Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 AM EDT Sun Jun 12 2022 Valid 12Z Wed Jun 15 2022 - 12Z Sun Jun 19 2022 ...Dangerous/Record Heat over the east-central/southeastern U.S. through at least Wednesday... ...Heat likely to become established over the northern-central Plains Friday-Sunday... ...Overview and Guidance/Predictability Evaluation... The start of the period early Wednesday will feature a strong upper ridge over the East, anchored by a high over the southern Appalachians, while an ejecting western trough reaches the High Plains. Then over the next two to three days the upper pattern will transition to an amplified West Coast trough/Plains ridge, with the latter ultimately helping to dig initially progressive southern Canada/northern U.S. energy through the Northeast and into the Atlantic. This configuration may nudge a bit to the east during the weekend. The change in pattern will shift the emphasis for most anomalous heat from the east-central/Southeast U.S. as of Wednesday more into the northern-central Plains during Friday-Sunday. A cold front pushing eastward from the Plains/Upper Midwest will focus showers and thunderstorms mid-late week, and possibly into the weekend over the South. A leading front over parts of the East may also promote areas of rainfall during Wednesday-Thursday. The wavy front ahead of the West Coast upper trough should bring areas of rainfall to the Northwest, while rainfall may expand through parts of the Four Corners states late week through the weekend as moisture flows northward ahead of this system. Most of the latest guidance continues to agree upon most aspects of the large scale pattern evolution but some individual runs still offer meaningful differences with one or more aspects of the forecast. UKMET runs have been less agreeable than other models/means with details of flow across the northern U.S./southern Canada so the updated forecast did not incorporate that model's input. Meanwhile the operational models have been showing a lot of run-to-run variability for details within the West Coast trough after Thursday or so, favoring maintenance of a blend/ensemble mean approach for depicting that feature. Finally, increasingly significant differences arise with flow details over the Northeast into western Atlantic by next weekend. Overall the ECMWF/CMC and their means develop stronger/westward troughing than forecast by GFS/GEFS mean runs. The new 00Z GFS has become the most extreme with its higher heights over the Northeast and vicinity, actually extending its ridge into this region in contrast to the GEFS mean which at least has northwesterly flow (but with higher heights than other guidance). Teleconnections relative to Upper Midwest and Northeast Atlantic positive height anomaly centers in the D+8 multi-day means favor some upper troughing along or a little offshore the Northeast U.S. coast but perhaps not quite as amplified as in the ECMWF cluster. Above considerations led to using the 18Z GFS and 12Z ECMWF/CMC in a blend to start the updated forecast early in the period, followed by a transition to slightly more than half total weight of the 18Z GEFS/12Z ECMWF means by day 7 Sunday. ...Sensible Weather/Threat Highlights... The cold front pushing eastward from the Upper Midwest/Great Lakes/Plains will produce areas of showers and thunderstorms during the mid-late week time frame. It will take additional time to resolve the details but for now there is at least some signal for locally moderate to heavy activity over the Upper Midwest as well as portions of the Appalachians and Mid-Atlantic. A leading front draped over parts of the East Wednesday-Thursday could focus other areas of rainfall. The initial Plains/Midwest front should reach the South by next weekend. Even before this front's arrival, locations across the Southeast and Gulf Coast may see diurnally favored showers and thunderstorms on one or more days. The upper trough nearing the West Coast toward the end of the week should bring mainly light rainfall to parts of the Northwest, with some increase in amounts possible over the northern Rockies by the weekend as the system drifts inland. Meanwhile the amplified pattern 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/intensity of rainfall across the region. Around midweek expect highs to be 10-20F above normal from the Great Lakes into the Carolinas, with numerous locations challenging record highs. A broad area of record warm lows will be possible as well. The heat may persist to some extent into Thursday but highs will tend to be a few degrees cooler, so any daily records should be more isolated. The northern two-thirds of the East will see a steady cooling trend into the weekend. The eastern Great Lakes/Northeast may even see modestly below normal highs. Uncertainty with the upper flow pattern over the Northeast at that time lowers confidence in the forecast though. Areas from the southern Plains into the Southeast will be on the hot side through the period with highs persistently 5-10F above normal. Lingering cool highs over the northern Rockies/Plains on Wednesday will quickly give way to a pronounced warming trend that initially brings a day or so of plus 5-15F anomalies across California and the Great Basin mid-late week, followed by highs of 15-25F above normal settling over the northern-central Plains by Friday-Sunday. Max temperatures could reach high enough to challenge daily records over parts of the central Plains by next Sunday. Meanwhile the upper trough near the West Coast should spread modestly below normal highs gradually farther inland by next weekend. 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