textproduct: NWS Phoenix

UPDATE

Updated 18Z Aviation Discussion.

KEY MESSAGES

- Temperatures will slowly rise to above normal levels over the next few days creating widespread Moderate Heat Risk by Tuesday.

- Strong high pressure will peak across the region midweek with daytime highs reaching their peak on Thursday at between 110 to 114 degrees across the lower deserts.

- Localized Major Heat Risk will be possible on Wednesday and Thursday before a cooling period begins starting Friday.

SHORT TERM /TODAY THROUGH MONDAY/

The not so hot temperatures over the past couple of days has been due to a slow moving trough passing to our north, but that system is about to eject into the Central and Northern Plains. As this occurs later today into Monday, the subtropical high centered just to the south of Arizona and New Mexico will shift northward fully into our region. Temperatures will respond slightly today with readings a degree or two warmer than yesterday, before becoming more noticeably hot beginning Monday. Additionally, as the high center moves closer to our area it will shift our winds out of the south beginning tonight allowing for some moisture to seep northward off the Gulf of California. Between the rising heights from the high pressure ridge gradually raising temperatures and the increasing humidities, the air will become much more uncomfortable starting Monday. Daytime highs are forecast to rise to between 105-109 degrees on Monday putting the bulk of the area into the Moderate HeatRisk category. The increasing humidities will have a bigger impact on overnight temperatures starting Monday night with lows staying above 80 degrees in the Phoenix area to only down in the mid 70s for rural desert locations.

LONG TERM /TUESDAY THROUGH SATURDAY/

The main forecast concern for the rest of the coming week is the potential for Major HeatRisk to develop across portions of the area as early as Wednesday and remaining a possibility through Friday. Guidance is in good agreement showing the subtropical high strengthening into Wednesday, likely reaching peak H5 heights of 595-597dm late Tuesday and Wednesday. Additional Gulf moisture surges are also expected Monday night and Tuesday night increasing low level moisture enough to potentially bring some isolated showers and thunderstorms starting Tuesday across southwest Arizona and southeast California. The highest PoPs are between 10-15% across the higher terrain areas of southwest Arizona, while chances should remain well below 10% across south- central Arizona due to the stronger subsidence closer to the high center.

Models are somewhat trending away from even higher heights that looked possible a couple of days ago, but they are still right near the threshold of potentially needing Extreme Heat headlines. The latest NBM still shows some very localized Major HeatRisk developing by Wednesday before reaching its peak coverage of roughly 20-30% of the lower deserts on Thursday. Forecast highs are also 1-2 degrees lower than previously advertised with peak readings of 111-114 degrees on Thursday. Due to the remaining uncertainty in the strength of the ridge, we will hold off for now on any Extreme Heat Watches. Models are also now trending toward a quicker decline in heights later this week, starting as early as Wednesday night. Heights are favored to slowly decrease on Thursday and likely continuing through next weekend as another trough is forecast to pass by to our north. Daytime highs should fall below 110 degrees by Saturday and potentially go back into the normal range by next Sunday. Moisture levels are also expected to begin to drop off starting Thursday with any isolated convective potential disappearing by Friday.

AVIATION

Updated at 1740Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No aviation weather concerns expected throughout the TAF period. The overall wind pattern will continue to follow the typical diurnal tendencies with overall speeds aob 10 kts. Some occasional afternoon/early evening gusts into the mid/upper teens will be possible once again. Clear skies will persist this afternoon before FEW-SCT high cirrus cloud decks move in this evening before clearing out again late tomorrow morning.

Southeast California/Southwest Arizona including KIPL and KBLH: No major aviation weather concerns expected throughout the TAF period. At KIPL, expect winds to shift out of the south this afternoon and then back out of the west this evening. At KBLH, winds will generally fluctuate between the south and southwest. Overall wind speeds will generally remain aob 10 kts along with some minor afternoon/evening gustiness becoming light a variable tomorrow morning. Clear skies will persist into this afternoon before FEW- SCT high cirrus cloud decks move in this evening.

FIRE WEATHER

Near normal temperatures and very dry conditions will continue through Monday with fairly light winds. MinRHs will be in the single digits each day, while overnight recoveries will be poor, ranging between 15-35%. Some afternoon and early evening upslope breeziness will be common, but gusts will mostly stay below 20 mph. Even with the light breezes, the very low RHs should still lead to elevated fire weather conditions during the latter half of the afternoon/early evening hours. Going into the middle part of next week, moisture will improve raising MinRHs to between 10-15% by Wednesday, but temperatures will also warm to above normal. Daytime breeziness should also increase with more gusts reaching the 20-25 mph range.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...None. CA...None.