Another upper-level trough will dig southward along the West Coast and slowly move across Arizona tomorrow and Wednesday. An upper trough is a low pressure “dip” that propagates generally west to east with the jet stream and corresponds to a colder airmass. Troughs create decreasing pressure at the earth’s surface and provide lifting before passing through an area. Thus, as the trough approaches Arizona tomorrow and Wednesday, expect decreasing pressure and strengthening pressure contrasts again across the southwest, and thus increasing the wind. Also, expect much cooler conditions by Wednesday, as a surface cold front forms and moves across the state Tuesday afternoon – Wednesday.
Forecast models are not in good agreement as to how much moisture this storm system will draw into Arizona. Some forecasts are indicating that there will be enough moisture and upper-level cooling to produce scattered showers and thunderstorms. Other forecasts are much less optimistic. The range of ensemble forecast solutions indicates anywhere from 0 – 0.5” of rain by Wednesday afternoon, with the mean being about 0.13”. The most likely scenario is less than 0.10” of rain. This would be enough rain to remove some of the dust and smoke out of the air (this is called aerosol scavenging) and wet the dry ground a little, but not enough to thwart the bad fire conditions that we have been experiencing and anticipate to continue the next couple of months until the monsoon gets underway. Here’s hoping and praying for more substantial rainfall than forecasts are indicating.
Wild fires are already brewing across Arizona (see https://www.wrh.noaa.gov/forecast/wxtables/index.php), and have been fueled by dry grasses and brush/shrubs as well as windy conditions. Expect these conditions to continue, especially tomorrow.
Temperatures will rise back into the lower 80s by this coming weekend.
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