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 2024-01-13.

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	17% 12% 5% 8% 7% 3 5% 4 5% 6% 29%	75030
	Night	15% 13% 5% 9% 7% 3 4 4 5% 6% 29%	74692
Transparency	Day	55% 6% 10% 18% 9% 1	74736
	Night	56% 6% 11% 17% 9% 1	74523
Seeing	Day	24% 18% 32% 18% 7% 2	13565
	Night	23% 16% 31% 21% 8% 1	22591

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	12% 19% 9% 14% 9% 3 5% 3 4 5% 16%	1517
	11th to 20th	Day	16% 18% 7% 13% 8% 3 3 4 4 5% 19%	1456
	21st to end	Day	13% 13% 7% 13% 9% 4 6% 5% 4 5% 21%	1772
February	1st to 10th	Day	10% 17% 7% 13% 13% 4 5% 5% 4 4 17%	1620
	11th to 20th	Day	12% 14% 7% 12% 8% 4 6% 4 3 6% 24%	1573
	21st to end	Day	15% 18% 5% 10% 9% 3 5% 5% 4 5% 20%	1378
March	1st to 10th	Day	13% 14% 6% 11% 8% 4 5% 5% 4 5% 26%	1923
	11th to 20th	Day	12% 15% 7% 10% 9% 5% 5% 4 4 5% 25%	1980
	21st to end	Day	16% 12% 6% 7% 5% 3 4 3 5% 5% 34%	2201
April	1st to 10th	Day	20% 15% 6% 7% 5% 3 4 4 4 6% 27%	2160
	11th to 20th	Day	21% 11% 4 6% 5% 3 4 3 4 5% 34%	2173
	21st to end	Day	21% 12% 4 7% 5% 3 3 4 4 5% 33%	2340
May	1st to 10th	Day	18% 10% 4 7% 6% 3 5% 4 5% 6% 34%	2453
	11th to 20th	Day	18% 10% 4 6% 6% 3 4 4 4 6% 35%	2478
	21st to end	Day	15% 7% 3 6% 6% 3 4 5% 5% 8% 38%	2725
June	1st to 10th	Day	22% 8% 3 6% 5% 4 5% 4 5% 8% 30%	2520
	11th to 20th	Day	16% 7% 3 6% 5% 3 5% 5% 6% 8% 36%	2573
	21st to end	Day	17% 8% 3 6% 6% 4 5% 6% 5% 7% 32%	2700
July	1st to 10th	Day	14% 6% 2 5% 6% 4 7% 7% 6% 8% 38%	2624
	11th to 20th	Day	13% 6% 3 7% 7% 4 6% 6% 5% 7% 37%	2520
	21st to end	Day	13% 6% 3 6% 7% 4 6% 5% 6% 9% 34%	2742
August	1st to 10th	Day	14% 7% 3 7% 7% 4 6% 7% 5% 8% 34%	2327
	11th to 20th	Day	15% 7% 2 6% 5% 4 6% 5% 7% 7% 34%	2303
	21st to end	Day	16% 7% 3 7% 6% 4 6% 6% 7% 8% 32%	2455
September	1st to 10th	Day	16% 8% 3 5% 5% 3 4 4 6% 8% 38%	2160
	11th to 20th	Day	16% 7% 3 5% 5% 2 4 4 5% 7% 40%	2138
	21st to end	Day	19% 8% 4 6% 6% 4 4 5% 5% 6% 33%	1892
October	1st to 10th	Day	20% 11% 3 6% 6% 3 4 4 4 7% 32%	1800
	11th to 20th	Day	24% 15% 4 8% 7% 4 3 4 5% 5% 21%	1800
	21st to end	Day	27% 17% 5% 8% 6% 3 3 4 4 6% 18%	1944
November	1st to 10th	Day	16% 15% 5% 8% 6% 3 4 3 5% 7% 27%	1545
	11th to 20th	Day	17% 16% 7% 10% 7% 4 4 3 4 6% 21%	1520
	21st to end	Day	20% 20% 8% 12% 8% 3 5% 4 3 4 15%	1520
December	1st to 10th	Day	17% 23% 8% 12% 7% 3 4 3 4 4 14%	1520
	11th to 20th	Day	15% 19% 10% 12% 8% 4 4 4 4 4 17%	1906
	21st to end	Day	22% 21% 9% 13% 8% 2 2 2 3 4 15%	2772
January	1st to 10th	Night	15% 18% 8% 13% 10% 4 6% 4 4 4 14%	2649
	11th to 20th	Night	14% 17% 7% 14% 9% 5% 5% 4 4 4 16%	2560
	21st to end	Night	11% 14% 6% 13% 8% 4 7% 5% 5% 5% 23%	2583
February	1st to 10th	Night	11% 17% 8% 12% 10% 5% 5% 5% 5% 6% 17%	2340
	11th to 20th	Night	11% 15% 7% 11% 8% 4 4 4 5% 5% 26%	2273
	21st to end	Night	11% 18% 6% 11% 8% 4 5% 4 5% 5% 23%	1877
March	1st to 10th	Night	13% 11% 6% 12% 7% 4 5% 3 4 5% 30%	2020
	11th to 20th	Night	12% 14% 6% 9% 6% 3 4 4 5% 6% 30%	1979
	21st to end	Night	12% 12% 4 8% 6% 2 3 4 5% 6% 37%	2153
April	1st to 10th	Night	19% 14% 5% 8% 5% 2 3 5% 4 5% 30%	1800
	11th to 20th	Night	18% 10% 5% 6% 5% 3 4 4 4 6% 36%	1753
	21st to end	Night	19% 11% 4 8% 6% 3 4 4 4 6% 31%	1620
May	1st to 10th	Night	20% 8% 2 6% 4 3 4 4 5% 8% 36%	1505
	11th to 20th	Night	17% 8% 3 4 4 2 5% 4 7% 7% 40%	1415
	21st to end	Night	12% 6% 2 5% 5% 2 4 5% 6% 8% 44%	1550
June	1st to 10th	Night	17% 7% 3 7% 4 4 5% 5% 7% 7% 35%	1440
	11th to 20th	Night	13% 6% 2 5% 5% 3 4 4 5% 8% 44%	1380
	21st to end	Night	14% 9% 3 7% 5% 3 4 5% 5% 7% 37%	1260
July	1st to 10th	Night	10% 6% 2 5% 5% 3 4 5% 5% 8% 48%	1331
	11th to 20th	Night	13% 7% 2 5% 5% 4 4 4 5% 7% 45%	1440
	21st to end	Night	10% 5% 3 4 5% 3 5% 5% 7% 8% 45%	1574
August	1st to 10th	Night	11% 6% 2 5% 4 3 5% 4 6% 9% 45%	1610
	11th to 20th	Night	9% 7% 3 4 6% 3 5% 6% 6% 7% 45%	1598
	21st to end	Night	14% 6% 2 6% 4 3 4 4 7% 9% 41%	1881
September	1st to 10th	Night	11% 7% 2 4 5% 3 4 5% 6% 8% 46%	1800
	11th to 20th	Night	15% 9% 2 5% 4 2 3 3 5% 6% 46%	1819
	21st to end	Night	17% 9% 3 5% 5% 2 4 4 5% 7% 39%	2067
October	1st to 10th	Night	19% 10% 3 5% 5% 2 4 4 5% 6% 36%	2160
	11th to 20th	Night	22% 13% 4 7% 6% 3 5% 4 4 6% 26%	2160
	21st to end	Night	25% 16% 5% 8% 6% 3 4 3 5% 5% 21%	2412
November	1st to 10th	Night	17% 14% 5% 7% 6% 3 4 4 4 6% 29%	2531
	11th to 20th	Night	16% 15% 6% 9% 7% 4 5% 4 5% 6% 24%	2660
	21st to end	Night	18% 19% 7% 10% 8% 3 5% 4 4 5% 16%	2660
December	1st to 10th	Night	17% 21% 9% 13% 7% 3 4 4 4 4 13%	2660
	11th to 20th	Night	15% 20% 9% 12% 7% 3 4 4 4 4 19%	3288
	21st to end	Night	22% 21% 8% 13% 10% 2 3 3 3 4 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% 5% 7% 13% 5%	1518
	11th to 20th	Day	68% 5% 6% 10% 9% 2	1456
	21st to end	Day	65% 6% 7% 9% 10% 2	1772
February	1st to 10th	Day	69% 6% 6% 12% 6% 1	1620
	11th to 20th	Day	63% 5% 10% 12% 9% 2	1582
	21st to end	Day	66% 6% 6% 12% 9%	1378
March	1st to 10th	Day	61% 5% 10% 14% 9% 2	1926
	11th to 20th	Day	61% 5% 8% 15% 9% 2	1980
	21st to end	Day	53% 4 7% 18% 13% 5%	2201
April	1st to 10th	Day	60% 4 8% 17% 9% 3	2160
	11th to 20th	Day	53% 5% 8% 22% 12% 2	2173
	21st to end	Day	55% 5% 7% 17% 13% 3	2340
May	1st to 10th	Day	51% 5% 10% 18% 13% 3	2453
	11th to 20th	Day	50% 5% 8% 21% 14% 2	2482
	21st to end	Day	44% 8% 12% 19% 13% 3	2725
June	1st to 10th	Day	52% 7% 10% 19% 10% 1	2520
	11th to 20th	Day	45% 7% 11% 22% 13% 2	2573
	21st to end	Day	49% 9% 12% 19% 10% 1	2700
July	1st to 10th	Day	41% 8% 12% 26% 12% 1	2554
	11th to 20th	Day	43% 9% 12% 25% 10% 1	2445
	21st to end	Day	46% 8% 13% 24% 9%	2589
August	1st to 10th	Day	47% 9% 14% 21% 8% 1	2314
	11th to 20th	Day	44% 10% 15% 22% 7% 1	2303
	21st to end	Day	46% 9% 13% 21% 9% 1	2455
September	1st to 10th	Day	43% 8% 14% 24% 11% 1	2160
	11th to 20th	Day	42% 8% 13% 27% 11%	2138
	21st to end	Day	50% 8% 10% 24% 8%	1892
October	1st to 10th	Day	52% 7% 11% 18% 10% 1	1800
	11th to 20th	Day	66% 7% 10% 12% 5% 1	1800
	21st to end	Day	69% 6% 8% 11% 5% 1	1944
November	1st to 10th	Day	56% 7% 13% 18% 6% 1	1545
	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	72% 6% 9% 9% 4	2649
	11th to 20th	Night	71% 6% 6% 8% 7% 1	2560
	21st to end	Night	61% 6% 8% 13% 11% 1	2583
February	1st to 10th	Night	68% 5% 10% 10% 6% 1	2340
	11th to 20th	Night	61% 5% 9% 16% 8% 1	2275
	21st to end	Night	61% 6% 7% 16% 8% 1	1877
March	1st to 10th	Night	57% 4 9% 16% 11% 2	2030
	11th to 20th	Night	54% 6% 11% 16% 11% 2	1980
	21st to end	Night	47% 6% 9% 20% 15% 3	2153
April	1st to 10th	Night	57% 4 9% 17% 12% 2	1800
	11th to 20th	Night	50% 5% 7% 23% 14% 1	1753
	21st to end	Night	55% 5% 7% 16% 15% 2	1620
May	1st to 10th	Night	45% 7% 11% 19% 15% 3	1505
	11th to 20th	Night	42% 6% 10% 24% 16% 2	1416
	21st to end	Night	37% 8% 15% 20% 17% 3	1551
June	1st to 10th	Night	46% 7% 11% 22% 12% 1	1440
	11th to 20th	Night	38% 6% 14% 25% 16% 1	1380
	21st to end	Night	45% 8% 16% 21% 11%	1260
July	1st to 10th	Night	31% 10% 14% 24% 19% 1	1293
	11th to 20th	Night	39% 6% 14% 29% 12% 1	1392
	21st to end	Night	35% 8% 17% 28% 11% 1	1486
August	1st to 10th	Night	36% 8% 18% 26% 12% 1	1600
	11th to 20th	Night	34% 10% 19% 26% 9% 1	1598
	21st to end	Night	39% 7% 18% 25% 9% 1	1881
September	1st to 10th	Night	35% 9% 16% 27% 12% 1	1800
	11th to 20th	Night	39% 6% 14% 30% 11%	1819
	21st to end	Night	45% 7% 13% 27% 8%	2067
October	1st to 10th	Night	48% 7% 12% 18% 14%	2160
	11th to 20th	Night	58% 7% 13% 15% 6%	2160
	21st to end	Night	65% 5% 9% 13% 8% 1	2412
November	1st to 10th	Night	56% 7% 13% 17% 7%	2531
	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% 33% 12% 4 1	180
	11th to 20th	Day	30% 17% 34% 14% 3 1	164
	21st to end	Day	25% 22% 35% 14% 4	260
February	1st to 10th	Day	31% 30% 32% 5% 3	240
	11th to 20th	Day	26% 33% 36% 5%	240
	21st to end	Day	36% 24% 31% 7% 1	244
March	1st to 10th	Day	26% 23% 37% 13% 1	420
	11th to 20th	Day	26% 23% 32% 14% 4 1	420
	21st to end	Day	31% 22% 29% 14% 4	462
April	1st to 10th	Day	27% 22% 34% 12% 5% 1	420
	11th to 20th	Day	32% 21% 23% 14% 8% 3	412
	21st to end	Day	30% 17% 33% 13% 5% 1	420
May	1st to 10th	Day	26% 17% 31% 18% 5% 2	423
	11th to 20th	Day	23% 19% 32% 16% 8% 2	447
	21st to end	Day	20% 19% 31% 19% 8% 3	485
June	1st to 10th	Day	22% 16% 36% 20% 4 1	450
	11th to 20th	Day	17% 16% 36% 20% 9% 2	503
	21st to end	Day	19% 15% 35% 21% 8% 2	630
July	1st to 10th	Day	13% 11% 35% 31% 9% 1	549
	11th to 20th	Day	15% 14% 32% 25% 11% 3	444
	21st to end	Day	13% 12% 38% 27% 8% 2	488
August	1st to 10th	Day	17% 10% 33% 25% 9% 6%	446
	11th to 20th	Day	16% 10% 26% 30% 12% 5%	439
	21st to end	Day	17% 14% 32% 22% 11% 4	495
September	1st to 10th	Day	17% 14% 32% 20% 12% 5%	450
	11th to 20th	Day	18% 12% 26% 22% 15% 6%	450
	21st to end	Day	20% 19% 26% 20% 11% 4	450
October	1st to 10th	Day	26% 20% 25% 15% 11% 3	450
	11th to 20th	Day	30% 26% 28% 11% 4 1	450
	21st to end	Day	39% 19% 27% 13% 3	477
November	1st to 10th	Day	31% 20% 33% 12% 3	239
	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	27% 20% 31% 17% 4 1	732
	21st to end	Night	17% 19% 35% 22% 6% 1	792
February	1st to 10th	Night	22% 23% 39% 12% 3	720
	11th to 20th	Night	20% 21% 41% 14% 3	703
	21st to end	Night	25% 22% 33% 18% 2	592
March	1st to 10th	Night	22% 23% 34% 18% 3	720
	11th to 20th	Night	22% 21% 35% 16% 5% 2	720
	21st to end	Night	18% 20% 35% 20% 6% 1	792
April	1st to 10th	Night	27% 18% 33% 18% 4	720
	11th to 20th	Night	25% 19% 28% 18% 9%	689
	21st to end	Night	24% 14% 29% 22% 10% 1	540
May	1st to 10th	Night	24% 10% 28% 28% 10%	425
	11th to 20th	Night	22% 11% 33% 26% 8%	354
	21st to end	Night	15% 11% 38% 25% 11%	389
June	1st to 10th	Night	19% 9% 38% 27% 7%	360
	11th to 20th	Night	19% 8% 31% 32% 11%	360
	21st to end	Night	18% 11% 27% 32% 12% 1	360
July	1st to 10th	Night	12% 6% 32% 35% 15% 1	350
	11th to 20th	Night	17% 7% 29% 32% 15% 1	348
	21st to end	Night	11% 6% 36% 35% 11% 1	394
August	1st to 10th	Night	12% 6% 27% 35% 18% 2	536
	11th to 20th	Night	9% 6% 25% 35% 22% 3	534
	21st to end	Night	16% 8% 32% 26% 17% 2	693
September	1st to 10th	Night	13% 9% 31% 29% 17% 2	720
	11th to 20th	Night	20% 9% 26% 26% 15% 3	720
	21st to end	Night	22% 11% 22% 27% 16% 2	720
October	1st to 10th	Night	25% 16% 27% 19% 10% 2	720
	11th to 20th	Night	28% 18% 31% 16% 7% 1	720
	21st to end	Night	34% 18% 28% 17% 3	792
November	1st to 10th	Night	29% 17% 29% 19% 6%	740
	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

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