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 2024-11-01.

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% 3 7% 4 4 4 3 5% 6% 38%	101479
	Night	19% 10% 3 7% 4 4 4 3 4 5% 37%	97661
Transparency	Day	46% 6% 11% 18% 14% 6%	101228
	Night	49% 5% 12% 18% 11% 4	97501
Seeing	Day	22% 12% 24% 27% 12% 2	14824
	Night	24% 6% 18% 31% 19% 2	23763

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% 18% 4 10% 6% 5% 4 3 4 4 10%	2539
	11th to 20th	Day	39% 15% 3 8% 5% 4 3 2 3 4 14%	2642
	21st to end	Day	31% 14% 5% 10% 5% 5% 5% 3 5% 5% 13%	3146
February	1st to 10th	Day	27% 13% 5% 9% 5% 5% 5% 4 5% 6% 14%	1710
	11th to 20th	Day	27% 15% 4 9% 6% 5% 5% 3 4 5% 18%	1665
	21st to end	Day	29% 17% 3 9% 5% 4 5% 3 3 4 17%	1475
March	1st to 10th	Day	21% 18% 4 9% 6% 5% 5% 3 5% 5% 18%	3399
	11th to 20th	Day	20% 11% 3 8% 5% 4 4 3 4 5% 34%	3490
	21st to end	Day	27% 14% 4 10% 6% 6% 6% 4 5% 4 14%	3841
April	1st to 10th	Day	26% 15% 4 11% 6% 6% 5% 3 4 4 18%	2280
	11th to 20th	Day	24% 15% 4 8% 6% 4 4 3 5% 5% 22%	2251
	21st to end	Day	24% 10% 3 8% 5% 5% 4 4 6% 7% 25%	2470
May	1st to 10th	Day	20% 8% 3 8% 5% 5% 5% 3 5% 5% 34%	4193
	11th to 20th	Day	11% 6% 2 5% 4 3 3 3 5% 8% 51%	4377
	21st to end	Day	16% 6% 2 7% 5% 5% 6% 5% 7% 8% 32%	4813
June	1st to 10th	Day	21% 10% 3 7% 5% 4 4 3 5% 7% 32%	2660
	11th to 20th	Day	15% 8% 3 8% 6% 4 4 4 6% 8% 34%	2660
	21st to end	Day	9% 5% 2 4 3 3 3 3 5% 8% 55%	2660
July	1st to 10th	Day	3 2 1 3 2 2 2 2 2 5% 77%	4420
	11th to 20th	Day	4 3 1 3 2 2 2 2 3 5% 72%	4420
	21st to end	Day	3 3 2 3 2 2 2 2 3 5% 74%	4612
August	1st to 10th	Day	2 4 1 4 3 3 3 2 5% 7% 66%	4091
	11th to 20th	Day	5% 5% 1 4 3 3 3 3 5% 7% 60%	4026
	21st to end	Day	7% 5% 2 4 3 3 3 3 5% 7% 59%	4314
September	1st to 10th	Day	6% 3 1 4 3 2 3 3 4 6% 66%	2280
	11th to 20th	Day	11% 6% 3 6% 4 3 4 3 5% 6% 47%	2228
	21st to end	Day	13% 5% 2 7% 3 4 4 3 5% 7% 46%	2028
October	1st to 10th	Day	15% 9% 2 7% 4 4 4 3 4 5% 42%	1900
	11th to 20th	Day	17% 8% 3 7% 5% 6% 5% 5% 5% 7% 33%	1900
	21st to end	Day	22% 11% 3 8% 4 4 5% 3 5% 7% 28%	2090
November	1st to 10th	Day	29% 11% 4 9% 5% 5% 4 3 6% 6% 18%	1617
	11th to 20th	Day	31% 10% 4 9% 5% 4 4 5% 4 6% 18%	1520
	21st to end	Day	27% 11% 3 8% 5% 5% 6% 3 5% 7% 20%	1520
December	1st to 10th	Day	25% 10% 4 10% 6% 4 4 4 5% 5% 23%	1520
	11th to 20th	Day	28% 12% 5% 10% 7% 5% 6% 5% 6% 5% 11%	1928
	21st to end	Day	32% 16% 4 11% 8% 4 3 3 4 5% 10%	2794
January	1st to 10th	Night	34% 17% 4 12% 6% 4 4 3 3 3 9%	4406
	11th to 20th	Night	37% 14% 4 9% 5% 4 3 2 3 4 15%	4318
	21st to end	Night	37% 15% 4 8% 4 3 3 2 3 5% 15%	4521
February	1st to 10th	Night	26% 13% 4 9% 6% 5% 5% 3 5% 6% 17%	2470
	11th to 20th	Night	26% 11% 4 8% 5% 5% 4 3 4 5% 25%	2402
	21st to end	Night	26% 15% 3 8% 4 4 5% 4 5% 6% 21%	1979
March	1st to 10th	Night	22% 20% 4 7% 5% 4 4 3 5% 6% 21%	3474
	11th to 20th	Night	18% 11% 3 7% 5% 4 3 3 4 4 38%	3490
	21st to end	Night	24% 16% 5% 11% 6% 5% 5% 3 4 5% 18%	3812
April	1st to 10th	Night	26% 13% 4 9% 5% 5% 4 2 4 5% 23%	1900
	11th to 20th	Night	19% 13% 3 7% 5% 4 4 3 5% 6% 31%	1874
	21st to end	Night	22% 10% 2 7% 4 4 4 5% 5% 7% 31%	1710
May	1st to 10th	Night	21% 10% 3 6% 4 3 4 3 3 4 39%	2774
	11th to 20th	Night	8% 6% 2 5% 3 3 3 2 4 5% 57%	2516
	21st to end	Night	14% 7% 2 5% 4 4 4 4 6% 8% 44%	2762
June	1st to 10th	Night	17% 7% 2 6% 5% 4 4 3 4 6% 41%	1520
	11th to 20th	Night	10% 7% 2 5% 3 3 3 3 6% 9% 49%	1520
	21st to end	Night	8% 3 2 3 2 2 4 2 5% 7% 63%	1520
July	1st to 10th	Night	2 2 1 2 1 1 1 1 2 3 84%	2540
	11th to 20th	Night	3 2 3 2 3 2 2 3 5% 75%	2540
	21st to end	Night	2 2 1 4 2 2 2 1 3 4 76%	2942
August	1st to 10th	Night	2 3 1 3 2 2 3 3 5% 7% 70%	2848
	11th to 20th	Night	3 4 2 6% 4 4 3 4 5% 7% 59%	2812
	21st to end	Night	4 4 2 4 2 2 3 2 3 6% 68%	3360
September	1st to 10th	Night	5% 4 1 3 2 2 3 2 4 7% 68%	1900
	11th to 20th	Night	8% 5% 2 6% 4 3 4 3 4 7% 55%	1949
	21st to end	Night	11% 6% 2 5% 3 3 3 3 5% 7% 54%	2151
October	1st to 10th	Night	14% 6% 2 5% 4 3 3 3 4 5% 51%	2280
	11th to 20th	Night	17% 7% 2 7% 4 4 4 3 4 7% 41%	2280
	21st to end	Night	22% 10% 3 6% 4 4 4 2 4 5% 34%	2508
November	1st to 10th	Night	27% 10% 3 8% 5% 4 4 4 5% 6% 25%	2465
	11th to 20th	Night	31% 9% 3 9% 6% 5% 4 4 5% 5% 20%	2660
	21st to end	Night	22% 11% 3 8% 5% 5% 4 4 5% 6% 27%	2660
December	1st to 10th	Night	25% 10% 3 8% 5% 5% 4 3 5% 6% 25%	2660
	11th to 20th	Night	30% 13% 4 9% 5% 5% 5% 3 4 5% 17%	3276
	21st to end	Night	28% 12% 4 12% 7% 5% 5% 4 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	65% 6% 10% 16% 3	3399
	11th to 20th	Day	51% 6% 8% 22% 12% 1	3490
	21st to end	Day	68% 10% 11% 8% 3	3841
April	1st to 10th	Day	70% 5% 10% 11% 5%	2280
	11th to 20th	Day	63% 6% 11% 12% 6% 2	2254
	21st to end	Day	57% 7% 13% 15% 7% 1	2470
May	1st to 10th	Day	50% 8% 13% 19% 10%	4193
	11th to 20th	Day	32% 5% 15% 33% 15% 1	4380
	21st to end	Day	44% 11% 25% 18% 2	4814
June	1st to 10th	Day	52% 5% 15% 21% 6% 1	2660
	11th to 20th	Day	46% 7% 17% 22% 7% 1	2660
	21st to end	Day	28% 4 17% 33% 16% 3	2660
July	1st to 10th	Day	13% 3 7% 17% 26% 34%	4351
	11th to 20th	Day	16% 3 5% 17% 29% 30%	4345
	21st to end	Day	14% 2 8% 26% 39% 11%	4466
August	1st to 10th	Day	19% 3 9% 26% 33% 11%	4076
	11th to 20th	Day	23% 4 11% 39% 18% 4	4065
	21st to end	Day	25% 5% 12% 25% 25% 8%	4313
September	1st to 10th	Day	20% 4 9% 30% 25% 13%	2280
	11th to 20th	Day	35% 6% 12% 23% 18% 6%	2228
	21st to end	Day	37% 6% 11% 24% 17% 6%	2028
October	1st to 10th	Day	43% 6% 10% 17% 19% 6%	1900
	11th to 20th	Day	48% 7% 11% 16% 15% 3	1900
	21st to end	Day	55% 6% 10% 14% 12% 3	2090
November	1st to 10th	Day	67% 5% 10% 12% 6%	1617
	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% 7% 12% 14% 3	3474
	11th to 20th	Night	49% 6% 13% 21% 10% 2	3490
	21st to end	Night	67% 7% 14% 11% 2	3812
April	1st to 10th	Night	63% 6% 12% 15% 4	1900
	11th to 20th	Night	53% 7% 16% 16% 5% 3	1874
	21st to end	Night	53% 6% 14% 20% 6% 2	1710
May	1st to 10th	Night	48% 5% 15% 21% 10% 1	2774
	11th to 20th	Night	29% 4 13% 38% 14% 2	2516
	21st to end	Night	36% 8% 34% 19% 3	2762
June	1st to 10th	Night	43% 7% 16% 29% 4 1	1520
	11th to 20th	Night	32% 6% 22% 31% 8% 1	1520
	21st to end	Night	20% 4 20% 37% 15% 4	1520
July	1st to 10th	Night	9% 2 9% 21% 25% 35%	2500
	11th to 20th	Night	12% 3 7% 19% 30% 30%	2492
	21st to end	Night	12% 3 9% 28% 40% 8%	2850
August	1st to 10th	Night	14% 3 10% 30% 33% 10%	2839
	11th to 20th	Night	24% 4 16% 34% 19% 4	2839
	21st to end	Night	19% 4 10% 33% 27% 7%	3360
September	1st to 10th	Night	17% 4 9% 31% 26% 13%	1900
	11th to 20th	Night	29% 6% 13% 29% 16% 7%	1949
	21st to end	Night	30% 5% 14% 25% 17% 8%	2151
October	1st to 10th	Night	36% 5% 10% 23% 18% 7%	2280
	11th to 20th	Night	43% 5% 14% 21% 15% 3	2280
	21st to end	Night	52% 5% 10% 16% 14% 4	2508
November	1st to 10th	Night	59% 7% 11% 14% 8% 1	2465
	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	36% 17% 25% 17% 5% 1	460
	11th to 20th	Day	31% 13% 22% 23% 9% 2	460
	21st to end	Day	35% 16% 21% 20% 6% 1	506
April	1st to 10th	Day	34% 17% 20% 20% 8% 2	460
	11th to 20th	Day	34% 17% 24% 15% 7% 3	452
	21st to end	Day	30% 16% 25% 20% 7% 2	460
May	1st to 10th	Day	23% 14% 29% 20% 11% 2	463
	11th to 20th	Day	26% 14% 27% 17% 13% 3	488
	21st to end	Day	21% 14% 23% 26% 13% 2	529
June	1st to 10th	Day	20% 14% 24% 30% 11% 1	490
	11th to 20th	Day	17% 19% 30% 26% 8% 1	490
	21st to end	Day	7% 10% 26% 40% 14% 2	490
July	1st to 10th	Day	7% 6% 27% 41% 16% 2	486
	11th to 20th	Day	4 7% 32% 39% 15% 3	484
	21st to end	Day	2 5% 25% 47% 18% 3	531
August	1st to 10th	Day	4 5% 27% 40% 21% 3	487
	11th to 20th	Day	4 5% 20% 40% 26% 4	477
	21st to end	Day	7% 8% 28% 37% 17% 3	539
September	1st to 10th	Day	7% 8% 28% 37% 17% 3	490
	11th to 20th	Day	14% 10% 27% 29% 16% 4	490
	21st to end	Day	17% 10% 31% 28% 9% 5%	490
October	1st to 10th	Day	19% 12% 27% 22% 17% 3	490
	11th to 20th	Day	21% 11% 21% 26% 18% 4	490
	21st to end	Day	29% 14% 22% 21% 10% 4	539
November	1st to 10th	Day	28% 21% 22% 19% 8% 3	263
	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	760
	11th to 20th	Night	29% 6% 19% 29% 14% 2	760
	21st to end	Night	35% 8% 18% 25% 13%	836
April	1st to 10th	Night	33% 9% 18% 24% 15% 1	760
	11th to 20th	Night	25% 11% 22% 26% 15% 1	746
	21st to end	Night	26% 8% 17% 29% 19% 1	570
May	1st to 10th	Night	18% 8% 25% 30% 17% 2	523
	11th to 20th	Night	18% 5% 19% 33% 23% 2	374
	21st to end	Night	18% 4 23% 32% 22% 1	411
June	1st to 10th	Night	18% 5% 17% 40% 19% 1	380
	11th to 20th	Night	11% 5% 26% 40% 14% 3	380
	21st to end	Night	9% 2 19% 46% 24%	380
July	1st to 10th	Night	4 2 18% 47% 27% 1	370
	11th to 20th	Night	4 2 20% 54% 20% 1	368
	21st to end	Night	2 2 16% 47% 31% 2	522
August	1st to 10th	Night	3 2 15% 45% 31% 4	567
	11th to 20th	Night	4 2 12% 43% 35% 4	564
	21st to end	Night	6% 3 22% 41% 26% 2	750
September	1st to 10th	Night	7% 3 21% 40% 27% 1	760
	11th to 20th	Night	9% 5% 16% 32% 32% 5%	760
	21st to end	Night	14% 4 19% 36% 25% 3	760
October	1st to 10th	Night	17% 4 20% 33% 23% 3	760
	11th to 20th	Night	20% 4 16% 31% 24% 5%	760
	21st to end	Night	27% 8% 19% 25% 17% 4	836
November	1st to 10th	Night	31% 8% 15% 29% 17% 1	742
	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 2024-10-29 08:20:52. Version ac07

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