Quantitative Precipitation Forecast Discussion NWS Weather Prediction Center College Park MD 422 PM EDT Sat Jun 02 2018 Final Day 1, Day 2 and Day 3 QPF Discussion Valid Jun 03/0000 UTC thru Jun 06/0000 UTC Reference AWIPS Graphics under...Precip Accum - 24hr For the 03/00z QPF issuance: not much in the way of change to the 02/18z QPF issuance. A few tweaks were made over the Mid Atlantic for the first period, based in part on radar trends and in part on the most recent HRRR runs. ...Eastern U.S.... A Moderate Risk for flash flooding remains in place across portions of Maryland, Delaware and the Virginas as a shortwave trough drifting east from the Virginias interacts with a deep moisture pool -- supporting heavy rains across the northern Mid Altantic, including areas that were impacted by heavy rains earlier in the week. Guidance shows the aforementioned trough drifting slowly east from the Virginias to the coast over the next 24-36 hours, with deep moisture (PWs around 2 inches) pooling near the associated low level circulation. Expanding coverage of moderate to heavy rainfall rates is expected to continue as instability increases this afternoon. Weak flow aloft is expected to support slow moving cells with high RH through the mid levels and tall 'skinny' CAPE supporting efficient rainfall processes. Threat for heavy rainfall rates is expected to peak during the afternoon into the evening hours, with a downward trend as instability decreases overnight. The return of daytime heating is expected to support an upward trend in rainfall rates closer the Mid Atlantic coast tomorrow afternoon. WPC QPF utilized the HREF Mean as a starting point through much of the period, with moderate to heavy amounts from eastern West Virginia to the mid Atlantic coast over the 24-30 hours. ...Upper Midwest/Great Lakes/Ohio Valley... A negatively-tilted upper trough will continue to push showers and storms eastward across the upper Midwest and Great Lakes region this afternoon/evening. The progressive nature of the system along with modest instability should limit the potential for heavy amounts, with generally light to moderate accumulations expected as the system moves across the upper Great Lakes region tonight. As the system pushes further east on Sunday, increasing instability supported by daytime heating is expected to raise the threat for locally heavy rains across the Ohio valley Sunday afternoon-evening. The HREF Mean was utilized as a starting point with a slight shift toward the more progressive members, including the HRW-NMMB. ...Mid and Lower Mississippi Valley... Divergent flow along of the base of the aforementioned trough along with deepening moisture ahead of the associated cold front will continue to support developing convection across from the mid Mississippi valley and Ozark region southward into the lower Mississippi valley and ArkLaTex region. Deep moisture and instability are expected to support locally heavy amounts with the hi-res models continuing to show a good signal for heavier amounts centered across Arkansas this evening. However these storms should be fairly progressive in nature, limiting the threat for more widespread heavy amounts. The HREF Mean was utilized as a starting point, with a slight shift toward the more progressive members. ...Southern Rockies/High Plains... Guidance shows a good signal for developing precipitation, with locally heavy amounts possible across portions of the region tomorrow. Increasing southeasterly low level inflow ahead of a shortwave trough moving across the Four Corners region is expected to support developing showers and storms during the afternoon and evening hours tomorrow, with some signal for moderate to locally heavy amounts across the southern Colorado and the New Mexico ranges. Day 2 ..Eastern Great Lakes---Upstate/Eastern NY---coastal Northern Mid-Atlantic into southern to central New England... The negatively tilted mid to upper level trof moving through the Great Lakes region day 1 will continue to push eastward day 2 and undergo amplification as additional upstream height falls dive southeast from the upper to eastern Great Lakes region. Model differences are not as acute as yesterday with fairly good overall agreement with this evolution. Some timing differences with the associated secondary low moving from the Mid-Atlantic coast to in the vicinity of southeast New England with the NAM fastest. Shied away from this outlier solution with respect to qpf timing day 2--more toward in house ensemble means and the ECMWF---which as per the latest pmdhmd is closest to the EC/GEFS/NAEFS means. A broad region of moderate to heavy rains will stretch ahead of the mid to upper level center along the Ontario/QB border---southeast into upstate and eastern NY---eastern PA---NJ and into central to southern New England ahead of the coastal surface wave which will enhance onshore south southeasterly flow. Drier conditions expected over the Mid-Atlantic/Central Appalachians day 2 as the focus for heavy precip shifts northeastward. ...Southern High Plains.. The Southern to Central Rockies height falls will be pushing eastward day 2 into the Central to Southern Plains. Organized convection possible ahead of these height falls---especially along the southern end of them across the Southern High Plains from south-central to southeast NM into Southwest TX. Confidence not great with timing---but there is a model signal for potentially heavy to isolated excessive rainfall amounts across these regions. No changes planned to the previous day 2 marginal risk area on the Excessive Rainfall Outlook across this area. ...Southeast---northern Gulf coast into central TX... Scattered convection likely along and ahead of the cold front pressing southward off the northern Gulf coast---into North Florida and through the Southeast day 2. Not a lot of confidence with qpf in this scattered convective regime with light to moderate areal average totals depicted. Day 3 ..Northern NY state into Northern New England... Strong southeast low level flow will continue ahead of the surface low moving from off the southeast New England coast to the south coast of Nova Scotia day 3. Timing issues continue day 3 with the NAM remaining the most progressive. WPC day 3 qpf stuck with the EC/GFS in house qpf mean which were more similar and showed moderate to heavy precip potential across these areas with the greatest heavy rain threat across central to eastern Maine in the region of strongest onshore flow. ...Lower Great Lakes into the Northern Mid-Atlantic... Additional height falls rotating southeast into the mean trof position across southeast Canada day 3 will help push a cold front south thru the Great Lakes. The NAM was a northern outlier with the axis of precip associated with this front. WPC favored the farther south GFS/EC solutions--depicting areal average .10-.25"+ amounts from the Lower Great Lakes into the Northern Mid-Atlantic. The NAM axis was oriented from the Upper Great Lakes into much of western to northern NY state. ..Southern Plains... Convection may fire in the northwesterly mid to upper level flow parallel to the surface front over the Southern Plains day 3. The GFS and NAM were fairly similar with the potential moderate to heavy qpf axis from western to central OK into northeast TX. This axis is in between the ECMWF's depiction of two separate axes---one over NW TX and the other from eastern OK into western LA. Confidence is typically low for a day 3 convective qpf axis. At the moment---we favored the GFS-EC depiction. Pereira/Oravec Graphics available at www.wpc.ncep.noaa.gov/qpf/qpf2.shtml