Weatherforecast for Seelöwe

[Huszar666]

Morning, Folks,

I know, the weather in the Channel was mentioned here and there in the myriad of Seelöwe-Threads, but I fail to find the mentions (reading through all those threads was enough once...)
Do anyone have reliable and concrete data for the possible days? Wind, sea state, visibility?

Those would be 15-22 of September.
(OKM wanted at least "half illumination", in September that would be 08-22, but only after the 15th was the Moon out at (most of the) night. OKH wanted peak tide a few hours before sunrise, I will try to find when peak tide happened each day - I do remember reading it somewhere - but for now I suppose we can work with those seven days)

Thanks!

[Richard Anderson]

Weather and visibility requirements.

The KM required at least a half-moon for maneuvering visibility, which restricts the days to:

Full Moon – 16 September to Third Quarter Moon – 24 September

16th September 1940
Weather: General rain and cloud. German S-Boot operations cancelled due to weather conditions.
Full Moon

17th September 1940
Weather: Squally showers with thunder and bright intervals. German S-Boot operations cancelled due to weather conditions.
Moon 99%

18th September 1940
Weather: Bright and squally. German S-Boot operations cancelled due to weather conditions.
Moon 97%

19th September 1940
Weather: Showery. Operations by German destroyers from Cherbourg to the Lizard cancelled due to heavy weather. German S-Boot operations cancelled due to weather conditions.
Moon 93%

20th September 1940 German S-Boot operations cancelled due to weather conditions.
Weather: Fair with bright periods, showery. Operations by German destroyers from Cherbourg to the Lizard cancelled due to heavy weather. German S-Boot operations cancelled due to weather conditions.
Moon 87%

21st September 1940
Weather: Mainly fine. Operations by German S-Boot resume for the first time since 9 September due to weather conditions.
Moon 80%

22nd September 1940
Weather: Dull with fog in the morning. Cloud clearing during the afternoon. Some rain.
Moon 72%

23rd September 1940
Weather: Fine
Moon 62%

24th September 1940
Weather: Early morning fog in northern France. Channel cloudy with haze in the Straits and Thames Estuary.
Last Quarter Moon

[Huszar666]

Thanks!

Do you have any info what those "weather conditions" meant that warranted the cancelation of the S-Boot activity?
Some squall and rain doesn't look like overly bad weather that would warrant the cancelation. I don't think anything below Beaufort 5 or 6 would mean a cancellation, and the two days, where the destroyers stayed home would mean Beaufort 7 or 8. Is there any info on the sea state ?

[Richard Anderson]

Thanks!

Do you have any info what those "weather conditions" meant that warranted the cancelation of the S-Boot activity?
Some squall and rain doesn't look like overly bad weather that would warrant the cancelation. I don't think anything below Beaufort 5 or 6 would mean a cancellation, and the two days, where the destroyers stayed home would mean Beaufort 7 or 8. Is there any info on the sea state ?

I don't recall running across anything. It is complicated by the S-Boot being based out of Belgian and Dutch ports, so the localized weather there was critical for them, while the Z-Boot were at Cherbourg and Le Havre. I suspect the weather that halted S-Boot operations was a North Sea storm that later moved down the Channel and intensified affecting the Z-Boot. You may want to check the RN war diaries. https://www.naval-history.net/xDKWarDia ... ntents.htm

[Huszar666]

Morning,

I did a cursory check, for the Destroyers, Home Fleet, they were active in the whole time frame, the weather was only mentioned once:

Wednesday, 18th September 1940

S.S. LADY OF MANN on passage to Lerwick sustaining damage to forecastle due to weather returned toAberdeen with VERSATILE, who had damaged D.G. gear.

The TROMs weren't that much helpfull either. On the 15.09 the weather was good enough for Highlander, Harvester, Beagle, Bulldog being able to bombard Cherbourg. Nothing much...
However, it looks like the East-Coast convoys were under way in this time frame, so there shouldn't been extremly bad weather.

EDIT:
I did know, there was something. Found this:
viewtopic.php?f=54&t=207767&p=1937766&h ... s#p1937766
#102Post by sitalkes » 01 Apr 2015, 00:31

he worst it got in September was Force 6 on the 17th, and even then the sea state doesn't get worse than 4.

Srangly I remember a longer paragraph about it...

[Knouterer]

Some info I collected:
from netweather.tv:

14th September 1940: Again no sign in an improvement in the weather, and it remained unsettled with rain periods and thunderstorms in all areas. Over the Channel, the heavy cloud and rain gave way to lighter higher cloud during the day, but the showers persisted.

15th September (BoB Day): Heavy cloud and rain periods overnight cleared and the forecast for the day was fine in most areas with patchy cloud. No rain was forecast but some areas had an odd shower. The fine conditions of the morning gave way to incoming cloud although it remained dry. Cloud was stratocumulus providing about 8/10ths cover at a height of 5,000 feet. Wind was slight and from the northwest.

16 Sept.: Much cooler conditions coming in from the North Sea. Most areas had heavy cloud cover and rain in all districts that was heavy at times. Full moon at night.
Luftwaffe flew 395 (fighters) plus 96 (bombers by day) plus 223 (bombers by night) combat missions, makes 714. Fighter Command flew 428.

17 Sept.: Overcast with squally showers with drizzle and low cloud.
Luftwaffe flew 350 (fighters est.) plus 74 (bombers by day) plus 338 (bombers by night) combat missions, makes 762. Fighter Command flew 544 by day plus 45 by night.

18 Sept.: Conditions were similar to the previous day except that the low to medium cloud that brought the rain periods disappeared. The day was bright and clear although the squally winds continued.
Accordingly, there was more air activity. Luftwaffe flew 1024 (fighters) plus 92 (bombers by day) plus 371 (bombers by night) combat missions, makes 1487. Fighter Command flew 1165 by day, leading to 236 planes making contact with the enemy, and 65 by night.

Source: Operation Sea Lion by Richard Cox (1974):
Weather and Sea Conditions in SE England and the Channel in September 1940
Taken from Air Ministry reports at Dungeness.
Tidal information from Office of Hydrographer of the Navy, Taunton.

Thursday, 19th September, 1940, Dungeness
Time Weather Visibility Wind Force Sea
700 Blue sky, cloudy, some squalls. Good W 4-6 3
1300 Cloudy, squalls Good WSW 6-7 4
1800 Cloudy Good WSW 6 4
High water Dover 0021, 17.8 ft and 1234, 18.4 ft
Low Water Dover 0736, 0.6 ft and 1953, 0.4 ft
RAF campaign diary: showery. Netweather.tv: Heavy cloud continued throughout the day and rain periods, heavy at times were experienced over much of Britain. The Channel areas had very low cloud base with early morning fog and mist patches in coastal districts.

General weather forecast at noon for the next 24 hours: Moderate to fresh SW to W winds, strong at times locally on coast, occasional rain, brighter intervals with risk of local thunder later, average temperatures.

Friday, 20th September
Time Weather Visibility Wind Force Sea
0700 Cloudy, squalls and blue sky Good W 4-6 3
1300 Cloudy, squalls Good WSW 6-7 4
1800 Cloudy Good WSW 6 4
High Water Dover 0052, 17.6 ft and 1304, 18.2 ft
Low Water Dover 0801, 0.9 ft and 2017, 1.1 ft
RAF campaign diary: Fair with bright periods, showery. Netweather.tv: The morning was reasonably fair with scattered cloud with showers by midday, which continued throughout the day. It was another of those mornings where there was an abundance of blue sky and scattered cloud, but the radar screens at the south coast radar stations were totally clear.
Luftwaffe flew 280 (fighters) plus 24 (bombers by day) plus 136 (bombers by night) combat missions, makes 440. Fighter Command flew 540 by day plus 46 by night.


General weather forecast for next 24 hours: Fresh northerly winds decreasing moderate to light tonight; winds backing and freshening tomorrow, considerable bright periods; a few showers today; fine tonight and tomorrow.

Saturday, 21st September
Time Weather Visibility Wind Force Sea
0700 Overcast, continuous drizzle Poor W 1 1
1300 Overcast Poor NE 2 2
1800 Cloudy Good Calm - 0
High Water Dover 0122, 17.4 ft and 1332, 17.6ft
Low Water Dover 0831, 1.6 ft and 2044, 1.7 ft
RAF campaign diary: Mainly fine. Netweather.tv: The day opened to scattered cloud although along the Estuary and the River Thames as far as London there was considerable haze. Once this cleared, most of the south was fine with scattered cloud but by midday cloud had started to build up. In the north there was cloud with sunny spells but it remained dry.
Luftwaffe flew 175 (fighters) plus 54 (bombers by day) plus 170 (bombers by night) combat missions, makes 399. Fighter Command flew 536 by day plus 46 by night.

General weather forecast from noon for the next 24 hours: Light NE variable winds, becoming moderate SE; rain, then a fairer interval, followed by more rain, local fog night and morning; average temperatures.

Sunday, 22nd September
Time Weather Visibility Wind Force Sea
0700 Cloudv Good S 2 1
1300 Cloudy Good SSW 4 3
1800 Cloudy, heavy rain Mod SW 4 3
High Water Dover 0152, 16.9 ft and 1402, 16.8ft
Low Water Dover 0856, 2.0 ft and 2112, 2.5ft
RAF campaign diary: Dull with fog in the morning. Cloud clearing during the afternoon. Some rain. Netweather.tv: The day opened to many fog covered areas and a mist layer remained for most of the morning period. During the afternoon visibility had increased lengthy sunny periods, but the heavy cloud rolled in late in the afternoon and many areas especially in the south experienced periods of rain.
Luftwaffe flew 44 (fighters) plus 43 (bombers by day) plus 143 (bombers by night) combat missions, makes 230. Fighter Command flew 158 by day plus 45 by night.

General weather forecast from noon for the next 24 hours: Light to moderate southerly winds, becoming cloudy or dull; a period of rain or drizzle, spreading from SW today; local fog near S. Coast; becoming mild.

Monday, 23rd September
Time Weather Visibility Wind Force Sea
0700 Cloudy Good W 4 1
1300 Cloudy Good W 4 3
1800 Cloudy blue sky Good WSW 4 3
High Water Dover 0223, 15.9 ft and 1441, 15.6 ft
Low Water Dover 0926, 2.8 ft and 2147, 3.3ft
RAF campaign diary: Fine. Netweather.tv: Mist and fog patches in most areas giving way to a mainly fine day. Some patchy cloud, but mainly fine weather over most areas.
General weather forecast from noon for the next 24 hours: Moderate to light westerly wind, variable later; fine; local fog in morning; average temperatures, slight ground frost locally at night.

Tuesday, 24th September
Time Weather Visibility Wind Force Sea
0700 Blue sky, cloudy Good NW 1 1
1300 Cloudy Good SW 3 2
1800 Cloudy Good N 2 2
High Water Dover 0305, 15.1 ft and 1537, 14.7 ft
Low Water Dover 1006, 3.6 ft and 2236, 4.2ft
RAF campaign diary: Early morning fog in northern France. Channel cloudy with haze in the Straits and Thames Estuary. Netweather.tv: Mist and fog patches were widespread in most areas especially over the French and British coastlines during the morning. Mist or haze was prevalent for most of the day, with high cloud clearing by late afternoon.

General weather forecast from noon for next 24 hours: Light westerly to variable winds; fair with a little local morning fog. Average day temperature, cool at night.

Wednesday, 25th September

Time Weather Visibility Wind Force Sea
0700 Blue sky, cloudy, some mist Poor NNW 2 1
1300 Cloudy Good NNE 4 2
1800 Blue sky, cloudy Good NE 4 3

High Water Dover 0412, 14.3 ft and 1707, 14.1 ft
Low Water Dover 1113, 4.4 ft and 2352, 4.8 ft
Sunrise 0650, 0750 German time (GMT + 2), sunset 1852. 6 days to new moon.
RAF campaign diary: Fair to fine in most areas. Cool.
Netweather.tv: Overcast with thunder and rain generally, clearing later with showers in the South East?
WD 136th Inf Bde: Weather fine but cold, with North-east wind.
General weather forecast from noon for next 24 hours: Light or moderate northerly winds, fresh locally on East Coast. Fair, apart from scattered showers near East Coast; rather cool.

Thursday, 26th September

Time Weather Visibility Wind Force Sea
0700 Cloudy Mod N 2 1
1300 Overcast, mist Mod NE by E 4 3
1800 Overcast, mist Mod N 4 3

High Water Dover 0535, 14.0 ft and 1829, 14.0 ft
Low Water Dover 1237, 4.6 ft
Sunrise 0652, 0752 German time (GMT + 2), sunset 1850. 5 days to new moon.

RAF campaign diary: Mainly fair to cloudy.
Netweather.tv: Generally fine, clouding up in the South later in the day
WD 136th Inf Bde: Weather fine but cold, wind: North-west



General weather forecast from noon for next 24 hours: Light north or north-westerly winds, mainly cloudy, brighter intervals locally. Rather cool.


Friday, 27th September
Time Weather Visibility Wind Force Sea
0700 Cloudy Poor WNW 3 2
1300 Cloudy, mist Mod W 4 1
1800 Overcast, cloudy, mist Mod WSW 5 3
High Water Dover 0711, 14.6 ft and 1948, 15.2ft
Low Water Dover 0127,4.6 ft and 1413, 3.2ft
Sunrise 0652, 0752 German time (GMT + 2), sunset 1850. 4 days to new moon.

RAF campaign diary: Fair in the extreme south and south-west. Cloudy in the Channel with light rain over southern England.
Netweather.tv: Fair in the extreme south and southwest. Cloudy in the Channel with light rain over southern England
War Diary 136th Inf Bde (on the south coast): Weather fine and warm with little wind.

[Huszar666]

Hehe, the Emperor of all Sea Lions strikes again!
Many thanks!

So, from the 19th forwards, it doesn't look like ideal weather, but maybe possible (looking at sea state).
HOWEVER. OKH wanted to land at sunrise at high tide (or at least near high tide). Save for 25/26 it was the exact opposite, almost dead center low tide.
I did found this:
https://wwii.germandocsinrussia.org/de/ ... ect/zoom/7
Date: High tide / Low tide
15.09: 10:28+2252 / 5:13+1736
16.09: 1102+2324 / 0553+1814
17.09: 1132+2353 / 0629+1849
18.09: -+1202 / 0700+1919

According to the table OKH's wish (sunrise landing, about 2 hours after high tide) would only be fulfilled on the 9th, 10th, maybe the 11th, and then again on the 24th, 25th, 26th and maybe 27th.
And here is the interesting part: OKM's wish (at least 50% moon at night) was only fulfilled on the 15th to 22nd... There are no overlapping days.

I know I can't get enough, but do you have sea states before the 19th?