mid-Atlantic day 1 will continue to press slowly eastward across the Mid-Atlantic day 2. While there is a typical amount of spread for day 2 with the exact axis of this precip area---there is consensus for additional moderate to heavy totals across these areas and the continuation of potential for local runoff issues given low ffg values across this area. Day 3 ...Eastern Great Lakes---northern Mid-Atlantic into Southern New England... The day 2 issues with the strength of the southern portion of the elongated trof over the Great Lakes continues as this trof pushes eastward across the eastern Great Lakes---Northern Mid-Atlantic and into New England. The GFS continues more amplified and slower with the trof and heavier with the precip ahead of it---especially from the coastal northern Mid-Atlantic---eastern NY state into Southern New England. There are a variety of qpf solutions across these areas from the heavy GFS to the dry NAM and solutions in between. Not wanting to favor either of the outlier solutions here---day 3 qpf leaned for lighter precip than the GFS but heavier than the NAM across these areas---more in line with the latest ECMWF (1200 UTC)---depicting .25-.50"+ amounts. Timing wise...also trending faster than the GFS toward the latest ECMWF. ...Southern to Central High Plains... Height falls moving into the Southern to Central Rockies day 2 will press eastward into the Central to Southern High Plains day 3. Strengthening southerly low level flow ahead of these height falls will support increasing pw values and increasing chances of organized convection moving eastward into the Southern to Central High Plains. Model are showing potential for both a northern and southern area of organized precip day 3. Not a lot of confidence in exact placement---but moderate to locally heavy totals possible as the height falls push east day 3. Pereira/Oravec Graphics available at www.wpc.ncep.noaa.gov/qpf/qpf2.shtml