Thursday, July 19, 2012
A Cloudy Morning
At sunrise, the NWS TUS radar indicated light showers to the east near Benson. The spike that points at Silver City depicts microwave energy from the sun. Heavy middle-level cloudiness has spread rapidly northward across most of Arizona (visible satellite image at 7:30 am MST is below) during the night. Precipitable water has inched up to around 1.25" across southern Arizona, and a push of higher dewpoints from the GoC is indicated by latest observations from Yuma.
Thunderstorm activity will return to southeastern Arizona today, however, it is not clear whether much CAPE will develop over lower elevations. The Phoenix morning sounding is very dry below 600 mb and the early WRF-GFS forecasts (above is composite radar at 4 pm MST and below is total forecast rainfall ending at midnight tonight) keep the significant storms at higher elevations. There is no sounding data for Tucson this morning. The early WRF did not have nearly enough cloudiness in its initialization, and heating during the morning is probably over-forecast. Will be interesting to see what the 12 UTC runs forecast for this afternoon. Storms will likely form later than the model currently predicts. The upper-level cyclone currently is centered near the Big Bend of the Rio Grande. This feature is forecast to move slowly westward for the next several days, as it gradually weakens. It appears that, because of the cyclone, there be pronounced upper-level difluence over southeastern Arizona the next two days. Although thunderstorm activity will increase, the degree to which we might have storms at lower elevations will depend upon how the moisture and CAPE evolves.
Posted by Bob Maddox at 8:44 AM