Area Forecast Discussion
Issued by NWS Phoenix, AZ

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161 FXUS65 KPSR 281046 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 346 AM MST TUE JUN 28 2016 .SYNOPSIS... High pressure will move somewhat north and east of Arizona this week allowing warm temperatures to prevail, but also bring a couple of weather disturbances through the state. An increase in monsoon moisture will accompany these weather systems providing a threat of afternoon and evening showers and thunderstorms the remainder of week. && .DISCUSSION... Numerous circulations and a few outflows are present on this AM`s IR/WV imagery, fairly typical this time of year between inverted wave advection, remnant convective meso-lows and gravity waves. Lingering light shower activity has exited the forecast area to the northwest, heading into Mohave and Yavapai Counties this early AM. Widely isolated showers are still drifting westward on Tucson`s radar near a localized meso-low and along the northwestern flank and deformation zone of a larger inverted wave over Chihuahua and Sonora sampled best at the 500mb level. Vertically speaking, the anticyclonic circulation placement throughout the significant levels (i.e. 700mb, 500mb, 300mb) is really all over the map, with the 700mb circ east of the Rockies, 500mb over the Great Basin and the UL centers well to our south over Mexico. The upper difluence observed last evening over N AZ doesn`t appear to be as great tonight however advection of favorable ML lapse rates down along portions of the Rim are part of today`s set-up. Several Hi-Res models develop storms over the Rim again today with several solns pointing to a more organized outflow intrusion from the northeast around or post 29/00z (5 pm local) into Phoenix. While always a concern during the Monsoon, northeasterly outflows into Phoenix aren`t typical dust producers. What could lead to blowing dust later into the evening would be the propagation of storm activity along intersecting outflows surviving into the lower desert elevations. PoP chances go as far west as the Colorado River Valley and Southwest AZ Deserts, with drier conditions in terms of PoPs but not much by way of humidities for the western forecast zones. Broader anticyclonic flow and a drier atmospheric column will support much warmer-than-normal temperatures for portions of southeast CA, especially for the Imperial Valley today and Wednesday. Conditions look to just escape Excessive Heat Warning criteria today, but may develop for Wednesday. It`s tricky this time of year to gauge if long-traveling outflows or MCVs could import moisture or cloud cover to limit the diurnal curve, so will hold off as upstream moisture and convective activity today over AZ could work in SE CA`s favor for temperatures Wednesday. Increasing Monsoon moisture levels and persistent inverted wave breaking through the 700-500mb level will introduce deeper moisture and additional dynamics to promote better chances for showers and storms over the lower AZ deserts each day through the end of the work week. Peak of the moisture and wave activity looks to be Thursday into Friday, with significant enough cloud cover and potential for rain-cooled air to cool forecast highs Friday across the south- central AZ deserts into the upper 90s to low 100s. Gridded sky cover guidance and several moisture fields (mixing ratio, humidities, dewpoints) indicate a tight gradient lying in the vicinity of the CO River Valley. While debris clouds are possible, increasing southwesterly flow may prevent significant cloud cover development west of the River and keep temperatures near normals through the end of the week. Beginning Saturday, low pressure will take shape over the Pac NW, shifting the 500mb circulation further to our east/southeast and allowing for stronger southwesterly steering flow to transition through the area. Dry air advection from the Pacific results, relegating the slight chances for the precip to the eastern AZ mountains and out of the lower desert elevations. Under clearing skies temperatures will see a warm-up, compared to those observed at the end of the work week, and return to normal and seasonable values by the Fourth of the July holiday. && .AVIATION... South-Central Arizona including KPHX, KIWA, and KSDL: Lower confidence forecast as several competing outflow boundaries will create frequent wind shifts through the evening, before settling on a predominant easterly direction overnight. There is a fairly low chance of blowing dust making it into the Phoenix terminals and lesser chance of actual storms impacting the terminal sites. Easterly sfc winds should prevail much longer into the late afternoon Tuesday than is typical. Southeast California/Southwest Arizona including KIPL and KBLH: Wind shifts will be the main forecast challenge in SE CA through tonight as outflow boundaries move into the region from AZ. Brief gusts will be possible at KBLH, but likely minimal impact at KIPL. Periods of variability in sfc winds will be likely overnight, then favor a southerly component Tuesday afternoon. Periodic cloud decks 12K-15K ft will be common across the region. Aviation discussion not updated for amended TAFs. && .FIRE WEATHER... Thursday through Monday... Temperatures will continue to cool with highs in the 100-110F range by Sunday. Monsoon moisture levels continue to increase over the region with slight chances for isolated afternoon thunderstorms. The best chances for convective weather remains over the mountains in central and eastern Arizona. Any storms that develop have the ability to produce lightning, gusty winds, and wetting rains. Daytime relative humidities will drop to 15-25 percent but will have nighttime recoveries. Otherwise, winds will be relatively normal in the 5 to 15 mph outside of any storm influenced winds. && .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...None. && $$ Visit us on Facebook...Twitter...and at DISCUSSION...Nolte AVIATION...MO FIRE WEATHER...Deemer is the U.S. government's official web portal to all federal, state and local government web resources and services.