The Oxbow
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The Oxbow clear sky chart from 2005-11-06 to 2024-03-06.

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	21% 9% 3 6% 5% 3 4 4 5% 6% 33%	78550
	Night	22% 9% 3 6% 5% 3 4 4 4 6% 33%	81004
Transparency	Day	51% 6% 11% 18% 12% 3	78259
	Night	53% 6% 11% 18% 10% 3	80816
Seeing	Day	23% 12% 24% 27% 12% 2	13864
	Night	25% 6% 18% 31% 19% 2	23009

By Month

Percentage Cloud Cover SW (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	33% 17% 5% 8% 7% 4 5% 4 4 4 10%	2539
	11th to 20th	Day	39% 14% 3 7% 6% 3 4 3 3 4 14%	2642
	21st to end	Day	31% 14% 5% 8% 6% 4 5% 4 5% 5% 13%	3146
February	1st to 10th	Day	27% 12% 6% 8% 7% 4 6% 5% 5% 6% 14%	1710
	11th to 20th	Day	28% 14% 4 8% 7% 4 5% 4 4 5% 18%	1665
	21st to end	Day	30% 15% 4 8% 6% 3 5% 4 3 4 17%	1475
March	1st to 10th	Day	28% 15% 5% 8% 8% 4 5% 4 5% 4 15%	2004
	11th to 20th	Day	30% 12% 4 7% 6% 3 4 4 4 6% 20%	1980
	21st to end	Day	31% 13% 4 8% 7% 4 6% 5% 4 5% 13%	2182
April	1st to 10th	Day	28% 13% 4 10% 7% 4 6% 3 4 4 17%	2160
	11th to 20th	Day	25% 13% 5% 7% 6% 3 5% 4 4 5% 22%	2130
	21st to end	Day	24% 10% 3 6% 6% 4 5% 4 5% 7% 26%	2340
May	1st to 10th	Day	17% 8% 4 6% 5% 3 4 5% 5% 7% 34%	2384
	11th to 20th	Day	20% 10% 4 7% 6% 3 4 4 5% 9% 28%	2477
	21st to end	Day	26% 7% 2 6% 6% 3 5% 4 6% 7% 28%	2723
June	1st to 10th	Day	22% 8% 4 6% 5% 3 4 4 5% 7% 32%	2520
	11th to 20th	Day	16% 7% 4 7% 7% 3 4 4 6% 8% 34%	2520
	21st to end	Day	9% 5% 2 4 3 2 3 3 5% 8% 55%	2520
July	1st to 10th	Day	5% 3 2 3 3 2 3 4 4 7% 63%	2520
	11th to 20th	Day	7% 3 2 4 2 1 3 3 4 6% 65%	2520
	21st to end	Day	4 3 1 2 2 1 2 3 3 5% 73%	2638
August	1st to 10th	Day	3 3 1 3 3 2 3 3 5% 9% 63%	2328
	11th to 20th	Day	4 3 1 3 3 2 3 3 4 6% 68%	2298
	21st to end	Day	5% 4 2 4 2 2 3 4 4 8% 62%	2458
September	1st to 10th	Day	6% 3 1 3 3 2 2 3 4 6% 67%	2160
	11th to 20th	Day	11% 6% 3 5% 5% 2 5% 4 5% 6% 48%	2111
	21st to end	Day	14% 5% 2 6% 5% 3 4 5% 5% 7% 44%	1922
October	1st to 10th	Day	16% 9% 3 6% 5% 3 4 4 5% 5% 41%	1800
	11th to 20th	Day	18% 7% 2 6% 5% 4 6% 5% 5% 8% 33%	1800
	21st to end	Day	22% 10% 3 6% 5% 3 5% 4 5% 7% 29%	1980
November	1st to 10th	Day	30% 11% 4 8% 6% 4 4 4 6% 6% 18%	1616
	11th to 20th	Day	31% 10% 4 8% 6% 3 4 5% 4 6% 19%	1520
	21st to end	Day	27% 10% 3 8% 6% 3 6% 5% 5% 7% 20%	1520
December	1st to 10th	Day	25% 9% 5% 9% 6% 2 4 4 5% 6% 23%	1520
	11th to 20th	Day	28% 11% 5% 9% 8% 4 6% 6% 6% 6% 11%	1928
	21st to end	Day	32% 15% 4 10% 9% 3 4 4 4 5% 10%	2794
January	1st to 10th	Night	34% 16% 5% 10% 7% 3 4 4 3 3 9%	4406
	11th to 20th	Night	38% 14% 4 8% 6% 3 3 3 3 4 15%	4318
	21st to end	Night	38% 15% 4 8% 5% 2 3 3 3 5% 15%	4521
February	1st to 10th	Night	26% 12% 4 8% 7% 4 5% 5% 5% 6% 17%	2470
	11th to 20th	Night	26% 11% 4 8% 6% 4 4 4 4 5% 25%	2402
	21st to end	Night	26% 13% 4 7% 5% 3 5% 5% 5% 6% 21%	1979
March	1st to 10th	Night	26% 13% 4 7% 6% 3 4 5% 5% 6% 21%	2071
	11th to 20th	Night	25% 10% 3 7% 7% 4 5% 4 5% 5% 25%	1980
	21st to end	Night	30% 13% 4 8% 6% 3 4 4 4 4 21%	2174
April	1st to 10th	Night	27% 12% 4 8% 6% 3 5% 3 4 5% 23%	1800
	11th to 20th	Night	20% 11% 4 6% 5% 3 4 3 5% 7% 31%	1775
	21st to end	Night	22% 9% 3 6% 5% 3 5% 5% 5% 7% 31%	1620
May	1st to 10th	Night	13% 7% 3 6% 6% 3 5% 4 5% 6% 42%	1576
	11th to 20th	Night	15% 9% 4 6% 6% 4 6% 4 5% 6% 36%	1416
	21st to end	Night	17% 6% 3 5% 4 3 4 5% 6% 8% 40%	1552
June	1st to 10th	Night	17% 7% 2 6% 6% 2 4 4 4 6% 42%	1440
	11th to 20th	Night	11% 6% 2 4 3 2 3 4 6% 10% 48%	1440
	21st to end	Night	8% 2 2 3 2 1 3 3 5% 8% 64%	1440
July	1st to 10th	Night	4 3 1 2 3 2 2 2 3 5% 73%	1440
	11th to 20th	Night	4 3 1 3 3 2 2 3 3 5% 71%	1440
	21st to end	Night	2 2 1 2 2 1 2 2 3 6% 79%	1676
August	1st to 10th	Night	2 2 1 2 2 1 3 4 5% 8% 69%	1611
	11th to 20th	Night	2 2 1 3 3 1 2 4 4 6% 71%	1602
	21st to end	Night	4 3 1 3 3 2 3 3 3 7% 68%	1898
September	1st to 10th	Night	5% 4 1 3 2 1 2 2 3 7% 69%	1800
	11th to 20th	Night	8% 5% 2 5% 5% 2 4 4 4 6% 56%	1846
	21st to end	Night	11% 6% 2 4 4 3 3 4 5% 7% 52%	2037
October	1st to 10th	Night	15% 6% 2 4 5% 2 4 3 4 5% 50%	2160
	11th to 20th	Night	17% 6% 3 6% 4 3 3 4 4 7% 43%	2160
	21st to end	Night	22% 10% 3 5% 5% 3 4 3 4 6% 35%	2376
November	1st to 10th	Night	27% 9% 3 6% 6% 3 4 4 5% 6% 25%	2460
	11th to 20th	Night	31% 8% 4 8% 7% 4 4 4 5% 5% 20%	2660
	21st to end	Night	22% 10% 4 7% 6% 4 5% 5% 5% 6% 28%	2660
December	1st to 10th	Night	25% 9% 4 7% 6% 4 5% 4 5% 6% 25%	2660
	11th to 20th	Night	30% 13% 5% 8% 6% 4 5% 4 4 5% 17%	3276
	21st to end	Night	28% 12% 5% 10% 8% 4 5% 5% 5% 5% 13%	4862

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	77% 6% 8% 6% 2 1	2539
	11th to 20th	Day	76% 4 6% 6% 4 4	2642
	21st to end	Day	70% 8% 9% 8% 5% 1	3146
February	1st to 10th	Day	67% 7% 9% 11% 5% 1	1710
	11th to 20th	Day	68% 6% 11% 9% 4 2	1674
	21st to end	Day	70% 6% 8% 10% 5% 1	1475
March	1st to 10th	Day	71% 5% 9% 12% 4	2004
	11th to 20th	Day	64% 5% 9% 15% 5% 1	1980
	21st to end	Day	72% 7% 8% 11% 2	2182
April	1st to 10th	Day	71% 4 10% 11% 5%	2160
	11th to 20th	Day	64% 5% 11% 11% 6% 2	2133
	21st to end	Day	57% 7% 13% 15% 7% 1	2340
May	1st to 10th	Day	48% 7% 16% 20% 9%	2384
	11th to 20th	Day	54% 6% 14% 19% 6% 1	2480
	21st to end	Day	55% 7% 16% 19% 4	2724
June	1st to 10th	Day	52% 5% 16% 22% 5%	2520
	11th to 20th	Day	48% 7% 18% 21% 6%	2520
	21st to end	Day	28% 4 17% 32% 16% 3	2520
July	1st to 10th	Day	22% 5% 12% 29% 24% 8%	2451
	11th to 20th	Day	21% 4 7% 23% 32% 12%	2445
	21st to end	Day	14% 2 7% 28% 39% 9%	2491
August	1st to 10th	Day	19% 5% 13% 36% 22% 6%	2312
	11th to 20th	Day	18% 4 11% 35% 27% 7%	2298
	21st to end	Day	21% 5% 11% 31% 27% 5%	2458
September	1st to 10th	Day	20% 4 9% 30% 25% 13%	2160
	11th to 20th	Day	35% 6% 11% 24% 18% 6%	2111
	21st to end	Day	38% 6% 11% 22% 17% 6%	1922
October	1st to 10th	Day	44% 6% 10% 17% 18% 5%	1800
	11th to 20th	Day	48% 8% 11% 15% 15% 3	1800
	21st to end	Day	54% 6% 10% 14% 13% 3	1980
November	1st to 10th	Day	67% 5% 10% 12% 6%	1616
	11th to 20th	Day	66% 6% 9% 9% 7% 3	1520
	21st to end	Day	61% 7% 9% 7% 13% 3	1520
December	1st to 10th	Day	61% 6% 9% 12% 11% 1	1520
	11th to 20th	Day	71% 8% 8% 9% 3	1928
	21st to end	Day	77% 6% 8% 7% 3 1	2794
January	1st to 10th	Night	79% 6% 6% 5% 3 1	4406
	11th to 20th	Night	74% 5% 6% 8% 4 3	4318
	21st to end	Night	74% 4 6% 10% 5% 1	4521
February	1st to 10th	Night	67% 6% 9% 13% 4	2470
	11th to 20th	Night	61% 6% 12% 13% 6% 2	2404
	21st to end	Night	63% 7% 10% 11% 6% 2	1979
March	1st to 10th	Night	63% 6% 10% 15% 6% 1	2071
	11th to 20th	Night	61% 5% 12% 16% 6% 1	1980
	21st to end	Night	67% 6% 13% 12% 3	2174
April	1st to 10th	Night	65% 5% 11% 15% 4	1800
	11th to 20th	Night	54% 6% 16% 15% 5% 3	1775
	21st to end	Night	53% 6% 14% 19% 7% 2	1620
May	1st to 10th	Night	44% 5% 17% 24% 9% 1	1576
	11th to 20th	Night	48% 5% 17% 22% 6% 3	1416
	21st to end	Night	42% 7% 23% 23% 5%	1552
June	1st to 10th	Night	43% 7% 16% 29% 4	1440
	11th to 20th	Night	33% 6% 22% 30% 8% 1	1440
	21st to end	Night	20% 4 20% 37% 15% 4	1440
July	1st to 10th	Night	16% 3 15% 31% 25% 10%	1400
	11th to 20th	Night	16% 3 10% 25% 34% 12%	1392
	21st to end	Night	8% 2 6% 33% 40% 11%	1583
August	1st to 10th	Night	14% 4 15% 40% 21% 6%	1602
	11th to 20th	Night	15% 4 10% 36% 29% 7%	1602
	21st to end	Night	17% 4 10% 36% 26% 8%	1898
September	1st to 10th	Night	17% 4 9% 31% 26% 13%	1800
	11th to 20th	Night	28% 6% 12% 29% 17% 8%	1846
	21st to end	Night	32% 5% 14% 23% 17% 9%	2037
October	1st to 10th	Night	37% 6% 11% 23% 17% 7%	2160
	11th to 20th	Night	42% 5% 13% 21% 16% 3	2160
	21st to end	Night	51% 5% 10% 15% 15% 4	2376
November	1st to 10th	Night	59% 7% 11% 14% 8% 1	2460
	11th to 20th	Night	65% 6% 10% 11% 6% 2	2660
	21st to end	Night	56% 6% 11% 11% 11% 5%	2660
December	1st to 10th	Night	59% 6% 10% 15% 10% 1	2660
	11th to 20th	Night	69% 7% 9% 10% 4	3276
	21st to end	Night	71% 10% 8% 8% 2 1	4862

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	41% 16% 24% 12% 7% 1	180
	11th to 20th	Day	42% 12% 20% 15% 9% 2	243
	21st to end	Day	31% 14% 20% 19% 13% 1	407
February	1st to 10th	Day	32% 14% 22% 20% 11% 1	370
	11th to 20th	Day	37% 18% 16% 20% 8% 1	365
	21st to end	Day	37% 16% 20% 20% 6% 1	337
March	1st to 10th	Day	37% 17% 25% 16% 5% 1	441
	11th to 20th	Day	33% 13% 22% 24% 8% 1	420
	21st to end	Day	35% 16% 21% 20% 7% 1	462
April	1st to 10th	Day	36% 18% 19% 19% 7% 2	420
	11th to 20th	Day	35% 16% 24% 15% 6% 4	412
	21st to end	Day	29% 16% 25% 21% 7% 2	420
May	1st to 10th	Day	21% 15% 29% 21% 12% 3	423
	11th to 20th	Day	28% 15% 25% 17% 13% 3	448
	21st to end	Day	22% 14% 22% 26% 13% 2	485
June	1st to 10th	Day	20% 14% 24% 29% 12% 1	450
	11th to 20th	Day	18% 18% 29% 26% 8% 1	450
	21st to end	Day	8% 9% 26% 40% 15% 2	450
July	1st to 10th	Day	7% 6% 26% 41% 17% 2	446
	11th to 20th	Day	4 7% 31% 39% 16% 3	444
	21st to end	Day	2 4 24% 48% 18% 3	487
August	1st to 10th	Day	4 5% 26% 40% 21% 3	447
	11th to 20th	Day	4 4 20% 42% 27% 4	437
	21st to end	Day	7% 7% 28% 39% 17% 3	495
September	1st to 10th	Day	7% 8% 29% 36% 17% 2	450
	11th to 20th	Day	15% 10% 25% 30% 17% 4	450
	21st to end	Day	18% 10% 30% 28% 10% 5%	450
October	1st to 10th	Day	20% 12% 26% 22% 16% 3	450
	11th to 20th	Day	22% 10% 21% 25% 18% 4	450
	21st to end	Day	29% 13% 21% 22% 11% 4	495
November	1st to 10th	Day	28% 21% 22% 19% 8% 3	262
	11th to 20th	Day	28% 16% 22% 22% 11% 2	180
	21st to end	Day	32% 16% 18% 21% 13% 1	180
December	1st to 10th	Day	33% 11% 22% 20% 11% 3	180
	11th to 20th	Day	39% 10% 23% 22% 5% 1	180
	21st to end	Day	40% 11% 21% 20% 8%	198
January	1st to 10th	Night	43% 9% 16% 20% 9% 3	760
	11th to 20th	Night	37% 8% 15% 23% 15% 2	760
	21st to end	Night	32% 6% 13% 31% 16% 3	836
February	1st to 10th	Night	31% 9% 15% 28% 16% 2	760
	11th to 20th	Night	32% 8% 17% 29% 14% 1	744
	21st to end	Night	31% 13% 16% 27% 13%	628
March	1st to 10th	Night	34% 8% 17% 28% 12% 1	742
	11th to 20th	Night	30% 7% 19% 29% 14% 1	720
	21st to end	Night	37% 7% 17% 26% 13%	792
April	1st to 10th	Night	34% 8% 18% 23% 15% 1	720
	11th to 20th	Night	26% 10% 21% 26% 15% 1	707
	21st to end	Night	26% 7% 17% 29% 20% 1	540
May	1st to 10th	Night	17% 7% 26% 31% 18% 2	496
	11th to 20th	Night	19% 5% 18% 32% 24% 2	354
	21st to end	Night	18% 3 23% 32% 23% 1	389
June	1st to 10th	Night	18% 4 18% 40% 19% 1	360
	11th to 20th	Night	12% 5% 25% 40% 15% 3	360
	21st to end	Night	9% 2 19% 46% 24%	360
July	1st to 10th	Night	5% 3 16% 47% 28% 1	350
	11th to 20th	Night	4 2 20% 53% 21% 1	348
	21st to end	Night	2 1 16% 48% 32% 1	494
August	1st to 10th	Night	3 2 14% 44% 33% 4	537
	11th to 20th	Night	4 2 11% 43% 36% 4	534
	21st to end	Night	7% 2 22% 42% 26% 2	710
September	1st to 10th	Night	8% 3 21% 39% 28% 1	720
	11th to 20th	Night	9% 4 15% 32% 34% 6%	720
	21st to end	Night	14% 4 18% 35% 26% 3	720
October	1st to 10th	Night	18% 4 19% 33% 23% 3	720
	11th to 20th	Night	21% 4 15% 31% 24% 5%	720
	21st to end	Night	27% 8% 19% 24% 18% 4	792
November	1st to 10th	Night	31% 7% 15% 29% 17% 1	740
	11th to 20th	Night	33% 9% 19% 24% 14% 2	760
	21st to end	Night	26% 8% 19% 29% 16% 2	760
December	1st to 10th	Night	31% 7% 17% 27% 16% 3	760
	11th to 20th	Night	39% 6% 16% 23% 15% 1	760
	21st to end	Night	41% 10% 18% 23% 7%	836

Page generated at 2024-03-03 03:28:57. Version ac07

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