Extended Forecast Discussion NWS Weather Prediction Center College Park MD 346 PM EDT Fri Jun 07 2019 Valid 12Z Mon Jun 10 2019 - 12Z Fri Jun 14 2019 ...One or more episodes of heavy rainfall and flash flood/flooding threats possible over parts of the Appalachians/East Coast states next week... ...Overview and Guidance/Predictability Assessment... During Mon-Wed guidance agrees in principle that initially weak Pacific shortwave energy reaching western North America by early Mon will steadily amplify toward the east-central U.S. as a ridge builds into the western part of the continent. This evolution will occur behind a couple leading features--a Southeast U.S./eastern Gulf trough and separate northern stream shortwave. The overall combination will lead to one or more periods of enhanced rainfall over some areas of the East. By Thu-Fri details aloft over much of the Lower 48 become increasingly uncertain but most models/ensembles show a general theme of diffuse shortwave energy moving into the West while the amplified/reinforced eastern trough that persists into Thu becomes more shallow on Fri as it lifts northeastward into Canada. From day 3 Mon into day 5 Wed a blend of the 06Z GFS/00Z ECMWF (and some varying weighting of the 00Z UKMET, 06Z GEFS mean, 00Z ECMWF ensemble mean and continuity) represented the synoptic consensus well, while yielding an intermediate solution for important smaller scale differences that are within typical error ranges--and have below average predictability--for the time frame of interest. In particular some of these differences affect the location/intensity/duration of heavy rainfall over the East. Broadly speaking most models and ensemble means have shown fairly stable evolutions over the past 24-36 hours with no pronounced trends evident. In this scenario, a consensus solution often performs best. During the latter half of the period there are multiple detail questions that arise: whether the sharpening trough energy reaching the Mississippi Valley around midweek closes off a low for some period of time (a solution somewhat in the minority thus far), the evolution of energy over Ontario, and the particulars of multiple pieces of energy that will comprise the overall diffuse shortwave trough moving into the West. Increased weighting of the 06Z GEFS mean and 00Z ECMWF ensemble mean guidance helped to downplay the less confident details within the more agreeable large scale evolution. This resulted in only some minor changes to the previous forecast mostly in system timing. ...Sensible Weather Highlights/Threats... Expect highest rainfall totals for the full Mon-Fri period to be over an area encompassing the eastern Great Lakes/Appalachians/East Coast states. Early in the week a north-south front heading into the East and wavy front over the Southeast will provide focus for rainfall. The trailing front and embedded wave(s) will likely stall over the Southeast Tue-Wed and finally be dislodged as the upper trough amplifying into the East brings another surface low/frontal system into and through the region. Over the central third of the U.S. there will likely be areas of showers/storms with some moderate to heavy amounts but on a more localized scale. Low level upslope flow may enhance rainfall over the southern High Plains early in the week and a frontal system/low pressure may bring rainfall to portions of the northern half of the Plains and points east from Mon night or Tue through midweek. The shortwave energy moving into the West late in the week may promote scattered convection with some activity possibly reaching the Plains as well. The upper ridge building into the West early-mid week will bring very warm to hot temperatures to the region, with fairly broad coverage of plus 10F and greater anomalies Mon-Wed. Readings will begin to moderate later in the week as heights aloft decline. Expect highest temperatures Tue-Wed with locations along the Medford-Portland corridor seeing the best potential for highs 20F or more above normal. Daily records for highs/warm lows will be possible over the West Coast states as temperatures climb into the 90s and perhaps near or just over 100F which will likely be the hottest temperatures so far this year. Meanwhile the pattern will tend to favor below normal temperatures over most of the central U.S. aside from a possible trend toward normal by Fri. Clouds/rainfall should produce a decent area of minus 10-20F anomalies for highs over the southern High Plains on Mon (only in the 70s). The East will see above normal mins early in the week ahead of the lead front but otherwise should see near to below normal min/max readings as the frontal systems lift through the region. Fracasso/Rausch Additional 3-7 Day Hazards information can be found on the WPC medium range hazards chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php Hazards: - Heavy rain across portions of the Northeast, the Central/Southern Appalachians, the Mid-Atlantic, the Great Lakes, and the Ohio Valley, Mon, Jun 10. - Heavy rain across portions of the Southeast, the Southern/Central Appalachians, and the Mid-Atlantic, Tue-Wed, Jun 11-Jun 12. - Flooding possible across portions of the Mid-Atlantic and the Southern Appalachians. - Flooding occurring or imminent across portions of the Plains, the Mississippi Valley, the Great Lakes, the Northern Rockies, the Northern Great Basin, and the Ohio Valley. - Flooding likely across portions of the Central Plains and the Central Great Basin. - Excessive heat across portions of the Southern Plains, Mon, Jun 10. - Much above normal temperatures across portions of the Central/Northern Great Basin, the Northern Rockies, California, and the Pacific Northwest, Mon-Thu, Jun 10-Jun 13. - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Tue-Wed, Jun 11-Jun 12. - Heavy rain across portions of the Alaska Panhandle, Mon-Wed, Jun 10-Jun 12. - High winds across portions of the Aleutians, Tue-Wed, Jun 11-Jun 12. WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indices are at: https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml