McCleary
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the McCleary clear sky chart from 2005-11-06 to 2026-02-01.

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% 11% 3 7% 5% 4 4 3 5% 6% 30%	131889
	Night	23% 12% 3 7% 4 4 4 3 4 5% 29%	128808
Transparency	Day	53% 8% 13% 17% 8% 1	131602
	Night	54% 8% 13% 17% 7% 1	128672
Seeing	Day	25% 13% 24% 23% 13% 3	16752
	Night	28% 9% 21% 27% 14% 1	25215

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% 15% 4 10% 5% 5% 4 3 4 4 8%	3249
	11th to 20th	Day	22% 12% 3 7% 5% 4 4 4 6% 7% 26%	3600
	21st to end	Day	35% 12% 3 7% 4 3 3 2 3 5% 24%	4392
February	1st to 10th	Day	32% 14% 3 10% 6% 4 6% 3 5% 5% 11%	1801
	11th to 20th	Day	34% 16% 4 8% 5% 4 4 3 4 4 16%	1755
	21st to end	Day	31% 16% 4 8% 6% 4 3 3 4 5% 15%	1518
March	1st to 10th	Day	24% 15% 5% 10% 7% 7% 5% 3 5% 5% 14%	4755
	11th to 20th	Day	28% 16% 4 8% 4 4 3 2 3 4 24%	5000
	21st to end	Day	30% 15% 5% 11% 6% 5% 5% 4 4 4 11%	5572
April	1st to 10th	Day	31% 13% 4 10% 5% 5% 5% 4 5% 5% 14%	2400
	11th to 20th	Day	26% 12% 4 8% 6% 5% 4 3 4 5% 23%	2435
	21st to end	Day	23% 12% 4 8% 6% 5% 4 4 5% 6% 22%	2600
May	1st to 10th	Day	17% 9% 3 7% 5% 4 5% 3 5% 6% 35%	6276
	11th to 20th	Day	17% 11% 4 8% 5% 5% 6% 5% 6% 8% 25%	6277
	21st to end	Day	20% 9% 3 8% 6% 6% 5% 4 7% 7% 25%	6903
June	1st to 10th	Day	22% 11% 3 8% 5% 5% 4 3 5% 8% 27%	2885
	11th to 20th	Day	19% 12% 4 10% 5% 6% 6% 5% 7% 6% 21%	3000
	21st to end	Day	15% 9% 3 8% 5% 5% 4 4 6% 6% 34%	3000
July	1st to 10th	Day	8% 5% 2 4 2 3 2 2 4 6% 62%	6780
	11th to 20th	Day	6% 6% 2 5% 3 2 3 2 4 5% 62%	6564
	21st to end	Day	10% 9% 3 5% 3 3 3 3 4 6% 50%	6874
August	1st to 10th	Day	7% 9% 2 5% 3 3 4 3 5% 7% 52%	4327
	11th to 20th	Day	12% 8% 3 7% 5% 5% 5% 4 7% 8% 35%	4156
	21st to end	Day	17% 9% 3 5% 4 3 4 3 4 6% 42%	4515
September	1st to 10th	Day	11% 8% 3 7% 5% 4 4 3 5% 7% 44%	2400
	11th to 20th	Day	16% 9% 4 8% 5% 5% 3 3 5% 7% 35%	2375
	21st to end	Day	20% 8% 3 7% 4 4 5% 3 4 6% 36%	2118
October	1st to 10th	Day	17% 7% 2 6% 4 4 5% 4 6% 10% 35%	3280
	11th to 20th	Day	31% 9% 3 6% 5% 4 3 3 5% 8% 23%	3261
	21st to end	Day	28% 9% 4 8% 6% 4 5% 4 5% 6% 20%	3447
November	1st to 10th	Day	37% 12% 3 8% 5% 5% 5% 3 5% 5% 12%	1658
	11th to 20th	Day	36% 11% 3 8% 6% 5% 5% 3 5% 4 15%	1680
	21st to end	Day	33% 11% 4 7% 5% 5% 4 3 4 5% 18%	1680
December	1st to 10th	Day	26% 10% 3 9% 6% 5% 4 3 4 5% 25%	2700
	11th to 20th	Day	40% 13% 4 8% 5% 5% 4 3 5% 5% 7%	3081
	21st to end	Day	36% 17% 5% 10% 5% 5% 4 3 4 4 8%	3575
January	1st to 10th	Night	38% 17% 4 9% 5% 4 4 3 4 4 10%	6916
	11th to 20th	Night	22% 11% 3 7% 4 4 4 3 6% 8% 29%	6500
	21st to end	Night	33% 11% 4 7% 3 3 3 2 3 4 27%	6816
February	1st to 10th	Night	31% 14% 4 7% 5% 4 4 3 4 6% 18%	2600
	11th to 20th	Night	29% 16% 3 8% 5% 4 2 3 4 4 22%	2532
	21st to end	Night	29% 15% 3 8% 5% 4 4 3 5% 5% 20%	2111
March	1st to 10th	Night	19% 17% 5% 11% 7% 5% 4 3 5% 6% 19%	5124
	11th to 20th	Night	24% 15% 4 7% 4 3 3 3 4 4 29%	4999
	21st to end	Night	33% 17% 4 10% 5% 4 4 3 4 5% 13%	5402
April	1st to 10th	Night	26% 13% 4 9% 5% 5% 4 4 4 5% 21%	2000
	11th to 20th	Night	19% 11% 3 9% 5% 5% 4 4 5% 7% 28%	1911
	21st to end	Night	21% 11% 3 8% 5% 5% 4 3 5% 6% 29%	1800
May	1st to 10th	Night	17% 8% 3 5% 4 3 3 3 3 5% 47%	3686
	11th to 20th	Night	16% 13% 3 8% 4 4 4 4 5% 6% 33%	3616
	21st to end	Night	13% 17% 3 7% 4 4 4 4 6% 8% 29%	3972
June	1st to 10th	Night	18% 9% 2 7% 5% 4 4 4 6% 7% 36%	1510
	11th to 20th	Night	14% 7% 2 8% 6% 4 5% 5% 7% 8% 34%	1400
	21st to end	Night	10% 9% 2 8% 5% 3 3 3 5% 8% 44%	1400
July	1st to 10th	Night	4 6% 2 4 3 2 2 2 3 5% 68%	3180
	11th to 20th	Night	3 5% 2 5% 4 3 4 2 4 6% 61%	3382
	21st to end	Night	6% 11% 4 7% 3 3 3 2 3 6% 51%	3969
August	1st to 10th	Night	4 10% 4 7% 4 3 3 3 4 7% 50%	2828
	11th to 20th	Night	11% 13% 3 8% 3 3 3 2 4 5% 45%	2902
	21st to end	Night	17% 9% 2 5% 3 3 3 2 4 6% 47%	3397
September	1st to 10th	Night	8% 7% 3 7% 3 3 3 2 4 7% 54%	2000
	11th to 20th	Night	15% 9% 3 6% 4 4 4 4 5% 7% 40%	2020
	21st to end	Night	17% 9% 4 7% 4 4 3 3 4 7% 40%	2281
October	1st to 10th	Night	15% 7% 2 6% 4 3 4 3 5% 8% 42%	3920
	11th to 20th	Night	29% 11% 3 6% 3 3 3 3 4 5% 30%	3897
	21st to end	Night	28% 10% 3 7% 4 4 4 3 5% 5% 26%	4359
November	1st to 10th	Night	35% 11% 3 6% 4 4 4 3 5% 4 19%	2855
	11th to 20th	Night	35% 12% 3 7% 6% 4 4 3 4 4 19%	2940
	21st to end	Night	31% 10% 3 8% 5% 5% 5% 4 5% 4 21%	2940
December	1st to 10th	Night	25% 10% 3 7% 4 5% 4 3 5% 7% 26%	4700
	11th to 20th	Night	41% 15% 4 8% 4 4 4 3 4 4 10%	5320
	21st to end	Night	36% 17% 5% 9% 5% 4 4 3 3 3 11%	7623

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	79% 7% 6% 5% 2	3249
	11th to 20th	Day	56% 10% 11% 17% 6% 1	3624
	21st to end	Day	65% 5% 7% 14% 9%	4392
February	1st to 10th	Day	73% 8% 9% 7% 3	1801
	11th to 20th	Day	73% 6% 7% 8% 5% 1	1764
	21st to end	Day	71% 6% 7% 10% 5% 1	1518
March	1st to 10th	Day	69% 8% 11% 10% 2	4755
	11th to 20th	Day	63% 6% 10% 19% 2 1	5000
	21st to end	Day	74% 8% 10% 7% 1	5572
April	1st to 10th	Day	69% 7% 13% 9% 1	2400
	11th to 20th	Day	63% 6% 11% 13% 7% 1	2435
	21st to end	Day	61% 7% 13% 14% 4 1	2600
May	1st to 10th	Day	46% 8% 15% 21% 11%	6276
	11th to 20th	Day	50% 13% 19% 15% 3	6280
	21st to end	Day	52% 10% 19% 15% 3	6904
June	1st to 10th	Day	55% 7% 17% 15% 6%	2885
	11th to 20th	Day	60% 9% 13% 15% 3	3000
	21st to end	Day	46% 9% 17% 19% 7% 2	3000
July	1st to 10th	Day	23% 6% 18% 21% 20% 12%	6706
	11th to 20th	Day	20% 5% 14% 29% 29% 3	6483
	21st to end	Day	30% 8% 17% 32% 12% 1	6681
August	1st to 10th	Day	26% 7% 14% 29% 21% 3	4310
	11th to 20th	Day	41% 11% 20% 19% 8% 2	4195
	21st to end	Day	42% 7% 11% 25% 14% 1	4514
September	1st to 10th	Day	39% 7% 15% 20% 14% 5%	2400
	11th to 20th	Day	47% 7% 11% 18% 14% 2	2375
	21st to end	Day	49% 7% 14% 18% 11% 1	2118
October	1st to 10th	Day	43% 8% 13% 30% 6%	3280
	11th to 20th	Day	58% 7% 13% 14% 7%	3261
	21st to end	Day	62% 9% 11% 11% 8% 1	3447
November	1st to 10th	Day	72% 8% 8% 8% 3	1658
	11th to 20th	Day	73% 7% 7% 8% 5% 1	1680
	21st to end	Day	69% 7% 7% 10% 7%	1680
December	1st to 10th	Day	61% 6% 6% 12% 13%	2700
	11th to 20th	Day	78% 8% 7% 6% 1	3084
	21st to end	Day	80% 8% 7% 4 2	3575
January	1st to 10th	Night	76% 8% 8% 5% 2 1	6916
	11th to 20th	Night	50% 10% 12% 20% 6% 1	6538
	21st to end	Night	61% 5% 6% 15% 10% 1	6816
February	1st to 10th	Night	68% 7% 11% 9% 5%	2600
	11th to 20th	Night	66% 7% 10% 9% 8% 1	2534
	21st to end	Night	67% 6% 11% 11% 5%	2111
March	1st to 10th	Night	64% 7% 12% 12% 5%	5124
	11th to 20th	Night	57% 7% 14% 19% 2 1	5000
	21st to end	Night	73% 9% 11% 7% 1	5402
April	1st to 10th	Night	63% 7% 14% 15% 2	2000
	11th to 20th	Night	55% 6% 16% 14% 8% 1	1911
	21st to end	Night	54% 8% 15% 16% 7% 1	1800
May	1st to 10th	Night	39% 6% 13% 31% 11%	3683
	11th to 20th	Night	45% 11% 22% 16% 7%	3616
	21st to end	Night	48% 12% 21% 18% 1	3972
June	1st to 10th	Night	45% 7% 20% 21% 6% 1	1510
	11th to 20th	Night	44% 10% 22% 22% 2	1400
	21st to end	Night	36% 8% 26% 21% 6% 3	1400
July	1st to 10th	Night	18% 6% 24% 26% 16% 11%	3145
	11th to 20th	Night	16% 8% 17% 31% 26% 3	3340
	21st to end	Night	26% 10% 16% 33% 13% 3	3857
August	1st to 10th	Night	21% 9% 18% 28% 20% 3	2820
	11th to 20th	Night	36% 9% 22% 20% 10% 3	2929
	21st to end	Night	38% 5% 14% 26% 15% 2	3397
September	1st to 10th	Night	27% 8% 18% 25% 16% 5%	2000
	11th to 20th	Night	40% 7% 14% 20% 15% 4	2020
	21st to end	Night	42% 7% 14% 22% 13% 2	2281
October	1st to 10th	Night	38% 7% 15% 33% 7%	3920
	11th to 20th	Night	55% 5% 12% 21% 6%	3897
	21st to end	Night	57% 8% 11% 15% 8% 1	4359
November	1st to 10th	Night	66% 8% 10% 12% 4	2855
	11th to 20th	Night	69% 6% 9% 9% 5% 1	2940
	21st to end	Night	64% 8% 11% 8% 8% 1	2940
December	1st to 10th	Night	57% 7% 11% 14% 11%	4700
	11th to 20th	Night	78% 7% 8% 5% 2	5316
	21st to end	Night	77% 8% 7% 7% 2	7623

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% 14% 20% 15% 6%	220
	11th to 20th	Day	37% 11% 22% 21% 7% 1	220
	21st to end	Day	39% 12% 18% 21% 9% 1	373
February	1st to 10th	Day	38% 16% 18% 21% 7% 1	401
	11th to 20th	Day	42% 11% 27% 13% 6%	395
	21st to end	Day	38% 20% 19% 17% 5% 1	349
March	1st to 10th	Day	34% 16% 23% 20% 7% 1	500
	11th to 20th	Day	33% 13% 24% 16% 10% 4	500
	21st to end	Day	35% 15% 25% 15% 8% 1	550
April	1st to 10th	Day	35% 16% 23% 17% 8% 2	500
	11th to 20th	Day	28% 17% 25% 17% 9% 3	492
	21st to end	Day	27% 18% 26% 18% 10% 1	500
May	1st to 10th	Day	22% 12% 25% 27% 13% 2	503
	11th to 20th	Day	28% 14% 20% 20% 14% 4	528
	21st to end	Day	21% 11% 27% 28% 10% 4	573
June	1st to 10th	Day	23% 13% 26% 22% 12% 4	615
	11th to 20th	Day	20% 18% 34% 19% 7% 2	730
	21st to end	Day	14% 14% 28% 26% 15% 3	730
July	1st to 10th	Day	11% 10% 28% 34% 15% 3	721
	11th to 20th	Day	8% 8% 28% 31% 20% 6%	632
	21st to end	Day	7% 6% 23% 31% 23% 9%	575
August	1st to 10th	Day	11% 8% 21% 30% 22% 8%	527
	11th to 20th	Day	9% 6% 21% 29% 27% 8%	517
	21st to end	Day	15% 10% 24% 28% 16% 7%	583
September	1st to 10th	Day	13% 9% 23% 31% 18% 6%	530
	11th to 20th	Day	17% 11% 23% 27% 19% 3	530
	21st to end	Day	21% 11% 22% 30% 15% 2	530
October	1st to 10th	Day	25% 10% 23% 20% 18% 3	530
	11th to 20th	Day	31% 11% 20% 23% 14% 2	530
	21st to end	Day	32% 20% 21% 17% 9% 2	521
November	1st to 10th	Day	38% 15% 20% 17% 7% 2	225
	11th to 20th	Day	42% 15% 18% 15% 9% 1	220
	21st to end	Day	33% 14% 17% 23% 12% 1	220
December	1st to 10th	Day	42% 13% 17% 19% 8% 1	220
	11th to 20th	Day	49% 13% 19% 14% 5% 1	220
	21st to end	Day	45% 11% 21% 18% 5%	242
January	1st to 10th	Night	48% 12% 16% 16% 7%	950
	11th to 20th	Night	37% 8% 14% 30% 11%	859
	21st to end	Night	35% 7% 16% 27% 13% 1	924
February	1st to 10th	Night	36% 12% 16% 24% 11% 1	800
	11th to 20th	Night	35% 13% 20% 22% 10%	784
	21st to end	Night	34% 13% 20% 22% 10% 1	660
March	1st to 10th	Night	32% 10% 20% 23% 13% 2	800
	11th to 20th	Night	35% 10% 21% 24% 10% 1	800
	21st to end	Night	34% 13% 23% 21% 9% 1	880
April	1st to 10th	Night	30% 12% 22% 24% 11% 1	800
	11th to 20th	Night	22% 13% 23% 28% 13% 1	723
	21st to end	Night	24% 11% 22% 31% 12%	600
May	1st to 10th	Night	18% 9% 23% 36% 13% 1	420
	11th to 20th	Night	20% 8% 28% 29% 14% 2	394
	21st to end	Night	17% 9% 29% 29% 15% 1	433
June	1st to 10th	Night	17% 10% 26% 35% 12%	400
	11th to 20th	Night	13% 10% 38% 28% 11%	400
	21st to end	Night	11% 8% 31% 33% 17% 1	400
July	1st to 10th	Night	6% 6% 29% 42% 16% 1	390
	11th to 20th	Night	6% 5% 27% 43% 17% 1	388
	21st to end	Night	4 4 31% 40% 18% 2	438
August	1st to 10th	Night	8% 5% 21% 37% 26% 3	526
	11th to 20th	Night	8% 4 16% 34% 33% 5%	594
	21st to end	Night	12% 6% 25% 33% 21% 3	747
September	1st to 10th	Night	10% 5% 23% 32% 27% 3	800
	11th to 20th	Night	15% 8% 18% 31% 25% 3	800
	21st to end	Night	20% 8% 20% 31% 19% 2	800
October	1st to 10th	Night	20% 8% 17% 31% 23% 3	800
	11th to 20th	Night	29% 6% 17% 26% 20% 3	800
	21st to end	Night	31% 9% 21% 25% 14% 1	880
November	1st to 10th	Night	38% 8% 18% 27% 8% 1	820
	11th to 20th	Night	38% 11% 18% 24% 8% 1	840
	21st to end	Night	33% 9% 20% 25% 12% 2	840
December	1st to 10th	Night	35% 7% 18% 27% 12% 1	840
	11th to 20th	Night	44% 8% 16% 24% 7% 1	840
	21st to end	Night	43% 12% 20% 18% 7%	1045

Page generated at 2026-01-28 22:21:42. Version ac07

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