A push of subtropical moisture is moving into Arizona this week, setting up a brief increase in storm potential even before the monsoon officially begins on June 15. Temperatures across the Valley remain stubbornly hot — flirting with the 110-degree mark for Phoenix — but the incoming gulf of moisture will prod the atmosphere enough that isolated showers and a few thunderstorms are possible in parts of the state later this week and into the weekend. Forecasters say the increase in humidity will be most noticeable in southwestern Arizona, where dew points have already climbed.
This surge of subtropical moisture is essentially a stream of more humid air originating from lower latitudes that has shifted northward into the region. Even though it falls short of a sustained monsoon pattern, that extra moisture raises atmospheric instability enough for convective clouds to form. Higher dew points mean the air will feel noticeably muggier, especially overnight and in low-lying areas, and provide the fuel storms need to develop when other conditions — like daytime heating and localized lift — line up.
In the Phoenix metro area, the arrival of that moisture brings the chance for a few isolated rain showers on Friday, Saturday or Sunday. Officials are not forecasting widespread, measurable rainfall for the Valley from this early surge, but they caution there are still weather hazards to watch. Embedded storms can produce strong, gusty winds that kick up blowing dust across desert and urban surfaces. In addition, storms that produce little to no rain at the surface can still generate dry lightning — lightning strikes that occur with minimal rainfall — which pose a risk of igniting new wildfires in dry fuels.
Those specific hazards stem from how isolated convective cells tend to behave over the lower desert. A rapidly forming thunderstorm can produce strong downdrafts and outflow winds that lift fine dust and sand, reducing visibility and creating hazardous driving conditions. Meanwhile, lightning without accompanying measurable rain is especially dangerous this time of year because fuels — grasses, shrubs and other vegetation left dry from a dry spring — remain receptive to ignition. Even brief, localized strikes in these conditions can start fires that spread quickly if winds are strong.
Higher terrain to the north of the Valley looks more likely to see measurable precipitation as storm chances ramp up over the weekend. Mountain locations and areas of the high country can typically tap more of the available lift and moisture, which increases the likelihood of heavier downpours there compared with the lower desert. Forecasters expect that scattered thunderstorm development in those elevated zones will be the main way this early moisture surge produces measurable rain across the state.
Orographic lift — the process by which air is forced upward as it moves over higher terrain — often enhances storm development in mountainous areas. As that air rises it cools, condensation increases and rainfall rates can intensify, producing brief but sometimes heavy bursts of rain. Those downpours in steep terrain also can generate rapid runoff, so residents and visitors in the high country are typically advised to be alert for sudden changes in weather and localized flooding in washes or steep drainage areas during active thunderstorm periods.
Even as moisture returns to parts of Arizona, the heat will remain a defining feature of the week. Phoenix has yet to record a 110-degree reading this season, but models and local forecasts suggest the region could reach that milestone either over the coming weekend or in the days shortly after. The climatological average for the area’s first 110-degree day historically falls near June 11, meaning this year’s potential first 110 would occur roughly around the typical date for such heat to arrive.
Sustained high temperatures bring familiar stresses: increased demand for electricity for air conditioning, greater risk of heat-related illnesses among outdoor workers and vulnerable populations, and higher evaporative losses that limit how much short-lived rainfall can improve drought or reservoir conditions. Residents are generally advised to take normal heat precautions during hot stretches — limiting strenuous outdoor activity during peak heat, staying hydrated and checking on those who are elderly or medically vulnerable.
Rainfall totals so far this year remain well below normal in the Valley. Sky Harbor’s official rainfall for 2026 sits at 0.32 inches to date, leaving the airport about 2.60 inches below its average by this point in the year. Long-term rainfall metrics have shifted slightly in recent decades: the historically reported average monsoon rainfall for Phoenix based on the 1981–2010 period was 2.71 inches, while the more recent 1991–2020 average shows a slightly lower figure of 2.43 inches. Annual rainfall averages have also been updated in that same comparison, with the older 1981–2010 average listed at 8.03 inches and the newer 1991–2020 average shown as 7.22 inches.
Those updated climatological figures reflect revisions to the baseline periods meteorologists and hydrologists use to characterize "average" conditions; they do not change current deficits, however. Sky Harbor’s current shortfall illustrates how little measurable precipitation has fallen so far this calendar year in the Valley, and why a handful of isolated storms this week would be unlikely to move large-scale drought indicators or reservoir storage by a meaningful amount.
A reservoir shoreline with a pronounced 'bathtub ring' showing low water levels, pictured as Arizona faces building heat while storm chances return.
The combination of ongoing hot conditions and only modest early-season rain amounts highlights the uneven nature of this moisture surge: it can increase localized storm risk without necessarily providing the widespread relief that would significantly reduce drought or dramatically improve reservoir levels. That reality helps explain why forecasters emphasize the potential for hazards like gusty winds and dry lightning even as they temper expectations for substantial rainfall totals in the lower deserts. Any storms that do develop over the Valley are more likely to be brief and isolated rather than part of a broad, soaking event.
From a water-resource and land-management perspective, that distinction matters. Brief, isolated storms can produce localized benefits — brief soil wetting and small, temporary reductions in fire hazard at very local scales — but they are seldom sufficient to refill reservoirs, substantially recharge groundwater, or erase seasonal water deficits. Water managers and wildfire agencies typically look for a sustained wet pattern to meaningfully shift those conditions, which is why the official June 15 monsoon start is watched closely as a potential inflection point.
Readers seeking more detailed, day-by-day information can consult the region’s seven-day forecast and interactive radar resources available online for up-to-the-minute storm tracking and timing. Daily rainfall reports for locations across the Valley are also maintained and updated regularly. Viewers who capture weather photos or videos during this active stretch of weather are encouraged to share them with the newsroom through the station’s designated submission channel. The official start of the monsoon on June 15 could bring a more sustained pattern of showers and storms, but for the immediate days ahead the story will likely be a mix of persistent heat in the lowlands with spotty thunderstorm activity and isolated heavy rain in the high country.
Live Updates and Reactions from X
The National Weather Service Phoenix office (@NWSPhoenix) has posted multiple updates this week confirming the subtropical moisture return, including graphics showing dew-point increases across southwestern Arizona and the greatest thunderstorm chances over elevated terrain north and east of the Valley this weekend. Local meteorologists and news accounts such as @azfamily and @12News have amplified these forecasts, noting the same dry-lightning and blowing-dust risks already described. Resident posts reflect widespread commentary on the stubborn heat, with many sharing real-time observations of rising humidity in Yuma and Tucson that match the forecast. Wildfire awareness has been a recurring theme in replies and quote tweets, with users and fire agencies highlighting the ongoing dry fuels and urging caution. Activity around the topic is moderately high but largely echoes the official outlook rather than introducing new verified measurements.