Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000 FXUS65 KPSR 272100 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 200 PM MST WED JUL 27 2016 .SYNOPSIS... Despite lingering moisture across the region, strong high pressure will keep thunderstorm activity isolated for the next couple days as well as keeping temperatures unusually hot. As this high pressure system weakens by the end of the week, better moisture profiles will stream north throughout the state. In addition to bringing somewhat cooler temperatures, increased thunderstorm activity will impact the area through at least the beginning of next week. && .DISCUSSION...
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Latest WV imagery shows a well-defined moisture discontinuity between drier air across northern Arizona and moist air across southern AZ. Recent AMDAR flights out of KPHX shows steering flow out of the east and northeast around 10 kt. Model soundings indicate that northeasterly steering flow around the anticyclone to the north will increase to around 20 kt this afternoon, which will be favorable for storms to propagate out of the higher terrain and into the lower deserts. Earlier trends in the CAMs including the HRRR suggested a greater chance for convection in the lower deserts. Most recent trends are not as bullish, however latest satellite imagery does show towering CU developing directly upstream across the Mogollon Rim. Dewpoints remain above average, generally in the upper 50s and lower 60s. Another day of 110+ degrees (25th so far this year) is likely in Phoenix, which will produce MLCAPE between 500 and 1000 J/kg. Some CIN is evident in the latest observed soundings, though the expectation is that this will be mostly eroded once temperatures peak late this afternoon. Above normal PoPs are warranted for this evening across south- central Arizona and points to the east. The strongest storms will be capable of producing brief heavy rainfall, strong to severe wind gusts and small hail. Meanwhile, trajectory is not ideal for a big dust storm, though there is a discernible threat for blowing dust across mainly Pinal County.
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&& .PREVIOUS DISCUSSION... Perhaps the most significant impact over the next 48 hours will be excessively hot conditions manifesting through southeast California and the Lower Colorado River Valley. In addition to strong heights aloft, ensemble means depict the H7 thermal ridge nearing the 99th percentile while best performing guidance suggests afternoon highs peaking near 115F in the population centers of El Centro, Blythe, and Parker today and Thursday. While this isn`t the hottest weather of the summer thus far, it certainly will be dangerous for those outdoors during peak heating; and have issued an Excessive Heat Warning highlighting these larger population centers. All indications suggest Friday being a transition day where heights and temperatures aloft begin to deteriorate while more substantial deep moisture seeps north and west into a larger chunk of Arizona. Forecast soundings still only depict around 9 g/kg boundary layer mixing ratios, however the depth of this moisture may begin to reach above the H7 layer and deeper more organized outflow boundaries may become capable of initiating convection at lower elevations with these type of sounding profiles. Based on SREF probabilities and sounding appearance, not overly enthused about widespread rainfall Friday though it certainly looks like events occurring on Friday evening will set the stage for more activity over the weekend. At this time, its difficult to ascertain which specific day during a Saturday through Tuesday time frame would be more convectively active or provide the most significant impacts. However, all model indications point towards at least one of these days yielding well organized thunderstorms with the potential for isolated severe weather and flooding. Forecast soundings show sfc-H7 mixing ratios markedly improving to 11-12 g/kg while H5 temperature cool to around -6C yielding MLCapes 1000-1500 J/kg which would be readily released by any good inverted trough or deep combination of outflow boundaries. Certainly, there will also likely be one of these days where the environment become convectively overturned and contaminated leading to gross inactivity, though conceptually any one of these days justifies elevated POPs. && .AVIATION...
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South-Central Arizona Including KPHX, KIWA, and KSDL: The best chance of thunderstorms will be this evening between 5 and 8 PM as they track in from the east. Mainly light westerly component winds during the afternoon should turn easterly with gusts of 22 to 28 kts. with any early evening thunderstorms along with variable bkn cigs from 8 to 10K ft. Otherwise expect periodic mid to high level debris cloud cigs. Southeast California/Southwest Arizona including KIPL and KBLH: Expect mostly light to occasionally breezy southerly and westerly component winds along with typical diurnal shifts. Otherwise skies will be clear to partly cloudy with few to sct mid and occasionally bkn high clouds. Aviation Discussion not updated for amended TAFs.
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&& .FIRE WEATHER...
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Saturday through Wednesday... A sequence of Monsoon disturbances from northwest Mexico will help to maintain demonstrable moisture flow over the region throughout the period. As a result, significant chances of scattered wetting rains from thunderstorms from the lower deserts to southern Gila county are expected every afternoon and evening. Maximum temperatures are expected to hold near to slightly below normal. Minimum humidities will range from 22 to 32 percent in the lower deserts to 33 to 50 percent from the Tonto foothills to the high country. Seasonably breezy south to southwest winds in the late afternoons are also likely. Overnight recoveries will be good to excellent.
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&& .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...Excessive Heat Warning until 11 PM MST Thursday for AZZ020. CA...Excessive Heat Warning until 11 PM PDT Thursday for CAZ031>033. && $$ Visit us on Facebook...Twitter...and at weather.gov/phoenix DISCUSSION...Hirsch PREVIOUS DISCUSSION...MO AVIATION...Sawtelle FIRE WEATHER...Sawtelle

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