Port Dover
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Port Dover clear sky chart from 2005-11-06 to 2025-01-22.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	15% 9% 3 8% 5% 5% 5% 4 6% 8% 33%	105092
	Night	16% 10% 3 8% 5% 4 5% 4 5% 7% 33%	104262
Transparency	Day	27% 46% 8% 12% 6% 1	108699
	Night	29% 45% 7% 12% 7% 1	108743
Seeing	Day	17% 10% 26% 27% 15% 5%	14669
	Night	20% 10% 28% 28% 13% 2	24307

By Month

Percentage Cloud Cover NE (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	16% 16% 8% 11% 5% 5% 5% 3 4 5% 22%	2694
	11th to 20th	Day	13% 19% 7% 19% 9% 6% 5% 2 4 5% 12%	2930
	21st to end	Day	22% 17% 5% 13% 7% 5% 4 3 4 5% 14%	3133
February	1st to 10th	Day	16% 17% 4 12% 8% 5% 6% 4 5% 5% 19%	1710
	11th to 20th	Day	14% 13% 6% 13% 7% 6% 5% 4 5% 4 23%	1663
	21st to end	Day	19% 13% 4 11% 6% 5% 4 4 5% 5% 24%	1510
March	1st to 10th	Day	20% 11% 3 9% 6% 5% 5% 3 5% 5% 27%	3427
	11th to 20th	Day	10% 14% 4 10% 6% 5% 4 4 6% 7% 30%	3480
	21st to end	Day	18% 9% 3 9% 6% 5% 5% 3 5% 5% 34%	3815
April	1st to 10th	Day	16% 10% 3 9% 6% 5% 4 3 6% 6% 31%	2204
	11th to 20th	Day	17% 9% 3 8% 4 4 4 3 6% 7% 35%	2352
	21st to end	Day	18% 9% 3 7% 5% 5% 4 4 5% 7% 34%	2470
May	1st to 10th	Day	18% 8% 3 7% 5% 6% 5% 4 6% 7% 32%	4108
	11th to 20th	Day	15% 9% 3 8% 6% 5% 5% 4 6% 8% 31%	4203
	21st to end	Day	10% 5% 2 6% 5% 5% 5% 4 6% 8% 45%	4837
June	1st to 10th	Day	11% 6% 3 6% 5% 5% 5% 4 7% 8% 41%	2660
	11th to 20th	Day	11% 6% 2 6% 5% 5% 5% 4 8% 8% 41%	2660
	21st to end	Day	11% 5% 2 6% 4 5% 4 4 6% 10% 43%	2660
July	1st to 10th	Day	8% 4 2 6% 5% 4 4 4 6% 11% 45%	4440
	11th to 20th	Day	10% 5% 2 6% 4 4 4 4 7% 11% 43%	4263
	21st to end	Day	6% 4 2 6% 4 5% 5% 5% 7% 11% 44%	4466
August	1st to 10th	Day	15% 5% 2 5% 3 4 5% 4 6% 9% 40%	4104
	11th to 20th	Day	10% 6% 3 7% 4 5% 6% 5% 7% 10% 37%	4044
	21st to end	Day	9% 5% 2 6% 4 5% 5% 5% 6% 10% 42%	4384
September	1st to 10th	Day	12% 6% 2 5% 4 5% 5% 4 6% 8% 44%	2280
	11th to 20th	Day	9% 5% 2 5% 4 5% 4 4 5% 9% 49%	2109
	21st to end	Day	16% 6% 2 6% 5% 5% 5% 4 6% 7% 38%	2085
October	1st to 10th	Day	16% 7% 2 6% 5% 4 5% 4 6% 8% 37%	1900
	11th to 20th	Day	19% 7% 3 8% 6% 4 5% 4 5% 7% 31%	1900
	21st to end	Day	22% 10% 4 9% 5% 4 4 4 7% 7% 25%	2090
November	1st to 10th	Day	14% 7% 3 7% 6% 4 5% 4 6% 8% 37%	1765
	11th to 20th	Day	15% 11% 3 8% 5% 5% 6% 4 6% 7% 31%	1600
	21st to end	Day	20% 14% 3 7% 6% 5% 5% 5% 6% 7% 21%	1600
December	1st to 10th	Day	19% 15% 5% 9% 7% 6% 6% 5% 7% 6% 15%	2600
	11th to 20th	Day	22% 17% 5% 8% 5% 5% 5% 3 5% 6% 20%	2986
	21st to end	Day	25% 18% 5% 11% 5% 4 4 3 4 6% 13%	3960
January	1st to 10th	Night	18% 16% 5% 11% 6% 4 4 3 4 5% 24%	4470
	11th to 20th	Night	15% 16% 6% 12% 6% 6% 7% 4 6% 6% 16%	4250
	21st to end	Night	24% 17% 7% 13% 6% 4 4 3 3 4 15%	4546
February	1st to 10th	Night	16% 16% 4 10% 6% 5% 5% 4 6% 6% 23%	2470
	11th to 20th	Night	15% 13% 4 10% 5% 5% 5% 4 6% 6% 25%	2403
	21st to end	Night	18% 13% 4 10% 5% 5% 5% 4 5% 7% 24%	1941
March	1st to 10th	Night	19% 9% 3 8% 5% 5% 4 4 4 5% 34%	3413
	11th to 20th	Night	14% 10% 3 7% 4 4 4 3 5% 7% 38%	3479
	21st to end	Night	16% 8% 3 6% 4 3 4 3 5% 5% 41%	3817
April	1st to 10th	Night	19% 10% 3 6% 5% 5% 4 5% 4 6% 33%	1976
	11th to 20th	Night	18% 8% 2 7% 5% 5% 4 3 6% 6% 36%	1793
	21st to end	Night	15% 7% 3 7% 5% 5% 5% 4 5% 7% 37%	1710
May	1st to 10th	Night	20% 8% 3 7% 4 4 3 3 4 7% 37%	2833
	11th to 20th	Night	11% 8% 3 8% 6% 5% 6% 4 6% 7% 36%	2686
	21st to end	Night	10% 5% 2 5% 4 3 4 4 6% 9% 48%	2738
June	1st to 10th	Night	11% 6% 3 6% 4 4 4 5% 7% 8% 41%	1520
	11th to 20th	Night	9% 4 2 7% 5% 6% 5% 6% 7% 8% 42%	1520
	21st to end	Night	11% 5% 2 6% 4 4 4 4 5% 9% 45%	1520
July	1st to 10th	Night	7% 5% 2 7% 5% 4 4 3 5% 10% 49%	2520
	11th to 20th	Night	9% 5% 2 5% 4 4 5% 4 6% 8% 49%	2680
	21st to end	Night	6% 4 2 6% 5% 5% 5% 5% 7% 8% 49%	3087
August	1st to 10th	Night	11% 6% 2 6% 5% 4 4 4 5% 9% 44%	2825
	11th to 20th	Night	11% 5% 2 5% 4 4 4 4 6% 9% 45%	2785
	21st to end	Night	8% 4 2 5% 4 4 5% 4 6% 10% 49%	3238
September	1st to 10th	Night	12% 6% 3 6% 4 4 3 4 4 7% 47%	1900
	11th to 20th	Night	10% 5% 2 5% 3 3 3 3 5% 7% 56%	2068
	21st to end	Night	17% 5% 2 7% 4 4 5% 3 7% 6% 39%	2095
October	1st to 10th	Night	15% 6% 2 6% 5% 3 4 4 6% 7% 42%	2280
	11th to 20th	Night	17% 10% 3 8% 5% 5% 4 3 5% 6% 36%	2280
	21st to end	Night	22% 9% 2 6% 4 4 5% 4 5% 5% 33%	2508
November	1st to 10th	Night	14% 8% 3 6% 4 4 5% 4 6% 6% 41%	2527
	11th to 20th	Night	16% 11% 3 7% 5% 5% 5% 4 7% 7% 30%	2800
	21st to end	Night	19% 13% 3 8% 5% 5% 5% 4 6% 7% 26%	2800
December	1st to 10th	Night	16% 16% 4 10% 5% 6% 6% 4 6% 6% 21%	4580
	11th to 20th	Night	19% 17% 4 9% 6% 5% 4 3 4 5% 22%	5208
	21st to end	Night	24% 17% 5% 10% 5% 4 5% 3 5% 5% 17%	6996

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	43% 38% 7% 5% 6%	2695
	11th to 20th	Day	51% 39% 6% 3 1	2930
	21st to end	Day	48% 42% 6% 3 1	3133
February	1st to 10th	Day	24% 66% 3 4 2	1710
	11th to 20th	Day	22% 65% 3 7% 3	1672
	21st to end	Day	19% 66% 5% 6% 3 1	1510
March	1st to 10th	Day	36% 42% 5% 14% 3	3430
	11th to 20th	Day	29% 45% 11% 12% 3	3480
	21st to end	Day	28% 43% 6% 14% 8% 1	3815
April	1st to 10th	Day	23% 65% 3 6% 3	2204
	11th to 20th	Day	18% 66% 4 8% 4 1	2352
	21st to end	Day	19% 66% 5% 5% 4 1	2470
May	1st to 10th	Day	30% 44% 9% 10% 5% 1	4120
	11th to 20th	Day	31% 46% 10% 12% 1	4207
	21st to end	Day	21% 43% 7% 14% 12% 3	4837
June	1st to 10th	Day	16% 66% 4 8% 6% 1	2660
	11th to 20th	Day	14% 67% 6% 7% 5% 1	2660
	21st to end	Day	13% 64% 5% 10% 8%	2660
July	1st to 10th	Day	23% 36% 9% 19% 11% 2	4370
	11th to 20th	Day	22% 37% 9% 23% 9%	4189
	21st to end	Day	20% 38% 12% 13% 15% 1	4324
August	1st to 10th	Day	28% 38% 10% 15% 9% 1	4091
	11th to 20th	Day	28% 39% 11% 17% 4	4083
	21st to end	Day	24% 38% 8% 23% 8%	4384
September	1st to 10th	Day	14% 62% 6% 12% 6%	2280
	11th to 20th	Day	11% 61% 5% 12% 10%	2109
	21st to end	Day	18% 61% 6% 10% 5%	2085
October	1st to 10th	Day	20% 38% 10% 20% 12% 1	3160
	11th to 20th	Day	21% 38% 10% 20% 11%	3140
	21st to end	Day	27% 36% 12% 19% 5%	3428
November	1st to 10th	Day	23% 57% 7% 9% 3 1	1765
	11th to 20th	Day	22% 58% 6% 10% 4	1600
	21st to end	Day	28% 59% 7% 4 2	1600
December	1st to 10th	Day	47% 36% 10% 5% 1	2600
	11th to 20th	Day	45% 34% 9% 5% 6%	2986
	21st to end	Day	55% 28% 6% 7% 3	3960
January	1st to 10th	Night	39% 40% 8% 10% 3	4470
	11th to 20th	Night	42% 41% 11% 4 2	4250
	21st to end	Night	50% 41% 4 4 1	4546
February	1st to 10th	Night	21% 66% 5% 6% 2	2470
	11th to 20th	Night	21% 64% 4 7% 4	2405
	21st to end	Night	21% 66% 4 6% 3 1	1941
March	1st to 10th	Night	33% 42% 8% 14% 3	3423
	11th to 20th	Night	26% 42% 12% 11% 8% 1	3480
	21st to end	Night	23% 43% 7% 14% 12% 1	3817
April	1st to 10th	Night	21% 66% 3 6% 3	1976
	11th to 20th	Night	17% 66% 3 8% 5% 1	1793
	21st to end	Night	15% 65% 5% 8% 5% 2	1710
May	1st to 10th	Night	30% 41% 9% 11% 7% 3	2840
	11th to 20th	Night	30% 43% 11% 14% 2	2687
	21st to end	Night	20% 43% 7% 14% 15% 1	2739
June	1st to 10th	Night	15% 66% 4 9% 6% 1	1520
	11th to 20th	Night	13% 66% 5% 10% 6% 1	1520
	21st to end	Night	14% 64% 5% 8% 8% 1	1520
July	1st to 10th	Night	23% 36% 8% 15% 13% 4	2480
	11th to 20th	Night	22% 36% 9% 22% 10%	2631
	21st to end	Night	23% 36% 12% 14% 14% 1	2988
August	1st to 10th	Night	25% 38% 8% 17% 10% 2	2814
	11th to 20th	Night	27% 37% 10% 21% 4	2812
	21st to end	Night	20% 38% 9% 23% 10%	3238
September	1st to 10th	Night	13% 60% 6% 11% 9%	1900
	11th to 20th	Night	12% 60% 5% 13% 10%	2068
	21st to end	Night	17% 61% 5% 11% 6%	2095
October	1st to 10th	Night	19% 37% 4 20% 20% 1	3800
	11th to 20th	Night	26% 36% 8% 18% 12%	3779
	21st to end	Night	21% 37% 11% 19% 11%	4120
November	1st to 10th	Night	22% 57% 6% 8% 6%	2527
	11th to 20th	Night	21% 58% 5% 10% 4	2800
	21st to end	Night	26% 59% 7% 7% 1	2800
December	1st to 10th	Night	42% 36% 13% 7% 2	4580
	11th to 20th	Night	45% 34% 5% 9% 6% 1	5208
	21st to end	Night	52% 28% 8% 8% 4	6996

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	22% 17% 35% 17% 7% 1	230
	11th to 20th	Day	25% 15% 40% 14% 5% 1	300
	21st to end	Day	19% 20% 37% 17% 6% 1	300
February	1st to 10th	Day	21% 18% 39% 18% 4	270
	11th to 20th	Day	21% 20% 39% 19% 2	270
	21st to end	Day	23% 30% 31% 14% 2	225
March	1st to 10th	Day	22% 11% 33% 27% 8%	455
	11th to 20th	Day	20% 13% 34% 26% 6% 1	460
	21st to end	Day	26% 13% 31% 22% 8%	506
April	1st to 10th	Day	15% 15% 34% 27% 8%	460
	11th to 20th	Day	21% 15% 28% 23% 9% 4	452
	21st to end	Day	22% 8% 29% 30% 8% 2	460
May	1st to 10th	Day	21% 7% 28% 27% 11% 5%	463
	11th to 20th	Day	16% 7% 21% 30% 23% 3	487
	21st to end	Day	12% 4 23% 33% 22% 7%	529
June	1st to 10th	Day	11% 5% 30% 36% 17% 2	490
	11th to 20th	Day	12% 5% 22% 33% 22% 6%	490
	21st to end	Day	13% 4 21% 40% 18% 4	490
July	1st to 10th	Day	8% 2 17% 31% 32% 10%	485
	11th to 20th	Day	13% 4 17% 31% 24% 11%	484
	21st to end	Day	9% 3 18% 38% 25% 8%	532
August	1st to 10th	Day	10% 3 18% 30% 28% 12%	486
	11th to 20th	Day	10% 4 16% 33% 25% 11%	479
	21st to end	Day	12% 3 18% 30% 27% 10%	539
September	1st to 10th	Day	13% 4 18% 29% 23% 12%	490
	11th to 20th	Day	8% 3 16% 23% 31% 18%	490
	21st to end	Day	17% 8% 23% 28% 17% 8%	490
October	1st to 10th	Day	17% 9% 24% 24% 20% 7%	490
	11th to 20th	Day	19% 13% 31% 24% 10% 4	490
	21st to end	Day	25% 12% 31% 22% 9% 1	539
November	1st to 10th	Day	17% 19% 26% 26% 9% 3	318
	11th to 20th	Day	22% 19% 30% 20% 9% 2	200
	21st to end	Day	26% 15% 38% 19% 3	200
December	1st to 10th	Day	27% 22% 27% 17% 7% 1	200
	11th to 20th	Day	27% 25% 31% 15% 3	200
	21st to end	Day	25% 22% 33% 16% 4	220
January	1st to 10th	Night	24% 17% 37% 17% 5%	800
	11th to 20th	Night	27% 16% 33% 20% 4	800
	21st to end	Night	20% 14% 37% 24% 5%	841
February	1st to 10th	Night	26% 14% 34% 23% 3	760
	11th to 20th	Night	21% 13% 36% 24% 5%	743
	21st to end	Night	24% 14% 36% 23% 3	628
March	1st to 10th	Night	19% 9% 36% 27% 8%	760
	11th to 20th	Night	22% 10% 35% 25% 8% 1	760
	21st to end	Night	21% 9% 31% 29% 9% 1	836
April	1st to 10th	Night	21% 11% 32% 30% 6%	760
	11th to 20th	Night	21% 9% 31% 28% 9% 1	669
	21st to end	Night	19% 5% 31% 35% 10%	570
May	1st to 10th	Night	18% 5% 27% 31% 17% 1	570
	11th to 20th	Night	15% 4 24% 38% 17% 1	487
	21st to end	Night	13% 4 21% 35% 24% 4	411
June	1st to 10th	Night	13% 4 25% 39% 19% 1	380
	11th to 20th	Night	13% 2 24% 38% 24%	380
	21st to end	Night	13% 3 21% 42% 21% 1	380
July	1st to 10th	Night	7% 2 19% 39% 27% 6%	370
	11th to 20th	Night	10% 3 19% 38% 26% 4	462
	21st to end	Night	8% 2 19% 43% 25% 3	624
August	1st to 10th	Night	10% 3 12% 41% 31% 4	567
	11th to 20th	Night	9% 3 15% 34% 34% 5%	564
	21st to end	Night	10% 2 18% 36% 28% 4	689
September	1st to 10th	Night	14% 5% 18% 32% 25% 6%	760
	11th to 20th	Night	12% 4 15% 29% 33% 8%	760
	21st to end	Night	17% 7% 19% 30% 22% 6%	760
October	1st to 10th	Night	20% 5% 23% 28% 21% 3	760
	11th to 20th	Night	22% 11% 29% 26% 10% 2	760
	21st to end	Night	25% 12% 31% 26% 6%	836
November	1st to 10th	Night	20% 11% 29% 28% 11% 1	780
	11th to 20th	Night	22% 18% 30% 22% 7% 2	800
	21st to end	Night	28% 12% 35% 20% 6%	800
December	1st to 10th	Night	31% 16% 30% 17% 5% 1	800
	11th to 20th	Night	27% 19% 34% 17% 4	800
	21st to end	Night	29% 14% 33% 21% 3	880

Page generated at 2025-01-19 03:06:48. Version ac07

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