Extended Forecast Discussion NWS Weather Prediction Center College Park MD 259 AM EDT Mon Jun 10 2019 Valid 12Z Thu Jun 13 2019 - 12Z Mon Jun 17 2019 ...Overview and Guidance/Predictability Assessment... The one fairly agreeable and stable aspect of the forecast is the amplified eastern U.S. upper trough and associated surface reflection lifting northeastward from early Thu onward. Otherwise the expected transition of the pattern to a lower amplitude regime with embedded medium to smaller scale features (having low predictability) continues to cause significant difficulty in resolving important details. The one common signal comes from teleconnections relative to the best defined height anomaly centers in the D+8 means--positive ones northeast of Hudson Bay and off Vancouver Island along with a negative one associated with a mean upper low near the Aleutians--all suggesting broadly cyclonic flow over the eastern U.S. Model/ensemble spread and variability among consecutive runs keep confidence fairly low for the time being, but over the past 24 hours there has been a strengthening signal that the pattern could support heavy rainfall potential over parts of the south-central Plains and extending east/northeast. This emerging threat will require close monitoring given the high sensitivity of some of these areas to any significant rainfall. Within the overall eastern trough aloft which should trend more shallow with time, the key uncertainty remains with the energy that starts the period early Thu in the vicinity of northern Ontario/southern shore of Hudson Bay. Individual solutions are too varied to describe in detail but essentially break down into one of two scenarios, the feature either remaining over Canada or else at some point dropping farther south and brushing the northeastern quadrant of the Lower 48. Adding to the confusion, multiple models have switched between the two ideas in consecutive runs. The ultimate path of this energy will determine the southward extent/timing of a front expected to reach at least as far as the northern tier states and possibly much farther south. Meanwhile shortwaves from multiple streams will filter across the West and into the Plains from late week onward. Compared to yesterday the guidance as a whole has suggested a somewhat weaker and faster trend for this energy in the days 3-5 Thu-Sat time frame. Then by days 6-7 Sun-Mon solutions still diverge considerably over the eastern Pacific/western U.S., involving flow at the leading edge of the broad North Pacific upper low (more eastward elongation in the ECMWF/CMC) and then details of ridging that may build over the eastern Pacific and corresponding response downstream. Most individual solutions could be plausible from a multi-day mean perspective incorporating the late extended/early week two period. However established consensus indicates the new 00Z GFS/FV3 GFS could become a too strong with the eastern Pacific ridge by next Mon, leading to the deepest West Coast trough. For the latest forecast update the multitude of low confidence detail issues required a steady increase of ensemble input after a multi-model consensus to start day 3 Thu, with the 18Z GEFS and 12Z ECMWF/NAEFS means used exclusively by days 6-7 Sun-Mon. This provided more subtle adjustments from continuity than following any particular model scenario. ...Sensible Weather Highlights/Threats... The system affecting the Great Lakes/Northeast early in the period will bring rainfall of varying intensity Thu-Thu night. Emerging consensus indicates highest totals may remain offshore while system progression could limit rainfall accumulations as well. Then the rainfall focus will shift westward as weak shortwaves move into/through the West and emerge over the central U.S. This energy may produce at least a modest surface low/frontal system while southern Canada/northern U.S. flow east of the Rockies could push a separate front southward. Expect periods of showers/thunderstorms on multiple days over the northern two-thirds of the West with best organization likely in the northern-central Rockies. Farther east there is still considerable uncertainty over specifics of surface features that will serve to focus convection. However in principle guidance over the past day has trended toward higher potential for heavy rainfall within an area extending from the south-central High Plains into the Ohio Valley. Some individual solutions display such potential elsewhere as well. Currently the ensembles as a whole focus the greatest probability of highest totals for the five-day period over parts of Kansas/Oklahoma/Missouri/Arkansas. Expect the Florida peninsula to be another favored area of meaningful rainfall during the period. Temperatures over the West should remain above normal though to a lesser extreme than expected through Wed. Some scattered plus 10-15F anomalies for highs will be possible from extreme northern California into the interior Northwest and extreme northern Rockies while the West will see a broader expanse of plus 5-15F anomalies for morning lows from late week into next Mon. Below normal readings will prevail over much of the eastern half of the country Thu-Fri. Then anticipate temperatures closer to normal though perhaps averaging slightly below average overall. 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 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