Sunday, March 29, 2015

The Palm Sunday Tornado Outbreak Of 1965


Nearly 50 years ago there was a deadly outbreak of tornadoes across the upper Midwest (states with tornadoes were IN, OH, MI, WI, IL, and IA) on Palm Sunday 1965. Palm Sunday that year was on April 11th. This was the largest outbreak of tornadoes on a single day up to that point in our recorded weather history. There were at least 47 tornadoes and fatalities exceeded 261 people.

The image above has become an icon of severe storm photography and was taken by Paul Huffman near Elkhart, Indiana. It captures a double vortex tornado crossing a highway and railroad tracks - the tornado is so close that debris can be seen in the air near left side of photo. Fujita et al. published a detailed study of the event in Monthly Weather Review (January 1970 issue) and the abstract is below. Fujita's aerial survey documented numerous tracks of looping, "suction spots", which are now known to be damage tracks of sub-vortices embedded within multi-vortex tornadoes. The paper demonstrates how crude the radar and satellite data were 50 years ago.

I remember that day vividly. I was a junior in college and was home, in southern Illinois, for the Spring/Easter break. I was playing golf that afternoon with my Dad and several others at a course on the Mississippi River bluffs east of St. Louis. The dryline came through and we finished our round in winds gusting to at least 50 mph from the southwest. Even though the area was within a tornado watch, all of the thunderstorms and tornadoes occurred far to the north of where we were.



This year the severe thunderstorm season has been very calm so far. The two maps here are from SPC and show the areas affected by tornado watches above and severe thunderstorm watches below - only 4 of each flavor have been issued so far during 2015.


High Clouds On Increase Next Couple of Days


A weak 500 mb low west of Baja will impact our weather the next several days - mainly by spewing some high and middle-level clouds across southern Arizona. The WRF-NAM model (06 UTC run) currently forecasts some weak radar echoes over southeast Arizona tomorrow (above is forecast of composite radar echoes valid at 9:00 pm MST Monday). The forecast of PW valid at same time (below) indicates values reaching amounts just over half an inch. So, not surprising that the model forecasts little in the way of rain to actually reach the ground.

Second graphic below shows the 500 mb forecast (on the 5.4 km grid) valid at 9:00 pm tomorrow. At that time the closed low is forecast to still be west of Baja, while a weak short wave to its north is inching across Arizona. 




The GFS average 500 mb heights from the ensemble runs are shown above (valid March 31st at 5:00 pm MST) and below (valid April 4th at 5:00 pm). The model indicates that the Southwest remains in weak flow through the next several days. But after that the main branch of the westerlies shifts southward as the Pacific ridge and split flow regime shifts (at least temporarily) west to the central Pacific. So even if precipitation with systems in early April stays north of us, we'll probably see some spring winds starting to blow dust and pollen around. Gesundheit!


Saturday, March 28, 2015

Record High Today Plus Bright Yellows


Sparkling clear skies again today over most of the Southwest. High this afternoon (above visible image from 1:30 pm MST) at the airport reached a record for the date, 93F, breaking the old record of 91F. Here at the house the morning low was 39F, giving another day with a very large diurnal temperature range.


Some bright yellows out in the yard. Above, an agave doing its thing, with the waxing moon up there in the background. Palo Verde tree below, was a volunteer years ago, sprouting from a wind-blown seed.


And a bit of red too, from blooming ocotillas below.



Friday, March 27, 2015

March 27th - Severe Clear


Clear skies dominate much of the Southwest this afternoon. Temperatures in Tucson area have climbed into the low 90s for the first time this spring and are close to the daily record for the 27th. More tomorrow.

Edited to add: High at airport reached 93F today - one degree below the daily record of 94F. Low here at house this morning was 37F, giving a diurnal swing of about 56F up here along the Rillito.

Wednesday, March 25, 2015

Weather Miscellany


Winter is still hanging on in parts of the country as March winds down. Above is a view in Green Bay, Wisconsin, early this morning (Wednesday, March 25th).


Here in Tucson area there has not been much to talk about this week. It's been dry and sunny, which leads to continued big differences in low temperatures here along the Rillito versus the "official" lows at the airport. Yesterday was fairly typical of much of the month - low here at house was 37F, while low at the airport ASOS was 50F.

Dewpoints yesterday afternoon dropped into the single digits at the airport and the high temperature hit 84F. The WRF-NAM forecast (from 00 UTC last evening) above is for PW valid at 6:00 pm MST tomorrow, the 26th. Note that the entire domain is forecast to have PW of less than 10 mm - so dry continues to be a main weather word here, as will hot by the weekend. 

Monday, March 23, 2015

It's World Meteorological Day


Hug a Meteorologist Today: Today is World Meteorological Day, celebrating the inception and continued contributions of the World Meteorological Organization, and this year's theme is "Climate knowledge for climate action." See
https://www.wmo.int/media/content/world-meteorological-day-23-march-2015-climate-knowledge-climate-action                  
Above is this year's WMO poster and below is that from 2014.


Sunday, March 22, 2015

A Beautiful Sunday Afternoon


Saw a bird I'd never seen before on my walk this morning. I think it was a Say's Phoebe (a flycatcher), shown above (not my photo). After a chilly low of 40F this morning, temperatures now up into mid-80s.


Kitt Peak web cams a bit before 4:30 pm MST show cirrus to the north and clear skies deep into Mexico to the south.



The GFS 500 mb ensembles (spaghetti chart above) continue to forecast a ridge dominating western North America (charts above valid at 12 UTC on March 29th). Considerable "spaghetti" within the weak, southern branch of the split flow regime over West and east Pacific. Looks like cold trough prevails over the eastern U.S., where Spring is a bit delayed this year.

Saturday, March 21, 2015

Isolated Showers Yesterday - Ridging In The Future


Atmosphere over southeastern Arizona dried considerably during the day yesterday (PW was at 0.75" at 12 UTC but had fallen to 0.39" by 00 UTC) resulting in only isolated moderate buildups over higher elevations (as per 6:00 pm view of the Catalinas above). There were some puny Cbs around eastern Pima County, but most substantial thunderstorm activity was far to north and northeast. Below is 24-hour precipitation through 6:00 am this morning (from MesoWest), showing very little happening yesterday.



For the coming week (as per the GFS ensemble forecasts' average 500 mb heights), we'll start with zonal flow, with stronger flow far to our north (top, valid at 12 UTC on the 24th). But by the end of week the GFS forecasts a strong re-building of the western U.S. ridge (below valid at 00 UTC on the 28th). Flow does remain weak and chopped up over Arizona and northwestern Mexico, so the most unusual warmth will be over Utah and northward. We are heading rapidly toward our dry and hot months of April through June, and so time is running out for a final, significant rain event for southern Arizona.