Two Rivers Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Two Rivers Observatory clear sky chart from 2005-11-06 to 2024-11-10.

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	21% 13% 4 9% 5% 5% 4 3 5% 6% 24%	101664
	Night	21% 12% 4 9% 5% 5% 4 3 5% 6% 25%	97605
Transparency	Day	58% 6% 13% 16% 6% 1	105143
	Night	56% 7% 13% 17% 6%	102224
Seeing	Day	27% 16% 30% 19% 7% 1	17707
	Night	27% 12% 30% 23% 7% 1	25022

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	14% 13% 6% 19% 7% 6% 5% 4 4 6% 17%	2526
	11th to 20th	Day	13% 14% 6% 19% 8% 6% 4 3 4 6% 16%	2530
	21st to end	Day	15% 12% 9% 12% 7% 6% 5% 4 4 5% 21%	2818
February	1st to 10th	Day	20% 11% 4 14% 10% 7% 4 4 6% 5% 15%	1710
	11th to 20th	Day	16% 15% 6% 11% 7% 6% 5% 4 5% 5% 18%	1680
	21st to end	Day	12% 16% 6% 10% 8% 5% 4 3 4 5% 29%	1570
March	1st to 10th	Day	23% 14% 4 8% 5% 6% 3 3 3 4 28%	3114
	11th to 20th	Day	15% 26% 8% 11% 6% 4 4 3 4 4 16%	3432
	21st to end	Day	28% 17% 7% 11% 4 4 3 3 4 4 16%	4062
April	1st to 10th	Day	23% 15% 5% 9% 6% 4 4 3 5% 4 22%	2280
	11th to 20th	Day	22% 15% 3 8% 3 4 3 3 4 5% 31%	2254
	21st to end	Day	25% 16% 3 7% 4 4 3 3 4 5% 27%	2437
May	1st to 10th	Day	26% 21% 3 7% 4 4 3 3 4 5% 21%	4425
	11th to 20th	Day	22% 15% 3 7% 5% 4 3 3 5% 6% 28%	4398
	21st to end	Day	22% 11% 3 7% 5% 5% 4 4 6% 8% 26%	4836
June	1st to 10th	Day	31% 12% 3 7% 5% 4 4 4 5% 6% 20%	2660
	11th to 20th	Day	22% 10% 3 6% 5% 4 4 4 5% 6% 31%	2660
	21st to end	Day	31% 12% 3 6% 3 3 4 4 4 6% 21%	2660
July	1st to 10th	Day	23% 9% 3 8% 6% 5% 5% 4 5% 8% 26%	4440
	11th to 20th	Day	18% 8% 2 9% 6% 5% 5% 4 7% 8% 27%	4440
	21st to end	Day	18% 8% 3 6% 4 4 5% 5% 7% 8% 32%	4815
August	1st to 10th	Day	21% 10% 4 8% 5% 5% 5% 4 6% 7% 25%	4424
	11th to 20th	Day	22% 8% 3 8% 5% 5% 5% 4 6% 8% 27%	3995
	21st to end	Day	15% 7% 2 6% 5% 5% 4 3 5% 8% 39%	4180
September	1st to 10th	Day	21% 8% 3 6% 4 5% 4 3 5% 7% 34%	2280
	11th to 20th	Day	20% 9% 3 7% 5% 4 5% 3 5% 6% 33%	2262
	21st to end	Day	22% 6% 3 8% 5% 4 3 3 5% 6% 36%	2057
October	1st to 10th	Day	19% 9% 3 9% 5% 4 3 4 5% 7% 31%	1900
	11th to 20th	Day	20% 9% 4 9% 5% 6% 5% 4 6% 6% 25%	1900
	21st to end	Day	24% 13% 4 10% 6% 5% 4 3 5% 6% 21%	1904
November	1st to 10th	Day	23% 15% 3 8% 5% 5% 4 4 6% 6% 22%	1751
	11th to 20th	Day	23% 17% 5% 11% 6% 5% 5% 3 4 6% 17%	1535
	21st to end	Day	18% 16% 6% 12% 6% 5% 6% 5% 6% 6% 17%	1520
December	1st to 10th	Day	24% 16% 7% 11% 8% 5% 4 3 4 4 13%	1520
	11th to 20th	Day	31% 15% 6% 13% 7% 5% 3 3 3 4 9%	1906
	21st to end	Day	22% 17% 8% 11% 7% 5% 5% 3 4 4 14%	2783
January	1st to 10th	Night	12% 12% 5% 17% 6% 6% 6% 4 5% 6% 21%	4429
	11th to 20th	Night	21% 12% 4 21% 7% 6% 4 3 4 5% 14%	4440
	21st to end	Night	14% 12% 6% 13% 7% 6% 6% 4 6% 6% 20%	4843
February	1st to 10th	Night	20% 12% 4 11% 7% 6% 6% 5% 6% 5% 18%	2470
	11th to 20th	Night	17% 13% 5% 10% 8% 6% 5% 4 5% 5% 20%	2384
	21st to end	Night	11% 14% 5% 13% 7% 6% 4 4 5% 6% 25%	1884
March	1st to 10th	Night	20% 14% 4 9% 6% 5% 4 3 4 4 26%	3726
	11th to 20th	Night	21% 17% 5% 10% 5% 4 4 4 4 5% 21%	3525
	21st to end	Night	29% 14% 7% 10% 6% 4 3 2 3 3 20%	3569
April	1st to 10th	Night	24% 12% 4 6% 5% 5% 4 4 5% 6% 26%	1900
	11th to 20th	Night	20% 11% 3 8% 5% 4 4 3 4 7% 30%	1876
	21st to end	Night	25% 14% 3 6% 4 3 3 2 4 5% 31%	1739
May	1st to 10th	Night	27% 13% 3 7% 3 3 4 4 5% 6% 26%	2525
	11th to 20th	Night	20% 12% 4 7% 4 4 4 2 5% 6% 32%	2506
	21st to end	Night	20% 13% 3 7% 5% 4 4 3 5% 8% 27%	2749
June	1st to 10th	Night	31% 14% 3 7% 5% 3 4 3 4 5% 22%	1520
	11th to 20th	Night	24% 10% 2 5% 4 4 3 3 4 7% 34%	1520
	21st to end	Night	29% 13% 3 8% 4 3 3 4 6% 6% 21%	1520
July	1st to 10th	Night	24% 11% 4 7% 6% 4 5% 4 5% 7% 24%	2530
	11th to 20th	Night	21% 11% 3 8% 4 4 5% 4 6% 6% 28%	2530
	21st to end	Night	21% 9% 3 7% 5% 4 4 4 5% 6% 32%	2750
August	1st to 10th	Night	22% 9% 3 7% 5% 4 5% 3 5% 8% 27%	2516
	11th to 20th	Night	20% 10% 3 6% 4 4 5% 4 6% 9% 29%	2816
	21st to end	Night	17% 6% 2 5% 3 4 4 3 5% 8% 42%	3476
September	1st to 10th	Night	19% 6% 2 6% 5% 5% 5% 3 5% 7% 39%	1900
	11th to 20th	Night	21% 7% 2 6% 4 3 4 3 5% 7% 38%	1917
	21st to end	Night	21% 9% 2 6% 4 4 3 3 4 7% 37%	2121
October	1st to 10th	Night	18% 8% 3 7% 4 5% 4 4 6% 7% 35%	2280
	11th to 20th	Night	22% 8% 3 6% 5% 4 3 3 5% 7% 33%	2280
	21st to end	Night	24% 12% 3 7% 5% 4 5% 4 5% 7% 25%	2693
November	1st to 10th	Night	22% 11% 3 8% 5% 5% 4 4 5% 8% 26%	2532
	11th to 20th	Night	24% 13% 4 8% 6% 5% 5% 4 5% 5% 20%	2642
	21st to end	Night	21% 13% 4 9% 6% 5% 6% 4 6% 6% 20%	2660
December	1st to 10th	Night	24% 14% 5% 11% 7% 5% 4 3 6% 6% 16%	2660
	11th to 20th	Night	30% 14% 5% 11% 6% 5% 5% 3 4 4 13%	3293
	21st to end	Night	27% 15% 6% 12% 5% 5% 4 3 4 4 16%	4884

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	61% 8% 15% 15% 2	2527
	11th to 20th	Day	61% 7% 15% 14% 3	2530
	21st to end	Day	60% 7% 12% 11% 10% 1	2818
February	1st to 10th	Day	63% 6% 12% 13% 6%	1710
	11th to 20th	Day	60% 6% 14% 14% 4 1	1688
	21st to end	Day	56% 4 11% 15% 11% 3	1570
March	1st to 10th	Day	58% 5% 8% 18% 10% 1	3118
	11th to 20th	Day	68% 5% 9% 13% 5% 1	3432
	21st to end	Day	71% 4 8% 10% 5% 1	4062
April	1st to 10th	Day	62% 5% 9% 15% 8% 2	2280
	11th to 20th	Day	56% 4 11% 17% 11% 1	2254
	21st to end	Day	59% 5% 10% 14% 10% 1	2437
May	1st to 10th	Day	66% 5% 10% 13% 5% 1	4440
	11th to 20th	Day	56% 8% 13% 16% 5%	4402
	21st to end	Day	54% 9% 15% 16% 6% 1	4836
June	1st to 10th	Day	64% 8% 8% 15% 5%	2660
	11th to 20th	Day	52% 8% 12% 19% 8% 1	2660
	21st to end	Day	65% 9% 8% 12% 6%	2660
July	1st to 10th	Day	58% 7% 14% 12% 9%	4370
	11th to 20th	Day	54% 7% 17% 16% 6%	4364
	21st to end	Day	48% 7% 18% 21% 6%	4662
August	1st to 10th	Day	57% 8% 14% 16% 5%	4410
	11th to 20th	Day	52% 6% 15% 22% 4	4034
	21st to end	Day	43% 6% 12% 28% 11%	4180
September	1st to 10th	Day	48% 6% 13% 22% 9% 1	2280
	11th to 20th	Day	50% 6% 12% 23% 8% 1	2262
	21st to end	Day	48% 6% 12% 26% 9% 1	2057
October	1st to 10th	Day	56% 5% 12% 19% 8%	3160
	11th to 20th	Day	45% 7% 12% 26% 10%	3140
	21st to end	Day	55% 6% 13% 19% 7%	3126
November	1st to 10th	Day	58% 6% 14% 17% 5%	1751
	11th to 20th	Day	64% 5% 15% 13% 3	1535
	21st to end	Day	60% 8% 16% 10% 4	1520
December	1st to 10th	Day	69% 6% 14% 9% 3	1520
	11th to 20th	Day	74% 5% 10% 10% 2	1905
	21st to end	Day	69% 7% 14% 8% 2	2783
January	1st to 10th	Night	54% 8% 22% 13% 2	4429
	11th to 20th	Night	68% 6% 13% 10% 3	4440
	21st to end	Night	54% 8% 16% 14% 7%	4843
February	1st to 10th	Night	60% 7% 13% 12% 6% 1	2470
	11th to 20th	Night	59% 6% 14% 15% 5% 1	2387
	21st to end	Night	54% 7% 13% 15% 10% 2	1884
March	1st to 10th	Night	58% 5% 8% 20% 9% 1	3735
	11th to 20th	Night	61% 7% 11% 14% 6% 1	3526
	21st to end	Night	69% 3 7% 13% 6% 2	3569
April	1st to 10th	Night	57% 6% 11% 16% 9% 1	1900
	11th to 20th	Night	51% 6% 11% 19% 12% 1	1876
	21st to end	Night	57% 4 9% 17% 11% 2	1739
May	1st to 10th	Night	58% 8% 14% 14% 6% 1	2530
	11th to 20th	Night	52% 7% 13% 20% 7% 1	2507
	21st to end	Night	55% 10% 13% 17% 5%	2750
June	1st to 10th	Night	66% 6% 8% 14% 5% 1	1520
	11th to 20th	Night	52% 6% 10% 20% 11% 1	1520
	21st to end	Night	66% 8% 8% 12% 6% 1	1520
July	1st to 10th	Night	61% 7% 11% 12% 8%	2491
	11th to 20th	Night	57% 6% 13% 14% 9% 1	2482
	21st to end	Night	53% 6% 12% 21% 7% 1	2663
August	1st to 10th	Night	55% 7% 15% 20% 4	2505
	11th to 20th	Night	51% 8% 19% 19% 3	2842
	21st to end	Night	40% 6% 16% 31% 8%	3475
September	1st to 10th	Night	43% 9% 13% 23% 12%	1900
	11th to 20th	Night	46% 6% 13% 24% 10% 1	1917
	21st to end	Night	49% 5% 11% 25% 10%	2121
October	1st to 10th	Night	48% 6% 13% 21% 11%	3800
	11th to 20th	Night	42% 6% 12% 31% 9%	3779
	21st to end	Night	50% 5% 16% 21% 8%	4431
November	1st to 10th	Night	54% 9% 16% 16% 5%	2532
	11th to 20th	Night	59% 8% 16% 13% 5%	2642
	21st to end	Night	58% 8% 17% 13% 4	2660
December	1st to 10th	Night	63% 8% 15% 12% 2	2660
	11th to 20th	Night	69% 6% 12% 10% 3	3295
	21st to end	Night	67% 7% 14% 11% 1	4884

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	26% 26% 32% 14% 2	370
	11th to 20th	Day	28% 22% 30% 15% 5%	370
	21st to end	Day	22% 18% 40% 17% 3	407
February	1st to 10th	Day	31% 23% 27% 16% 2	370
	11th to 20th	Day	23% 31% 28% 16% 2 1	366
	21st to end	Day	21% 21% 35% 17% 6%	307
March	1st to 10th	Day	23% 23% 34% 14% 5%	370
	11th to 20th	Day	21% 23% 32% 16% 7% 1	445
	21st to end	Day	30% 25% 26% 13% 4 2	506
April	1st to 10th	Day	32% 25% 30% 8% 4	460
	11th to 20th	Day	29% 22% 29% 15% 3 1	452
	21st to end	Day	30% 18% 30% 17% 3 1	549
May	1st to 10th	Day	34% 17% 27% 15% 4 2	653
	11th to 20th	Day	26% 13% 28% 21% 10% 2	674
	21st to end	Day	26% 14% 31% 21% 6% 1	735
June	1st to 10th	Day	37% 10% 25% 22% 6% 1	680
	11th to 20th	Day	25% 12% 34% 21% 6% 2	680
	21st to end	Day	38% 11% 22% 20% 8% 1	680
July	1st to 10th	Day	26% 9% 30% 26% 9% 1	670
	11th to 20th	Day	24% 8% 28% 27% 12%	668
	21st to end	Day	27% 10% 28% 26% 9% 1	740
August	1st to 10th	Day	22% 6% 31% 28% 12% 2	675
	11th to 20th	Day	26% 9% 27% 24% 11% 2	493
	21st to end	Day	22% 10% 28% 26% 11% 2	539
September	1st to 10th	Day	21% 12% 31% 26% 8% 2	490
	11th to 20th	Day	25% 15% 30% 20% 9% 2	480
	21st to end	Day	25% 13% 28% 22% 10% 2	390
October	1st to 10th	Day	22% 12% 32% 24% 8% 3	390
	11th to 20th	Day	24% 14% 31% 19% 9% 3	390
	21st to end	Day	28% 20% 31% 14% 7%	429
November	1st to 10th	Day	27% 18% 30% 15% 7% 2	392
	11th to 20th	Day	29% 22% 27% 16% 4 1	370
	21st to end	Day	28% 21% 30% 18% 4	370
December	1st to 10th	Day	33% 15% 32% 15% 4	370
	11th to 20th	Day	32% 22% 31% 11% 3	370
	21st to end	Day	22% 26% 32% 13% 6% 1	407
January	1st to 10th	Night	25% 20% 34% 17% 4	850
	11th to 20th	Night	27% 19% 34% 17% 3	850
	21st to end	Night	23% 16% 37% 19% 5%	922
February	1st to 10th	Night	27% 16% 31% 23% 3	760
	11th to 20th	Night	23% 23% 35% 17% 3	743
	21st to end	Night	19% 16% 36% 23% 7%	628
March	1st to 10th	Night	23% 16% 36% 21% 4 1	760
	11th to 20th	Night	23% 14% 31% 24% 7% 1	760
	21st to end	Night	28% 14% 30% 22% 5% 1	692
April	1st to 10th	Night	30% 13% 31% 21% 4	570
	11th to 20th	Night	25% 10% 36% 23% 6%	564
	21st to end	Night	32% 9% 31% 20% 7% 1	570
May	1st to 10th	Night	34% 7% 30% 19% 7% 2	570
	11th to 20th	Night	29% 8% 29% 24% 10% 1	562
	21st to end	Night	25% 8% 35% 24% 8%	616
June	1st to 10th	Night	38% 9% 24% 23% 6%	570
	11th to 20th	Night	28% 9% 26% 28% 9%	570
	21st to end	Night	36% 9% 23% 25% 6% 1	570
July	1st to 10th	Night	27% 6% 28% 29% 9% 1	556
	11th to 20th	Night	28% 9% 22% 33% 8%	552
	21st to end	Night	29% 8% 22% 32% 8% 1	623
August	1st to 10th	Night	25% 5% 21% 36% 13%	568
	11th to 20th	Night	26% 6% 18% 35% 13% 2	562
	21st to end	Night	21% 6% 21% 36% 15%	627
September	1st to 10th	Night	21% 6% 25% 35% 11% 2	570
	11th to 20th	Night	26% 8% 24% 29% 11% 1	570
	21st to end	Night	25% 9% 30% 26% 8% 1	601
October	1st to 10th	Night	24% 7% 29% 30% 11% 1	760
	11th to 20th	Night	25% 8% 30% 26% 9% 2	760
	21st to end	Night	28% 13% 32% 21% 5%	933
November	1st to 10th	Night	28% 13% 31% 21% 6% 1	878
	11th to 20th	Night	30% 17% 28% 18% 6% 1	850
	21st to end	Night	28% 16% 33% 18% 4 1	850
December	1st to 10th	Night	32% 15% 31% 17% 5%	850
	11th to 20th	Night	31% 18% 32% 16% 4	850
	21st to end	Night	27% 19% 33% 18% 2 1	935

Page generated at 2024-11-07 07:55:49. Version ac07

Copyright © 2024 Attilla Danko.