Again, models and our predictions were not wrong. Excessive rainfalls clearly verified over the northern Adriatic in the morning of Saturday, June 20th 2009. The cold front was slowly progressing over the Alps in the Friday’s afternoon and overnight to Saturday. Few severe storms initiated in NW Italy and clustered into a large MCS over the N-ern Italy, moving ESE-wards towards Veneto region. In the early night hours this MCS diminished a bit, but its remnants were already over N-ern Adriatic with heavy rainfalls over Friuli region. It diminished totally later on in the Julian Alps.
Right after midnight, a new MCS was rapidly forming over Veneto region and was moving onto N-ern Adriatic sea. A strong squall-line/bow echo was racing on its front side at this complex’s first stages, cleary visible on this radar image at 0335z:
During the next hour the squall-line still showed bowing segments while the MCS was moving across northern Adriatic. Notice also an extensive rainfalls over much of eastern Veneto and western Friuli. A near-surface cold front was already racing across Slovenia and few storms and showers were initiated along it, clearly seen on both radar images.
In the early morning hours the leading edge of this MCS was placed over the gulf of Trieste, heavy rainfalls took place over whole Friuli and parts of western Slovenia. The most extreme rainfalls were right over the gulf of Trieste as a result of strong convergence along the frontal boundary that was now sitting there. Strong SSE-erly winds were blowing across Istria while NNE-rly winds were already behind the front over Friuli and northern Adriatic. Combined with moderate shear and instability, slow storm motion and high PW values it resulted in excessive rainfalls. MCS was Q-stationary for some time, storms were moving very slow and heavy rainfalls were on going over the same areas, mostly over the eastern coast of Trieste gulf for a few hours. The next few radar images at 0430z, 0500z and 0545z claerly showing the heaviest rainfalls over Trieste gulf.
Strong Bora with gusts 70-100km/h was blasting behind the leading edge of this MCS, interacting with outflow from the storms and made some minor damage to the coastal areas over the N-ern Istrian peninsula.
Radar image at 0845z showing extensive rainfalls still on going all over the gulf of Trieste and surrounding areas. Notice the more isolated cell along the western Istria coast. This storm dropped two weak waterspouts near village Vrsar. At this time strong Scirocco SE-erly winds were blowing along the coast there while very strong post-frontal Bora winds were blowing over the rest of nothern Adriatic.
This is the radar image at 0840z when the third waterspout was observed near Pula and caused extensive damage to the tourist camp with badly damaged trailers and many uprooted trees. Several people were injured in this event.
Here is a map of 24hrs accumulated rainfalls over Slovenia and N-ern Italy where one can notice several precipitation max areas where high amounts of rainfalls were measured. Notice the areas with less precipitation on the southern Karst and also around Trieste. This is likely an effect of strong Bora, which is usually the strongest right in these areas and precipitation probably ‘avoided’ these areas. Surfer 8 software was used for plotting these maps.
Here are now two zoomed maps around the northern Adriatic sea, overlayed with google map to better show places which were affected the most. The second image below shows cropped area on the Italian Karst region which received near 120mm of rainfalls in less than 4hrs period.
Several stations reported really an extreme values for these areas, especially if one keeps in mind that mostly all precipitation felt in less than 4hrs period! For example:
Roiano – 103mm
Borgo Grotta Gigante – 115mm
Prosecco – 114mm
Here is a detailed graph for village Borgo Grotte Gigante with 5-minute interval accumulations in blue color and cummulative graph of daily precipitation in red color. Notice the high peak near 0645-0700z time period and compare it with the radar image above.
Image courtesy of OSMER-CNR
Pretty impressive values with such high amount of precipitation in short time period. It was also very local event as can be seen from the maps. The peak was right onshore near Barcola when very warm/humid airmass rapidly raises onto the Karst plateau. And if its accompanied also with strong frontal wind convergence, its actually not a surprise such amounts resulted. Models were pretty well predicting it might happen in these areas. Though it was impossible to know where, but high probabilities were there. This event definatelly had near 50 years of return period for such events in the costal areas north of Trieste. The map represents 6hrs accumulated rainfalls between Saturday 03z and 09z.
This map represents 12hrs accumulated rainfalls between Friday 23z and Saturday 11z. Easily confirmed measured values of total accumulations exceeding 100mm in a couple of hours at some places.
Here is the map of numerous reported of excessive rainfalls around the northern Adriatic sea on the coastal areas. Several objects were flooded in extreme SW Slovenia due to these heavy rainfalls, many roads were also flooded and blocked for awhile. Notice also waterspout reports in Istria, Croatia.
Image courtesy of ESSL/ESWD
A bit more detailed report will follow in the next days and will be added as a link in the bottom of this post.