Pontiac
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Pontiac clear sky chart from 2005-11-06 to 2024-12-06.

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	17% 10% 3 8% 5% 5% 4 4 5% 7% 32%	101843
	Night	17% 12% 4 9% 5% 4 4 3 5% 6% 31%	97887
Transparency	Day	28% 47% 7% 12% 5%	105339
	Night	29% 47% 7% 11% 5%	102480
Seeing	Day	24% 17% 31% 19% 8% 2	14515
	Night	23% 14% 29% 24% 9% 1	23649

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% 19% 6% 13% 6% 5% 5% 3 4 4 21%	2517
	11th to 20th	Day	14% 13% 7% 15% 7% 6% 5% 3 5% 5% 20%	2520
	21st to end	Day	13% 17% 7% 14% 8% 6% 5% 3 5% 4 18%	2904
February	1st to 10th	Day	13% 15% 5% 13% 7% 5% 5% 3 5% 6% 23%	1710
	11th to 20th	Day	12% 16% 5% 11% 6% 4 5% 3 5% 6% 27%	1663
	21st to end	Day	19% 13% 4 10% 5% 5% 4 4 6% 4 26%	1556
March	1st to 10th	Day	21% 15% 4 9% 5% 4 4 3 4 5% 26%	3143
	11th to 20th	Day	11% 16% 6% 11% 7% 5% 4 3 5% 5% 26%	3480
	21st to end	Day	13% 8% 3 7% 6% 4 4 3 5% 6% 41%	4004
April	1st to 10th	Day	22% 13% 3 6% 6% 4 4 3 4 5% 30%	2280
	11th to 20th	Day	22% 10% 3 6% 4 4 3 2 5% 4 35%	2254
	21st to end	Day	22% 10% 4 7% 5% 4 4 4 3 5% 32%	2428
May	1st to 10th	Day	21% 8% 3 7% 5% 5% 4 4 6% 7% 31%	4426
	11th to 20th	Day	16% 9% 3 8% 5% 4 4 4 5% 8% 33%	4398
	21st to end	Day	17% 7% 3 7% 5% 4 5% 4 5% 7% 37%	4837
June	1st to 10th	Day	21% 9% 3 6% 5% 5% 5% 4 5% 7% 29%	2660
	11th to 20th	Day	15% 6% 3 6% 4 5% 5% 4 7% 7% 38%	2660
	21st to end	Day	18% 8% 3 7% 5% 5% 5% 5% 6% 8% 31%	2660
July	1st to 10th	Day	11% 6% 3 8% 5% 5% 5% 5% 8% 9% 34%	4440
	11th to 20th	Day	12% 6% 2 6% 5% 5% 5% 5% 6% 8% 40%	4440
	21st to end	Day	11% 6% 3 5% 4 4 4 4 6% 8% 45%	4814
August	1st to 10th	Day	14% 6% 3 8% 6% 5% 5% 4 6% 9% 34%	4336
	11th to 20th	Day	16% 7% 2 6% 4 4 4 4 7% 10% 36%	4022
	21st to end	Day	13% 5% 2 6% 4 5% 4 5% 8% 10% 39%	4180
September	1st to 10th	Day	14% 6% 2 5% 4 4 5% 4 6% 7% 43%	2280
	11th to 20th	Day	12% 6% 2 6% 4 4 5% 3 6% 7% 45%	2280
	21st to end	Day	18% 6% 2 7% 4 4 4 3 5% 8% 39%	2022
October	1st to 10th	Day	21% 8% 2 7% 5% 4 5% 4 5% 6% 34%	1900
	11th to 20th	Day	23% 10% 3 7% 5% 5% 4 3 5% 8% 27%	1900
	21st to end	Day	26% 9% 3 9% 4 5% 4 3 4 5% 27%	1948
November	1st to 10th	Day	17% 9% 3 6% 5% 5% 5% 4 6% 7% 33%	1743
	11th to 20th	Day	19% 13% 4 9% 6% 4 5% 4 5% 6% 26%	1600
	21st to end	Day	22% 15% 4 10% 6% 6% 6% 3 4 5% 20%	1600
December	1st to 10th	Day	20% 20% 7% 12% 5% 4 4 3 5% 5% 15%	1560
	11th to 20th	Day	20% 14% 4 11% 6% 4 4 4 4 5% 24%	1906
	21st to end	Day	27% 19% 5% 11% 4 4 3 2 3 3 19%	2772
January	1st to 10th	Night	17% 19% 7% 13% 6% 4 4 3 4 4 19%	4429
	11th to 20th	Night	12% 15% 5% 14% 7% 5% 5% 4 5% 6% 22%	4440
	21st to end	Night	15% 19% 6% 13% 7% 6% 5% 3 3 4 20%	4749
February	1st to 10th	Night	13% 15% 6% 12% 7% 5% 5% 3 5% 6% 23%	2470
	11th to 20th	Night	13% 14% 6% 11% 7% 5% 4 3 4 5% 29%	2403
	21st to end	Night	16% 13% 4 10% 6% 5% 5% 3 5% 5% 28%	1897
March	1st to 10th	Night	21% 13% 4 8% 5% 4 3 3 3 4 31%	3696
	11th to 20th	Night	15% 17% 5% 11% 5% 5% 4 3 5% 6% 25%	3479
	21st to end	Night	14% 11% 3 8% 5% 4 4 3 4 6% 39%	3627
April	1st to 10th	Night	21% 11% 3 8% 5% 4 4 3 4 6% 32%	1900
	11th to 20th	Night	18% 10% 3 8% 5% 4 4 4 4 6% 35%	1875
	21st to end	Night	20% 10% 4 8% 4 5% 4 3 4 5% 33%	1767
May	1st to 10th	Night	19% 11% 3 7% 4 4 5% 4 6% 7% 30%	2514
	11th to 20th	Night	19% 9% 3 6% 4 4 5% 4 5% 7% 34%	2495
	21st to end	Night	14% 7% 2 7% 5% 4 5% 5% 5% 7% 38%	2738
June	1st to 10th	Night	16% 7% 3 7% 5% 5% 5% 4 6% 9% 33%	1520
	11th to 20th	Night	13% 6% 2 7% 5% 4 3 4 6% 8% 43%	1520
	21st to end	Night	17% 8% 3 6% 4 5% 5% 3 6% 8% 36%	1520
July	1st to 10th	Night	12% 7% 3 8% 6% 6% 5% 4 6% 7% 35%	2520
	11th to 20th	Night	13% 7% 3 6% 5% 4 4 3 6% 9% 41%	2520
	21st to end	Night	10% 6% 2 5% 5% 4 5% 4 6% 8% 45%	2739
August	1st to 10th	Night	13% 7% 3 7% 5% 4 5% 4 6% 9% 38%	2591
	11th to 20th	Night	15% 7% 3 6% 4 4 4 4 5% 8% 40%	2785
	21st to end	Night	14% 5% 2 6% 4 4 5% 4 6% 8% 42%	3466
September	1st to 10th	Night	11% 5% 3 6% 5% 4 4 4 5% 7% 47%	1900
	11th to 20th	Night	14% 5% 2 4 3 4 4 3 5% 7% 49%	1900
	21st to end	Night	19% 6% 2 6% 4 3 3 2 4 6% 43%	2156
October	1st to 10th	Night	19% 7% 3 6% 4 5% 4 3 5% 6% 39%	2280
	11th to 20th	Night	21% 8% 3 7% 6% 5% 5% 4 5% 6% 30%	2280
	21st to end	Night	22% 11% 3 8% 5% 4 5% 3 5% 6% 27%	2650
November	1st to 10th	Night	18% 11% 3 7% 6% 4 4 4 6% 6% 32%	2552
	11th to 20th	Night	20% 12% 4 9% 6% 5% 5% 3 5% 5% 28%	2800
	21st to end	Night	21% 14% 4 10% 5% 4 5% 3 5% 6% 22%	2800
December	1st to 10th	Night	20% 18% 5% 11% 6% 5% 5% 4 6% 5% 16%	2737
	11th to 20th	Night	22% 16% 5% 10% 5% 4 3 2 4 4 25%	3288
	21st to end	Night	28% 19% 4 11% 5% 4 3 2 3 4 17%	4884

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	43% 40% 8% 4 5%	2518
	11th to 20th	Day	43% 39% 7% 8% 3	2520
	21st to end	Day	46% 43% 5% 5% 1	2904
February	1st to 10th	Day	23% 65% 3 6% 1 1	1710
	11th to 20th	Day	21% 64% 3 7% 4	1672
	21st to end	Day	21% 65% 4 4 5% 1	1556
March	1st to 10th	Day	38% 41% 5% 9% 7%	3146
	11th to 20th	Day	36% 43% 6% 8% 6% 2	3480
	21st to end	Day	23% 42% 5% 16% 13% 1	4004
April	1st to 10th	Day	21% 65% 3 5% 5% 1	2280
	11th to 20th	Day	20% 65% 2 8% 4 1	2254
	21st to end	Day	20% 65% 3 6% 6%	2428
May	1st to 10th	Day	32% 43% 7% 14% 4	4440
	11th to 20th	Day	29% 44% 11% 12% 4	4402
	21st to end	Day	29% 42% 8% 12% 9%	4837
June	1st to 10th	Day	18% 65% 4 9% 4	2660
	11th to 20th	Day	17% 65% 5% 8% 5% 1	2660
	21st to end	Day	17% 64% 5% 9% 4	2660
July	1st to 10th	Day	30% 37% 11% 16% 6%	4370
	11th to 20th	Day	26% 37% 11% 22% 4	4365
	21st to end	Day	22% 36% 10% 24% 7%	4661
August	1st to 10th	Day	31% 37% 11% 15% 5%	4322
	11th to 20th	Day	30% 39% 9% 18% 4	4061
	21st to end	Day	24% 38% 12% 18% 7%	4180
September	1st to 10th	Day	16% 61% 7% 11% 5%	2280
	11th to 20th	Day	14% 60% 5% 15% 6%	2280
	21st to end	Day	14% 60% 6% 12% 7%	2022
October	1st to 10th	Day	32% 38% 7% 20% 3	3160
	11th to 20th	Day	28% 40% 9% 18% 7%	3140
	21st to end	Day	32% 38% 14% 13% 3	3186
November	1st to 10th	Day	27% 57% 5% 8% 2	1743
	11th to 20th	Day	25% 58% 5% 8% 3	1600
	21st to end	Day	30% 59% 4 3 4	1600
December	1st to 10th	Day	31% 59% 4 5% 2	1560
	11th to 20th	Day	34% 50% 8% 6% 3	1906
	21st to end	Day	47% 38% 2 10% 2	2772
January	1st to 10th	Night	41% 40% 12% 6% 2	4429
	11th to 20th	Night	38% 40% 11% 9% 2	4440
	21st to end	Night	47% 40% 6% 4 2	4749
February	1st to 10th	Night	22% 65% 4 6% 2	2470
	11th to 20th	Night	21% 64% 3 8% 4	2405
	21st to end	Night	20% 65% 3 6% 6%	1897
March	1st to 10th	Night	34% 42% 7% 10% 7% 1	3706
	11th to 20th	Night	38% 42% 6% 8% 5% 1	3480
	21st to end	Night	26% 41% 6% 14% 10% 3	3627
April	1st to 10th	Night	19% 66% 3 7% 4 1	1900
	11th to 20th	Night	18% 65% 2 8% 6% 1	1875
	21st to end	Night	18% 65% 3 6% 7% 1	1767
May	1st to 10th	Night	32% 46% 7% 12% 3	2520
	11th to 20th	Night	30% 44% 9% 13% 4	2496
	21st to end	Night	29% 43% 7% 12% 9% 1	2739
June	1st to 10th	Night	15% 66% 4 10% 4 1	1520
	11th to 20th	Night	13% 66% 3 9% 7%	1520
	21st to end	Night	18% 64% 4 9% 6%	1520
July	1st to 10th	Night	34% 36% 10% 10% 9% 1	2480
	11th to 20th	Night	27% 37% 11% 21% 4	2472
	21st to end	Night	24% 37% 10% 21% 8%	2651
August	1st to 10th	Night	28% 39% 9% 18% 7%	2581
	11th to 20th	Night	31% 39% 10% 18% 3	2812
	21st to end	Night	26% 38% 9% 17% 8% 2	3466
September	1st to 10th	Night	13% 62% 6% 13% 6%	1900
	11th to 20th	Night	14% 60% 6% 15% 5% 1	1900
	21st to end	Night	14% 60% 5% 14% 7%	2156
October	1st to 10th	Night	24% 37% 9% 21% 8%	3800
	11th to 20th	Night	27% 38% 11% 17% 6%	3779
	21st to end	Night	31% 38% 13% 12% 6%	4362
November	1st to 10th	Night	26% 57% 7% 7% 3	2552
	11th to 20th	Night	26% 58% 4 9% 4	2800
	21st to end	Night	27% 58% 6% 6% 3	2800
December	1st to 10th	Night	29% 59% 4 6% 2	2737
	11th to 20th	Night	34% 49% 4 8% 4	3288
	21st to end	Night	48% 37% 3 9% 3	4884

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	23% 23% 34% 17% 3	180
	11th to 20th	Day	26% 17% 39% 14% 3 1	180
	21st to end	Day	22% 21% 34% 18% 6%	236
February	1st to 10th	Day	30% 26% 31% 11% 2	270
	11th to 20th	Day	27% 28% 38% 6% 1	270
	21st to end	Day	32% 25% 28% 14% 1	368
March	1st to 10th	Day	28% 20% 34% 13% 5%	460
	11th to 20th	Day	26% 22% 33% 14% 3 1	460
	21st to end	Day	30% 20% 30% 14% 4 1	506
April	1st to 10th	Day	32% 23% 25% 15% 5% 1	460
	11th to 20th	Day	35% 20% 22% 13% 8% 1	452
	21st to end	Day	31% 23% 29% 12% 5% 1	460
May	1st to 10th	Day	26% 17% 32% 16% 6% 3	463
	11th to 20th	Day	21% 18% 30% 22% 7% 2	487
	21st to end	Day	23% 17% 31% 20% 9% 2	529
June	1st to 10th	Day	27% 11% 33% 21% 7% 1	490
	11th to 20th	Day	18% 16% 31% 24% 9% 3	490
	21st to end	Day	22% 14% 32% 20% 10% 2	490
July	1st to 10th	Day	11% 10% 33% 33% 11% 3	485
	11th to 20th	Day	14% 10% 35% 25% 12% 3	484
	21st to end	Day	14% 7% 35% 29% 11% 3	532
August	1st to 10th	Day	14% 9% 30% 29% 14% 4	486
	11th to 20th	Day	18% 6% 25% 30% 14% 7%	479
	21st to end	Day	17% 12% 29% 24% 13% 6%	539
September	1st to 10th	Day	16% 13% 30% 23% 12% 6%	490
	11th to 20th	Day	15% 10% 24% 23% 19% 10%	490
	21st to end	Day	19% 14% 29% 20% 12% 6%	490
October	1st to 10th	Day	25% 16% 24% 21% 10% 3	490
	11th to 20th	Day	28% 19% 30% 15% 7% 1	490
	21st to end	Day	30% 19% 30% 17% 5%	464
November	1st to 10th	Day	28% 16% 31% 19% 5% 1	377
	11th to 20th	Day	28% 25% 32% 13% 3 1	200
	21st to end	Day	31% 24% 31% 11% 3 1	200
December	1st to 10th	Day	35% 11% 38% 14% 3	190
	11th to 20th	Day	27% 27% 35% 9% 1 1	180
	21st to end	Day	32% 23% 33% 11% 1 1	198
January	1st to 10th	Night	27% 16% 35% 19% 3	760
	11th to 20th	Night	27% 19% 29% 20% 5%	760
	21st to end	Night	18% 15% 38% 23% 5% 1	836
February	1st to 10th	Night	20% 21% 34% 22% 3	760
	11th to 20th	Night	22% 20% 37% 17% 4	743
	21st to end	Night	23% 22% 29% 23% 4	628
March	1st to 10th	Night	25% 18% 33% 20% 4	760
	11th to 20th	Night	24% 21% 31% 18% 6%	760
	21st to end	Night	23% 18% 33% 19% 7%	836
April	1st to 10th	Night	27% 16% 29% 23% 5%	760
	11th to 20th	Night	25% 19% 29% 19% 7%	751
	21st to end	Night	27% 16% 28% 22% 7%	627
May	1st to 10th	Night	23% 11% 29% 28% 9% 1	380
	11th to 20th	Night	25% 10% 25% 30% 9%	374
	21st to end	Night	15% 11% 36% 28% 10%	411
June	1st to 10th	Night	19% 9% 29% 34% 8%	380
	11th to 20th	Night	17% 8% 26% 35% 13% 1	380
	21st to end	Night	19% 7% 27% 32% 15%	380
July	1st to 10th	Night	12% 5% 29% 38% 17%	370
	11th to 20th	Night	14% 2 26% 39% 17% 1	368
	21st to end	Night	10% 4 28% 42% 15% 2	416
August	1st to 10th	Night	13% 5% 23% 38% 20% 1	424
	11th to 20th	Night	13% 3 22% 36% 22% 3	564
	21st to end	Night	15% 6% 26% 34% 17% 2	826
September	1st to 10th	Night	14% 8% 29% 29% 18% 1	760
	11th to 20th	Night	17% 6% 23% 28% 22% 3	760
	21st to end	Night	22% 8% 25% 25% 18% 2	760
October	1st to 10th	Night	23% 13% 26% 22% 15% 1	760
	11th to 20th	Night	25% 14% 29% 23% 7% 1	760
	21st to end	Night	29% 15% 28% 24% 5%	836
November	1st to 10th	Night	26% 16% 26% 24% 7% 1	780
	11th to 20th	Night	27% 17% 32% 15% 9%	800
	21st to end	Night	30% 19% 25% 20% 5%	800
December	1st to 10th	Night	29% 19% 30% 19% 4	783
	11th to 20th	Night	27% 19% 29% 20% 5% 1	760
	21st to end	Night	34% 17% 30% 15% 3	836

Page generated at 2024-12-03 06:45:09. Version ac07

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