Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1209 PM EDT Mon Jun 10 2019 Valid 12Z Thu Jun 13 2019 - 12Z Mon Jun 17 2019 ...Overview and Guidance/Predictability Assessment... A fairly amplified trough with embedded shortwave energy trough will be over the northeast/eastern U.S. through the extended period, although steadily becoming more shallow with time. Model consensus has improved with the last two runs in regards to amplitude, placement and timing- at least for earlier periods. The spread increases Saturday afternoon particularly over the north-central region likely in response to the western U.S. transitioning to a less amplified pattern. A trough over the Gulf of Alaska/north Pacific will be deepening as it progresses toward the West Coast. 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. For the East, 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. The path of this energy will dictate the speed and how far south the front will extend. Multiple shortwaves tracking across the West and Plains will increase the likelihood for a pattern that could support heavy rainfall potential over parts of the south-central Plains and extending east/northeast. This section of the country continues to have historic river flooding and are highly sensitive to any significant rainfall. The guidance continues to suggest a somewhat weaker and faster trend for this energy in the days 3-5 Thu-Sat time frame. Once again, the GFS solution becomes the deepest over the Southwest Sunday and Monday, which deviates from the model consensus. This low confidence forecast was comprised of the 00Z ECMWF, 00/06 GFS, 06Z FV3 and increasing weight of the 06 GEFS and 00Z ECMWF/NAEFS means 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 throughout Thursday. 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/Campbell 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