How should the Swiss international airlines flight 850 METAR reports be interpreted? From the Wikipedia page on the Swiss International Airlines Flight 850 crash investigation, it was stated that the initial METAR did not reflect the situation and the METAR less than an hour (a moment before the approach was started) was drastically different.

Initial METAR:


  EDDT 04001KT CAVOK 30/17 Q1002 A2959 0998 2947 NOSIG. 


Later:


  EDDT VRB01KT 9999 FEW040CB SCT120 BKN260 29/17 Q1002 A2959 0998 2947 TEMPO 27025G55KT 2000 +TSRA BKN009 BKN015CB COMMENTS: OCNL LTNG AND CB SW OF STN.


I'm not very familiar with these reports, or how they are generated. From some research it sounds like the second report is much more serious, however I'm having trouble understanding a few things:


  VRB01KT


This seems to suggest variable visible range, but I'm not sure what the 01KT means. 


Can someone clarify?


The later report first mentions scattered cumulonimbus clouds, but then says the coverage is up to broken. 


Why are there multiple mentions of the same types of clouds? 
Are they talking about different height/direction?


The Wikipedia article seems to suggest that there was a massive storm moving rapidly into the area. My understanding is that NOSIG means the weather is not expected to significantly change in the next two hours. 


What would cause the initial report to include NOSIG?
Given how much worse the weather seems to be in the later report, why would it take the station almost an hour to file a new report? 
Why wouldn't they file a new report as soon as it seemed like the weather was degrading?
Can someone clarify?


I can try to clarify the METAR report:

From the Wikipedia source link on METAR:


EDDT:  METAR for Tegel Airport
VRB01KT: Wind variable at 1 knot (1.9 km/h)
9999: visibility in excess of 10 kilometres (5.4 nmi)
FEW040CB: few clouds at 4000 ft. including cumulonimbus
SCT120:  scattered clouds at 12000 ft
BKN260:  broken clouds at 26000 ft 
29/17: temperature 29 degrees Celsius, dew point 17 degrees Celsius
Q1002: current altimeter setting (in QNH) is 1002 hPa 
A2959 0998 2947: current altimeter setting 29.59 in.Hg, falling to 998 HPa, 29.47 in.Hg. 
TEMPO: Temporarily


27025G55KT: Temporarily winds from 270° at 25 knots (46 km/h), gusting to 55 knots (102 km/h)
2000 +TSRA: visibility 2000 meters (1.1 nmi)
+TSRA: heavy thunderstorm and rain
BKN009: broken clouds at 900 ft
BKN015CB: broken clouds at 1500 ft including cumulonimbus

COMMENTS: OCNL LTNG AND CB SW OF STN: Occasional lightning and cumulonimbus clouds south west of the station



  Why are there multiple mentions of the same types of clouds? 


The TEMPO group is used for any conditions in wind, visibility, weather, or sky condition which are expected to last for generally less than an hour at a time (occasional), and are expected to occur during less than half the time period.


  Are they talking about different height/direction?


The Sky Condition (i.e.:FEW040CB SCT120 BKN260 ) reports the sky coverage and is given for different height, the following three-digit height is given in hundreds of feet.

For further clarification of METAR convention I find this useful!


  My understanding is that NOSIG means the weather is not expected to significantly change in the next two hours. 


Correct, NOSIG stands for NO SIGnificant change, doesn't mean that the weather will not change!