Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 AM EDT Mon Jun 13 2022 Valid 12Z Thu Jun 16 2022 - 12Z Mon Jun 20 2022 ...East-central/southeastern U.S. heat to begin moderating after midweek... ...Heat likely to become established over the northern-central Plains Friday through at least the weekend... ...Overview and Guidance/Predictability Evaluation... Latest guidance continues to show significant amplification of the upper pattern from late week into the weekend, with a trough and embedded closed low nearing the West Coast and a strong ridge over the central U.S. Meanwhile a trough will progress across the northeastern quadrant of the lower 48. Then after early Saturday the West Coast trough should drift a little inland and weaken somewhat, depending on exactly how energy may eject from the feature, while the strength of the central U.S. ridge should favor further amplification/persistence of upper troughing along or just offshore the East Coast. This pattern should promote the highest temperature anomalies over the northern-central Plains from late week through the weekend, with a frontal system potentially starting to erode this area of heat from the west by next Monday. Notable areas of precipitation during the period will likely be with a front crossing the East late this week into the weekend, diurnally favored convection over the Gulf Coast and Florida, across parts of the Four Corners states with a northward surge of moisture, and over portions of the northwestern U.S. plus eventually the northern Plains with the West Coast trough and associated surface waves/fronts. Over recent runs one of the most contentious parts of the forecast has been with upper flow over the Northeast during the weekend, with some GFS runs so strong and eastward/northeastward with the central U.S. ridge that ridging would extend into the Northeast in contrast to amplified/westward troughing in ECMWF runs that would have an upper low near the coast of New England or even the northern Mid-Atlantic. The full array of other models/ensemble means along with teleconnections relative to consensus ideas for the central U.S. ridge and another ridge over the east-central/northern Atlantic Ocean have been favoring a mean trough near or just offshore the East Coast but with some mixed signals for exact amplitude. The 18Z GFS improved upon the 12Z run and now the 00Z GFS has adjusted very close to the ECMWF scenario by Saturday, followed by an evolution closer to the ensemble means versus the 12Z ECMWF that kept the core of the trough farther south. For the upper trough reaching the West Coast and then drifting inland, the ensemble means have been quite consistent overall in recent days. Operational models have tended to agree well for the embedded upper low out to about four days before going astray with respect to how energy may become distributed within the trough and potentially eject northeastward. By day 7 Monday the 12Z ECMWF and 12Z/18Z GFS brought the strongest energy into west-central Canada while the latest CMC runs have been over the Interior West. The corresponding surface reflection in the means is closer to but a bit slower than those ECMWF/GFS runs. The new 00Z GFS/ECMWF have made considerable detail changes, highlighting the continued uncertainty with specifics later in the period. Based on the above considerations, the updated forecast started with a 12Z/18Z operational model composite for the first half of the period and then steadily incorporated increasing 18Z GEFS/12Z ECMWF mean input so that the models/means each had half weight by day 7. This solution provided fairly good continuity, by the latter half of the period accounting for ensemble mean consistency/detail uncertainty for the western trough while depicting an intermediate approach for the upper trough near the East Coast. ...Sensible Weather/Threat Highlights... The cold front progressing eastward from the Great Lakes and central Plains will produce areas of showers and thunderstorms over the East during the latter half of the week. Some locally moderate to heavy activity will be possible. Best potential currently appears to be over and near the Appalachians but other locations could see enhanced totals as well. While most areas should see a drier trend after frontal passage, increasing potential for upper troughing/possible closed low over or near the Northeast may lead to multiple days of showery weather over that region. The Southeast and Gulf Coast regions may see diurnally favored showers and thunderstorms on one or more days, with some potential focus along the front as it reaches the Southeast by the weekend. Convection over Florida may become somewhat heavier during the weekend relative to late this week. The upper trough nearing the West Coast toward the end of the week should initially bring mainly light rainfall to parts of the Northwest, with an increase in amounts at least on a localized basis possible farther inland during the weekend. Some of this activity could reach the northern Plains by early next week. The deep-layer flow between the West Coast trough and central U.S. ridge will likely bring much above normal amounts of moisture for the time of year northward through the Four Corners states and vicinity Friday through the weekend, supporting an increase in coverage and intensity of rainfall across the region. Rain/thunderstorms could continue over this region into early next week and the moisture may interact with the front slowly advancing through the West. The east-central U.S. heat wave should persist into Thursday to some extent, with highs up to 10-15F above normal. A few locations may see record highs after very warm morning lows, but overall expect Thursday to be less extreme than prior days. Then the eastern U.S. will see a pronounced cooling trend, including below normal highs over the eastern Great Lakes/Northeast during the weekend into early next week. Meanwhile the heat focus will shift westward, with the Great Basin seeing a couple very warm to hot days late this week and the northern-central Plains likely to experience highs of 15-25F above normal Friday-Sunday, with the axis of highest anomalies drifting a bit eastward with time. Scattered record highs will be possible. By Monday a cold front may bring cooler air to the High Plains and push plus 10-20F anomalies a little farther east. Southern portions of the Plains should stay on the hot side with highs 5-10F above normal through the period. Moderately below normal highs will spread eastward across the West Friday-Sunday and then trend closer to normal by Monday. Rausch Additional 3-7 Day Hazard information can be found on the WPC medium range hazards outlook chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, experimental excessive rainfall outlook, 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/#page=ero https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml