Baker Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Baker Observatory clear sky chart from 2005-11-06 to 2024-01-13.

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	12% 7% 3 5% 5% 3 5% 5% 5% 7% 43%	74634
	Night	12% 7% 3 5% 4 3 4 4 5% 7% 47%	75116
Transparency	Day	40% 6% 11% 24% 16% 3	74357
	Night	38% 5% 11% 25% 19% 3	74913
Seeing	Day	16% 11% 26% 27% 16% 4	14394
	Night	16% 11% 32% 28% 12% 1	24346

By Month

Percentage Cloud Cover SE (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	11% 8% 3 6% 5% 3 4 4 4 5% 47%	1707
	11th to 20th	Day	13% 9% 5% 7% 6% 3 4 4 5% 7% 38%	1643
	21st to end	Day	13% 8% 4 7% 4 2 3 4 4 7% 42%	1782
February	1st to 10th	Day	14% 12% 4 6% 7% 3 5% 4 5% 5% 36%	1620
	11th to 20th	Day	13% 9% 4 7% 6% 3 4 5% 5% 6% 40%	1606
	21st to end	Day	16% 12% 3 5% 5% 2 5% 4 5% 6% 37%	1525
March	1st to 10th	Day	13% 11% 4 6% 4 2 4 4 4 6% 43%	1980
	11th to 20th	Day	20% 10% 4 6% 5% 2 4 3 4 7% 36%	1980
	21st to end	Day	19% 10% 3 6% 6% 3 5% 5% 5% 6% 31%	2178
April	1st to 10th	Day	11% 7% 2 6% 5% 3 4 4 5% 7% 45%	2145
	11th to 20th	Day	16% 10% 3 6% 5% 3 3 4 5% 6% 39%	2134
	21st to end	Day	19% 9% 3 6% 5% 3 4 5% 5% 6% 36%	2160
May	1st to 10th	Day	19% 7% 3 6% 5% 3 5% 4 5% 6% 37%	2287
	11th to 20th	Day	15% 5% 2 5% 6% 3 5% 4 5% 7% 42%	2302
	21st to end	Day	11% 5% 3 7% 6% 4 6% 6% 8% 9% 35%	2663
June	1st to 10th	Day	8% 4 2 5% 5% 3 5% 4 7% 10% 46%	2520
	11th to 20th	Day	7% 4 2 4 4 3 5% 5% 8% 10% 47%	2520
	21st to end	Day	5% 3 2 3 4 3 5% 6% 5% 10% 54%	2520
July	1st to 10th	Day	9% 4 1 5% 6% 4 6% 6% 7% 11% 40%	2405
	11th to 20th	Day	4 3 2 3 5% 3 6% 6% 7% 11% 49%	2340
	21st to end	Day	9% 5% 2 5% 6% 4 6% 6% 7% 9% 41%	2546
August	1st to 10th	Day	8% 5% 3 5% 5% 4 7% 6% 7% 9% 41%	2328
	11th to 20th	Day	8% 6% 3 6% 6% 3 5% 5% 7% 9% 43%	2234
	21st to end	Day	7% 4 2 5% 5% 4 6% 4 6% 8% 50%	2376
September	1st to 10th	Day	12% 5% 2 5% 3 3 4 4 6% 7% 50%	2160
	11th to 20th	Day	10% 6% 3 6% 6% 3 4 5% 4 6% 47%	2123
	21st to end	Day	7% 5% 1 4 5% 3 5% 5% 5% 7% 53%	1896
October	1st to 10th	Day	11% 5% 2 4 4 2 3 5% 4 5% 55%	1800
	11th to 20th	Day	13% 6% 3 5% 3 2 3 3 4 5% 52%	1800
	21st to end	Day	17% 7% 3 5% 4 2 3 3 4 5% 46%	1980
November	1st to 10th	Day	11% 5% 2 4 4 1 3 3 3 5% 57%	1858
	11th to 20th	Day	12% 8% 3 5% 5% 2 3 3 5% 7% 48%	1734
	21st to end	Day	14% 8% 4 5% 3 2 3 3 4 6% 48%	1520
December	1st to 10th	Day	12% 9% 4 5% 6% 2 4 4 5% 7% 42%	1520
	11th to 20th	Day	12% 11% 5% 7% 5% 3 4 3 3 6% 42%	1918
	21st to end	Day	13% 17% 6% 8% 6% 3 4 4 4 6% 29%	2824
January	1st to 10th	Night	12% 8% 3 6% 5% 3 4 4 5% 6% 44%	2458
	11th to 20th	Night	13% 8% 3 7% 5% 3 3 4 4 6% 44%	2379
	21st to end	Night	12% 10% 4 7% 4 3 4 4 5% 6% 43%	2574
February	1st to 10th	Night	14% 11% 4 6% 4 2 3 4 4 7% 41%	2340
	11th to 20th	Night	14% 8% 4 6% 4 3 4 3 4 6% 43%	2239
	21st to end	Night	15% 8% 3 6% 5% 3 4 4 4 6% 41%	1745
March	1st to 10th	Night	14% 9% 3 6% 4 2 4 3 4 5% 46%	1980
	11th to 20th	Night	19% 9% 3 6% 4 3 4 4 4 4 40%	1980
	21st to end	Night	17% 9% 4 6% 6% 2 5% 5% 4 6% 34%	2178
April	1st to 10th	Night	10% 6% 2 3 3 3 4 4 5% 8% 52%	1814
	11th to 20th	Night	13% 9% 2 4 4 2 4 4 5% 8% 45%	1775
	21st to end	Night	17% 7% 3 5% 5% 3 4 4 5% 6% 41%	1800
May	1st to 10th	Night	14% 5% 3 5% 4 2 4 4 5% 7% 47%	1670
	11th to 20th	Night	14% 5% 2 6% 4 2 4 4 6% 7% 47%	1593
	21st to end	Night	11% 7% 3 5% 6% 3 5% 4 7% 9% 41%	1608
June	1st to 10th	Night	7% 4 2 4 3 2 4 5% 5% 10% 54%	1440
	11th to 20th	Night	5% 3 1 4 3 3 4 5% 7% 11% 54%	1440
	21st to end	Night	3 2 1 2 3 3 3 4 5% 9% 65%	1440
July	1st to 10th	Night	7% 3 2 3 4 3 5% 6% 7% 9% 52%	1550
	11th to 20th	Night	4 2 1 3 3 3 3 5% 7% 10% 59%	1620
	21st to end	Night	5% 4 2 4 4 3 4 5% 7% 11% 51%	1772
August	1st to 10th	Night	6% 3 2 5% 5% 3 4 5% 7% 9% 51%	1611
	11th to 20th	Night	7% 3 1 4 5% 2 3 4 6% 8% 58%	1664
	21st to end	Night	5% 4 2 4 4 3 4 4 5% 8% 57%	1980
September	1st to 10th	Night	9% 5% 2 4 5% 2 3 3 4 7% 56%	1800
	11th to 20th	Night	10% 4 2 4 4 3 4 3 5% 8% 54%	1833
	21st to end	Night	9% 3 1 4 4 3 3 3 5% 6% 59%	2044
October	1st to 10th	Night	8% 3 2 3 3 2 3 3 4 7% 60%	2160
	11th to 20th	Night	14% 5% 1 3 4 2 3 3 4 5% 54%	2160
	21st to end	Night	17% 7% 2 4 3 2 3 3 4 6% 49%	2376
November	1st to 10th	Night	11% 5% 2 4 3 2 2 4 4 5% 59%	2220
	11th to 20th	Night	13% 6% 3 4 3 3 3 3 4 7% 51%	2436
	21st to end	Night	13% 8% 3 5% 4 2 3 3 4 6% 48%	2660
December	1st to 10th	Night	14% 9% 4 6% 5% 2 4 4 4 8% 41%	2660
	11th to 20th	Night	14% 10% 4 6% 5% 3 3 3 4 6% 42%	3279
	21st to end	Night	14% 17% 6% 8% 5% 3 4 4 4 5% 29%	4838

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	40% 4 10% 25% 19% 2	1708
	11th to 20th	Day	47% 5% 9% 21% 16% 1	1643
	21st to end	Day	43% 4 12% 25% 13% 3	1782
February	1st to 10th	Day	51% 4 10% 22% 12% 1	1620
	11th to 20th	Day	47% 4 10% 20% 15% 4	1615
	21st to end	Day	48% 4 7% 21% 14% 6%	1525
March	1st to 10th	Day	44% 4 9% 19% 19% 5%	1980
	11th to 20th	Day	51% 4 8% 19% 14% 3	1980
	21st to end	Day	56% 5% 11% 18% 9% 1	2178
April	1st to 10th	Day	40% 4 13% 23% 18% 1	2145
	11th to 20th	Day	46% 5% 12% 20% 14% 3	2134
	21st to end	Day	50% 6% 10% 23% 10% 1	2160
May	1st to 10th	Day	49% 5% 12% 21% 12% 1	2287
	11th to 20th	Day	42% 6% 14% 24% 14% 1	2306
	21st to end	Day	43% 9% 14% 22% 11% 1	2663
June	1st to 10th	Day	33% 7% 15% 28% 16% 1	2520
	11th to 20th	Day	31% 7% 14% 32% 14% 2	2520
	21st to end	Day	26% 7% 15% 31% 17% 4	2520
July	1st to 10th	Day	36% 9% 16% 24% 13% 3	2341
	11th to 20th	Day	27% 8% 15% 26% 20% 3	2271
	21st to end	Day	37% 8% 14% 30% 11% 1	2405
August	1st to 10th	Day	37% 8% 16% 24% 14% 1	2314
	11th to 20th	Day	36% 9% 11% 29% 15% 1	2234
	21st to end	Day	33% 6% 11% 23% 21% 7%	2376
September	1st to 10th	Day	34% 6% 12% 27% 14% 7%	2160
	11th to 20th	Day	38% 5% 7% 22% 26% 2	2123
	21st to end	Day	31% 6% 8% 27% 24% 3	1896
October	1st to 10th	Day	31% 5% 9% 26% 24% 5%	1800
	11th to 20th	Day	36% 3 8% 26% 22% 7%	1800
	21st to end	Day	41% 4 7% 24% 18% 6%	1980
November	1st to 10th	Day	32% 3 8% 28% 23% 5%	1858
	11th to 20th	Day	38% 3 7% 21% 25% 6%	1734
	21st to end	Day	40% 4 9% 24% 21% 3	1520
December	1st to 10th	Day	43% 4 9% 29% 13% 2	1520
	11th to 20th	Day	47% 3 6% 19% 22% 2	1915
	21st to end	Day	58% 5% 8% 16% 12% 2	2824
January	1st to 10th	Night	42% 3 10% 23% 19% 2	2458
	11th to 20th	Night	43% 4 11% 25% 16% 1	2379
	21st to end	Night	43% 4 10% 25% 15% 3	2574
February	1st to 10th	Night	45% 4 11% 23% 15% 2	2340
	11th to 20th	Night	44% 4 10% 22% 17% 3	2240
	21st to end	Night	45% 4 7% 22% 16% 5%	1745
March	1st to 10th	Night	42% 4 8% 20% 19% 7%	1980
	11th to 20th	Night	48% 5% 9% 19% 16% 3	1980
	21st to end	Night	51% 6% 9% 22% 11% 1	2178
April	1st to 10th	Night	32% 4 13% 25% 21% 4	1814
	11th to 20th	Night	38% 5% 11% 23% 18% 6%	1775
	21st to end	Night	45% 4 10% 24% 15% 1	1800
May	1st to 10th	Night	39% 5% 11% 26% 18% 1	1670
	11th to 20th	Night	37% 7% 14% 24% 16% 2	1594
	21st to end	Night	40% 8% 15% 24% 11% 1	1609
June	1st to 10th	Night	27% 6% 16% 30% 18% 2	1440
	11th to 20th	Night	24% 6% 15% 32% 21% 3	1440
	21st to end	Night	17% 6% 18% 33% 21% 6%	1440
July	1st to 10th	Night	27% 8% 16% 27% 16% 4	1505
	11th to 20th	Night	20% 7% 15% 31% 25% 2	1566
	21st to end	Night	25% 8% 14% 37% 15% 1	1673
August	1st to 10th	Night	28% 7% 15% 36% 13% 1	1601
	11th to 20th	Night	25% 7% 12% 33% 22% 2	1664
	21st to end	Night	25% 6% 14% 26% 23% 7%	1980
September	1st to 10th	Night	30% 5% 11% 28% 20% 6%	1800
	11th to 20th	Night	30% 5% 9% 25% 27% 4	1833
	21st to end	Night	28% 4 9% 25% 31% 4	2044
October	1st to 10th	Night	25% 5% 10% 28% 27% 6%	2160
	11th to 20th	Night	33% 3 8% 25% 25% 6%	2160
	21st to end	Night	39% 3 8% 22% 22% 6%	2376
November	1st to 10th	Night	29% 4 9% 27% 23% 7%	2220
	11th to 20th	Night	35% 3 6% 24% 26% 5%	2436
	21st to end	Night	40% 4 7% 23% 22% 3	2660
December	1st to 10th	Night	43% 5% 11% 22% 18% 2	2660
	11th to 20th	Night	47% 3 7% 21% 20% 2	3281
	21st to end	Night	58% 4 10% 16% 9% 2	4838

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	22% 22% 37% 17% 1	270
	11th to 20th	Day	29% 22% 37% 12%	248
	21st to end	Day	18% 25% 44% 12% 2	264
February	1st to 10th	Day	21% 22% 45% 10% 2	240
	11th to 20th	Day	29% 25% 31% 14% 2	240
	21st to end	Day	31% 23% 34% 10% 2	198
March	1st to 10th	Day	22% 26% 38% 14% 1	240
	11th to 20th	Day	30% 19% 31% 17% 3	240
	21st to end	Day	31% 23% 34% 9% 2	264
April	1st to 10th	Day	19% 20% 36% 19% 5% 1	405
	11th to 20th	Day	23% 20% 33% 19% 5%	412
	21st to end	Day	26% 16% 34% 18% 5% 1	420
May	1st to 10th	Day	23% 13% 33% 23% 7% 1	550
	11th to 20th	Day	20% 12% 28% 25% 13% 2	625
	21st to end	Day	14% 7% 33% 26% 14% 6%	679
June	1st to 10th	Day	10% 5% 19% 33% 26% 7%	630
	11th to 20th	Day	8% 3 21% 39% 24% 4	630
	21st to end	Day	7% 3 29% 37% 20% 5%	630
July	1st to 10th	Day	11% 3 14% 31% 32% 10%	621
	11th to 20th	Day	4 3 15% 40% 31% 6%	618
	21st to end	Day	11% 1 12% 34% 31% 11%	684
August	1st to 10th	Day	10% 3 12% 41% 28% 6%	626
	11th to 20th	Day	9% 3 17% 35% 29% 7%	548
	21st to end	Day	10% 2 11% 33% 34% 10%	495
September	1st to 10th	Day	11% 2 11% 37% 30% 8%	450
	11th to 20th	Day	11% 1 18% 37% 24% 8%	413
	21st to end	Day	9% 6% 27% 33% 20% 4	270
October	1st to 10th	Day	13% 11% 30% 29% 13% 4	270
	11th to 20th	Day	17% 17% 38% 22% 6%	270
	21st to end	Day	31% 15% 29% 22% 3 1	297
November	1st to 10th	Day	16% 12% 40% 23% 9% 1	270
	11th to 20th	Day	19% 21% 33% 20% 6% 1	270
	21st to end	Day	24% 21% 30% 20% 4 1	270
December	1st to 10th	Day	19% 23% 35% 15% 6% 2	270
	11th to 20th	Day	22% 19% 38% 16% 5%	270
	21st to end	Day	20% 29% 37% 13% 1	297
January	1st to 10th	Night	18% 20% 37% 20% 5%	950
	11th to 20th	Night	21% 18% 40% 16% 4	915
	21st to end	Night	19% 19% 40% 20% 2	990
February	1st to 10th	Night	20% 17% 44% 16% 2	900
	11th to 20th	Night	21% 17% 42% 18% 2	845
	21st to end	Night	21% 20% 40% 17% 2	561
March	1st to 10th	Night	20% 15% 40% 22% 3	540
	11th to 20th	Night	25% 14% 34% 21% 6%	540
	21st to end	Night	23% 16% 36% 21% 4	594
April	1st to 10th	Night	14% 15% 39% 27% 4	540
	11th to 20th	Night	18% 14% 37% 26% 5%	533
	21st to end	Night	23% 10% 39% 21% 6%	540
May	1st to 10th	Night	16% 7% 37% 33% 7%	540
	11th to 20th	Night	16% 5% 30% 32% 15% 1	531
	21st to end	Night	14% 5% 30% 31% 18% 2	584
June	1st to 10th	Night	10% 2 18% 42% 26% 2	540
	11th to 20th	Night	5% 2 24% 43% 24% 1	540
	21st to end	Night	4 2 23% 48% 22% 1	540
July	1st to 10th	Night	8% 1 12% 42% 31% 5%	525
	11th to 20th	Night	4 1 15% 43% 33% 4	522
	21st to end	Night	5% 1 12% 46% 33% 3	591
August	1st to 10th	Night	7% 2 14% 43% 32% 2	537
	11th to 20th	Night	10% 1 11% 48% 26% 3	534
	21st to end	Night	7% 13% 40% 35% 5%	594
September	1st to 10th	Night	10% 2 15% 38% 32% 3	540
	11th to 20th	Night	12% 1 14% 43% 27% 3	540
	21st to end	Night	11% 3 25% 38% 19% 3	604
October	1st to 10th	Night	8% 5% 31% 33% 20% 3	720
	11th to 20th	Night	18% 10% 35% 29% 7% 1	720
	21st to end	Night	22% 11% 33% 26% 8%	792
November	1st to 10th	Night	14% 10% 41% 26% 9%	740
	11th to 20th	Night	18% 14% 36% 24% 7%	769
	21st to end	Night	20% 14% 37% 22% 7%	950
December	1st to 10th	Night	22% 15% 38% 22% 4	950
	11th to 20th	Night	23% 13% 38% 22% 3	950
	21st to end	Night	21% 18% 40% 19% 2	1045

Page generated at 2024-01-10 18:35:22. Version ac07

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