This is the time of year where we look for the seasonal wind shift in the Southwest, commonly called the Summer Monsoon. The usual west-to-east wind pattern shifts to some version of east to west or southeast to northwest. This wind shift brings tropical moisture from the Gulf of Mexico and even eastern Pacific into New Mexico, Arizona and parts of California, Nevada and Utah. With the arrival of this moisture, we end the everyday dry weather pattern to one that is considerably more humid and uncomfortable. The moisture is also converted into showers and thunderstorms by the strong heating of the day. The thunderstorms can also bring with them haboobs, or severe dust storms.
The rain with the monsoon season is mostly welcomed. It helps to bring at least some rain to a part of the year that would normally have none. However, too much rain can fall too quickly in thunderstorms and produce violent, life-threatening flash floods in normally dry washes. Thunderstorms, while bringing rain, can also bring lightning that starts fires miles away from where any rain falls.
The models are showing that this shift in the winds could come as soon as early next week as high pressure aloft builds around the Four Corners. Here is a look at what the GFS is forecasting for the 500 mb flow by July 1.
Other models, including the fairly reliable European model, is forecasting something similar.
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A rather extended period of unsettled weather will be occurring over parts of California and the Southwest
The remainder of the week a large building ridge of high pressure takes over
There will be more showers and thunderstorms are likely that can produce very heavy downpours in Arizona.
This rain caused problems with flash flooding producing some damage and there were a few swift water rescues.
Computer models are insistent that a rather strong piece of energy will move through California Tuesday, bringing more widespread rainfall.