Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000 FXUS65 KPSR 041130 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 430 AM MST Thu Mar 4 2021 .UPDATE.. Aviation discussion update. && .SYNOPSIS... Cooler air will settle into the region today with highs dropping back to slightly below normal readings. Increasing high pressure into Friday will however bring a quick return to above normal temperatures and highs in the lower 80s, lasting through the weekend. A more unsettled weather pattern is likely for at least the first half of next week, but rain chances on any particular day remain fairly low. This pattern should also lead to a cooling trend early next week with temperatures falling to slightly below normal by next Tuesday or Wednesday. && .DISCUSSION... The strong upper level low that brought fairly widespread windy conditions yesterday continues to track northeastward with the low center about to enter southern Utah. Farther south into central Arizona, weak wrap around moisture and lingering system dynamics are bringing some isolated light showers mainly over the high terrain north of Phoenix. This shower activity will likely diminish completely by sunrise, with the lower deserts very likely seeing nothing but a few very isolated light showers. Upper level ridging will begin to move in from the west later today, but the cooler air behind the exiting upper level low will keep highs right around 70 degrees. Drier and warmer air will eventually mix down to the surface beginning Friday as the ridge axis slowly moves through Arizona. This should give around a 10 degree boost in temperatures with highs likely topping 80 degrees over the lower deserts. Although this ridge is shown to break down slightly into the weekend as a decaying shortwave trough moves through the Great Basin, the warm air mass will stay put allowing high temperatures to remain in a 80-85 degree range. Both weekend days show around a 40% probability of Phoenix reaching 85 degrees. Starting Sunday, there is good model agreement showing a deep northern Pacific trough diving southward off the NW U.S. coast. This trough is likely to result in increasing southwesterly flow into the Desert Southwest starting Sunday, as well as a decent stream of upper level moisture moving into our region later Sunday. This slug of moisture should then result in a fairly cloudy Sunday night through Monday period, but forecast soundings show very dry air remaining below 15K feet. The cloudy skies Monday are likely to hamper temperatures somewhat and this is shown in forecast highs dropping into the 75-80 degree range. For Tuesday through the middle of next week, the ensemble cluster analysis shows the deep Pacific trough slowly digging southward to off the California coast before eventually tracking eastward into the Great Basin and/or our region maybe starting on Wednesday. The model spread mainly involves slight timing as well as minimal strength and depth differences. Overall, for being 5-7 days out, there is fairly good agreement among the majority of the ensemble members. This shows the most likely scenario to be a cooling trend through the middle of next week and likely at least a period of minimal rain chances, probably no earlier than Wednesday. At this point, neither the GEFS or the EPS really shows any decent chances for widespread rainfall for this next unsettled weather pattern. && .AVIATION...Updated at 1130Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: SCT clouds around 10kft will gradually decrease through the morning, but a modest return could happen this afternoon. Wind fields will be light today but we should see typical east-west direction changes occur during the afternoon and evening. Southeast California/Southwest Arizona including KIPL and KBLH: SCT clouds around 8kft will persist a few more hours then decrease during the late morning hours. Winds will remain light through the forecast period. && .FIRE WEATHER... Saturday through Wednesday: Modest high pressure will dominate the region through the weekend bringing continued dry and warm conditions. Daily highs of 80-85 degrees are expected over the lower deserts this weekend with increasing clouds on Sunday. Winds will occasionally be breezy this weekend, but gusts will mostly remain below 20 mph. A more unsettled weather pattern is likely for the first half of next week with gradual cooling temperatures and breezier winds, but fairly dry conditions are likely to prevail. Minimum afternoon humidities are likely to fall into the teens most days during the period. && .SPOTTER INFORMATION STATEMENT... Spotters should follow standard reporting procedures. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...None. && $$ DISCUSSION...Kuhlman AVIATION...Iniguez FIRE WEATHER...Kuhlman

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