Sunday, March 31, 2013

The Tri-State Tornado

A number of meteorologists have been working on re-analyses of the conditions associated with the Tri-State tornado of March 1925. The project has dragged out to more than a decade, but I can happily report that our paper on the supportive meteorological conditions has just been published in the the EJSSM.

The paper can be found at:

Our paper on the re-analysis of the damage track and related issues will appear shortly.

Sun Comes Out For Easter

Late in the day yesterday Tucson finally got a bit of sun before dark - above image is from 6 pm. This morning, Easter Sunday - 31 March, is dawning clear and sunny, as image looking north from Kitt Peak (below) shows at around 6:30 am.

Obviously, March is coming to a close after producing almost nothing in the way of precipitation for the Tucson area. Only rainfall here at the house was 0.03" on the 9th. Compared to last March, this past month has been dry and also warmer - wrt morning lows. During March 2012 there were 19 mornings here at the house with lows below 40F, 8 mornings with freezing or below, and 5 mornings with lows in the 20sF. This month there were only 9 mornings with lows below 40F and 1 day (the 1st of March) with a low below freezing (29F). Quite some difference between the two years! April 2012 brought 6 days in the 30s, as well as the year's first 100+ high - we'll see what this year has in store for us.

There continues to be little on the weather horizon. It has been interesting watching the ECMWF the past 5 days or so. That model has continued to forecast an interesting weather pattern, with a 500 mb closed low over the Southwest. However, the interesting pattern has continued to be forecast out at day 9 or 10 - thus, the next weather-maker has not gotten any closer. The 500 mb ECMWF forecast below is valid at 00 UTC on April 10th. This seems, at least to me, to be somewhat unusual behavior for the European model.

Saturday, March 30, 2013

Gloomy Start To Easter Weekend

Middle and high clouds streaming into the Southwest are making for a dreary start to the Easter weekend. Above is 7 am MST view of the Catalinas from campus. Below is 8 am MST water vapor image showing larger, upper-tropospheric low spinning well west of central California, with a long fetch of moisture into the Southwest from low latitudes.

The blended PW product from CIMSS at Univ. of Wisconsin (above for 5 am MST) indicates higher PW values of over an inch approaching Baja and southern California. However, the forecast models do little with the moisture increase, except well to the north, as the system comes in across the Great Basin from the Pacific. Below is today's early morning forecast from the Atmo WRF-GFS model on the 5.4 km domain. The forecast is of total precipitation through midnight on April 1st. The model keeps most of Arizona dry through this period. The morning soundings do indicate that some slight bits of middle-level CAPE may be coming by today, so the month may bow out with some more virga aloft.

Thursday, March 28, 2013

Dearth Of Weather Continues

The lack of weather continues here in the south of Arizona. There was a stacked, lenticular cloud over the Catalinas before sunrise, but by the time there was enough light for a photograph it had dissipated. The folks at the NWS Forecast Office may be bored also.

The above is yesterday's graphic for the Easter weekend. What can I say?

On a more meteorological note - I noticed mid-level buildups to the southwest when I walked this morning. Some had just enough vertical extent to produce ice-crystal virga. The 8 am MST visible satellite image above captures this cloud field. The Tucson sounding this morning - skewT plot below - indicates that a layer just below 500 mb may have a tiny sliver of CAPE. I know I'm really stretching to find something to write about, but that's pretty much been the story here since March 10th. So it goes.

Sunday, March 24, 2013

Spring Snowstorm

Very heavy snows in eastern Colorado yesterday with accumulations of 1 to 3 feet along the northern Front Range. Above is near whiteout at Denver International Airport, which is out in a very exposed location.

The surface low has moved to the Missouri Bootheel this morning, bringing tough travel conditions along I-40 from Topeka to St. Louis - above is 14 UTC surface chart from College of DuPage. Below is graphic showing current NWS warnings etc. The big band of "pink" is area under winter storm warnings.

Saturday, March 23, 2013

How Did 72-Hour NAM Forecast Do?

The NAM 72-hour forecast of radar echoes valid for 1200 UTC this morning (Saturday March 23rd) is shown above in the middle graphic. The 1145 UTC WV satellite image is at top and the regional radar at 1220 UTC is just above. The model had the right idea but was off some in space, with the verifying storms to the south and southeast over northern Alabama and Georgia. Model forecast was too strong also, but all-in-all not too bad for a three day forecast.

Friday, March 22, 2013

Fits Me

Thursday, March 21, 2013

Miscellany March 21, 2013

For the third straight morning skies have been dreary here in Tucson, with thick, high overcast and visibly dirty air. This morning there has even been some very high-level virga passing by - view above is from 8 am.

Re previous post - the new NAM 48-hour forecast this morning has a markedly different forecast for Saturday morning over Tennessee. Appears that the forecast MCS was a model hallucination, but will watch to see what evolves for Saturday.

This weekend is the first of the month-long Cherry Blossom Festival in Washington D.C. - see nice photo below. Looks like it will be a cold and wet and wintry weekend to kick-off this year's events.

David Blanchard has some beautiful photos of the comet PanSTARRS posted on his blog. One is below - link to his blog is at the right.

Wednesday, March 20, 2013

A Look East To The Tennessee Valley

The morning run of the NWS NAM forecast model this morning is very interesting, and it appears that an interesting forecast situation is developing over the Tennessee Valley for Friday night and Saturday morning (March 22nd and 23rd). The 72-hour forecast for 500 mb is shown above, valid 12 UTC 23 March. Not much exciting there, with strongest vorticity advection over Colorado and Nebraska and a ridge from the Gulf of Mexico to the Great Lakes. However, the same forecast for 700 mb (below) is very interesting, with an area of strong upward motion forecast to be centered on Tennessee.

The forecast for 850 mb (above) indicates a region of strong warm advection from northern Arkansas eastward across Tennessee. Forecast precipitation for the 3-hours ending at 12 UTC on the 23rd (below) indicates maximum precipitation centered near Nashville.

Finally the NAM forecast of simulated radar echoes (above) indicates an MCS over Tennessee, with strongest convective storms again near Nashville. So, the model forecasts a distinct, nocturnal and early morning MCS, with the vertical motion maximum produced both by meso-convection and low-level warm advection. Back in the late 1970s and 1980s, when the NWS was working hard to improve forecasts of heavy rain and flash floods, this was the type event that the models of that day could not forecast well. I'll keep an eye on how this situation evolves and report further. I do note that the forecast shown above also forecasts a nearly straight line hodograph, above a cool stable surface layer, with very strong wind speeds - a situation conducive to derechoes, if significant CAPE actually develops.

The situation becomes even more interesting in light of the latest NWS forecast for Nashville:

Note that snow is forecast Thursday night and Friday morning, with no thunderstorms until Saturday night.All-in-all, a very complex forecast, and I doubt that the model will get the details correct 3-days out.

Tuesday, March 19, 2013

Bats Have Returned

Our resident Western Pipistrella bats have returned to spend the summer hunting insects from the sanctuary of our front porch roof. They seem to be about two weeks early this year.

There is a serious explosion of Penstemons underway this year in our yard. However, a year ago today a heavy thunderstorm with graupel was pounding away at the flowers. Nothing like that this year.

Monday, March 18, 2013

Another Look At Long-Term

I took another look at the long-term GFS forecasts from the operational version of the model this morning. The forecasts were from 00 UTC last evening. The above is the forecast for total precipitation through the coming week. Much of the Southwest continues high and dry in the forecasts. I looked on out through the forecasts all the way to Easter Sunday (March 31st this year). Still no precipitation forecast for southern Arizona. Looks like the weather has gone on an extended Spring Break for us. Last March we had only one storm event, but that one brought 0.66", much better than this March's single storm so far.

Sunday, March 17, 2013

Wednesday, March 13, 2013

Long Spell Of Fair Weather

Looks like a long period of fair weather, with little hope for precipitation over much of the Southwest. Below is GFS operational model forecast of total precipitation through March 23rd. Quite warm the next few days - looks like a record high for today with 89F currently at airport. I think old record was 88F. The morning low here at house was 37F - so another day with more than 50F diurnal swing.

Sunday, March 10, 2013

Re Friday And Saturday Storm

We were away Friday afternoon and Saturday and so I wasn't able to observe all that happened here in Tucson. Precipitation amounts seem to have not been as great or widespread as expected. Only 0.03" total here at house, sometime between 5 pm MST on Friday and 5 pm on Saturday. The short wave and front did produce lots of convection and thunderstorms. Most significant were the strong winds of 40 to 60+ mph across most of southeast Arizona. As we drove south on Highway 83, winds at the Barrel Canyon USGS stream gauge were essentially calm. However, a few miles south, where the highway crosses an east-west ridge, the winds were very strong from the west at 30 to 40 mph with higher gusts. The winds at Santa Rita Abbey around 6 pm were quite ferocious. I checked the data from the Empire RAWS station and see that gusts to 51 mph were recorded Friday afternoon. The very windy RAWS site at Guthrie had winds to 64 mph. The two photos are of Mt. Wrightson, with some new snow, on Saturday morning - above was right at sunrise and below, with the bare winter branches of several cottonwoods framing the mountain, was an hour or so later. Several folks who had a booth at the book festival told us this afternoon that Saturday morning was very raw and challenging.

Friday, March 08, 2013

Many Thunderstorms Across Arizona

As I was driving to the University this morning about 9:30 am MST there was frequent cloud-to-ground lightning occurring west of the Tucson Mountains.The lightning plot for CGs above shows that storms occurred across much of the state during the six hours ending at noon today.

Friday Morning - Storm progress

At 6 am MST this morning the middle and upper-level cyclone is over the Pacific, west of southern California (see 13 UTC IR satellite image above). The first band of showers and thunderstorms has bypassed much of the Tucson area, staying south toward Green Valley. The morning sounding taken at TWC (Tucson NWS Office on campus) had serious data problems (below) and has a reported 500 mb temperature that is too low by several degrees C. (Eventually the unreliable Sippican sondes will be be replaced - see earlier post.) The wind profile is quite strong and gusty winds were already occurring across parts of the metro area before sunrise. Graphic below the sounding shows the composite reflectivity from the NWS Tucson radar at 6:23 am this morning - apparently a thunderstorm moved near Green Valley with the first band of showers.

I show the early WRF-GFS forecasts of total precipitation and total new snowfall through 5 pm MST on Saturday 9 March. The graphic above is the forecast for precipitation on the regional, 5.4 km forecast grid. Note the Tucson metro minimum. Below is the snowfall forecast from the high-resolution 1.8 km grid. The area of the Rim just north of Payson is forecast to receive around two feet of new snow by the model. Lesser amounts forecast for the higher mountains of southeast Arizona. Will be quite a change after yesterday's high of 80F.

Thursday, March 07, 2013

From Tony Carrillo and F Minus

Quick Look At Tomorrow And Saturday

Have taken a look at Atmo's early run of the WRF-GFS model for the coming storm system. The new forecast is even a bit faster than yesterday's run. The first band of light showers is forecast across eastern Pima County around 4 am tomorrow morning (Friday 8 March 2013). By 4 pm tomorrow afternoon the model forecasts two more bands of showers moving across Pima County (radar echo forecast below).

The forecast of 10-m winds for 3 pm tomorrow afternoon indicates quite strong and gusty winds ahead of the front (above). At 3pm the front is forecast to be in western Pima County, and it moves across the metro area between 5 and 6 pm. Note the large number of forecast winds of 25 and greater mph. High temperatures are down about 15 degrees tomorrow because of the clouds and showers and then stay in the lower 50s on Saturday. The image below is the radar forecast valid at 3 pm MST on Saturday afternoon, indicating scattered, light showers.

The forecast for total precipitation through midnight Saturday night (above) indicates light amounts over most of Pima County with the highest precipitation up in the Catalinas, where the model forecasts 7-12" of new snow. It is important to remember that the model forecast of total precipitation has been too low for the last two events.