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 2024-12-24.

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%	101621
	Night	14% 10% 4 8% 5% 5% 5% 4 5% 7% 35%	98565
Transparency	Day	44% 9% 14% 21% 11% 1	105160
	Night	47% 7% 13% 21% 11% 1	103115
Seeing	Day	15% 8% 28% 30% 15% 4	15586
	Night	17% 8% 30% 30% 13% 2	25178

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% 11% 8% 12% 6% 5% 4 3 6% 6% 23%	2527
	11th to 20th	Day	14% 15% 5% 15% 10% 10% 6% 4 5% 5% 12%	2530
	21st to end	Day	19% 15% 6% 11% 6% 5% 5% 4 5% 5% 18%	2885
February	1st to 10th	Day	12% 13% 5% 10% 7% 6% 6% 5% 5% 7% 24%	1710
	11th to 20th	Day	11% 11% 4 12% 7% 7% 6% 5% 5% 5% 27%	1760
	21st to end	Day	13% 11% 3 8% 8% 6% 6% 4 7% 7% 27%	1570
March	1st to 10th	Day	14% 11% 3 8% 6% 5% 5% 4 6% 6% 32%	3169
	11th to 20th	Day	12% 10% 5% 9% 6% 5% 6% 5% 6% 7% 30%	3480
	21st to end	Day	15% 9% 4 9% 7% 6% 6% 4 6% 6% 28%	3815
April	1st to 10th	Day	17% 11% 3 8% 5% 4 5% 4 5% 7% 31%	2237
	11th to 20th	Day	17% 7% 3 7% 4 4 4 4 6% 7% 38%	2428
	21st to end	Day	15% 8% 3 7% 5% 5% 4 4 5% 7% 36%	2470
May	1st to 10th	Day	13% 9% 3 8% 4 5% 5% 4 6% 6% 37%	4108
	11th to 20th	Day	14% 6% 2 7% 5% 5% 5% 4 6% 8% 38%	4081
	21st to end	Day	10% 6% 3 5% 4 4 4 3 5% 8% 49%	4849
June	1st to 10th	Day	11% 5% 3 6% 5% 5% 5% 5% 7% 8% 41%	2850
	11th to 20th	Day	10% 5% 2 6% 5% 4 4 5% 7% 9% 44%	2850
	21st to end	Day	11% 6% 2 5% 4 5% 5% 5% 6% 9% 43%	2850
July	1st to 10th	Day	10% 5% 2 7% 5% 6% 6% 5% 7% 8% 39%	4553
	11th to 20th	Day	7% 4 2 5% 4 5% 5% 4 7% 8% 49%	4440
	21st to end	Day	7% 4 2 5% 4 4 6% 5% 8% 10% 46%	4720
August	1st to 10th	Day	9% 4 2 5% 5% 5% 6% 4 8% 9% 44%	4104
	11th to 20th	Day	11% 4 2 6% 5% 5% 4 4 7% 10% 43%	4044
	21st to end	Day	9% 5% 2 6% 4 4 5% 4 6% 8% 46%	4532
September	1st to 10th	Day	10% 5% 2 6% 5% 5% 5% 3 7% 9% 43%	2175
	11th to 20th	Day	11% 4 2 4 4 4 4 5% 5% 8% 49%	2090
	21st to end	Day	12% 6% 2 7% 5% 5% 5% 4 6% 8% 38%	2090
October	1st to 10th	Day	14% 6% 2 7% 4 5% 5% 4 6% 7% 40%	2028
	11th to 20th	Day	20% 10% 3 7% 5% 4 5% 5% 5% 7% 29%	1900
	21st to end	Day	19% 10% 2 8% 5% 5% 7% 4 7% 8% 24%	1891
November	1st to 10th	Day	13% 11% 3 8% 7% 5% 5% 4 6% 7% 32%	1762
	11th to 20th	Day	13% 12% 4 8% 7% 6% 5% 5% 7% 8% 26%	1760
	21st to end	Day	16% 14% 6% 9% 6% 7% 6% 4 5% 5% 22%	1600
December	1st to 10th	Day	13% 14% 5% 11% 8% 6% 6% 3 7% 7% 20%	1532
	11th to 20th	Day	15% 16% 4 9% 6% 6% 5% 4 6% 6% 23%	1741
	21st to end	Day	27% 22% 6% 11% 6% 4 4 3 3 4 12%	2490
January	1st to 10th	Night	15% 14% 5% 12% 6% 5% 5% 3 4 6% 26%	4428
	11th to 20th	Night	13% 14% 7% 14% 10% 7% 7% 3 5% 5% 16%	4440
	21st to end	Night	17% 16% 7% 12% 6% 6% 5% 4 5% 5% 18%	4777
February	1st to 10th	Night	12% 15% 4 11% 7% 5% 5% 4 7% 6% 23%	2470
	11th to 20th	Night	13% 13% 4 9% 6% 5% 5% 4 6% 6% 29%	2305
	21st to end	Night	14% 14% 5% 11% 6% 5% 4 4 5% 6% 26%	1884
March	1st to 10th	Night	13% 9% 3 6% 5% 4 4 3 4 7% 41%	3670
	11th to 20th	Night	9% 10% 3 7% 4 4 4 4 5% 7% 42%	3479
	21st to end	Night	14% 9% 4 8% 6% 5% 4 4 6% 6% 35%	3817
April	1st to 10th	Night	17% 11% 3 6% 5% 4 4 3 4 7% 35%	1957
	11th to 20th	Night	17% 9% 3 6% 5% 4 4 3 5% 7% 38%	1701
	21st to end	Night	17% 9% 3 8% 6% 4 5% 3 5% 6% 36%	1710
May	1st to 10th	Night	12% 8% 3 8% 5% 5% 5% 4 5% 8% 37%	2833
	11th to 20th	Night	13% 7% 2 7% 5% 5% 5% 4 6% 9% 39%	2812
	21st to end	Night	12% 4 2 5% 4 4 5% 4 5% 7% 48%	2729
June	1st to 10th	Night	12% 7% 2 5% 5% 4 5% 4 5% 8% 44%	1330
	11th to 20th	Night	10% 5% 2 7% 4 5% 4 4 8% 8% 44%	1330
	21st to end	Night	8% 6% 3 7% 5% 5% 5% 5% 7% 7% 43%	1330
July	1st to 10th	Night	7% 6% 3 8% 5% 4 4 4 7% 8% 44%	2398
	11th to 20th	Night	7% 4 1 4 4 4 4 4 6% 8% 55%	2530
	21st to end	Night	7% 4 2 6% 4 4 5% 5% 6% 8% 49%	2839
August	1st to 10th	Night	9% 5% 2 5% 4 3 4 4 6% 8% 48%	2825
	11th to 20th	Night	12% 5% 2 4 2 3 4 4 6% 9% 49%	2785
	21st to end	Night	8% 4 2 5% 4 4 5% 5% 7% 8% 49%	3124
September	1st to 10th	Night	8% 6% 2 5% 4 4 4 4 6% 8% 48%	1983
	11th to 20th	Night	10% 4 1 5% 4 3 4 3 6% 7% 53%	2090
	21st to end	Night	15% 5% 3 7% 4 4 4 4 5% 7% 42%	2090
October	1st to 10th	Night	15% 6% 2 6% 5% 4 4 3 6% 8% 42%	2152
	11th to 20th	Night	18% 9% 3 8% 5% 4 4 3 5% 6% 35%	2280
	21st to end	Night	20% 10% 3 8% 4 4 5% 4 4 7% 31%	2706
November	1st to 10th	Night	12% 9% 3 7% 5% 5% 4 4 6% 9% 38%	2536
	11th to 20th	Night	13% 12% 4 9% 8% 6% 4 4 6% 6% 27%	2637
	21st to end	Night	17% 12% 4 9% 6% 5% 4 4 5% 7% 26%	2800
December	1st to 10th	Night	16% 14% 4 10% 6% 6% 5% 3 5% 7% 24%	2865
	11th to 20th	Night	15% 14% 5% 9% 6% 5% 5% 4 7% 6% 24%	3676
	21st to end	Night	25% 21% 6% 11% 5% 4 3 3 4 5% 13%	5247

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	61% 9% 15% 11% 3	2528
	11th to 20th	Day	71% 9% 12% 7% 2	2530
	21st to end	Day	67% 9% 13% 8% 3	2885
February	1st to 10th	Day	57% 10% 12% 16% 5%	1710
	11th to 20th	Day	57% 9% 12% 15% 7% 1	1769
	21st to end	Day	52% 9% 14% 18% 6% 1	1570
March	1st to 10th	Day	51% 8% 13% 21% 6% 1	3172
	11th to 20th	Day	48% 8% 17% 18% 8% 2	3480
	21st to end	Day	53% 9% 11% 15% 11% 1	3815
April	1st to 10th	Day	52% 7% 12% 17% 10% 1	2237
	11th to 20th	Day	44% 6% 14% 20% 14% 1	2428
	21st to end	Day	45% 8% 15% 16% 13% 2	2470
May	1st to 10th	Day	43% 8% 13% 17% 18% 2	4120
	11th to 20th	Day	39% 9% 14% 26% 11% 1	4085
	21st to end	Day	33% 7% 13% 20% 22% 5%	4849
June	1st to 10th	Day	37% 8% 14% 26% 13% 2	2850
	11th to 20th	Day	35% 8% 13% 24% 18% 2	2850
	21st to end	Day	35% 10% 14% 25% 14% 1	2850
July	1st to 10th	Day	38% 10% 15% 20% 15% 2	4484
	11th to 20th	Day	28% 10% 16% 32% 13% 1	4365
	21st to end	Day	30% 10% 18% 21% 19% 2	4571
August	1st to 10th	Day	32% 11% 15% 28% 13% 1	4091
	11th to 20th	Day	34% 10% 17% 26% 12% 1	4083
	21st to end	Day	34% 9% 17% 27% 12% 1	4531
September	1st to 10th	Day	36% 10% 13% 27% 12% 1	2175
	11th to 20th	Day	32% 9% 16% 30% 12% 1	2090
	21st to end	Day	42% 9% 16% 23% 10%	2090
October	1st to 10th	Day	31% 7% 11% 34% 14% 3	3366
	11th to 20th	Day	44% 6% 14% 25% 11%	3140
	21st to end	Day	50% 8% 15% 19% 8%	3091
November	1st to 10th	Day	50% 8% 13% 20% 9%	1762
	11th to 20th	Day	54% 8% 17% 14% 7%	1760
	21st to end	Day	61% 8% 15% 12% 3 1	1600
December	1st to 10th	Day	61% 10% 15% 12% 2	1532
	11th to 20th	Day	60% 9% 13% 14% 4	1741
	21st to end	Day	78% 7% 8% 6% 2	2490
January	1st to 10th	Night	58% 7% 14% 14% 6% 1	4428
	11th to 20th	Night	69% 7% 11% 10% 3	4440
	21st to end	Night	67% 8% 10% 11% 4	4777
February	1st to 10th	Night	58% 7% 12% 16% 7% 1	2470
	11th to 20th	Night	53% 7% 13% 19% 7% 1	2307
	21st to end	Night	58% 7% 10% 16% 9%	1884
March	1st to 10th	Night	43% 7% 16% 25% 8% 1	3680
	11th to 20th	Night	39% 7% 18% 23% 12% 1	3480
	21st to end	Night	47% 8% 13% 21% 10% 1	3817
April	1st to 10th	Night	49% 6% 10% 20% 13% 2	1957
	11th to 20th	Night	45% 5% 10% 21% 17% 3	1701
	21st to end	Night	48% 6% 9% 18% 15% 4	1710
May	1st to 10th	Night	41% 8% 13% 18% 17% 3	2840
	11th to 20th	Night	39% 8% 11% 26% 13% 2	2813
	21st to end	Night	34% 6% 13% 23% 18% 5%	2730
June	1st to 10th	Night	40% 5% 11% 25% 18% 2	1330
	11th to 20th	Night	34% 8% 14% 23% 20% 2	1330
	21st to end	Night	37% 8% 12% 22% 18% 3	1330
July	1st to 10th	Night	35% 7% 15% 22% 16% 6%	2358
	11th to 20th	Night	26% 8% 14% 37% 15% 1	2482
	21st to end	Night	31% 9% 17% 22% 19% 1	2749
August	1st to 10th	Night	31% 7% 15% 30% 15% 1	2814
	11th to 20th	Night	30% 7% 18% 31% 13% 2	2812
	21st to end	Night	29% 9% 16% 32% 13% 1	3124
September	1st to 10th	Night	33% 7% 14% 28% 17% 1	1983
	11th to 20th	Night	29% 7% 15% 34% 14%	2090
	21st to end	Night	40% 7% 16% 25% 11% 1	2090
October	1st to 10th	Night	29% 6% 12% 32% 20% 1	3594
	11th to 20th	Night	43% 5% 13% 24% 14%	3779
	21st to end	Night	45% 6% 15% 25% 9%	4456
November	1st to 10th	Night	43% 7% 14% 25% 9% 1	2536
	11th to 20th	Night	55% 7% 16% 16% 6%	2637
	21st to end	Night	57% 9% 16% 14% 3	2800
December	1st to 10th	Night	60% 9% 15% 13% 4	2865
	11th to 20th	Night	58% 9% 15% 11% 6% 1	3675
	21st to end	Night	74% 8% 8% 7% 3	5247

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% 37% 23% 7%	270
	21st to end	Day	22% 8% 36% 27% 7% 1	297
February	1st to 10th	Day	19% 19% 38% 20% 4 1	270
	11th to 20th	Day	15% 18% 42% 21% 3	270
	21st to end	Day	20% 20% 42% 17% 1	225
March	1st to 10th	Day	18% 19% 39% 18% 6%	296
	11th to 20th	Day	17% 14% 32% 27% 9% 1	460
	21st to end	Day	21% 10% 33% 29% 6% 2	506
April	1st to 10th	Day	20% 9% 37% 26% 8%	460
	11th to 20th	Day	21% 13% 30% 22% 11% 3	452
	21st to end	Day	18% 10% 32% 28% 11% 2	460
May	1st to 10th	Day	17% 9% 31% 30% 10% 3	463
	11th to 20th	Day	17% 4 27% 31% 16% 5%	487
	21st to end	Day	13% 5% 23% 33% 22% 4	648
June	1st to 10th	Day	10% 5% 28% 39% 16% 3	680
	11th to 20th	Day	11% 4 27% 36% 18% 4	680
	21st to end	Day	13% 3 25% 38% 18% 3	680
July	1st to 10th	Day	7% 3 20% 37% 27% 5%	671
	11th to 20th	Day	9% 4 21% 39% 21% 7%	668
	21st to end	Day	9% 3 20% 38% 24% 6%	682
August	1st to 10th	Day	9% 3 20% 33% 27% 8%	486
	11th to 20th	Day	7% 4 15% 37% 29% 9%	479
	21st to end	Day	11% 6% 18% 32% 27% 6%	539
September	1st to 10th	Day	9% 6% 26% 30% 20% 9%	490
	11th to 20th	Day	9% 6% 19% 28% 27% 12%	490
	21st to end	Day	14% 7% 24% 27% 21% 7%	490
October	1st to 10th	Day	17% 9% 27% 25% 18% 4	490
	11th to 20th	Day	22% 14% 27% 28% 8% 1	490
	21st to end	Day	24% 10% 37% 24% 5%	340
November	1st to 10th	Day	17% 12% 36% 26% 8% 1	300
	11th to 20th	Day	18% 19% 34% 23% 6% 1	280
	21st to end	Day	25% 13% 40% 19% 4	200
December	1st to 10th	Day	23% 14% 38% 18% 8% 1	200
	11th to 20th	Day	27% 15% 37% 20% 3	200
	21st to end	Day	28% 16% 35% 17% 4	217
January	1st to 10th	Night	19% 12% 37% 25% 7% 1	950
	11th to 20th	Night	21% 13% 36% 24% 7%	950
	21st to end	Night	18% 7% 34% 32% 9% 1	977
February	1st to 10th	Night	19% 9% 39% 29% 5%	760
	11th to 20th	Night	21% 10% 35% 29% 5%	743
	21st to end	Night	20% 12% 38% 26% 4	628
March	1st to 10th	Night	17% 7% 36% 30% 9%	760
	11th to 20th	Night	15% 10% 37% 28% 8% 1	760
	21st to end	Night	20% 9% 30% 32% 7% 1	836
April	1st to 10th	Night	21% 8% 34% 29% 7% 1	627
	11th to 20th	Night	20% 9% 28% 30% 11% 2	563
	21st to end	Night	21% 6% 24% 35% 14% 1	570
May	1st to 10th	Night	14% 4 27% 41% 13% 2	570
	11th to 20th	Night	17% 4 21% 37% 21% 1	561
	21st to end	Night	14% 2 18% 38% 25% 2	530
June	1st to 10th	Night	12% 3 25% 37% 22% 1	380
	11th to 20th	Night	11% 4 20% 41% 23% 2	380
	21st to end	Night	8% 3 18% 42% 26% 3	380
July	1st to 10th	Night	7% 2 17% 43% 29% 3	475
	11th to 20th	Night	7% 1 16% 41% 28% 7%	552
	21st to end	Night	9% 2 15% 43% 29% 2	624
August	1st to 10th	Night	9% 2 14% 39% 32% 4	567
	11th to 20th	Night	10% 2 15% 32% 35% 6%	564
	21st to end	Night	11% 3 18% 36% 29% 4	627
September	1st to 10th	Night	10% 4 23% 35% 21% 7%	660
	11th to 20th	Night	11% 3 18% 34% 26% 7%	760
	21st to end	Night	16% 5% 24% 28% 20% 7%	760
October	1st to 10th	Night	16% 8% 29% 28% 17% 2	760
	11th to 20th	Night	21% 11% 32% 26% 9%	760
	21st to end	Night	24% 11% 31% 27% 6% 1	836
November	1st to 10th	Night	17% 10% 34% 27% 11% 1	780
	11th to 20th	Night	19% 15% 36% 22% 8%	800
	21st to end	Night	23% 12% 39% 22% 4	800
December	1st to 10th	Night	23% 14% 36% 22% 5%	865
	11th to 20th	Night	21% 14% 40% 21% 4 1	1000
	21st to end	Night	29% 10% 35% 23% 2	1063

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