CIN City (Sorry I can't help myself)

 Overview:

Last Night

Last night was really a case of too little/too late. The scenario where a moist outflow boundary was pushed north into the greater Tucson area eventually played out at about midnight-1am instead of shortly after sunset. By this time, CAPES where small enough and convective inhibition was large enough that only a few short lived updrafts formed along the Rincon mountains. From the Tucson mountains east, more numerous showers/storms developed in the axis of deeper moisture although these were also relatively short lived.

Today

This morning's sounding indicated 300-400 J/kg of convective inhibition, some of the largest values we have seen so far this summer. At the very least, this will once again mean a later start to convective buildups. Lapse rates continue to become lass favorable for the development of CAPE and wind profiles that look decent this morning are expected to deteriorate throughout the day. As the sun sets, CIN looks to reappear rather quickly minimizing the chances for storms in valley locations after dark.

Tomorrow

Tomorrow looks to be a transitional day as the upper-level high that has been situated over New Mexico for the last couple of days retrogrades to the west. Upper-level flow will transition from easterly to northeasterly over the course of the day, increasing the odds of impacts from Rim based activity.  Moisture is also forecast to improve south of the Rim in strong southeasterly flow in the morning in the Gila River Basin. While mid-level lapse rates are forecast to steepen, we will once again start the day with significant convective inhibition meaning a later start to convection that does develop. The 12Z UAWRF HRRR intialization shows maximum convective coverage in the region after sunset, in the 8-11 PM time frame while the NSSL deterministic HRRR indicates an interesting low probability event for even later that night. The NSSL HRRR shows moist outflows from RIM activity to the north and Sonoran activity to the south, converging over the greater Tucson area close to 11 PM. The marked increase in moisture and lift results in the development of CAPE and widespread storm coverage. This scenario would require fairly fortuitous timing and ensembles indicate about a 20% chance of this materializing. In the event that this does occur, minimal DCAPE should mean that severe winds are not likely to be an issue.

Last Night:

The 00Z sounding from Tucson last night indicated that conditions were already fairly marginal at 5 PM. MLCAPES were about 500 J/kg and there was already a 100 J/kg of MLCIN.

5 PM Tuesday Sounding from KTUS

Given the already marginal thermodynamic conditions, when the moist outflow finally reached Tuscon at about 1 AM.....

                                             Surface Observations from 1 AM MST Wednesday

The broader thermodynamic conditions were simply too unfavorable, with CIN exceeding 250 J/kg, for any significant activity....

                                       CAPE/CIN Mesoanalysis from 1 AM MST Wednesday

Today:

As mentioned in the overview, we started this morning with a very "meh" sounding. 

                                     KTUS Sounding from 5 AM MST Wednesday

Mixed layer and surface based CIN values were -332 and -435 J/kg respectively. Lapse rates in the standard layers were all less than 7 C/km with a max of 7.6 C/km just above a warm layer situated at approximately 680 hPa. In addition DCAPE values were 1000 J/kg, significantly less than we have seen in previous morning soundings which has resulted in the removal of the area from the "marginal risk" category for severe winds in the outlook from SPC.

A PWTR value of 1.54" is certainly sufficient, but forecast to drop through the day. Wind speeds in the mid levels are also decent with general easterlies ranging between 15-30 knots, but part of this is a function of overnight activity, and these winds are expected to decrease in strength over the course of the day.

The forecast drop in PWTR values seems to be a function of boundary layer mixing, as well as advection of drier air from NM into eastern AZ in the southeasterly 500 hPa flow around the high pressure center in NM.

                 Low-level Water Vapor and 500 hPa analysis from 10 AM MST Wednesday

The 12Z UAWRF HRRR initialization is showing peak CAPE values around 4 PM MST, although the best thermodynamic conditions at that time are south of the border, where most convective activity is forecast outside of the Mogollon Rim.

            UAWRF Reflectivity (left) and CAPE forecast valid at 4 PM MST Wednesday

Even at this time, we still manage to hold on to some mixed layer negative buoyancy in the 700-600 hPa  as indicated by the forecast UAWRF forecast sounding.

                   UAWRF HRRR KTUS forecast sounding valid at 4 PM MST Wednesday

Any activity that does develop today will have to depend on outflow from southern activity reaching us before the thermodynamics become too unfavorable and like yesterday, I think it will be too little too late.

Note that the HREF are in line with the UAWRF forecast and indicate a 10-20% chance of precipitation largely in the higher terrain south of Tucson..

              HREF 6hr probability of measurable precip KTUS valid at 11 PM MST Wednesday

Tomorrow:

(Note that I will be using graphics from the NSSL HRRR and the UAWRF interchangeably for clarity of visualization. I will be sure to note where departures between the forecasts occur.)

Tomorrow will be a transitional day as the upper-level high starts its adverstized shift to the the west as weakening southeasterlies at 500 hPa at 5 AM MST tomorrow are replaced by strengthening northeasterlies by 5 AM MST on Friday. 

                  NSSL HRRR 500 hPa heights wind forecast valid at 5 AM MST Thursday

              NSSL HRRR 500 hPa heights wind forecast valid at 5 AM MST Friday

At the surface, increasing southeasterly flow along the Gila River Basin will act to bring in higher PWTR values into eastern AZ and western NM.

                            12Z UAWRF 10m wind valid at 9 AM MST Thursday

                            12Z UAWRF PWTR valid at 9 AM MST Thursday

perhaps setting the stage for more significant Rim activity as the upper-level flow starts to turn to the northeast as indicated by the Springerville (Apache County) sounding valid at 4:30 PM MST....

                            12Z UAWRF KJTJ forecast sounding valid at 4:30 PM MST Thursday

As well as the UAWRF reflectivity valid at the same time.

                       12Z UAWRF reflectivity forecast valid at 4:30 PM MST Thursday

This is where it potentially gets interesting and the timing in the forecasts between the UAWRF and HRRR diverge. In the UAWRF forecast, outflow from the southern activity as well as activity over the White Mountains coverage on Tucson at about 6 PM MST

                 UAWRF 10m winds (left) and reflectivity forecast valid at 6 PM MST Thursday

The outflow boundaries significantly increase the dewpoints in the area and create a more favorable envornment for convection in the area which maximizes in coverage between 8-9 PM.

                                   UAWRF Reflectivity valid at 8:30 PM MST Wednesday

The NSSL HRRR tells a similar story, but later in the evening and with more dramatic results. In the NSSL HRRR, the outflows approach the Tuscon metro at about 11 PM MST and result in a drastic modification of the thermodynamics over Tucson between 9 PM and 1 AM. 

                                   12Z HRRR 10m wind forecast valid at 11 PM Thursday

I am showing the evolution of the soundings below in 2 hr increments.

At 9PM MST, CAPE values at Tuscon range between 200-400 J/kg, with between 100 and 400 J/kg of CIN and a DCAPE of 1400 J/kg and a PWTR of 1.29".

                                 12Z HRRR KTUS sounding valid at 9 PM Thursday

By 11 PM, CAPE values have increased to 700 J/kg and PWTR has increased to 1.54" although there is still sigficant CIN. 

                                   12Z HRRR KTUS sounding valid at 11 PM Thursday

By 1 AM, surface dewpoints of 68 F have essentially eliminated the CIN and CAPE values are between 800-1200 J/kg in a largely saturated sounding.

                                   12Z HRRR KTUS sounding valid at 1 AM Friday

My take:

While interesting, the scenarios in the UAWRF and the NSSL HRRR require a number of things to come together with fortuitous timing. The fact that the both show a similar, although differently timed, evolutions certainly keeps me from dismissing the scenarios. From an ensemble perspective, there is about a 30-50% chance of precipitation between scenarios on the early side of the envelope like the UAWRF and those on the last side like the NSSL HRRR. In either case, given the thermodynamics earlier in the day, I do think it will require a convergence of outflow boundaries to see activity tomorrow.

                         12Z HREF 6hr probability of measurable precip valid at 11 PM Thursday