Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1200 PM EDT Mon Oct 08 2018 Valid 12Z Thu Oct 11 2018 - 12Z Mon Oct 15 2018 ...Michael/heavy rainfall lift from the Southeast to off the Eastern Seaboard Thu/Fri... ...Sergio moisture/rains to reach Arizona and Southern Rockies/Plains into Fri/Sat... ...Pattern Overview and Guidance/Predictability Assessment... Latest guidance maintains decent continuity for the evolution of the larger scale mean pattern aloft, showing a transition from a positively tilted southern Canada into western U.S. trough day 3 Thu toward strong ridge building near the West Coast and downstream amplified troughing settling from west-central to east -central North America over this period. Meanwhile most solutions show some degree of smaller-scale troughing likely to persist over the southwestern U.S. and northwestern Mexico. Over the West, the greatest uncertainty will be with the specifics of initial western energy for which models/ensembles are showing an increasing signal of closing off for a time near southern California--plus interaction with Sergio which should be tracking northeastward ahead of the aforementioned energy. This interaction will be very sensitive to the exact timing of Sergio and how the western U.S. shortwave energy is evolving at a specific point in time (and what proportion feeds southwestward versus continuing along in the westerlies. The overall pattern appears supportive for faster progression than what has been depicted in ECMWF/ECMWF mean runs thus far and the latest forecast from the NHC seems closest to the 00 UTC UKMET and to a lesser extent the 00 UTC GFS. Please consult National Hurricane Center Products for the latest info on Michael. Meanwhile the forecast for Michael, which has reached Hurricane status at this time and should affect the Southeast and East mid-later week, is also uncertain in light of continued very broad model/ensemble spread for track and especially timing. At the very least the overall pattern appears supportive for faster progression than what has been depicted in ECMWF/ECMWF mean runs thus far and the latest forecast from the NHC seems closest to the 00 UTC UKMET and to a lesser extent the 00 UTC GFS. Please consult National Hurricane Center Products for the latest info on Michael. WPC surface fronts/pressures and 500mb mass field progs were accordingly primarily derived from a solution closest to the 00 UKMET days 3-5 to best match the NHCforecasts of Michael and Sergio. Later, blended the 06 UTC GEFS mean and the 00 UTC ECMWF ensemble mean that develops a blended solution aloft over the lower 48 on the more amplified side of the full envelope of solutions in consideration of amplified upstream ridge development over the eastern Pacific in most guidance. ...Weather Highlights/Threats... Parts of the eastern U.S. will experience a period of heavy rainfall with the combination of Michael and interaction with an approaching cold front. Guidance continues to vary widely for track and timing of Michael so confidence is fairly low with respect to precise location of heaviest rainfall and timing-dependent duration of this rainfall. While Michael begins to track away from the East Coast, Sergio may bring moisture into portions of Arizona and the southern Rockies/Plains. Highly sensitive details for evolution aloft lead to low confidence in exact coverage/intensity of rainfall here as well--especially the latitude of the axis of heavier rainfall. This lack of confidence extends to how much moisture may interact with a front that drops into the Plains during the weekend--with solutions spanning the whole spectrum from considerable to more modest amounts. Elsewhere, the initial front over the East will likely decelerate/stall over the Florida peninsula leading to periods of rainfall in its vicinity. The clipper system brushing the extreme Northern Tier will be accompanied by an area of mostly light rain and trailing rain/snow from Sat onward. 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