McKim Alpena County Observation Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the McKim Alpena County Observation Site clear sky chart from 2005-11-06 to 2026-04-02.

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% 11% 4 9% 5% 5% 5% 4 5% 7% 32%	130692
	Night	13% 12% 5% 10% 6% 5% 5% 4 5% 6% 30%	131295
Transparency	Day	50% 6% 11% 20% 12% 1	134198
	Night	52% 6% 12% 19% 10% 1	135864
Seeing	Day	21% 16% 32% 20% 8% 3	17284
	Night	19% 14% 32% 26% 9% 1	26941

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	14% 16% 7% 21% 8% 4 3 3 3 5% 17%	4691
	11th to 20th	Day	10% 19% 8% 20% 9% 7% 5% 4 3 4 11%	4679
	21st to end	Day	11% 16% 7% 14% 8% 5% 5% 4 6% 6% 18%	5213
February	1st to 10th	Day	11% 16% 6% 12% 11% 7% 4 3 4 5% 20%	1890
	11th to 20th	Day	12% 15% 6% 14% 9% 4 5% 3 4 6% 22%	1951
	21st to end	Day	11% 17% 6% 13% 8% 6% 5% 3 4 5% 21%	1730
March	1st to 10th	Day	12% 11% 4 11% 5% 5% 5% 4 5% 6% 32%	4616
	11th to 20th	Day	12% 14% 5% 10% 6% 5% 5% 4 6% 7% 26%	5090
	21st to end	Day	19% 14% 6% 10% 6% 4 4 3 4 5% 24%	5586
April	1st to 10th	Day	17% 17% 4 9% 5% 4 4 3 5% 5% 28%	2392
	11th to 20th	Day	18% 13% 3 7% 3 4 4 3 5% 6% 34%	2552
	21st to end	Day	16% 12% 3 8% 5% 4 3 4 5% 7% 33%	2600
May	1st to 10th	Day	18% 10% 3 6% 4 4 4 3 5% 7% 36%	5888
	11th to 20th	Day	13% 8% 3 7% 5% 4 5% 3 5% 7% 41%	5861
	21st to end	Day	15% 7% 2 6% 4 5% 4 3 5% 7% 41%	7165
June	1st to 10th	Day	12% 6% 3 7% 5% 5% 5% 4 6% 8% 40%	3000
	11th to 20th	Day	12% 6% 2 7% 5% 5% 4 5% 6% 9% 39%	3000
	21st to end	Day	13% 7% 2 7% 6% 5% 5% 4 6% 7% 38%	3000
July	1st to 10th	Day	13% 6% 2 7% 5% 5% 4 4 6% 9% 40%	6602
	11th to 20th	Day	10% 5% 2 7% 5% 5% 5% 4 6% 9% 43%	6360
	21st to end	Day	8% 5% 2 6% 4 5% 5% 4 7% 9% 46%	6891
August	1st to 10th	Day	9% 5% 2 6% 5% 5% 6% 4 9% 9% 39%	4234
	11th to 20th	Day	13% 6% 2 7% 4 3 5% 4 6% 8% 41%	4174
	21st to end	Day	12% 6% 3 8% 5% 4 5% 4 6% 7% 40%	4659
September	1st to 10th	Day	11% 7% 2 7% 5% 4 6% 4 6% 8% 39%	2302
	11th to 20th	Day	12% 6% 2 5% 4 4 5% 3 6% 7% 46%	2200
	21st to end	Day	17% 8% 3 7% 4 4 5% 3 6% 8% 36%	2200
October	1st to 10th	Day	16% 9% 2 7% 5% 4 4 3 5% 7% 38%	2140
	11th to 20th	Day	21% 11% 4 9% 6% 5% 5% 3 4 6% 25%	1979
	21st to end	Day	20% 14% 4 9% 7% 5% 4 4 6% 7% 21%	1980
November	1st to 10th	Day	13% 16% 4 8% 5% 5% 5% 5% 5% 7% 28%	1852
	11th to 20th	Day	13% 16% 5% 11% 6% 5% 6% 4 6% 6% 23%	1832
	21st to end	Day	17% 18% 7% 11% 6% 5% 3 4 5% 5% 19%	1680
December	1st to 10th	Day	11% 22% 6% 16% 6% 6% 5% 4 6% 5% 12%	2459
	11th to 20th	Day	15% 21% 6% 12% 7% 6% 5% 4 4 5% 15%	2691
	21st to end	Day	23% 23% 9% 14% 6% 5% 3 2 3 3 8%	3553
January	1st to 10th	Night	12% 12% 5% 22% 10% 5% 5% 4 5% 5% 14%	8233
	11th to 20th	Night	9% 17% 8% 17% 10% 9% 6% 4 4 4 11%	8236
	21st to end	Night	8% 14% 7% 15% 8% 7% 6% 4 5% 6% 20%	8984
February	1st to 10th	Night	9% 17% 5% 13% 9% 6% 6% 4 5% 6% 21%	2730
	11th to 20th	Night	11% 14% 5% 12% 8% 5% 6% 4 5% 7% 23%	2554
	21st to end	Night	14% 16% 6% 12% 7% 4 4 3 5% 5% 24%	2076
March	1st to 10th	Night	13% 10% 4 9% 6% 4 4 3 5% 7% 35%	5443
	11th to 20th	Night	10% 12% 4 8% 5% 5% 5% 4 6% 8% 34%	5089
	21st to end	Night	19% 14% 4 9% 5% 4 4 3 4 5% 31%	5588
April	1st to 10th	Night	17% 13% 4 8% 4 3 4 5% 6% 6% 32%	2047
	11th to 20th	Night	18% 9% 3 6% 4 5% 4 4 5% 5% 36%	1796
	21st to end	Night	15% 12% 4 7% 5% 5% 5% 3 5% 6% 34%	1800
May	1st to 10th	Night	13% 10% 3 7% 6% 4 5% 4 5% 7% 37%	4053
	11th to 20th	Night	15% 9% 2 6% 4 4 5% 4 6% 7% 39%	4032
	21st to end	Night	19% 8% 2 5% 3 3 3 3 4 6% 42%	3724
June	1st to 10th	Night	12% 6% 2 5% 5% 4 5% 4 6% 8% 43%	1400
	11th to 20th	Night	9% 5% 2 6% 5% 5% 4 5% 8% 9% 42%	1400
	21st to end	Night	11% 6% 3 6% 4 4 4 3 6% 7% 45%	1400
July	1st to 10th	Night	11% 6% 2 5% 5% 4 4 4 6% 9% 44%	3359
	11th to 20th	Night	8% 5% 2 6% 4 4 4 3 5% 7% 51%	3620
	21st to end	Night	8% 5% 2 4 3 4 4 3 6% 8% 52%	3981
August	1st to 10th	Night	8% 5% 2 6% 4 4 4 5% 6% 8% 48%	2915
	11th to 20th	Night	15% 5% 2 4 3 3 3 3 6% 8% 49%	2875
	21st to end	Night	9% 6% 2 5% 3 4 4 3 5% 8% 50%	3223
September	1st to 10th	Night	9% 6% 2 5% 4 3 5% 4 6% 7% 48%	2077
	11th to 20th	Night	11% 5% 1 5% 4 4 4 3 5% 7% 50%	2200
	21st to end	Night	16% 7% 2 7% 5% 4 4 3 6% 6% 40%	2200
October	1st to 10th	Night	16% 7% 2 6% 4 4 4 3 5% 5% 43%	2259
	11th to 20th	Night	18% 12% 4 8% 5% 4 4 3 5% 6% 32%	2419
	21st to end	Night	22% 11% 3 8% 5% 4 4 3 4 6% 29%	2860
November	1st to 10th	Night	12% 12% 4 9% 5% 4 5% 3 6% 7% 31%	2666
	11th to 20th	Night	12% 15% 5% 10% 6% 5% 6% 4 6% 7% 24%	2786
	21st to end	Night	17% 17% 6% 9% 6% 4 5% 3 5% 6% 21%	2940
December	1st to 10th	Night	12% 15% 6% 14% 7% 6% 5% 4 6% 7% 18%	4945
	11th to 20th	Night	11% 22% 7% 15% 7% 5% 5% 3 4 5% 17%	5736
	21st to end	Night	22% 23% 9% 12% 6% 5% 4 3 3 3 11%	7649

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	70% 5% 11% 10% 3 1	4692
	11th to 20th	Day	76% 6% 5% 8% 5%	4710
	21st to end	Day	65% 5% 12% 11% 7%	5213
February	1st to 10th	Day	65% 6% 9% 16% 4	1890
	11th to 20th	Day	62% 6% 10% 13% 8% 1	1960
	21st to end	Day	63% 6% 9% 14% 6%	1730
March	1st to 10th	Day	51% 5% 15% 17% 10% 2	4618
	11th to 20th	Day	54% 6% 12% 17% 8% 2	5090
	21st to end	Day	60% 5% 9% 16% 9% 1	5586
April	1st to 10th	Day	58% 6% 10% 16% 10% 1	2392
	11th to 20th	Day	50% 5% 10% 18% 16% 1	2552
	21st to end	Day	50% 6% 11% 16% 14% 3	2600
May	1st to 10th	Day	46% 6% 9% 18% 17% 3	5897
	11th to 20th	Day	42% 7% 10% 22% 17% 3	5865
	21st to end	Day	42% 6% 10% 19% 18% 5%	7165
June	1st to 10th	Day	40% 7% 11% 25% 15% 3	3000
	11th to 20th	Day	40% 7% 12% 22% 17% 2	3000
	21st to end	Day	43% 7% 12% 22% 13% 2	3000
July	1st to 10th	Day	41% 5% 11% 25% 16% 1	6533
	11th to 20th	Day	36% 6% 11% 30% 15% 1	6285
	21st to end	Day	33% 6% 12% 29% 18% 1	6693
August	1st to 10th	Day	38% 8% 13% 26% 14% 1	4221
	11th to 20th	Day	41% 6% 13% 26% 13% 1	4213
	21st to end	Day	41% 7% 14% 27% 10% 1	4658
September	1st to 10th	Day	41% 7% 12% 24% 15% 1	2302
	11th to 20th	Day	36% 7% 13% 30% 14% 1	2200
	21st to end	Day	46% 7% 13% 23% 11% 1	2200
October	1st to 10th	Day	34% 5% 9% 33% 17% 1	3491
	11th to 20th	Day	53% 5% 8% 20% 14%	3195
	21st to end	Day	58% 6% 10% 19% 7%	3180
November	1st to 10th	Day	55% 7% 11% 19% 7%	1852
	11th to 20th	Day	59% 7% 15% 14% 5%	1832
	21st to end	Day	65% 6% 14% 11% 3 1	1680
December	1st to 10th	Day	71% 8% 11% 9% 1	2459
	11th to 20th	Day	71% 5% 10% 10% 4	2691
	21st to end	Day	82% 4 4 6% 4	3553
January	1st to 10th	Night	67% 7% 11% 9% 5%	8233
	11th to 20th	Night	73% 6% 7% 9% 4	8280
	21st to end	Night	62% 6% 9% 14% 9%	8984
February	1st to 10th	Night	62% 6% 11% 15% 6% 1	2730
	11th to 20th	Night	58% 6% 11% 17% 6% 1	2556
	21st to end	Night	61% 4 12% 16% 7%	2076
March	1st to 10th	Night	48% 5% 16% 19% 11% 1	5454
	11th to 20th	Night	46% 7% 20% 20% 7% 1	5090
	21st to end	Night	55% 6% 10% 17% 11% 1	5588
April	1st to 10th	Night	52% 6% 9% 19% 13% 2	2047
	11th to 20th	Night	47% 5% 8% 23% 14% 2	1796
	21st to end	Night	50% 7% 10% 16% 15% 3	1800
May	1st to 10th	Night	44% 8% 10% 17% 19% 3	4060
	11th to 20th	Night	42% 8% 10% 23% 17% 1	4033
	21st to end	Night	42% 6% 11% 21% 15% 4	3725
June	1st to 10th	Night	37% 7% 12% 26% 16% 2	1400
	11th to 20th	Night	34% 8% 14% 25% 17% 2	1400
	21st to end	Night	37% 8% 12% 25% 15% 3	1400
July	1st to 10th	Night	35% 6% 15% 25% 17% 2	3320
	11th to 20th	Night	32% 6% 10% 34% 18% 1	3572
	21st to end	Night	29% 6% 16% 31% 17% 1	3865
August	1st to 10th	Night	33% 7% 15% 29% 15% 1	2904
	11th to 20th	Night	33% 5% 17% 30% 14% 1	2902
	21st to end	Night	32% 6% 15% 33% 13% 1	3223
September	1st to 10th	Night	32% 8% 14% 28% 16% 1	2077
	11th to 20th	Night	33% 5% 15% 32% 14%	2200
	21st to end	Night	43% 7% 15% 25% 10%	2200
October	1st to 10th	Night	31% 4 12% 34% 17% 1	3688
	11th to 20th	Night	46% 4 12% 24% 14%	3930
	21st to end	Night	49% 5% 13% 25% 6%	4610
November	1st to 10th	Night	49% 7% 14% 22% 7% 1	2666
	11th to 20th	Night	57% 6% 14% 17% 6% 1	2786
	21st to end	Night	62% 7% 14% 13% 3	2940
December	1st to 10th	Night	63% 8% 16% 11% 3	4945
	11th to 20th	Night	68% 7% 9% 10% 6%	5735
	21st to end	Night	78% 6% 6% 7% 3	7649

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	26% 18% 39% 13% 4	330
	11th to 20th	Day	20% 26% 37% 14% 2	330
	21st to end	Day	29% 18% 38% 10% 5% 1	363
February	1st to 10th	Day	29% 25% 31% 12% 2 1	330
	11th to 20th	Day	28% 29% 32% 10% 1	330
	21st to end	Day	34% 26% 32% 8% 1	273
March	1st to 10th	Day	29% 24% 35% 10% 2	342
	11th to 20th	Day	27% 18% 35% 14% 5% 1	540
	21st to end	Day	32% 16% 29% 17% 4	594
April	1st to 10th	Day	27% 20% 31% 17% 4 1	504
	11th to 20th	Day	32% 20% 26% 11% 8% 2	492
	21st to end	Day	25% 18% 32% 15% 7% 2	500
May	1st to 10th	Day	24% 20% 31% 14% 7% 3	503
	11th to 20th	Day	19% 17% 30% 22% 8% 4	527
	21st to end	Day	16% 14% 35% 25% 7% 3	761
June	1st to 10th	Day	15% 19% 36% 22% 7% 1	730
	11th to 20th	Day	16% 16% 37% 22% 7% 2	730
	21st to end	Day	18% 14% 37% 23% 6% 2	730
July	1st to 10th	Day	11% 11% 36% 28% 12% 2	721
	11th to 20th	Day	12% 13% 35% 26% 10% 4	718
	21st to end	Day	12% 8% 37% 27% 12% 5%	784
August	1st to 10th	Day	11% 9% 26% 30% 16% 8%	526
	11th to 20th	Day	13% 6% 25% 29% 16% 10%	519
	21st to end	Day	17% 8% 30% 28% 13% 4	583
September	1st to 10th	Day	17% 12% 28% 24% 12% 8%	530
	11th to 20th	Day	12% 9% 21% 33% 17% 8%	530
	21st to end	Day	21% 12% 23% 25% 13% 5%	530
October	1st to 10th	Day	21% 17% 28% 18% 14% 2	530
	11th to 20th	Day	27% 18% 32% 18% 5% 1	509
	21st to end	Day	29% 23% 33% 12% 2	363
November	1st to 10th	Day	27% 20% 34% 14% 4	330
	11th to 20th	Day	25% 26% 31% 13% 3 1	300
	21st to end	Day	31% 18% 35% 14% 1	220
December	1st to 10th	Day	31% 16% 37% 11% 4	220
	11th to 20th	Day	30% 23% 35% 9% 2	220
	21st to end	Day	33% 26% 27% 12% 2 1	242
January	1st to 10th	Night	21% 20% 35% 20% 3	1050
	11th to 20th	Night	22% 21% 33% 20% 5%	1050
	21st to end	Night	17% 16% 37% 24% 5% 1	1133
February	1st to 10th	Night	19% 20% 38% 20% 4	840
	11th to 20th	Night	21% 21% 31% 23% 4	823
	21st to end	Night	25% 17% 35% 20% 2	692
March	1st to 10th	Night	19% 17% 36% 22% 5%	840
	11th to 20th	Night	21% 18% 35% 21% 5%	840
	21st to end	Night	23% 15% 33% 23% 5% 1	924
April	1st to 10th	Night	24% 15% 36% 19% 5% 1	640
	11th to 20th	Night	25% 14% 28% 25% 7% 2	593
	21st to end	Night	19% 13% 32% 28% 7% 1	600
May	1st to 10th	Night	14% 10% 37% 30% 7% 1	600
	11th to 20th	Night	19% 10% 28% 32% 10% 1	591
	21st to end	Night	15% 8% 29% 34% 13%	531
June	1st to 10th	Night	14% 9% 32% 37% 8%	400
	11th to 20th	Night	10% 10% 34% 33% 12% 1	400
	21st to end	Night	13% 9% 29% 36% 13% 1	400
July	1st to 10th	Night	6% 4 30% 44% 15% 1	468
	11th to 20th	Night	9% 4 26% 39% 19% 3	582
	21st to end	Night	10% 5% 23% 43% 18% 1	657
August	1st to 10th	Night	9% 3 25% 40% 23% 1	597
	11th to 20th	Night	11% 3 21% 33% 27% 4	594
	21st to end	Night	15% 5% 21% 38% 20% 2	660
September	1st to 10th	Night	12% 7% 26% 33% 19% 4	677
	11th to 20th	Night	13% 6% 26% 33% 19% 4	800
	21st to end	Night	20% 9% 22% 29% 17% 3	800
October	1st to 10th	Night	18% 11% 29% 29% 12% 1	800
	11th to 20th	Night	25% 13% 34% 22% 7%	800
	21st to end	Night	28% 14% 30% 22% 5% 1	880
November	1st to 10th	Night	20% 15% 36% 21% 7% 1	820
	11th to 20th	Night	21% 20% 33% 20% 5%	840
	21st to end	Night	26% 16% 39% 16% 3	840
December	1st to 10th	Night	22% 18% 36% 19% 4	974
	11th to 20th	Night	24% 20% 35% 16% 4 1	1050
	21st to end	Night	29% 16% 36% 16% 3	1155

Page generated at 2026-03-30 02:18:44. Version ac07

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