Wallace
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wallace clear sky chart from 2005-11-06 to 2025-09-19.

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% 11% 4 8% 5% 5% 4 4 5% 7% 30%	127630
	Night	18% 13% 4 9% 5% 5% 4 3 5% 6% 29%	121588
Transparency	Day	54% 4 12% 21% 9% 1	131181
	Night	56% 4 11% 20% 9% 1	126127
Seeing	Day	26% 19% 33% 17% 5% 1	18717
	Night	26% 17% 32% 19% 5%	25771

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% 23% 8% 17% 7% 4 4 3 3 3 14%	3616
	11th to 20th	Day	11% 17% 8% 12% 6% 5% 5% 3 5% 5% 22%	3591
	21st to end	Day	10% 11% 5% 12% 5% 6% 4 4 5% 6% 32%	4440
February	1st to 10th	Day	17% 14% 4 9% 7% 6% 4 3 4 5% 28%	1800
	11th to 20th	Day	16% 15% 5% 9% 6% 5% 5% 4 5% 5% 26%	1753
	21st to end	Day	10% 15% 5% 9% 6% 5% 5% 3 5% 8% 30%	1523
March	1st to 10th	Day	18% 14% 5% 11% 6% 5% 4 4 4 5% 23%	4831
	11th to 20th	Day	13% 15% 6% 11% 6% 5% 5% 4 5% 7% 24%	4980
	21st to end	Day	21% 19% 5% 10% 6% 4 4 3 4 4 19%	5511
April	1st to 10th	Day	22% 14% 3 8% 6% 4 4 3 4 6% 27%	2400
	11th to 20th	Day	20% 11% 3 8% 4 4 4 4 5% 7% 30%	2437
	21st to end	Day	21% 12% 3 7% 4 5% 4 4 5% 6% 29%	2600
May	1st to 10th	Day	30% 13% 2 6% 4 4 4 3 5% 6% 23%	6179
	11th to 20th	Day	21% 9% 3 7% 5% 5% 4 4 5% 6% 32%	6318
	21st to end	Day	18% 9% 3 7% 5% 4 4 4 6% 8% 32%	6948
June	1st to 10th	Day	25% 9% 2 7% 6% 4 4 5% 6% 7% 25%	2800
	11th to 20th	Day	20% 8% 2 6% 5% 4 4 3 6% 8% 34%	2970
	21st to end	Day	23% 9% 3 7% 6% 4 4 4 5% 6% 30%	3000
July	1st to 10th	Day	17% 8% 3 7% 5% 5% 5% 5% 7% 9% 29%	6775
	11th to 20th	Day	12% 6% 3 6% 4 4 4 4 6% 8% 42%	6360
	21st to end	Day	12% 6% 2 6% 5% 5% 5% 5% 6% 9% 39%	6913
August	1st to 10th	Day	15% 9% 3 8% 5% 5% 6% 4 7% 8% 31%	4235
	11th to 20th	Day	13% 6% 2 6% 4 5% 5% 5% 6% 8% 38%	4175
	21st to end	Day	11% 5% 2 6% 4 4 5% 4 6% 8% 45%	4480
September	1st to 10th	Day	17% 5% 2 5% 4 4 4 3 6% 7% 43%	2400
	11th to 20th	Day	17% 7% 2 7% 5% 4 5% 3 5% 7% 39%	2340
	21st to end	Day	18% 8% 3 4 4 4 4 3 5% 8% 38%	2005
October	1st to 10th	Day	19% 7% 3 7% 4 4 4 4 5% 8% 34%	1900
	11th to 20th	Day	19% 11% 3 8% 4 5% 5% 3 6% 8% 29%	1900
	21st to end	Day	18% 13% 3 9% 6% 4 5% 4 5% 6% 27%	2057
November	1st to 10th	Day	20% 15% 3 7% 5% 4 5% 4 5% 6% 27%	1605
	11th to 20th	Day	18% 17% 5% 9% 6% 6% 4 4 4 5% 22%	1600
	21st to end	Day	17% 17% 5% 8% 5% 5% 5% 4 5% 7% 22%	1600
December	1st to 10th	Day	15% 15% 5% 11% 5% 4 4 3 5% 5% 26%	2610
	11th to 20th	Day	18% 16% 5% 12% 6% 4 3 3 4 3 26%	2996
	21st to end	Day	16% 13% 11% 13% 6% 5% 6% 5% 4 4 17%	3982
January	1st to 10th	Night	14% 20% 5% 14% 7% 6% 4 3 3 3 18%	6349
	11th to 20th	Night	13% 17% 8% 13% 6% 5% 4 3 3 4 23%	6314
	21st to end	Night	10% 11% 6% 14% 6% 4 4 3 5% 5% 33%	6513
February	1st to 10th	Night	18% 14% 5% 10% 6% 4 4 3 5% 4 26%	2600
	11th to 20th	Night	17% 15% 4 11% 6% 5% 5% 4 4 6% 24%	2533
	21st to end	Night	12% 16% 5% 8% 5% 5% 4 5% 5% 5% 31%	2106
March	1st to 10th	Night	22% 15% 6% 11% 6% 5% 4 3 4 3 21%	5009
	11th to 20th	Night	18% 15% 5% 9% 5% 4 4 4 4 5% 25%	4979
	21st to end	Night	23% 17% 5% 12% 5% 4 4 3 3 3 22%	5421
April	1st to 10th	Night	21% 15% 4 8% 4 5% 5% 3 4 5% 26%	2000
	11th to 20th	Night	22% 12% 3 6% 3 3 4 4 4 5% 33%	1911
	21st to end	Night	24% 13% 4 7% 5% 4 4 3 4 5% 27%	1800
May	1st to 10th	Night	32% 12% 3 7% 4 5% 5% 3 4 5% 20%	3774
	11th to 20th	Night	21% 10% 3 7% 5% 4 5% 3 5% 7% 31%	3596
	21st to end	Night	17% 11% 3 7% 5% 6% 5% 4 6% 8% 30%	3948
June	1st to 10th	Night	24% 9% 3 7% 5% 3 4 4 5% 8% 29%	1600
	11th to 20th	Night	18% 8% 2 7% 3 3 4 4 5% 8% 39%	1444
	21st to end	Night	22% 8% 2 6% 5% 5% 5% 5% 6% 7% 30%	1400
July	1st to 10th	Night	13% 8% 3 9% 6% 6% 6% 4 8% 9% 28%	3160
	11th to 20th	Night	10% 8% 2 7% 4 5% 5% 4 6% 9% 40%	3614
	21st to end	Night	14% 7% 2 6% 5% 4 5% 4 7% 9% 38%	3948
August	1st to 10th	Night	15% 9% 3 6% 6% 5% 5% 4 6% 8% 32%	2914
	11th to 20th	Night	11% 7% 2 7% 5% 5% 5% 4 7% 8% 39%	2872
	21st to end	Night	13% 6% 2 5% 3 4 4 4 6% 8% 44%	3416
September	1st to 10th	Night	14% 5% 2 6% 4 4 4 4 6% 8% 43%	2000
	11th to 20th	Night	17% 6% 2 6% 4 4 3 3 6% 6% 43%	2014
	21st to end	Night	18% 7% 2 6% 4 4 5% 4 5% 7% 39%	2173
October	1st to 10th	Night	19% 6% 2 7% 4 4 4 3 6% 6% 38%	2280
	11th to 20th	Night	18% 9% 3 7% 5% 5% 4 3 7% 7% 33%	2280
	21st to end	Night	26% 11% 3 7% 5% 4 4 3 4 5% 28%	2541
November	1st to 10th	Night	19% 16% 4 8% 6% 4 4 3 4 4 28%	2690
	11th to 20th	Night	21% 14% 4 8% 6% 6% 5% 4 4 5% 23%	2800
	21st to end	Night	23% 17% 4 8% 5% 4 4 3 4 5% 22%	2800
December	1st to 10th	Night	15% 13% 4 9% 6% 5% 5% 3 5% 5% 30%	4580
	11th to 20th	Night	17% 16% 5% 10% 6% 6% 5% 3 4 4 25%	5213
	21st to end	Night	21% 14% 6% 16% 5% 4 4 2 3 5% 21%	6996

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	74% 2 11% 9% 3	3617
	11th to 20th	Day	65% 3 9% 15% 8% 1	3620
	21st to end	Day	55% 2 8% 16% 14% 5%	4440
February	1st to 10th	Day	61% 2 10% 15% 10% 1	1800
	11th to 20th	Day	61% 3 8% 17% 9% 1	1761
	21st to end	Day	55% 2 11% 18% 11% 2	1523
March	1st to 10th	Day	64% 3 7% 17% 8% 2	4835
	11th to 20th	Day	61% 3 13% 17% 5% 1	4980
	21st to end	Day	70% 2 5% 15% 6% 1	5511
April	1st to 10th	Day	62% 3 7% 15% 11% 3	2400
	11th to 20th	Day	56% 3 7% 21% 12% 1	2437
	21st to end	Day	57% 4 10% 17% 11% 2	2600
May	1st to 10th	Day	65% 3 9% 16% 7%	6191
	11th to 20th	Day	54% 3 13% 24% 5%	6322
	21st to end	Day	52% 4 13% 21% 10%	6948
June	1st to 10th	Day	59% 3 11% 20% 6%	2800
	11th to 20th	Day	50% 4 11% 25% 9% 1	2970
	21st to end	Day	56% 4 12% 18% 9% 1	3000
July	1st to 10th	Day	51% 5% 15% 20% 9%	6700
	11th to 20th	Day	40% 5% 15% 29% 10%	6284
	21st to end	Day	41% 7% 19% 27% 6%	6716
August	1st to 10th	Day	51% 6% 13% 23% 7%	4222
	11th to 20th	Day	43% 5% 13% 28% 11%	4214
	21st to end	Day	37% 5% 13% 29% 15% 1	4480
September	1st to 10th	Day	41% 4 14% 29% 13% 1	2400
	11th to 20th	Day	46% 3 12% 25% 12% 1	2340
	21st to end	Day	45% 4 11% 28% 12%	2005
October	1st to 10th	Day	50% 4 12% 25% 9%	3160
	11th to 20th	Day	48% 4 10% 29% 9%	3140
	21st to end	Day	46% 4 14% 23% 12% 1	3373
November	1st to 10th	Day	59% 5% 10% 19% 8%	1605
	11th to 20th	Day	61% 3 12% 18% 7%	1600
	21st to end	Day	60% 5% 13% 16% 6%	1600
December	1st to 10th	Day	58% 2 11% 25% 5%	2610
	11th to 20th	Day	62% 3 9% 15% 11% 1	2995
	21st to end	Day	67% 3 11% 15% 4 1	3982
January	1st to 10th	Night	67% 2 9% 18% 3	6349
	11th to 20th	Night	66% 3 8% 16% 7%	6360
	21st to end	Night	54% 2 7% 21% 13% 2	6513
February	1st to 10th	Night	61% 3 9% 13% 12% 2	2600
	11th to 20th	Night	62% 3 9% 15% 10% 1	2536
	21st to end	Night	55% 3 9% 21% 12% 2	2106
March	1st to 10th	Night	69% 3 4 12% 11% 2	5018
	11th to 20th	Night	61% 3 11% 17% 8% 1	4980
	21st to end	Night	69% 2 5% 15% 8% 1	5421
April	1st to 10th	Night	60% 4 9% 14% 11% 2	2000
	11th to 20th	Night	54% 2 7% 24% 12% 1	1911
	21st to end	Night	59% 3 8% 15% 13% 2	1800
May	1st to 10th	Night	66% 4 9% 14% 7%	3779
	11th to 20th	Night	55% 3 12% 21% 8% 1	3597
	21st to end	Night	53% 3 17% 20% 6%	3949
June	1st to 10th	Night	55% 4 11% 22% 8%	1600
	11th to 20th	Night	44% 3 13% 27% 12% 1	1444
	21st to end	Night	51% 7% 15% 17% 9% 1	1400
July	1st to 10th	Night	50% 6% 15% 22% 6% 1	3125
	11th to 20th	Night	40% 6% 19% 24% 10%	3567
	21st to end	Night	43% 6% 17% 24% 9%	3831
August	1st to 10th	Night	49% 7% 15% 24% 5%	2903
	11th to 20th	Night	41% 7% 18% 26% 8%	2899
	21st to end	Night	36% 5% 18% 28% 13%	3415
September	1st to 10th	Night	38% 4 13% 32% 12%	2000
	11th to 20th	Night	42% 3 13% 28% 12% 1	2014
	21st to end	Night	45% 4 12% 27% 12%	2173
October	1st to 10th	Night	51% 3 12% 24% 9%	3800
	11th to 20th	Night	40% 4 11% 33% 12%	3779
	21st to end	Night	51% 3 12% 22% 12% 1	4177
November	1st to 10th	Night	59% 3 13% 16% 8% 1	2690
	11th to 20th	Night	61% 3 12% 16% 8%	2800
	21st to end	Night	63% 4 13% 16% 4	2800
December	1st to 10th	Night	52% 4 11% 25% 8%	4580
	11th to 20th	Night	58% 6% 8% 18% 8% 2	5215
	21st to end	Night	67% 2 12% 14% 4	6996

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	31% 24% 29% 14% 2	400
	11th to 20th	Day	29% 24% 28% 16% 3	400
	21st to end	Day	21% 28% 37% 12% 3	440
February	1st to 10th	Day	30% 24% 32% 12% 2 1	400
	11th to 20th	Day	33% 28% 27% 11% 1	396
	21st to end	Day	24% 24% 31% 15% 5%	331
March	1st to 10th	Day	28% 26% 33% 11% 1	476
	11th to 20th	Day	24% 25% 33% 14% 4	500
	21st to end	Day	33% 26% 29% 11% 1	550
April	1st to 10th	Day	35% 30% 27% 6% 2	500
	11th to 20th	Day	32% 26% 29% 11% 2	492
	21st to end	Day	30% 21% 30% 15% 4	500
May	1st to 10th	Day	36% 20% 29% 9% 4 1	628
	11th to 20th	Day	27% 18% 31% 17% 5% 2	724
	21st to end	Day	28% 16% 37% 15% 3	790
June	1st to 10th	Day	34% 13% 31% 17% 5%	730
	11th to 20th	Day	25% 14% 36% 19% 5% 1	730
	21st to end	Day	28% 15% 30% 19% 6% 1	730
July	1st to 10th	Day	21% 11% 40% 21% 6% 1	720
	11th to 20th	Day	15% 10% 42% 24% 8%	718
	21st to end	Day	19% 10% 37% 25% 7%	793
August	1st to 10th	Day	14% 7% 41% 30% 7% 1	526
	11th to 20th	Day	20% 10% 32% 25% 10% 2	519
	21st to end	Day	16% 13% 34% 27% 8% 2	583
September	1st to 10th	Day	16% 16% 40% 19% 7% 2	530
	11th to 20th	Day	23% 15% 30% 24% 7% 1	522
	21st to end	Day	22% 16% 31% 22% 7% 2	445
October	1st to 10th	Day	22% 16% 34% 19% 7% 2	390
	11th to 20th	Day	23% 22% 32% 17% 6% 1	390
	21st to end	Day	26% 25% 31% 13% 4	429
November	1st to 10th	Day	29% 25% 30% 11% 4 1	395
	11th to 20th	Day	37% 24% 28% 7% 4 1	400
	21st to end	Day	36% 25% 28% 10% 2	400
December	1st to 10th	Day	36% 22% 31% 10% 2	400
	11th to 20th	Day	36% 27% 27% 9% 1	400
	21st to end	Day	25% 29% 30% 14% 2	440
January	1st to 10th	Night	29% 24% 31% 13% 3	900
	11th to 20th	Night	27% 24% 30% 16% 3	900
	21st to end	Night	20% 25% 34% 16% 3 1	885
February	1st to 10th	Night	29% 20% 31% 18% 2	800
	11th to 20th	Night	30% 25% 31% 11% 2	783
	21st to end	Night	20% 22% 34% 20% 4	660
March	1st to 10th	Night	27% 23% 33% 16% 2	800
	11th to 20th	Night	25% 19% 31% 19% 5% 1	800
	21st to end	Night	27% 21% 31% 16% 5%	860
April	1st to 10th	Night	31% 21% 28% 17% 3	600
	11th to 20th	Night	31% 17% 30% 15% 6%	594
	21st to end	Night	32% 13% 29% 20% 5% 1	600
May	1st to 10th	Night	34% 15% 28% 18% 6% 1	600
	11th to 20th	Night	28% 11% 32% 22% 6%	592
	21st to end	Night	23% 13% 42% 18% 4	649
June	1st to 10th	Night	29% 12% 33% 22% 4	600
	11th to 20th	Night	21% 12% 38% 23% 5%	444
	21st to end	Night	25% 10% 33% 26% 6% 1	400
July	1st to 10th	Night	19% 7% 42% 25% 6%	390
	11th to 20th	Night	15% 7% 43% 30% 5%	577
	21st to end	Night	18% 7% 37% 31% 7%	656
August	1st to 10th	Night	16% 6% 38% 30% 9% 1	598
	11th to 20th	Night	17% 7% 38% 29% 8% 1	592
	21st to end	Night	16% 9% 33% 33% 9%	660
September	1st to 10th	Night	15% 10% 41% 27% 6% 1	600
	11th to 20th	Night	21% 9% 32% 29% 8%	628
	21st to end	Night	22% 14% 33% 25% 6% 1	760
October	1st to 10th	Night	24% 12% 32% 25% 7%	760
	11th to 20th	Night	23% 17% 35% 18% 7% 1	760
	21st to end	Night	34% 21% 28% 14% 3	853
November	1st to 10th	Night	31% 21% 30% 13% 4	880
	11th to 20th	Night	31% 23% 27% 14% 4	900
	21st to end	Night	34% 23% 26% 15% 2	900
December	1st to 10th	Night	33% 20% 31% 13% 3	900
	11th to 20th	Night	32% 26% 29% 10% 3	900
	21st to end	Night	31% 24% 28% 13% 2 1	990

Page generated at 2025-09-16 02:49:16. Version ac07

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