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 2024-01-16.

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% 4 6% 6% 4 5% 5% 6% 8% 35%	74613
	Night	14% 10% 4 7% 6% 3 5% 5% 5% 7% 34%	75195
Transparency	Day	46% 9% 14% 20% 10% 1	74324
	Night	49% 7% 13% 20% 10% 1	75020
Seeing	Day	15% 8% 28% 30% 15% 4	14303
	Night	18% 8% 29% 30% 13% 2	23972

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	15% 11% 6% 10% 8% 4 5% 5% 7% 7% 21%	1517
	11th to 20th	Day	15% 12% 7% 10% 9% 5% 6% 6% 6% 7% 17%	1485
	21st to end	Day	13% 13% 7% 11% 9% 4 6% 6% 6% 5% 21%	1647
February	1st to 10th	Day	13% 12% 6% 9% 8% 5% 7% 5% 5% 7% 23%	1620
	11th to 20th	Day	12% 9% 5% 10% 9% 5% 6% 6% 5% 5% 27%	1665
	21st to end	Day	13% 11% 4 7% 8% 4 8% 6% 7% 7% 26%	1480
March	1st to 10th	Day	12% 9% 4 8% 9% 4 6% 5% 6% 7% 30%	1821
	11th to 20th	Day	11% 9% 4 8% 6% 4 6% 6% 6% 7% 32%	1980
	21st to end	Day	16% 7% 4 7% 7% 4 6% 4 5% 7% 32%	2178
April	1st to 10th	Day	18% 10% 4 8% 6% 3 5% 4 5% 7% 30%	2119
	11th to 20th	Day	17% 7% 3 6% 5% 3 4 5% 5% 7% 38%	2298
	21st to end	Day	15% 7% 4 6% 6% 4 5% 6% 5% 7% 36%	2340
May	1st to 10th	Day	15% 8% 4 6% 5% 3 5% 5% 6% 7% 36%	2340
	11th to 20th	Day	16% 5% 3 7% 6% 3 5% 4 4 7% 41%	2301
	21st to end	Day	11% 6% 3 4 4 4 5% 4 6% 8% 46%	2723
June	1st to 10th	Day	11% 5% 3 5% 5% 3 5% 6% 6% 9% 43%	2700
	11th to 20th	Day	10% 5% 2 5% 5% 3 5% 6% 6% 9% 43%	2700
	21st to end	Day	10% 5% 3 4 5% 3 5% 6% 6% 9% 44%	2700
July	1st to 10th	Day	6% 3 2 4 4 3 6% 6% 7% 9% 51%	2591
	11th to 20th	Day	8% 5% 2 5% 5% 4 6% 5% 6% 8% 46%	2520
	21st to end	Day	8% 3 2 5% 5% 3 6% 6% 8% 10% 45%	2689
August	1st to 10th	Day	9% 4 2 5% 5% 4 6% 5% 7% 9% 45%	2327
	11th to 20th	Day	7% 3 2 5% 5% 3 5% 6% 7% 10% 47%	2303
	21st to end	Day	9% 6% 2 5% 5% 3 5% 5% 7% 8% 46%	2574
September	1st to 10th	Day	10% 5% 2 6% 6% 4 5% 4 6% 9% 42%	2061
	11th to 20th	Day	12% 4 2 4 4 3 4 6% 4 8% 48%	1980
	21st to end	Day	13% 6% 2 6% 6% 3 6% 6% 6% 9% 38%	1980
October	1st to 10th	Day	15% 6% 3 6% 5% 3 6% 5% 6% 7% 38%	1922
	11th to 20th	Day	21% 10% 3 6% 6% 4 5% 6% 5% 7% 28%	1800
	21st to end	Day	20% 10% 3 7% 6% 4 7% 5% 6% 8% 24%	1792
November	1st to 10th	Day	12% 10% 3 7% 8% 4 6% 5% 7% 7% 32%	1672
	11th to 20th	Day	13% 11% 5% 7% 8% 4 6% 6% 7% 8% 26%	1672
	21st to end	Day	17% 13% 6% 7% 8% 4 6% 5% 5% 6% 23%	1520
December	1st to 10th	Day	13% 13% 5% 10% 8% 4 7% 4 6% 9% 21%	1456
	11th to 20th	Day	15% 14% 5% 8% 7% 4 6% 5% 5% 7% 24%	1671
	21st to end	Day	27% 21% 7% 10% 7% 3 4 4 3 4 11%	2469
January	1st to 10th	Night	15% 11% 5% 10% 8% 5% 6% 5% 5% 7% 24%	2648
	11th to 20th	Night	16% 14% 7% 10% 7% 4 5% 4 5% 6% 22%	2603
	21st to end	Night	12% 12% 6% 10% 8% 4 5% 5% 6% 8% 24%	2707
February	1st to 10th	Night	13% 14% 5% 9% 8% 4 6% 5% 7% 6% 23%	2340
	11th to 20th	Night	14% 13% 4 8% 7% 3 6% 5% 5% 6% 28%	2180
	21st to end	Night	15% 14% 6% 10% 7% 4 4 5% 4 6% 26%	1776
March	1st to 10th	Night	12% 9% 4 7% 7% 3 4 4 5% 7% 38%	2125
	11th to 20th	Night	12% 9% 4 6% 6% 3 3 5% 5% 7% 40%	1979
	21st to end	Night	18% 9% 3 6% 6% 3 5% 5% 4 5% 36%	2178
April	1st to 10th	Night	17% 9% 4 5% 5% 3 5% 4 4 7% 36%	1854
	11th to 20th	Night	17% 8% 3 5% 5% 3 4 4 6% 8% 38%	1611
	21st to end	Night	16% 8% 3 6% 7% 3 5% 4 4 6% 36%	1620
May	1st to 10th	Night	12% 7% 3 7% 5% 3 5% 6% 6% 8% 37%	1620
	11th to 20th	Night	15% 7% 3 5% 5% 4 4 5% 5% 7% 40%	1592
	21st to end	Night	12% 3 2 4 4 3 5% 5% 5% 9% 48%	1548
June	1st to 10th	Night	12% 6% 2 4 5% 3 5% 4 5% 8% 44%	1260
	11th to 20th	Night	10% 5% 2 5% 5% 3 5% 4 7% 9% 45%	1260
	21st to end	Night	7% 6% 3 6% 6% 4 5% 6% 6% 7% 44%	1260
July	1st to 10th	Night	5% 3 2 4 5% 2 3 6% 6% 8% 55%	1364
	11th to 20th	Night	6% 5% 2 4 5% 3 5% 5% 7% 9% 50%	1440
	21st to end	Night	8% 3 3 5% 5% 3 4 5% 6% 8% 51%	1627
August	1st to 10th	Night	7% 4 2 4 4 3 5% 6% 6% 9% 51%	1611
	11th to 20th	Night	8% 3 2 4 3 2 5% 5% 6% 9% 55%	1598
	21st to end	Night	10% 5% 2 4 4 2 4 6% 6% 8% 49%	1782
September	1st to 10th	Night	9% 6% 2 4 5% 3 4 4 6% 9% 47%	1878
	11th to 20th	Night	10% 4 2 5% 5% 2 4 5% 6% 7% 51%	1980
	21st to end	Night	15% 5% 3 5% 6% 3 4 5% 5% 8% 42%	1980
October	1st to 10th	Night	16% 6% 2 5% 6% 2 4 4 6% 8% 40%	2038
	11th to 20th	Night	19% 9% 4 7% 6% 3 4 4 5% 6% 33%	2160
	21st to end	Night	21% 10% 3 6% 5% 3 5% 4 4 7% 30%	2563
November	1st to 10th	Night	12% 8% 3 6% 6% 3 4 4 6% 9% 38%	2406
	11th to 20th	Night	13% 11% 4 9% 9% 5% 4 5% 6% 7% 28%	2505
	21st to end	Night	18% 11% 5% 8% 7% 4 5% 5% 5% 7% 27%	2660
December	1st to 10th	Night	17% 13% 5% 9% 7% 4 5% 5% 4 7% 24%	2721
	11th to 20th	Night	15% 13% 6% 7% 7% 4 5% 6% 7% 6% 24%	3526
	21st to end	Night	26% 21% 6% 10% 6% 3 4 3 4 5% 13%	5195

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	60% 8% 15% 11% 5%	1518
	11th to 20th	Day	65% 9% 12% 10% 3	1485
	21st to end	Day	63% 8% 10% 13% 5% 1	1647
February	1st to 10th	Day	59% 9% 11% 15% 5%	1620
	11th to 20th	Day	57% 8% 12% 14% 7% 1	1674
	21st to end	Day	53% 9% 13% 17% 7% 1	1480
March	1st to 10th	Day	52% 8% 13% 17% 8% 2	1824
	11th to 20th	Day	49% 8% 13% 18% 8% 3	1980
	21st to end	Day	51% 8% 12% 18% 9% 1	2178
April	1st to 10th	Day	52% 8% 12% 17% 10% 1	2119
	11th to 20th	Day	45% 6% 14% 20% 14% 1	2298
	21st to end	Day	46% 8% 15% 16% 13% 2	2340
May	1st to 10th	Day	45% 8% 10% 22% 13% 2	2340
	11th to 20th	Day	43% 7% 10% 23% 15% 2	2305
	21st to end	Day	35% 8% 16% 23% 15% 3	2723
June	1st to 10th	Day	36% 8% 15% 26% 14% 2	2700
	11th to 20th	Day	36% 8% 14% 24% 18% 2	2700
	21st to end	Day	35% 10% 14% 25% 14% 1	2700
July	1st to 10th	Day	26% 9% 15% 28% 19% 3	2522
	11th to 20th	Day	33% 10% 13% 27% 15% 2	2445
	21st to end	Day	32% 11% 17% 22% 15% 3	2540
August	1st to 10th	Day	33% 12% 16% 26% 11% 1	2314
	11th to 20th	Day	30% 11% 18% 26% 14% 1	2303
	21st to end	Day	34% 9% 15% 27% 13% 1	2574
September	1st to 10th	Day	37% 10% 13% 26% 12% 1	2061
	11th to 20th	Day	32% 10% 17% 30% 10%	1980
	21st to end	Day	42% 9% 16% 23% 9%	1980
October	1st to 10th	Day	43% 9% 12% 23% 11% 1	1922
	11th to 20th	Day	54% 7% 15% 18% 6%	1800
	21st to end	Day	56% 9% 16% 13% 5% 1	1792
November	1st to 10th	Day	50% 8% 14% 19% 8%	1672
	11th to 20th	Day	55% 7% 17% 14% 7%	1672
	21st to end	Day	61% 8% 15% 12% 3 1	1520
December	1st to 10th	Day	61% 9% 15% 12% 2	1456
	11th to 20th	Day	60% 9% 14% 14% 4	1671
	21st to end	Day	78% 7% 8% 5% 2	2469
January	1st to 10th	Night	59% 8% 14% 13% 6%	2648
	11th to 20th	Night	64% 8% 12% 12% 4	2603
	21st to end	Night	58% 8% 13% 14% 6%	2707
February	1st to 10th	Night	59% 7% 11% 16% 6% 1	2340
	11th to 20th	Night	55% 7% 13% 18% 7% 1	2182
	21st to end	Night	59% 7% 10% 16% 9%	1776
March	1st to 10th	Night	46% 7% 12% 23% 10% 1	2135
	11th to 20th	Night	44% 7% 12% 21% 14% 2	1980
	21st to end	Night	50% 7% 10% 20% 12% 1	2178
April	1st to 10th	Night	48% 6% 10% 20% 14% 2	1854
	11th to 20th	Night	44% 5% 10% 21% 17% 3	1611
	21st to end	Night	48% 6% 9% 18% 15% 4	1620
May	1st to 10th	Night	43% 7% 12% 21% 14% 2	1620
	11th to 20th	Night	44% 6% 10% 21% 16% 4	1593
	21st to end	Night	33% 7% 13% 28% 15% 4	1549
June	1st to 10th	Night	39% 6% 11% 25% 17% 2	1260
	11th to 20th	Night	34% 8% 14% 23% 20% 2	1260
	21st to end	Night	37% 7% 12% 22% 19% 3	1260
July	1st to 10th	Night	25% 6% 15% 27% 23% 4	1324
	11th to 20th	Night	28% 9% 16% 28% 18% 1	1392
	21st to end	Night	31% 8% 16% 27% 16% 2	1537
August	1st to 10th	Night	28% 9% 17% 31% 15% 1	1600
	11th to 20th	Night	26% 7% 18% 32% 15% 2	1598
	21st to end	Night	31% 9% 15% 28% 14% 2	1782
September	1st to 10th	Night	34% 7% 14% 27% 17% 1	1878
	11th to 20th	Night	31% 7% 15% 34% 13%	1980
	21st to end	Night	40% 7% 17% 26% 9% 1	1980
October	1st to 10th	Night	42% 7% 13% 24% 13% 1	2038
	11th to 20th	Night	52% 7% 13% 21% 7% 1	2160
	21st to end	Night	53% 7% 14% 18% 7%	2563
November	1st to 10th	Night	43% 7% 14% 25% 9% 1	2406
	11th to 20th	Night	55% 7% 16% 16% 6%	2505
	21st to end	Night	57% 9% 16% 14% 3	2660
December	1st to 10th	Night	60% 9% 14% 14% 4	2721
	11th to 20th	Night	58% 9% 15% 11% 5% 1	3525
	21st to end	Night	74% 8% 8% 7% 3	5195

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	17% 14% 36% 25% 7% 1	270
	11th to 20th	Day	21% 12% 36% 23% 8%	257
	21st to end	Day	20% 8% 37% 26% 8% 1	264
February	1st to 10th	Day	21% 20% 37% 20% 3	240
	11th to 20th	Day	16% 18% 43% 20% 3	240
	21st to end	Day	21% 19% 41% 17% 2	198
March	1st to 10th	Day	19% 19% 39% 18% 6%	264
	11th to 20th	Day	16% 14% 32% 28% 9% 1	420
	21st to end	Day	22% 10% 30% 30% 6% 2	462
April	1st to 10th	Day	20% 9% 34% 27% 9%	420
	11th to 20th	Day	20% 13% 29% 23% 12% 3	412
	21st to end	Day	18% 9% 31% 29% 11% 2	420
May	1st to 10th	Day	18% 8% 32% 29% 11% 3	423
	11th to 20th	Day	17% 4 28% 29% 16% 5%	447
	21st to end	Day	13% 4 23% 33% 22% 5%	597
June	1st to 10th	Day	10% 4 27% 39% 17% 3	630
	11th to 20th	Day	12% 4 27% 35% 18% 4	630
	21st to end	Day	13% 3 23% 39% 18% 4	630
July	1st to 10th	Day	6% 3 20% 36% 29% 5%	621
	11th to 20th	Day	9% 4 21% 38% 21% 7%	618
	21st to end	Day	9% 3 22% 39% 22% 5%	630
August	1st to 10th	Day	10% 3 18% 33% 28% 8%	446
	11th to 20th	Day	6% 4 15% 37% 29% 10%	439
	21st to end	Day	11% 6% 18% 32% 26% 6%	495
September	1st to 10th	Day	10% 6% 25% 31% 19% 9%	450
	11th to 20th	Day	10% 6% 20% 29% 25% 10%	450
	21st to end	Day	15% 7% 26% 24% 22% 6%	450
October	1st to 10th	Day	18% 10% 26% 24% 19% 3	450
	11th to 20th	Day	24% 14% 28% 27% 6% 1	450
	21st to end	Day	25% 10% 36% 23% 5%	307
November	1st to 10th	Day	14% 12% 37% 27% 9% 1	270
	11th to 20th	Day	17% 20% 35% 21% 6% 1	252
	21st to end	Day	26% 12% 40% 19% 3	180
December	1st to 10th	Day	21% 15% 38% 17% 8% 1	180
	11th to 20th	Day	28% 15% 36% 18% 3	180
	21st to end	Day	27% 16% 36% 16% 4	211
January	1st to 10th	Night	19% 12% 37% 25% 7% 1	950
	11th to 20th	Night	21% 12% 35% 24% 7%	930
	21st to end	Night	17% 7% 34% 32% 9% 1	925
February	1st to 10th	Night	20% 8% 39% 29% 4	720
	11th to 20th	Night	22% 9% 35% 28% 5%	703
	21st to end	Night	21% 12% 37% 26% 4	592
March	1st to 10th	Night	17% 7% 36% 30% 9%	720
	11th to 20th	Night	16% 9% 37% 29% 9% 1	720
	21st to end	Night	21% 9% 30% 32% 8% 1	792
April	1st to 10th	Night	21% 8% 34% 29% 8% 1	594
	11th to 20th	Night	19% 8% 28% 31% 12% 2	533
	21st to end	Night	21% 6% 24% 35% 14% 1	540
May	1st to 10th	Night	14% 3 28% 40% 13% 2	540
	11th to 20th	Night	17% 4 21% 36% 21% 1	531
	21st to end	Night	14% 2 18% 39% 25% 2	502
June	1st to 10th	Night	13% 3 24% 38% 23% 1	360
	11th to 20th	Night	11% 4 20% 39% 24% 2	360
	21st to end	Night	8% 3 18% 42% 26% 3	360
July	1st to 10th	Night	6% 2 18% 42% 30% 3	449
	11th to 20th	Night	8% 2 16% 41% 28% 7%	522
	21st to end	Night	9% 2 15% 44% 27% 2	591
August	1st to 10th	Night	9% 3 13% 39% 32% 4	537
	11th to 20th	Night	10% 2 16% 32% 35% 6%	534
	21st to end	Night	11% 3 18% 37% 28% 4	594
September	1st to 10th	Night	10% 4 22% 36% 20% 7%	625
	11th to 20th	Night	12% 3 19% 36% 23% 7%	720
	21st to end	Night	16% 5% 24% 28% 20% 7%	720
October	1st to 10th	Night	17% 8% 27% 28% 18% 2	720
	11th to 20th	Night	22% 12% 33% 26% 8%	720
	21st to end	Night	25% 11% 31% 26% 6% 1	792
November	1st to 10th	Night	17% 10% 34% 27% 11% 1	740
	11th to 20th	Night	19% 14% 37% 21% 8%	760
	21st to end	Night	23% 12% 38% 22% 5%	760
December	1st to 10th	Night	23% 14% 36% 21% 5%	821
	11th to 20th	Night	21% 13% 40% 21% 4 1	950
	21st to end	Night	29% 10% 35% 22% 2	1045

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