textproduct: NWS Phoenix

UPDATE...Updated 00z 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 likely reaching their peak on Wednesday or Thursday 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 subtropical high, which current 500 mb RAP analysis centers over northern Sonora, remains flattened under broad troughing to our north. Guidance remains in excellent agreement that this troughing in the northern stream will progress from the Intermountain West into the Northern and Central Plains early in the upcoming work week. As this troughing departs, heights aloft will begin to rebound Monday, resulting in a warming trend through the first half of the work week. Ensemble means advertise current H5 heights rising from 590 dam to around 593-596 dam late Monday, with the subtropical high building to our southeast over far Northern Mexico near the AZ/NM and international borders. These H5 heights late Monday represent values around the 96th-98th percentile of climatology. Following one more morning with widespread lows in the 70s, lower desert highs are forecast to rise to between 105-109 degrees on Monday putting the bulk of the area into the Moderate HeatRisk category. The placement of the subtropical high will also switch flow aloft out of the south, supporting an increase of moisture especially for the western CWA beginning Monday. 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 2320Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No aviation weather concerns under some passing high cirrus cloud decks can be expected throughout the TAF period. The overall wind pattern will favor the typical diurnal tendencies with overall speeds aob 10 kts. Some occasional afternoon/early evening gusts in the mid to upper teens will be possible.

Southeast California/Southwest Arizona including KIPL and KBLH: No major aviation weather concerns under some passing high cirrus cloud decks can be expected throughout the TAF period. At KIPL, winds out of the west will prevail into the overnight period before shifting out of the southeast Monday morning. At KBLH, winds will generally fluctuate out of the south-southeast to southwest. Overall wind speeds will remain aob 12 kts along with some minor afternoon/early evening gustiness.

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 the 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...Extreme Heat Watch from Tuesday morning through Wednesday evening for AZZ560.

CA...None.