Seems the spring rasputitsa was worse than normal. And while it might have been over by end of May it might not have been clear to the Germans that that was the case in early May. Besides, it isn't at all clear they even needed the forces in Greece if they wanted to launch the attack earlier. They just weren't all that large.
Finally, it wasn't the winter that stopped the Germans at Moscow. It was the Russians. They were there, in force, and dug in. And they had the power by the end of November to launch a counter attack.
But let's take it a step further.... let's say the Germans were able to close the 30km to Moscow. What then? Moscow was 10 times bigger than Stalingrad. The depleted Wehrmacht at the end of its supply line is not going to be able to encircle it (another 100 km? A further thinning of their lines at the end of a now very long and tenuous supply chain? What about entering, in winter, a city that is much larger and would be more tenaciously defended, than Stalingrad?)
Some more on the spring rasputitsa:
http://www.ww2f.com/topic/42605-spring-rasputitsa-1941/?p=476573
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All, for those interested I've been given some enlightening details elsewhere...from Andrew Zapantis
Quote
At Wlodawa (a town circa 60 kilometers south of Brest on the Soviet-Polish border), following the March 3 thaw of the ice, the level of the water of the Bug rose and it was high on March 5. After this, by April 2 the water level dropped considerably; however, on April 23 it began to rise again and attained a very high level on May 5 after which the river's water level began to decrease gradually. The monthly maximum levels (not the monthly mean levels however) were flood levels, but not very unusual ones because such floods occur in that area evera four or five years; the damage, if any, was probably not very serious.
At Frankopol (situated north of the city of Sokolow Podlaski which is some 75 kilometers northeast of Warsaw and about 100 kilometers west of Brest) high water levels occurred in March, April and May; and the monthly maximum levels in March and then in the beginning of May (the maximum value was reached on May 7) were flood levels.
Since the thaw began on March 3 and the rainfall in the areas of Warsaw, Wyszkow, Koden (only approximately 36 kilometers from Wlodawa) and Zamosc-Mokre was not heavy the question was asked as to what may have caused the high water levels at Wlodawa and Frankopol. In response the Instytut stated that (regarding Wlodawa and Frankopol) rainfall data for the period in question practically do not exist; one may guess that the rain in the tributary areas must have been sufficient enough to cause such high spring water levels.
It thus appears that the statement made by Guderian that there were floods in the beginning of May seems to be fairly accurate at least on the basis of evidence at Wlodawa. The claim that the floods lasted until June 1941 does not seem to be accurate on the basis of the data quoted
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I'm not sure about the last question - for the important thing is what the prospect seemed to be when the decision to delay BARBAROSSA was made.
BUT - we now have a start date....and an interesting little piece of information that fopr some reason (records incomplete/nonexistent) there were TWO, and possibly THREE major periods of flooding during the Spring Thaw....
"...following the March 3 thaw of the ice, the level of the water of the Bug rose and it was high on March 5. After this, by April 2 the water level dropped considerably; however, on April 23 it began to rise again and attained a very high level on May 5 after which the river's water level began to decrease gradually.
At Frankopol (situated north of the city of Sokolow Podlaski which is some 75 kilometers northeast of Warsaw and about 100 kilometers west of Brest) high water levels occurred in March, April and May; and the monthly maximum levels in March and then in the beginning of May (the maximum value was reached on May 7) were flood levels."
...and the final one in May was high enough to constitute a flood.
The Rasputitsa ALSO seems to have lasted longer than the normal ~6 weeks - if it began on the 3rd of March, and wasn't winding down again until AFTER May 5th-7th! That's over eight weeks....