textproduct: NWS Phoenix

UPDATE

Updated Aviation Discussion

KEY MESSAGES

- A pronounced warming trend will continue this week resulting in a period of well above normal temperatures.

- Widespread moderate HeatRisk will develop over the weekend with isolated major HeatRisk early next week.

- Monday should be the warmest day next week with lower desert high temperatures peaking between 105 and 110 degrees.

SHORT TERM /Today through Saturday/

An innocuous, moisture starved closed low and vorticity center continues to propagate across northern Sonora early this afternoon as pronounced East Pacific ridging slowly builds towards the SW Conus. The former feature has restricted more rapid warming with H5 heights holding in a 574-578dm range, while the latter will boost heights above 582dm by the weekend resulting in a marked increase in temperatures. Ensemble numerical spread is extremely narrow yielding excellent forecast confidence of daily highs reaching around 10F above normal Friday, then 10F-15F above normal Saturday. Given the very dry airmass in place, nocturnal cooling will be far more efficient with morning lows only a few degrees above normal. Otherwise, strong high pressure ridging will preclude any rainfall chances, much less appreciable cloud cover.

LONG TERM /Sunday through Thursday/

As ridging fully envelops the Southwestern U.S. this weekend, H5 heights are projected to rise even further 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 nearing high temperature thresholds.

As peak heights occur on Monday, temperatures are forecast to rise to 105-110 degrees out west to 104-108 degrees around the Phoenix metro. For this time of year, this would result in daytime max temperatures in a major HeatRisk category, but overnight lows will still be quite mild (minor HeatRisk). As a result, the total HeatRisk mostly falls within the (high-end) moderate category, but with localized major areas on Monday. Ensemble probabilities of major HeatRisk are sufficient through western Imperial County to justify an Extreme Heat Watch Sunday and Monday. Other considerations were given to the Phoenix metro, however the limited areal expanse of major HeatRisk temporally limited to Monday, along with cooler overnight lows and fact that the region has already experienced prolonged, anomalously warm temperatures above 100F this season are arguments against heat headlines. However, if forecast temperatures (particularly low temperatures) increase a few more degrees, headlines may become necessary.

Models 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 2325Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No major aviation concerns are expected during the TAF period. Winds will continue to favor light and diurnal trends, with periods of VRB to calm conditions, mainly during directional shifts. Other than a FEW distant mid-level bases and passing high cirrus, skies will be mostly clear.

Southeast California/Southwest Arizona including KIPL and KBLH: No major aviation concerns are expected during the next 24 hours. Outside of periods of variability, winds should favor some degree of a W'rly component. Speeds will be generally light through tonight, but a brief window of gusts around 20 kt at KIPL cannot be ruled out. Mostly clear skies will be common through Friday 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...Extreme Heat Watch from Sunday morning through Monday evening for CAZ562-563-566.