Sunrise 5:37 AM   Sunset 8:00 PM Moonrise 3:13 AM   Moonset 6:25 PM

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FXUS65 KPSR 030507 AFDPSR

Area Forecast Discussion National Weather Service Phoenix AZ 1005 PM MST Tue Jul 2 2024

UPDATE
Updated Aviation

SYNOPSIS
Enough moisture will still be present through Wednesday to generate some afternoon convection over the higher terrain areas. Starting on Thursday and continuing into the weekend and through most of next week, as strong high pressure builds over the region, much drier air will result near zero storm chances. Along with the drier air will come hotter temperatures as highs across the lower deserts are expected to top out at 115+ degrees, resulting in excessive heat conditions.

DISCUSSION
Latest water vapor satellite imagery as well as streamline analysis currently show a trough situated over the northern Plains with a strong ridge of high pressure off the California coast. Our region is currently under southwesterly flow aloft as a result of the trough to the north and thus drier air is gradually making its way eastward into Arizona. This is reflected well in the latest SPC mesoanalysis which shows PWATs across south-central AZ ranging between 1.1-1.5", which is a significant drop from the near 2" that was present yesterday. Despite this drop in moisture, enough will still be present to allow for the development of afternoon convection across the higher terrain areas east of Phoenix. Gusty winds and localized heavy rainfall will continue to be the main threat with the storms. Although the south-central AZ lower deserts are expected to be spared from storm activity, outflows emanating from the higher terrain activity may still make its way into the lower deserts with the latest HRRR indicating about a 30% chance of winds of 35+ mph. Heading into Wednesday, as the aforementioned ridge of high pressure off the Pacific moves closer to the California coast, the overall flow will switch out of the north, which will push in drier air with PWATs across south-central AZ dropping to around 1". This will decrease storm chances even further across the higher terrain areas with NBM PoPs below 20%.

Starting on Thursday and continuing through the upcoming weekend, as the ridge settles over California/Nevada, northerly flow will scour out any lingering boundary layer moisture, which will essentially end storm chances. The main concern then switches over to the excessive heat. 500 mb height fields are expected to build into the 594-597dm range. This will result in hotter temperatures with a lot of the lower desert communities forecast to see temperatures rise to near 115 degrees, with the potential for some of the western deserts to approach 120 degrees. This will result in a more widespread areal coverage of major HeatRisk. Excessive Heat Warnings are in effect for all of southeast CA with an Excessive Heat Watch in effect for southwest and south-central AZ (expected to be upgraded to a warning within the next 12-24 hours). Therefore, given the excessive heat conditions expected to materialize, it is very essential for anyone planning outdoor activities during the Holiday Weekend to take all the necessary heat precautions to avoid any heat-related illnesses.

Heading into next week, ensembles are in excellent agreement in showing the ridge parked over the Great Basin Region, with a dry northerly flow persisting through the majority of next week. Thus, storm chances will continue to remain null with excessive heat conditions continuing as highs across the majority of the lower desert communities remain or even exceed 115 degrees. The excessive heat headlines remain in effect through next Tuesday, however, there is potential that it may need to be extended even further in time in the following days.

AVIATION
Updated at 0505Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: No significant weather issues will exist through Wednesday night with cloud decks concentrated mainly over higher terrain areas east of the terminals. A long traveling outflow will induce an easterly component across the metro around midnight with good confidence that directions will revert back to a westerly direction much earlier than usual mid/late Wednesday morning. Occasional gusts 15-20kt will be common again during the afternoon/early evening. Storms and outflow winds should not be an issue for the metro aerodromes Wednesday.

Southeast California/Southwest Arizona including KIPL and KBLH: No major weather issues will exist through Wednesday night under clear skies. Confidence is good that winds should revert to a S/SE direction overnight with variability likely becoming more common towards sunrise. Only modest occasional afternoon/evening gusts should be experienced Wednesday with typical veering to a SW direction during the evening.

FIRE WEATHER
Drier conditions will continue to filter into the region over the next few days. Isolated afternoon showers and a few thunderstorms are expected this afternoon over the Arizona higher terrain with chances on Wednesday even lower. As conditions continue to dry out, even hotter temperatures are expected, especially later this week.
Humidities will drop considerably today over the majority of the area. The lower deserts will see MinRHs mostly fall to around 15%, while higher terrain areas east of Phoenix will see 25-35%. Winds will follow diurnal trends, occasionally gusting to 20 mph during the afternoon hours. Starting Thursday, essentially all of the monsoon moisture will get ejected from the area leaving very dry and hot conditions, likely well into next week. MinRHs starting Thursday will mostly be between 10-15% over the lower deserts to 15-20% over higher terrain areas. The dry air will also end any rain chances during this time. Temperatures are expected to climb to well above normal by Thursday with lower desert highs between 112-120 degrees.

PSR WATCHES/WARNINGS/ADVISORIES
AZ...Excessive Heat Warning until 8 PM MST Tuesday for AZZ530.

Excessive Heat Watch from Thursday morning through Tuesday evening for AZZ531>544-546-548>551-553>555-559.

CA...Excessive Heat Warning until 8 PM PDT Tuesday for CAZ562-566-567- 569-570.

Excessive Heat Warning from 10 AM Thursday to 8 PM PDT Tuesday for CAZ560-561-563>565-568.

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