textproduct: NWS Phoenix

KEY MESSAGES

- Temperatures will continue to warm through the weekend and into next week, reaching above normal levels by around Monday. - As the heat builds, it will lead to increasing coverage of Moderate Heat Risk and highs eventually reaching 110 degrees next week.

- Dry conditions will prevail through the weekend, although a sprinkle cannot be ruled out Saturday into Sunday, before isolated storm chances return over the Arizona high terrain by the middle part of next week.

SHORT TERM /TODAY THROUGH SUNDAY/

The subtropical high pressure ridge is slowly working its way into the Desert Southwest from the southeast as the trough which has brought cooler than normal weather lately shifts to the north. Additionally, a weak tropical system is also present centered 900 miles west of southern Baja. The atmosphere for our region remains unseasonably dry at the moment with PWATs as low as 20% of normal for early July. However, this will begin to change later today as a good amount of upper level moisture begins to advect northward into our region. High level clouds are forecast to spread into the area by late morning, but they should remain fairly thin today, likely not impacting temperatures much. The rising heights from the ridge taking over will however lead some warming, pushing daytime highs this afternoon to between 103-107 degrees.

Fairly expansive high clouds will continue tonight into Saturday with cloud decks eventually lowering and thickening during the latter half of the day. Models are also advertising an upper level trough axis swinging northward through our region later on Saturday, associated with what's left of the rapidly decaying tropical system off the coast of California. Weak vorticity associated with the trough axis, along with a more focused moist layer between 13-16K feet, should bring some virga showers Saturday afternoon/evening leading to some sprinkles at times. Can't completely rule out a very light localized shower or two and possibly some brief gusty winds from these showers, but no measurable rainfall is expected. The temperature forecast for Saturday is of lower than typical confidence due to the cloud cover. The NBM is calling for another 103-107 degree day, but it would not be surprising if we fall short by as much as 2 or 3 degrees due to the lower amount of insolation.

Sunday's weather looks to be even less exciting as the trough axis lifts to the north leaving increasing subsidence and diminishing cloud cover. The western deserts are likely to clear out first sometime late morning/early afternoon, while a good portion of central and eastern Arizona may see some clouds lingering through the afternoon. As H5 heights remain virtually unchanged from Saturday, the more sunshine should result in afternoon highs Sunday more in a 105-109 degree range.

LONG TERM /MONDAY THROUGH THURSDAY/

The weather pattern is expected to gradually shift more into a monsoonal pattern starting next week. However, a good deal of uncertainty remains with the positioning of the subtropical ridge and thus the amount of subsidence, and whether or not much moisture will advect into the area. The ridge is expected strengthen early next week and briefly form a center somewhere along the Arizona/New Mexico border, but guidance is now leaning toward the center of the high eventually shifting westward to off the southern California coast by around Thursday.

H5 heights are still expected to fall within seasonal normals on Monday, but some strengthening Tuesday into Wednesday is likely to push heights just into the 90th percentile. The more favorable positioning of the high by Monday should also allow for some modest Gulf of California moisture surges, potentially leading to surface dew points nearing 50 degrees and low level mixing ratios of 6-7 g/kg. Although this moisture will be an improvement, it will not be enough to counteract the subsidence from the ridge, at least on Monday. Some further improvement in moisture over the eastern Arizona high terrain into the middle of next week should finally allow for some isolated convection, but as of now it does not look to be much more than 10-20% chances.

The bigger forecast concern next week will be the widespread Moderate HeatRisk developing by Tuesday and potentially some localized areas of Major HeatRisk. Ensemble peak H5 heights of 594-596dm look to occur on Tuesday into early Wednesday and this should lead to daytime highs rising into a 110-114 degree range both days. Overnight lows will also trend upward with many locations staying in the 80s and potentially near 90 degrees in central Phoenix. Guidance then indicates lowering heights over at least Arizona later next week as the ridge center shifts west southwestward to off the coast of California. If this occurs, it should shave off 2-3 degrees from our highs by next Friday.

AVIATION

Updated at 0900Z.

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

No aviation weather concerns are expected through the TAF period under gradually increasing mid to high clouds. The overall wind pattern will exhibit the typical diurnal tendencies with overall speeds aob 10 kts, with some occasional afternoon gusts in the mid to upper teens possible.

Southeast California/Southwest Arizona including KIPL and KBLH:

No aviation weather concerns are expected through Friday evening under gradually increasing mid to high clouds. At KIPL, light and variable winds early this morning will go southeasterly this afternoon before shifting out of the west once again this evening and through the overnight hours. At KBLH, winds will generally fluctuate between the south-southeast to southwest. Overall speeds will remain under 12 kts with some occasional gusts in the mid to upper teens possible during the afternoon/early evening hours.

FIRE WEATHER

Building high pressure over the next several days will lead to warming temperatures, eventually leading to above normal temperatures by early next week. Winds will remain fairly light into next week with only the typical afternoon upslope/upvalley 15-20 mph gusts and mainly starting Sunday. Afternoon minimum humidities will continue to range between 5-10% through at least Saturday with overnight recoveries only reaching 15-30% through Saturday before improving to 10-15% starting Sunday. Despite the diminished winds, seasonably elevated fire danger will persist through the weekend due to very dry conditions and very dry and receptive fuels. Moisture is still expected to gradually increase over the region during the first half of next week, but overall dry conditions should persist.

PSR WATCHES/WARNINGS/ADVISORIES

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