Big Idea

• It’s cooler & more humid
• There has been a flash flood watch in place through early Wednesday morning
• Recent areas with wildfire burn scars are most at risk for flooding
• Might also have winds
• Read more...

It’s cooled off, and gotten wetter

Forecast Summary:

A cooler and more humid airmass has moved into the area and will remain here throughout the week. This has prompted the issuance of a flash flood watch through 5:00 am on Wednesday by the National Weather Service. Stay tuned to local forecasts! Expect widespread thunderstorm activity this week. Thunderstorms will generally propagate towards the west or northwest at 5-10 mph and will be capable of very heavy rain, small hail, and frequent lightning. Low-lying areas, especially those near recent wildfire burn scars, will be especially susceptible to flash flooding. High temperatures in the mid to upper 80s, low temperatures in the low to mid 60s. Surface winds will be generally southwesterly from 5-10 mph most of the day, but thunderstorm outflows of up to 20 mph will be possible.

Forecast Table:

https://www.wrh.noaa.gov/forecast/wxtables/

Navigate on the map to your location and click for a detailed local forecast.

Discussion:

The strong  high pressure that brought us unusually warm temperatures and limited thunderstorm activity for the past couple of weeks has finally spread to our north and east and weakened over Arizona. As a result, the subsidence over northern Arizona has ended, allowing temperatures to cool off to near or below normal temperatures and allowing a very moist subtropical airmass to spread across the entire area. Long-range forecasts indicate that the air will remain moist for the next couple of weeks, with dew points generally between the mid 50s and mid 60s most days. Precipitable water amounts are forecast to be around 1.40” for the next few days, which is much higher than normal for this time of year. Precipitable water is the total integrated water vapor in the column of air above us, converted to liquid. When precipitable water amounts are high during the monsoon, thunderstorms are much more likely to develop, and we may observe multiple bands of thunderstorms forming and moving across our area on a given day. At times, thunderstorms can become locked over a given topographic feature or build backward into the wind, leading to prolonged heavy rainfall in some areas. Rainfall rates up to 2 to 4” per hour have been observed under such conditions. The National Weather Service has therefore issued a flash flood watch for most of Arizona through Wednesday morning, and I suspect that they might extend the flash flood watch through the latter part of the week. Stay tuned to local forecasts!

Already by 9:15 am this morning, scattered strong thunderstorms have already developed over the Black Hills to our east and the Bradshaw Mountains to our southeast. The vertical wind shear will not be strong enough these next few days to support severe thunderstorms, so the main threat will be heavy rains/flooding in low-lying areas, small hail, and lightning. By most indications. Storm motion will be towards the west or northwest at 5-10 mph. We will experience an active monsoon period this week.

C. James / A. Infante

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Curtis N. James, Ph.D.                                                                       
Professor of Meteorology

Applied Aviation Sciences

Prescott Campus

3700 Willow Creek Road                                                                                          
Prescott, AZ 86301-3720                                                                                         
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Further Information:

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Official National Weather Service forecast

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