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).
The axis of the persistent West Coast ridge that has brought warmer-than-normal conditions to Arizona in recent weeks has shifted to the west a little, and this is allowing a northerly flow to develop in the upper atmosphere. Embedded in this northerly flow will be a series of troughs. The first one is dropping into northern Arizona today, bringing some breezes and high clouds. A second stronger upper-level trough will dig southward this weekend and stall over Central California, bringing a slight chance of rain showers from Sunday - Tuesday next week along with breezy conditions. As a result of the increased cloud cover and the transport of cooler air into the state from the north (called cold advection), daytime temperatures will gradually cool into the 50s and overnight lows will cool into the lower 30s by next week.
A third trough is on tap for next Thursday – Friday, with a slight chance of precipitation, although considerable variability in the forecast model solutions for next week indicate uncertainty in the forecasts. Stay tuned for an update next week when hopefully better agreement between the models will give us better certainty…
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Official National Weather Service forecast