Tuesday, March 20, 2018

Sun Pillar

There was a very colorful, but partially broken, sun pillar at sunset on Friday the 16th. Katie took these images with her cell phone from Campbell and River.

Sunday, March 18, 2018

Sunday March 18th - Updated Monday AM

Updated Monday morning, 19 March - Yesterday's weather "event" played out as expected, with mostly light sprinkle showers and Traces of rain around the area. Plots above and below show 24-hour precipitation ending at 7:00 am MST this morning (top from ALERT and below from MesoWest). Just a couple of gauges with measurable precipitation, mostly in and near the Catalinas. The GEFS forecasts are now trending toward dry for this week - so it goes.

Cold front is approaching this morning with attendant band of cloudiness. The IR satellite image above (from 6:00 am MST) shows this cloud band across southern Arizona. The MIMIC PW analysis below (also from 6:00 am) indicates a slight increase in PW associated with the band, but with amounts that are very low - around a half an inch or less.

As the front crosses the metro area this morning the 06 UTC WRF-GFS forecast (below - precipitation through midnight tonight) indicates sprinkles across the metro area. The blues range from a Trace to around a quarter of an inch. Main impact of this system will be briefly cooler temperatures, and then we'll await next system toward end of new week.

Saturday, March 17, 2018

Back from Road Trip

We have been away this past week on a road trip to northern New Mexico. The main weather word for the trip was "wind" and I'll cover that in a later post. View above is of the sparsely snow-covered southern end of the Sangre de Cristo mountains (looking north-northwestward from Pecos, New Mexico). Significant drought continues over much of the Southwest and Spring snow cover in the mountains is well below normal.

This weekend another short wave at 500 mb will be crossing the Southwest - below are four panels from the GEFS run at 00 UTC last evening showing the forecast of this feature over Arizona at 12 UTC tomorrow morning (Sunday).

The 06 UTC GEFS QPF plumes for TUS (above) indicate a slight chance for light showers with this system tomorrow morning, and perhaps another system on the horizon at the end of next week. The plumes for PW (below) show the current system to be quite starved for moisture, while the models try to pick up a Pacific moisture plume in the forecasts for the end of the week.

At the bottom is the 06 UTC WRF-GFS forecast from Atmo - shown is that model's dismal forecast for precipitation through 06 pm MST tomorrow for southern Arizona, with the weekend precipitation confined to higher elevations of north and east Arizona.

Sunday, March 11, 2018

Our Latest Event - Heavy Clouds and Sprinkles

Folks at the Book Festival were mostly under the tents late in day yesterday, as sprinkles moved in after 3:00 pm MST.

All the various models I looked at yesterday were off considerably - especially with their trend overnight for a wetter event. Sadly, the GEFS back on March 8th was much better, with a consensus  QPF for airport of a Trace to around .02". None of the ASOS sites in southeast Arizona had recorded more than a Trace when I took a look at 6:00 am this morning.

ALERT measurements at that time (above) had only Mt. Lemmon (and Keystone Peak) stations with 0.04" or more. The MesoWest local plots an hour later (below) indicated a few spots with measurable precipitation. We had 0.01" here at the house.

Best ensemble forecasts yesterday morning for this "event" were the dry outliers in the plot from the SREF forecasts shown in previous post.

Saturday, March 10, 2018

System Tonight Looks Wetter Than Expected

During the night forecast models have picked up the substantial moisture plume headed our way from lower latitude,s and become wetter for tonight's precipitation. The 13 UTC MIMIC TPW (above) shows values around an inch already creeping into southwest Arizona. The analysis also picks up two cyclonic circulations that are heading northeastward - one is near 26 W just north of 30 N and the other is near 133 W just south of 30 N.

The 1330 UTC IR satellite image below indicates how substantial the cloud/moisture plume is - extending far to the west-southwest and reaching below 25 N. The Yuma NWS radar (KYUX - second below) is already detecting light showers over southwestern AZ. Note - the small, bright red echo between Mexicali and San Diego is return from a wind farm just south of the border.

The model forecast plumes have also become wetter during the night - above shows QPF plumes for TUS from the 09 UTC SREF run and is from the plume-viewer at SPC. The spread is fairly large for tonight's event, ranging from a Trace to almost half an inch. The means are similar for both the GEFS and SREF plumes - around 0.15". Forecasts are basically for a light rain event at low elevations, but one with essentially 100% coverage.

The graphic below shows the changes in the plume mean for the last four forecast runs of the SREF (color code for run times at top right). The runs yesterday were quite dry, but the two runs after 00 UTC have become considerably wetter.

Finally, a look at a couple of forecasts from the 06 UTC WRF-GFs. Above is forecast skew-T for TUS valid at 06 UTC tonight. The sounding is forecast to be deeply moist, with over an inch of PW - very substantial changes between now and then. Below is model forecast of total precipitation through 06 UTC tomorrow morning.

Impacts for the Book Festival - much of which is outdoors along the University Mall - will be a damp and cool morning tomorrow, with perhaps some lingering light showers. Will showers develop before today's events wind down? That's a close call and we'll just have to watch.

Friday, March 09, 2018

Tucson Festival Of Books This Weekend

The Tenth Annual Tucson festival of Books will be occurring this weekend. Models continue to forecast a threat of sprinkles or light showers Saturday night, but most of weekend should be pretty good for the Festival - perhaps some clouds providing a nice change from last year when it was sunburn city.

Middle clouds over the Catalinas this morning. Below is 06 UTC WRF-GFS forecast of total precipitation through 5:00 am MST on Sunday morning - model forecasts a Trace to around a tenth of an inch across southern Arizona. 

Note that Daylight Savings Time begins Sunday morning, but most of Arizona will remain on MST.

Thursday, March 08, 2018

A Dreary Start To Day

It's a mild but dreary morning here with heavy, high clouds from the Pacific - as per above view from campus. Below is 6:00 am MST IR image showing the cloud stream from the Pacific across much of central and southern Arizona.

Not much in the 06 UTC GEFS plumes for QPF at airport this morning - some chance for sprinkles on Sunday and some possible activity out at an uncertain week away. The plumes for PW indicate some moistening occurring on Saturday afternoon into Sunday, and then increasing chaos after that. 

Image at bottom shows hostile conditions at the South Pole this morning.