20170823

Eclipse

I’m back after a mostly successful trip to Idaho to see the total eclipse.  The weather could have not been better as a weak trough came through during the night and as it departed, 700mb winds became northwesterly which then cleared out all the smoke. A bit of cirrus associated with the trough moved to the east and by 9 am, skies were cloudless and a deep blue.  Once totality began, the corona was visible out a couple of solar radii and through binoculars, it was absolutely amazing with significant detail visible as well as three areas of prominences clearly visible.  Venus was very bright and Mercury could also be seen.  As some of you know, I’m an astrophotographer and I had a little f4.8 80mm refractor and astro camera with me.  My main goal was to watch as much of the eclipse as possible as at the last eclipse (1979!) I mostly monkeyed around with the camera and telescope and didn’t really watch the eclipse.  This time, I had automated the whole imaging process and I just had to push “start” on the computer and it would do everything and had practiced many times.  Once totality began,  I neglected to take the solar filter off of the telescope so all images were blank! My primary goal was accomplished though so I don’t feel too bad as there are plenty of great images available now. I also wanted to mention that many people in Boise thought that 99% would be “enough” and it wasn’t worth the 60-minute drive north for an extra 1%.  They could not have been more wrong.  You can’t see any of the corona or prominences/chromosphere or see how dark the immediate vicinity becomes.  Also, photographs are unable to capture the large dynamic range unless using HDR techniques and even then, they don’t give you the visceral feel of looking at this amazing spectacle with your own eyes.

This image taken by astrophotographer Dennis Sprinkle comes close.

Initializations

The model runs yesterday forecasted an increase in activity today.  Looking at the 500mb plot, the setup doesn't look all that great as the high center is just to the east of Tucson with mainly SW flow over most of the state.  Plus, 500mb temperatures are a warm -4C.  A weak MCV/IT is located over northern Sonora and is moving slowly north along with quite a bit of cloud.  Upper troposphere flow is quite strong as SW winds are above 50 knots at 250mb.   The morning sounding at Tucson does have 1100 J/kg of MLCAPE present along with wet air almost to 500mb. There’s a significant inversion just below 500 mb, but with enough heating and CAPE it will probably break at some point.  The RRx mid level initialization is good and does have the IT initialized. The GFS and NAM do not.   There are some thin mid level clouds over SE Arizona which are slowly dissipating.  The RRx and GFS actually have SE Arizona too cloudy while the NAM looks a bit clearer. IPW errors are mainly small except for a wet bias in all three, especially the GFS. Overall, it’s hard to say which is best due to the cloud issues in SE Arizona.  Elsewhere, the initializations look fair and there is no clear favorite.

Day 1

A weak gulf surge has increased moisture over southern Arizona and pushed IPW into the min 30mm range. The surge continues to advect moist air into the state during the day.

CAPE is forecast to be moderate to high over much of southern Arizona and into New Mexico.  The question is if there is enough heating to overcome the slight cooling in the lower troposphere due to the surge.

The WRFNAM and WRFRRx runs have the weak IT just south of Nogales by midday. This is too fast as the center of circulation is still about 200km south of the border at 17Z and the WRFGFS has the best initialization.  It may be important to get this right as this feature is likely to enhance and organize deep convection.   Another problem is that the three runs have a range of IPW early this afternoon from 34 to 41mm (WRFGFS).    The middle of the road is the WRFRRx which is below.  It has around 1000 J/kg but poor winds as they are mainly unidirectional from the SW.   So, my guess is there will be plenty of storms around SE Arizona but won’t show much organization.

There are some areas of upper divergence over SE and east central Arizona which may help storm organization.  However, anvil shading may be a problem for lower elevations. Anvils will race ahead of the storms as mid level flow is only 15 to 20 knots.

The general message that the three 12Z runs have a lot of activity around SE Arizona by early afternoon.  Some isolated severe storms are possible.  There is some uncertainty about the influence of the upper IT and its poor initialization in the WRFRRx and WRFNAM.

DCAPE from the 12Z Tucson sounding was quite high at around 1500 J/kg, thus there is a risk of strong to isolated severe microburst winds and strong outflow winds.

As always, it’s a tough call in and around Phoenix.  The WRFNAM keeps the PBL shallow in the Phoenix area due to the gulf surge. The WRFRRx (below) mixes fairly deeply by late afternoon accompanied by a moderate amount of CAPE as moisture slowly increases and mid level temperatures cool slightly. The wind field is poor with mainly unidirectional flow of only 10 to 20 knots below 500mb.

SE AZ storms develop along the outflow boundary into Pinal County by late afternoon or early evening.  

A moderate to strong outflow is ejected from this activity towards the Phoenix area.  There are no storms forecast to the north or northeast of Phoenix, thus no intersecting outflows, thus the question is if the outflow from the SE will be strong enough to trigger additional deep convection.

The answer is a definite ‘maybe’ as the WRFNAM does develop a few weak storms this evening.  

A quick peek at the 15Z WRFRRx shows more activity around Phoenix this evening.  The model forecasts may be an hour or two early.

The 15z WRFRRx also has stronger outflow winds thus there is a risk of a large dust storm/haboob this evening for Phoenix.

Day 2

That was about it for the big return of the monsoon as very dry air once again advects into the state.  Activity is restricted to the higher elevations of eastern and northern Arizona.