textproduct: NWS Phoenix

KEY MESSAGES

- Hot temperatures will continue through the rest of this week resulting in areas of major Heat Risk and Extreme Heat Warnings through Thursday across lower desert locations.

- Chances for showers and thunderstorms will also continue over higher terrain areas of eastern Arizona today and to a lesser degree for Thursday and Friday.

- The weather pattern will become very favorable for moisture import and more widespread thunderstorm activity by early next week.

SHORT TERM /Today through Thursday/

A modestly strong high pressure ridge continues to impact the region bringing hot temperatures and areas of Major HeatRisk. The ridge is becoming more elongated with a new ridge center forecast to form off the coast of southern California later today. Despite this subtle shift, H5 heights over the Desert Southwest will remain stable between 593-596dm through most of Thursday. Forecast highs peak today and/or Thursday across the region, ranging from 110-114 degrees across the south-central Arizona lower deserts to 112-117 degrees across southeast California and far southwest Arizona. Overnight lows will also be very uncomfortable as low level moisture has increased enough to prevent efficient nocturnal cooling. Lows over the next couple of nights will range from around 80 degrees over the cooler rural lower desert areas to as warm as the lower 90s in central Phoenix. Extreme Heat Warnings remain in effect for the bulk of the area through Thursday evening.

Moisture within the region has improved since last week, but it mostly lies on the eastern fringes of the ridge as dry air continues to advect northeastward through southern California into the western 2/3rds of Arizona. Moisture profiles across the area are expected to remain stable today, but then somewhat decrease Thursday into Friday. Today's daytime convection should be very similar to what occurred yesterday with most of the scattered showers and storms remaining east of the Globe area, but another modest outflow is likely to form and attempt to push into eastern portions of the Phoenix area. Decreasing shower and storm coverage is then expected for Thursday as moisture decreases slightly and the upper level pattern becomes less favorable for deeper convection.

LONG TERM /Friday through Tuesday/

The weather pattern will undergo a noticeable shift Friday and through the weekend as the high pressure ridge quickly tracks northeastward, with the center reaching Utah Saturday. The ridge is then forecast to expand, strengthen, and become the main driver of strong moisture advection back into the Desert Southwest going into next week.

Friday should be another mostly dry day with hot temperatures still being the main concern across the area. Forecast highs are shown dipping a couple of degrees, but lower desert highs are still likely to top 110 degrees with small pockets of Major HeatRisk remaining, mainly across southeast California. Very limited convective potential on Friday should be confined to southeast Arizona with less than 10% PoPs across our CWA.

As the high center finally shifts to our north into Saturday, it should first open up eastern and southern Arizona to an easterly moisture fetch. Moisture is still likely to be fairly limited on Saturday with afternoon convection currently favored more across southeast Arizona, but once the steering flow shifts out of the east moisture advection and storm chances are expected to spread westward through the rest of Arizona starting Sunday. Although forecast uncertainty remains fairly high going into next week, ensembles generally agree we will enter a period of active monsoon weather. The subtropical high is favored to stay positioned over the Northern Plains into the Central Rockies for much of next week which will allow for fairly persistent moist easterly flow into the Desert Southwest. Ensemble member forecast PWATs show a wide spread, but also a meaningful average increase likely pushing past 1.3-1.4" starting Sunday. Forecast PoPs increase into a 20-40% range starting Sunday and generally stay there through the first half of next week. Any notable easterly waves moving through the flow will surely help drive our convective potential, but pinpointing those this far out is a dubious proposition. Outside of the expected increase in monsoon storm activity, temperatures should slip further toward seasonal normals.

AVIATION

Updated at 0900Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:

Gusty outflow winds this evening from distant storms will be the main aviation weather issue throughout the TAF period. Through this afternoon, the overall wind pattern will follow the typical diurnal tendencies with light easterly to variable winds early this morning shifting out of the west by the mid/late morning hours with some occasional afternoon gusts in the upper teens to around 20 kts. Thereafter, thunderstorm activity materializing well to the east and southeast of Phoenix is likely to send an outflow boundary from the south and east early this evening with potential peak gusts between 20-25 kts. Winds should diminish a few hours after the outflow passage with easterly winds prevailing through the overnight hours. FEW mid to high level clouds will persist through the TAF period.

Southeast California/Southwest Arizona including KIPL and KBLH:

No major aviation weather concerns under clear skies can be expected throughout the TAF period. At KIPL, southeasterly winds will prevail throughout most of the period with the exception of a temporary shift out of the west early this evening. At KBLH, winds will generally fluctuate between the south-southeast to south-southwest with occasional afternoon gusts between 20-25 kts.

FIRE WEATHER

Gusty and erratic thunderstorm winds with isolated lightning over the far eastern districts the next few afternoons will be the main fire weather concern. Outside of any potential outflows, winds should favor light and diurnal trends with typical afternoon breeziness around 20 mph. Afternoon RH values between 10-15% will be common across the region. Overnight recoveries will offer only limited to modest relief as MaxRH values range generally between 20- 45%. Temperatures are expected to run well above normal through the middle of the week, with the lowest elevations reaching between 110- 115 degrees. A decrease in monsoon activity is likely late week, before picking up again and becoming more widespread by early next week. Moisture levels and humidities should also improve considerably by early next week, alleviating much of the fire weather concerns.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Extreme Heat Warning until 8 PM MST Thursday for AZZ530>534- 536>551-553>555-559-560-562.

CA...Extreme Heat Warning until 8 PM PDT Thursday for CAZ562-564>570.