Og's Bog
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Og's Bog clear sky chart from 2005-11-06 to 2024-11-05.

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% 11% 4 9% 5% 5% 5% 4 5% 7% 31%	101902
	Night	14% 11% 4 8% 5% 5% 4 4 5% 6% 33%	97094
Transparency	Day	51% 5% 12% 21% 11% 1	105506
	Night	50% 5% 12% 22% 11% 1	101581
Seeing	Day	21% 16% 31% 19% 9% 4	14791
	Night	20% 14% 31% 24% 10% 1	23801

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% 14% 5% 12% 6% 5% 5% 4 5% 5% 23%	2517
	11th to 20th	Day	11% 20% 7% 16% 10% 7% 4 3 4 4 13%	2758
	21st to end	Day	20% 22% 7% 12% 6% 4 3 3 3 4 15%	3124
February	1st to 10th	Day	14% 17% 5% 13% 8% 6% 6% 4 5% 4 18%	1710
	11th to 20th	Day	11% 16% 7% 13% 8% 5% 5% 4 4 6% 20%	1663
	21st to end	Day	16% 18% 5% 11% 6% 4 5% 3 4 5% 24%	1465
March	1st to 10th	Day	17% 14% 6% 9% 6% 4 4 3 4 5% 29%	3432
	11th to 20th	Day	10% 19% 6% 10% 5% 5% 5% 3 4 5% 28%	3480
	21st to end	Day	15% 13% 3 8% 6% 4 4 3 4 5% 35%	3815
April	1st to 10th	Day	15% 16% 4 8% 5% 4 5% 3 5% 5% 28%	2232
	11th to 20th	Day	19% 12% 3 6% 3 4 3 4 5% 7% 35%	2349
	21st to end	Day	20% 10% 4 8% 4 3 3 3 4 6% 33%	2470
May	1st to 10th	Day	17% 9% 3 7% 4 4 4 4 5% 7% 35%	4108
	11th to 20th	Day	17% 9% 3 8% 5% 5% 5% 4 6% 7% 32%	4357
	21st to end	Day	12% 5% 2 6% 4 4 4 4 6% 7% 45%	4837
June	1st to 10th	Day	16% 7% 2 6% 5% 4 5% 4 7% 8% 35%	2660
	11th to 20th	Day	12% 6% 2 6% 4 4 5% 4 7% 10% 39%	2722
	21st to end	Day	14% 6% 2 6% 4 5% 5% 4 6% 8% 38%	2850
July	1st to 10th	Day	11% 5% 2 7% 5% 5% 6% 5% 7% 10% 37%	4646
	11th to 20th	Day	10% 5% 2 6% 5% 5% 5% 5% 6% 9% 42%	4440
	21st to end	Day	9% 6% 2 7% 5% 5% 5% 4 7% 9% 40%	4483
August	1st to 10th	Day	15% 8% 3 7% 4 5% 6% 4 7% 7% 35%	4104
	11th to 20th	Day	12% 8% 3 7% 6% 5% 5% 5% 7% 9% 33%	4044
	21st to end	Day	11% 6% 2 6% 5% 5% 5% 4 6% 9% 41%	4382
September	1st to 10th	Day	13% 7% 3 7% 5% 5% 4 4 6% 7% 39%	2280
	11th to 20th	Day	11% 6% 2 7% 5% 5% 4 4 5% 8% 43%	2151
	21st to end	Day	14% 7% 2 9% 6% 6% 5% 3 6% 7% 34%	2062
October	1st to 10th	Day	19% 9% 3 8% 6% 4 5% 3 4 6% 33%	1900
	11th to 20th	Day	20% 10% 4 9% 6% 5% 4 4 5% 6% 28%	1900
	21st to end	Day	25% 16% 3 9% 4 4 4 4 5% 6% 20%	2090
November	1st to 10th	Day	12% 14% 3 8% 6% 5% 4 4 5% 8% 29%	1633
	11th to 20th	Day	12% 15% 4 10% 7% 6% 6% 4 6% 7% 23%	1520
	21st to end	Day	16% 18% 6% 12% 6% 5% 5% 4 5% 5% 18%	1520
December	1st to 10th	Day	16% 19% 7% 15% 7% 6% 4 4 5% 5% 13%	1520
	11th to 20th	Day	17% 16% 5% 13% 6% 4 5% 4 5% 6% 17%	1906
	21st to end	Day	26% 19% 7% 16% 5% 4 4 3 3 3 10%	2772
January	1st to 10th	Night	16% 17% 7% 12% 6% 5% 4 4 5% 5% 19%	4429
	11th to 20th	Night	12% 15% 8% 14% 11% 8% 6% 4 5% 5% 13%	4184
	21st to end	Night	19% 14% 7% 11% 10% 5% 5% 3 5% 5% 15%	4532
February	1st to 10th	Night	13% 16% 5% 11% 7% 5% 5% 3 5% 6% 23%	2470
	11th to 20th	Night	12% 15% 6% 11% 6% 6% 5% 4 6% 5% 24%	2403
	21st to end	Night	12% 14% 4 11% 7% 5% 5% 4 6% 6% 27%	1985
March	1st to 10th	Night	16% 12% 4 9% 6% 4 4 4 4 6% 31%	3408
	11th to 20th	Night	12% 13% 4 8% 4 4 4 4 5% 6% 35%	3479
	21st to end	Night	15% 9% 3 7% 4 4 4 3 5% 5% 41%	3817
April	1st to 10th	Night	18% 13% 3 8% 5% 4 4 3 5% 6% 31%	1947
	11th to 20th	Night	16% 10% 3 5% 4 4 5% 4 5% 7% 38%	1796
	21st to end	Night	14% 11% 4 7% 4 4 5% 4 5% 6% 36%	1710
May	1st to 10th	Night	16% 8% 2 7% 4 4 4 4 5% 6% 40%	2833
	11th to 20th	Night	16% 8% 2 6% 5% 4 4 3 5% 7% 40%	2532
	21st to end	Night	10% 5% 2 5% 3 3 4 3 6% 8% 51%	2738
June	1st to 10th	Night	13% 5% 3 5% 5% 5% 5% 4 6% 9% 40%	1520
	11th to 20th	Night	9% 4 2 6% 4 4 6% 5% 6% 10% 43%	1450
	21st to end	Night	12% 5% 2 6% 4 3 4 4 5% 7% 47%	1330
July	1st to 10th	Night	6% 4 3 5% 5% 5% 4 4 5% 8% 51%	2301
	11th to 20th	Night	11% 4 1 5% 4 3 4 3 5% 7% 53%	2520
	21st to end	Night	7% 6% 2 5% 3 4 4 5% 6% 7% 51%	3053
August	1st to 10th	Night	10% 6% 2 6% 4 4 4 3 5% 7% 49%	2825
	11th to 20th	Night	13% 6% 2 5% 3 4 4 4 5% 8% 48%	2785
	21st to end	Night	11% 6% 2 4 4 4 4 3 6% 8% 47%	3242
September	1st to 10th	Night	9% 5% 2 6% 4 4 4 4 7% 7% 48%	1900
	11th to 20th	Night	10% 5% 2 4 4 3 3 3 5% 7% 54%	2026
	21st to end	Night	16% 7% 3 7% 5% 3 4 2 4 7% 41%	2118
October	1st to 10th	Night	17% 7% 2 7% 5% 5% 4 4 5% 7% 38%	2280
	11th to 20th	Night	17% 10% 3 8% 4 5% 4 4 5% 6% 33%	2280
	21st to end	Night	21% 11% 4 8% 5% 5% 5% 4 5% 6% 26%	2508
November	1st to 10th	Night	16% 11% 3 7% 5% 4 4 4 5% 6% 35%	2541
	11th to 20th	Night	15% 14% 4 8% 6% 5% 5% 5% 6% 7% 27%	2660
	21st to end	Night	16% 16% 5% 10% 5% 6% 5% 4 5% 6% 22%	2660
December	1st to 10th	Night	18% 16% 5% 11% 6% 5% 5% 4 6% 6% 18%	2660
	11th to 20th	Night	15% 19% 6% 12% 6% 5% 5% 4 6% 6% 18%	3288
	21st to end	Night	27% 18% 7% 14% 5% 5% 4 3 4 4 10%	4884

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	62% 5% 16% 13% 5%	2518
	11th to 20th	Day	74% 4 9% 9% 4	2758
	21st to end	Day	74% 3 9% 9% 4 1	3124
February	1st to 10th	Day	68% 5% 7% 15% 4 1	1710
	11th to 20th	Day	64% 6% 7% 15% 6% 1	1672
	21st to end	Day	63% 4 8% 16% 8% 1	1465
March	1st to 10th	Day	59% 3 11% 17% 9%	3435
	11th to 20th	Day	58% 5% 8% 19% 8% 2	3480
	21st to end	Day	50% 4 9% 19% 15% 2	3815
April	1st to 10th	Day	57% 5% 9% 19% 10% 1	2232
	11th to 20th	Day	50% 4 8% 23% 15% 1	2349
	21st to end	Day	52% 4 10% 20% 12% 2	2470
May	1st to 10th	Day	48% 3 11% 22% 14% 1	4120
	11th to 20th	Day	52% 4 13% 21% 9% 1	4361
	21st to end	Day	38% 4 14% 23% 18% 3	4837
June	1st to 10th	Day	44% 5% 12% 22% 15% 1	2660
	11th to 20th	Day	38% 5% 14% 25% 16% 1	2722
	21st to end	Day	41% 5% 14% 25% 13% 1	2850
July	1st to 10th	Day	40% 6% 15% 22% 15% 1	4575
	11th to 20th	Day	35% 6% 13% 34% 11% 1	4365
	21st to end	Day	39% 7% 12% 24% 17% 1	4340
August	1st to 10th	Day	44% 6% 14% 23% 11% 1	4091
	11th to 20th	Day	43% 6% 17% 24% 10%	4083
	21st to end	Day	37% 7% 13% 32% 11% 1	4382
September	1st to 10th	Day	43% 6% 12% 28% 10% 2	2280
	11th to 20th	Day	38% 5% 12% 30% 14%	2151
	21st to end	Day	48% 5% 12% 26% 9%	2062
October	1st to 10th	Day	43% 6% 13% 26% 12% 1	3160
	11th to 20th	Day	43% 5% 14% 24% 14%	3140
	21st to end	Day	58% 6% 13% 18% 5%	3428
November	1st to 10th	Day	53% 6% 13% 20% 8% 1	1633
	11th to 20th	Day	60% 4 13% 14% 8% 1	1520
	21st to end	Day	68% 5% 12% 13% 3	1520
December	1st to 10th	Day	72% 5% 10% 11% 2	1520
	11th to 20th	Day	65% 9% 11% 11% 4	1906
	21st to end	Day	80% 4 6% 9% 2	2772
January	1st to 10th	Night	65% 5% 13% 13% 4	4429
	11th to 20th	Night	73% 4 9% 10% 3 1	4184
	21st to end	Night	71% 4 10% 10% 4 1	4532
February	1st to 10th	Night	60% 6% 9% 19% 5%	2470
	11th to 20th	Night	60% 5% 9% 17% 8%	2405
	21st to end	Night	56% 4 12% 20% 8% 1	1985
March	1st to 10th	Night	55% 4 10% 23% 7% 1	3418
	11th to 20th	Night	48% 4 13% 22% 11% 2	3480
	21st to end	Night	43% 5% 9% 24% 17% 2	3817
April	1st to 10th	Night	54% 4 9% 19% 13% 1	1947
	11th to 20th	Night	47% 4 10% 22% 16% 2	1796
	21st to end	Night	48% 5% 10% 20% 16% 2	1710
May	1st to 10th	Night	45% 3 12% 20% 16% 3	2840
	11th to 20th	Night	45% 3 14% 24% 11% 2	2533
	21st to end	Night	32% 3 14% 27% 21% 3	2739
June	1st to 10th	Night	40% 5% 10% 26% 17% 2	1520
	11th to 20th	Night	36% 5% 13% 25% 19% 2	1450
	21st to end	Night	36% 5% 13% 28% 16% 1	1330
July	1st to 10th	Night	31% 6% 15% 26% 20% 3	2264
	11th to 20th	Night	31% 5% 12% 35% 16% 1	2472
	21st to end	Night	29% 8% 14% 32% 15% 2	2956
August	1st to 10th	Night	36% 4 13% 30% 15% 2	2814
	11th to 20th	Night	35% 4 16% 32% 12% 1	2812
	21st to end	Night	34% 6% 13% 33% 13% 1	3242
September	1st to 10th	Night	34% 6% 16% 30% 14% 1	1900
	11th to 20th	Night	30% 4 11% 35% 19% 1	2026
	21st to end	Night	44% 4 13% 28% 10%	2118
October	1st to 10th	Night	34% 5% 10% 29% 22% 1	3800
	11th to 20th	Night	43% 5% 14% 25% 13%	3779
	21st to end	Night	45% 8% 15% 24% 9%	4120
November	1st to 10th	Night	48% 5% 12% 24% 10% 1	2541
	11th to 20th	Night	55% 5% 12% 18% 9% 1	2660
	21st to end	Night	61% 5% 15% 15% 3 1	2660
December	1st to 10th	Night	65% 6% 12% 14% 4	2660
	11th to 20th	Night	65% 5% 12% 14% 3	3288
	21st to end	Night	78% 5% 9% 7% 2	4884

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% 22% 34% 17% 4 1	180
	11th to 20th	Day	26% 27% 29% 14% 3 2	249
	21st to end	Day	28% 23% 33% 13% 2	297
February	1st to 10th	Day	30% 29% 28% 10% 3	270
	11th to 20th	Day	25% 27% 41% 6% 1	270
	21st to end	Day	37% 29% 28% 6%	228
March	1st to 10th	Day	23% 22% 35% 16% 4	460
	11th to 20th	Day	23% 21% 37% 15% 4	460
	21st to end	Day	30% 20% 30% 14% 5% 1	506
April	1st to 10th	Day	25% 23% 32% 14% 6%	460
	11th to 20th	Day	34% 19% 25% 12% 8% 3	452
	21st to end	Day	26% 20% 33% 15% 5% 2	460
May	1st to 10th	Day	23% 14% 33% 18% 10% 3	463
	11th to 20th	Day	22% 14% 29% 22% 9% 4	487
	21st to end	Day	14% 15% 30% 25% 11% 5%	529
June	1st to 10th	Day	19% 13% 33% 25% 8% 2	490
	11th to 20th	Day	16% 13% 34% 24% 12% 2	552
	21st to end	Day	18% 13% 35% 22% 8% 3	680
July	1st to 10th	Day	11% 8% 34% 28% 15% 4	612
	11th to 20th	Day	12% 7% 32% 27% 14% 7%	484
	21st to end	Day	11% 7% 36% 28% 11% 7%	532
August	1st to 10th	Day	11% 9% 26% 29% 14% 10%	486
	11th to 20th	Day	10% 8% 29% 25% 19% 9%	479
	21st to end	Day	16% 8% 29% 24% 16% 7%	539
September	1st to 10th	Day	14% 11% 27% 26% 13% 8%	490
	11th to 20th	Day	11% 8% 26% 23% 20% 13%	490
	21st to end	Day	16% 13% 29% 22% 15% 5%	490
October	1st to 10th	Day	24% 15% 25% 19% 12% 5%	490
	11th to 20th	Day	23% 19% 33% 17% 7% 2	490
	21st to end	Day	34% 18% 29% 15% 4	539
November	1st to 10th	Day	25% 22% 31% 17% 4 1	259
	11th to 20th	Day	27% 21% 34% 13% 4 1	180
	21st to end	Day	29% 23% 37% 10% 1	180
December	1st to 10th	Day	28% 27% 31% 13% 2	180
	11th to 20th	Day	28% 29% 28% 12% 2 1	180
	21st to end	Day	26% 28% 35% 8% 3	198
January	1st to 10th	Night	24% 22% 34% 14% 5% 1	760
	11th to 20th	Night	27% 20% 31% 17% 4	760
	21st to end	Night	20% 15% 36% 21% 7%	836
February	1st to 10th	Night	21% 22% 38% 18% 2	760
	11th to 20th	Night	22% 21% 38% 15% 4	743
	21st to end	Night	21% 23% 35% 18% 3	628
March	1st to 10th	Night	21% 22% 34% 20% 3	760
	11th to 20th	Night	23% 20% 32% 19% 5% 1	760
	21st to end	Night	22% 17% 32% 21% 7%	836
April	1st to 10th	Night	25% 16% 36% 21% 3	760
	11th to 20th	Night	21% 17% 35% 19% 8% 1	672
	21st to end	Night	21% 14% 31% 26% 8%	570
May	1st to 10th	Night	19% 7% 30% 32% 11% 2	570
	11th to 20th	Night	16% 9% 31% 34% 10% 1	398
	21st to end	Night	10% 8% 34% 33% 14% 1	411
June	1st to 10th	Night	15% 6% 34% 33% 12%	380
	11th to 20th	Night	12% 9% 29% 36% 14%	380
	21st to end	Night	12% 5% 31% 35% 16% 1	380
July	1st to 10th	Night	7% 3 26% 42% 19% 2	370
	11th to 20th	Night	13% 4 27% 34% 20% 2	368
	21st to end	Night	8% 4 29% 38% 19% 2	603
August	1st to 10th	Night	11% 2 23% 38% 25% 2	567
	11th to 20th	Night	8% 6% 19% 40% 24% 3	564
	21st to end	Night	12% 4 27% 33% 22% 2	693
September	1st to 10th	Night	11% 7% 28% 30% 19% 5%	760
	11th to 20th	Night	13% 6% 24% 29% 23% 6%	760
	21st to end	Night	19% 9% 22% 29% 17% 4	760
October	1st to 10th	Night	20% 9% 29% 24% 15% 2	760
	11th to 20th	Night	24% 14% 32% 21% 9% 1	760
	21st to end	Night	28% 17% 30% 21% 5%	836
November	1st to 10th	Night	24% 15% 30% 22% 8% 1	760
	11th to 20th	Night	23% 21% 29% 20% 6% 1	760
	21st to end	Night	26% 17% 32% 22% 4	760
December	1st to 10th	Night	29% 18% 35% 14% 3 1	760
	11th to 20th	Night	23% 22% 34% 17% 4	760
	21st to end	Night	32% 17% 31% 18% 2	836

Page generated at 2024-11-03 02:11:11. Version ac07

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