Extended Forecast Discussion NWS Weather Prediction Center College Park MD 259 AM EDT Thu Jun 13 2019 Valid 12Z Sun Jun 16 2019 - 12Z Thu Jun 20 2019 ...Overview and Guidance/Predictability Assessment... Latest guidance maintains the idea of broadly cyclonic mean flow aloft over the lower 48, between ridges over the western Atlantic and eastern Pacific. Consensus still shows robust strengthening of the Pacific ridge from late weekend into early next week. This ridge may ultimately promote more energetic troughing over parts of the western-central U.S. by next Tue-Thu in contrast to the weaker/more diffuse features likely to be embedded within the mean flow early in the period. The overall pattern should lead to broad coverage of rainfall from the Rockies eastward. Details at any particular point in time are still quite uncertain but the general signal for heaviest rainfall potential within an area from the southern half of the Plains into the Ohio Valley/central Appalachians has been consistent over multiple days. The setup appears favorable as a decelerating wavy front settles into a Northeast U.S. to southern Plains orientation during the Sun-Tue period while steady low level inflow from the Gulf provides ample moisture, and one or more shortwaves aloft likely encourage convective development. The front should return north as a warm front late Tue onward as a system emerges over the Plains. This latter system should bring some enhanced rainfall to areas across the northern tier as well. The additional rainfall would be problematic over areas already experiencing flooding or have wet ground. Guidance continues to vary for the precise handling of shortwave energy progressing eastward from the northern Plains Sun onward, keeping confidence low for specifics of a general area of waviness likely to track from the Midwest/Lower Great Lakes into the Northeast during the first half of the period. Separate shortwave energy tracking out of the central Plains could have an influence on the forecast as well. Prefer maintaining a blend approach to reflect the most common themes of guidance without committing to any extreme aspects of some individual solutions. Farther west the greatest forecast problem involves the character of the Pacific ridge and specifics of energy expected to amplify into the downstream trough. The past couple ECMWF runs through 12Z June 12 were the quickest to flatten the ridge (by way of upstream trough progression), leading to faster system timing over the northern states by Wed-Thu. Although the new 00Z GFS (note the FV3 GFS become the operational run as of the 12Z June 12 run) adjusted toward a slower variation of the ECMWF, strength of the ridge by mid-period seems to favor leaning away from any solution that is quickest to weaken it. Beyond the issue of the ridge, there are also various possibilities for details of energy around the top of the ridge and feeding into the downstream trough. The 12Z ECMWF mean is most enthusiastic to bring the upper low just south of Alaska bodily southeastward. Remaining solutions show greater potential for the upper low to hang farther back but at the same time have energy flowing to its south amplify into the trough. The GEFS mean becomes slowest with the trough. Ultimately favored a blended approach (increasing ensemble input while reducing/removing weight of the 12Z ECMWF with time) that led to an intermediate solution closest in principle to a deeper version of the 12Z CMC mean. ...Sensible Weather Highlights/Threats... The expected pattern evolution at the surface and aloft continues to be favorable for multiple episodes of convection/heavy rainfall from the southern half of the Plains into the Ohio Valley/Appalachians. However there is still considerable uncertainty for some of the day-to-day details, and in fact guidance spread over the southern Plains appears to have increased compared to previous days. As a result the potential for highest five-day totals within the full threat area seems to be more evenly distributed versus concentrating more toward the Plains in previous days. Some of the activity across this area will likely extend into the Northeast/Mid-Atlantic with locally moderate-heavy rainfall possible. It will likely take fairly far into the short range time frame to resolve the specifics given the low predictability of important small scale features and the difficulty that models sometimes have in representing convection. Over the West the best concentration of showers/thunderstorms should be over the northern-central Rockies. Coverage and intensity become increasingly uncertain by Wed-Thu given spread for details of flow aloft. During Tue-Thu expect rainfall of varying intensity to spread into the northern Plains/Upper Mississippi Valley with the system forecast to affect those regions. The Florida peninsula should see diurnal convection through the period. Over the West expect broad coverage of above normal temperatures (greater for morning lows than daytime highs) Sun-Mon with some pockets of greater than plus 10F anomalies. Readings should then trend cooler as jet energy reaches the Northwest by Tue, leaving parts of California as the primary area of warmth heading into midweek. Areas across the northern/central Rockies and Plains will tend to see moderately below normal highs, perhaps trending cooler over northern locations late in the period. Over the East areas of clouds/rainfall should favor near to above normal lows but near to slightly below average highs. 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