Area Forecast Discussion
Issued by NWS Phoenix, AZ
Issued by NWS Phoenix, AZ
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031 FXUS65 KPSR 281708 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 1008 AM MST Fri Jun 28 2024 .UPDATE...Updated 18Z Aviation Discussion. && .SYNOPSIS... Above normal temperatures are likely to persist well into next week, with many lower desert communities experiencing high temperatures that approach or exceed 110 degrees each afternoon. Temperatures Sunday are shaping up to be the hottest over the next week resulting in an Excessive Heat Watch for portions of Southeastern California on Sunday and Monday. Unfavorable monsoon conditions are expected through Saturday with only very minimal chances for an isolated shower or thunderstorm east and southeast of Phoenix. Moisture and subsequent rain chances will increase starting Sunday, likely lasting through the middle of next week. && .DISCUSSION... The current synoptic pattern continues to show the elongated sub- tropical ridge stretching across Sonora Mexico northeastward into Texas. An active wave pattern is also seen across the Pacific Northwest into the Northern Plains. Between the two systems, westerly flow will persist across the Desert Southwest today before beginning to shift more out of the south on Saturday as the center of the ridge fully establishes itself over Texas and Oklahoma. The ridge will also quickly strengthen over the weekend, giving a slight boost to our upper level heights and temperatures over our region. Forecast highs this weekend look to rise around a degree a day with Sunday still expected to have the hottest temperatures with highs of 110-114 degrees across the lower deserts. The westerly flow currently over our area continues to bring in drying aloft, but boundary layer moisture has mostly stuck around. We have seen surface dew points drop on the order 10 degrees, but it has not been as much as models had originally forecast. Aside from the mid level drying, the other main deterrent for monsoon activity over the past couple of days has been the strong subsidence aloft provided by the ridge. As the ridge begins to shift eastward today, subsidence will be less of a factor. Now with less than expected CIN today and a little better than previously forecast instability, it seems there may be a slight chance of some showers and maybe a weak thunderstorm across Pinal into northeast Maricopa and southern Gila Counties. NBM PoPs of around 5% do not really represent this potential, but the last several runs of the HRRR are picking up on some weak afternoon convection, especially in Pinal County. Have made some upward adjustments to PoPs to account for this rain potential. Starting Saturday as the ridge becomes established over the Southern Plains, an easterly wave is forecast to progress across northern Mexico likely allowing for considerable convection. Flow in the mid levels will also turn out of the south southeast into Arizona on Saturday. Strong moisture advection is then expected to stream into southern Arizona Saturday night with the help of a likely MCS south of the border. Between the easterly wave likely reaching far southeast Arizona on Sunday and PWATs increasing to around 1.5-1.75", this should provide a good recipe for an active monsoon day Sunday afternoon into Sunday night across much of southeast and south-central Arizona. NBM PoPs of 20-40% are likely underdone for Sunday, but we should have a better idea by this time tomorrow night. If Sunday ends up being active, then Monday should be fairly quiet and there are already signs of this happening within the guidance. The synoptic pattern will remain favorable for monsoon activity into the middle of next week as an unseasonably strong ridge builds off the West Coast and the ridge over the Southern Plains remains in place. There should also be some northern stream wave influence into our area around next Tuesday and Wednesday which would provide for some upper level support for any monsoon thunderstorm activity. Either or both of those days could end up being fairly active across south-central and eastern Arizona. Guidance eventually signals the strong ridge coming ashore into California late next week providing persistent dry northerly flow working through Arizona. This should mostly end rain chances over much of the area by next Thursday for Friday, while temperatures potentially climb toward the 115 degree mark. && .AVIATION...Updated at 1710Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: Overall quiet weather pattern this forecast period, but monitoring a very low chance (10%) of a storm late this afternoon, mainly near KIWA if at all. Typical westerly wind component will develop this afternoon with some local gusts upwards of 20 kts. After 20z, we`ll be monitoring closely any storm development. If it does occur, KIWA would have the best chance to have any impact from these storms for lightning and gusty outflow winds. No impacts to the other terminals is expected. Southeast California/Southwest Arizona including KIPL and KBLH: Winds will follow their typical diurnal patterns through the TAF period. Speeds will generally be aob 12 kt with the exception of some gusty winds this afternoon at KBLH with gusts of 20-25 kt. Skies will remain mostly clear through the TAF period. && .FIRE WEATHER... Unfavorable monsoon conditions today into Saturday will continue to lead to clear to mostly clear skies with only minimal (10%) chances for isolated showers and maybe a thunderstorm across Pinal and Gila Counties. Above normal temperatures will persist with readings running 3-5 degrees above normal. Humidities will continue to drop across the western districts today and likely into south-central Arizona on Saturday with lower desert MinRHs between 15-20%. Humidities over the Arizona higher terrain should stay above 25%. Afternoon breeziness will be common today with gusts reaching to or just over 20 mph in many locations before winds settle down a bit on Saturday. Starting Saturday night, moisture will increase across much of southern Arizona leading to a return of shower and thunderstorm chances on Sunday. Monsoon storm chances should persist through at least south-central Arizona for much of the first half of next week, while humidities rebound to 20-25% across the lower deserts to upwards of 35-40% over the eastern Arizona high terrain. Temperatures next week will remain several degrees above normal each day. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...Excessive Heat Watch from Sunday morning through Monday evening for AZZ530. CA...Excessive Heat Watch from Sunday morning through Monday evening for CAZ562-566-567-569-570. && $$ DISCUSSION...Kuhlman AVIATION...Frieders FIRE WEATHER...Kuhlman