Treynor
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Treynor clear sky chart from 2005-11-06 to 2024-11-02.

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	11% 7% 3 7% 5% 4 4 4 5% 7% 42%	101172
	Night	11% 7% 3 7% 4 4 4 3 5% 7% 46%	97885
Transparency	Day	40% 7% 13% 24% 14% 2	100984
	Night	37% 6% 13% 25% 16% 2	97745
Seeing	Day	15% 8% 30% 29% 15% 3	15804
	Night	14% 8% 33% 33% 11% 1	25643

By Month

Percentage Cloud Cover SE (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% 12% 5% 16% 8% 5% 5% 4 5% 6% 26%	2847
	11th to 20th	Day	9% 12% 5% 10% 6% 5% 8% 3 5% 7% 29%	2850
	21st to end	Day	10% 13% 6% 18% 8% 5% 5% 3 4 5% 24%	3135
February	1st to 10th	Day	10% 12% 4 11% 6% 6% 5% 4 5% 6% 31%	1710
	11th to 20th	Day	10% 10% 3 8% 5% 4 4 4 5% 8% 39%	1664
	21st to end	Day	12% 8% 4 9% 4 4 4 4 6% 5% 40%	1565
March	1st to 10th	Day	14% 10% 3 7% 3 3 3 2 3 5% 47%	3430
	11th to 20th	Day	11% 7% 3 6% 4 4 4 3 4 7% 48%	3480
	21st to end	Day	21% 12% 4 10% 5% 4 4 3 5% 7% 23%	3814
April	1st to 10th	Day	16% 8% 3 7% 4 4 4 3 3 6% 43%	2171
	11th to 20th	Day	16% 9% 2 7% 4 4 3 4 5% 6% 39%	2325
	21st to end	Day	19% 8% 2 6% 4 4 4 4 5% 7% 36%	2470
May	1st to 10th	Day	16% 8% 3 7% 5% 4 6% 4 5% 8% 33%	4082
	11th to 20th	Day	14% 8% 3 7% 4 4 4 3 5% 6% 41%	4082
	21st to end	Day	14% 6% 3 6% 5% 5% 4 4 6% 8% 39%	4720
June	1st to 10th	Day	8% 5% 2 5% 4 5% 4 4 7% 9% 47%	2660
	11th to 20th	Day	8% 6% 2 5% 5% 5% 4 3 7% 9% 47%	2660
	21st to end	Day	7% 5% 2 6% 4 4 4 4 6% 8% 49%	2660
July	1st to 10th	Day	12% 5% 2 5% 4 4 5% 4 7% 8% 43%	4294
	11th to 20th	Day	6% 4 1 5% 4 4 4 4 6% 7% 56%	4120
	21st to end	Day	4 3 1 5% 4 4 4 4 7% 11% 53%	4465
August	1st to 10th	Day	6% 4 2 5% 5% 5% 5% 5% 7% 9% 46%	4104
	11th to 20th	Day	13% 7% 3 6% 4 4 5% 4 6% 7% 41%	4041
	21st to end	Day	7% 5% 2 6% 5% 4 5% 4 6% 8% 48%	4412
September	1st to 10th	Day	12% 4 1 4 3 4 3 2 6% 6% 55%	2250
	11th to 20th	Day	9% 6% 2 5% 3 4 4 3 5% 7% 53%	2090
	21st to end	Day	10% 5% 2 4 3 4 4 3 4 6% 55%	2090
October	1st to 10th	Day	15% 5% 1 5% 3 2 3 3 5% 7% 52%	1919
	11th to 20th	Day	13% 5% 2 5% 3 3 3 2 4 5% 56%	1900
	21st to end	Day	13% 8% 3 5% 4 4 3 4 4 5% 47%	2090
November	1st to 10th	Day	10% 5% 3 4 4 2 4 3 4 7% 55%	1735
	11th to 20th	Day	10% 8% 2 8% 5% 5% 4 4 4 6% 44%	1596
	21st to end	Day	13% 10% 3 6% 4 3 3 3 6% 7% 43%	1520
December	1st to 10th	Day	9% 9% 3 8% 6% 5% 4 3 5% 7% 42%	1520
	11th to 20th	Day	9% 10% 4 9% 6% 4 6% 3 6% 7% 35%	1918
	21st to end	Day	17% 11% 5% 16% 6% 5% 4 4 4 5% 22%	2783
January	1st to 10th	Night	8% 10% 4 19% 9% 5% 4 3 5% 5% 26%	4108
	11th to 20th	Night	8% 12% 4 8% 5% 5% 8% 4 9% 6% 32%	4120
	21st to end	Night	12% 14% 5% 13% 6% 5% 4 3 5% 6% 29%	4532
February	1st to 10th	Night	11% 12% 4 10% 5% 4 4 4 5% 7% 36%	2470
	11th to 20th	Night	10% 9% 3 7% 4 5% 4 3 6% 7% 43%	2403
	21st to end	Night	9% 8% 3 8% 5% 4 3 3 4 6% 48%	1903
March	1st to 10th	Night	12% 7% 2 5% 3 3 3 3 4 6% 51%	3424
	11th to 20th	Night	11% 7% 2 5% 3 3 3 2 4 6% 55%	3480
	21st to end	Night	18% 10% 4 9% 4 4 5% 4 5% 7% 30%	3817
April	1st to 10th	Night	12% 8% 3 5% 3 4 3 3 5% 7% 46%	2009
	11th to 20th	Night	12% 9% 2 6% 4 4 3 3 5% 6% 46%	1801
	21st to end	Night	16% 8% 3 6% 3 4 3 2 4 7% 43%	1710
May	1st to 10th	Night	18% 7% 2 5% 4 3 3 3 5% 7% 43%	2823
	11th to 20th	Night	12% 7% 2 5% 4 3 4 3 5% 8% 49%	2823
	21st to end	Night	15% 8% 2 5% 4 4 4 3 5% 6% 45%	2842
June	1st to 10th	Night	7% 3 2 5% 4 3 4 3 7% 9% 54%	1520
	11th to 20th	Night	7% 4 2 4 3 3 4 4 8% 10% 50%	1520
	21st to end	Night	4 4 1 5% 4 5% 4 3 6% 8% 55%	1520
July	1st to 10th	Night	7% 5% 2 5% 4 4 4 4 5% 9% 51%	2657
	11th to 20th	Night	5% 2 1 3 3 2 3 3 5% 7% 65%	2850
	21st to end	Night	4 2 2 4 3 3 4 4 7% 10% 57%	3098
August	1st to 10th	Night	4 3 1 4 3 4 4 4 6% 10% 58%	2836
	11th to 20th	Night	10% 6% 2 5% 4 4 4 3 5% 8% 50%	2798
	21st to end	Night	7% 4 2 4 3 3 4 4 5% 8% 56%	3250
September	1st to 10th	Night	9% 4 2 4 3 3 3 2 4 7% 59%	1927
	11th to 20th	Night	9% 4 1 4 3 2 3 3 5% 7% 57%	2090
	21st to end	Night	9% 5% 1 4 3 3 3 2 4 6% 60%	2090
October	1st to 10th	Night	12% 5% 2 5% 3 3 3 2 5% 7% 53%	2240
	11th to 20th	Night	13% 7% 1 4 3 3 3 3 4 5% 54%	2280
	21st to end	Night	13% 6% 2 5% 2 3 4 3 4 6% 50%	2508
November	1st to 10th	Night	9% 4 2 4 3 3 3 3 5% 7% 57%	2375
	11th to 20th	Night	10% 6% 2 6% 4 3 4 3 4 7% 51%	2582
	21st to end	Night	12% 8% 3 5% 4 3 3 2 4 6% 50%	2660
December	1st to 10th	Night	9% 9% 3 8% 5% 4 4 4 6% 6% 42%	2660
	11th to 20th	Night	9% 9% 4 7% 5% 4 3 3 4 6% 45%	3279
	21st to end	Night	17% 14% 6% 13% 4 3 3 3 4 4 28%	4880

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	57% 7% 14% 15% 7% 1	2848
	11th to 20th	Day	54% 5% 12% 22% 7%	2850
	21st to end	Day	63% 6% 12% 13% 6%	3135
February	1st to 10th	Day	53% 6% 13% 17% 10% 1	1710
	11th to 20th	Day	45% 3 13% 24% 12% 2	1673
	21st to end	Day	44% 6% 13% 22% 13% 3	1565
March	1st to 10th	Day	41% 5% 10% 24% 18% 2	3430
	11th to 20th	Day	36% 6% 12% 27% 17% 2	3480
	21st to end	Day	58% 9% 17% 11% 4	3814
April	1st to 10th	Day	43% 5% 12% 26% 12% 2	2171
	11th to 20th	Day	44% 5% 14% 22% 12% 2	2325
	21st to end	Day	46% 7% 12% 23% 13% 1	2470
May	1st to 10th	Day	45% 10% 13% 19% 11% 2	4120
	11th to 20th	Day	42% 7% 11% 24% 15% 1	4086
	21st to end	Day	39% 8% 14% 21% 16% 1	4733
June	1st to 10th	Day	32% 8% 18% 27% 13% 3	2660
	11th to 20th	Day	32% 7% 14% 30% 16% 1	2660
	21st to end	Day	31% 8% 16% 28% 14% 3	2660
July	1st to 10th	Day	36% 7% 16% 28% 12% 2	4229
	11th to 20th	Day	26% 7% 12% 32% 21% 2	4051
	21st to end	Day	21% 10% 18% 31% 19% 2	4325
August	1st to 10th	Day	30% 8% 16% 28% 17% 1	4090
	11th to 20th	Day	40% 7% 12% 26% 15%	4080
	21st to end	Day	33% 7% 15% 26% 15% 4	4411
September	1st to 10th	Day	30% 4 13% 29% 19% 5%	2250
	11th to 20th	Day	31% 6% 11% 33% 18% 1	2090
	21st to end	Day	30% 4 10% 32% 23% 1	2090
October	1st to 10th	Day	32% 4 12% 28% 23% 1	1919
	11th to 20th	Day	32% 4 9% 27% 23% 4	1900
	21st to end	Day	40% 5% 11% 21% 19% 4	2090
November	1st to 10th	Day	30% 4 15% 28% 20% 3	1735
	11th to 20th	Day	41% 5% 13% 24% 16% 1	1596
	21st to end	Day	41% 4 12% 29% 13% 1	1520
December	1st to 10th	Day	42% 6% 16% 24% 12% 1	1520
	11th to 20th	Day	47% 6% 16% 25% 5%	1915
	21st to end	Day	62% 6% 9% 16% 5% 1	2783
January	1st to 10th	Night	57% 6% 11% 15% 10% 1	4108
	11th to 20th	Night	48% 6% 14% 22% 10% 1	4120
	21st to end	Night	56% 6% 14% 15% 8% 1	4532
February	1st to 10th	Night	47% 6% 13% 20% 12% 2	2470
	11th to 20th	Night	41% 5% 13% 24% 16% 2	2404
	21st to end	Night	38% 4 9% 24% 20% 4	1903
March	1st to 10th	Night	34% 5% 10% 27% 22% 3	3424
	11th to 20th	Night	31% 5% 8% 33% 17% 6%	3480
	21st to end	Night	51% 9% 21% 14% 5% 1	3817
April	1st to 10th	Night	37% 6% 10% 27% 17% 3	2009
	11th to 20th	Night	38% 5% 11% 26% 16% 3	1801
	21st to end	Night	42% 5% 13% 23% 15% 2	1710
May	1st to 10th	Night	40% 6% 12% 22% 17% 2	2850
	11th to 20th	Night	34% 7% 11% 25% 19% 3	2824
	21st to end	Night	39% 6% 13% 20% 19% 3	2850
June	1st to 10th	Night	26% 7% 15% 33% 15% 4	1520
	11th to 20th	Night	26% 7% 16% 26% 20% 4	1520
	21st to end	Night	26% 5% 16% 31% 19% 3	1520
July	1st to 10th	Night	30% 6% 16% 30% 16% 2	2614
	11th to 20th	Night	18% 6% 16% 34% 24% 3	2796
	21st to end	Night	19% 9% 17% 34% 20% 1	2999
August	1st to 10th	Night	21% 6% 15% 35% 20% 2	2826
	11th to 20th	Night	33% 6% 14% 26% 19% 2	2825
	21st to end	Night	26% 6% 17% 27% 17% 8%	3250
September	1st to 10th	Night	26% 5% 12% 28% 23% 6%	1927
	11th to 20th	Night	27% 5% 12% 35% 19% 3	2090
	21st to end	Night	27% 4 8% 30% 27% 3	2090
October	1st to 10th	Night	31% 5% 10% 26% 25% 3	2240
	11th to 20th	Night	33% 4 7% 25% 25% 6%	2280
	21st to end	Night	35% 4 13% 22% 23% 2	2508
November	1st to 10th	Night	27% 5% 16% 24% 23% 4	2375
	11th to 20th	Night	34% 4 13% 30% 17% 2	2582
	21st to end	Night	37% 4 12% 28% 17% 2	2660
December	1st to 10th	Night	41% 5% 12% 29% 11% 1	2660
	11th to 20th	Night	39% 5% 15% 32% 8%	3281
	21st to end	Night	59% 6% 9% 19% 6% 1	4880

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% 11% 34% 24% 7% 2	270
	11th to 20th	Day	20% 14% 36% 22% 6% 1	270
	21st to end	Day	16% 10% 42% 25% 6% 1	297
February	1st to 10th	Day	20% 15% 42% 20% 3	270
	11th to 20th	Day	19% 15% 37% 22% 6% 1	270
	21st to end	Day	16% 14% 44% 20% 5%	225
March	1st to 10th	Day	20% 11% 45% 18% 4 1	270
	11th to 20th	Day	27% 9% 38% 20% 6% 1	270
	21st to end	Day	34% 12% 38% 13% 3 1	297
April	1st to 10th	Day	24% 14% 38% 19% 4 1	351
	11th to 20th	Day	22% 14% 34% 23% 6%	523
	21st to end	Day	23% 13% 35% 20% 8% 1	650
May	1st to 10th	Day	21% 11% 33% 26% 8% 1	653
	11th to 20th	Day	20% 8% 29% 28% 12% 3	675
	21st to end	Day	19% 7% 27% 29% 16% 2	734
June	1st to 10th	Day	7% 5% 22% 36% 24% 6%	680
	11th to 20th	Day	8% 5% 30% 36% 17% 3	680
	21st to end	Day	9% 6% 32% 34% 16% 3	680
July	1st to 10th	Day	11% 2 17% 32% 29% 9%	671
	11th to 20th	Day	6% 1 25% 37% 24% 7%	668
	21st to end	Day	5% 1 18% 43% 27% 5%	739
August	1st to 10th	Day	8% 3 20% 40% 24% 5%	676
	11th to 20th	Day	11% 2 19% 37% 27% 3	665
	21st to end	Day	10% 3 17% 42% 21% 5%	680
September	1st to 10th	Day	13% 2 27% 35% 19% 4	460
	11th to 20th	Day	8% 4 32% 32% 18% 6%	300
	21st to end	Day	14% 7% 33% 28% 16% 1	300
October	1st to 10th	Day	18% 6% 29% 26% 16% 5%	300
	11th to 20th	Day	13% 15% 41% 23% 8% 1	300
	21st to end	Day	20% 14% 38% 17% 9% 2	330
November	1st to 10th	Day	16% 11% 39% 27% 5% 2	273
	11th to 20th	Day	15% 16% 42% 21% 6% 1	270
	21st to end	Day	22% 11% 37% 22% 7% 1	270
December	1st to 10th	Day	10% 13% 38% 30% 8% 1	270
	11th to 20th	Day	16% 13% 37% 25% 9% 1	270
	21st to end	Day	22% 13% 44% 18% 3	297
January	1st to 10th	Night	13% 12% 36% 30% 8% 1	950
	11th to 20th	Night	15% 12% 37% 29% 6%	950
	21st to end	Night	18% 9% 37% 30% 6%	1045
February	1st to 10th	Night	17% 11% 38% 29% 4	950
	11th to 20th	Night	14% 11% 40% 30% 5%	929
	21st to end	Night	15% 13% 42% 24% 5% 1	647
March	1st to 10th	Night	17% 13% 36% 27% 6% 1	575
	11th to 20th	Night	20% 8% 37% 28% 7%	570
	21st to end	Night	22% 11% 39% 22% 5%	627
April	1st to 10th	Night	18% 13% 41% 23% 5%	570
	11th to 20th	Night	17% 12% 39% 27% 4	563
	21st to end	Night	20% 8% 38% 25% 8% 1	570
May	1st to 10th	Night	18% 8% 31% 34% 8%	570
	11th to 20th	Night	17% 7% 31% 33% 12% 1	561
	21st to end	Night	17% 4 29% 35% 14%	617
June	1st to 10th	Night	8% 3 25% 46% 19% 1	570
	11th to 20th	Night	8% 3 31% 44% 14% 1	570
	21st to end	Night	6% 3 32% 43% 15%	570
July	1st to 10th	Night	7% 1 17% 45% 28% 1	555
	11th to 20th	Night	4 1 20% 51% 23% 2	552
	21st to end	Night	5% 1 15% 52% 25% 1	624
August	1st to 10th	Night	6% 1 20% 47% 23% 3	567
	11th to 20th	Night	8% 3 15% 48% 25% 1	564
	21st to end	Night	9% 2 21% 43% 22% 3	627
September	1st to 10th	Night	12% 2 25% 39% 21% 2	570
	11th to 20th	Night	11% 2 29% 39% 17% 2	570
	21st to end	Night	13% 4 31% 36% 15% 1	570
October	1st to 10th	Night	15% 6% 32% 32% 12% 2	720
	11th to 20th	Night	17% 8% 36% 30% 9%	760
	21st to end	Night	19% 10% 33% 30% 8%	836
November	1st to 10th	Night	12% 10% 34% 35% 9%	879
	11th to 20th	Night	14% 11% 41% 28% 6%	950
	21st to end	Night	17% 10% 36% 28% 8%	950
December	1st to 10th	Night	15% 10% 37% 32% 6%	950
	11th to 20th	Night	16% 8% 37% 31% 7%	950
	21st to end	Night	21% 13% 35% 27% 4	1045

Page generated at 2024-10-30 12:19:21. Version ac07

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