and that is fifty !

Today, 21 october, was the 50th thunderstorm day of 2010. In the early afternoon, thunderstorms passed my village just to the north and, for the time of year, were quite active. Also they were moving rather fast due to the high windspeeds at all levels of the atmosphere. There was also a decent vertical windshear, so this helped the organization of the storms.

Thunderstorm Climatology part II

My follow-up of the thunderstorm climate of Romania.
From the extensive database of www.tutiempo.net I calculated the number of thunderstorm days for numerous places in Romania. After that I drew a map to see the spatial distribution:


Average annual number of thunderstorm days for Romania, 1991-2010. Iso-lines: pink=38, red=34, yellow=30, green=26 and blue=22.







It's clear that the central part of Transylvania and a belt just south of the southern Carpathian mountains (Transylvanian Alps) receive most thunderstorm-days, with 35 to 40 on average. This is among the highest in Europe. Other area's in Europe with comparable numbers of thunderstorm days are the southern French Alps, the Po River Valley, the Croatian coastal areas and western Bulgaria.

An other conclusion is that the number of thunderstorms decreases in east and northeasterly direction. One cause could be the dryer/more arid conditions in the east/northeast. The town of Sulina for example, with 15 annual thunderstorm days, gets only 400-450 mm of precipitation per year.
Other interesting observation is the local maximum about 20 kilometers inland from the Black Sea coast. Here thunderstorm development on the seabreeze-front is a plausible explanation for this local maximum.

For the decrease in number near the southern border I have no good explanation. On the Bulgarian side of the river Danube, the annual number is comparable to that of extreme southern Romania. However, further to the southwest it increases dramatically to around 40 near Sofia, Bulgaria.

last thunderstorm of the year ?

Sunday evening, September 19th, a coldfront came in from the west-northwest. On the front edge of the precipitation area thunderstorms developed. For the time of year they were rather active thunderstorms. Lightning activity was around 15-20 flashes per minute at it's peak. Also there were a few exceptionally bright CG's (cloud to ground lightning) nearby. Even with a setting of f/10 on my photo-camera they caused a completely white-out of the image.....
Because of the heavy rain and because the thunderstorms were a bit unexpected, I couldn't make much images.


















Autumn is a short season in Transylvania, so it is likely that this was the last thunderstorm of the year.

Thunderstorm Climatology part I

Summer is ending soon, here in Romania. For thunderstorms it was a rather good year with numerous thunderstorms, although most thunderstorms were of the airmass thunderstorm type. Well organized storms didn't occur often.

On average nearly 40 thunderstorms days do occur here in central Transylvania. To see how this is distributed over the year I did some statistical research. And this is the result:






Table 1. Number of thunderstorm days for LRTM (Tirgu Mures) for the last 20 years. Data extracted from www.tutiempo.net

Season starts rapidly in the month of May, with July as peak month. However, my experience is that most severe thunderstorms do occur in the month of June, when the jet-stream is stronger. In July and August the jetstream shifts to the north (on average of course). Rapid decline of the number of thunderstorm-days is from August to September when, again on average, dry arid conditions are the norm. Besides, the air in the upper levels is warmer by then, reducing the instability.

Because the continental airmass in winter is often cold and stable, winter thunderstorms are extremely rare in Transylvania. However they do happen in the period december till february: once in four or five years or so. Mainly in cases with an active coldfront or in a situation with wintry showers in northwesterly flow.

At last I will show my own observations of thunderdays from the village of Curteni (near Tirgu Mures) with data from the last three years:

* This number may change






Table 2. Number of thunderstorm days for Curteni in the period oktober 2007 - august 2010.

July 2010 Reprise

A few photographs from last month of July which were not published in my blog:


Thunderstorm with strong updraft in the late afternoon of 13 July.

















Two pictures of a rather flat, blocked shelfcloud in the evening of 13 July.
















Anvil with sheet lightning in the evening of 13 July.












First decent lightning-shot of 2010 in the evening of 13 July.












Strange, extremely high towering cumulus in the early evening of 19 July.