Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000 FXUS65 KPSR 312158 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 258 PM MST TUE MAY 31 2016 .SYNOPSIS... A weak low pressure system will move slowly through southeast Arizona tonight. This will result in a few evening thunderstorms over the Mogollon Rim and White Mountains, and in far southeast Arizona. The low pressure system will move into New Mexico on Wednesday, with a building high pressure system over the region the remainder of the week and weekend. High pressure will result in a strong warming trend with excessive heat forecast for the deserts Friday and the weekend. && .DISCUSSION... The remainder of today and tonight... A very interesting pattern will continue to develop the remainder of this afternoon and evening, particularly with regards to high elevation mountain thunderstorms over the Mogollon Rim and White Mountains. You never like to see a late spring cutoff low, with cool air aloft, move over a very warm boundary layer. This can lead to a deep vertically mixed and turbulent atmosphere with the potential for high based mtn thunderstorms even if meager amounts of moisture are present. Like today for example, afternoon thermals along the Mogollon Rim are still forecast to lift to 22 thsd ft msl. Thermals at Douglas AZ in far southeast AZ will lift to 20 thsd ft msl. Globe/Miami 19.6 thsd ft, Tucson 14.6 thsd, and Phoenix 14 thsd ft. In other words a deeper than normal vertically mixed atmosphere is expected. The Flagstaff morning weather balloon sounding showed a nearly saturated moist layer at 18 thsd ft, and satellite imagery at 2 pm showed an abundance of clouds over the central AZ mountains with a cluster of thunderstorms over the White Mountains just outside our zone 24 southern Gila County. Atmospheric mid level steering currents later this afternoon are still forecast to blow from the northeast, with higher elevation convection being steered toward portions of southern Gila County zone 24. However since the airmass is dry, there is a greater threat for gusty convective outflow boundaries/gusty sfc winds later this afternoon and evening. Gusty convective outflows this time of year in a very dry airmass can theoretically survive into the lower deserts toward Phoenix and Casa Grande. We will keep a watch on this. Furthermore, convective debris clouds at or above 18 thsd ft will spread from the Mogollon Rim south into the lower deserts tonight, toward Phoenix, Gila Bend, and Casa Grande for a relatively warm Wednesday morning. Wednesday and Thursday... The cutoff low over southern AZ will move into southern New Mexico Wednesday, with only a slight threat of afternoon high based convection in the White Mountains of east central AZ. Current forecasts for a slight chance of high based thunderstorms over the higher terrain of southern Gila County bordering the White Mountains are still expected. The big news however is the increasing desert heat Thursday with temps warming into the 107 to 111 degree range. However excessive heat will develop Friday through Sunday. Friday through Monday...Excessive Afternoon Heat is Forecast... A strong high pressure system over the region is forecast to produce some of the warmest temperatures of the season, which is not a surprise for the AZ deserts in June. However forecast temperatures Friday through Sunday, under clear skies, are expected to exceed our excessive heat criteria. Therefore the Excessive Heat Watch issued earlier has been upgraded to an Excessive Heat Warning and extended another day...i.e. Friday through Sunday. && .AVIATION... South-Central Arizona Including KPHX, KIWA, and KSDL: Thunderstorms will remain well north and east of Phoenix terminals this afternoon and evening, however distant outflow boundaries may allow winds to shift back to an easterly direction (with some brief higher gusts) sooner than anticipated. Confidence is low regarding any wind shift timing, and not fully accounted for in this TAF package. Otherwise, only some Sct-Bkn clouds from thunderstorm remnants will pass over air fields with bases AOA 12K ft. Southeast California/Southwest Arizona Including KIPL and KBLH: No aviation concerns for SE CA terminals through Wednesday morning under clear skies. Sfc winds will occasionally be light and variable (especially near sunrise), but in general will favor some sort of southerly directional component. Aviation discussion not updated for amended TAFs. && .FIRE WEATHER... Friday through Tuesday... Unseasonably hot weather will prevail across all districts through the end of this week and early next week with lower elevation locations exceeding 110F on most days, and even elevations near 3000ft close to 100F. Winds through the weekend will not be unusually strong, but still obtain the typical afternoon upslope gusts. Speeds will increase somewhat next week, though remain well below critical thresholds. Regardless given the excessive warmth, any ongoing incidents will be slightly more difficult to manage with these frequent wind gusts and low relative humidity levels falling into a 5 to 10 percent range during the afternoon. Overnight recovery will be mostly fair to poor and little help to any fire suppression. && .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected. && .CLIMATE... Record high temperatures later this week: Date Phoenix Yuma ---- --------- ------ June 2 110 in 2014 115 in 1957 June 3 112 in 2006 113 in 2006 June 4 113 in 1990 114 in 1990 June 5 112 in 1990 115 in 1957 June 6 110 in 2013 114 in 1928 && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...Excessive Heat Warning from 10 AM Friday to 8 PM MST Sunday for AZZ020>023-025>028. CA...Excessive Heat Warning from 10 AM Friday to 8 PM PDT Sunday for CAZ031>033. && $$ Visit us on Facebook...Twitter...and at weather.gov/phoenix DISCUSSION...Vasquez AVIATION...MO CLIMATE...MO FIRE WEATHER...MO

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