Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000 FXUS65 KPSR 222127 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 227 PM MST Wed Mar 22 2017 .SYNOPSIS... A strong low pressure system moving through during the late day into the overnight hours today will bring rainfall chances producing light rainfall amounts as well as significantly cooler daytime temperatures. Isolated thunderstorms are possible mainly west of Phoenix this afternoon the associated cold front moves across the area. Dry conditions and near normal temperatures will return across the Lower Desert elevations for the late week and weekend periods while an active storm track remains over the West. && .DISCUSSION...
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An upper trough continues to move eastward across the California coast this afternoon. A preceding low-level cold front is surging eastward across the Imperial Valley towards the lower Colorado River Valley, with a distinct shift in westerly winds noted in the wake of the front. Visible satellite imagery shows some low-topped convection developing west of Yuma, where stronger heating has occurred between swaths of high-level clouds. A band of mid-upper ascent noted on water vapor imagery is also located over far northern Baja and near the San Diego area and will spread eastward, and should aid in increasing precipitation potential late this afternoon and evening across southeastern California. Hi-res model guidance continues to depict spotty precipitation development across the lower deserts, eventually spreading eastward into south-central Arizona. A few thunderstorms are also possible given meager destabilization amidst modestly steep lapse rates aloft. With low-level winds quickly veering overnight and tomorrow morning in the wake of the fast-moving front, the temporal window for favorable upslope precipitation enhancement should remain fairly limited. As a result, still forecasting generally light storm-total rainfall totals area-wide with lower desert locations generally under 0.15 inch, while 0.25-0.50 inch is possible in higher terrain locations. The other short-term forecast impact will breezy westerly winds, which will persist into Thursday across the entire forecast area. Currently not expecting widespread advisory-level winds, with wind gusts of 20-25 mph forecast for tomorrow, but locally stronger winds are possible especially across parts of southeast California. Precipitation chances will continue into tomorrow mainly north and east of Phoenix as the storm system quickly shifts eastward, but only spotty light showers are expected. Drier air will overspread the region as the upper trough shifts into the Great Plains, but only modest warming will occur through Friday as midlevel ridging will remain transient ahead of another upper trough. However, with the progressive pattern, moisture return associated with this system will be quite limited, with the highest precipitation chances remaining across the higher terrain of central and northern Arizona, with only light showers at best across the lower deserts.
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&& .AVIATION...
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South-Central Arizona Including KPHX, KIWA, and KSDL: Winds will be the primary aviation concern this afternoon and evening with westerly gusts between 20 to 30 kts. The winds will stay primarily out of the west although there may be some temporary variability in wind direction due to passing showers late tonight and early Thursday. However, there is no tempo group for these changes due to uncertainty regarding the timing and duration of any variable winds. The aforementioned showers will likely move through the terminal between 8z and 14z. Decided to leave as VCSH in the TAFs at this time although any showers late tonight should be brief and light. There is the potential for cigs around 6K ft (and mountain obscuration) to impact the terminals as showers pass through. Southeast California/Southwest Arizona Including KIPL and KBLH: Strong and gusty winds will prevail through the area for much of the day with gusts approaching 30 kts. The stronger winds near Imperial may cause blowing dust that could also reduce visibility. In addition, there is potential for showers, a thunderstorm, and ceilings to drop below 6K ft during the afternoon and early evening. Aviation discussion not updated for amended TAFs.
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&& .FIRE WEATHER... Friday through Tuesday... Temperatures will moderate back towards the seasonal normal over the weekend as high pressure and dry weather build back into the region. Breezy weather will be common through most of the districts, especially Saturday and Monday afternoon. Despite the stronger winds and drying trend, humidity levels will be manageable only falling into a 15-30 percent range. Overnight recovery will be good to excellent. Periods of stronger winds may lead to a locally elevated fire danger at times, but critical conditions should not be breached. && .SPOTTER INFORMATION STATEMENT... Spotter reports will not be needed through the weekend. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...None. && $$ Visit us on Facebook, Twitter, and at weather.gov/phoenix DISCUSSION...Rogers AVIATION...Deemer FIRE WEATHER...MO

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