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 2024-11-05.

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	18% 11% 4 8% 5% 4 4 4 5% 7% 30%	102262
	Night	18% 12% 4 9% 5% 5% 4 3 5% 6% 29%	96862
Transparency	Day	54% 4 12% 21% 9% 1	105831
	Night	56% 3 12% 20% 8% 1	101385
Seeing	Day	26% 19% 33% 17% 5% 1	17476
	Night	26% 17% 32% 19% 5%	24625

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	14% 16% 8% 16% 9% 4 4 3 3 4 20%	2526
	11th to 20th	Day	12% 14% 6% 11% 6% 5% 6% 4 5% 5% 27%	2530
	21st to end	Day	14% 11% 5% 14% 6% 5% 4 3 5% 6% 28%	3098
February	1st to 10th	Day	17% 14% 4 9% 6% 5% 4 3 4 5% 28%	1710
	11th to 20th	Day	17% 15% 4 9% 6% 4 5% 4 5% 5% 26%	1663
	21st to end	Day	10% 14% 5% 8% 6% 5% 5% 3 6% 8% 29%	1449
March	1st to 10th	Day	22% 15% 4 7% 5% 4 4 3 4 5% 28%	3359
	11th to 20th	Day	12% 19% 8% 12% 7% 5% 4 3 4 5% 21%	3480
	21st to end	Day	22% 19% 6% 9% 6% 4 4 3 4 3 20%	3847
April	1st to 10th	Day	21% 14% 3 8% 6% 4 4 3 4 6% 27%	2280
	11th to 20th	Day	20% 11% 3 7% 4 4 4 4 4 8% 31%	2314
	21st to end	Day	21% 12% 3 6% 4 5% 4 4 5% 6% 29%	2470
May	1st to 10th	Day	29% 13% 3 6% 4 4 4 3 4 6% 23%	4315
	11th to 20th	Day	18% 9% 2 7% 4 4 4 4 6% 7% 36%	4398
	21st to end	Day	16% 9% 3 8% 6% 4 5% 4 7% 8% 30%	4836
June	1st to 10th	Day	26% 10% 2 7% 6% 4 4 4 6% 7% 24%	2660
	11th to 20th	Day	21% 8% 2 6% 5% 4 4 3 6% 8% 33%	2821
	21st to end	Day	23% 9% 3 7% 6% 4 4 4 5% 6% 30%	2850
July	1st to 10th	Day	18% 7% 2 6% 5% 5% 5% 5% 7% 8% 33%	4729
	11th to 20th	Day	13% 7% 3 7% 5% 5% 5% 4 6% 9% 37%	4440
	21st to end	Day	13% 7% 2 6% 5% 4 5% 4 6% 9% 38%	4801
August	1st to 10th	Day	15% 9% 3 9% 5% 5% 6% 4 7% 8% 30%	4105
	11th to 20th	Day	13% 6% 3 6% 4 5% 5% 5% 6% 8% 38%	4045
	21st to end	Day	11% 5% 2 6% 4 4 4 4 6% 8% 45%	4343
September	1st to 10th	Day	17% 5% 2 5% 4 4 4 3 6% 7% 42%	2280
	11th to 20th	Day	17% 7% 2 7% 4 4 5% 3 5% 6% 39%	2244
	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 8% 5% 4 5% 3 5% 6% 27%	1558
	11th to 20th	Day	15% 17% 5% 10% 6% 6% 4 4 4 5% 23%	1520
	21st to end	Day	16% 17% 5% 8% 5% 5% 4 4 6% 7% 23%	1520
December	1st to 10th	Day	21% 18% 5% 10% 5% 4 5% 4 5% 5% 18%	1520
	11th to 20th	Day	20% 19% 6% 13% 6% 5% 4 3 4 3 16%	1906
	21st to end	Day	19% 15% 9% 12% 5% 4 4 3 4 4 20%	2783
January	1st to 10th	Night	13% 14% 5% 15% 8% 7% 4 3 4 4 23%	4429
	11th to 20th	Night	14% 12% 6% 11% 6% 6% 5% 3 4 5% 28%	4440
	21st to end	Night	13% 14% 5% 15% 6% 4 4 3 5% 5% 26%	4555
February	1st to 10th	Night	18% 14% 5% 10% 6% 4 4 4 5% 4 26%	2470
	11th to 20th	Night	17% 15% 4 11% 6% 5% 4 3 4 6% 23%	2403
	21st to end	Night	11% 16% 5% 8% 5% 5% 4 5% 5% 5% 30%	2004
March	1st to 10th	Night	23% 13% 5% 9% 5% 5% 4 3 4 4 23%	3481
	11th to 20th	Night	20% 19% 6% 10% 6% 4 4 3 4 4 20%	3479
	21st to end	Night	22% 16% 4 11% 6% 5% 4 3 3 3 22%	3785
April	1st to 10th	Night	21% 15% 4 8% 4 5% 4 4 4 5% 26%	1900
	11th to 20th	Night	21% 12% 3 6% 3 3 4 4 4 5% 34%	1815
	21st to end	Night	23% 13% 4 7% 5% 4 5% 3 4 6% 28%	1710
May	1st to 10th	Night	31% 12% 3 7% 4 5% 4 3 3 5% 22%	2632
	11th to 20th	Night	17% 9% 2 7% 5% 4 5% 3 6% 7% 35%	2506
	21st to end	Night	15% 10% 3 9% 6% 6% 6% 5% 6% 8% 27%	2749
June	1st to 10th	Night	25% 10% 3 7% 5% 3 4 3 5% 8% 28%	1520
	11th to 20th	Night	18% 8% 2 7% 3 3 3 4 5% 8% 38%	1372
	21st to end	Night	22% 8% 2 6% 5% 5% 5% 5% 6% 7% 30%	1330
July	1st to 10th	Night	14% 9% 3 8% 5% 6% 5% 4 8% 9% 31%	2210
	11th to 20th	Night	13% 7% 2 7% 5% 5% 5% 5% 7% 9% 35%	2524
	21st to end	Night	12% 7% 2 6% 4 4 4 3 6% 8% 42%	2750
August	1st to 10th	Night	15% 9% 3 7% 6% 5% 6% 4 7% 8% 30%	2824
	11th to 20th	Night	11% 7% 2 7% 5% 5% 5% 4 7% 8% 38%	2782
	21st to end	Night	13% 6% 2 5% 3 4 5% 4 6% 8% 44%	3311
September	1st to 10th	Night	14% 5% 2 7% 4 4 4 4 6% 8% 42%	1900
	11th to 20th	Night	17% 6% 2 6% 4 4 3 3 6% 6% 43%	1933
	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	20% 16% 4 8% 6% 4 4 3 4 5% 28%	2617
	11th to 20th	Night	19% 14% 4 9% 7% 6% 5% 4 5% 5% 24%	2660
	21st to end	Night	22% 17% 4 8% 5% 4 4 4 5% 6% 23%	2660
December	1st to 10th	Night	23% 17% 5% 10% 5% 5% 5% 3 5% 5% 18%	2660
	11th to 20th	Night	21% 19% 5% 11% 6% 5% 4 3 3 5% 19%	3293
	21st to end	Night	25% 15% 5% 12% 5% 3 3 2 3 5% 21%	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	68% 2 14% 10% 5%	2527
	11th to 20th	Day	61% 3 6% 19% 11% 1	2530
	21st to end	Day	61% 2 9% 15% 12% 1	3098
February	1st to 10th	Day	61% 2 10% 16% 10% 1	1710
	11th to 20th	Day	62% 3 9% 17% 9% 1	1671
	21st to end	Day	55% 2 11% 18% 11% 2	1449
March	1st to 10th	Day	62% 2 8% 20% 7% 1	3363
	11th to 20th	Day	67% 2 8% 16% 6% 1	3480
	21st to end	Day	72% 1 6% 13% 7% 1	3847
April	1st to 10th	Day	61% 3 7% 15% 11% 3	2280
	11th to 20th	Day	55% 3 7% 21% 13% 1	2314
	21st to end	Day	56% 4 10% 17% 11% 2	2470
May	1st to 10th	Day	66% 2 9% 17% 6% 1	4330
	11th to 20th	Day	50% 3 15% 25% 7%	4402
	21st to end	Day	53% 4 14% 20% 9% 1	4836
June	1st to 10th	Day	60% 3 11% 19% 6%	2660
	11th to 20th	Day	51% 3 11% 24% 9% 1	2821
	21st to end	Day	56% 4 12% 17% 9% 1	2850
July	1st to 10th	Day	48% 5% 14% 21% 12%	4654
	11th to 20th	Day	43% 6% 16% 26% 8%	4364
	21st to end	Day	43% 7% 18% 26% 6%	4648
August	1st to 10th	Day	52% 7% 13% 23% 5%	4092
	11th to 20th	Day	44% 5% 13% 27% 11%	4084
	21st to end	Day	37% 5% 13% 29% 15% 1	4343
September	1st to 10th	Day	41% 4 14% 28% 12% 1	2280
	11th to 20th	Day	46% 3 12% 25% 12% 1	2244
	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% 4 9% 19% 8%	1558
	11th to 20th	Day	59% 3 12% 19% 7%	1520
	21st to end	Day	59% 5% 14% 16% 7%	1520
December	1st to 10th	Day	67% 2 12% 15% 4	1520
	11th to 20th	Day	71% 3 7% 14% 4 1	1905
	21st to end	Day	69% 1 14% 11% 4 1	2783
January	1st to 10th	Night	60% 1 12% 22% 4	4429
	11th to 20th	Night	60% 3 8% 19% 10% 1	4440
	21st to end	Night	62% 2 9% 20% 7%	4555
February	1st to 10th	Night	61% 3 9% 13% 11% 2	2470
	11th to 20th	Night	63% 3 9% 14% 10% 1	2406
	21st to end	Night	55% 2 9% 20% 12% 2	2004
March	1st to 10th	Night	68% 2 4 16% 8% 2	3490
	11th to 20th	Night	68% 2 7% 16% 6% 1	3480
	21st to end	Night	69% 2 6% 15% 8% 1	3785
April	1st to 10th	Night	60% 4 9% 14% 11% 3	1900
	11th to 20th	Night	54% 2 7% 24% 12% 1	1815
	21st to end	Night	58% 4 8% 15% 14% 2	1710
May	1st to 10th	Night	67% 2 10% 15% 6% 1	2637
	11th to 20th	Night	51% 2 16% 23% 8% 1	2507
	21st to end	Night	55% 3 18% 18% 5%	2750
June	1st to 10th	Night	56% 4 12% 21% 7%	1520
	11th to 20th	Night	46% 3 13% 26% 11% 1	1372
	21st to end	Night	51% 7% 15% 18% 9% 1	1330
July	1st to 10th	Night	48% 6% 17% 21% 7% 1	2175
	11th to 20th	Night	43% 6% 22% 20% 8%	2477
	21st to end	Night	41% 6% 17% 25% 10%	2663
August	1st to 10th	Night	50% 7% 16% 23% 4	2813
	11th to 20th	Night	41% 7% 18% 26% 8%	2809
	21st to end	Night	36% 5% 18% 28% 13%	3310
September	1st to 10th	Night	39% 4 14% 31% 12%	1900
	11th to 20th	Night	41% 3 14% 28% 13% 1	1933
	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	2617
	11th to 20th	Night	59% 3 12% 17% 8%	2660
	21st to end	Night	62% 4 14% 17% 4	2660
December	1st to 10th	Night	66% 3 10% 16% 4	2660
	11th to 20th	Night	68% 3 7% 17% 5%	3295
	21st to end	Night	68% 1 14% 12% 4 1	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	29% 25% 29% 14% 2	370
	11th to 20th	Day	30% 25% 28% 14% 3	370
	21st to end	Day	21% 26% 37% 13% 3	407
February	1st to 10th	Day	29% 25% 30% 13% 2 1	370
	11th to 20th	Day	32% 28% 27% 11% 1	366
	21st to end	Day	23% 25% 32% 15% 4	307
March	1st to 10th	Day	28% 26% 33% 12% 1	438
	11th to 20th	Day	25% 25% 32% 14% 4	460
	21st to end	Day	33% 25% 29% 11% 1	506
April	1st to 10th	Day	34% 30% 28% 7% 2	460
	11th to 20th	Day	30% 26% 30% 11% 2	452
	21st to end	Day	29% 20% 31% 15% 4	460
May	1st to 10th	Day	36% 20% 28% 10% 5% 1	582
	11th to 20th	Day	26% 18% 31% 18% 6% 2	674
	21st to end	Day	28% 16% 38% 15% 3	735
June	1st to 10th	Day	35% 13% 31% 16% 5%	680
	11th to 20th	Day	25% 14% 36% 19% 4 1	680
	21st to end	Day	28% 14% 31% 20% 7% 1	680
July	1st to 10th	Day	20% 11% 40% 21% 7% 1	670
	11th to 20th	Day	15% 10% 43% 24% 8%	668
	21st to end	Day	20% 9% 37% 26% 8%	738
August	1st to 10th	Day	15% 6% 41% 30% 7% 1	486
	11th to 20th	Day	21% 10% 32% 25% 10% 2	479
	21st to end	Day	16% 12% 33% 28% 9% 3	539
September	1st to 10th	Day	17% 17% 40% 19% 7% 1	490
	11th to 20th	Day	24% 16% 29% 24% 7% 1	490
	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	30% 25% 29% 12% 4 1	378
	11th to 20th	Day	33% 24% 30% 8% 4 1	370
	21st to end	Day	33% 26% 28% 10% 2	370
December	1st to 10th	Day	37% 22% 30% 9% 2	370
	11th to 20th	Day	36% 28% 27% 9%	370
	21st to end	Day	27% 30% 29% 13% 1	407
January	1st to 10th	Night	28% 23% 32% 14% 3	850
	11th to 20th	Night	27% 24% 30% 15% 3	850
	21st to end	Night	21% 24% 34% 17% 3 1	841
February	1st to 10th	Night	29% 20% 31% 18% 2	760
	11th to 20th	Night	30% 25% 31% 11% 2	743
	21st to end	Night	20% 21% 34% 20% 4	628
March	1st to 10th	Night	26% 22% 34% 16% 2	760
	11th to 20th	Night	25% 19% 30% 20% 5% 1	760
	21st to end	Night	27% 21% 30% 16% 5%	817
April	1st to 10th	Night	29% 21% 29% 18% 3	570
	11th to 20th	Night	29% 17% 31% 16% 6%	564
	21st to end	Night	32% 13% 29% 20% 5% 1	570
May	1st to 10th	Night	33% 15% 28% 18% 6% 1	570
	11th to 20th	Night	27% 11% 32% 22% 7%	562
	21st to end	Night	23% 13% 42% 18% 4	616
June	1st to 10th	Night	29% 12% 33% 21% 4	570
	11th to 20th	Night	21% 12% 37% 24% 6%	422
	21st to end	Night	25% 10% 33% 26% 6% 1	380
July	1st to 10th	Night	20% 7% 42% 25% 6%	370
	11th to 20th	Night	15% 7% 43% 30% 5%	547
	21st to end	Night	18% 7% 37% 31% 7%	623
August	1st to 10th	Night	16% 7% 39% 29% 8% 1	568
	11th to 20th	Night	18% 7% 37% 29% 8% 1	562
	21st to end	Night	16% 9% 33% 33% 9%	627
September	1st to 10th	Night	16% 10% 41% 27% 6% 1	570
	11th to 20th	Night	22% 9% 33% 28% 8%	603
	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% 20% 30% 14% 4	854
	11th to 20th	Night	28% 24% 28% 15% 4	850
	21st to end	Night	32% 23% 27% 16% 2	850
December	1st to 10th	Night	34% 20% 30% 13% 3	850
	11th to 20th	Night	32% 26% 29% 10% 3	850
	21st to end	Night	32% 24% 29% 12% 2 1	935

Page generated at 2024-11-03 03:11:12. Version ac07

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