July 9th - Some convection east and south of Tucson today with significant relief potentially this weekend

 Overview:

Some moisture has made its way back into the southeastern corner of Arizona this morning. Moisture from the easterly surge in New Mexico has advected into parts of Graham and Geely counties along the Gila River Basin while higher dewpoints from Sonora have pushed their way into north into southern Pima county with this morning sounding in Tucson reporting a more respectable .95" of precipitable water. However, the increase in moisture is shallow and not really part of an organized trend of moisture return either from the Pacific or the Gulf of Mexico. Consequently, I expect the pattern for the next couple of days at least to continue to be a race between between surface heating eroding convective inhibition and the drying of the boundary layer due to vertical mixing. I think that the moisture return into Graham and Geely this morning should support convective initation in the higher terrain. Any convection initiated there should work its may southward into Cochise County with more convection potentially initiated in Santa Cruz near the international border in response to the Sonoran moisture. Outflows from this activity may induce activity in the higher terrain east of Tucson. To be clear, most activity will be short lived and outflow dominated with nominal precipitation accumulation. For folks in the lower elevations, precipitation will continue to be a low probability proposition for at least the next couple of days. I don't expect any significant changes to the pattern until this weekend when it appears that upper level heights may fall in response to an anticyclonic wave break of a trough that is forecast to work its way into New Mexico by the weekend. This in combination with forecast moisture increases from the Pacific and Gulf will hopefully signal a return to more active conditions by Saturday.

 This Morning (current conditions):

Surface dewpoints in southeastern Arizona have recovered from the 30's yesterday evening to the mid to upper 50's as of 8 AM this morning. Further west, dewpoints remain a bit lower with values in the upper 40's and lower 50's with no real indications of an overnight surge in moisture from the Gulf of California.

Surface observations valid at 8:43 AM MST July 9th

(weather.ral.ucar.edu)


However, as mentioned in the overview, the moisture return is somewhat shallow in nature. While moisture has recovered a bit, with precipitable water values approaching an 1", this morning's sounding from Tucson indicates a mixed layer surface dewpoint in the low 40's,

12Z KTUS sounding July 9th

(spc.noaa.gov)

minimizing the potential for CAPE during the mid-late afternoon. While the surface dewpoints have increased since the sounding, a HRRR intial analysis (not shown) indicates that the depth of moisture has not changed. DCAPE values of > 2000 J/kg this morning should only increase during the course of the day with any storms that do develop in the higher terrain being short lived and outflow dominated. 

On the larger-scale, the upper-level flow regime has not changed significantly with high pressure off to the west and the Central Plains trough slowly moving to the east. The upper-level water vapor still has a suggestion of drier air with a history of subsidence extending southwestward from the upper-level trough to the east hide of the West Coast high.

Water Vapor Sat and 500 hPa Mesoanalysis valid at 8 AM MST July 9th

(weather.cod.edu)


Given the flow pattern and water vapor distribution, I do not really expect any significant increases in column precipitable water values over the next 24-48 hours, with changes coming mostly from low-level advection of moisture from Chihauhau and Sonora Mexico. 

Forecast for Today:

I expect the earliest activity today to be associated with the moisture surge along the Gila River Basin which is illustrated in the axis of higher dewpoint values in the southeasterly flow 

12Z UAWRF HRRR Surface dewpoint valid at 10 AM MST July 9th

(weather.arizona.edu)


12Z UAWRF HRRR relectivities valid at 1 PM MST July 9th

(atmo.arizona.edu)


The combination of moisture gradient, surface heating, and terrain induced circulations should result in some storms initiating in the early afternoon in the higher terrain north of the river basin. The 12Z run of the UAWRF shows storms firing up as early as 1 PM.


Given the downdraft potential of the environment today with the HRRR showing DCAPE values in near 2000 J/kg at Safford and Nogales,

15Z HRRR Sounding at Safford valid at 2 PM MST July 9th

(tropicaltidbits.com)


15Z HRRR Sounding at Nogales valid at 2 PM MST July 9th

(tropicaltidbits.com)




expect storms that do initiate to produce significant outflows and gusty winds with wind speeds easily in excess of 30 knots.

12Z UAWRF HRRR 10m wind valid at 4 PM MST July 9th

(atmo.arizona.edu)


As convection and outflows spread southward during the course of the afternoon, 

12Z UAWRF HRRR 10m wind valid at 6 PM MST July 9th

(atmo.arizona.edu)


convection may occur as close as the Rincon Mountain Range

12Z UAWRF HRRR relectivities valid at 5 PM MST July 9th

(atmo.arizona.edu)


The HRRR ensemble forecasts highlight the potential of strong winds especially along the Gila River Basin southward into Cochise County and Sonora Mexico....

12Z HRRR ensemble 4hr max wind and prob > 30 knots valid at 6 PM MST July 9th

(spc.noaa.gov)



Especially as juxtaposed to the potential of heavy rains with generally a less than 10% chance of 1" accumulations.

12Z HRRR ensemble 3 hr mean QPF and prob > 1" valid at 5 PM MST July 9th

(spc.noaa.gov)





Tomorrow:

On the synoptic-scale, we can expect fairly similar conditions tomorrow, with high pressure still situated to our NW and the trough to our east gradually shifting into the Midwest.

12Z GFS 500 hPa heights/winds and vortictity valid at 11 AM MST July 10th

(tropicaltidbits.com)



On the large scale, mositure will still be an issue with PWTR values running below normal for the entire region.

12Z GFS PWTR anomaly and 850 wind valid at 11 AM MST July 10th

(tropicaltidbits.com)


While moist outflow from Sonoran convection may push into our region this evening and overnight,

12Z UAWRF HRRR PWTR and 10m wind valid at 8:30 PM MST July 9th

(atmo.arizona.edu)


by tomorrow afternoon, moisture has largely dissipated with values dropping back to under an 1" 

12Z UAWRF HRRR PWTR and 10m wind valid at 12:30 PM MST July 10th

(atmo.arizona.edu)


The main difference appears to be the lack of a moisture surge through the Gila River Basin, which should limit activity to our northeast. Consequently, convection should be more confined to Cochise and Santa Cruz counties.

12Z UAWRF HRRR reflectivity valid at 3 PM MST July 9th

(atmo.arizona.edu)



Looking Ahead:

Significant changes appear to be on tap for the weekend as moisture surges from the Gulf of California and the Guld of Mexico converge on the area.

12Z GFS PWTR anomaly and 850 wind valid at 11 AM MST July 13th

(tropicaltidbits.com)



This will occur in conjunction with a couple of upper-air features that are best depicted on the dynamic tropopause as defined by the 2 Potential Vorticity Unit Surface. 

12Z GFS pressure on the dynamic tropopause anomaly valid at 11 AM MST July 10th

(tropicaltidbits.com)



The feature in New Mexico is the result of an anticyclonic wave break of a weak trough moving through the Central Plains on Friday.

More conventionally, these features can be thought of as upper-level cyclones and can bee seen in the 500 hPa analysis as low pressure off the coast of California and an inverted trough

12Z GFS 500 hPa heights and vorticity valid at 11 AM MST July 13th

(tropicaltidbits.com)


across the big bend of Texas. The combination of these features will result in increased moisture as well as a decrease in the upper-level heights as the high get "pinched" northward into the great basin. This should result in more widespread convection across the area and a decrease in temperatures with ensemble means indicating below normal high temperatures by Sunday.

12Z GFS Ensemble 2m T anomaly valid at 11 AM MST July 14th

(tropicaltidbits.com)





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