Arizona WRF Discussion: 20220618

Previous Forecast

Activity increased slightly in southeastern Arizona, but not as much as was forecast. At least western NM got dumped on. WRF forecasts had the majority of activity in the right place, except around Tucson. The model runs had activity in and near Tucson, but it ended up being west, in central Pima County. It appears it did rain on Kitt Peak, so I'm glad I was wrong!

As I wrote the discussion yesterday, a little voice was nagging me, saying, "what about all the clouds from the MCV?" It turns out that clouds didn't burn off as rapidly as in the forecasts due to the presence of the MCV. This can be seen in the plot of the Average Tucson Temperature plot as WRF forecasts were quite a bit warmer compared to what was observed, resulting in too much activity.

Discussion

The pattern over the CONUS is amplified, with deep troughs over the coasts and a dominated ridge over the country's center. Flow over most of the state is quite strong from the SW. Moisture has increased over the state, with PW being as high as 34mm at Tucson due to moisture from TS Blas. Another interesting feature, best seen in WV imagery, is a large upper-level inverted trough covering much of northern and central Mexico. 300mb analysis indicates a significant area of upper divergence exists over much of Sonora, and this is likely to help enhance storms today and tonight.

The increase in moisture has not been sufficient to increase CAPE that much. Phoenix does have around 350 J/kg of MLCAPE, which seems to be enough to support the ongoing activity between Tucson and Phoenix. Based on the wind field, lack of CAPE, and widespread cloud inhibiting heating, it doesn't look like it will be very active for the lower elevations.

Initializations

It's a complicated morning with multiple MCVs spinning over SW NM and NE Sonora and storms over Pinal County. Some of the WRF runs from yesterday did have the central Arizona activity. The RR wasn't too bad initializing the MCVs as it has a broad weak cyclone circulation approximately in the correct location. The HRRR also had a weak circulation in the vicinity. Clouds look well initialized by all, but we'll have to see how WRF handles the burnoff. Only the 9Z RR developed the weak storms in central Arizona. Generally, initializations look good with no major issues.

Day 1

Moisture advection into Arizona continues today, resulting in 850mb dewpoints around 10C. South central and southeastern Arizona will be the most active today. An area of drying due to subsidence is over NM, with the boundary right along the NM/AZ border. This boundary could be the focal point for convection today and tonight.

Like yesterday's forecast, CAPE becomes relatively high by early afternoon and more than enough to support some strong thunderstorms with the caveat that these areas see some surface heating. As of 1730Z, most runs have burned off clouds too quickly. The 9Z WRFRR has a pretty good handle on clouds, so perhaps it will be the model of choice, especially considering it was also able to forecast the ongoing morning convection reasonably accurately.

Storms developed during the early afternoon over much of southeastern Arizona, with some producing heavy rain.

Besides heating/clouds, there is another model error, moisture. GPSIPW is only 34mm at Tucson, while all the model runs are 2 to 6mm too wet. The 12Z WRFHRRR is the closest to observed, and the forecast vertical profile indicated around 1000 J/kg of CAPE, which may still be too high. The wind profile is unfavorable, mainly unidirectional flow and minimal speed shear.