Watch Observatory 2
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Watch Observatory 2 clear sky chart from 2005-11-06 to 2024-02-10.

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% 9% 4 7% 6% 4 5% 5% 5% 7% 32%	78082
	Night	18% 10% 4 7% 6% 3 5% 4 5% 6% 31%	80877
Transparency	Day	53% 3 11% 21% 11% 1	77787
	Night	56% 3 11% 20% 10% 1	80706
Seeing	Day	24% 16% 30% 19% 8% 2	13500
	Night	24% 14% 29% 24% 9% 1	22688

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	17% 15% 6% 10% 7% 4 5% 4 4 5% 22%	2517
	11th to 20th	Day	14% 14% 7% 9% 7% 4 6% 5% 5% 5% 23%	2520
	21st to end	Day	16% 16% 6% 8% 7% 4 6% 5% 6% 6% 19%	2776
February	1st to 10th	Day	16% 15% 5% 11% 7% 4 5% 5% 5% 5% 24%	1701
	11th to 20th	Day	14% 13% 5% 9% 8% 4 5% 4 4 7% 27%	1636
	21st to end	Day	21% 12% 6% 8% 7% 4 5% 3 4 5% 26%	1480
March	1st to 10th	Day	16% 12% 5% 10% 8% 4 5% 4 4 5% 29%	1797
	11th to 20th	Day	17% 12% 4 7% 7% 3 5% 4 4 5% 32%	1907
	21st to end	Day	20% 10% 4 6% 6% 3 5% 4 4 5% 35%	2344
April	1st to 10th	Day	21% 10% 4 7% 5% 4 3 4 3 5% 33%	2160
	11th to 20th	Day	21% 8% 3 7% 6% 3 4 4 5% 5% 35%	2134
	21st to end	Day	23% 8% 4 7% 6% 3 5% 4 4 5% 31%	2267
May	1st to 10th	Day	20% 7% 4 7% 5% 4 5% 4 5% 6% 34%	2520
	11th to 20th	Day	17% 7% 3 6% 5% 3 5% 4 5% 6% 39%	2478
	21st to end	Day	17% 6% 3 6% 6% 3 5% 5% 6% 8% 37%	2725
June	1st to 10th	Day	23% 6% 3 5% 6% 3 5% 5% 5% 8% 30%	2520
	11th to 20th	Day	15% 5% 3 5% 6% 3 5% 5% 7% 8% 38%	2520
	21st to end	Day	19% 6% 3 6% 5% 4 5% 7% 6% 8% 31%	2520
July	1st to 10th	Day	12% 5% 3 6% 5% 4 6% 5% 5% 9% 41%	2520
	11th to 20th	Day	13% 5% 3 5% 5% 4 6% 6% 7% 9% 37%	2520
	21st to end	Day	12% 6% 3 5% 5% 4 5% 6% 7% 10% 38%	2744
August	1st to 10th	Day	12% 6% 3 5% 6% 4 5% 5% 6% 9% 39%	2506
	11th to 20th	Day	10% 4 2 6% 6% 4 5% 6% 6% 9% 41%	2258
	21st to end	Day	14% 5% 2 5% 5% 4 5% 6% 7% 8% 39%	2376
September	1st to 10th	Day	13% 5% 3 5% 5% 3 4 5% 6% 8% 43%	2160
	11th to 20th	Day	13% 4 2 5% 4 3 4 5% 4 7% 48%	2112
	21st to end	Day	16% 7% 2 5% 5% 3 5% 4 5% 7% 40%	1980
October	1st to 10th	Day	20% 8% 3 6% 5% 4 4 5% 5% 5% 35%	1816
	11th to 20th	Day	20% 9% 4 8% 7% 4 4 4 5% 5% 29%	1796
	21st to end	Day	24% 10% 4 7% 5% 3 4 5% 5% 5% 27%	1782
November	1st to 10th	Day	17% 8% 4 7% 6% 4 6% 5% 4 8% 33%	1671
	11th to 20th	Day	18% 10% 4 7% 7% 5% 5% 5% 4 7% 28%	1601
	21st to end	Day	20% 11% 5% 8% 8% 4 5% 4 7% 6% 22%	1520
December	1st to 10th	Day	24% 13% 5% 8% 7% 4 5% 5% 5% 6% 18%	1520
	11th to 20th	Day	22% 14% 6% 8% 6% 3 4 4 4 6% 24%	1906
	21st to end	Day	28% 17% 4 8% 6% 3 4 3 3 3 21%	2772
January	1st to 10th	Night	17% 15% 6% 10% 7% 4 4 5% 4 5% 21%	4429
	11th to 20th	Night	13% 13% 6% 13% 9% 5% 6% 5% 5% 6% 20%	4440
	21st to end	Night	17% 18% 6% 9% 7% 4 5% 3 3 5% 23%	4875
February	1st to 10th	Night	15% 12% 5% 10% 8% 4 7% 5% 5% 6% 21%	2464
	11th to 20th	Night	14% 11% 5% 9% 7% 4 6% 5% 5% 5% 28%	2208
	21st to end	Night	16% 12% 5% 9% 6% 3 4 4 4 5% 30%	1776
March	1st to 10th	Night	16% 12% 5% 8% 8% 3 5% 5% 5% 5% 28%	2150
	11th to 20th	Night	17% 13% 4 6% 7% 3 5% 3 4 5% 32%	2051
	21st to end	Night	17% 10% 4 6% 6% 3 4 3 3 5% 37%	2012
April	1st to 10th	Night	24% 8% 3 7% 6% 3 4 4 4 6% 31%	1800
	11th to 20th	Night	22% 7% 4 6% 5% 2 4 4 5% 5% 35%	1775
	21st to end	Night	22% 8% 3 6% 6% 3 4 4 5% 6% 33%	1692
May	1st to 10th	Night	22% 8% 3 5% 6% 3 5% 4 4 6% 35%	1454
	11th to 20th	Night	17% 8% 4 6% 5% 2 2 4 5% 6% 40%	1415
	21st to end	Night	14% 7% 3 4 6% 3 5% 4 5% 8% 42%	1550
June	1st to 10th	Night	20% 6% 3 5% 7% 3 5% 5% 7% 9% 30%	1440
	11th to 20th	Night	17% 6% 3 4 5% 2 5% 4 6% 7% 41%	1440
	21st to end	Night	15% 7% 3 7% 6% 3 5% 6% 5% 9% 35%	1440
July	1st to 10th	Night	10% 4 2 6% 5% 3 5% 7% 5% 9% 45%	1440
	11th to 20th	Night	11% 5% 2 5% 5% 3 5% 5% 7% 10% 40%	1440
	21st to end	Night	12% 5% 3 4 5% 3 5% 6% 6% 9% 42%	1574
August	1st to 10th	Night	11% 4 3 4 6% 3 5% 4 6% 10% 43%	1432
	11th to 20th	Night	11% 5% 3 5% 6% 3 5% 5% 5% 7% 44%	1620
	21st to end	Night	12% 7% 2 5% 5% 3 4 6% 6% 8% 42%	1980
September	1st to 10th	Night	11% 6% 3 7% 6% 4 5% 4 6% 7% 43%	1800
	11th to 20th	Night	15% 5% 2 4 5% 3 4 3 5% 7% 48%	1846
	21st to end	Night	16% 5% 2 4 5% 3 5% 4 5% 7% 42%	1980
October	1st to 10th	Night	20% 6% 2 6% 5% 4 4 4 5% 6% 37%	2142
	11th to 20th	Night	19% 8% 4 7% 6% 3 5% 5% 5% 6% 32%	2162
	21st to end	Night	23% 9% 4 6% 6% 4 5% 4 5% 5% 29%	2574
November	1st to 10th	Night	19% 9% 3 7% 6% 3 4 4 5% 6% 34%	2407
	11th to 20th	Night	18% 9% 3 7% 6% 4 5% 5% 5% 6% 32%	2577
	21st to end	Night	20% 12% 5% 8% 6% 3 4 5% 5% 6% 25%	2660
December	1st to 10th	Night	20% 15% 6% 10% 7% 3 5% 5% 4 5% 20%	2660
	11th to 20th	Night	22% 16% 4 7% 7% 3 5% 4 4 4 25%	3288
	21st to end	Night	31% 16% 4 8% 6% 3 3 3 3 4 20%	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	67% 1 13% 13% 5% 1	2518
	11th to 20th	Day	64% 1 11% 15% 8% 1	2520
	21st to end	Day	67% 3 13% 11% 5% 1	2776
February	1st to 10th	Day	63% 2 8% 20% 5% 2	1701
	11th to 20th	Day	60% 3 11% 18% 8% 1	1645
	21st to end	Day	63% 2 9% 14% 10% 1	1480
March	1st to 10th	Day	60% 2 9% 17% 10% 1	1800
	11th to 20th	Day	56% 2 11% 15% 13% 3	1907
	21st to end	Day	53% 2 7% 19% 15% 4	2344
April	1st to 10th	Day	56% 2 6% 20% 13% 3	2160
	11th to 20th	Day	52% 2 6% 22% 17% 2	2134
	21st to end	Day	57% 2 8% 16% 13% 4	2267
May	1st to 10th	Day	52% 3 6% 21% 16% 2	2520
	11th to 20th	Day	47% 3 8% 23% 16% 3	2482
	21st to end	Day	47% 3 13% 21% 14% 2	2725
June	1st to 10th	Day	54% 3 10% 20% 12% 1	2520
	11th to 20th	Day	45% 3 11% 25% 13% 3	2520
	21st to end	Day	51% 4 14% 20% 10% 1	2520
July	1st to 10th	Day	41% 4 12% 29% 14% 1	2450
	11th to 20th	Day	42% 4 14% 30% 10%	2445
	21st to end	Day	42% 4 16% 27% 11%	2591
August	1st to 10th	Day	42% 4 17% 28% 9%	2492
	11th to 20th	Day	40% 4 18% 27% 11%	2258
	21st to end	Day	42% 3 13% 28% 13% 1	2376
September	1st to 10th	Day	40% 3 14% 29% 13%	2160
	11th to 20th	Day	37% 3 11% 33% 15% 1	2112
	21st to end	Day	44% 3 14% 29% 10%	1980
October	1st to 10th	Day	50% 3 9% 26% 11%	1816
	11th to 20th	Day	59% 2 12% 19% 8%	1796
	21st to end	Day	60% 2 11% 18% 8% 1	1782
November	1st to 10th	Day	52% 3 13% 23% 9% 1	1671
	11th to 20th	Day	57% 3 11% 17% 11% 1	1601
	21st to end	Day	63% 4 13% 14% 5%	1520
December	1st to 10th	Day	69% 4 12% 12% 3	1520
	11th to 20th	Day	65% 3 13% 15% 4	1906
	21st to end	Day	72% 2 8% 14% 4	2772
January	1st to 10th	Night	67% 2 15% 12% 4	4429
	11th to 20th	Night	68% 2 11% 13% 5%	4440
	21st to end	Night	67% 2 12% 13% 6% 1	4875
February	1st to 10th	Night	63% 3 9% 17% 7% 1	2464
	11th to 20th	Night	58% 3 10% 20% 8% 1	2210
	21st to end	Night	57% 2 8% 18% 13% 1	1776
March	1st to 10th	Night	59% 3 9% 17% 11% 2	2160
	11th to 20th	Night	56% 2 8% 19% 12% 3	2052
	21st to end	Night	52% 2 5% 22% 15% 4	2012
April	1st to 10th	Night	56% 2 7% 19% 14% 2	1800
	11th to 20th	Night	52% 3 6% 22% 16% 2	1775
	21st to end	Night	52% 2 7% 19% 15% 4	1692
May	1st to 10th	Night	51% 2 6% 20% 17% 4	1454
	11th to 20th	Night	46% 3 6% 22% 20% 4	1416
	21st to end	Night	42% 4 13% 21% 17% 3	1551
June	1st to 10th	Night	51% 3 11% 22% 12% 1	1440
	11th to 20th	Night	43% 4 11% 23% 18% 2	1440
	21st to end	Night	47% 4 13% 21% 14%	1440
July	1st to 10th	Night	36% 4 13% 28% 18% 1	1400
	11th to 20th	Night	39% 4 12% 32% 13%	1392
	21st to end	Night	38% 4 17% 27% 14% 1	1486
August	1st to 10th	Night	37% 4 19% 28% 12%	1422
	11th to 20th	Night	40% 3 16% 28% 12% 1	1620
	21st to end	Night	40% 3 15% 30% 11% 1	1980
September	1st to 10th	Night	43% 2 10% 28% 16% 1	1800
	11th to 20th	Night	37% 3 12% 35% 12% 1	1846
	21st to end	Night	42% 3 11% 31% 12%	1980
October	1st to 10th	Night	48% 4 10% 25% 13% 1	2142
	11th to 20th	Night	54% 3 11% 23% 9%	2162
	21st to end	Night	59% 3 12% 17% 9% 1	2574
November	1st to 10th	Night	53% 2 13% 22% 9% 1	2407
	11th to 20th	Night	55% 3 12% 20% 10% 1	2577
	21st to end	Night	61% 2 13% 17% 6%	2660
December	1st to 10th	Night	69% 3 9% 15% 4	2660
	11th to 20th	Night	65% 2 8% 18% 7% 1	3288
	21st to end	Night	72% 1 8% 14% 4	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	31% 16% 32% 18% 3	180
	11th to 20th	Day	32% 26% 27% 9% 4 1	180
	21st to end	Day	20% 21% 39% 18% 4	200
February	1st to 10th	Day	33% 30% 25% 9% 2	267
	11th to 20th	Day	27% 28% 37% 8%	303
	21st to end	Day	32% 20% 32% 14% 2	346
March	1st to 10th	Day	28% 22% 31% 15% 4	420
	11th to 20th	Day	30% 21% 32% 14% 3 1	420
	21st to end	Day	33% 20% 24% 16% 7% 1	462
April	1st to 10th	Day	31% 19% 31% 14% 5%	420
	11th to 20th	Day	33% 18% 26% 15% 7% 1	412
	21st to end	Day	32% 18% 29% 13% 7% 1	420
May	1st to 10th	Day	26% 17% 34% 16% 6% 1	423
	11th to 20th	Day	20% 18% 34% 19% 8% 2	447
	21st to end	Day	20% 18% 33% 21% 7% 1	485
June	1st to 10th	Day	28% 11% 31% 22% 6% 2	450
	11th to 20th	Day	18% 15% 32% 24% 8% 2	450
	21st to end	Day	23% 10% 34% 20% 11% 3	450
July	1st to 10th	Day	17% 7% 32% 27% 14% 3	445
	11th to 20th	Day	13% 11% 33% 28% 13% 2	444
	21st to end	Day	17% 8% 34% 28% 11% 2	488
August	1st to 10th	Day	16% 8% 28% 30% 14% 4	446
	11th to 20th	Day	15% 6% 28% 31% 13% 7%	439
	21st to end	Day	16% 10% 32% 22% 14% 6%	495
September	1st to 10th	Day	18% 9% 30% 21% 15% 6%	450
	11th to 20th	Day	16% 8% 28% 22% 17% 9%	450
	21st to end	Day	18% 14% 31% 19% 14% 4	450
October	1st to 10th	Day	24% 15% 26% 20% 12% 3	450
	11th to 20th	Day	26% 20% 27% 20% 7% 1	448
	21st to end	Day	34% 13% 29% 17% 6%	396
November	1st to 10th	Day	29% 17% 27% 19% 6% 1	365
	11th to 20th	Day	26% 24% 29% 17% 5%	261
	21st to end	Day	28% 22% 28% 17% 6% 1	180
December	1st to 10th	Day	30% 17% 34% 15% 4	180
	11th to 20th	Day	32% 23% 32% 11% 1 1	180
	21st to end	Day	35% 24% 26% 14% 2	198
January	1st to 10th	Night	28% 18% 35% 15% 4	760
	11th to 20th	Night	29% 20% 26% 20% 5% 1	760
	21st to end	Night	21% 18% 34% 21% 5%	836
February	1st to 10th	Night	23% 19% 33% 22% 3	759
	11th to 20th	Night	23% 22% 33% 18% 4	703
	21st to end	Night	25% 19% 30% 23% 2	592
March	1st to 10th	Night	24% 20% 30% 22% 4	720
	11th to 20th	Night	26% 18% 32% 19% 4 1	720
	21st to end	Night	24% 17% 26% 26% 7% 1	792
April	1st to 10th	Night	31% 16% 28% 21% 4	720
	11th to 20th	Night	26% 18% 29% 22% 5%	711
	21st to end	Night	29% 13% 29% 20% 8%	612
May	1st to 10th	Night	26% 12% 29% 24% 7% 2	374
	11th to 20th	Night	23% 11% 30% 26% 10% 1	354
	21st to end	Night	17% 10% 37% 27% 9%	389
June	1st to 10th	Night	22% 8% 29% 31% 9% 1	360
	11th to 20th	Night	21% 8% 26% 31% 13% 1	360
	21st to end	Night	16% 8% 29% 28% 17% 1	360
July	1st to 10th	Night	12% 7% 30% 34% 16% 1	350
	11th to 20th	Night	14% 4 29% 36% 16%	348
	21st to end	Night	14% 4 32% 37% 13% 1	394
August	1st to 10th	Night	14% 6% 22% 37% 20% 1	358
	11th to 20th	Night	14% 2 26% 33% 22% 2	556
	21st to end	Night	16% 6% 28% 30% 18% 2	792
September	1st to 10th	Night	14% 6% 31% 34% 14% 1	720
	11th to 20th	Night	20% 6% 22% 30% 19% 3	720
	21st to end	Night	19% 10% 28% 24% 18% 2	720
October	1st to 10th	Night	24% 10% 27% 27% 11% 1	720
	11th to 20th	Night	25% 12% 29% 24% 10%	720
	21st to end	Night	29% 15% 28% 24% 4	792
November	1st to 10th	Night	27% 16% 24% 23% 8% 1	740
	11th to 20th	Night	24% 19% 32% 16% 9% 1	760
	21st to end	Night	28% 18% 26% 20% 7%	760
December	1st to 10th	Night	31% 18% 28% 19% 4	760
	11th to 20th	Night	31% 21% 26% 16% 5% 1	760
	21st to end	Night	38% 18% 26% 14% 4	836

Page generated at 2024-02-07 06:11:52. Version ac07

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