textproduct: NWS Phoenix

UPDATE

Updated Aviation Discussion.

KEY MESSAGES

- A pronounced warming trend will persist into the weekend leading to well above normal temperatures starting Friday.

- Expect lower desert highs topping 100 degrees as early as Friday before peaking between 105 and 110 degrees early next week.

SHORT TERM /TODAY THROUGH FRIDAY/

A quiet weather pattern is settling in across the Western U.S., including the Desert Southwest with the only forecast concern through next week entailing the widespread Moderate to localized Major HeatRisk developing early next week.

In the near-term, the lingering closed low which has no moisture left to even produce clouds will continue to drift eastward across northern Mexico through tonight. Despite the near proximity of the closed low, upper level ridging is already taking over across the Desert Southwest with H5 heights gradually rising toward 580dm. Under clear skies and rising heights today, temperatures will warm substantially from yesterday reaching the mid to upper 90s across the western lower deserts to the mid 90s in the Phoenix area. Once the closed low finally moves far enough away on Friday, H5 heights of 581-583dm should be realized leading to daytime highs topping out in the 101-104 degree range across southeast California to around 100 degrees in the Phoenix area. These hot temperatures will translate to a fairly widespread Moderate HeatRisk starting Friday.

LONG TERM /SATURDAY THROUGH WEDNESDAY/

As ridging fully takes over across the Southwestern U.S. starting Saturday, the stronger parent ridge will be nearing the California coast before eventually moving over our region late Sunday into Monday. H5 heights are projected to rise even further during this time reaching 585-588dm on Sunday before peaking as high as 589-591dm Monday. The strength of this ridge would fall around 97-99% of climatological records for the period likely pushing temperatures close to records.

The latest NBM forecast highs have increased by a degree or two on Sunday and Monday, while lowering slightly for Tuesday. Sunday's highs are expected to reach 105-108 degrees across southeast California and southwest Arizona to 103-106 degrees in the Phoenix area. As peak heights occur on Monday, temperatures are forecast to rise to 108-110 degrees out west to 106-108 degrees in Phoenix. For this time of year, this would easily result in daytime max temperatures into the Major HeatRisk category, but overnight lows will still be mild (Minor HeatRisk). As a result, the total HeatRisk mostly falls within the (high-end) Moderate category but with some localized Major areas showing up on Monday. Considering some minor uncertainty remains, we are still holding off on any Extreme Heat headlines. However, any further boost in forecast temperatures is likely to put it over our typical threshold for a Watch. Either way, this next heat event will be at least on par with the mid March event but more likely even a couple degrees hotter. Models then mostly favor a slight decrease in heights going into the middle of next week, largely due to a weak cut-off low that is likely to develop west of Baja before moving northward along the coast of California. This should begin a slow cooling trend starting next Tuesday, but the above normal temperatures are expected to persist through the rest of next week.

AVIATION

Updated at 1128Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No major aviation weather concerns are expected during the TAF period. Winds will favor light and diurnal tends, with extended periods of VRB to calm conditions this morning. Confidence in timing of the W'rly wind shift at KPHX is medium as there may be additional extended variability midday through early afternoon. Skies will be mostly clear.

Southeast California/Southwest Arizona including KIPL and KBLH: No aviation weather concerns are expected during the next 24 hours under mostly clear skies. Outside of periods of VRB to calm conditions, winds will mostly range between the WSW and NW at KIPL, while KBLH sees window of N/NE flow this morning and and may continue to slowly veer clockwise to a S/SW by this evening.

FIRE WEATHER

High pressure building into the region will lead to much warmer temperatures and continued low RHs into the weekend. Highs will reach well into the 90s today before topping 100 degrees by Friday or Saturday. Expect MinRHs from 7-12% each day through at least the weekend. Winds will remain relatively light for much of the period, but some afternoon breeziness with gusts to around 20 mph is likely. The combination of the very low RHs and breezy conditions likely focused during the late afternoon hours on Friday and Saturday may result in elevated fire weather conditions for portions of the area. Hot and dry conditions will continue to prevail into next week with afternoon breeziness and elevated fire weather conditions still a possibility each day.

PSR WATCHES/WARNINGS/ADVISORIES

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