Tuesday, October 21, 2014
There were isolated showers yesterday afternoon over higher elevations of eastern Pima County. The plot above shows CG lightning flashes through midnight last night - very large decrease in activity when compared to the same plot for Sunday in yesterday's post. Rainfall was measured at 9 ALERT stations (10% coverage) and these sites were in the Catalinas/Redington Pass area and also at the far south edges of network. The early WRF-NAM forecast yesterday was quite good again. Today's model run forecasts only light showers at the very highest elevations of eastern Pima County.
Posted by Bob Maddox at 5:49 AM
Monday, October 20, 2014
This morning was clear and crisp, as per view of Catalinas above, with temperatures this part of town in lower 50s around sunrise. Yesterday was an active thunderstorm day, especially for October, and the plot of CGs below is for 24-hours ending at 1 am MST this morning (Monday, October 20th). There were two severe storm reports locally - lines and poles down somewhere between Ft. Lowell and River and hail to size of golf balls near Tubac. I suspect that the lines were felled near here, because of power surges and blinking lights.
Across the ALERT network areal coverage of rainfall was more than 70% for 24-hours ending at 5 am MST this morning. There were 19 sites with more than 1/4 inch and 5 with more than 1/2 inch. Keystone Peak, off in southwest part of network had 0.83 inches. Largest amount I noted this morning was 1.14 inches, with thunder and gusts to 52 mph, at Safford. Here at house we had thunder, wind, dust, gusts of 40 to 50 mph, but just 0.14 inches of rain.
It was interesting that storms avoided the higher elevations of the nearby Sky Islands with little rainfall noted at spots like Mt. Lemmon, where POPs and amounts are usually much higher than at lower elevations. The early run of the WRF-NAM model was quite good for yesterday afternoon and it kept the rain at lower elevations here in the metro area. Its areal coverage also appeared fairly accurate.
This morning's sounding at TWC on campus (skew-T plot above) is much stabilized, compared to yesterday's. There is at most a sliver of afternoon CAPE at low elevations and the early WRF-NAM reflects this, with its forecast of only some very isolated showers on the mountains today.
Posted by Bob Maddox at 8:25 AM
Sunday, October 19, 2014
Showers and thunderstorm are moving across the Tucson area this afternoon and web cam view above shows high storm bases and light showers between the University and the western Catalinas. Here at the house we had strong outflows (estimated gusts 40 to 50 mph) about half an hour ago, with blowing dust and several power surges.
Composite radar image from NWS TUS below at 2:36 pm shows a number of strong storm cores over southeast Arizona with reflectivities of 50 to 60 dBZ.
Shown here are two products from the TUS radar that are available at the College of DuPage weather site. Thunderstorm tops (at 2:41 pm MST, above) are in the 26 to 32,000 ft msl range, with some higher tops indicated at long ranges (this may be a bit of an artifact due to beam width at those ranges). The 0.5 degree beam, dual-polarization hydrometeor type algorithm (below, also at 2:41 pm) indicates hail and graupel with the storms cores. Quite an interesting afternoon.
Posted by Bob Maddox at 3:28 PM
Friday evening sunset - Katie took this photo with her phone as we were driving south on Highway 83. Ridge to west is the north end of the Santa Rita Mountains. Earlier in the afternoon showers over metro Tucson produced a couple of sprinkles and a Trace at the house.
Unusual and somewhat strange situation today. A weak short-wave and closed low is centered out near the north end of the GoC this morning in lower levels. The circulation has a pronounced tilt toward the northeast with height and very warm upper-tropospheric air is within the upper part of the circulation. This results in a very strong inversion just above 400 mb. The above skew-T plot is the early WRF-NAM forecast for Tucson valid at 2 pm MST this afternoon. The inversion is weaker in the model forecast, as would be expected, but still provides a formidable cap to convection rooted at lower levels. The forecast sounding exhibits CAPE from just above 700 mb up to just above 400 mb. Note that the lifted parcel temperature excesses are actually quite large around 500 mb, indicating substantial vertical accelerations in any convection that develops. Any thunderstorms that occur would be fairly short and stubby towers, with bases around 11,000 feet and tops around 26,000 ft MSL. However, the updrafts should be potent enough to produce some lightning and perhaps small hail or graupel. The graphic below shows the early WRF-NAM forecast of composite radar echoes valid at 3 pm MST this afternoon.
Posted by Bob Maddox at 10:57 AM
Friday, October 17, 2014
A weak, middle and upper-level short wave is moving into Arizona today from the Pacific. There are several bands of very light showers ahead of this feature. The graphic above is TUS NWS radar composite chart for 8:22 am MST this morning - showers are moving generally northward while the bands are inching eastward. Visible satellite image from 8 am below shows that most of Arizona has heavy cloud cover this morning.
Perspective from the water vapor image, at same time above, indicates the upper-tropospheric vorticity center is probably near Yuma this morning. The 12 UTC TUS sounding plot below indicates that cloud bases are very high - near 500 mb (i.e., around 16,000 ft msl) with temperatures at cloud base being around -6 to -10 C. Today's short wave will be followed by another on Sunday and yet another Wednesday - so some cloudy periods and perhaps more light showers off and on for next five days or so.
Posted by Bob Maddox at 8:47 AM
Tuesday, October 14, 2014
The NHC has upgraded Gonzalo first to a hurricane today and now to a Category 3 storm. Visible image above is from 2115 UTC this afternoon and shows Gonzalo well to the north of Puerto Rico. The wind speed probabilities plot below shows that the current track forecasts take Gonzalo near Bermuda, which is cleaning up after being struck by Fay.
Posted by Bob Maddox at 3:16 PM
Monday, October 13, 2014
Sunday, October 12, 2014
Tropical Storm Fay struck Bermuda overnight with some wind gusts over 80 mph. The storm is now expected to move rapidly east-northeastward. The NHC forecasts high chances of development of a depression or storm from a disturbance that is currently approaching the Windward Islands. Above is current NHC activity chart for the Atlantic and below is a visible satellite image from 1345 UTC this morning.
Over the U. S. the coming week will feature unsettled weather over the central and eastern portions of the country, as well as the far Northwest. A 500 trough currently over the northern Rockis will will amplify as it moves southeastward across the Four Corners Region, developing into a major trough over the Southern Plains. This system closes off and moves slowly eastward during midweek, before imapcting the northeast. Shown here are the GFS ensemble 500 mb means and spaghetti plots. Above graphic is valid at 1200 UTC on 15 October and below is valid at 1200 UTC on 19 October. The GFS ensemble members display little spread in their forecasts (except high latitudes, through next weekend. The West will enjoy mostly mild and fairly typical Fall weather.
Posted by Bob Maddox at 7:49 AM