Weather Photos blog

After the extensive rainfalls on going in the last few days over the eastern half of Slovenia and eastern Austria, rivers flooding in NE-ern Slovenia are expected. High amounts of precipitation for these parts, which are normally quite dry against the other parts of Slovenia, rising the waters rapidly and especially Mura river is expected to start flooding overnight. Few other small rivers over Pomurje and Podravje regions could rise up and flooding as well.

Here are just a couple of rada images today showing precipitation still on going almost over the same areas in NE-ern Slovenia and SE-ern Austria and giving additional amounts of water to the places which are already pretty full of it.

The EARS/ARSO issued high water warning for these areas mentioning the extensive precipitation in Austria, which resulted in Mura river to additionally rising. It could reach a maximum flow of 900 m3/s and 1000m3/s in Gornja Radgona today afternoon and evening. It will be flooding within anti-flooding banks. Small rivers will begin to decline in the evening, while the Mura river’s flow will be increasing well into Thursday.

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.

Large trough over central Europe affects southern Alpine region with a strong cold front crossing Slovenia, N-ern Italy and N-ern Adriatic overnight and morning hours tomorrow. Moderate mid-level jet streak ejects into the Alps overnight with its left-exit jet region over NE-ern Italy by tomorrow morning hours. Very hot, but relatively dry boundary layer conditions are placed ahead of the coming front, while rich moisture lies over NW Italy.

Clear skies will provide strong surface heating during the day over the whole southern Alpine region with rather strong WAA into northern Mediterranean and therefore stable conditions will persist over the most areas under the stoup capping inversion. Weak Lee cyclogenesis is expected to form over N-ern Italy, backing flow will be present and therefore few convergence zones.

Mostly only NW-ern Italy will see some activity before evening as SW-NE oriented cold front with prefrontal convergence will probably initiate some isolated storms there. Models simulate very high near-surface dewpoints in NW Italy with values near 20°C and therefore also high values of MLCAPE. Weakening cap after the strong heating in the afternoon hours and steepening mid-level lapse rates along the approaching trough, should allow few isolated storms to form along SFC convergences. Given the only moderate deep-layer shear and weak LL shear, but high CAPE values, multicells or an isolated supercell with threat for very large hail and strong winds are the main threat.

Over the other areas, convection will be on going since early afternoon only over the mountainous terrain of the Alps, storms will be triggered along the local convergence zones and orography. As the cold front continues to move SE-wards overnight, storms will continue to fire and organize into all over the souther Alpine region. A resulted one or two small MCS clusters cannot be excluded along the trailing front, one of them over the central Alps in the evening hours is very likely, while another one could also form in NW Italy after clustering storms from the late afternoon activity after front surges in. Storms will bring extensive rainfalls over whole Slovenia and North Italy and rapid cooling behind the front is expected as strong NE-erly winds will blast through. Given the high values of PWAT, 30-40mm by GFS model, local excessive rainfalls and flash flooding events are possible.

The most interesting focus point will be a passage of the cold front overnight and morning hours tomorrow across N-ern Adriatic. Models suggest a robust activity in the early morning hours which could continue towards the midday tomorrow. SFC cold front over Slovenia should be over already in the early morning hours, while SFC low over N Italy should not allow the quick frontal passage there. Increasing SSE-erly flow will bring better moisture into N-ern Adriatic region and enhanced PWAT is clearly visible, ranging from 30-almost 50mm.

As a result of increasing LL flow overnight, LL shear will also rapidly increase and storms should organize into multicells and also few discrete supercells as high values of SR helicity in the lowest 3kms (300-500m^2/s^2) are also expected along the racing cold front. given the limited instability, but enhanced shear and helicity along with very high PWAT values and additionally rather slow storm motion ENE-wards, storms with excessive rainfalls will become increasingly likely.

Another morning MCS complex will likely form, however a lot of precipitation will also result from a strong frontal forcing. Therefore augmented risk for flash floods will exist. All models do suggest very high values of accumulated rainfalls in 12h period, ranging from 50-150mm possible locally. Additional risk could be an increasing Bora winds and strong frontal forcing, therefore strong gusts could take place over N-ern Adriatic.

I have also issued a convective outlook for this frontal passage. Here is the ESTOFEX map with level-2 issued for NW Italy for the threat of very large hail, winds and a possible tornadoes. A level-1 area was issued for the rest of N-ern Italy given the main threat for strong winds and excesive rainfalls:

In addition to the above forecast, here are few local forecasts from Slovenian EARS warnings and also Friuli region office OSMER, which have strong wording as regarding the activity tomorrow morning.

Translation of the above forecast for Friuli region says:

Extensive rainfalls in the morning hours over the mountains, strong storms and intense rainfalls over the Friuli plains and coastal areas with possible very strong rainfalls. Strong northerly winds over coastal areas, strong Bora winds in the gulf of Trieste. Very strong gusts possible. Rapid temperature falls.

Here are meteoalarm warning graphics for Slovenia with orange color for SW Slovenia where rainfalls 75-100mm/24hrs, strong winds 100-120km/h and high storm surge are possible. It has to be mentioned that coastal areas should be aware of very strong winds of possible interaction of downbursts and strong Bora at the same time. Very strong winds gusts in excess of 120km/h cannot be excluded over the northern Adriatic. EARS might also upgrade the warning graphics to the highest threat, the red color for SW Slovenia.

Models confidence with extensive rainfalls expected should now finally end up the serious drought on going lately over SW-ern Slovenia and without these rainfalls, it would become critical as it was back in summer 2003. Cooler days are expected after tomorrow over southern Alpine region, accompanied by variable weather and NE-erly winds as the cut off upper-level low which forms after this trough passage, will be placed right over the Alps for the next couple of days.