In this chapter some typical phenomena of convection and convective cells will be investigated using the Meteosat-8 IR 10.8 channel with a colour enhancement in the temperature range from -24 to -64°C (see IR Enhanced legend) or click upon the key symbol (above). This helps us to interpret the information in the IR channel and will show more clearly following structures:
In this chapter we will also compare the IR-enhanced images with radar and the composite "Convective Storms".
At this time no high extending convective clouds can be seen.
No high extending convective clouds existed.
During the last 15 minutes high extending convection started (Central Germany) which is also represented in the IR-enhanced (cloud top temperatures -52 to -56°C). No other significant convective structures can be seen. At this time, the radar delivers more information (red circle) about the convective cells.
The convective cell over Central Germany became bigger. However, the cloud top temperatures did not change significantly. The radar reveals better information about the fine structures of the convective cells (small areas with red and blue pixels extending from Central to Northwest Germany).
The IR enhanced shows clouds top temperatures between -52 and -56°C over Central and North Germany. The radar contains better information about severe weather conditions with dBz values of partly more than 59 (high risk to hail).
A squall line formed (extending from Central to North Germany). We find often cloud top temperatures between -56 and -60°C, partly below (violet, risk of hail). This corresponds well with the radar (reflectivities partly between 53 and 59 dBz).
The Squall line extending from North Germany to the South continued moving to the East and intensified. At its southern part we see a so-called cold ring (violet: cloud top temperaturen -60 to -64°C).
The Squall line extending from North Germany to the South continued moving to the East. In its middle part we see a small V-structure. This is a hint to hazardous weather like heavy rain, hail and strong gusts. The relative coarse observation network revealed thunderstorms and precipitation amounts of up to 15 mm/3h. However, no heavy gusts and no hail were reported.
The squall line moved to the East. It becomes more difficult to identify the most active parts in the squall line. Only the small violet areas give some hints in this context. More information can be obtained from the radar image.
The squall line over Germany moved to the East without changing its intensity significantly. The IR-enhanced reveals east of Hamburg a region with very low cloud top temperatures (partly less than -64°C). The corresponding radar image gives much more information about most active parts in the convective complex. We see even a V-structure.
One reason for the discrepancies between satellite image and radar might be that the radar image is about 5 minutes earlier available than the satellite image. Especially during heavy summer convection 5 minutes time difference can lead to significant differences in the cell structures and cell development.
The squall line over Central/East Germany started weakening. A new convective complex can be found near the border triangle of France, Germany and Switzerland. The IR reveals cloud top temperatures between -60 and -64°C.
The new convective complex intensified and arrived East France and Switzerland. The IR reveals cloud top temperatures between -60 and -64°C.
The cell over east France exhibits clear hints to a dangerous situation: An enhanced V directed to the south (in accordance to the wind direction in 200 and 300 hPa, not shown). High radar reflectivity's were detected (more than 53 dBz, partly more than 59 dBz, hail very likely).
From East France to the northern Alps we see several convective cells with cloud top temperatures between -60 and -64°, partly even below. radar reflectivity's of 55 to 59 dBz were measured (hail likely).
An interesting detail can be seen near the border triangle of France, Germany and Switzerland (in the satellite image the central and south part of the marked area). Whereas we find low cloud top temperatures (between -60 and -64°C) the radar image reveals almost no signal. That is an example that high extending clouds are not necessarly connected with Cb activities below.
The IR-enhanced reveals three super cells: Southwest Germany, North Switzerland (both with a V-shape) and Germany/Austria. Cloud top temperatures of up to -69°C were measured. Not only the very low cloud top temperature is a hint to Convective Storms but also the V-shape is a clear indication to hazardous weather like heavy gusts, rain and even hail. The corresponding radar image reveals in this area reflectivity's of up to 55 dBz (hail possible).
The three super cells over Southwest Germany (V-structure), Switzerland and Austria moved slowly to Northeast. The radar data reveal risk of hail over Southwest Germany.
The two super cells merged over Southwest Germany. The northern one reveals still the V-structure. New smaller convective cells with cloud top temperatures between -60 and -64°C developed during the last 30 minutes. The radar detected up to 59 dBZ and at Messstetten (Black Forrest) a severe thunderstorm with hail (code=99) was observed.
This image exhibits a big complex over Southwest Germany with cloud top temperatures below -52°C and several white pixels (measured cloud top temperatures of -69°C). We recognise a V-structure, a cold ring (northern and southern part of the marked area, respectively) and a new cell on the west flank of the entire convective complex.
The entire complex over Southwest Germany continued spreading. In its south part we see again an example of a cold ring (violet ring around a blue area). Also at 21 UTC a severe thunderstorm with hail (code=99) was reported at Messstetten (Southwest Germany, Black Forrest).
The IR-enhanced shows a big area with cloud top temperatures of less than -55°C which is equivalent to a risk to hail. However, the radar image reveals over Southwest Germany more structures: The dark blue, violet and even a few white pixels indicate the locations with highest risk to hail more precisely. Additionally, we find some bow-echo forms indicating heavy gusts.
In the meanwhile the area of cloud top temperatures below -52°C covered almost 500 km x 250 km. This is an area of more than 50,000 km². When this condition lasts more than 6 hours without any interruption we have a clear hint to a MCC. However, all the other criteria of a MCC are not evident.
The lowest cloud top temperatures were still over the Black Forrest.
The two regions with cloud top temperatures of partly less than -64°C moved to the East whereas the bluish areas moved more to the Northeast. The development of new (daughter) cells at the Southeast flank of cell complexes (white pixels in this image) leads to the right movement of the entire cell comlex against the general streaming (can be seen from the bluish and greenish fields).
A further cell with very low cloud top temperature moved to Southwest Switzerland.
The big cell complex over Southwest Germany moved slowly to East-Northeast. A next near the French-Swiss border moved slowly to the Northeast. Both cell complexes exhibit cloud top temperatures of partly less than -64°C.
This image shows the lowest cloud top temperatures over South Germany and over the French-Swiss border. Both convective complexes moved slowly to Northeast.
The radar exhibits at about 11°E in the frontal part of the MCC a line with high reflectivity's. A surface convergence and a dipole structure of surface pressure tendencies existed near 10°E (not shown). Together with the area of more than 50,000 km² with cloud top temperatures below -52°C we find many criteria for an MCC. However, the three dimensional structures of the wind field cannot be derived from the measurements.
Two cells (East France/Switzerland and South Germany) moved to the East. We still see big areas of low cloud top temperatures (-60 to -64°C, partly less).
Both cell complexes moved to the North.
The cells continued moving to the North.
In the meanwhile one of these cells arrived Central Germany. It exhibits a relatively big area with cloud top temperatures below -64°C. In Wuerzburg (North Bavaria) heavy thunderstorms were observed. The corresponding radar reveals near Wuerzburg up to 55 dBz.
Both cells moved to North-Northeast.
The cells kept on moving to North-Northeast without changing significantly.
The cell complexes continued moving. Over Central Germany a V-shape (cold ring) developed. The area of cloud top temperatures equal or below -52°C was bigger than 50,000 km² and existed during the last 6 hours without interruption. We find some additional hints to a MCC (no images shown): From 23 UTC till now a dipole of surface pressure tendency (decreasing and increasing in the fore field and rear site, respectively). The radar images exhibit from 22:30 UTC till 02:30 UTC a line orientated structure with relatively high dBz values in the frontal part of the big convective complex. With the available data material it was not possible to investigate the three dimensional wind structure carefully enough.
The MCC continued moving to North-Northeast and started decaying. At its west part a new cell with cold cloud tops developed.
The MCC continued weakening. The cell further to the West kept on increasing.
All cell complexes over the Middle Germany started merging. A clearer separation between the two cell complexes can be seen in the corresponding radar image (data errors at about 51°N/10°E).
The big cell complex continued moving to the North. A new one developed over the Rhein-Main-Area (Wiesbaden).
The big cell complex over Central Germany moved slowly to the North and started weakening. The new cell north of the river Main moved to the North and exhibits now lower cloud top temperatures (up to -64°C). However, the highest radar reflectivity's (more than 45 to 53 dBz, equivalent to heavy rain) and the highest precipitation amounts were measured further to the South (Frankfurt airport (46 mm/h) and Langen even 70 mm/h). Severe thunderstorms (no hail) were reported at Frankfurt-Airport.
The corresponding composite "Convective Storms" exhibits two very bright yellow spots (indicating a strong updraft and a cell with a high potential to intensify). The first one was near Frankfurt. Additionally, to the other data, this composite contains the information about the most probable cell development during the next minutes. The other bright yellow spot can be seen north of Dresden. However, in this case it is difficult to relate that to reports of thunderstorms, heavy precipitation or high radar reflectivity's (red circle). We recognise in the big convective complex over almost the whole northern Germany some yellowish pixels. They indicate more active regions of this big cell complex. However, more precise insight about the position of the most intense precipitation and about hail can be obtained from the radar .
All cell complexes moved to the North. The entire region with cloud top temperatures below -52°C covered big parts of West, Central and North Germany. The IR-satellite image reveals the most intense parts of the cell complex as violet pixels (cloud top temperature between -60 and -64°C) and the radar image exhibits in these regions bluish pixels (41 to 53 dBz, heavy rain). However, we find more precise information from that. Severe thunderstorms (no hail) were reported at Frankfurt-Airport and Erfurt-Airport (Central Germany).
The composite "Convective Storms" reveals still some yellowish spots over the northern half of Germany. The cell which moved from Frankfurt to the North (see marker) shows still a bright yellow spot. However, it became smoother during the last 30 minutes indicating that this cell has started to weaken.
Considering the big cell complex over the northern parts of Germany, we see from the IR-image that the size of violet areas became smaller. Only in the central and southeast part we see bigger areas with low cloud top temperatures. However, the composite "Convective Storms" contains more information: We see yellow spots indicating more active convective cells and the radar image gives us information about the precipitation. We find several regions with bluish areas, equivalent to heavy rain. Many thunderstorms and precipitation amounts of up to 29 mm/h were reported in this area.
First hints to a further intense convection came from the observations in the western parts of Switzerland with heavy thunderstorms, in one case even with hail (code=99). Near the latter, the IR image reveals a small violet spot. However, no hints came from the composite "Convective Storms".
No significant changes occurred in general.
This image reveals over parts of North Germany convective cells with cloud top temperatures of partly between -60 to -64°C and thunderstorms (partly severe) were still observed. However, the entire system kept on weakening. In the composite "Convective Storms" we see some yellow spots which give indications to the most active cells. However, from the corresponding radar image it is difficult to find an explanation why high reflectivity's are not only limited to cells which exhibit the yellow spot (red ellipse). One reason may be that we were not able to investigate individual convective cells in relation to the vertical distribution of the radar reflectivity maxima.
More interesting is the cell at the border triangle France, Germany and Switzerland (see marker). We find a few pixels with cloud top temperatures below -60°C (violet). The radar reveals over Switzerland a line with partly more than 53 dBz: Some white pixels give hints to reflectivity's of more than 59 dBz (hail very likely). Heavy thunderstorms (no hail) were reported over Central Switzerland. The reason for that might be that the time of measurement and observation are slightly different and the hail happened not directly at the observation's location.
No additional information are available from the the composite " Convective Storms".
The big cell complex over the northern parts of Germany continued moving to the North and weakening. Near the Swiss-German border we recognise a small violet area (cloud top temperatures between -60 and -64°C).
The IR-enhance shows still low cloud top temperatures (violet) over East Germany. The composite "Convective Storms" reveals additionally that the violet area most to the Northwest seems to have the highest potential for intensifying. In the radar we find in the frontal part of the cloud complex several centres of high reflectivitys's. Because we do not have information about the 3-D structures the best hint to the development's potential of this situation can be taken from the composite "Convective Storms".
The other cell crossed the Rhine and can be found west of the Lake Constance. No significant changes happened during the last 30 minutes. The radar image reveals a line orientated area with reflectivity's of about 50 dBZ (heavy rain).
In the following images, we will see over the south part of Germany and in the frontal part of the super cell a line of convective cells which moved fast to the East. At the southeast new cells continuously developed. Sometimes a bow shape could be observed. In the following we will only concentrate upon this structure.
We see in the IR-enhanced new areas of low cloud top temperatures (violet) that can be interpretated as new cells which developed at the Southeast to East part of the super cell
The corresponding composite "Convective Storms" reveals here a yellowish area (not like a spot) that could be a hint that this cell will weaken during the next minutes. Further to the northeast we see a small yellow spot. The forecaster should be aware that this cell will intensify during the next few minutes.
The Northwest to Southeast orientated bluish structure in the radar image (with some violet pixels (up to 55 dBZ, hail possible)) give more information about the precipitation intensity and type. At this line heavy gusts of up to 57 knots in flat areas and up to 80 knots in mountainous regions were measured. However, it is difficult to estimate the cells’ potential for further developing from a 2-D radar image.
We recognise in this image the development of a new cell at the southeast part of the cell (Southwest Germany). However, the cloud top temperatures does not reveal a high risk to hail which fits well with the corresponding radar image (almost no violet or white pixel).
The composite "Convective Storms" gives a good example of additional information. Over South Germany we find some yellow spots. We considered already the bright yellow area situated most to the southeast in the image from 08:30 UTC. It was the new cell that developed at the southeast part of the super cell and exhibited the highest potential to intensify. We find this cell in the radar image of 09 UTC at the southeast tip of the blueish line. Often, we observe here the most intense convection and the highest potential for intensifying cells.
The convective cell over Southwest Germany moved very fast to the East. New cells developed at the southeast edge of the big cell complex. Cloud top temperatures above -60°C reveals a low risk to hail that corresponds well to the radar images. The radar image still exhibits a bluish line with some violet pixels (53-55 dBz, hail possible).
The composite "Convective Storms" shows one bright yellow spot. In southeast direction we find a few orange to yellowish pixels that fits well with the radar image. West of Munich a heavy thunderstorm was observed.
During the last 30 minutes this structure moved fast to the East. We clearly see the development of new cells at the southeast tip (also in the radar image). Over South Bavaria (Lechfeld) heavy thunderstorms occurred.
In the composite "Convective Storms" we see some yellowish areas. However, no potential for intensifying can be derived for the southeast tip of the cloud complex.
The system continued moving to the East and weakened momentarily.
In this IR image we see a new development over Bavaria (near the Danube) and at the East flank of the cell complex. However, the violet area (risk to hail) was very small. Only the radar gives hints to a dangerous weather situation: We see a bow echo and at its south part and many reflectivity's between 55 and 59, partly even more (high risk to hail).
The composite "Convective Storms" shows very small yellowish pixels. However, for cells over Bavaria no conclusions about decaying or intensifying cells are possible.
This IR-image reveals the bow structure and cloud top temperature between -60 and -64°C. The best information about rain and hail can be obtained from radar (dBz-values in many cases between 55 and 59, partly even more).
The composite "Convective Storms" reveals the bow structure. However, no additional information in comparison to the other data can be retrieved.
The bow structure is still to be seen and arrived in the meanwhile the Bavarian Forrest. We still observe high radar reflectivity's. However, the entire system started weakening.