Blythewood
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Blythewood 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	13% 6% 2 6% 4 4 5% 4 6% 8% 42%	101194
	Night	14% 6% 2 6% 4 4 4 4 6% 7% 43%	97807
Transparency	Day	38% 7% 12% 19% 18% 6%	104897
	Night	38% 6% 11% 18% 19% 7%	102243
Seeing	Day	15% 10% 25% 25% 18% 7%	15340
	Night	15% 8% 24% 31% 19% 2	25402

By Month

Percentage Cloud Cover SE (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	17% 5% 2 5% 3 3 3 3 5% 7% 47%	2836
	11th to 20th	Day	13% 6% 2 5% 4 3 3 2 3 6% 53%	2840
	21st to end	Day	19% 8% 3 6% 4 3 3 3 4 4 43%	3124
February	1st to 10th	Day	15% 7% 3 6% 5% 4 5% 3 5% 6% 41%	1712
	11th to 20th	Day	20% 6% 2 5% 3 3 3 3 4 5% 45%	1848
	21st to end	Day	19% 7% 3 6% 4 5% 3 3 5% 5% 41%	1632
March	1st to 10th	Day	22% 9% 3 6% 4 3 4 3 4 5% 38%	3435
	11th to 20th	Day	10% 4 2 5% 4 3 4 4 5% 6% 53%	3480
	21st to end	Day	18% 7% 2 6% 4 4 3 3 5% 5% 42%	3815
April	1st to 10th	Day	10% 3 1 6% 4 3 5% 4 7% 7% 50%	2090
	11th to 20th	Day	10% 5% 2 6% 4 4 5% 4 6% 7% 47%	2235
	21st to end	Day	9% 5% 2 4 3 4 4 4 6% 8% 51%	2391
May	1st to 10th	Day	9% 7% 3 7% 5% 5% 5% 4 7% 9% 39%	4082
	11th to 20th	Day	17% 7% 3 6% 4 4 5% 4 6% 7% 37%	4081
	21st to end	Day	6% 4 2 5% 4 5% 6% 4 7% 9% 48%	4476
June	1st to 10th	Day	9% 7% 2 7% 6% 5% 6% 5% 8% 10% 36%	2470
	11th to 20th	Day	7% 5% 2 6% 5% 5% 6% 5% 8% 11% 41%	2470
	21st to end	Day	6% 5% 2 6% 5% 6% 7% 5% 8% 11% 38%	2470
July	1st to 10th	Day	12% 6% 2 7% 6% 5% 6% 6% 8% 11% 30%	4120
	11th to 20th	Day	6% 5% 3 7% 6% 6% 7% 7% 10% 13% 30%	4120
	21st to end	Day	9% 8% 3 9% 7% 6% 7% 5% 10% 13% 22%	4466
August	1st to 10th	Day	21% 7% 2 8% 5% 6% 6% 5% 7% 10% 22%	4104
	11th to 20th	Day	11% 5% 2 7% 5% 5% 6% 5% 8% 11% 33%	4044
	21st to end	Day	7% 4 2 5% 4 5% 5% 5% 8% 11% 46%	4217
September	1st to 10th	Day	8% 6% 2 7% 5% 6% 5% 4 7% 10% 40%	2094
	11th to 20th	Day	12% 7% 3 7% 4 4 5% 4 6% 7% 39%	2090
	21st to end	Day	16% 7% 2 6% 4 4 4 3 5% 6% 42%	2090
October	1st to 10th	Day	14% 6% 2 5% 4 4 3 4 4 6% 50%	1981
	11th to 20th	Day	10% 5% 1 5% 3 3 3 2 4 5% 58%	1900
	21st to end	Day	11% 5% 2 5% 3 3 4 2 3 4 58%	2090
November	1st to 10th	Day	12% 6% 2 4 3 3 3 2 4 6% 55%	1898
	11th to 20th	Day	14% 6% 2 5% 2 2 3 3 4 6% 54%	1796
	21st to end	Day	14% 6% 2 6% 4 3 3 3 4 6% 49%	1710
December	1st to 10th	Day	19% 7% 3 6% 4 4 4 4 5% 6% 39%	1710
	11th to 20th	Day	16% 4 2 5% 3 3 3 3 4 5% 51%	2153
	21st to end	Day	19% 7% 3 5% 3 3 3 3 4 6% 44%	3124
January	1st to 10th	Night	17% 6% 2 5% 3 3 3 3 4 6% 48%	4109
	11th to 20th	Night	11% 6% 2 7% 4 4 5% 3 6% 7% 45%	4120
	21st to end	Night	18% 8% 3 5% 4 3 3 3 4 4 45%	4532
February	1st to 10th	Night	17% 6% 2 5% 4 4 3 3 5% 6% 45%	2466
	11th to 20th	Night	18% 7% 2 6% 4 3 3 3 4 6% 43%	2218
	21st to end	Night	15% 6% 2 6% 4 4 4 3 5% 7% 44%	1822
March	1st to 10th	Night	22% 10% 3 7% 4 3 3 3 5% 6% 35%	3418
	11th to 20th	Night	12% 5% 1 4 4 4 4 3 5% 7% 51%	3480
	21st to end	Night	19% 5% 2 5% 4 4 3 4 6% 7% 42%	3817
April	1st to 10th	Night	11% 5% 2 5% 3 3 4 3 6% 6% 51%	2090
	11th to 20th	Night	12% 5% 2 5% 3 4 4 3 5% 7% 52%	1893
	21st to end	Night	9% 5% 1 4 5% 3 3 3 6% 7% 53%	1803
May	1st to 10th	Night	10% 6% 3 6% 4 4 5% 4 7% 10% 42%	2813
	11th to 20th	Night	15% 7% 3 7% 4 5% 4 3 6% 8% 39%	2812
	21st to end	Night	6% 4 2 5% 4 5% 4 5% 8% 9% 47%	3079
June	1st to 10th	Night	12% 6% 3 6% 5% 5% 5% 4 9% 10% 33%	1710
	11th to 20th	Night	8% 6% 2 6% 6% 6% 5% 5% 9% 10% 38%	1710
	21st to end	Night	7% 6% 2 6% 5% 6% 7% 6% 10% 11% 34%	1710
July	1st to 10th	Night	13% 8% 3 7% 6% 5% 6% 5% 7% 10% 29%	2840
	11th to 20th	Night	9% 6% 2 7% 6% 6% 7% 6% 10% 12% 29%	2840
	21st to end	Night	11% 9% 4 10% 7% 7% 6% 6% 8% 9% 22%	3087
August	1st to 10th	Night	21% 8% 2 9% 6% 5% 5% 5% 7% 9% 22%	2825
	11th to 20th	Night	10% 7% 2 8% 5% 5% 5% 5% 8% 10% 35%	2785
	21st to end	Night	5% 4 2 5% 4 4 4 4 7% 11% 50%	3407
September	1st to 10th	Night	8% 6% 2 6% 5% 6% 5% 5% 7% 11% 40%	2081
	11th to 20th	Night	13% 7% 3 8% 5% 5% 5% 3 6% 7% 38%	2090
	21st to end	Night	16% 7% 2 6% 4 4 5% 3 5% 6% 43%	2090
October	1st to 10th	Night	12% 7% 2 6% 3 3 2 3 5% 6% 52%	2199
	11th to 20th	Night	13% 5% 2 4 3 2 2 3 4 6% 55%	2280
	21st to end	Night	10% 6% 2 4 3 3 3 3 4 5% 57%	2508
November	1st to 10th	Night	11% 6% 2 5% 3 3 3 3 4 5% 54%	2280
	11th to 20th	Night	14% 6% 2 4 3 3 3 3 4 5% 53%	2379
	21st to end	Night	14% 5% 2 5% 3 4 3 3 6% 7% 47%	2470
December	1st to 10th	Night	17% 8% 2 6% 4 4 4 3 4 5% 42%	2470
	11th to 20th	Night	17% 5% 2 5% 3 3 2 2 4 5% 52%	3042
	21st to end	Night	20% 7% 2 6% 4 3 4 3 4 6% 41%	4532

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	35% 4 7% 24% 22% 7%	2837
	11th to 20th	Day	34% 4 6% 17% 31% 9%	2840
	21st to end	Day	45% 3 4 17% 24% 8%	3124
February	1st to 10th	Day	42% 5% 9% 19% 19% 6%	1712
	11th to 20th	Day	42% 5% 5% 18% 25% 6%	1858
	21st to end	Day	45% 4 7% 15% 20% 8%	1632
March	1st to 10th	Day	49% 5% 7% 15% 14% 10%	3435
	11th to 20th	Day	31% 5% 8% 15% 29% 11%	3480
	21st to end	Day	44% 4 7% 18% 23% 5%	3815
April	1st to 10th	Day	32% 6% 11% 19% 27% 6%	2090
	11th to 20th	Day	34% 6% 10% 19% 20% 11%	2235
	21st to end	Day	31% 6% 10% 26% 22% 5%	2391
May	1st to 10th	Day	38% 8% 16% 22% 14% 2	4120
	11th to 20th	Day	44% 7% 11% 20% 17% 1	4085
	21st to end	Day	29% 9% 16% 20% 22% 3	4489
June	1st to 10th	Day	40% 9% 16% 24% 10% 2	2470
	11th to 20th	Day	34% 10% 16% 26% 13% 2	2470
	21st to end	Day	35% 11% 17% 20% 15% 2	2470
July	1st to 10th	Day	44% 11% 19% 18% 7% 1	4055
	11th to 20th	Day	38% 15% 26% 17% 4 1	4051
	21st to end	Day	48% 14% 17% 17% 4 1	4324
August	1st to 10th	Day	53% 9% 18% 14% 4	4091
	11th to 20th	Day	41% 10% 15% 20% 14%	4083
	21st to end	Day	28% 9% 15% 31% 15% 2	4217
September	1st to 10th	Day	37% 9% 13% 17% 19% 4	2094
	11th to 20th	Day	41% 8% 11% 16% 20% 4	2090
	21st to end	Day	42% 5% 9% 21% 15% 7%	2090
October	1st to 10th	Day	33% 3 8% 18% 28% 10%	3293
	11th to 20th	Day	19% 2 5% 17% 28% 29%	3140
	21st to end	Day	26% 3 4 22% 30% 15%	3428
November	1st to 10th	Day	32% 4 7% 18% 27% 12%	1898
	11th to 20th	Day	33% 4 7% 21% 25% 10%	1796
	21st to end	Day	37% 4 8% 19% 23% 9%	1710
December	1st to 10th	Day	45% 6% 9% 19% 17% 5%	1710
	11th to 20th	Day	35% 3 7% 21% 23% 10%	2150
	21st to end	Day	42% 4 7% 22% 23% 3	3124
January	1st to 10th	Night	37% 4 7% 19% 25% 8%	4109
	11th to 20th	Night	38% 5% 9% 18% 24% 7%	4120
	21st to end	Night	44% 4 4 15% 27% 6%	4532
February	1st to 10th	Night	41% 4 8% 18% 20% 9%	2466
	11th to 20th	Night	43% 4 7% 17% 21% 8%	2219
	21st to end	Night	40% 4 9% 17% 20% 9%	1822
March	1st to 10th	Night	50% 6% 9% 13% 15% 7%	3418
	11th to 20th	Night	32% 4 8% 14% 26% 15%	3480
	21st to end	Night	40% 5% 8% 20% 19% 8%	3817
April	1st to 10th	Night	32% 5% 11% 19% 23% 9%	2090
	11th to 20th	Night	32% 6% 10% 20% 22% 11%	1893
	21st to end	Night	29% 5% 12% 26% 22% 5%	1803
May	1st to 10th	Night	36% 8% 13% 25% 14% 3	2840
	11th to 20th	Night	41% 8% 14% 20% 16% 1	2813
	21st to end	Night	28% 10% 13% 26% 19% 3	3087
June	1st to 10th	Night	40% 11% 17% 19% 11% 2	1710
	11th to 20th	Night	37% 11% 16% 22% 11% 2	1710
	21st to end	Night	37% 14% 18% 18% 11% 2	1710
July	1st to 10th	Night	47% 11% 20% 14% 7% 2	2795
	11th to 20th	Night	42% 15% 25% 14% 4 1	2786
	21st to end	Night	54% 13% 15% 13% 5%	2988
August	1st to 10th	Night	55% 10% 18% 14% 3 1	2814
	11th to 20th	Night	42% 9% 22% 19% 7% 1	2812
	21st to end	Night	27% 7% 15% 31% 17% 3	3407
September	1st to 10th	Night	37% 10% 15% 18% 14% 5%	2081
	11th to 20th	Night	44% 7% 12% 16% 18% 3	2090
	21st to end	Night	41% 7% 12% 18% 17% 5%	2090
October	1st to 10th	Night	33% 4 9% 18% 30% 7%	3667
	11th to 20th	Night	21% 3 5% 16% 26% 30%	3779
	21st to end	Night	25% 4 5% 19% 28% 19%	4120
November	1st to 10th	Night	32% 4 9% 15% 26% 14%	2280
	11th to 20th	Night	34% 4 7% 17% 25% 13%	2379
	21st to end	Night	35% 4 8% 19% 24% 9%	2470
December	1st to 10th	Night	44% 5% 8% 18% 18% 6%	2470
	11th to 20th	Night	36% 3 7% 18% 25% 10%	3044
	21st to end	Night	44% 4 7% 20% 21% 4	4532

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	20% 24% 40% 12% 3	270
	11th to 20th	Day	22% 20% 37% 18% 4	270
	21st to end	Day	22% 26% 38% 11% 3	297
February	1st to 10th	Day	18% 24% 38% 15% 5%	270
	11th to 20th	Day	35% 16% 39% 8% 1	270
	21st to end	Day	27% 23% 32% 14% 4	287
March	1st to 10th	Day	20% 16% 34% 22% 7%	460
	11th to 20th	Day	19% 19% 41% 16% 4 1	460
	21st to end	Day	19% 19% 36% 18% 7% 1	506
April	1st to 10th	Day	19% 18% 34% 18% 10%	460
	11th to 20th	Day	14% 17% 29% 24% 13% 3	452
	21st to end	Day	13% 11% 30% 27% 15% 4	460
May	1st to 10th	Day	10% 14% 34% 24% 14% 4	463
	11th to 20th	Day	17% 6% 22% 29% 19% 8%	487
	21st to end	Day	13% 5% 19% 27% 24% 12%	529
June	1st to 10th	Day	11% 4 19% 30% 26% 9%	490
	11th to 20th	Day	8% 6% 19% 25% 27% 14%	490
	21st to end	Day	8% 2 15% 32% 29% 13%	490
July	1st to 10th	Day	9% 2 10% 25% 31% 23%	485
	11th to 20th	Day	9% 2 12% 29% 33% 16%	484
	21st to end	Day	7% 3 10% 35% 32% 13%	532
August	1st to 10th	Day	14% 5% 15% 22% 29% 15%	486
	11th to 20th	Day	14% 4 11% 28% 28% 15%	479
	21st to end	Day	12% 2 12% 29% 29% 16%	539
September	1st to 10th	Day	10% 4 12% 32% 31% 12%	490
	11th to 20th	Day	17% 4 13% 27% 29% 11%	490
	21st to end	Day	19% 5% 18% 27% 26% 7%	490
October	1st to 10th	Day	16% 6% 21% 29% 20% 8%	490
	11th to 20th	Day	10% 9% 25% 29% 20% 6%	490
	21st to end	Day	13% 6% 28% 30% 18% 5%	539
November	1st to 10th	Day	17% 9% 27% 27% 15% 5%	472
	11th to 20th	Day	19% 14% 32% 26% 8% 1	356
	21st to end	Day	12% 15% 37% 25% 9% 2	270
December	1st to 10th	Day	27% 13% 38% 17% 4	270
	11th to 20th	Day	22% 13% 38% 19% 6% 2	270
	21st to end	Day	27% 16% 34% 16% 5% 2	297
January	1st to 10th	Night	21% 14% 31% 27% 7%	760
	11th to 20th	Night	20% 13% 31% 29% 6%	760
	21st to end	Night	20% 15% 34% 28% 3	836
February	1st to 10th	Night	20% 12% 33% 31% 4	760
	11th to 20th	Night	22% 14% 38% 23% 2	743
	21st to end	Night	18% 17% 33% 27% 5%	628
March	1st to 10th	Night	18% 11% 35% 30% 6%	760
	11th to 20th	Night	19% 13% 37% 24% 8%	760
	21st to end	Night	16% 14% 36% 26% 8%	836
April	1st to 10th	Night	15% 15% 32% 30% 8%	760
	11th to 20th	Night	14% 12% 31% 29% 14%	751
	21st to end	Night	14% 7% 31% 37% 12%	663
May	1st to 10th	Night	10% 8% 30% 38% 14%	570
	11th to 20th	Night	13% 4 29% 34% 18% 2	561
	21st to end	Night	9% 3 16% 36% 33% 3	617
June	1st to 10th	Night	12% 4 15% 39% 25% 5%	570
	11th to 20th	Night	10% 3 15% 33% 32% 8%	570
	21st to end	Night	9% 2 15% 38% 31% 6%	570
July	1st to 10th	Night	10% 1 10% 37% 34% 8%	555
	11th to 20th	Night	10% 1 7% 35% 40% 7%	552
	21st to end	Night	8% 2 10% 36% 39% 5%	624
August	1st to 10th	Night	12% 2 10% 31% 38% 7%	567
	11th to 20th	Night	14% 3 9% 31% 38% 6%	564
	21st to end	Night	11% 1 12% 30% 38% 7%	793
September	1st to 10th	Night	10% 2 11% 32% 39% 6%	760
	11th to 20th	Night	16% 2 14% 29% 35% 4	760
	21st to end	Night	20% 4 13% 34% 26% 3	760
October	1st to 10th	Night	15% 5% 20% 29% 27% 4	760
	11th to 20th	Night	15% 7% 23% 31% 21% 2	760
	21st to end	Night	12% 8% 23% 32% 23% 2	836
November	1st to 10th	Night	15% 7% 25% 32% 18% 3	760
	11th to 20th	Night	16% 11% 28% 31% 12% 1	760
	21st to end	Night	15% 8% 27% 34% 15% 1	760
December	1st to 10th	Night	19% 12% 27% 32% 9% 1	760
	11th to 20th	Night	20% 9% 25% 34% 11% 1	760
	21st to end	Night	25% 13% 25% 28% 9%	836

Page generated at 2024-11-03 02:11:25. Version ac07

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