Saturday, October 21, 2017

Seven-Days Out

I have been watching the longer-term forecasts toward the end of the coming week. The ECMWF operational model has trended westward with the large 500 mb trough forecast by 00 UTC on October 28th (above). The shift west and southward was quite abrupt between the 12 UTC runs yesterday morning and the 00 UTC run last evening (above).

However, the GFS ( same forecast below, also from 00 UTC) has continued to be very progressive with the trough. It is interesting that at this time frame the ECMWF 500 mb heights over the Four Corners are 300 m lower than those in the GFS forecast (300 m is a really significant difference). So again we'll have to watch how both models trend as the week evolves.

The 00 UTC GEFS spaghetti plot for 500 mb (above) indicates considerable uncertainty for western U.S. and eastern North Pacific.

Super typhoon Lan (IR image below, from about an hour ago) seems headed toward Tokyo, and may be a wild card player in the longer range forecasts.

Thursday, October 19, 2017

Continued Dry

Last two days have provided some clouds after five days or so of mostly clear skies. Top is view to north from campus last evening. The cloud band over the Catalinas moved eastward (above) and was colored by the setting sun. This morning, as a weak short wave at 500 mb approaches, there were some build-ups at sunrise (below) off to the northwest.

The 06 UTC run of the WRF-GFS at Atmo forecasts some light showers from just north of us northeastward across the White Mountains - below for total precipitation though 5:00 am MST tomorrow morning.. The GEFS plumes indicate some chances for light sprinkles at airport today, and that's about the best models can do

Tuesday, October 17, 2017

Atmo Seminar This Thursday

Alexander B. Prescott posted a comment to the previous post about an Atmo seminar this Thursday, and I thought I should highlight it here.

Complete abstract above - see

As for our very dry October - above is the 06 UTC GEFS ensemble forecast plumes for precipitation at TUS out through the 25th - not good.

Monday, October 16, 2017

Mild Easterly Breezes And Temperatures At Sunrise

Very dry October continues with little hope for precipitation indicated by forecast models.

Was very mild at sunrise today - currently at house it's 70 F vs 50 F yesterday, and looks like airport low will be 71 F. Surface plot above from 7:00 am MST indicates anticyclone center at southeast corner of New Mexico. Winds gusted to 41 mph (below, with gust speeds indicated in far right column) at the Mt. Hopkins RAWS site during the night, illustrating again the usefulness of the WRF forecast sounding at Sonoita.

The GFS forecast has come into sync with the ECMWF, and both models now forecast next short wave at 500 mb to move rapidly across the Southwest, before closing off over Texas.

Sunday, October 15, 2017

Backdoor Front Will Bring Winds From East

Cool morning here with low of 50 F at house and noticeably cooler down along the Rillito - very pleasant given the hot afternoons.

Strong pressure gradients with front moving westward across southern New Mexico will bring east winds later today. Sea-level pressures are over 12 mb higher over southeastern New Mexico than here in Tucson note the gust to 48 mph at Guadalupe Pass (above - 7:00 am MST surface plot). The lightning report from White Mountains is a bad observation. The 06 UTC WRF-GFS forecast skew-T for Sonoita at 1:00 am tonight (below) indicates that winds may gust from 30 to 45 mph at the Mt. Hopkins RAWS site tonight.

In the longer term, the operational ECMWF (above) and NWS GFS (below) are both forecasting the tail-end of a short wave to dig into the Southwest next weekend - both forecasts valid at 5:00 pm next Saturday. The last several days the ECMWF was forecasting  this feature to close-off over Arizona, but has now become progressive. However, several of the GEFS members forecast a closed low over Arizona at this time. So, we'll watch to see which model prevails.

Couple of shots here from Mesa Verde NP. Above is highest peak of Sleeping Ute Mountain looking west-northwest from Wetherill Mesa. Below is looking west from the visitor center at the entrance to the NP.

Saturday, October 14, 2017

Very Dry Period Continues; For How Long?

The very dry period continues, since beginning on August 13th - just over a quarter of an inch here in that period. The 168-hour, 500 mb GEFS spaghetti plot above is valid at 5:00 pm on October 20th and provides little hope for relief here in southern Arizona. There is little spaghetti at this long range, and that is over Europe and the Middle East. Models predict that we stay on the windy and dry side of the trough over the Northwest.

We've been away the past week on a road trip to the Four Corners region, and included time at our favorite hotel, La Posada, in Winslow. Even though it's October, the large cottonwoods there had only a slight hint of yellow. However, some other varieties were turning and providing very nice Fall colors.

The temperature there was below freezing on Tuesday morning, the tenth, but the sprinklers were still on - as per icicles on the tree shown at bottom.

Saturday, October 07, 2017

Cool Morning Here

Morning view above from downtown looking west toward "A" Mountain. Skies clear with very low RH and dry conditions - PW values at sounding time around 5 mm (see GPS time series on campus below). Conditions very good for nighttime radiational cooling allowed temperature to fall from 95 F at airport yesterday to a morning low of 46 F here at house this morning.

Main weather news this morning is that hurricane Nate is moving rapidly northward toward New Orleans/Biloxi areas and strengthening some. NHC predicts Category 2 at landfall early tonight. The IR image of Nate, at bottom, is from 1415 UTC this morning.