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 2026-08-15.

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% 10% 4 9% 5% 5% 5% 4 5% 7% 31%	144162
	Night	14% 12% 4 10% 5% 4 4 3 5% 6% 31%	137698
Transparency	Day	52% 4 11% 21% 12% 1	147746
	Night	54% 3 10% 20% 12% 1	142203
Seeing	Day	19% 10% 28% 24% 13% 5%	17367
	Night	20% 9% 28% 30% 11% 1	26472

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% 17% 7% 26% 6% 4 4 2 3 3 12%	4584
	11th to 20th	Day	10% 22% 11% 23% 9% 7% 4 2 3 2 6%	5246
	21st to end	Day	15% 17% 7% 15% 8% 7% 6% 3 4 4 14%	5780
February	1st to 10th	Day	15% 17% 5% 13% 8% 7% 6% 4 4 4 17%	1890
	11th to 20th	Day	14% 14% 8% 15% 9% 6% 4 3 5% 5% 18%	1844
	21st to end	Day	15% 17% 6% 13% 5% 4 5% 4 4 5% 22%	1730
March	1st to 10th	Day	17% 12% 7% 13% 7% 3 3 3 4 5% 26%	4903
	11th to 20th	Day	12% 14% 5% 10% 5% 4 4 3 5% 7% 30%	5090
	21st to end	Day	20% 13% 6% 10% 5% 4 3 3 4 4 28%	5586
April	1st to 10th	Day	17% 15% 4 8% 4 4 4 4 5% 7% 28%	2383
	11th to 20th	Day	18% 11% 3 7% 4 4 3 4 5% 8% 34%	2691
	21st to end	Day	19% 11% 4 7% 5% 3 4 3 5% 6% 34%	2730
May	1st to 10th	Day	19% 9% 3 8% 4 4 4 4 5% 7% 35%	7642
	11th to 20th	Day	16% 8% 3 7% 4 4 5% 4 6% 8% 35%	7626
	21st to end	Day	17% 7% 2 6% 4 4 4 3 4 6% 43%	9056
June	1st to 10th	Day	14% 5% 2 7% 5% 5% 5% 4 6% 8% 40%	2940
	11th to 20th	Day	11% 6% 3 6% 5% 5% 6% 5% 7% 8% 39%	3149
	21st to end	Day	13% 6% 2 6% 4 5% 5% 4 6% 8% 41%	3150
July	1st to 10th	Day	12% 6% 2 7% 5% 5% 5% 4 6% 8% 40%	8879
	11th to 20th	Day	8% 4 2 5% 5% 4 5% 4 6% 10% 46%	7890
	21st to end	Day	9% 5% 2 6% 4 5% 5% 4 6% 8% 45%	8340
August	1st to 10th	Day	15% 5% 2 5% 4 4 5% 5% 7% 9% 38%	4364
	11th to 20th	Day	11% 6% 3 7% 5% 5% 5% 5% 7% 11% 34%	4226
	21st to end	Day	9% 5% 2 7% 5% 6% 5% 4 6% 8% 42%	4619
September	1st to 10th	Day	11% 6% 3 7% 4 5% 7% 4 6% 8% 41%	2339
	11th to 20th	Day	11% 5% 2 6% 4 4 4 4 6% 9% 47%	2200
	21st to end	Day	17% 6% 2 7% 5% 4 5% 4 7% 8% 35%	2200
October	1st to 10th	Day	17% 7% 2 7% 4 4 4 4 5% 8% 37%	2045
	11th to 20th	Day	20% 10% 3 8% 5% 5% 5% 3 6% 6% 29%	2000
	21st to end	Day	24% 13% 3 8% 5% 5% 5% 3 5% 6% 22%	2155
November	1st to 10th	Day	16% 13% 3 8% 5% 6% 4 3 5% 7% 30%	1852
	11th to 20th	Day	16% 17% 4 8% 5% 4 5% 4 6% 7% 24%	1726
	21st to end	Day	20% 20% 6% 9% 6% 6% 4 4 6% 5% 15%	1680
December	1st to 10th	Day	18% 21% 8% 13% 5% 5% 5% 4 4 5% 12%	2680
	11th to 20th	Day	21% 20% 7% 12% 6% 4 4 4 4 5% 15%	3066
	21st to end	Day	26% 20% 8% 13% 5% 4 4 3 4 4 9%	3881
January	1st to 10th	Night	14% 16% 8% 25% 6% 4 4 3 3 4 12%	8296
	11th to 20th	Night	10% 19% 8% 19% 10% 6% 6% 4 4 4 11%	7639
	21st to end	Night	14% 15% 7% 15% 6% 6% 6% 3 5% 5% 18%	8401
February	1st to 10th	Night	15% 15% 5% 12% 8% 6% 4 4 5% 5% 20%	2730
	11th to 20th	Night	15% 14% 6% 10% 6% 6% 6% 4 6% 6% 22%	2658
	21st to end	Night	15% 13% 5% 14% 7% 5% 5% 4 4 5% 22%	2076
March	1st to 10th	Night	14% 11% 4 9% 6% 4 5% 4 5% 6% 32%	5155
	11th to 20th	Night	10% 9% 4 9% 5% 5% 5% 4 6% 8% 35%	5089
	21st to end	Night	18% 11% 4 9% 4 4 4 3 4 4 35%	5588
April	1st to 10th	Night	17% 12% 4 8% 5% 4 4 4 6% 6% 31%	2237
	11th to 20th	Night	17% 9% 3 7% 5% 4 4 4 6% 6% 36%	1894
	21st to end	Night	14% 9% 3 8% 5% 4 5% 4 6% 7% 34%	1890
May	1st to 10th	Night	19% 8% 3 7% 4 4 4 3 6% 6% 36%	5257
	11th to 20th	Night	14% 9% 3 8% 5% 4 4 3 5% 7% 38%	5234
	21st to end	Night	19% 7% 2 4 3 3 3 3 5% 6% 45%	5115
June	1st to 10th	Night	12% 6% 2 5% 4 4 4 4 6% 8% 45%	1675
	11th to 20th	Night	9% 6% 2 5% 5% 5% 5% 4 7% 10% 41%	1470
	21st to end	Night	10% 5% 2 6% 4 5% 5% 3 5% 8% 47%	1470
July	1st to 10th	Night	8% 5% 2 6% 4 4 4 4 6% 9% 48%	4110
	11th to 20th	Night	8% 5% 2 5% 3 4 4 4 6% 9% 50%	5045
	21st to end	Night	9% 5% 2 6% 4 4 4 4 5% 7% 50%	5737
August	1st to 10th	Night	12% 6% 2 5% 4 4 4 4 6% 8% 45%	3005
	11th to 20th	Night	12% 8% 2 6% 3 3 4 3 5% 7% 47%	2911
	21st to end	Night	9% 5% 2 6% 4 4 4 4 5% 8% 49%	3245
September	1st to 10th	Night	10% 6% 2 7% 4 4 4 3 5% 7% 48%	2058
	11th to 20th	Night	10% 4 2 4 3 4 3 3 5% 7% 54%	2200
	21st to end	Night	17% 7% 3 7% 4 4 3 3 5% 6% 41%	2200
October	1st to 10th	Night	15% 7% 3 7% 4 4 4 3 5% 8% 42%	2355
	11th to 20th	Night	20% 9% 3 7% 5% 4 4 3 5% 6% 34%	2400
	21st to end	Night	22% 12% 3 8% 4 4 4 4 5% 6% 28%	2682
November	1st to 10th	Night	14% 11% 3 7% 5% 4 5% 4 6% 6% 36%	2666
	11th to 20th	Night	16% 15% 4 8% 5% 4 6% 5% 6% 8% 24%	2893
	21st to end	Night	21% 16% 6% 9% 5% 5% 5% 3 5% 6% 19%	2940
December	1st to 10th	Night	13% 20% 8% 14% 7% 6% 6% 4 6% 5% 12%	4720
	11th to 20th	Night	15% 22% 7% 12% 6% 4 4 3 4 5% 18%	5348
	21st to end	Night	24% 19% 7% 11% 6% 4 4 3 4 4 14%	7309

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	80% 2 7% 8% 2	4585
	11th to 20th	Day	87% 2 4 5% 2	5280
	21st to end	Day	74% 3 9% 7% 6%	5780
February	1st to 10th	Day	69% 3 9% 13% 5%	1890
	11th to 20th	Day	68% 3 7% 14% 7%	1853
	21st to end	Day	65% 3 10% 14% 6% 1	1730
March	1st to 10th	Day	63% 2 12% 18% 5%	4906
	11th to 20th	Day	54% 2 15% 19% 8% 2	5090
	21st to end	Day	62% 2 9% 17% 9% 1	5586
April	1st to 10th	Day	56% 3 10% 21% 9% 1	2383
	11th to 20th	Day	51% 3 11% 21% 13% 1	2691
	21st to end	Day	51% 3 11% 21% 12% 2	2730
May	1st to 10th	Day	50% 3 10% 22% 11% 4	7651
	11th to 20th	Day	48% 4 12% 22% 12% 2	7630
	21st to end	Day	44% 2 8% 22% 21% 3	9057
June	1st to 10th	Day	42% 4 11% 26% 15% 2	2940
	11th to 20th	Day	42% 4 12% 23% 17% 2	3149
	21st to end	Day	40% 5% 12% 26% 16% 1	3150
July	1st to 10th	Day	41% 5% 11% 26% 15% 1	8806
	11th to 20th	Day	32% 4 11% 34% 17% 1	7816
	21st to end	Day	35% 4 13% 24% 22% 1	8156
August	1st to 10th	Day	41% 5% 13% 24% 15% 1	4351
	11th to 20th	Day	42% 6% 15% 27% 9% 1	4265
	21st to end	Day	38% 5% 12% 31% 13% 1	4619
September	1st to 10th	Day	41% 5% 13% 27% 13% 1	2339
	11th to 20th	Day	35% 3 13% 33% 16%	2200
	21st to end	Day	46% 4 13% 25% 11% 1	2200
October	1st to 10th	Day	39% 5% 12% 25% 17% 1	3331
	11th to 20th	Day	43% 4 12% 22% 19%	3240
	21st to end	Day	52% 4 16% 21% 7%	3457
November	1st to 10th	Day	53% 5% 10% 22% 8% 2	1852
	11th to 20th	Day	58% 4 14% 15% 8% 1	1726
	21st to end	Day	71% 4 10% 13% 3	1680
December	1st to 10th	Day	74% 4 12% 9% 1	2680
	11th to 20th	Day	73% 3 9% 9% 5%	3066
	21st to end	Day	81% 2 8% 7% 1	3881
January	1st to 10th	Night	78% 2 7% 10% 3	8296
	11th to 20th	Night	78% 3 7% 8% 4	7680
	21st to end	Night	69% 2 8% 14% 7%	8401
February	1st to 10th	Night	66% 4 9% 15% 6%	2730
	11th to 20th	Night	62% 5% 11% 16% 7%	2660
	21st to end	Night	64% 3 10% 17% 6%	2076
March	1st to 10th	Night	54% 2 12% 21% 10% 1	5165
	11th to 20th	Night	47% 3 17% 22% 11% 1	5090
	21st to end	Night	55% 2 9% 19% 14% 1	5588
April	1st to 10th	Night	53% 3 9% 20% 13% 1	2237
	11th to 20th	Night	49% 3 9% 21% 17% 2	1894
	21st to end	Night	48% 4 9% 20% 15% 3	1890
May	1st to 10th	Night	50% 2 10% 16% 16% 6%	5264
	11th to 20th	Night	48% 4 9% 25% 12% 2	5235
	21st to end	Night	42% 2 10% 24% 19% 3	5116
June	1st to 10th	Night	36% 4 10% 28% 19% 3	1675
	11th to 20th	Night	36% 5% 13% 26% 18% 2	1470
	21st to end	Night	36% 3 14% 26% 20% 1	1470
July	1st to 10th	Night	33% 4 14% 29% 16% 4	4075
	11th to 20th	Night	31% 4 10% 30% 23% 2	4996
	21st to end	Night	33% 4 12% 23% 25% 3	5606
August	1st to 10th	Night	37% 4 13% 26% 18% 2	2994
	11th to 20th	Night	38% 4 13% 31% 13% 1	2938
	21st to end	Night	34% 4 12% 33% 16% 1	3245
September	1st to 10th	Night	36% 3 14% 28% 17% 2	2058
	11th to 20th	Night	30% 3 12% 33% 20% 1	2200
	21st to end	Night	45% 4 12% 25% 14% 1	2200
October	1st to 10th	Night	33% 3 8% 29% 25% 1	3849
	11th to 20th	Night	44% 2 14% 22% 16% 1	3899
	21st to end	Night	46% 4 13% 24% 12% 1	4330
November	1st to 10th	Night	46% 5% 11% 26% 12% 1	2666
	11th to 20th	Night	57% 4 12% 19% 7% 1	2893
	21st to end	Night	66% 4 14% 13% 3	2940
December	1st to 10th	Night	73% 4 11% 9% 3	4720
	11th to 20th	Night	69% 3 9% 12% 7% 1	5348
	21st to end	Night	75% 3 9% 10% 3	7309

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	22% 22% 32% 19% 5% 1	292
	11th to 20th	Day	20% 18% 44% 13% 3 1	330
	21st to end	Day	29% 14% 35% 19% 4	363
February	1st to 10th	Day	25% 18% 37% 16% 4	330
	11th to 20th	Day	26% 20% 35% 17% 1	330
	21st to end	Day	26% 23% 38% 10% 2	273
March	1st to 10th	Day	26% 14% 38% 17% 6%	474
	11th to 20th	Day	24% 15% 33% 22% 4 1	540
	21st to end	Day	29% 14% 31% 21% 5% 1	594
April	1st to 10th	Day	23% 16% 33% 21% 7% 1	540
	11th to 20th	Day	27% 14% 29% 18% 10% 3	532
	21st to end	Day	24% 10% 33% 23% 9% 2	540
May	1st to 10th	Day	22% 11% 30% 26% 9% 3	543
	11th to 20th	Day	18% 9% 30% 21% 17% 5%	567
	21st to end	Day	16% 7% 27% 26% 17% 7%	617
June	1st to 10th	Day	14% 5% 34% 28% 15% 4	570
	11th to 20th	Day	12% 10% 28% 31% 14% 3	779
	21st to end	Day	14% 6% 28% 33% 15% 4	780
July	1st to 10th	Day	11% 6% 22% 31% 22% 9%	771
	11th to 20th	Day	14% 4 25% 30% 20% 7%	634
	21st to end	Day	10% 4 20% 32% 24% 9%	620
August	1st to 10th	Day	12% 4 17% 31% 23% 14%	566
	11th to 20th	Day	14% 4 18% 27% 23% 14%	535
	21st to end	Day	11% 4 20% 30% 24% 11%	583
September	1st to 10th	Day	11% 7% 22% 25% 22% 12%	530
	11th to 20th	Day	9% 2 19% 23% 32% 15%	530
	21st to end	Day	19% 7% 22% 28% 15% 8%	530
October	1st to 10th	Day	20% 7% 24% 25% 18% 6%	530
	11th to 20th	Day	22% 12% 33% 22% 8% 2	530
	21st to end	Day	28% 13% 33% 20% 5% 1	538
November	1st to 10th	Day	22% 17% 33% 18% 8% 2	330
	11th to 20th	Day	30% 15% 32% 16% 6% 2	244
	21st to end	Day	30% 14% 36% 17% 4	220
December	1st to 10th	Day	28% 17% 30% 19% 5%	220
	11th to 20th	Day	27% 20% 30% 17% 5%	220
	21st to end	Day	32% 17% 32% 15% 3	242
January	1st to 10th	Night	24% 16% 37% 17% 5% 1	1005
	11th to 20th	Night	27% 16% 32% 21% 4	840
	21st to end	Night	22% 12% 35% 24% 6%	924
February	1st to 10th	Night	24% 14% 35% 24% 3	840
	11th to 20th	Night	24% 14% 31% 26% 5%	823
	21st to end	Night	23% 15% 37% 21% 3	692
March	1st to 10th	Night	20% 12% 36% 25% 7%	840
	11th to 20th	Night	21% 12% 36% 23% 6%	840
	21st to end	Night	24% 11% 29% 27% 8% 1	924
April	1st to 10th	Night	24% 13% 31% 27% 5%	840
	11th to 20th	Night	22% 11% 32% 26% 9% 1	650
	21st to end	Night	19% 7% 34% 31% 8%	630
May	1st to 10th	Night	21% 5% 31% 31% 12% 1	630
	11th to 20th	Night	15% 5% 28% 38% 12% 2	621
	21st to end	Night	15% 3 28% 39% 15% 1	457
June	1st to 10th	Night	15% 4 28% 40% 13% 1	420
	11th to 20th	Night	13% 4 25% 44% 13%	420
	21st to end	Night	11% 4 20% 48% 16% 1	420
July	1st to 10th	Night	6% 2 17% 52% 22% 1	410
	11th to 20th	Night	10% 2 18% 41% 26% 2	602
	21st to end	Night	10% 3 14% 48% 24% 2	690
August	1st to 10th	Night	9% 1 12% 44% 31% 3	627
	11th to 20th	Night	11% 2 12% 40% 31% 5%	606
	21st to end	Night	12% 2 16% 40% 28% 3	669
September	1st to 10th	Night	10% 5% 21% 35% 24% 5%	800
	11th to 20th	Night	11% 3 15% 38% 29% 4	800
	21st to end	Night	19% 7% 18% 34% 17% 5%	800
October	1st to 10th	Night	17% 5% 25% 32% 19% 2	800
	11th to 20th	Night	24% 9% 27% 28% 11% 1	800
	21st to end	Night	27% 9% 31% 28% 5%	880
November	1st to 10th	Night	20% 12% 27% 30% 9% 1	820
	11th to 20th	Night	24% 12% 36% 21% 6% 1	840
	21st to end	Night	30% 11% 30% 24% 5%	840
December	1st to 10th	Night	29% 15% 32% 19% 5%	840
	11th to 20th	Night	25% 16% 37% 18% 4	840
	21st to end	Night	29% 13% 35% 20% 3	992

Page generated at 2026-08-12 03:37:20. Version ac07

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