371 FXUS65 KREV 241831 AFDREV Area Forecast Discussion National Weather Service Reno NV 1131 AM PDT Thu Jun 24 2021 .SYNOPSIS... Temperatures remain seasonable with chances for thunderstorms through Friday. Some thunderstorms may be strong and produce heavy rain today. Another heat wave is expected this weekend, which may last into next week. Thunderstorms chances look to return Monday through Wednesday early next week. && .DISCUSSION... Few changes were made as the overall forecast looks on track. An upper-level low will continue to bring chances for thunderstorms today and Friday along with near-normal temperatures. Winds will be lighter today into the weekend with periodic shifts to the east- northeast and back to the west. Temperatures will quickly begin to increase this weekend into next week as the upper low fills and an upper ridge builds over the western US. Tonight through Friday morning: * Increased thunderstorm coverage will continue into the evening provided from the nearly stationary upper low over the West Coast as it overspreads into western Nevada. PWAT values that climbed in response to the southeast mid to upper level flow pulling moisture from the subtropical Gulf of California still range between 0.6-0.9 inches. Convection should continue late into the evening across the Sierra front and much of western Nevada as residual daytime heating continues to add that extra measure of lift to sustain thunderstorm activity late into the evening. Light upper-level flow (easterly SFC-6km mean wind 5-10 kts), high storm bases atop deep inverted V thermodynamic profiles, and steep mid-level lapse rates will bring local heavy rainfall concerns along with hail, and strong outflow winds over 50 mph. Given the potential east to west development and outflow of these storms, blowing dust will also be a possibility, especially for the main population centers of western Nevada such as Fallon, Fernley, Sparks-Reno, and Carson City. Friday through Sunday morning: * Thunderstorm chances look to decrease Friday as the upper low continues to fill and open into a positive tilted long-wave trough that extends southwest into the Desert Southwest. Concurrently a strong upper ridge begins to build into the far Eastern Pacific and into the western US. A few isolated storms are still possible in the central Sierra south of Lake Tahoe along the Sierra Front. Higher based dry thunderstorms could bring a few cloud-to-ground strikes to the region during the afternoon hours. Upper-level warming and subsidence will begin to strengthen the mid-level CAP over the region, diminishing the thunderstorm potential over region through Sunday. Daytime highs for some lower valley locations could see triple-digit readings as the high pressure spreads over western NV. Sunday through Thursday next week: Ensemble model uniformly messages the onset of strong high pressure building over the Pacific Northwest. A north-south orientated ridge axis will extend over Nevada by this weekend. This will bring together the elements needed for a major heatwave over much of the western US through middle of the work week. Hot summertime above average daytime temperatures will settle over California and western Nevada, with triple-digit readings still possible over western Nevada lower valley locations Sunday into the beginning of the work week. Based on ensemble guidance, record heat during day remains a distinct possibility for our area through midweek with some record higher low temperature values being observed during this period. On the outside chance that the anticipated northward push of monsoonal moisture into western Nevada increases into next week, then accompanying thunderstorms could dampen the hotter daytime temperatures. Any thunderstorm activity will be stifled Sunday and Monday by upper level warming spreading over the region as mid level subsidence slowly becomes the dominating factor over the Sierra and western Nevada. But the North American monsoon looks to be on the horizon as the upper level flow adjusts into a favorable position and opens the gates to increased sub-tropical moisture. Some uncertainty centers as to the timing and strength of the monsoonal push northward into western NV as model guidance offer differing solutions going into the mid-week forecast period. If mid-level moistening does initiate earlier in the week by Monday as shown by some guidance this may inhibit the heat slightly. This early arrival could also bring additional moisture in the area and increase the instability across our region along with the possible return of thunderstorms. -AY && .AVIATION... The forecast is on track for increased thunderstorm coverage this afternoon through this evening. There is a 25-40% chance for seeing a storm impact at any of the terminals. Storms may bring periods of reduced CIGS/VIS and terrain obscuration due to locally heavy rainfall. Hail and gusty/erratic outflow winds in excess of 40 kts also are possible this afternoon with storms. The winds could also produce dust storms. The storms are expected to continue through 04-06z, with potential for a few to linger overnight. Thunderstorm coverage will decrease for Friday as the upper low weakens, but with chances persisting mainly south of I-80. There is a 10-15% chance of a storm across western Nevada south of I-80 and around 25% chance for the terminals of the Eastern Sierra from KTVL south, including KBAN and KMMH. Storm chances are less than 10% over the Sierra this weekend and less than 5% across western NV and northeast CA as a strong ridge of high pressure begins to build over the west. With near record heat possible, density altitude concerns will return this weekend and persist into next week. JCM && .FIRE WEATHER... The forecast is on track for scattered storms to develop this afternoon and persist through this evening with a 25-40% chance for seeing a storm over any particular location. Slow storm motions and plentiful moisture should limit new fire start efficiency, but as always, new starts due to lightning are not out of the question. Storms may also bring gusty and erratic outflow winds in excess of 45 mph. Storms linger Friday, mainly south of I-80, with less coverage compared to today, and should still be on the wetter side of the spectrum. Less than a 10% chance for a thunderstorm for the weekend, as high pressure brings a a warming and drying trend. Near record highs and poor RH recoveries return by Sunday and persist into next week. JCM && .REV Watches/Warnings/Advisories... NV...Excessive Heat Watch from Sunday afternoon through Wednesday evening NVZ001-003>005. CA...Excessive Heat Watch from Sunday afternoon through Wednesday evening CAZ070-071. && $$ For more information from the National Weather Service visit... http://weather.gov/reno