McDonald Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the McDonald Park clear sky chart from 2005-11-06 to 2025-08-05.

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	22% 10% 3 7% 4 4 4 3 4 5% 32%	129874
	Night	26% 11% 3 7% 4 4 4 3 4 5% 30%	126903
Transparency	Day	31% 40% 10% 12% 6% 1	129585
	Night	35% 39% 10% 11% 5% 1	126769
Seeing	Day	28% 11% 24% 23% 11% 3	16157
	Night	34% 6% 16% 24% 17% 2	24375

By Month

Percentage Cloud Cover NW (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	39% 16% 4 9% 5% 3 3 3 4 3 12%	3179
	11th to 20th	Day	20% 12% 3 7% 4 4 4 2 4 5% 35%	3315
	21st to end	Day	35% 12% 3 6% 3 3 3 2 2 3 27%	4004
February	1st to 10th	Day	33% 12% 5% 9% 4 4 4 3 4 4 18%	1787
	11th to 20th	Day	30% 15% 4 7% 5% 4 3 3 4 4 22%	1755
	21st to end	Day	27% 18% 3 8% 6% 6% 3 3 3 3 19%	1537
March	1st to 10th	Day	23% 16% 4 9% 6% 4 4 3 4 6% 19%	4579
	11th to 20th	Day	21% 15% 5% 11% 6% 5% 4 2 4 4 23%	5000
	21st to end	Day	25% 14% 4 10% 6% 5% 5% 4 5% 5% 16%	5698
April	1st to 10th	Day	28% 13% 4 10% 5% 4 5% 4 4 5% 16%	2400
	11th to 20th	Day	23% 12% 4 10% 6% 5% 5% 3 5% 6% 22%	2422
	21st to end	Day	27% 11% 4 8% 6% 5% 4 3 5% 5% 22%	2693
May	1st to 10th	Day	17% 10% 3 8% 4 4 4 3 4 5% 38%	6320
	11th to 20th	Day	23% 10% 4 9% 5% 5% 4 4 6% 6% 23%	6277
	21st to end	Day	26% 9% 3 8% 4 5% 5% 4 6% 7% 24%	6903
June	1st to 10th	Day	25% 9% 3 7% 5% 5% 4 3 5% 6% 27%	2980
	11th to 20th	Day	28% 11% 4 8% 6% 4 4 4 5% 5% 20%	3000
	21st to end	Day	17% 9% 3 8% 5% 5% 5% 3 6% 6% 34%	3000
July	1st to 10th	Day	10% 4 1 4 3 3 3 3 4 6% 59%	6780
	11th to 20th	Day	6% 4 1 3 2 2 2 2 3 5% 69%	6740
	21st to end	Day	11% 4 1 4 3 3 3 3 5% 6% 57%	6874
August	1st to 10th	Day	7% 3 1 4 3 3 3 3 5% 6% 63%	4458
	11th to 20th	Day	13% 8% 4 6% 4 4 4 4 5% 7% 42%	4057
	21st to end	Day	17% 8% 3 8% 5% 4 4 3 4 6% 39%	4366
September	1st to 10th	Day	14% 7% 3 6% 4 3 3 3 4 6% 47%	2280
	11th to 20th	Day	18% 8% 3 8% 5% 5% 4 3 5% 4 38%	2280
	21st to end	Day	25% 6% 3 7% 4 4 4 3 4 4 36%	2012
October	1st to 10th	Day	23% 7% 3 6% 5% 4 5% 4 6% 7% 30%	3180
	11th to 20th	Day	37% 8% 3 7% 4 3 4 3 4 5% 23%	3161
	21st to end	Day	31% 12% 4 9% 5% 5% 5% 3 5% 6% 16%	3195
November	1st to 10th	Day	38% 10% 3 8% 5% 4 4 2 4 5% 17%	1575
	11th to 20th	Day	38% 14% 3 7% 4 2 3 2 3 3 21%	1600
	21st to end	Day	37% 12% 4 7% 4 4 3 2 4 4 19%	1600
December	1st to 10th	Day	24% 11% 3 9% 5% 4 4 3 4 4 28%	2620
	11th to 20th	Day	35% 16% 4 9% 4 3 4 2 4 3 14%	2749
	21st to end	Day	35% 17% 5% 10% 5% 4 4 3 4 4 10%	3498
January	1st to 10th	Night	37% 16% 5% 9% 5% 3 3 2 3 3 15%	6766
	11th to 20th	Night	22% 12% 2 5% 3 3 4 3 5% 6% 35%	6580
	21st to end	Night	32% 12% 4 7% 3 3 3 2 2 3 29%	6952
February	1st to 10th	Night	34% 13% 4 7% 5% 4 4 3 3 4 19%	2610
	11th to 20th	Night	30% 16% 3 7% 5% 4 3 2 3 4 22%	2532
	21st to end	Night	30% 14% 4 7% 5% 4 3 2 3 5% 23%	2092
March	1st to 10th	Night	22% 17% 4 8% 4 4 4 3 4 6% 22%	5315
	11th to 20th	Night	24% 16% 4 9% 4 4 4 2 4 4 25%	4999
	21st to end	Night	34% 15% 4 8% 5% 4 3 3 3 4 17%	5276
April	1st to 10th	Night	27% 14% 4 8% 5% 5% 5% 3 5% 5% 20%	2000
	11th to 20th	Night	23% 11% 3 8% 5% 6% 5% 4 4 5% 26%	1926
	21st to end	Night	30% 11% 3 8% 5% 4 3 4 5% 5% 22%	1706
May	1st to 10th	Night	16% 9% 4 8% 4 3 3 2 3 5% 42%	3640
	11th to 20th	Night	21% 11% 3 8% 5% 4 4 3 5% 5% 31%	3616
	21st to end	Night	19% 12% 3 9% 5% 5% 6% 4 5% 6% 26%	3972
June	1st to 10th	Night	19% 9% 3 8% 6% 6% 5% 3 5% 5% 31%	1417
	11th to 20th	Night	23% 10% 4 7% 6% 6% 4 4 6% 6% 24%	1400
	21st to end	Night	17% 8% 1 6% 4 4 4 3 5% 7% 41%	1400
July	1st to 10th	Night	10% 4 1 4 2 2 3 3 4 6% 62%	3180
	11th to 20th	Night	4 3 1 2 2 2 2 2 3 4 76%	3216
	21st to end	Night	8% 4 1 4 3 2 2 2 4 6% 64%	3969
August	1st to 10th	Night	6% 2 1 3 2 1 3 3 5% 7% 66%	2561
	11th to 20th	Night	10% 6% 2 6% 3 4 4 3 5% 7% 49%	2777
	21st to end	Night	18% 6% 2 7% 4 4 4 3 5% 8% 40%	3305
September	1st to 10th	Night	12% 5% 1 4 3 3 4 3 5% 7% 51%	1900
	11th to 20th	Night	19% 6% 3 7% 4 4 4 3 4 6% 41%	1900
	21st to end	Night	21% 8% 2 7% 4 3 4 3 4 5% 39%	2164
October	1st to 10th	Night	24% 10% 3 8% 5% 5% 5% 3 5% 5% 28%	3800
	11th to 20th	Night	37% 8% 2 5% 3 3 3 2 4 6% 28%	3777
	21st to end	Night	31% 12% 4 9% 4 4 4 3 4 4 22%	4366
November	1st to 10th	Night	38% 12% 4 6% 4 3 4 3 4 4 18%	2720
	11th to 20th	Night	39% 12% 3 6% 5% 4 2 2 3 4 20%	2800
	21st to end	Night	38% 12% 3 7% 4 4 3 3 3 4 19%	2800
December	1st to 10th	Night	24% 12% 3 7% 4 3 4 3 4 6% 29%	4560
	11th to 20th	Night	38% 15% 3 9% 4 4 3 3 3 4 13%	5451
	21st to end	Night	37% 17% 4 9% 5% 4 4 3 4 3 11%	7458

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	56% 27% 6% 8% 2	3179
	11th to 20th	Day	33% 28% 13% 17% 6% 2	3336
	21st to end	Day	44% 28% 7% 14% 6%	4004
February	1st to 10th	Day	28% 61% 2 2 5% 2	1787
	11th to 20th	Day	26% 61% 4 5% 3 1	1764
	21st to end	Day	26% 62% 4 4 3 1	1537
March	1st to 10th	Day	44% 30% 8% 13% 5%	4579
	11th to 20th	Day	43% 33% 8% 15% 1	5000
	21st to end	Day	47% 32% 11% 7% 3	5698
April	1st to 10th	Day	27% 63% 4 6%	2400
	11th to 20th	Day	22% 63% 5% 6% 2 1	2422
	21st to end	Day	24% 62% 5% 6% 3	2693
May	1st to 10th	Day	31% 31% 10% 20% 8%	6320
	11th to 20th	Day	43% 33% 15% 8% 1	6280
	21st to end	Day	39% 31% 16% 12% 1	6904
June	1st to 10th	Day	19% 62% 7% 8% 3	2980
	11th to 20th	Day	21% 62% 6% 7% 2	3000
	21st to end	Day	19% 61% 9% 9% 2	3000
July	1st to 10th	Day	15% 28% 17% 17% 16% 7%	6706
	11th to 20th	Day	10% 26% 15% 25% 20% 3	6659
	21st to end	Day	19% 29% 23% 22% 6%	6681
August	1st to 10th	Day	9% 38% 8% 28% 16% 1	4441
	11th to 20th	Day	26% 44% 15% 10% 4 1	4097
	21st to end	Day	30% 40% 8% 14% 8%	4365
September	1st to 10th	Day	19% 60% 6% 9% 5% 1	2280
	11th to 20th	Day	22% 60% 5% 6% 7% 1	2280
	21st to end	Day	21% 59% 7% 8% 5%	2012
October	1st to 10th	Day	33% 41% 11% 13% 3	3180
	11th to 20th	Day	42% 38% 8% 6% 6%	3161
	21st to end	Day	41% 42% 7% 7% 4	3195
November	1st to 10th	Day	30% 57% 6% 7% 1	1575
	11th to 20th	Day	29% 57% 4 6% 3 2	1600
	21st to end	Day	27% 57% 3 8% 4 1	1600
December	1st to 10th	Day	34% 39% 9% 11% 6%	2620
	11th to 20th	Day	53% 33% 7% 6% 1	2752
	21st to end	Day	57% 28% 10% 4 1	3498
January	1st to 10th	Night	55% 27% 7% 9% 2	6766
	11th to 20th	Night	31% 30% 15% 14% 6% 3	6621
	21st to end	Night	43% 29% 10% 14% 4	6952
February	1st to 10th	Night	26% 61% 3 3 4 2	2610
	11th to 20th	Night	28% 60% 3 6% 3 1	2534
	21st to end	Night	23% 62% 5% 7% 3 1	2092
March	1st to 10th	Night	43% 31% 9% 10% 7%	5315
	11th to 20th	Night	42% 32% 10% 15% 1	5000
	21st to end	Night	51% 30% 13% 5% 1	5276
April	1st to 10th	Night	25% 62% 5% 6% 1	2000
	11th to 20th	Night	22% 62% 7% 5% 3 1	1926
	21st to end	Night	23% 62% 6% 7% 2	1706
May	1st to 10th	Night	31% 29% 9% 23% 8%	3637
	11th to 20th	Night	40% 32% 17% 10% 1	3616
	21st to end	Night	40% 32% 15% 11% 1	3972
June	1st to 10th	Night	17% 62% 9% 8% 3	1417
	11th to 20th	Night	19% 63% 7% 8% 2	1400
	21st to end	Night	18% 60% 9% 11% 2	1400
July	1st to 10th	Night	14% 26% 15% 23% 15% 6%	3145
	11th to 20th	Night	8% 25% 14% 27% 24% 2	3174
	21st to end	Night	18% 26% 21% 23% 11% 1	3857
August	1st to 10th	Night	7% 38% 12% 28% 15% 1	2553
	11th to 20th	Night	21% 44% 20% 11% 3 1	2803
	21st to end	Night	28% 41% 12% 11% 7%	3305
September	1st to 10th	Night	18% 60% 7% 8% 6% 1	1900
	11th to 20th	Night	21% 60% 6% 6% 5% 2	1900
	21st to end	Night	20% 60% 6% 9% 4	2164
October	1st to 10th	Night	37% 42% 12% 7% 2	3800
	11th to 20th	Night	39% 39% 7% 11% 5%	3777
	21st to end	Night	39% 42% 7% 8% 3	4366
November	1st to 10th	Night	31% 56% 6% 5% 2	2720
	11th to 20th	Night	29% 57% 4 5% 4 2	2800
	21st to end	Night	29% 57% 3 4 5% 1	2800
December	1st to 10th	Night	33% 39% 12% 11% 5%	4560
	11th to 20th	Night	52% 34% 7% 5% 1	5447
	21st to end	Night	58% 29% 7% 4 2	7458

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	44% 16% 18% 13% 7% 4	200
	11th to 20th	Day	42% 13% 17% 18% 11% 1	200
	21st to end	Day	43% 9% 22% 16% 8% 2	220
February	1st to 10th	Day	46% 13% 20% 13% 6% 2	387
	11th to 20th	Day	42% 11% 24% 18% 4 1	395
	21st to end	Day	40% 13% 28% 14% 6% 1	359
March	1st to 10th	Day	36% 14% 26% 16% 8% 1	500
	11th to 20th	Day	36% 13% 22% 17% 11% 1	500
	21st to end	Day	38% 15% 21% 17% 8%	550
April	1st to 10th	Day	36% 15% 24% 17% 7% 1	500
	11th to 20th	Day	29% 15% 28% 17% 10% 1	492
	21st to end	Day	29% 17% 25% 17% 11% 2	500
May	1st to 10th	Day	22% 12% 30% 26% 9% 1	503
	11th to 20th	Day	26% 11% 24% 25% 11% 4	528
	21st to end	Day	29% 12% 23% 23% 10% 3	573
June	1st to 10th	Day	25% 12% 31% 23% 8% 2	710
	11th to 20th	Day	29% 14% 27% 23% 7% 1	730
	21st to end	Day	20% 12% 26% 27% 14% 2	730
July	1st to 10th	Day	16% 8% 29% 34% 10% 2	721
	11th to 20th	Day	12% 9% 27% 36% 14% 3	704
	21st to end	Day	11% 6% 24% 37% 15% 7%	575
August	1st to 10th	Day	13% 6% 23% 32% 17% 9%	504
	11th to 20th	Day	10% 5% 25% 31% 21% 7%	477
	21st to end	Day	18% 11% 23% 28% 15% 5%	539
September	1st to 10th	Day	19% 11% 23% 29% 15% 3	490
	11th to 20th	Day	23% 9% 21% 27% 15% 4	490
	21st to end	Day	28% 10% 22% 25% 12% 3	490
October	1st to 10th	Day	30% 9% 21% 21% 17% 3	490
	11th to 20th	Day	36% 10% 18% 21% 13% 3	490
	21st to end	Day	38% 13% 20% 17% 9% 2	387
November	1st to 10th	Day	40% 13% 22% 19% 5%	203
	11th to 20th	Day	50% 9% 15% 12% 11% 3	200
	21st to end	Day	47% 9% 20% 10% 11% 4	200
December	1st to 10th	Day	43% 8% 18% 15% 11% 6%	200
	11th to 20th	Day	51% 8% 20% 15% 5% 2	200
	21st to end	Day	48% 11% 20% 15% 5% 1	220
January	1st to 10th	Night	49% 10% 17% 15% 8% 1	900
	11th to 20th	Night	43% 8% 17% 21% 11% 1	865
	21st to end	Night	42% 8% 19% 22% 9% 1	880
February	1st to 10th	Night	43% 10% 21% 20% 6% 1	800
	11th to 20th	Night	42% 7% 20% 22% 8%	784
	21st to end	Night	39% 10% 20% 22% 8% 1	660
March	1st to 10th	Night	34% 10% 19% 23% 15% 1	800
	11th to 20th	Night	40% 6% 20% 22% 12% 1	800
	21st to end	Night	41% 8% 18% 23% 9% 2	880
April	1st to 10th	Night	37% 8% 16% 27% 11% 1	800
	11th to 20th	Night	30% 7% 22% 26% 14% 1	738
	21st to end	Night	36% 5% 15% 29% 14% 2	506
May	1st to 10th	Night	22% 8% 15% 31% 23% 1	400
	11th to 20th	Night	23% 3 11% 29% 29% 4	394
	21st to end	Night	26% 4 10% 32% 26% 3	433
June	1st to 10th	Night	23% 4 17% 33% 21% 4	400
	11th to 20th	Night	26% 6% 14% 28% 22% 5%	400
	21st to end	Night	21% 3 11% 30% 31% 4	400
July	1st to 10th	Night	14% 3 10% 30% 40% 3	390
	11th to 20th	Night	10% 4 9% 31% 40% 6%	388
	21st to end	Night	9% 3 3 28% 50% 7%	438
August	1st to 10th	Night	13% 1 4 22% 49% 11%	386
	11th to 20th	Night	10% 1 6% 25% 46% 12%	541
	21st to end	Night	16% 3 8% 30% 38% 5%	721
September	1st to 10th	Night	16% 2 11% 38% 28% 5%	760
	11th to 20th	Night	22% 4 14% 22% 32% 6%	760
	21st to end	Night	28% 5% 13% 28% 24% 3	760
October	1st to 10th	Night	29% 4 16% 26% 23% 2	760
	11th to 20th	Night	38% 5% 14% 24% 16% 3	760
	21st to end	Night	41% 8% 17% 23% 9% 2	836
November	1st to 10th	Night	47% 7% 19% 22% 5%	780
	11th to 20th	Night	51% 7% 17% 16% 8% 1	800
	21st to end	Night	46% 10% 17% 16% 10% 2	800
December	1st to 10th	Night	36% 7% 22% 23% 12% 1	800
	11th to 20th	Night	51% 7% 21% 16% 4 1	865
	21st to end	Night	51% 8% 21% 15% 3	990

Page generated at 2025-08-01 22:32:26. Version ac07

Copyright © 2025 Attilla Danko.