Lee Born

What Are Climate Normals?

Traditionally, scientists define climate normals as three-decade averages of climatological variables. Since 2010 the batch of 30-year Climate Normals developed and used by NOAA covered the period from 1981 to 2010 and was calculated from observations at approximately 9,800 stations across the U.S. operated by NOAA National Weather Service.

Every 10 years NOAA releases the latest 30 year "normals" or averages, which now cover the period 1991-2020.

Following an extremely warm, dry monsoon, fall and early winter in which precipitation totals were the driest in recorded history for much of the region, a wet and snowy January has finally brought some drought relief. Snowfall from recent storms has allowed the high country to rebound to nearly 70% of average values. Much of the drought impacts have been focused in short term influences such as forage for ranchers, water availability for land wildlife, and small streams for aquatic ecosystems.

Historically dry weather across Arizona has intensified the ongoing drought. The U.S. drought monitor put out by the USGS and NOAA has the majority of Arizona in the highest classification of drought, “exceptional”. Impacts includes and are not limited to low reservoirs and water tables, forage is limited affecting grazing and ranching, forest life is under stress, increased fire danger and more (see table for complete list).

A major winter storm will enter Arizona early Thanksgiving Day morning. A prolonged period of heavy snowfall is expected Thursday into Friday, which will bring heafty snow accumulations to much of the region. Snow levels Thanksgiving day will initially hover near 6000' in elevation and gradually lower to 5500' by evening. Snow levels crash to near 3500' Thursday night into the day Friday. Preliminary indications are for 12 - 27" of snow above 6000', 4 - 12" between 4500' - 6000', and a few inches down to valley floors.

Typically late summer and fall are not know for being the "fire season" across Arizona. Arizona fire season is more commonly associated with late spring and early summer as we wait for the monsoon rain to arrive. This monsoon  been unusually dry with many locations across Arizona reporting record low rainfall.

The Museum Fire burning near Flagstaff is pumping large amounts of smoke into the atmosphere. Efficient summertime ventilation has kept health impacts to a minimum thus far as the plumes are dispersing as they travel north and east of the fire. So far, there have been no health advisories issued by Arizona Department of Air Quality (ADEQ) or the National Weather Service. This can change with the varying conditions and those with sensitivities to smoke are encouraged to stay alert and informed. Monday night, light northerly winds are forecast to bring smoke into Flagstaff communities.

It has been one of the slowest and driest starts to the Arizona rain season, know as the Monsoon. In a more typical year the region would have already have experienced significant moisture. This year has been different, with not one location receiving over a half inch of rain as of Monday, July 22nd. This has lead to tinder dry conditions and a late fire season.  

The season within a season, the "Southwest monsoon" is beginning to establish itself across the region. The word "monsoon" is defined as any seasnonal shift in the wind. Over the coming days high pressure centered over the four corners region will gradually transport moisture into Arizona from south. 

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The moisture source is the Gulf of Mexico and the Gulf of California. You probably have noticed the increase in our mugginess the past couple days as humidity levels are on the rise.

Monsoon season officially began June 15th. The word "monsoon" is derived from the Arabic word "mausim" which means season . During the summer months, winds shift from our predominant westerly direction to  a southerly  direction. This allows moisture from the Gulf of California and the Gulf of Mexico to stream into the region. This year El Niño (warmer than average tropical Pacific Ocean water) is still present and predicted to continue through summer.

A major winter storm will bring severe impacts from heavy snow from late tonight through Friday afternoon. The heaviest snow is forecast Thursday morning through Friday morning. This will be the greatest snow seen at low elevations in many years.

Winter Storm Warnings are effect through Friday for the entire region.