The figure above indicates the forecasted high in orange (with error bar denoting the range of ensemble forecast members), average high for this time of year in orange (dashed line), forecasted low in blue (with error bar), average low this time of year in blue (dashed line), and forecasted wind speed in purple. Note that the wind speed forecast is sustained wind (not gusts), and it is based on only one model (not an ensemble).
Last weekend, high pressure rebuilt over Arizona, bringing temperatures a little above normal and moisture levels a bit below normal. The high pressure will not move much over the next few days, but some moist air has surged back across the area and could lead to a slight possibility of thunderstorms these next few days despite the residual dry air aloft. We will remain on the monsoon moisture boundary tomorrow and Wednesday, so I am keeping a slight chance of thunderstorms in the forecast through Wednesday.
By about Thursday, low pressure is expected to form along the West Coast and persist through the weekend. With low pressure to our West and high pressure over the Southwest, we will likely see southerly winds and additional moisture moving into the region by Thursday. Thus, I expect a slightly better chance for thunderstorms later in the week. If thunderstorms form, they will generally be slow-moving airmass thunderstorms and capable of producing brief but locally heavy rain, possibly small hail, and frequent lightning.
Some forecast models are indicating that the low pressure along the West Coast will begin to tilt more toward the northeast over the weekend, which could begin to produce some drying again over the weekend, but I expect at least a daily slight chance of thunderstorms to continue into next week.
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