July 10 Moisture increases and convective initiation likely imminent. Weekly live discussion tomorrow at 11 AM

 Overview:

Moisture continues to increase over southern Arizona with precipitable water values exceeding 1.5 inches in the Tuscon sounding this morning and surface dewpoints exceeding 60 F. With the increasing moisture and decreasing dewpoint depressions, the hazard focus will shift slightly from gusty winds to heavier precipitation accumulations over short durations. Focus for convection for the next three days will continue to be Sierra Vista and Cochise Counties as well as parts of the Sonoran Desert in Pima County. Tucson will continue to see some chance of thunderstorm activity over the next three days with Tuesday having the greatest potential for measurable precipitation in the Tucson metro region. 

There will be a more detailed look into the week ahead tomorrow at 11 AM. You can join us at https://arizona.zoom.us/j/5237305771


This Morning:

Clouds from this morning have cleared out from SE to NW across the region, clearing the way for increasing instability. Towering Cumulus Clouds are currently starting to bubble up over the higher terrain in Sierra Vista in particular.




Precipitable water values are well over an inch throughout the area with an axis of higher precipitable water values running through western Pima County.
However, the analysis above may actually be underdone as the 12Z sounding from Tucson showed a precipitable water value of 1.55 inches
Which places us near the 80th percentile of available moisture for 12Z soundings for this time of year.

The moisture and higher dewpoints have done a good job of sticking around so far today with dewpoints still near 60F at 1 pm
Both the temperatures and the dewpoints are running higher than forecasts from the 12Z and 15Z runs of the UA-WRF_HRRR valid at the same time.

The GFS initialization is slightly better 

These differences may seem small, but they can have a significant impact on destabilization. The mesoanalysis indicates about 500 J/kg of CAPE over the Tucson metro, with a 1000 J/kg near the Sierra Vista/Pima County border.
Which already exceeds the highest values of CAPE in the wither of the UA_WRF_HRRR runs from this morning. The 12 Z run keeps convection confined to Sierra Vista, and the exterme Southern Sonoran Desert.
While the 15Z run has activity spilling into southern Pima County

The GFS initialization, which has the best current thermodynamics relative to observations is a bit more aggressive, showing more convection moving into Pima county between 6 and 8 PM.

6 PM
8PM

A comparison of the soundings makes the differences a little clearer.
15Z HRRR
12Z GFS



The small difference in Dewpoint of say 51 to 54F between the models is sufficient to produce a 300 J/kg in CAPE.

My Take on Today: Instability and moisture availability today leads me to think that initiation of convection along the higher elevation of the Catalinas and Rincons is at least possible today. The initiation of convection in Sierra Vista I think is a given and might be a little ahead of schedule relative to forecasts. Some of the activity in Sierra Vista may spill over across the border into southern Pima County.

Outlook for Tomorrow: There is a general consensus among numerical guidance products tomorrow will have the best chance of convection for the week. The following are all 24h accumulations from different model Guidance
ECMWF
GFS
HRRR
However, much of the specialized numerical guidance keeps precipitation south of the Tucson Metro.















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