A monsoon-like surge of moist tropical air is underway today, with dew point temperatures expected to rise into the 50s or lower 60s tonight – tomorrow. This unusually early moisture surge is associated with the remnants of what was once Hurricane Bud off the southern tip of Baja California. The cool, deep airmass is being drawn northward by high pressure to our east over the Southern Plains and a weak upper- air trough over southern California to our west. Expect breezy, cooler weather today and tomorrow, along with mostly cloudy skies and a chance for showers or thunderstorms tonight to tomorrow night.
The greatest uncertainty is to what extent the atmosphere will become unstable over Prescott tomorrow, as it will mostly depend on how much solar heating we experience. Thunderstorms that develop in northern Arizona will be capable of producing locally heavy rainfall, gusty wind, small hail and lightning. The greatest threats, if thunderstorms develop, are possible flooding in some areas and ignition of wildfires by lightning. Storms that develop will likely propagate toward the north or northeast at 10-20 mph, but some backbuilding of thunderstorms is possible, allowing for heavy precipitation to rebuild over some of the same areas.
By Saturday night, dry, cool air will stream back across Arizona from the northwest. Next week will be dry, high temperatures warming back into the mid 80s, lows in the upper 50s. It is unclear when moisture will return again to the area. This is really unusual for such a pronounced moisture surge to occur this early in the season (and unusual for tropical cyclone remnants to move into Arizona in June). Widespread rainfall over much of Arizona tonight and tomorrow, if it occurs, will help provide some relief from the drought and extreme fire conditions we have been experiencing.