Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1200 PM EDT Mon Sep 03 2018 Valid 12Z Thu Sep 06 2018 - 12Z Mon Sep 10 2018 ...Pattern Overview and Guidance/Predictability Assessment... Guidance continues to advertise relatively progressive mean flow across the northern contiguous U.S. and southern Canada into the weekend, with a tendancy to amplify into next week downstream from a northeast Pacific trough that exists in response to a very strong Bering Sea ridge. Within this ridge, guidance suggests potential for heights that could reach 3-4 standard deviations above climatology late in the week. This seems reasonable as the ridge itself is downstream of a extratropical low associated with current western Pacific Typhoon Jebi that is forecast to lift into the high latitudes. Meanwhile, flow around a weakening eastern U.S. ridge aloft should guide current Tropical Storm Gordon into south-central U.S. mid-later week. Farther east, this may allow an inverted upper trough/rainfall focus to work from the Bahamas into Florida. The WPC medium range product suite was primarily derived from the 00 UTC ECMWF Thu-Sat whose inland track of weakening but still heavy rain producing Gordon seems the closest guidance match to the latest NHC forecast track. However, this ECMWF run is seemingly too progressive with northeastern Pacific to Pacific Northwest storm energies/height falls into days 6/7 given upstream flow amplitude. Accordingly, quickly transitioned guidance preference more in line with 06 UTC GEFS mean and 00 UTC ECMWF ensemble mean to account for this upstream flow issue. The subsequent track of Gordon meanwhile may still be in line in this ECMWF run. ...Weather Highlights/Hazards... Tropical Storm Gordon has developed near southern FL. By later week into medium range time scales, there will be a substantial threat for locally heavy rainfall for parts of the south-central Plains/mid-lower MS valley and vicinity near the path of slowly weakening Gordon as per NHC and northeastward as an extratropical low over the Midwest/Great Lakes into days 6/7 as per WPC. Deep tropical moisture will feed into a larger scale band of moisture extending from the southern Plains northeastward, interacting with the front that stalls over mid-latitudes of the lower 48 and then lifts northeastward as a warm front. Significant details have yet to be resolved so confidence is not yet as high as desired for pinpointing the best focus for highest rainfall amounts within a favored zone from the southern-central Plains through the Midwest into parts of the northern Mid-Atlantic/Northeast. Mid level energy and a surface trough reaching Florida from the Bahamas may enhance rainfall at times over/near that state, while lingering moisture may aid some activity along portions of the Gulf Coast. The Pacific Northwest should see a period of light-moderate precipitation late week into the weekend with potentially another around the start of next week. Expect very warm and humid conditions over the East late this week ahead of the backdoor front that reaches into the Mid-Atlantic. The best signal for most extreme anomalies (at least plus 10-15F) continues to be for min temps from the Ohio Valley/Appalachians into Mid-Atlantic/Northeast with some readings possibly exceeding daily record warm min values. Clouds/rainfall will temper high temperatures over the East after Fri but keep the lows fairly warm. Schichtel WPC medium range 500 mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indexes are found 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