Pit Road
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Pit Road clear sky chart from 2005-11-06 to 2026-01-17.

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	16% 10% 4 9% 5% 4 4 4 5% 6% 32%	127819
	Night	16% 12% 4 10% 5% 5% 4 4 5% 6% 30%	123870
Transparency	Day	51% 6% 11% 21% 10% 1	131323
	Night	54% 6% 12% 18% 9% 1	128453
Seeing	Day	22% 16% 30% 20% 9% 3	15815
	Night	22% 13% 30% 25% 9% 1	25059

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% 16% 6% 17% 9% 6% 4 3 3 4 19%	3677
	11th to 20th	Day	12% 16% 7% 17% 8% 5% 4 3 4 6% 18%	3618
	21st to end	Day	12% 18% 8% 15% 7% 6% 3 3 4 4 21%	4259
February	1st to 10th	Day	12% 15% 6% 14% 8% 5% 5% 4 5% 5% 21%	1800
	11th to 20th	Day	12% 15% 6% 11% 7% 5% 4 4 6% 6% 24%	1753
	21st to end	Day	17% 15% 4 10% 7% 5% 5% 3 5% 5% 24%	1596
March	1st to 10th	Day	19% 13% 5% 12% 6% 4 4 3 4 5% 25%	4630
	11th to 20th	Day	12% 13% 5% 12% 6% 4 5% 4 5% 7% 28%	4980
	21st to end	Day	17% 12% 4 8% 5% 4 3 3 4 5% 38%	5664
April	1st to 10th	Day	21% 14% 3 7% 5% 3 4 4 4 5% 31%	2400
	11th to 20th	Day	22% 10% 3 7% 4 3 4 3 4 5% 35%	2374
	21st to end	Day	22% 10% 3 8% 5% 4 3 3 4 6% 33%	2566
May	1st to 10th	Day	21% 9% 3 8% 5% 4 4 3 5% 6% 31%	6346
	11th to 20th	Day	16% 9% 3 8% 5% 4 5% 4 6% 8% 34%	6318
	21st to end	Day	19% 9% 3 7% 5% 4 4 4 5% 6% 34%	6949
June	1st to 10th	Day	19% 9% 3 8% 6% 4 4 4 6% 6% 31%	2800
	11th to 20th	Day	16% 6% 2 6% 4 4 4 4 6% 8% 39%	2800
	21st to end	Day	17% 6% 3 7% 6% 5% 6% 5% 6% 8% 33%	2800
July	1st to 10th	Day	14% 6% 3 7% 5% 5% 5% 4 7% 9% 35%	6360
	11th to 20th	Day	10% 5% 2 6% 5% 4 5% 4 6% 8% 44%	6360
	21st to end	Day	9% 5% 2 6% 4 4 4 4 6% 9% 47%	6926
August	1st to 10th	Day	13% 7% 3 8% 5% 5% 6% 4 6% 8% 35%	4379
	11th to 20th	Day	17% 6% 2 7% 4 4 4 4 6% 8% 37%	4174
	21st to end	Day	10% 5% 2 6% 5% 5% 5% 4 8% 10% 40%	4355
September	1st to 10th	Day	13% 6% 2 7% 4 4 4 4 6% 8% 41%	2400
	11th to 20th	Day	13% 6% 2 6% 5% 5% 4 3 5% 6% 46%	2400
	21st to end	Day	18% 7% 3 7% 4 5% 4 3 5% 7% 37%	2109
October	1st to 10th	Day	19% 8% 3 8% 6% 4 5% 3 4 6% 35%	2000
	11th to 20th	Day	21% 11% 4 9% 5% 3 5% 4 4 6% 28%	2000
	21st to end	Day	25% 12% 3 9% 5% 4 4 3 5% 6% 24%	2090
November	1st to 10th	Day	15% 13% 4 8% 4 4 4 3 4 6% 33%	1782
	11th to 20th	Day	16% 15% 5% 10% 6% 5% 5% 4 5% 5% 25%	1680
	21st to end	Day	20% 19% 4 11% 6% 6% 4 3 5% 5% 17%	1680
December	1st to 10th	Day	18% 23% 7% 12% 7% 5% 5% 3 4 4 13%	2680
	11th to 20th	Day	16% 17% 7% 12% 7% 5% 4 3 4 5% 22%	3066
	21st to end	Day	21% 18% 5% 15% 6% 5% 3 3 4 3 19%	4048
January	1st to 10th	Night	13% 19% 9% 17% 7% 5% 4 3 3 4 17%	6489
	11th to 20th	Night	11% 15% 5% 16% 8% 6% 5% 4 5% 5% 19%	6400
	21st to end	Night	11% 19% 7% 13% 7% 6% 5% 3 4 4 20%	6695
February	1st to 10th	Night	12% 15% 6% 13% 8% 5% 6% 4 4 5% 22%	2600
	11th to 20th	Night	12% 15% 6% 12% 7% 6% 5% 3 4 6% 25%	2533
	21st to end	Night	14% 14% 6% 10% 6% 5% 4 4 5% 6% 27%	2033
March	1st to 10th	Night	19% 15% 5% 9% 5% 4 4 2 4 4 28%	5208
	11th to 20th	Night	12% 13% 4 9% 6% 5% 5% 5% 6% 8% 27%	4979
	21st to end	Night	17% 11% 4 10% 5% 4 3 4 5% 6% 31%	5267
April	1st to 10th	Night	19% 12% 4 8% 5% 4 4 2 4 6% 31%	2000
	11th to 20th	Night	20% 11% 3 6% 5% 4 4 3 4 6% 35%	1975
	21st to end	Night	21% 10% 3 8% 5% 4 4 3 6% 6% 31%	1848
May	1st to 10th	Night	22% 10% 3 7% 4 4 5% 4 5% 7% 29%	3594
	11th to 20th	Night	15% 7% 2 6% 4 5% 4 4 5% 7% 41%	3575
	21st to end	Night	17% 8% 3 7% 5% 5% 4 4 6% 6% 34%	3926
June	1st to 10th	Night	16% 7% 3 7% 5% 4 4 5% 6% 8% 34%	1600
	11th to 20th	Night	14% 5% 2 7% 4 4 4 4 6% 7% 44%	1600
	21st to end	Night	18% 7% 3 6% 4 5% 4 4 7% 7% 35%	1600
July	1st to 10th	Night	13% 6% 3 8% 6% 5% 5% 5% 7% 7% 36%	3600
	11th to 20th	Night	12% 5% 2 6% 4 4 5% 4 6% 9% 44%	3600
	21st to end	Night	8% 5% 2 6% 4 4 5% 4 6% 8% 47%	3926
August	1st to 10th	Night	11% 5% 2 7% 5% 5% 6% 5% 6% 8% 41%	2767
	11th to 20th	Night	15% 6% 2 6% 3 4 4 4 6% 7% 42%	2875
	21st to end	Night	13% 5% 2 6% 4 4 5% 4 6% 8% 43%	3510
September	1st to 10th	Night	11% 6% 3 7% 4 4 4 3 5% 7% 46%	2000
	11th to 20th	Night	15% 5% 2 5% 3 3 3 4 5% 7% 50%	2000
	21st to end	Night	17% 6% 2 7% 5% 4 4 3 4 7% 42%	2287
October	1st to 10th	Night	19% 7% 2 6% 4 4 4 4 4 4 41%	2400
	11th to 20th	Night	19% 11% 3 8% 5% 5% 6% 3 5% 5% 31%	2400
	21st to end	Night	23% 11% 3 8% 4 5% 5% 3 5% 5% 27%	2750
November	1st to 10th	Night	18% 13% 3 8% 5% 5% 4 4 5% 6% 31%	2735
	11th to 20th	Night	17% 14% 4 9% 5% 5% 5% 4 5% 6% 27%	2940
	21st to end	Night	20% 16% 5% 12% 6% 4 4 3 4 6% 20%	2940
December	1st to 10th	Night	19% 19% 6% 13% 6% 5% 5% 3 4 5% 15%	4720
	11th to 20th	Night	19% 15% 5% 11% 7% 4 4 3 4 4 24%	5348
	21st to end	Night	24% 17% 4 13% 6% 4 3 3 4 4 18%	7150

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	69% 6% 8% 10% 6%	3678
	11th to 20th	Day	67% 5% 10% 10% 7%	3648
	21st to end	Day	67% 5% 7% 12% 7% 1	4259
February	1st to 10th	Day	64% 7% 9% 15% 5% 1	1800
	11th to 20th	Day	58% 7% 13% 14% 8% 1	1762
	21st to end	Day	61% 5% 10% 13% 9% 2	1596
March	1st to 10th	Day	61% 4 8% 12% 13% 2	4633
	11th to 20th	Day	54% 5% 16% 15% 9% 2	4980
	21st to end	Day	50% 4 7% 20% 16% 3	5664
April	1st to 10th	Day	55% 5% 8% 18% 12% 3	2400
	11th to 20th	Day	52% 4 8% 20% 14% 2	2374
	21st to end	Day	53% 5% 7% 16% 16% 3	2566
May	1st to 10th	Day	52% 6% 8% 20% 10% 4	6357
	11th to 20th	Day	46% 8% 12% 21% 13% 1	6322
	21st to end	Day	49% 6% 11% 20% 12% 2	6949
June	1st to 10th	Day	52% 7% 9% 19% 12% 1	2800
	11th to 20th	Day	41% 7% 11% 23% 14% 2	2800
	21st to end	Day	47% 8% 12% 21% 12% 1	2800
July	1st to 10th	Day	44% 7% 13% 27% 9%	6290
	11th to 20th	Day	36% 7% 13% 31% 14%	6285
	21st to end	Day	32% 7% 14% 35% 11%	6728
August	1st to 10th	Day	46% 7% 14% 23% 10%	4365
	11th to 20th	Day	44% 6% 16% 26% 7%	4213
	21st to end	Day	37% 7% 15% 30% 10% 1	4355
September	1st to 10th	Day	39% 8% 15% 27% 11%	2400
	11th to 20th	Day	38% 6% 12% 32% 12%	2400
	21st to end	Day	47% 6% 15% 23% 10%	2109
October	1st to 10th	Day	50% 6% 9% 27% 8%	3260
	11th to 20th	Day	50% 5% 14% 23% 8%	3240
	21st to end	Day	55% 6% 18% 17% 5% 1	3354
November	1st to 10th	Day	50% 6% 15% 21% 7% 1	1782
	11th to 20th	Day	59% 7% 13% 13% 7% 1	1680
	21st to end	Day	69% 7% 11% 8% 5% 1	1680
December	1st to 10th	Day	75% 6% 9% 8% 2	2680
	11th to 20th	Day	65% 6% 7% 13% 8%	3066
	21st to end	Day	72% 3 8% 14% 4	4048
January	1st to 10th	Night	71% 5% 11% 10% 4	6489
	11th to 20th	Night	65% 7% 11% 12% 6%	6445
	21st to end	Night	68% 4 8% 9% 10% 1	6695
February	1st to 10th	Night	63% 6% 11% 14% 6% 1	2600
	11th to 20th	Night	59% 5% 11% 17% 6%	2535
	21st to end	Night	56% 6% 10% 18% 8% 1	2033
March	1st to 10th	Night	60% 4 9% 15% 9% 3	5218
	11th to 20th	Night	52% 7% 18% 14% 8% 1	4980
	21st to end	Night	52% 5% 9% 20% 12% 2	5267
April	1st to 10th	Night	55% 4 9% 18% 12% 2	2000
	11th to 20th	Night	49% 5% 8% 22% 14% 2	1975
	21st to end	Night	53% 4 8% 17% 16% 2	1848
May	1st to 10th	Night	52% 7% 10% 19% 9% 4	3600
	11th to 20th	Night	40% 8% 15% 19% 15% 3	3576
	21st to end	Night	48% 7% 14% 18% 12% 1	3927
June	1st to 10th	Night	45% 8% 13% 23% 10% 1	1600
	11th to 20th	Night	38% 7% 11% 25% 16% 2	1600
	21st to end	Night	45% 7% 14% 21% 13% 1	1600
July	1st to 10th	Night	43% 8% 16% 21% 12% 1	3560
	11th to 20th	Night	36% 6% 13% 31% 13%	3552
	21st to end	Night	32% 7% 11% 36% 13%	3809
August	1st to 10th	Night	39% 7% 15% 25% 13% 1	2757
	11th to 20th	Night	40% 7% 15% 28% 10%	2902
	21st to end	Night	38% 6% 15% 28% 11% 2	3510
September	1st to 10th	Night	37% 7% 13% 29% 13% 1	2000
	11th to 20th	Night	34% 6% 15% 34% 11%	2000
	21st to end	Night	42% 6% 14% 27% 10%	2287
October	1st to 10th	Night	39% 4 13% 30% 13%	3920
	11th to 20th	Night	48% 5% 16% 21% 9%	3899
	21st to end	Night	52% 6% 17% 17% 7%	4436
November	1st to 10th	Night	52% 6% 14% 19% 8%	2735
	11th to 20th	Night	57% 7% 13% 16% 7% 1	2940
	21st to end	Night	65% 6% 13% 13% 3	2940
December	1st to 10th	Night	71% 6% 11% 10% 3	4720
	11th to 20th	Night	65% 4 9% 12% 10% 1	5348
	21st to end	Night	71% 3 6% 11% 8%	7150

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	19% 21% 36% 21% 3	220
	11th to 20th	Day	28% 17% 36% 14% 4 1	212
	21st to end	Day	22% 22% 32% 18% 6%	285
February	1st to 10th	Day	25% 28% 30% 13% 3	300
	11th to 20th	Day	25% 30% 37% 7% 1	300
	21st to end	Day	31% 21% 34% 13% 1	360
March	1st to 10th	Day	28% 20% 33% 15% 3 1	500
	11th to 20th	Day	25% 21% 34% 16% 4	500
	21st to end	Day	30% 20% 31% 13% 5%	550
April	1st to 10th	Day	31% 22% 26% 15% 6%	500
	11th to 20th	Day	33% 21% 22% 14% 9% 2	492
	21st to end	Day	31% 18% 32% 13% 4 2	500
May	1st to 10th	Day	26% 15% 30% 18% 8% 2	503
	11th to 20th	Day	18% 17% 33% 20% 9% 3	527
	21st to end	Day	19% 17% 32% 21% 9% 2	573
June	1st to 10th	Day	23% 17% 30% 21% 8% 1	530
	11th to 20th	Day	17% 15% 29% 24% 12% 3	530
	21st to end	Day	18% 15% 32% 22% 11% 2	530
July	1st to 10th	Day	11% 8% 34% 32% 12% 3	525
	11th to 20th	Day	10% 12% 34% 28% 14% 3	524
	21st to end	Day	12% 9% 35% 28% 13% 4	576
August	1st to 10th	Day	13% 8% 27% 31% 15% 6%	526
	11th to 20th	Day	15% 7% 26% 30% 16% 7%	519
	21st to end	Day	13% 11% 30% 25% 15% 6%	583
September	1st to 10th	Day	17% 12% 28% 21% 15% 8%	530
	11th to 20th	Day	14% 10% 20% 25% 18% 14%	530
	21st to end	Day	16% 13% 30% 22% 12% 6%	530
October	1st to 10th	Day	24% 16% 22% 21% 14% 3	530
	11th to 20th	Day	26% 21% 31% 13% 7% 1	530
	21st to end	Day	29% 17% 29% 19% 5% 1	522
November	1st to 10th	Day	29% 18% 31% 17% 5% 1	356
	11th to 20th	Day	24% 25% 32% 12% 7% 1	220
	21st to end	Day	32% 21% 35% 7% 3 2	220
December	1st to 10th	Day	28% 14% 41% 14% 3	220
	11th to 20th	Day	27% 26% 35% 9% 3	220
	21st to end	Day	27% 23% 30% 16% 3 1	242
January	1st to 10th	Night	24% 19% 34% 20% 4	840
	11th to 20th	Night	28% 17% 27% 21% 6%	825
	21st to end	Night	18% 14% 37% 25% 6%	880
February	1st to 10th	Night	19% 18% 39% 21% 3	800
	11th to 20th	Night	20% 18% 39% 19% 3	783
	21st to end	Night	22% 20% 30% 26% 3	660
March	1st to 10th	Night	26% 17% 32% 21% 4	800
	11th to 20th	Night	23% 20% 31% 20% 5%	800
	21st to end	Night	22% 16% 33% 22% 7%	880
April	1st to 10th	Night	27% 15% 32% 22% 5%	800
	11th to 20th	Night	25% 17% 29% 22% 7%	791
	21st to end	Night	25% 14% 27% 25% 8% 1	648
May	1st to 10th	Night	24% 8% 30% 29% 10% 1	400
	11th to 20th	Night	20% 12% 30% 31% 7%	394
	21st to end	Night	16% 8% 37% 29% 10%	433
June	1st to 10th	Night	17% 8% 34% 35% 7% 1	400
	11th to 20th	Night	14% 10% 33% 33% 11%	400
	21st to end	Night	21% 8% 28% 30% 13%	400
July	1st to 10th	Night	11% 4 35% 36% 13% 1	390
	11th to 20th	Night	13% 5% 25% 43% 15%	388
	21st to end	Night	9% 5% 30% 42% 13% 1	438
August	1st to 10th	Night	10% 4 24% 39% 22% 1	501
	11th to 20th	Night	11% 3 23% 38% 21% 3	594
	21st to end	Night	13% 8% 27% 32% 18% 2	830
September	1st to 10th	Night	13% 7% 30% 30% 19% 2	800
	11th to 20th	Night	17% 6% 20% 30% 21% 5%	800
	21st to end	Night	19% 11% 23% 27% 19% 2	800
October	1st to 10th	Night	23% 8% 29% 25% 14% 1	800
	11th to 20th	Night	26% 13% 33% 19% 9% 1	800
	21st to end	Night	28% 14% 28% 24% 6%	880
November	1st to 10th	Night	26% 15% 27% 24% 6%	820
	11th to 20th	Night	25% 18% 30% 17% 9% 1	840
	21st to end	Night	31% 18% 26% 22% 4	840
December	1st to 10th	Night	29% 18% 31% 17% 4	840
	11th to 20th	Night	27% 19% 31% 20% 4	840
	21st to end	Night	32% 16% 29% 19% 4 1	924

Page generated at 2026-01-14 01:14:29. Version ac07

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