Four Corners Algonquin Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Four Corners Algonquin Observatory clear sky chart from 2005-11-06 to 2024-11-08.

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	16% 12% 4 9% 5% 5% 4 3 5% 6% 30%	102025
	Night	15% 14% 5% 10% 6% 4 4 3 5% 6% 29%	97038
Transparency	Day	54% 6% 10% 19% 9% 1	105597
	Night	55% 6% 11% 18% 9% 1	101557
Seeing	Day	24% 18% 31% 18% 7% 2	14716
	Night	22% 16% 31% 21% 8% 1	23572

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	13% 20% 7% 17% 6% 5% 4 2 4 4 18%	2517
	11th to 20th	Day	11% 15% 7% 20% 12% 6% 4 3 4 5% 14%	2520
	21st to end	Day	16% 21% 12% 14% 5% 3 4 3 2 3 17%	3100
February	1st to 10th	Day	10% 18% 7% 15% 10% 5% 4 4 4 4 19%	1710
	11th to 20th	Day	10% 15% 7% 14% 7% 6% 5% 3 3 6% 23%	1663
	21st to end	Day	15% 18% 5% 10% 8% 5% 5% 4 5% 5% 21%	1462
March	1st to 10th	Day	15% 19% 5% 10% 5% 4 3 3 5% 5% 26%	3340
	11th to 20th	Day	9% 19% 6% 14% 6% 5% 4 3 4 5% 24%	3480
	21st to end	Day	11% 11% 5% 10% 5% 5% 3 2 4 5% 39%	3865
April	1st to 10th	Day	20% 16% 5% 8% 4 4 4 3 4 6% 27%	2280
	11th to 20th	Day	21% 12% 3 7% 4 4 4 2 4 4 33%	2296
	21st to end	Day	21% 13% 4 8% 4 4 3 3 4 4 33%	2470
May	1st to 10th	Day	19% 10% 3 8% 5% 5% 5% 3 5% 6% 32%	4318
	11th to 20th	Day	16% 10% 4 7% 5% 4 4 4 5% 7% 35%	4398
	21st to end	Day	17% 7% 3 6% 5% 4 4 4 5% 7% 39%	4837
June	1st to 10th	Day	21% 9% 3 7% 5% 6% 4 4 5% 7% 29%	2660
	11th to 20th	Day	15% 8% 3 6% 4 5% 5% 4 6% 8% 35%	2716
	21st to end	Day	18% 8% 3 7% 5% 5% 5% 5% 5% 7% 32%	2850
July	1st to 10th	Day	15% 7% 2 7% 5% 6% 6% 5% 6% 8% 32%	4614
	11th to 20th	Day	14% 6% 2 6% 5% 5% 5% 4 6% 7% 39%	4440
	21st to end	Day	10% 6% 2 7% 4 4 5% 3 5% 8% 44%	4799
August	1st to 10th	Day	15% 7% 3 8% 6% 5% 6% 5% 6% 7% 32%	4104
	11th to 20th	Day	18% 8% 2 6% 4 5% 5% 4 7% 7% 33%	4044
	21st to end	Day	11% 5% 2 6% 5% 5% 5% 5% 7% 9% 40%	4315
September	1st to 10th	Day	16% 8% 3 6% 4 4 4 3 6% 8% 38%	2280
	11th to 20th	Day	15% 7% 3 6% 4 3 4 3 5% 7% 42%	2256
	21st to end	Day	20% 9% 4 6% 6% 4 4 4 5% 6% 33%	1997
October	1st to 10th	Day	19% 11% 3 7% 5% 3 5% 3 5% 7% 32%	1900
	11th to 20th	Day	23% 17% 4 8% 6% 5% 3 3 4 5% 22%	1900
	21st to end	Day	26% 17% 5% 9% 5% 4 3 2 4 6% 19%	2052
November	1st to 10th	Day	16% 15% 5% 10% 5% 4 3 3 5% 7% 27%	1604
	11th to 20th	Day	16% 17% 7% 12% 6% 5% 4 2 4 6% 21%	1520
	21st to end	Day	19% 21% 8% 13% 6% 5% 4 3 3 4 14%	1520
December	1st to 10th	Day	16% 25% 7% 14% 6% 5% 3 3 4 4 14%	1520
	11th to 20th	Day	15% 20% 9% 13% 7% 5% 4 3 4 3 17%	1906
	21st to end	Day	22% 22% 8% 15% 5% 3 2 2 3 3 15%	2772
January	1st to 10th	Night	14% 20% 9% 16% 8% 6% 5% 3 4 4 12%	4429
	11th to 20th	Night	10% 15% 6% 20% 13% 8% 6% 3 4 4 12%	4440
	21st to end	Night	14% 18% 9% 17% 6% 6% 6% 3 4 4 15%	4555
February	1st to 10th	Night	11% 18% 8% 13% 8% 6% 5% 4 5% 6% 18%	2470
	11th to 20th	Night	10% 16% 6% 14% 7% 5% 4 3 5% 5% 25%	2403
	21st to end	Night	11% 19% 5% 12% 8% 6% 4 3 5% 6% 23%	1991
March	1st to 10th	Night	15% 14% 5% 12% 5% 5% 4 2 4 6% 28%	3483
	11th to 20th	Night	12% 19% 7% 11% 5% 4 4 3 5% 6% 25%	3479
	21st to end	Night	11% 12% 5% 10% 7% 4 4 4 6% 6% 33%	3765
April	1st to 10th	Night	19% 16% 4 9% 4 2 3 3 4 5% 30%	1900
	11th to 20th	Night	18% 11% 5% 6% 4 4 4 3 4 5% 36%	1851
	21st to end	Night	19% 11% 4 9% 5% 4 4 3 4 6% 31%	1710
May	1st to 10th	Night	19% 10% 2 6% 4 3 4 4 6% 7% 35%	2621
	11th to 20th	Night	17% 10% 3 6% 5% 4 4 3 6% 7% 36%	2495
	21st to end	Night	12% 8% 3 8% 5% 4 4 3 5% 7% 41%	2738
June	1st to 10th	Night	17% 8% 2 8% 4 5% 5% 3 7% 6% 34%	1520
	11th to 20th	Night	13% 7% 2 6% 4 3 4 4 6% 7% 44%	1456
	21st to end	Night	15% 10% 3 7% 5% 3 4 4 6% 7% 36%	1330
July	1st to 10th	Night	12% 8% 2 7% 5% 5% 5% 4 5% 6% 40%	2333
	11th to 20th	Night	16% 8% 2 6% 4 4 4 3 5% 6% 43%	2520
	21st to end	Night	10% 6% 2 5% 4 4 4 4 6% 7% 48%	2739
August	1st to 10th	Night	12% 5% 2 5% 3 4 4 4 6% 9% 45%	2824
	11th to 20th	Night	16% 8% 3 5% 4 4 4 3 4 6% 42%	2785
	21st to end	Night	15% 4 2 5% 3 4 4 3 7% 9% 45%	3307
September	1st to 10th	Night	11% 7% 2 5% 5% 4 4 3 5% 8% 46%	1900
	11th to 20th	Night	14% 9% 2 6% 3 2 3 2 5% 6% 48%	1921
	21st to end	Night	18% 9% 3 6% 4 3 4 3 5% 7% 39%	2182
October	1st to 10th	Night	19% 10% 3 6% 4 3 4 3 5% 6% 37%	2280
	11th to 20th	Night	21% 14% 3 8% 5% 5% 4 3 4 6% 27%	2280
	21st to end	Night	24% 17% 5% 9% 5% 4 4 3 5% 5% 22%	2546
November	1st to 10th	Night	16% 15% 5% 8% 5% 4 4 3 4 5% 29%	2633
	11th to 20th	Night	15% 17% 5% 10% 6% 6% 4 3 5% 6% 24%	2660
	21st to end	Night	18% 21% 6% 12% 7% 4 4 4 4 5% 16%	2660
December	1st to 10th	Night	17% 24% 8% 15% 6% 4 4 3 4 4 12%	2660
	11th to 20th	Night	15% 21% 8% 13% 6% 4 4 3 4 4 19%	3288
	21st to end	Night	22% 21% 8% 15% 7% 3 3 2 3 3 11%	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	70% 7% 9% 9% 6%	2518
	11th to 20th	Day	72% 6% 6% 9% 5% 1	2520
	21st to end	Day	74% 4 6% 10% 6% 1	3100
February	1st to 10th	Day	68% 6% 7% 12% 6% 1	1710
	11th to 20th	Day	63% 5% 9% 12% 9% 1	1672
	21st to end	Day	64% 6% 7% 13% 9% 1	1462
March	1st to 10th	Day	60% 6% 11% 11% 11% 1	3343
	11th to 20th	Day	60% 7% 10% 14% 8% 1	3480
	21st to end	Day	47% 6% 8% 21% 15% 4	3865
April	1st to 10th	Day	59% 5% 8% 18% 9% 2	2280
	11th to 20th	Day	54% 5% 7% 21% 11% 1	2296
	21st to end	Day	55% 5% 7% 17% 13% 3	2470
May	1st to 10th	Day	50% 8% 9% 20% 10% 2	4331
	11th to 20th	Day	46% 7% 12% 25% 9% 1	4402
	21st to end	Day	44% 8% 12% 18% 15% 3	4837
June	1st to 10th	Day	52% 8% 10% 19% 10% 1	2660
	11th to 20th	Day	45% 7% 11% 22% 13% 2	2716
	21st to end	Day	49% 9% 12% 19% 10% 1	2850
July	1st to 10th	Day	46% 7% 14% 23% 9% 1	4544
	11th to 20th	Day	42% 7% 14% 28% 9%	4365
	21st to end	Day	38% 7% 11% 31% 13%	4646
August	1st to 10th	Day	49% 7% 12% 23% 8% 1	4091
	11th to 20th	Day	47% 7% 14% 25% 6% 1	4083
	21st to end	Day	38% 8% 12% 32% 10%	4315
September	1st to 10th	Day	43% 7% 14% 25% 11% 1	2280
	11th to 20th	Day	40% 7% 13% 27% 13%	2256
	21st to end	Day	50% 8% 10% 23% 9%	1997
October	1st to 10th	Day	51% 6% 11% 24% 8% 1	3160
	11th to 20th	Day	57% 5% 9% 19% 10% 1	3140
	21st to end	Day	65% 5% 11% 15% 4	3366
November	1st to 10th	Day	56% 7% 12% 18% 5% 1	1604
	11th to 20th	Day	65% 6% 10% 11% 6% 1	1520
	21st to end	Day	74% 5% 7% 8% 4 1	1520
December	1st to 10th	Day	74% 5% 8% 8% 4 1	1520
	11th to 20th	Day	71% 6% 6% 9% 7% 1	1906
	21st to end	Day	76% 3 4 12% 4	2772
January	1st to 10th	Night	73% 8% 9% 8% 3	4429
	11th to 20th	Night	73% 9% 7% 6% 5% 1	4440
	21st to end	Night	73% 6% 7% 8% 6% 1	4555
February	1st to 10th	Night	67% 6% 11% 11% 6% 1	2470
	11th to 20th	Night	62% 5% 9% 17% 8% 1	2405
	21st to end	Night	61% 7% 7% 17% 8% 1	1991
March	1st to 10th	Night	57% 5% 11% 14% 11% 1	3493
	11th to 20th	Night	58% 7% 13% 14% 7% 1	3480
	21st to end	Night	47% 8% 10% 20% 13% 2	3765
April	1st to 10th	Night	57% 4 9% 17% 12% 2	1900
	11th to 20th	Night	51% 5% 7% 22% 14% 1	1851
	21st to end	Night	55% 5% 7% 15% 15% 2	1710
May	1st to 10th	Night	45% 9% 12% 23% 10% 1	2627
	11th to 20th	Night	44% 9% 12% 24% 10% 1	2496
	21st to end	Night	40% 9% 11% 23% 15% 1	2739
June	1st to 10th	Night	47% 8% 11% 21% 12% 1	1520
	11th to 20th	Night	38% 6% 14% 26% 15% 1	1456
	21st to end	Night	46% 8% 15% 20% 11%	1330
July	1st to 10th	Night	42% 8% 16% 20% 14% 1	2295
	11th to 20th	Night	42% 5% 13% 31% 9%	2472
	21st to end	Night	34% 7% 12% 31% 15% 1	2651
August	1st to 10th	Night	36% 6% 17% 26% 13% 2	2814
	11th to 20th	Night	42% 7% 18% 25% 7% 1	2812
	21st to end	Night	35% 6% 16% 31% 10% 2	3307
September	1st to 10th	Night	35% 8% 16% 28% 12% 1	1900
	11th to 20th	Night	37% 6% 14% 30% 13%	1921
	21st to end	Night	45% 7% 13% 25% 10%	2182
October	1st to 10th	Night	42% 5% 11% 27% 15%	3800
	11th to 20th	Night	52% 5% 13% 19% 11%	3779
	21st to end	Night	57% 5% 18% 14% 5%	4182
November	1st to 10th	Night	56% 7% 12% 17% 7%	2633
	11th to 20th	Night	61% 8% 12% 13% 6% 1	2660
	21st to end	Night	70% 7% 10% 10% 3	2660
December	1st to 10th	Night	76% 6% 6% 8% 3	2660
	11th to 20th	Night	70% 5% 6% 12% 7% 1	3288
	21st to end	Night	79% 4 5% 8% 4	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	24% 26% 32% 12% 4 1	180
	11th to 20th	Day	30% 19% 32% 14% 3 1	180
	21st to end	Day	26% 20% 35% 15% 4	292
February	1st to 10th	Day	29% 28% 33% 6% 4	270
	11th to 20th	Day	25% 34% 35% 6%	270
	21st to end	Day	35% 26% 31% 7% 1	274
March	1st to 10th	Day	26% 23% 37% 12% 2	460
	11th to 20th	Day	25% 23% 33% 13% 4 1	460
	21st to end	Day	31% 23% 29% 13% 4	506
April	1st to 10th	Day	28% 22% 34% 12% 5% 1	460
	11th to 20th	Day	35% 21% 22% 13% 7% 2	452
	21st to end	Day	30% 18% 32% 13% 5% 1	460
May	1st to 10th	Day	26% 17% 31% 18% 6% 2	463
	11th to 20th	Day	21% 19% 31% 18% 8% 2	487
	21st to end	Day	20% 19% 31% 19% 8% 2	529
June	1st to 10th	Day	22% 16% 36% 21% 4 1	490
	11th to 20th	Day	17% 16% 36% 20% 8% 2	546
	21st to end	Day	22% 15% 34% 20% 7% 1	680
July	1st to 10th	Day	14% 11% 35% 30% 8% 1	594
	11th to 20th	Day	14% 14% 34% 25% 10% 2	484
	21st to end	Day	12% 12% 37% 27% 9% 3	532
August	1st to 10th	Day	17% 10% 32% 26% 9% 5%	486
	11th to 20th	Day	17% 9% 26% 30% 13% 5%	479
	21st to end	Day	16% 14% 32% 24% 11% 4	539
September	1st to 10th	Day	18% 13% 32% 20% 12% 5%	490
	11th to 20th	Day	17% 11% 24% 22% 17% 9%	490
	21st to end	Day	21% 19% 25% 20% 12% 4	490
October	1st to 10th	Day	25% 21% 26% 15% 10% 3	490
	11th to 20th	Day	29% 26% 28% 11% 4 1	490
	21st to end	Day	38% 19% 28% 13% 3	519
November	1st to 10th	Day	32% 20% 32% 12% 3	256
	11th to 20th	Day	31% 21% 33% 10% 4 1	180
	21st to end	Day	32% 25% 34% 7% 1 1	180
December	1st to 10th	Day	32% 19% 33% 14% 1	180
	11th to 20th	Day	34% 27% 29% 8% 1 1	180
	21st to end	Day	29% 30% 26% 12% 3 1	198
January	1st to 10th	Night	25% 22% 36% 14% 3	760
	11th to 20th	Night	26% 21% 31% 17% 4 1	760
	21st to end	Night	17% 19% 35% 22% 6% 1	836
February	1st to 10th	Night	21% 23% 38% 14% 3	760
	11th to 20th	Night	20% 21% 42% 14% 3	743
	21st to end	Night	24% 23% 33% 18% 2	628
March	1st to 10th	Night	22% 23% 34% 18% 3	760
	11th to 20th	Night	21% 20% 36% 16% 5% 1	760
	21st to end	Night	18% 21% 36% 19% 6%	836
April	1st to 10th	Night	27% 18% 33% 18% 4	760
	11th to 20th	Night	25% 20% 29% 17% 9%	727
	21st to end	Night	24% 14% 29% 21% 11% 1	570
May	1st to 10th	Night	23% 10% 29% 28% 9%	448
	11th to 20th	Night	21% 11% 33% 26% 8%	374
	21st to end	Night	16% 11% 36% 26% 11%	411
June	1st to 10th	Night	19% 9% 37% 27% 7%	380
	11th to 20th	Night	18% 9% 31% 32% 10%	380
	21st to end	Night	20% 11% 27% 31% 11% 1	380
July	1st to 10th	Night	12% 6% 31% 35% 15% 1	370
	11th to 20th	Night	16% 7% 29% 33% 14% 1	368
	21st to end	Night	11% 6% 35% 35% 12% 1	416
August	1st to 10th	Night	12% 5% 27% 35% 19% 2	566
	11th to 20th	Night	11% 6% 24% 35% 22% 2	564
	21st to end	Night	16% 8% 31% 27% 17% 2	732
September	1st to 10th	Night	14% 9% 31% 29% 16% 1	760
	11th to 20th	Night	19% 9% 25% 25% 18% 4	760
	21st to end	Night	23% 11% 21% 27% 16% 2	760
October	1st to 10th	Night	25% 15% 28% 20% 11% 2	760
	11th to 20th	Night	28% 17% 30% 16% 8% 1	760
	21st to end	Night	33% 19% 28% 17% 4	836
November	1st to 10th	Night	29% 17% 29% 19% 5%	771
	11th to 20th	Night	25% 23% 30% 16% 7%	760
	21st to end	Night	31% 19% 29% 17% 3	760
December	1st to 10th	Night	30% 23% 32% 11% 4	760
	11th to 20th	Night	25% 24% 32% 15% 3 1	760
	21st to end	Night	34% 19% 30% 14% 2 1	836

Page generated at 2024-11-05 08:15:48. Version ac07

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