June 23, 2024: Record Moisture to Provide Another Round of Showers and Thunderstorms across SE AZ Today

 Synopsis

The mid level anticyclone will remain centered over Central New Mexico today with weak southeasterly/southerly winds aloft across AZ. Ample amounts of moisture combined with sufficient surface heating will allow CAPE to reach 1000 to 2000 J/kg by this afternoon across the region. CAMs forecast convection to initiate over the Sky Islands and near the International Border by early afternoon with additional development along outflow boundaries in lower elevations by late afternoon/early evening. Primary impacts will be lightning, gusty winds, and heavy rainfall which could cause isolated flash flooding.

Current Conditions

Quite an active afternoon in Tucson yesterday with a cluster of thunderstorms anchored in the vicinity with numerous lightning strikes, gusty winds, and heavy rainfall. The NWS issued a flash flood warning with multiple gauges in the metro recording 1.50 inches of rainfall within an hour! 

Unpleasant this morning in Tucson with dew points in the upper 60s to low 70s, temps climbing in the upper 80s to low 90s, and hardly a breathe of wind. 

Speaking of humidity, this morning's 12z TUS sounding measured total precipitable water of 1.88 inches which is well above the daily maximum record of 1.48 inches! It is also extremely unstable across SE AZ with the 12z TUS sounding measuring 3100 J/kg of CAPE and 16z  mesoanalyis indicating between 1500 and 2000 J/kg of CAPE across the region.

12z TUS sounding courtesy of SPC.

16z SPC mesoanalysis of CAPE/CIN.

There is some CIN this morning though due to mid level cloud cover. CIN should erode into early this afternoon as clear skies in SE AZ (indicated by vis imagery) will allow low level lapse rates to steepen.

GOES-17 visible imagery at 10:20 AM MST this morning courtesy of College of Dupage.

Not much change regarding the synoptic pattern with the mid level anticyclone centered over New Mexico and weak southeasterly/southerly mid level flow over AZ.

SPC 500mb analysis as of 17z this morning.

Today's Forecast

Synoptics/Kinematic Forcing

As mentioned above, no significant changes to the overall synoptic upper air pattern compared to yesterday with the mid level anticyclone remaining anchored over New Mexico and weak 5 to 10 knot mid level southeasterly/southerly flow over AZ. 

The past few days, convective initiation has been primarily dependent on a surface convergence boundary between easterly winds and diurnally driven westerly winds. Today, convective initiation will be primarily dependent on localized convergence over the Sky Islands in SE AZ due to differential heating which is more typical during the Monsoon. CAMs are in good agreement that convective initiation will likely occur over the Sky Islands with the main focus closer to the International Border between Sierra Vista and Nogales. 

15z WRF-HRRR simulated reflectivity for this afternoon at 1:30PM MST.

In addition, expecting convective initiation to be a couple hours later compared to yesterday due to more CIN. CAMs seem to agree convective initiation will occur between 2 and 3PM MST this afternoon.

Thermodynamics

Ample amounts of moisture will remain over AZ today, however drier air in the mid and upper levels is moving into extreme SE AZ this morning as indicated by the tight moisture gradient via SPC mesoanalysis.

SPC mesoanalyis of precipitable water as of 18z this morning.

12z GFS 700-300mb Mean Relative Humidity courtesy of Tropical Tidbits.

This drier air aloft shouldn't have too much of an impact on storm development today and is keeping skies clear across SE AZ. However, this drier air aloft could lead to decreased storm coverage in eastern Cochise County.

With plentiful amounts of low level moisture and clear skies, CAPE values will remain between 1000 and 2000 J/kg across SE AZ through this evening. The 15z KTUS WRF-HRRR sounding forecasting CAPE in that range this afternoon.

15z KTUS WRF-HRRR sounding for this afternoon at 1:30 PM MST.

In addition, sufficient heating of the surface will aid in steepening low level lapse rates and combined with an LCL around 700mb will promote evaporative cooling in the sub-cloud layer. DCAPE values around 1000 J/kg means significant outflow boundaries are likely this afternoon. 

What to Expect/Impacts

The 15z WRF-HRRR seems to be the most reasonable solution compared to the 12z so have opted to use the 15z for this discussion. CAM solutions (including recent runs of the HRRR) agree that the strongest storms will initiate over the higher terrain between Sierra Vista and Nogales around 2PM MST this afternoon. With DCAPE near 1000 J/kg, strong outflow boundaries are likely and CAMs agree that outflow winds will move through the Tucson vicinity by the middle to late afternoon. From the 15z KTUS WRF-HRRR sounding, diurnally driven warmer northwesterly winds converging with southeasterly outflow winds could act as a lifting mechanism for storm development in the Tucson area this afternoon which seems reasonable. 

15z WRF-HRRR simulated reflectivity for this afternoon at 5:00PM MST.

Overall, expect another active storm day across SE AZ. The primary impacts from thunderstorms will be lightning, gusty winds, and heavy rainfall. Isolated flash flooding is possible today (WPC has SE AZ in marginal risk) considering ample amounts of low level moisture and moist soil from yesterday's precipitation. 

The 12z HREF forecasts a 50 to 70% chance for wind speeds in excess of 30 knots this afternoon in eastern Pima, Santa Cruz, and western Cochise counties.

12z HREF probability of winds in excess of 30 knots and mean 10-meter wind speed at 5:00 PM MST this afternoon courtesy of SPC.

Traveling conditions will be hazardous especially along I10 between Willcox and Marana as well as along I19 between Tucson and Nogales. Driving conditions in the Tucson metro will also be impacted with the main risks being reduced visibility and potentially locally flooded roadways.

Activity will primarily remain confined to SE AZ and over the higher terrain in Northern AZ, so not expecting any storms in Phoenix this afternoon and evening.

Monday and Tuesday

The synoptic upper air pattern will remain pretty consistent Monday and Tuesday with the mid level high anchored over New Mexico and southeasterly flow over AZ. A wildcard which will need to be monitored is activity in Sonora with models indicating significant activity in Sonora tonight and tomorrow night. The 12z GFS forecasts a couple of weak waves to move northward into Southern AZ (one tomorrow and another Tuesday) which are likely associated with MCVs (Mesoscale Convective Vortex) from overnight convection in Sonora.

12z GFS 500mb absolute vorticity for tomorrow at 11:00AM MST courtesy of Tropical Tidbits.

12z GFS 500mb absolute vorticity for Tuesday at 5:00AM MST courtesy of Tropical Tidbits.

These features will need to be monitored closely as MCVs from Sonora can act as an additional lifting mechanism, but can bring extensive mid level clouds as well.

Besides those features, plenty of moisture and instability will remain in place Monday and Tuesday continuing a mid grade monsoon pattern with mainly afternoon and evening showers and thunderstorms across primarily the eastern half of AZ.