Tawas
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tawas clear sky chart from 2005-11-06 to 2026-04-17.

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% 8% 3 8% 5% 5% 5% 4 6% 7% 35%	130895
	Night	13% 10% 4 9% 5% 5% 5% 4 5% 7% 34%	131441
Transparency	Day	44% 8% 14% 21% 12% 1	134417
	Night	47% 7% 13% 20% 11% 1	136007
Seeing	Day	15% 9% 28% 30% 15% 4	17305
	Night	17% 8% 30% 30% 13% 2	26970

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	13% 11% 6% 15% 7% 6% 5% 4 6% 6% 21%	4691
	11th to 20th	Day	10% 15% 6% 17% 9% 8% 6% 4 4 5% 16%	4679
	21st to end	Day	12% 13% 5% 10% 7% 6% 7% 5% 7% 7% 23%	5362
February	1st to 10th	Day	12% 13% 4 10% 7% 6% 6% 4 5% 7% 25%	1890
	11th to 20th	Day	12% 11% 4 12% 7% 8% 6% 5% 5% 5% 26%	1951
	21st to end	Day	12% 12% 3 8% 8% 6% 7% 4 7% 7% 27%	1730
March	1st to 10th	Day	12% 8% 3 7% 6% 5% 5% 4 7% 7% 36%	4658
	11th to 20th	Day	12% 9% 4 9% 5% 5% 5% 5% 7% 9% 29%	5090
	21st to end	Day	18% 9% 4 9% 6% 6% 5% 3 5% 6% 28%	5586
April	1st to 10th	Day	17% 11% 3 9% 5% 5% 5% 4 5% 7% 31%	2473
	11th to 20th	Day	17% 8% 3 7% 4 4 4 4 6% 7% 38%	2634
	21st to end	Day	14% 8% 3 7% 5% 5% 4 5% 6% 7% 36%	2600
May	1st to 10th	Day	16% 8% 3 7% 4 5% 4 4 6% 7% 37%	5888
	11th to 20th	Day	14% 8% 3 8% 5% 4 5% 3 5% 7% 38%	5861
	21st to end	Day	14% 7% 3 6% 4 4 4 3 5% 7% 43%	6975
June	1st to 10th	Day	11% 5% 3 6% 4 5% 5% 5% 7% 9% 42%	3000
	11th to 20th	Day	10% 5% 2 6% 5% 4 5% 5% 7% 9% 43%	3000
	21st to end	Day	10% 6% 2 5% 4 5% 5% 5% 6% 9% 43%	3000
July	1st to 10th	Day	9% 5% 2 7% 5% 5% 5% 5% 7% 10% 41%	6528
	11th to 20th	Day	6% 5% 2 6% 4 5% 5% 4 6% 8% 50%	6360
	21st to end	Day	6% 3 2 5% 4 4 5% 4 7% 10% 50%	6790
August	1st to 10th	Day	9% 4 2 5% 5% 5% 6% 4 8% 9% 44%	4234
	11th to 20th	Day	11% 4 2 6% 4 5% 5% 4 7% 10% 43%	4174
	21st to end	Day	8% 5% 2 6% 4 4 5% 4 6% 8% 46%	4675
September	1st to 10th	Day	9% 5% 2 6% 5% 5% 5% 4 7% 9% 43%	2289
	11th to 20th	Day	11% 4 2 4 4 4 4 5% 5% 9% 49%	2200
	21st to end	Day	13% 7% 2 7% 5% 5% 5% 5% 6% 8% 38%	2200
October	1st to 10th	Day	14% 6% 2 6% 4 5% 5% 4 6% 7% 41%	2135
	11th to 20th	Day	19% 10% 3 7% 4 4 5% 5% 5% 7% 31%	2000
	21st to end	Day	18% 10% 2 8% 6% 5% 7% 4 7% 8% 25%	1990
November	1st to 10th	Day	12% 11% 3 8% 7% 5% 5% 4 7% 7% 31%	1852
	11th to 20th	Day	13% 11% 4 8% 6% 6% 5% 5% 7% 8% 26%	1848
	21st to end	Day	16% 14% 5% 9% 6% 7% 6% 4 5% 5% 22%	1680
December	1st to 10th	Day	15% 14% 5% 13% 7% 6% 6% 4 7% 7% 16%	2560
	11th to 20th	Day	17% 16% 6% 10% 7% 5% 6% 4 5% 5% 20%	2691
	21st to end	Day	26% 21% 6% 10% 6% 4 4 3 3 4 13%	3621
January	1st to 10th	Night	13% 12% 4 13% 7% 6% 5% 4 5% 6% 26%	8233
	11th to 20th	Night	10% 16% 7% 14% 9% 7% 7% 4 5% 5% 16%	8236
	21st to end	Night	10% 13% 6% 11% 7% 6% 6% 4 6% 7% 25%	8839
February	1st to 10th	Night	12% 14% 4 11% 7% 6% 5% 4 7% 6% 24%	2730
	11th to 20th	Night	13% 14% 4 9% 6% 5% 5% 4 5% 6% 29%	2554
	21st to end	Night	13% 14% 6% 11% 6% 5% 5% 4 5% 6% 26%	2076
March	1st to 10th	Night	13% 8% 3 7% 5% 4 4 3 5% 7% 40%	5401
	11th to 20th	Night	10% 9% 3 8% 4 4 4 4 7% 9% 37%	5089
	21st to end	Night	17% 10% 3 7% 6% 4 4 4 5% 5% 35%	5588
April	1st to 10th	Night	17% 10% 3 6% 5% 4 5% 3 5% 7% 35%	2163
	11th to 20th	Night	17% 10% 3 6% 5% 4 4 3 5% 7% 37%	1847
	21st to end	Night	16% 9% 3 8% 6% 4 5% 3 5% 6% 35%	1800
May	1st to 10th	Night	14% 9% 3 9% 5% 5% 5% 3 5% 8% 35%	4053
	11th to 20th	Night	14% 8% 3 7% 5% 5% 5% 4 5% 7% 37%	4032
	21st to end	Night	18% 5% 2 5% 4 4 4 3 5% 7% 44%	3910
June	1st to 10th	Night	11% 6% 2 6% 5% 5% 5% 4 5% 8% 44%	1400
	11th to 20th	Night	10% 5% 2 7% 4 5% 4 4 8% 9% 43%	1400
	21st to end	Night	9% 6% 3 7% 5% 5% 5% 5% 7% 7% 43%	1400
July	1st to 10th	Night	8% 6% 3 7% 4 4 4 4 7% 9% 44%	3432
	11th to 20th	Night	8% 4 2 5% 3 4 5% 4 6% 8% 53%	3620
	21st to end	Night	7% 4 2 5% 4 4 4 4 6% 8% 51%	4076
August	1st to 10th	Night	9% 5% 2 5% 4 4 4 4 6% 8% 48%	2915
	11th to 20th	Night	11% 5% 2 4 3 3 4 4 6% 9% 49%	2875
	21st to end	Night	8% 4 2 5% 4 4 5% 4 7% 8% 50%	3223
September	1st to 10th	Night	8% 6% 2 5% 4 4 4 4 6% 8% 48%	2088
	11th to 20th	Night	9% 4 1 5% 4 3 4 4 6% 7% 53%	2200
	21st to end	Night	15% 6% 3 7% 4 4 4 4 5% 7% 42%	2200
October	1st to 10th	Night	14% 6% 2 6% 5% 3 4 3 6% 8% 43%	2265
	11th to 20th	Night	18% 9% 3 8% 5% 4 4 3 5% 6% 35%	2400
	21st to end	Night	19% 9% 3 8% 4 4 4 4 5% 7% 32%	2849
November	1st to 10th	Night	12% 9% 3 7% 6% 5% 4 4 6% 9% 38%	2666
	11th to 20th	Night	13% 12% 4 9% 8% 6% 4 4 6% 6% 29%	2769
	21st to end	Night	17% 13% 4 9% 6% 5% 4 4 5% 7% 26%	2940
December	1st to 10th	Night	13% 13% 5% 11% 6% 5% 5% 4 6% 7% 25%	4840
	11th to 20th	Night	14% 17% 6% 10% 6% 5% 5% 4 5% 5% 24%	5736
	21st to end	Night	25% 20% 6% 10% 5% 4 4 3 4 5% 16%	7596

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	59% 10% 13% 12% 4 1	4692
	11th to 20th	Day	67% 7% 8% 10% 7%	4710
	21st to end	Day	56% 8% 14% 13% 9%	5362
February	1st to 10th	Day	56% 9% 11% 18% 6%	1890
	11th to 20th	Day	57% 8% 11% 15% 7% 1	1960
	21st to end	Day	52% 9% 13% 18% 6% 1	1730
March	1st to 10th	Day	44% 7% 17% 18% 10% 3	4661
	11th to 20th	Day	47% 7% 18% 17% 9% 2	5090
	21st to end	Day	54% 8% 12% 15% 10% 1	5586
April	1st to 10th	Day	52% 7% 12% 18% 10% 1	2473
	11th to 20th	Day	45% 6% 13% 20% 15% 1	2634
	21st to end	Day	45% 8% 14% 17% 13% 2	2600
May	1st to 10th	Day	43% 8% 13% 17% 17% 2	5897
	11th to 20th	Day	42% 8% 11% 23% 14% 2	5865
	21st to end	Day	40% 7% 11% 20% 18% 5%	6975
June	1st to 10th	Day	36% 8% 14% 26% 14% 2	3000
	11th to 20th	Day	36% 8% 14% 24% 17% 2	3000
	21st to end	Day	35% 10% 14% 25% 14% 1	3000
July	1st to 10th	Day	34% 9% 16% 25% 14% 2	6460
	11th to 20th	Day	29% 9% 14% 33% 14% 1	6285
	21st to end	Day	27% 9% 17% 28% 18% 1	6595
August	1st to 10th	Day	31% 10% 15% 29% 13% 1	4221
	11th to 20th	Day	34% 10% 17% 26% 12% 1	4213
	21st to end	Day	34% 9% 17% 28% 12% 1	4674
September	1st to 10th	Day	35% 10% 14% 27% 12% 1	2289
	11th to 20th	Day	31% 9% 17% 30% 12% 1	2200
	21st to end	Day	42% 9% 15% 23% 11%	2200
October	1st to 10th	Day	31% 7% 11% 35% 14% 3	3473
	11th to 20th	Day	43% 6% 14% 25% 11%	3240
	21st to end	Day	49% 8% 15% 20% 8%	3190
November	1st to 10th	Day	50% 8% 13% 20% 9%	1852
	11th to 20th	Day	54% 8% 17% 14% 7%	1848
	21st to end	Day	61% 8% 15% 12% 3 1	1680
December	1st to 10th	Day	63% 11% 15% 10% 1	2560
	11th to 20th	Day	64% 7% 11% 11% 6%	2691
	21st to end	Day	74% 6% 7% 7% 5%	3621
January	1st to 10th	Night	54% 9% 14% 14% 8% 2	8233
	11th to 20th	Night	66% 7% 11% 11% 5% 1	8280
	21st to end	Night	55% 7% 10% 17% 11%	8839
February	1st to 10th	Night	57% 7% 12% 16% 7% 1	2730
	11th to 20th	Night	53% 7% 13% 19% 7% 1	2556
	21st to end	Night	57% 7% 11% 17% 8%	2076
March	1st to 10th	Night	43% 6% 17% 21% 12% 1	5411
	11th to 20th	Night	41% 7% 21% 21% 9% 1	5090
	21st to end	Night	49% 7% 12% 18% 13% 1	5588
April	1st to 10th	Night	49% 6% 10% 20% 13% 2	2163
	11th to 20th	Night	46% 5% 9% 21% 16% 3	1847
	21st to end	Night	48% 6% 9% 18% 15% 4	1800
May	1st to 10th	Night	45% 8% 10% 16% 17% 3	4060
	11th to 20th	Night	44% 8% 9% 24% 14% 2	4033
	21st to end	Night	39% 6% 10% 24% 16% 4	3911
June	1st to 10th	Night	39% 5% 11% 25% 18% 2	1400
	11th to 20th	Night	35% 8% 14% 23% 19% 2	1400
	21st to end	Night	37% 8% 12% 22% 18% 3	1400
July	1st to 10th	Night	34% 7% 16% 22% 17% 4	3392
	11th to 20th	Night	28% 7% 13% 34% 18% 1	3572
	21st to end	Night	29% 8% 16% 28% 17% 1	3958
August	1st to 10th	Night	31% 7% 15% 31% 15% 1	2904
	11th to 20th	Night	30% 7% 18% 31% 12% 2	2902
	21st to end	Night	28% 9% 16% 33% 13% 1	3223
September	1st to 10th	Night	32% 7% 15% 29% 16% 1	2088
	11th to 20th	Night	29% 7% 15% 34% 15%	2200
	21st to end	Night	41% 7% 16% 25% 11% 1	2200
October	1st to 10th	Night	28% 6% 12% 33% 20% 1	3707
	11th to 20th	Night	43% 5% 13% 24% 15%	3899
	21st to end	Night	44% 6% 15% 26% 9%	4599
November	1st to 10th	Night	44% 7% 14% 25% 9% 1	2666
	11th to 20th	Night	54% 7% 16% 16% 6% 1	2769
	21st to end	Night	58% 9% 15% 14% 3	2940
December	1st to 10th	Night	56% 9% 19% 13% 3	4840
	11th to 20th	Night	60% 7% 13% 11% 8% 1	5735
	21st to end	Night	70% 8% 8% 9% 5%	7596

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	16% 15% 37% 26% 6% 1	330
	11th to 20th	Day	19% 12% 39% 22% 6%	330
	21st to end	Day	19% 8% 37% 27% 7% 1	363
February	1st to 10th	Day	18% 16% 38% 22% 5% 1	330
	11th to 20th	Day	15% 16% 41% 23% 4	330
	21st to end	Day	19% 19% 40% 20% 3	273
March	1st to 10th	Day	17% 18% 40% 20% 5%	359
	11th to 20th	Day	17% 14% 34% 26% 8% 1	540
	21st to end	Day	22% 10% 34% 27% 6% 1	594
April	1st to 10th	Day	19% 11% 37% 25% 8%	540
	11th to 20th	Day	21% 13% 30% 22% 11% 3	516
	21st to end	Day	17% 11% 32% 28% 11% 2	500
May	1st to 10th	Day	18% 8% 32% 29% 10% 3	503
	11th to 20th	Day	17% 4 28% 31% 16% 5%	527
	21st to end	Day	14% 6% 24% 32% 21% 4	699
June	1st to 10th	Day	10% 5% 28% 39% 15% 3	730
	11th to 20th	Day	11% 4 27% 37% 18% 4	730
	21st to end	Day	12% 3 25% 39% 18% 3	730
July	1st to 10th	Day	7% 3 20% 38% 27% 5%	721
	11th to 20th	Day	8% 4 21% 39% 21% 6%	718
	21st to end	Day	9% 3 20% 40% 24% 5%	734
August	1st to 10th	Day	9% 3 18% 33% 30% 8%	526
	11th to 20th	Day	7% 3 15% 37% 29% 9%	519
	21st to end	Day	10% 6% 18% 32% 27% 7%	583
September	1st to 10th	Day	9% 6% 25% 30% 21% 9%	530
	11th to 20th	Day	8% 6% 17% 27% 29% 13%	530
	21st to end	Day	14% 8% 23% 26% 22% 7%	530
October	1st to 10th	Day	16% 9% 25% 26% 19% 5%	530
	11th to 20th	Day	22% 13% 28% 29% 8% 1	530
	21st to end	Day	22% 9% 35% 27% 7%	373
November	1st to 10th	Day	16% 13% 36% 26% 8% 1	330
	11th to 20th	Day	17% 19% 34% 23% 7% 1	308
	21st to end	Day	24% 14% 40% 19% 4	220
December	1st to 10th	Day	22% 15% 36% 18% 8% 1	220
	11th to 20th	Day	26% 16% 37% 18% 3	220
	21st to end	Day	27% 16% 34% 18% 4	259
January	1st to 10th	Night	18% 12% 38% 26% 6% 1	1050
	11th to 20th	Night	20% 13% 37% 24% 6%	1050
	21st to end	Night	16% 8% 36% 31% 8% 1	1079
February	1st to 10th	Night	18% 9% 37% 30% 5%	840
	11th to 20th	Night	21% 9% 36% 29% 5%	823
	21st to end	Night	19% 12% 38% 27% 4	692
March	1st to 10th	Night	17% 7% 38% 29% 8%	840
	11th to 20th	Night	16% 11% 37% 28% 8% 1	840
	21st to end	Night	21% 9% 30% 32% 7% 1	924
April	1st to 10th	Night	20% 9% 35% 28% 7% 1	693
	11th to 20th	Night	21% 9% 28% 29% 11% 2	611
	21st to end	Night	20% 6% 25% 35% 13% 1	600
May	1st to 10th	Night	14% 4 27% 41% 13% 2	600
	11th to 20th	Night	17% 4 21% 36% 20% 1	591
	21st to end	Night	15% 3 18% 38% 25% 2	558
June	1st to 10th	Night	12% 3 25% 38% 22% 1	400
	11th to 20th	Night	11% 4 20% 41% 23% 2	400
	21st to end	Night	9% 3 18% 42% 26% 3	400
July	1st to 10th	Night	7% 2 17% 42% 30% 2	501
	11th to 20th	Night	8% 2 16% 41% 28% 6%	582
	21st to end	Night	9% 2 15% 44% 28% 2	657
August	1st to 10th	Night	9% 2 14% 38% 32% 5%	597
	11th to 20th	Night	9% 2 15% 33% 34% 6%	594
	21st to end	Night	10% 3 17% 37% 28% 4	660
September	1st to 10th	Night	9% 5% 23% 34% 22% 7%	695
	11th to 20th	Night	11% 3 17% 33% 27% 9%	800
	21st to end	Night	16% 6% 23% 29% 20% 7%	800
October	1st to 10th	Night	16% 7% 28% 28% 18% 2	800
	11th to 20th	Night	21% 11% 33% 26% 9%	800
	21st to end	Night	23% 11% 31% 28% 6% 1	880
November	1st to 10th	Night	17% 11% 35% 26% 10% 1	820
	11th to 20th	Night	19% 15% 36% 22% 8%	840
	21st to end	Night	23% 12% 39% 21% 4	840
December	1st to 10th	Night	22% 14% 36% 22% 5%	908
	11th to 20th	Night	21% 14% 41% 20% 4 1	1050
	21st to end	Night	30% 11% 35% 22% 3	1155

Page generated at 2026-04-14 02:44:26. Version ac07

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