Purple Crow Lidar Facility
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Purple Crow Lidar Facility clear sky chart from 2005-11-06 to 2025-04-11.

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	15% 11% 4 9% 5% 5% 5% 4 5% 7% 30%	113779
	Night	15% 12% 5% 10% 5% 4 4 4 5% 6% 30%	114468
Transparency	Day	54% 3 11% 20% 11% 1	117406
	Night	54% 3 11% 19% 11% 1	119005
Seeing	Day	19% 10% 28% 24% 13% 5%	15513
	Night	20% 9% 28% 30% 12% 1	24869

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	12% 17% 7% 27% 6% 4 4 2 3 3 14%	3524
	11th to 20th	Day	11% 21% 10% 23% 7% 7% 5% 3 3 3 7%	4026
	21st to end	Day	19% 19% 8% 14% 6% 6% 5% 3 3 4 14%	4466
February	1st to 10th	Day	16% 17% 5% 13% 8% 6% 5% 4 4 5% 17%	1800
	11th to 20th	Day	14% 15% 8% 15% 9% 6% 4 3 5% 4 18%	1754
	21st to end	Day	16% 17% 6% 13% 6% 4 5% 4 4 5% 22%	1650
March	1st to 10th	Day	17% 12% 7% 13% 7% 3 3 3 4 5% 26%	4796
	11th to 20th	Day	12% 14% 5% 9% 5% 4 4 3 5% 7% 30%	4980
	21st to end	Day	20% 14% 6% 10% 4 4 3 3 4 4 28%	5465
April	1st to 10th	Day	17% 15% 4 8% 4 4 4 4 6% 7% 28%	2270
	11th to 20th	Day	19% 11% 3 6% 4 4 4 3 5% 8% 34%	2432
	21st to end	Day	20% 11% 4 7% 5% 3 4 3 5% 6% 33%	2470
May	1st to 10th	Day	20% 7% 3 7% 4 4 4 4 5% 8% 34%	4108
	11th to 20th	Day	18% 9% 3 7% 5% 5% 5% 4 6% 8% 32%	4081
	21st to end	Day	13% 5% 2 6% 4 4 4 4 5% 7% 46%	4833
June	1st to 10th	Day	14% 5% 3 7% 5% 5% 5% 4 7% 8% 38%	2660
	11th to 20th	Day	11% 6% 3 6% 5% 5% 6% 5% 6% 8% 40%	2849
	21st to end	Day	13% 6% 2 6% 5% 4 5% 4 6% 8% 41%	2850
July	1st to 10th	Day	12% 5% 2 7% 5% 5% 5% 4 7% 9% 40%	4760
	11th to 20th	Day	12% 5% 2 5% 5% 4 5% 5% 6% 10% 42%	4232
	21st to end	Day	9% 5% 2 6% 5% 6% 5% 4 7% 8% 42%	4466
August	1st to 10th	Day	15% 5% 2 5% 4 4 5% 5% 7% 9% 38%	4104
	11th to 20th	Day	11% 6% 3 7% 5% 5% 5% 5% 7% 11% 34%	4044
	21st to end	Day	9% 5% 2 7% 5% 6% 5% 4 6% 8% 41%	4478
September	1st to 10th	Day	11% 6% 3 7% 4 5% 7% 4 6% 7% 40%	2222
	11th to 20th	Day	12% 5% 2 6% 4 4 4 3 6% 9% 45%	2090
	21st to end	Day	18% 6% 2 7% 5% 4 5% 4 7% 8% 34%	2090
October	1st to 10th	Day	17% 8% 2 7% 4 4 4 4 5% 8% 36%	1943
	11th to 20th	Day	20% 10% 3 8% 6% 5% 5% 3 6% 6% 27%	1900
	21st to end	Day	25% 13% 3 8% 5% 5% 5% 4 5% 6% 21%	2047
November	1st to 10th	Day	15% 12% 3 8% 5% 6% 4 3 5% 7% 30%	1762
	11th to 20th	Day	16% 17% 4 8% 5% 4 5% 4 6% 7% 24%	1644
	21st to end	Day	20% 20% 7% 9% 6% 6% 4 4 5% 5% 15%	1600
December	1st to 10th	Day	18% 21% 8% 13% 5% 5% 5% 4 5% 5% 12%	2600
	11th to 20th	Day	21% 20% 7% 12% 6% 4 4 4 4 5% 15%	2986
	21st to end	Day	27% 21% 8% 12% 5% 4 4 3 4 4 8%	3797
January	1st to 10th	Night	13% 16% 8% 24% 6% 4 4 3 3 4 14%	6399
	11th to 20th	Night	12% 18% 8% 18% 10% 7% 6% 4 4 4 9%	5859
	21st to end	Night	18% 17% 7% 15% 5% 4 5% 3 4 5% 18%	6490
February	1st to 10th	Night	16% 16% 5% 12% 8% 6% 4 4 5% 6% 18%	2600
	11th to 20th	Night	15% 15% 6% 10% 6% 6% 6% 4 6% 5% 21%	2528
	21st to end	Night	16% 13% 5% 14% 6% 5% 5% 4 4 5% 22%	1980
March	1st to 10th	Night	14% 11% 4 9% 6% 4 5% 4 5% 5% 32%	5042
	11th to 20th	Night	10% 9% 4 9% 5% 5% 5% 4 6% 8% 35%	4979
	21st to end	Night	18% 11% 4 9% 4 4 4 3 4 4 35%	5467
April	1st to 10th	Night	18% 12% 4 8% 5% 4 4 3 6% 6% 31%	2130
	11th to 20th	Night	18% 9% 3 7% 5% 4 4 3 6% 6% 36%	1719
	21st to end	Night	15% 10% 3 8% 5% 4 5% 4 6% 6% 34%	1710
May	1st to 10th	Night	19% 8% 2 6% 4 3 3 3 6% 7% 38%	2833
	11th to 20th	Night	11% 8% 3 8% 6% 5% 5% 4 5% 7% 37%	2812
	21st to end	Night	12% 5% 2 4 3 4 4 4 6% 7% 51%	2739
June	1st to 10th	Night	12% 7% 2 5% 4 4 4 4 6% 8% 44%	1515
	11th to 20th	Night	9% 6% 2 5% 5% 5% 5% 5% 8% 10% 41%	1330
	21st to end	Night	10% 5% 2 6% 4 5% 5% 3 5% 8% 47%	1330
July	1st to 10th	Night	7% 4 2 5% 4 3 4 4 6% 11% 51%	2210
	11th to 20th	Night	9% 5% 2 5% 3 3 4 3 5% 8% 53%	2723
	21st to end	Night	6% 5% 2 5% 5% 4 5% 5% 7% 9% 48%	3087
August	1st to 10th	Night	12% 6% 2 5% 4 4 4 4 7% 7% 45%	2825
	11th to 20th	Night	12% 8% 2 6% 3 3 4 3 5% 7% 46%	2785
	21st to end	Night	9% 5% 2 6% 4 4 4 4 5% 8% 48%	3145
September	1st to 10th	Night	10% 6% 3 7% 4 4 4 3 6% 7% 47%	1955
	11th to 20th	Night	11% 5% 2 4 3 4 3 3 5% 7% 52%	2090
	21st to end	Night	17% 7% 3 7% 4 4 3 3 5% 6% 41%	2090
October	1st to 10th	Night	15% 7% 3 7% 4 4 4 3 5% 7% 41%	2237
	11th to 20th	Night	20% 9% 3 7% 5% 3 4 3 5% 7% 33%	2280
	21st to end	Night	23% 12% 3 8% 5% 4 4 4 5% 6% 27%	2548
November	1st to 10th	Night	15% 10% 3 7% 5% 4 4 4 6% 6% 36%	2536
	11th to 20th	Night	16% 15% 4 8% 5% 4 6% 4 6% 8% 24%	2755
	21st to end	Night	21% 15% 6% 9% 5% 5% 5% 4 5% 6% 19%	2800
December	1st to 10th	Night	13% 20% 8% 14% 7% 6% 6% 4 6% 5% 12%	4580
	11th to 20th	Night	15% 23% 7% 11% 6% 4 4 3 4 5% 18%	5208
	21st to end	Night	24% 20% 7% 11% 6% 4 4 3 4 4 13%	7152

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	78% 2 8% 9% 3	3525
	11th to 20th	Day	85% 2 6% 5% 3	4060
	21st to end	Day	75% 3 9% 7% 6%	4466
February	1st to 10th	Day	70% 3 9% 13% 5% 1	1800
	11th to 20th	Day	68% 3 7% 14% 7%	1763
	21st to end	Day	65% 3 10% 14% 6% 1	1650
March	1st to 10th	Day	63% 2 12% 18% 5%	4799
	11th to 20th	Day	54% 2 16% 19% 8% 2	4980
	21st to end	Day	61% 2 9% 18% 9% 1	5465
April	1st to 10th	Day	55% 3 10% 21% 10% 1	2270
	11th to 20th	Day	50% 2 11% 21% 14% 1	2432
	21st to end	Day	52% 3 11% 20% 12% 2	2470
May	1st to 10th	Day	50% 2 10% 24% 12% 3	4120
	11th to 20th	Day	52% 3 14% 22% 8% 1	4085
	21st to end	Day	39% 3 12% 22% 20% 5%	4833
June	1st to 10th	Day	43% 4 12% 26% 13% 2	2660
	11th to 20th	Day	41% 4 12% 23% 18% 2	2849
	21st to end	Day	40% 5% 12% 26% 16% 1	2850
July	1st to 10th	Day	40% 4 12% 26% 15% 3	4686
	11th to 20th	Day	35% 5% 11% 34% 14% 1	4158
	21st to end	Day	39% 5% 13% 22% 20% 1	4324
August	1st to 10th	Day	42% 5% 13% 25% 15% 1	4091
	11th to 20th	Day	42% 6% 15% 27% 10% 1	4083
	21st to end	Day	39% 5% 12% 30% 13% 1	4478
September	1st to 10th	Day	41% 5% 13% 26% 13% 1	2222
	11th to 20th	Day	36% 3 13% 31% 16%	2090
	21st to end	Day	47% 4 13% 25% 10% 1	2090
October	1st to 10th	Day	40% 6% 13% 24% 17% 1	3229
	11th to 20th	Day	44% 4 13% 22% 18%	3140
	21st to end	Day	52% 4 16% 21% 6%	3349
November	1st to 10th	Day	53% 5% 11% 21% 8% 2	1762
	11th to 20th	Day	58% 4 14% 15% 8% 1	1644
	21st to end	Day	71% 4 11% 13% 3	1600
December	1st to 10th	Day	74% 4 12% 9% 2	2600
	11th to 20th	Day	74% 3 9% 9% 5%	2986
	21st to end	Day	81% 2 8% 7% 1	3797
January	1st to 10th	Night	75% 2 9% 12% 3	6399
	11th to 20th	Night	79% 3 8% 8% 3	5900
	21st to end	Night	70% 2 8% 12% 8%	6490
February	1st to 10th	Night	67% 4 9% 14% 6%	2600
	11th to 20th	Night	62% 5% 10% 16% 7%	2530
	21st to end	Night	64% 3 9% 17% 6%	1980
March	1st to 10th	Night	54% 2 12% 20% 10% 1	5052
	11th to 20th	Night	46% 3 17% 22% 11% 1	4980
	21st to end	Night	55% 2 9% 19% 15% 1	5467
April	1st to 10th	Night	53% 4 9% 21% 13% 2	2130
	11th to 20th	Night	49% 3 9% 20% 17% 2	1719
	21st to end	Night	49% 4 9% 20% 15% 3	1710
May	1st to 10th	Night	46% 2 10% 20% 16% 4	2840
	11th to 20th	Night	47% 3 11% 26% 10% 2	2813
	21st to end	Night	33% 3 13% 24% 23% 4	2740
June	1st to 10th	Night	38% 4 11% 28% 17% 2	1515
	11th to 20th	Night	35% 5% 13% 25% 18% 2	1330
	21st to end	Night	36% 3 14% 26% 19% 1	1330
July	1st to 10th	Night	30% 3 12% 29% 18% 7%	2175
	11th to 20th	Night	30% 4 13% 32% 19% 2	2674
	21st to end	Night	32% 5% 17% 23% 20% 3	2988
August	1st to 10th	Night	38% 4 13% 27% 17% 1	2814
	11th to 20th	Night	38% 4 13% 31% 13% 1	2812
	21st to end	Night	34% 5% 12% 32% 17% 1	3145
September	1st to 10th	Night	36% 3 14% 26% 17% 2	1955
	11th to 20th	Night	32% 3 11% 33% 19% 2	2090
	21st to end	Night	45% 4 12% 25% 13%	2090
October	1st to 10th	Night	34% 3 8% 28% 25% 1	3731
	11th to 20th	Night	44% 2 15% 22% 16% 1	3779
	21st to end	Night	46% 4 14% 25% 11%	4196
November	1st to 10th	Night	46% 5% 11% 26% 11% 1	2536
	11th to 20th	Night	57% 4 12% 19% 8% 1	2755
	21st to end	Night	65% 4 14% 13% 3	2800
December	1st to 10th	Night	73% 4 12% 9% 3	4580
	11th to 20th	Night	70% 3 8% 12% 7% 1	5208
	21st to end	Night	75% 3 10% 10% 3	7152

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	21% 22% 30% 20% 6% 1	265
	11th to 20th	Day	19% 17% 46% 14% 3 1	300
	21st to end	Day	30% 12% 35% 19% 4	330
February	1st to 10th	Day	25% 19% 38% 14% 3	300
	11th to 20th	Day	27% 21% 35% 16% 1	300
	21st to end	Day	27% 23% 37% 10% 2	249
March	1st to 10th	Day	25% 13% 38% 17% 6%	437
	11th to 20th	Day	23% 14% 34% 24% 4 2	500
	21st to end	Day	30% 13% 30% 22% 5% 1	550
April	1st to 10th	Day	22% 15% 33% 22% 7% 1	500
	11th to 20th	Day	27% 12% 28% 19% 10% 4	452
	21st to end	Day	24% 11% 31% 22% 9% 3	460
May	1st to 10th	Day	22% 9% 27% 27% 10% 4	463
	11th to 20th	Day	18% 8% 27% 22% 19% 6%	487
	21st to end	Day	14% 6% 25% 28% 19% 8%	529
June	1st to 10th	Day	15% 4 33% 29% 15% 4	490
	11th to 20th	Day	12% 9% 26% 33% 16% 4	679
	21st to end	Day	15% 6% 28% 32% 15% 4	680
July	1st to 10th	Day	11% 6% 20% 31% 23% 10%	671
	11th to 20th	Day	15% 4 24% 28% 20% 8%	547
	21st to end	Day	11% 4 19% 32% 25% 10%	532
August	1st to 10th	Day	12% 4 17% 30% 23% 14%	486
	11th to 20th	Day	15% 3 17% 26% 25% 15%	479
	21st to end	Day	11% 4 19% 30% 24% 11%	539
September	1st to 10th	Day	11% 7% 22% 27% 22% 12%	490
	11th to 20th	Day	10% 2 20% 24% 29% 15%	490
	21st to end	Day	20% 7% 23% 27% 15% 8%	490
October	1st to 10th	Day	21% 8% 25% 24% 16% 6%	490
	11th to 20th	Day	23% 12% 32% 22% 8% 2	490
	21st to end	Day	29% 13% 33% 20% 5% 1	496
November	1st to 10th	Day	22% 16% 32% 19% 8% 2	300
	11th to 20th	Day	27% 14% 35% 15% 6% 2	222
	21st to end	Day	29% 12% 39% 17% 4	200
December	1st to 10th	Day	27% 17% 32% 18% 6% 1	200
	11th to 20th	Day	28% 19% 31% 18% 5%	200
	21st to end	Day	32% 19% 30% 15% 3	220
January	1st to 10th	Night	24% 16% 37% 17% 5% 1	957
	11th to 20th	Night	28% 14% 32% 22% 4	800
	21st to end	Night	23% 11% 35% 25% 7%	880
February	1st to 10th	Night	25% 14% 35% 24% 3	800
	11th to 20th	Night	24% 14% 31% 26% 5%	783
	21st to end	Night	23% 15% 38% 21% 3	660
March	1st to 10th	Night	20% 12% 36% 26% 7%	800
	11th to 20th	Night	20% 12% 37% 24% 7% 1	800
	21st to end	Night	25% 10% 29% 28% 8% 1	880
April	1st to 10th	Night	24% 13% 30% 28% 5%	800
	11th to 20th	Night	23% 10% 32% 25% 9% 1	591
	21st to end	Night	20% 7% 34% 31% 8% 1	570
May	1st to 10th	Night	21% 4 30% 31% 13% 1	570
	11th to 20th	Night	15% 4 26% 40% 12% 2	561
	21st to end	Night	14% 2 27% 40% 16% 1	413
June	1st to 10th	Night	14% 4 28% 39% 14% 1	380
	11th to 20th	Night	13% 3 24% 44% 15%	380
	21st to end	Night	11% 4 20% 48% 16% 1	380
July	1st to 10th	Night	6% 1 18% 51% 23% 2	370
	11th to 20th	Night	11% 2 18% 41% 26% 2	543
	21st to end	Night	9% 2 14% 48% 24% 2	624
August	1st to 10th	Night	9% 1 12% 44% 31% 3	567
	11th to 20th	Night	10% 2 12% 38% 32% 5%	564
	21st to end	Night	12% 2 16% 39% 28% 3	635
September	1st to 10th	Night	11% 5% 21% 36% 23% 5%	760
	11th to 20th	Night	12% 3 15% 38% 28% 5%	760
	21st to end	Night	19% 7% 19% 34% 16% 5%	760
October	1st to 10th	Night	18% 5% 26% 31% 18% 2	760
	11th to 20th	Night	24% 9% 26% 28% 11% 1	760
	21st to end	Night	28% 9% 31% 27% 5%	836
November	1st to 10th	Night	20% 12% 27% 31% 9% 1	780
	11th to 20th	Night	24% 11% 35% 21% 6% 2	800
	21st to end	Night	29% 11% 30% 24% 6%	800
December	1st to 10th	Night	29% 15% 33% 19% 5%	800
	11th to 20th	Night	25% 16% 37% 18% 4	800
	21st to end	Night	29% 12% 35% 21% 3	945

Page generated at 2025-04-08 09:17:28. Version ac07

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