Twin Dogs Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Twin Dogs Observatory clear sky chart from 2005-11-06 to 2024-01-15.

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	19% 9% 4 7% 7% 4 5% 5% 5% 6% 30%	74608
	Night	17% 10% 4 7% 6% 3 5% 5% 5% 6% 32%	75164
Transparency	Day	54% 8% 12% 17% 9% 1	74301
	Night	52% 7% 13% 18% 9% 1	75006
Seeing	Day	25% 19% 31% 17% 7% 1	14724
	Night	23% 16% 32% 22% 6%	22957

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	15% 15% 7% 10% 8% 4 5% 5% 4 6% 21%	1360
	11th to 20th	Day	17% 14% 5% 10% 7% 4 5% 5% 5% 6% 22%	1472
	21st to end	Day	11% 10% 5% 10% 7% 4 5% 6% 6% 6% 30%	1584
February	1st to 10th	Day	10% 13% 6% 10% 9% 6% 5% 6% 5% 7% 23%	1566
	11th to 20th	Day	14% 16% 5% 10% 9% 4 5% 5% 5% 6% 22%	1611
	21st to end	Day	13% 11% 5% 9% 9% 5% 5% 5% 5% 6% 28%	1480
March	1st to 10th	Day	17% 13% 6% 9% 7% 3 4 4 4 6% 26%	1801
	11th to 20th	Day	17% 13% 5% 9% 8% 3 5% 4 4 6% 26%	1980
	21st to end	Day	16% 13% 6% 11% 6% 3 4 3 4 5% 29%	2178
April	1st to 10th	Day	22% 15% 4 8% 8% 3 4 4 4 5% 23%	2167
	11th to 20th	Day	20% 10% 3 6% 7% 3 4 5% 4 6% 33%	2312
	21st to end	Day	26% 11% 3 6% 5% 2 4 4 4 5% 31%	2340
May	1st to 10th	Day	24% 9% 4 6% 6% 3 4 4 5% 6% 29%	2340
	11th to 20th	Day	23% 8% 3 6% 6% 3 4 4 4 5% 34%	2439
	21st to end	Day	20% 7% 3 6% 7% 3 5% 5% 6% 7% 31%	2919
June	1st to 10th	Day	22% 7% 4 7% 7% 4 5% 4 6% 8% 26%	2700
	11th to 20th	Day	21% 6% 3 7% 6% 4 5% 4 5% 7% 31%	2700
	21st to end	Day	24% 9% 3 7% 7% 4 5% 5% 5% 6% 25%	2700
July	1st to 10th	Day	16% 7% 4 6% 6% 5% 6% 6% 7% 8% 30%	2700
	11th to 20th	Day	16% 6% 3 7% 7% 4 6% 5% 6% 9% 31%	2625
	21st to end	Day	14% 6% 4 8% 6% 4 6% 6% 8% 8% 30%	2744
August	1st to 10th	Day	18% 6% 3 6% 7% 4 6% 7% 7% 8% 28%	2374
	11th to 20th	Day	15% 7% 3 7% 7% 5% 6% 5% 6% 7% 31%	2304
	21st to end	Day	15% 6% 3 7% 6% 4 5% 5% 6% 7% 37%	2574
September	1st to 10th	Day	15% 7% 3 6% 5% 3 4 4 5% 7% 41%	2130
	11th to 20th	Day	17% 6% 3 6% 5% 3 4 3 4 5% 45%	1980
	21st to end	Day	18% 6% 3 6% 5% 3 4 3 4 7% 41%	1980
October	1st to 10th	Day	17% 8% 3 6% 5% 3 5% 5% 4 6% 38%	1904
	11th to 20th	Day	22% 9% 4 7% 6% 4 4 4 5% 5% 30%	1751
	21st to end	Day	26% 11% 3 7% 7% 3 3 4 4 6% 27%	1782
November	1st to 10th	Day	18% 11% 4 8% 6% 3 5% 5% 5% 5% 31%	1671
	11th to 20th	Day	19% 9% 4 8% 7% 4 7% 5% 6% 7% 26%	1536
	21st to end	Day	20% 13% 5% 8% 6% 4 4 4 3 5% 27%	1475
December	1st to 10th	Day	22% 14% 4 9% 8% 3 5% 4 5% 5% 22%	1330
	11th to 20th	Day	18% 14% 6% 8% 6% 4 5% 5% 5% 5% 26%	1668
	21st to end	Day	21% 12% 5% 10% 8% 4 5% 4 4 4 24%	2431
January	1st to 10th	Night	14% 13% 6% 12% 9% 4 6% 5% 5% 6% 19%	2802
	11th to 20th	Night	16% 13% 6% 9% 8% 4 5% 5% 5% 6% 23%	2577
	21st to end	Night	10% 9% 4 8% 8% 5% 5% 7% 7% 8% 30%	2772
February	1st to 10th	Night	11% 13% 6% 9% 7% 5% 5% 5% 6% 7% 27%	2394
	11th to 20th	Night	12% 16% 6% 9% 8% 4 6% 5% 5% 6% 24%	2233
	21st to end	Night	13% 13% 4 6% 8% 4 5% 4 3 6% 33%	1776
March	1st to 10th	Night	13% 12% 6% 8% 7% 4 6% 4 4 5% 30%	2145
	11th to 20th	Night	15% 10% 5% 7% 7% 5% 5% 5% 5% 5% 31%	1979
	21st to end	Night	14% 12% 5% 9% 8% 4 4 4 4 5% 31%	2178
April	1st to 10th	Night	22% 11% 4 6% 5% 3 4 4 4 5% 30%	1790
	11th to 20th	Night	20% 10% 3 6% 4 3 4 4 5% 7% 34%	1598
	21st to end	Night	28% 10% 3 5% 5% 3 3 3 3 6% 31%	1620
May	1st to 10th	Night	21% 10% 4 6% 5% 3 4 5% 5% 5% 32%	1620
	11th to 20th	Night	23% 7% 3 6% 6% 3 3 5% 5% 5% 34%	1468
	21st to end	Night	19% 7% 3 6% 6% 3 4 4 5% 7% 35%	1356
June	1st to 10th	Night	24% 8% 4 5% 4 3 6% 5% 5% 7% 29%	1260
	11th to 20th	Night	17% 5% 2 5% 4 3 5% 4 6% 8% 40%	1260
	21st to end	Night	22% 9% 3 6% 6% 3 4 4 5% 6% 31%	1260
July	1st to 10th	Night	16% 7% 2 5% 4 3 5% 4 5% 8% 39%	1260
	11th to 20th	Night	14% 6% 3 4 4 3 6% 5% 7% 9% 39%	1332
	21st to end	Night	16% 6% 2 5% 5% 3 6% 6% 7% 8% 36%	1574
August	1st to 10th	Night	14% 6% 3 5% 5% 3 5% 5% 6% 7% 42%	1545
	11th to 20th	Night	14% 6% 3 6% 6% 3 6% 6% 7% 8% 36%	1596
	21st to end	Night	11% 5% 2 5% 6% 4 5% 5% 6% 7% 46%	1782
September	1st to 10th	Night	14% 5% 2 5% 5% 3 4 4 5% 9% 44%	1825
	11th to 20th	Night	16% 6% 2 4 4 2 4 4 5% 5% 47%	1980
	21st to end	Night	16% 6% 2 5% 4 3 2 4 5% 5% 48%	1980
October	1st to 10th	Night	18% 6% 2 5% 5% 3 3 4 4 7% 42%	2055
	11th to 20th	Night	21% 7% 3 6% 5% 3 4 4 5% 6% 35%	2205
	21st to end	Night	22% 10% 3 6% 5% 4 4 4 4 6% 32%	2574
November	1st to 10th	Night	18% 10% 3 7% 6% 3 5% 5% 5% 7% 31%	2407
	11th to 20th	Night	19% 9% 4 7% 6% 3 5% 5% 6% 7% 31%	2642
	21st to end	Night	19% 9% 4 9% 8% 3 5% 5% 5% 6% 26%	2702
December	1st to 10th	Night	22% 12% 5% 8% 7% 4 4 4 5% 5% 24%	2850
	11th to 20th	Night	22% 10% 4 8% 6% 3 6% 5% 6% 6% 24%	3531
	21st to end	Night	20% 15% 4 8% 7% 3 4 4 4 5% 25%	5236

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	65% 6% 10% 12% 6%	1361
	11th to 20th	Day	62% 7% 8% 15% 6% 1	1472
	21st to end	Day	52% 7% 11% 17% 12% 1	1584
February	1st to 10th	Day	60% 6% 10% 12% 10% 1	1566
	11th to 20th	Day	62% 7% 11% 12% 7% 1	1619
	21st to end	Day	55% 7% 9% 19% 9% 2	1480
March	1st to 10th	Day	59% 5% 9% 14% 10% 2	1804
	11th to 20th	Day	59% 6% 10% 13% 9% 2	1980
	21st to end	Day	58% 5% 9% 17% 9% 2	2178
April	1st to 10th	Day	63% 6% 8% 13% 7% 2	2167
	11th to 20th	Day	53% 5% 10% 18% 12% 2	2312
	21st to end	Day	56% 5% 8% 16% 12% 3	2340
May	1st to 10th	Day	55% 6% 9% 15% 13% 2	2340
	11th to 20th	Day	52% 6% 10% 18% 12% 2	2443
	21st to end	Day	51% 8% 11% 19% 11%	2919
June	1st to 10th	Day	55% 9% 12% 14% 10% 1	2700
	11th to 20th	Day	51% 7% 13% 17% 11% 2	2700
	21st to end	Day	59% 8% 10% 14% 7% 1	2700
July	1st to 10th	Day	49% 10% 16% 17% 7% 1	2625
	11th to 20th	Day	47% 10% 15% 21% 8%	2544
	21st to end	Day	49% 10% 15% 18% 7% 1	2591
August	1st to 10th	Day	49% 12% 17% 17% 5%	2360
	11th to 20th	Day	49% 10% 15% 20% 6%	2304
	21st to end	Day	43% 9% 15% 24% 8%	2574
September	1st to 10th	Day	42% 7% 15% 23% 12%	2130
	11th to 20th	Day	42% 6% 12% 25% 15%	1980
	21st to end	Day	43% 8% 13% 24% 12%	1980
October	1st to 10th	Day	46% 6% 12% 25% 10%	1904
	11th to 20th	Day	55% 8% 15% 18% 5%	1751
	21st to end	Day	59% 7% 13% 13% 7% 1	1782
November	1st to 10th	Day	55% 7% 13% 17% 7%	1671
	11th to 20th	Day	57% 8% 13% 14% 8% 1	1536
	21st to end	Day	59% 7% 15% 15% 3	1475
December	1st to 10th	Day	65% 6% 11% 12% 5%	1330
	11th to 20th	Day	60% 7% 9% 13% 12%	1668
	21st to end	Day	60% 9% 12% 13% 5% 1	2431
January	1st to 10th	Night	64% 9% 10% 11% 5%	2802
	11th to 20th	Night	61% 7% 11% 14% 6%	2577
	21st to end	Night	49% 8% 12% 19% 11% 1	2772
February	1st to 10th	Night	56% 7% 11% 15% 10% 1	2394
	11th to 20th	Night	62% 6% 9% 15% 7% 1	2236
	21st to end	Night	54% 5% 11% 18% 12% 2	1776
March	1st to 10th	Night	56% 5% 8% 19% 10% 1	2155
	11th to 20th	Night	55% 6% 11% 16% 12% 1	1980
	21st to end	Night	55% 6% 9% 18% 10% 3	2178
April	1st to 10th	Night	57% 6% 8% 14% 12% 3	1790
	11th to 20th	Night	51% 5% 11% 18% 15% 1	1598
	21st to end	Night	56% 5% 8% 17% 13% 2	1620
May	1st to 10th	Night	53% 7% 9% 16% 14% 2	1620
	11th to 20th	Night	50% 7% 12% 19% 11% 1	1469
	21st to end	Night	48% 9% 11% 18% 14%	1357
June	1st to 10th	Night	53% 7% 13% 19% 7% 1	1260
	11th to 20th	Night	41% 9% 14% 22% 12% 2	1260
	21st to end	Night	53% 8% 14% 16% 8% 1	1260
July	1st to 10th	Night	44% 7% 20% 22% 7%	1225
	11th to 20th	Night	41% 10% 18% 23% 9% 1	1290
	21st to end	Night	44% 10% 18% 18% 9%	1486
August	1st to 10th	Night	41% 10% 19% 26% 4	1535
	11th to 20th	Night	42% 11% 20% 20% 6%	1596
	21st to end	Night	35% 9% 17% 28% 9%	1782
September	1st to 10th	Night	38% 8% 17% 24% 12% 1	1825
	11th to 20th	Night	38% 8% 15% 25% 13%	1980
	21st to end	Night	38% 7% 14% 26% 14% 1	1980
October	1st to 10th	Night	43% 6% 13% 27% 10% 1	2055
	11th to 20th	Night	48% 8% 14% 23% 6%	2205
	21st to end	Night	54% 6% 14% 17% 8% 1	2574
November	1st to 10th	Night	51% 8% 14% 20% 6%	2407
	11th to 20th	Night	52% 8% 14% 15% 10%	2642
	21st to end	Night	58% 8% 15% 13% 6%	2702
December	1st to 10th	Night	63% 7% 12% 15% 4	2850
	11th to 20th	Night	58% 8% 12% 14% 7%	3532
	21st to end	Night	59% 8% 12% 13% 6% 1	5236

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	27% 27% 33% 9% 3	180
	11th to 20th	Day	35% 19% 32% 11% 4	168
	21st to end	Day	22% 23% 36% 13% 7%	176
February	1st to 10th	Day	26% 24% 32% 14% 4	286
	11th to 20th	Day	26% 25% 32% 13% 3	354
	21st to end	Day	23% 25% 32% 15% 4 1	346
March	1st to 10th	Day	27% 22% 34% 15% 3	420
	11th to 20th	Day	28% 23% 29% 13% 8% 1	420
	21st to end	Day	27% 25% 25% 18% 5% 1	462
April	1st to 10th	Day	32% 26% 23% 13% 4 2	420
	11th to 20th	Day	30% 22% 28% 15% 6%	412
	21st to end	Day	33% 20% 32% 10% 4 1	420
May	1st to 10th	Day	35% 16% 33% 13% 3	423
	11th to 20th	Day	31% 19% 29% 16% 5%	500
	21st to end	Day	27% 21% 29% 18% 6%	680
June	1st to 10th	Day	27% 18% 32% 17% 6% 1	630
	11th to 20th	Day	24% 19% 26% 22% 8% 1	630
	21st to end	Day	24% 15% 32% 21% 8%	630
July	1st to 10th	Day	18% 16% 34% 22% 10%	620
	11th to 20th	Day	17% 13% 34% 26% 9% 1	543
	21st to end	Day	15% 11% 41% 23% 9% 1	488
August	1st to 10th	Day	17% 12% 33% 25% 9% 3	446
	11th to 20th	Day	18% 11% 31% 28% 10% 2	439
	21st to end	Day	22% 15% 26% 20% 13% 3	495
September	1st to 10th	Day	18% 16% 33% 20% 11% 3	450
	11th to 20th	Day	23% 13% 30% 21% 10% 3	450
	21st to end	Day	20% 19% 32% 15% 10% 5%	450
October	1st to 10th	Day	18% 19% 30% 18% 11% 4	412
	11th to 20th	Day	31% 18% 28% 14% 9% 2	360
	21st to end	Day	32% 20% 28% 15% 4 1	396
November	1st to 10th	Day	30% 22% 27% 16% 5% 1	365
	11th to 20th	Day	27% 21% 30% 15% 6% 1	370
	21st to end	Day	36% 18% 31% 12% 3 1	325
December	1st to 10th	Day	28% 24% 26% 14% 7% 1	180
	11th to 20th	Day	33% 23% 32% 9% 3 1	180
	21st to end	Day	33% 25% 25% 13% 3 1	198
January	1st to 10th	Night	21% 23% 37% 16% 2	832
	11th to 20th	Night	25% 22% 31% 18% 4	737
	21st to end	Night	16% 20% 39% 21% 4	792
February	1st to 10th	Night	20% 25% 34% 17% 4	720
	11th to 20th	Night	25% 25% 29% 17% 4	703
	21st to end	Night	23% 18% 38% 17% 4 1	592
March	1st to 10th	Night	20% 18% 40% 19% 3	720
	11th to 20th	Night	25% 19% 31% 18% 7% 1	720
	21st to end	Night	22% 17% 35% 20% 5%	792
April	1st to 10th	Night	30% 18% 29% 18% 4 1	706
	11th to 20th	Night	25% 19% 31% 19% 6%	534
	21st to end	Night	34% 15% 25% 20% 6%	540
May	1st to 10th	Night	25% 14% 33% 24% 4	540
	11th to 20th	Night	27% 13% 31% 21% 7% 1	462
	21st to end	Night	23% 14% 34% 23% 6%	389
June	1st to 10th	Night	28% 7% 29% 29% 6% 1	360
	11th to 20th	Night	19% 8% 27% 36% 10%	360
	21st to end	Night	25% 7% 30% 29% 9%	360
July	1st to 10th	Night	16% 9% 37% 27% 11%	350
	11th to 20th	Night	15% 5% 32% 35% 11%	348
	21st to end	Night	18% 6% 27% 36% 12% 1	394
August	1st to 10th	Night	17% 5% 29% 38% 11%	471
	11th to 20th	Night	14% 5% 32% 35% 14%	532
	21st to end	Night	12% 9% 30% 34% 13% 1	594
September	1st to 10th	Night	16% 10% 31% 30% 11%	670
	11th to 20th	Night	20% 11% 27% 29% 11% 2	720
	21st to end	Night	19% 13% 30% 26% 12%	720
October	1st to 10th	Night	21% 13% 30% 26% 8% 1	720
	11th to 20th	Night	23% 14% 33% 19% 10%	720
	21st to end	Night	29% 19% 28% 19% 5%	792
November	1st to 10th	Night	25% 19% 32% 19% 5%	740
	11th to 20th	Night	26% 19% 29% 19% 5% 1	842
	21st to end	Night	26% 21% 30% 20% 4	850
December	1st to 10th	Night	29% 17% 34% 15% 3 1	850
	11th to 20th	Night	28% 20% 31% 17% 3	850
	21st to end	Night	30% 22% 28% 15% 4 1	935

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