Tripp
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tripp clear sky chart from 2005-11-06 to 2025-12-18.

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	10% 6% 2 7% 4 4 4 3 5% 7% 45%	135456
	Night	9% 7% 2 7% 4 4 4 3 5% 7% 47%	132888
Transparency	Day	37% 6% 14% 25% 15% 2	130133
	Night	36% 6% 13% 26% 17% 2	129218
Seeing	Day	14% 10% 32% 30% 13% 2	17436
	Night	12% 9% 35% 33% 9% 1	27370

By Month

Percentage Cloud Cover SW (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	9% 11% 5% 16% 8% 8% 5% 4 4 5% 26%	3638
	11th to 20th	Day	4 10% 4 11% 8% 5% 6% 3 8% 7% 33%	3640
	21st to end	Day	4 7% 4 11% 6% 5% 5% 3 4 6% 44%	4416
February	1st to 10th	Day	10% 10% 4 9% 7% 5% 5% 4 5% 6% 34%	1800
	11th to 20th	Day	8% 10% 4 10% 6% 6% 4 4 5% 6% 38%	1851
	21st to end	Day	9% 9% 3 9% 5% 5% 4 4 6% 6% 41%	1650
March	1st to 10th	Day	9% 7% 3 8% 4 4 3 2 4 6% 49%	4632
	11th to 20th	Day	7% 6% 2 6% 4 4 3 3 5% 8% 52%	4980
	21st to end	Day	20% 11% 4 10% 5% 4 4 3 6% 6% 25%	5464
April	1st to 10th	Day	16% 7% 2 7% 4 4 4 4 6% 7% 41%	2286
	11th to 20th	Day	17% 8% 3 6% 4 4 4 3 4 6% 41%	2564
	21st to end	Day	18% 7% 2 7% 4 4 4 3 5% 6% 40%	2600
May	1st to 10th	Day	10% 5% 1 6% 3 4 4 4 6% 7% 49%	5900
	11th to 20th	Day	14% 6% 2 6% 4 3 3 3 4 6% 49%	5862
	21st to end	Day	19% 8% 2 6% 4 4 4 4 5% 7% 36%	6589
June	1st to 10th	Day	10% 5% 2 5% 4 4 3 4 6% 8% 50%	3000
	11th to 20th	Day	12% 5% 2 4 3 4 5% 4 6% 8% 46%	3000
	21st to end	Day	7% 5% 2 5% 4 4 4 4 6% 9% 51%	3000
July	1st to 10th	Day	8% 4 2 5% 4 5% 5% 5% 7% 9% 48%	6389
	11th to 20th	Day	9% 5% 2 4 3 4 3 3 5% 8% 53%	6340
	21st to end	Day	7% 5% 2 5% 4 4 5% 4 7% 9% 49%	6537
August	1st to 10th	Day	8% 5% 2 6% 5% 5% 6% 4 7% 8% 44%	5801
	11th to 20th	Day	12% 6% 2 6% 4 3 4 3 6% 9% 46%	5821
	21st to end	Day	9% 5% 2 5% 3 4 4 3 4 6% 55%	6490
September	1st to 10th	Day	12% 5% 1 4 3 2 4 3 5% 6% 55%	2288
	11th to 20th	Day	8% 4 1 5% 3 3 4 3 4 7% 57%	2200
	21st to end	Day	10% 4 1 4 3 3 3 3 5% 6% 58%	2200
October	1st to 10th	Day	7% 3 1 3 3 2 3 2 4 5% 66%	3442
	11th to 20th	Day	7% 5% 1 5% 3 4 3 3 5% 6% 57%	3240
	21st to end	Day	10% 7% 2 6% 4 4 4 4 5% 8% 46%	3292
November	1st to 10th	Day	7% 8% 3 6% 5% 4 5% 4 6% 7% 47%	1853
	11th to 20th	Day	6% 7% 2 8% 6% 5% 4 3 5% 7% 47%	1869
	21st to end	Day	9% 8% 3 7% 4 4 4 4 6% 7% 44%	1680
December	1st to 10th	Day	4 7% 3 9% 8% 7% 5% 4 6% 7% 41%	2690
	11th to 20th	Day	7% 10% 4 8% 5% 5% 6% 5% 5% 7% 38%	2796
	21st to end	Day	13% 9% 4 14% 5% 4 4 3 6% 6% 33%	3656
January	1st to 10th	Night	7% 12% 5% 13% 9% 8% 6% 4 6% 6% 25%	6327
	11th to 20th	Night	3 9% 3 9% 7% 5% 7% 4 8% 6% 38%	6340
	21st to end	Night	3 7% 4 11% 5% 5% 4 4 7% 6% 45%	6560
February	1st to 10th	Night	9% 10% 4 8% 6% 5% 5% 4 5% 6% 38%	2600
	11th to 20th	Night	7% 10% 3 8% 5% 5% 4 4 5% 6% 42%	2454
	21st to end	Night	8% 8% 3 6% 5% 4 4 5% 6% 6% 46%	1980
March	1st to 10th	Night	10% 7% 2 5% 3 3 4 3 5% 6% 51%	5222
	11th to 20th	Night	9% 6% 2 5% 3 3 3 3 5% 8% 52%	4980
	21st to end	Night	15% 11% 3 8% 5% 4 4 3 5% 6% 35%	5467
April	1st to 10th	Night	13% 8% 3 6% 3 4 4 4 6% 7% 43%	2110
	11th to 20th	Night	13% 8% 3 6% 4 3 3 3 5% 8% 44%	1783
	21st to end	Night	15% 8% 3 5% 4 5% 4 3 6% 7% 42%	1800
May	1st to 10th	Night	12% 4 1 5% 4 3 4 3 5% 7% 51%	4080
	11th to 20th	Night	12% 5% 2 5% 3 3 4 3 5% 6% 52%	4053
	21st to end	Night	18% 6% 3 6% 3 3 4 3 5% 8% 42%	4287
June	1st to 10th	Night	8% 4 1 5% 4 2 3 2 5% 8% 56%	1400
	11th to 20th	Night	9% 5% 1 4 3 4 4 4 7% 9% 52%	1400
	21st to end	Night	8% 4 1 3 3 4 5% 4 5% 9% 55%	1400
July	1st to 10th	Night	6% 4 2 5% 4 4 4 4 6% 9% 53%	3584
	11th to 20th	Night	8% 6% 2 4 3 3 4 3 5% 6% 56%	3640
	21st to end	Night	5% 3 1 5% 3 3 4 4 7% 10% 54%	4333
August	1st to 10th	Night	6% 5% 2 6% 4 4 5% 4 7% 11% 45%	4011
	11th to 20th	Night	7% 5% 2 5% 4 4 5% 4 6% 8% 50%	4028
	21st to end	Night	6% 3 2 6% 3 4 4 3 6% 8% 55%	4487
September	1st to 10th	Night	8% 4 2 3 3 3 3 3 4 7% 58%	2107
	11th to 20th	Night	6% 4 1 4 3 4 4 3 5% 7% 59%	2200
	21st to end	Night	8% 4 1 4 3 3 3 2 4 6% 62%	2200
October	1st to 10th	Night	9% 3 1 2 2 1 2 2 3 4 71%	3703
	11th to 20th	Night	8% 4 2 4 3 2 3 2 4 7% 62%	3899
	21st to end	Night	10% 6% 2 5% 4 4 4 4 5% 7% 48%	4503
November	1st to 10th	Night	8% 5% 1 5% 4 4 4 4 5% 7% 54%	2665
	11th to 20th	Night	8% 6% 2 7% 4 5% 4 4 6% 7% 48%	2747
	21st to end	Night	7% 8% 2 6% 4 4 4 4 6% 7% 47%	2940
December	1st to 10th	Night	5% 5% 3 9% 5% 5% 5% 4 5% 6% 48%	4720
	11th to 20th	Night	6% 9% 4 9% 6% 6% 6% 4 5% 7% 39%	5561
	21st to end	Night	13% 10% 4 12% 5% 4 4 4 4 5% 34%	7317

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	60% 5% 13% 15% 6%	3639
	11th to 20th	Day	49% 4 14% 17% 14% 1	3640
	21st to end	Day	41% 5% 16% 23% 12% 2	4416
February	1st to 10th	Day	50% 7% 15% 18% 9% 1	1800
	11th to 20th	Day	46% 6% 12% 21% 13% 2	1860
	21st to end	Day	43% 6% 15% 21% 12% 2	1650
March	1st to 10th	Day	37% 4 9% 30% 17% 2	4632
	11th to 20th	Day	30% 5% 11% 29% 23% 2	4980
	21st to end	Day	58% 7% 14% 16% 4 2	5464
April	1st to 10th	Day	42% 6% 13% 25% 13% 1	2286
	11th to 20th	Day	44% 5% 12% 22% 15% 2	2567
	21st to end	Day	45% 6% 12% 25% 12%	2600
May	1st to 10th	Day	32% 5% 11% 26% 25% 1	5900
	11th to 20th	Day	37% 5% 11% 23% 16% 9%	5866
	21st to end	Day	45% 7% 12% 23% 12% 1	6590
June	1st to 10th	Day	31% 8% 16% 30% 12% 2	3000
	11th to 20th	Day	34% 8% 16% 23% 17% 2	3000
	21st to end	Day	29% 8% 16% 29% 16% 2	3000
July	1st to 10th	Day	30% 8% 17% 31% 12% 2	6321
	11th to 20th	Day	30% 6% 11% 32% 18% 3	6265
	21st to end	Day	28% 9% 18% 25% 17% 3	6350
August	1st to 10th	Day	31% 8% 14% 29% 14% 4	4220
	11th to 20th	Day	41% 7% 14% 25% 12% 1	4210
	21st to end	Day	27% 7% 16% 26% 20% 3	4674
September	1st to 10th	Day	30% 6% 12% 29% 19% 4	2288
	11th to 20th	Day	28% 6% 15% 33% 18% 1	2200
	21st to end	Day	28% 5% 10% 30% 24% 2	2200
October	1st to 10th	Day	22% 4 8% 23% 38% 5%	3442
	11th to 20th	Day	28% 4 14% 30% 20% 5%	3240
	21st to end	Day	36% 5% 12% 26% 19% 2	3292
November	1st to 10th	Day	35% 6% 16% 25% 15% 2	1853
	11th to 20th	Day	38% 5% 15% 26% 14% 2	1869
	21st to end	Day	38% 5% 16% 27% 13% 1	1680
December	1st to 10th	Day	42% 6% 17% 26% 9% 1	2690
	11th to 20th	Day	44% 6% 19% 21% 9%	2793
	21st to end	Day	52% 4 12% 26% 6% 1	3656
January	1st to 10th	Night	57% 7% 11% 16% 8%	6327
	11th to 20th	Night	43% 7% 14% 21% 14% 2	6340
	21st to end	Night	37% 7% 15% 25% 16%	6560
February	1st to 10th	Night	46% 6% 15% 20% 12% 1	2600
	11th to 20th	Night	43% 5% 14% 21% 13% 4	2455
	21st to end	Night	37% 7% 13% 26% 14% 3	1980
March	1st to 10th	Night	33% 5% 10% 29% 22% 2	5222
	11th to 20th	Night	31% 3 9% 29% 26% 3	4980
	21st to end	Night	48% 7% 13% 23% 7% 1	5467
April	1st to 10th	Night	40% 6% 14% 24% 15% 1	2110
	11th to 20th	Night	39% 6% 10% 24% 20% 2	1783
	21st to end	Night	41% 7% 13% 25% 13% 2	1800
May	1st to 10th	Night	31% 6% 13% 24% 24% 3	4080
	11th to 20th	Night	32% 6% 11% 21% 22% 7%	4054
	21st to end	Night	41% 7% 12% 26% 14% 1	4288
June	1st to 10th	Night	27% 8% 14% 29% 19% 3	1400
	11th to 20th	Night	28% 8% 14% 25% 21% 5%	1400
	21st to end	Night	25% 7% 14% 31% 19% 3	1400
July	1st to 10th	Night	27% 6% 18% 32% 13% 3	3544
	11th to 20th	Night	28% 6% 11% 34% 17% 3	3592
	21st to end	Night	23% 8% 20% 29% 17% 3	4207
August	1st to 10th	Night	30% 7% 17% 29% 14% 3	2916
	11th to 20th	Night	33% 8% 15% 28% 15% 2	2915
	21st to end	Night	26% 7% 17% 24% 22% 5%	3234
September	1st to 10th	Night	26% 7% 13% 27% 22% 6%	2107
	11th to 20th	Night	23% 8% 13% 33% 21% 2	2200
	21st to end	Night	25% 4 9% 30% 28% 4	2200
October	1st to 10th	Night	20% 3 6% 19% 47% 6%	3703
	11th to 20th	Night	24% 3 9% 33% 24% 7%	3899
	21st to end	Night	34% 5% 14% 26% 20% 1	4503
November	1st to 10th	Night	30% 5% 14% 26% 21% 4	2665
	11th to 20th	Night	34% 5% 14% 24% 19% 4	2747
	21st to end	Night	34% 6% 15% 28% 16% 1	2940
December	1st to 10th	Night	36% 5% 15% 31% 12% 1	4720
	11th to 20th	Night	44% 6% 15% 27% 8%	5563
	21st to end	Night	52% 5% 12% 23% 8%	7317

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	15% 12% 32% 28% 13% 1	300
	11th to 20th	Day	12% 14% 39% 28% 6% 1	300
	21st to end	Day	12% 10% 45% 23% 8% 1	330
February	1st to 10th	Day	12% 21% 40% 23% 4	300
	11th to 20th	Day	14% 13% 42% 23% 7% 1	300
	21st to end	Day	14% 14% 40% 27% 4	249
March	1st to 10th	Day	13% 14% 43% 25% 4 1	300
	11th to 20th	Day	18% 10% 38% 23% 10% 1	300
	21st to end	Day	25% 14% 32% 23% 5% 1	330
April	1st to 10th	Day	23% 17% 38% 18% 4	386
	11th to 20th	Day	21% 17% 30% 25% 6%	685
	21st to end	Day	22% 14% 31% 22% 8% 2	700
May	1st to 10th	Day	17% 14% 31% 27% 11% 1	703
	11th to 20th	Day	19% 11% 28% 26% 14% 2	725
	21st to end	Day	18% 10% 30% 27% 12% 3	789
June	1st to 10th	Day	10% 8% 25% 33% 19% 5%	730
	11th to 20th	Day	12% 6% 36% 30% 14% 2	730
	21st to end	Day	10% 8% 31% 34% 16% 2	730
July	1st to 10th	Day	8% 3 22% 38% 26% 4	721
	11th to 20th	Day	7% 4 26% 43% 18% 2	718
	21st to end	Day	5% 3 26% 45% 19% 3	794
August	1st to 10th	Day	9% 3 26% 40% 19% 3	726
	11th to 20th	Day	9% 5% 25% 37% 19% 4	715
	21st to end	Day	7% 3 28% 39% 19% 3	803
September	1st to 10th	Day	13% 5% 30% 31% 17% 4	418
	11th to 20th	Day	7% 7% 37% 28% 17% 4	330
	21st to end	Day	15% 9% 29% 28% 16% 4	330
October	1st to 10th	Day	16% 6% 29% 31% 15% 4	330
	11th to 20th	Day	18% 13% 37% 23% 7% 1	330
	21st to end	Day	18% 18% 36% 20% 8% 1	363
November	1st to 10th	Day	16% 15% 35% 22% 9% 3	330
	11th to 20th	Day	12% 18% 41% 24% 6%	330
	21st to end	Day	20% 16% 32% 22% 9% 1	330
December	1st to 10th	Day	13% 10% 37% 29% 10% 1	330
	11th to 20th	Day	15% 15% 40% 23% 6%	321
	21st to end	Day	21% 12% 37% 25% 4	330
January	1st to 10th	Night	11% 11% 37% 32% 9% 1	1000
	11th to 20th	Night	9% 14% 38% 31% 6% 1	1000
	21st to end	Night	12% 10% 44% 27% 7%	1100
February	1st to 10th	Night	15% 12% 41% 26% 6%	1000
	11th to 20th	Night	12% 12% 41% 30% 5% 1	900
	21st to end	Night	14% 9% 38% 30% 7% 1	660
March	1st to 10th	Night	14% 11% 41% 29% 6%	739
	11th to 20th	Night	15% 11% 40% 30% 4	600
	21st to end	Night	19% 10% 39% 26% 6%	660
April	1st to 10th	Night	16% 15% 39% 28% 3	600
	11th to 20th	Night	18% 13% 35% 28% 6%	593
	21st to end	Night	17% 11% 39% 27% 6% 1	600
May	1st to 10th	Night	16% 9% 35% 30% 10%	600
	11th to 20th	Night	17% 8% 31% 33% 11%	591
	21st to end	Night	19% 6% 32% 34% 9%	650
June	1st to 10th	Night	9% 6% 28% 41% 15% 1	600
	11th to 20th	Night	10% 3 35% 41% 10%	600
	21st to end	Night	8% 4 30% 44% 15%	600
July	1st to 10th	Night	6% 3 22% 46% 22% 1	585
	11th to 20th	Night	5% 2 26% 51% 16%	582
	21st to end	Night	4 2 25% 53% 15%	657
August	1st to 10th	Night	8% 5% 25% 44% 18%	597
	11th to 20th	Night	7% 2 26% 44% 19% 1	594
	21st to end	Night	6% 3 29% 45% 16% 1	660
September	1st to 10th	Night	10% 5% 27% 43% 14% 2	600
	11th to 20th	Night	7% 5% 31% 42% 14% 2	600
	21st to end	Night	9% 9% 33% 34% 15% 1	600
October	1st to 10th	Night	18% 8% 31% 32% 10% 1	661
	11th to 20th	Night	15% 13% 35% 30% 8%	800
	21st to end	Night	15% 11% 36% 30% 8%	1030
November	1st to 10th	Night	12% 10% 39% 30% 8% 1	1025
	11th to 20th	Night	11% 13% 39% 29% 8%	1050
	21st to end	Night	12% 11% 37% 32% 9%	1050
December	1st to 10th	Night	12% 12% 39% 31% 5%	1050
	11th to 20th	Night	13% 10% 39% 31% 7%	1036
	21st to end	Night	19% 11% 35% 28% 7% 1	1100

Page generated at 2025-12-15 00:13:52. Version ac07

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