Synopsis
The synoptic setup today is favorable for shower and storm development, but widespread debris clouds will likely prevent significant destabilization by this afternoon. CAM solutions have been slowly becoming less and less bullish for widespread storms today. Albeit, with significant synoptic scale ascent combined with ample amounts of moisture and just enough instability should be sufficient enough for showers and storms across much of Arizona today. Today will likely be the coolest day of the summer thus far with temps remaining below 90 in Tucson and temps between Phoenix and Yuma in the low to mid 90s by this afternoon.
Current Conditions
Quite busy last night across southeastern and south-central Arizona with numerous showers and thunderstorms from just north of Tucson all the way into Phoenix and Gila Bend. Storms initiated late yesterday afternoon in Oro Valley and over the Tucson Mountains. Within a couple hours storms began to organize into a compact MCS which propagated into the Phoenix metro by late evening. 24-hour accumulated precipitation this morning showed highly variable precipitation amounts with some locations receiving over an inch of rain.
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| 24-hour Total Precipitation map courtesy of the NWS. |
Phoenix Sky Harbor only reported 0.07 in but some locations in the Phoenix vicinity received around 0.50 in or more.
However, rainfall wasn't the biggest highlight yesterday, but rather the strong outflow winds and blowing dust. Phoenix Sky Harbor reported a wind gust of 73 mph with visibility of 0.25 miles around 9:00 PM MST last night via surface obs.
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| Phoenix Sky Harbor Observations last night courtesy of the NWS. |
Currently, visible imagery displays numerous mid level clouds across Southern Arizona with a cluster of thunderstorms along the International Border in southwestern AZ.
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| Visible Imagery overlaid with GLM flashes courtesy of College of Dupage. |
The cluster of storms south of the border is associated with a weak, embedded shortwave moving northward which is helping to generate a bit of cyclonic vorticity advection and upper level divergence which is demonstrated on the current SPC 300mb analysis.
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| SPC 300mb analysis as of 17:00z this morning. |
The SPC 500mb analysis displays the mid level anticyclone centered over the Southern Plains, and a trough along the west coast putting Arizona under brisk southerly flow aloft.
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| SPC 500mb analysis as of 17:00z this morning. |
Moisture has sky-rocketed overnight with SPC mesoanalysis displaying pwats between 1.50 and 2.00 inches in south-central and southwestern AZ with pwats rapidly decreasing in southeastern AZ with pwats between 1 and 1.25 in.
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| SPC mesoanalysis of total precipitable water as of 17:00z. |
The 12z KTUS sounding displayed poor instability with only little over 100 J/kg of CAPE and around -300 J/kg of CIN.
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| 12z TUS sounding courtesy of the SPC. |
Today's Forecast
Synoptics
Very favorable synoptic pattern today due to brisk mid level southerly flow and some upper level divergence providing the region with some synoptic scale ascent. With a deep trough along the west coast and the mid level anticyclone over the Southern Plains, Arizona will be under brisk southerly mid level flow throughout the day today. Also, an embedded shortwave currently just south of the border will lift northward into Arizona this afternoon providing some additional upper level divergence and weak cyclonic vorticity advection as shown in the plots below.
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| 12z GFS 500mb absolute vorticity for 18z today. |
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| 12z GFS 250mb divergence for 18z today. |
The region of best synoptic scale support will be in the Colorado River Valley, Northwestern AZ, and Southern Nevada where better speed divergence (associated with a jet entrance region) will be present today as shown below.
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| 12z GFS 300mb winds at 5:00 PM MST this afternoon. |
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| 12z GFS 250mb divergence at 5:00 PM MST this afternoon. |
Overall, synoptics are favorable for ascent across Arizona today with western AZ in the best region of synoptic scale support this afternoon and evening.
Moisture and Instability
Moisture is most definitely not an issue today with pwats around 1.25 in in Tucson and increasing rapidly westward. The issue is poor insolation due to widespread mid level clouds. These mid level clouds across Southern Arizona this morning are associated with the embedded shortwave just south of the border moving northward throughout the day. The 12z KTUS and KPHX WRF-HRRR soundings forecasting less CAPE than was forecast yesterday with around 600 J/kg in Tucson and a little over 1000 J/kg in Phoenix by this afternoon.
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| 12z KTUS WRF-HRRR sounding for this afternoon at 2:00 PM MST. |
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| 12z KPHX WRF-HRRR sounding for this afternoon at 3:00 PM MST. |
Current SPC analysis of CAPE and CIN as of 18z has between 500 and 1000 J/kg of CAPE in the Tucson and Phoenix vicinities and CAPE between 1000 and 2000 J/kg in southwestern AZ. Am thinking CAPE will remain between 500 J/kg and 1000 J/kg in Tucson and Phoenix into this afternoon and evening which is plenty sufficient enough for storm development especially combined with synoptic scale support.
What to Expect/Potential Impacts
CAM solutions this morning are not very bullish regarding significant storm coverage across south-central and southeastern Arizona this afternoon and evening. However, both the 12z and 15z WRF-HRRR runs don't appear to be initialized properly as neither run has picked up the ongoing activity along the International Border and in Southern Arizona. Recent runs of the HRRR have also been less aggressive keeping most activity over western AZ today.
Considering that there is plenty of synoptic scale ascent, ample amounts of moisture, and marginal instability, bands of showers with embedded thunderstorms will still be possible today and tonight across most of Arizona with the most intense activity likely remaining in western AZ where better moisture, instability, and upper level divergence will be present. The 12z HREF, in my opinion, advertises the most reasonable solution today as I have the 6-hour mean precip shown below.
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| 12z HREF 6-hour mean precipitation between 11:00 AM MST and 5:00 PM MST today. |
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| 12z HREF 6-hour mean precipitation between 5:00 PM MST and 11:00 PM MST today. |
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| 12z HREF 6-hour mean precipitation between 11:00 PM MST tonight and 5:00 AM MST tomorrow. |
With ample amounts of moisture, some of the heavier bands of showers and storms could produce localized flooding. The WPC has a slight risk of excessive rainfall for Tucson, Phoenix and western Arizona today and tonight.
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| WPC Day 1 Excessive Rainfall Outlook. |
Overall, significant synoptic scale lift combined with ample amounts of moisture and just enough instability will be favorable for showers and embedded thunderstorms across much of Arizona. Less cloud cover in western Arizona will provide better surface heating and therefore better buoyancy leading to a greater chance for stronger, more widespread activity in those areas.
Enjoy the cooler temps today as widespread cloud cover as well as showers and thunderstorms will provide the lower deserts with temps well below triple digits today. Temps will likely remain below 90 degF in the Tucson area with temps between Phoenix and Yuma likely remaining in the low to mid 90s this afternoon.
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| 12z WRF-HRRR 2-meter temps for this afternoon at 3:00 PM MST. |
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