Extended Forecast Discussion NWS Weather Prediction Center College Park MD 228 PM EDT Mon Jun 14 2021 Valid 12Z Thu Jun 17 2021 - 12Z Mon Jun 21 2021 ...Record to dangerous heat continuing through the week across much of the Interior West... ...Extreme heat for the Southwest/California through the end of the week... ...Tropical system may bring heavy rainfall to Central Gulf Coast later this week and weekend... ...Overview... The anomalously strong upper ridge over the Four Corners region this week will fuel the dangerous and record heat wave for much of the Southwest to Interior West while downstream over the East Coast, a brief period of troughing and cyclonic flow allows for some drier and slightly cooler air to filter in. By this weekend, the aforementioned ridge begins to break down as large scale troughing sets up over the central U.S. and attention turns to the potential tropical system that could bring heavy rainfall hazards to portions of the central Gulf Coast. The National Hurricane Center is now advertising a high likelihood for increased development and organization of that system. Farther north, an area of low pressure ejecting out into the Plains Sunday and Monday will interact with a wavy stationary boundary in place and could be the focus for increased/enhanced rounds of thunderstorms. ...Guidance/Predictability Evaluation... For the tropical system in the Gulf, the most notable change from the previous model cycle was a faster trend as the system is influenced by deepening troughing over the central U.S. which helps draw it further to the north. Most of the available deterministic guidance trended this way and the early look at the latest 12Z guidance suggests this trend continues. There remains some west/east spread with the CMC being on the eastern envelope, and was largely discounted for this cycle. A consensus of the latest ECMWF and GFS with some influence toward the ensemble means was used for the forecast including QPF per WPC/NHC coordination. Outside of the tropical system, there is relatively good model consensus in the upper level pattern which provided a reasonable starting point for depicting the main synoptic features. The shortwave and associated low pressure coming out of the central Canada is expected to lay down a front across the Great Lakes to Ohio Valley. There is still some spread in how far south this sets up and will likely be dictated by prior convective outflows. Subsequently, its north/south waviness and later interaction with another low pressure system early next week in the Plains remains elusive. As a result, the WPC blend, which started mainly deterministic between the ECMWF/GFS/CMC/UKMET evolved into mostly a consensus of the ECENS/GEFS means by day 6/7. ...Weather Highlights/Hazards... Dangerous and record breaking heat wave for much of the western U.S. will continue through this week with some of the most extreme temperatures over the Southwest. Daily temperatures 15F to 20F above normal are expected with afternoon readings well into the 100s and 110s for the Southwest, California Central Valley, and portions of the Interior West. Further north, readings in the 90s are expected. The combination of extreme daily temperatures and duration, as well as being rather early in the season for such an event, will make this a dangerous heat wave for sensitive groups. Excessive heat warnings/watches are in place for many areas of the Southwest and the California Central Valley. The Central Plains region should experience some of the heat on Thursday as well with highs 10-20F above normal. After Thursday the front over the central/eastern U.S. will bring temperatures down toward normal with perhaps a few pockets a little below normal depending on the day. The East will be on the cool side late this week before rebounding toward normal, though clouds/rain reaching parts of the South may lead to below-normal highs late in the period. A potential tropical system in the Bay of Campeche is forecast to drift northward later this week and approach the central Gulf Coast by Friday into this weekend. The National Hurricane Center is monitoring for increased organization and development but regardless, the system will be capable of producing heavy rainfall over portions of the Central Gulf Coast and this could spread inland over the Southeast this weekend. Further north, interactions along a stationary front and another low pressure moving into the Plains/Upper Midwest could bring locally heavy rain to areas from the Ohio Valley, Great Lakes, or Upper Midwest. Details in convective complexes and potential interactions from the tropical system to the south lowers forecast confidence quite a bit so it may take a few days to resolve any potential heavy rain threat there. Taylor/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, 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