138 FXUS65 KPSR 100552 AAB AFDPSR Area Forecast Discussion...Updated National Weather Service Phoenix AZ 1050 PM MST Sun Aug 9 2020 .UPDATE...Updated aviation discussion. && .SYNOPSIS... Above normal temperatures and abnormally dry conditions are expected through the coming week. Daily highs across the lower deserts will mainly top out at around 110 degrees through Tuesday before likely warming to between 112 and 114 degrees during the latter part of the week. The dry conditions will at least allow overnight lows to be near seasonal normals. && .DISCUSSION... Little change in the overall theme of the forecast as abnormally hot and dry conditions continue across the region. Water vapor imagery this afternoon showed dry conditions aloft persisting over the Desert Southwest, while the 09/12Z PHX sounding recorded a well below normal PWAT value of 0.82" (~10th percentile). The weak trough located just off the California coast and the subtropical ridge centered over Southern Plains will continue to keep dry southwesterly flow aloft over the region through midweek. Mostly clear skies exist over the deserts this afternoon while temperatures make their climb above 110 degrees. The high temperature so far this afternoon in Phoenix has been 112 degrees, which breaks the record for number of 110+ degree days in a year. Today marks the 34th 110+ degree temperature of this year, breaking the record of 33 days back in 2011. An Excessive Heat Warning is in effect for parts of south- central Arizona, including Phoenix through Monday evening. Thunderstorm chances will remain minimal today (<5%) with any storms that develop remaining confined to the higher terrain of southern Gila County. It's not out of the question for any thunderstorm that develops to produce brief locally heavy rainfall, but overall lack of moisture and instability will limit the occurrence of this. Going forward to Monday morning, guidance suggests the possibility of increasing mid-level moisture with 12Z HREF guidance showing a band of higher PWAT values around 0.90"-1.00" pushing into Maricopa County. As a result, we may see mid-level clouds redevelop over Maricopa County tomorrow morning with a few virga showers not out of the question. Tuesday looks to be the "coolest" day of the week as heights aloft will remain stable as a weak shortwave trough is forecast to move through southern Utah and far northern Arizona. NBM guidance shows temperatures topping out around 108-110 degrees across lower desert locations Tuesday. Meanwhile, the subtropical ridge to our east will migrate westward, allowing for increasing heights and increasing temperatures across the state starting Wednesday. NBM temperature guidance shows temperatures increasing mid through late week with afternoon highs in Phoenix currently forecast to hit 114 degrees by Friday. Operational and ensemble guidance indicates the upper-level ridge strengthening during the latter half of the week with H5 heights climbing upwards of 596 dm over the state. Latest HeatRisk shows high to very high heat risk across much of the CWA during the second half of the week. An excessive heat product will likely need to be issued in the near future if current trends continue. In terms of shower/thunderstorm chances, very limited moisture levels through Friday should keep the entire area dry, but as the high center is shown drifting farther to the northwest, we may be able to finally see some high terrain storm chances by the weekend. && .AVIATION...Updated at 0550Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: The basic weather pattern remains virtually unchanged across the central deserts and as such, there will be very little change in the TAFs going forward for the next 24 hours. Dewpoints have fallen off and although skies have cleared, we may see development of a mid cloud deck after 10z Monday that could be thick enough to generate a few virga showers Monday morning. Bases should be 12-15k feet for the most part. Confidence at the moment not high enough to warrant any precip in the TAFs. Clouds should dissipate by late morning leaving only FEW high based cu decks for the afternoon. Winds will continue to follow typical diurnal patterns with light west winds that gradually become east after 09z. West wind will again develop after 19z Monday with a few gusts into the teens possible late afternoon and early evening. Southeast California/Southwest Arizona including KIPL and KBLH: Dry west flow aloft will persist across the western deserts leading to generally clear skies for the next 24 hours at the TAF sites. Winds to follow similar patterns as the past couple of days. At KIPL expect mostly west wind tonight past 12z Monday becoming southeast by later in the morning. Most sustained speeds 10kt or less. Winds at KBLH will favor the south to southwest with breeziness developing Monday afternoon. May see a few gusts over 20kt at times after 19z Monday becoming light and less than 10kt after 03z Tue. && .FIRE WEATHER... Wednesday through Sunday: Most days will be hot and dry. Minimum humidity values will drop below 15% for almost everywhere while overnight Max RH recoveries mostly top out in the 20-30% range. Winds will generally follow typical diurnal/terrain influences with speeds remaining light aside from some typical afternoon breezes. Thunderstorm activity will be very limited, and non existent through at least the first half of the week. Increasing moisture by Friday/Saturday looks better which may be enough for isolated thunderstorms to form over the higher terrain north and east of Phoenix. && .SPOTTER INFORMATION STATEMENT... Spotters should follow standard reporting procedures. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...Excessive Heat Warning until 8 PM MST Monday for AZZ537-540- 542>544-546-548-550-551-556-560-562. CA...None. && $$ DISCUSSION...Smith/Kuhlman AVIATION...CB FIRE WEATHER...Smith/AD/Kuhlman