Extended Forecast Discussion NWS Weather Prediction Center College Park MD 238 PM EDT Fri Jun 11 2021 Valid 12Z Mon Jun 14 2021 - 12Z Fri Jun 18 2021 ...Record to dangerous heat continuing through next week across much of the Interior West and at times into the northern Plains... ...Extreme heat possible for the Southwest next week... ...Overview... Guidance agrees that a very strong upper ridge will be centered over the Four Corners states next week while a mean trough prevails over the East into about Thursday. A portion of the energy from an eastern Pacific upper trough/low will eject northeastward and around the ridge, bringing a cold front into the Northwest late Monday into late Tuesday and then continuing across the northern tier states. This shortwave energy will eventually help to kick out the eastern trough late in the week. The persistence and strength of the western upper ridge will likely produce a broad area of temperatures that approach/exceed daily record values over the Interior West/Rockies on most days next week, making for a hazardous heat wave event. Some of this heat will extend into the northern Plains for a time as well. In the Gulf of Mexico, a disturbance may form near the Bay of Campeche and move northward late in the week but there remains a large degree of uncertainty in its evolution. ...Guidance/Predictability Evaluation... The models and means show better than average consensus for the strength and position of the Four Corners ridge/upper high through the period, leaving the guidance differences for areas around its periphery. Strength of the upper high is remarkable -- near +3 sigma 500mb heights that may breach record high heights for this early in the warm season. Within the eastern North America mean trough, there has been some spread for an eastern Canada upper low that may track into or just north of New England. Deterministic models were a bit removed, but clustered with each other, from the ensemble mean consensus with two areas of low pressure over/near New England Tue-Wed. With some adjustments still seen in the ensembles, leaned more toward the deterministic consensus that shows a bit stronger ridging over the West and Atlantic. Meanwhile the models show typical variability for the details of the eastern Pacific energy that ultimately tracks around the western ridge, favoring a blend approach that includes some ensemble means later in the period and which represents the most common elements of guidance. Did adjust the next Thu/Fri system quicker, supported by a flattening of the Pacific jet upstream. Over the Gulf of Mexico, the models and means show an area of increasing moisture and lower heights aloft/surface pressures lifting northward out of the Bay of Campeche, with some signals for possible tropical development per the ECMWF tropical cyclone formation probabilities >40-50%. By day 7 Friday the manual forecast shows an area of low pressure ~300 miles south of the TX/LA border per the NHC-WPC coordinated forecast. Monitor future forecasts for any adjustments. ...Weather Highlights/Hazards... Within the broad area of heat across the western and northern U.S., expect the most extreme anomalies to be over the northern Rockies and High Plains during Monday-Wednesday with highs at least 20-25F above normal. Ejection of an eastern Pacific trough and leading front that crosses northern portions of the West and continues into the Plains will bring some relief to those areas but otherwise the West should continue to see highs 10-20F above normal along with a westward expansion of the heat mid-late week. Morning lows should also be 10-20F above normal over a majority of the West through the period, as well as the northern Plains into Thursday. The combination of extreme daily temperatures and duration, as well as being rather early in the season for such an event, should make this a dangerous heat wave for sensitive groups. Excessive heat warnings are in place for many areas of the Southwest next week where temperatures may climb well into the 110s in the lower deserts. The eastern trough aloft and associated surface waves/fronts will produce some areas of rain and thunderstorms of varying intensity and during mid-late week some moderately below normal temperatures (perhaps 5 to no more than 10F below normal). The southern tier may see rain from both a wavy front and typical diurnal convective activity. Portions of the Gulf Coast region could see an increase of rainfall toward the end of next week as moisture pushes northward across the Gulf. Monitor forecasts/National Hurricane Center discussions over the coming days for the latest information regarding any potential tropical cyclone development. The upper trough/surface front initially near the Pacific Northwest will bring light-moderate rain to the region during the first half of the week. Toward late week this system may produce some rainfall from the northeastern Plains into the Great Lakes. Fracasso/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