Oxbow Trail Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Oxbow Trail Observatory clear sky chart from 2005-11-06 to 2024-11-05.

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	13% 9% 3 8% 5% 4 5% 4 6% 7% 38%	101485
	Night	13% 10% 4 8% 5% 4 4 3 5% 6% 38%	97642
Transparency	Day	43% 7% 12% 24% 12% 1	105000
	Night	45% 6% 12% 23% 13% 2	102267
Seeing	Day	17% 8% 29% 26% 15% 5%	15949
	Night	18% 7% 30% 32% 12% 1	25800

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% 14% 8% 13% 7% 5% 5% 3 4 4 26%	2527
	11th to 20th	Day	10% 13% 5% 13% 6% 5% 8% 7% 7% 6% 19%	2530
	21st to end	Day	15% 19% 8% 13% 5% 4 3 3 4 5% 19%	2847
February	1st to 10th	Day	11% 12% 4 10% 5% 5% 6% 4 5% 6% 31%	1710
	11th to 20th	Day	11% 12% 4 7% 6% 4 5% 4 5% 7% 35%	1779
	21st to end	Day	12% 12% 4 9% 7% 5% 5% 4 5% 6% 30%	1570
March	1st to 10th	Day	14% 8% 2 5% 4 3 4 3 5% 6% 46%	3120
	11th to 20th	Day	10% 7% 3 8% 5% 4 4 3 5% 8% 43%	3337
	21st to end	Day	22% 11% 3 10% 4 4 3 3 4 5% 29%	4132
April	1st to 10th	Day	17% 14% 3 8% 5% 4 4 4 5% 7% 31%	2280
	11th to 20th	Day	20% 10% 3 7% 5% 4 4 3 5% 6% 33%	2254
	21st to end	Day	20% 9% 3 7% 5% 4 5% 3 5% 6% 33%	2375
May	1st to 10th	Day	14% 7% 3 7% 5% 4 5% 3 6% 7% 40%	4242
	11th to 20th	Day	13% 5% 2 6% 4 4 4 4 5% 8% 45%	4399
	21st to end	Day	13% 7% 3 7% 5% 4 5% 4 5% 7% 40%	4824
June	1st to 10th	Day	12% 5% 2 6% 5% 4 5% 4 5% 8% 44%	2660
	11th to 20th	Day	13% 6% 3 6% 5% 4 4 4 6% 8% 41%	2660
	21st to end	Day	12% 6% 2 6% 4 5% 5% 4 7% 9% 42%	2660
July	1st to 10th	Day	12% 6% 3 7% 5% 5% 5% 5% 8% 9% 35%	4440
	11th to 20th	Day	5% 3 1 4 4 5% 5% 5% 8% 11% 49%	4440
	21st to end	Day	8% 6% 2 6% 5% 5% 5% 4 6% 8% 44%	4813
August	1st to 10th	Day	9% 5% 2 7% 5% 5% 6% 4 6% 9% 41%	4423
	11th to 20th	Day	13% 5% 2 5% 4 4 5% 4 6% 8% 46%	3838
	21st to end	Day	11% 6% 3 6% 5% 5% 5% 4 6% 8% 42%	4180
September	1st to 10th	Day	13% 6% 2 6% 4 4 4 4 5% 7% 46%	2280
	11th to 20th	Day	13% 5% 2 5% 4 4 4 4 5% 7% 49%	2211
	21st to end	Day	13% 7% 3 6% 4 4 4 4 5% 7% 43%	2090
October	1st to 10th	Day	13% 6% 3 6% 4 4 4 3 5% 7% 45%	1948
	11th to 20th	Day	19% 10% 3 8% 4 4 4 3 5% 7% 33%	1900
	21st to end	Day	18% 9% 3 8% 5% 4 3 3 5% 5% 37%	1886
November	1st to 10th	Day	13% 8% 3 6% 4 5% 4 3 6% 6% 42%	1708
	11th to 20th	Day	14% 13% 4 11% 6% 4 4 4 5% 7% 29%	1681
	21st to end	Day	14% 12% 4 8% 4 4 5% 3 5% 7% 35%	1520
December	1st to 10th	Day	12% 14% 5% 11% 6% 6% 4 3 4 6% 28%	1520
	11th to 20th	Day	12% 15% 4 11% 6% 5% 5% 4 5% 6% 26%	1918
	21st to end	Day	19% 20% 8% 13% 6% 4 4 3 4 5% 15%	2783
January	1st to 10th	Night	12% 14% 8% 13% 6% 4 3 3 3 4 32%	4428
	11th to 20th	Night	12% 13% 7% 14% 7% 5% 6% 6% 5% 4 20%	4440
	21st to end	Night	14% 20% 8% 10% 5% 4 3 3 4 4 24%	4816
February	1st to 10th	Night	9% 15% 5% 10% 5% 5% 4 4 4 4 33%	2470
	11th to 20th	Night	10% 10% 4 9% 5% 4 5% 3 4 6% 40%	2288
	21st to end	Night	16% 11% 5% 8% 4 4 4 3 5% 6% 34%	1884
March	1st to 10th	Night	15% 9% 3 6% 4 4 4 3 5% 5% 43%	3733
	11th to 20th	Night	10% 8% 2 6% 5% 5% 5% 4 6% 7% 42%	3654
	21st to end	Night	21% 11% 4 10% 4 4 4 3 3 5% 31%	3498
April	1st to 10th	Night	19% 11% 3 7% 4 3 4 3 4 5% 36%	1900
	11th to 20th	Night	20% 9% 3 7% 4 4 4 3 4 6% 37%	1875
	21st to end	Night	17% 9% 2 6% 4 5% 4 4 5% 6% 38%	1805
May	1st to 10th	Night	15% 9% 2 7% 5% 4 4 4 7% 8% 35%	2641
	11th to 20th	Night	11% 6% 2 6% 5% 4 5% 4 5% 7% 44%	2506
	21st to end	Night	14% 7% 3 7% 5% 5% 4 3 5% 6% 41%	2743
June	1st to 10th	Night	8% 6% 2 6% 5% 4 4 4 6% 7% 48%	1520
	11th to 20th	Night	10% 6% 2 6% 4 4 4 4 6% 9% 46%	1520
	21st to end	Night	9% 5% 2 5% 4 4 4 4 6% 8% 49%	1520
July	1st to 10th	Night	15% 6% 2 5% 4 3 4 3 5% 8% 44%	2530
	11th to 20th	Night	4 3 2 4 4 4 4 4 6% 8% 57%	2530
	21st to end	Night	8% 4 2 6% 4 4 5% 4 6% 9% 48%	2750
August	1st to 10th	Night	10% 5% 2 6% 4 3 4 4 6% 8% 47%	2517
	11th to 20th	Night	10% 7% 2 6% 5% 5% 4 4 6% 7% 44%	2990
	21st to end	Night	9% 5% 2 5% 4 4 4 4 6% 8% 49%	3476
September	1st to 10th	Night	10% 5% 3 5% 3 3 3 3 5% 7% 53%	1900
	11th to 20th	Night	13% 3 2 5% 3 3 3 4 5% 6% 52%	1949
	21st to end	Night	10% 7% 2 6% 4 3 4 3 4 7% 50%	2090
October	1st to 10th	Night	13% 6% 3 5% 4 3 4 3 4 7% 49%	2228
	11th to 20th	Night	17% 8% 2 6% 5% 4 4 4 5% 7% 39%	2280
	21st to end	Night	19% 9% 3 7% 5% 5% 4 3 5% 6% 35%	2710
November	1st to 10th	Night	13% 9% 3 6% 4 4 4 3 5% 5% 44%	2470
	11th to 20th	Night	14% 13% 4 8% 6% 5% 4 4 5% 5% 32%	2498
	21st to end	Night	15% 11% 4 7% 5% 4 4 3 5% 6% 37%	2660
December	1st to 10th	Night	13% 13% 5% 9% 5% 5% 5% 3 5% 6% 30%	2660
	11th to 20th	Night	13% 16% 6% 11% 6% 5% 4 4 4 4 27%	3279
	21st to end	Night	21% 17% 6% 11% 6% 5% 3 3 4 4 21%	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	61% 6% 14% 14% 5%	2528
	11th to 20th	Day	61% 9% 10% 16% 4	2530
	21st to end	Day	67% 5% 10% 13% 4	2847
February	1st to 10th	Day	53% 5% 13% 18% 9% 1	1710
	11th to 20th	Day	49% 6% 12% 22% 10% 2	1788
	21st to end	Day	55% 7% 10% 16% 10% 2	1570
March	1st to 10th	Day	38% 6% 11% 28% 14% 2	3120
	11th to 20th	Day	39% 5% 13% 27% 15% 1	3337
	21st to end	Day	57% 6% 10% 19% 7% 1	4132
April	1st to 10th	Day	53% 6% 11% 19% 11% 1	2280
	11th to 20th	Day	51% 6% 8% 20% 13% 2	2254
	21st to end	Day	50% 7% 12% 19% 11% 1	2375
May	1st to 10th	Day	41% 8% 12% 21% 17% 1	4280
	11th to 20th	Day	36% 7% 12% 31% 14% 1	4403
	21st to end	Day	41% 8% 10% 23% 16% 2	4837
June	1st to 10th	Day	36% 7% 14% 26% 15% 1	2660
	11th to 20th	Day	39% 8% 12% 25% 16% 1	2660
	21st to end	Day	36% 8% 15% 26% 13% 2	2660
July	1st to 10th	Day	42% 8% 14% 26% 9% 1	4371
	11th to 20th	Day	25% 9% 16% 33% 16% 1	4365
	21st to end	Day	35% 9% 13% 22% 18% 2	4662
August	1st to 10th	Day	37% 8% 16% 26% 12% 1	4408
	11th to 20th	Day	34% 7% 12% 35% 12%	3876
	21st to end	Day	38% 6% 12% 28% 15% 1	4179
September	1st to 10th	Day	37% 6% 12% 26% 18% 1	2280
	11th to 20th	Day	35% 6% 14% 31% 13% 1	2211
	21st to end	Day	39% 6% 12% 30% 12%	2090
October	1st to 10th	Day	24% 3 7% 41% 24% 1	3234
	11th to 20th	Day	40% 5% 9% 28% 16% 2	3140
	21st to end	Day	43% 3 13% 27% 12% 1	3086
November	1st to 10th	Day	41% 5% 16% 22% 14% 2	1708
	11th to 20th	Day	54% 6% 13% 19% 8% 1	1681
	21st to end	Day	50% 6% 15% 22% 7%	1520
December	1st to 10th	Day	58% 5% 14% 16% 6% 1	1520
	11th to 20th	Day	56% 5% 15% 15% 6% 2	1915
	21st to end	Day	72% 7% 7% 9% 4	2783
January	1st to 10th	Night	57% 5% 10% 20% 8% 1	4428
	11th to 20th	Night	63% 7% 10% 12% 7%	4440
	21st to end	Night	65% 5% 9% 16% 5%	4816
February	1st to 10th	Night	53% 6% 10% 20% 10% 2	2470
	11th to 20th	Night	45% 6% 11% 24% 11% 2	2289
	21st to end	Night	50% 6% 12% 19% 11% 2	1884
March	1st to 10th	Night	42% 6% 13% 26% 10% 4	3733
	11th to 20th	Night	36% 7% 11% 26% 18% 2	3654
	21st to end	Night	56% 6% 7% 20% 10% 2	3498
April	1st to 10th	Night	49% 6% 9% 18% 16% 1	1900
	11th to 20th	Night	48% 5% 8% 20% 16% 3	1875
	21st to end	Night	44% 7% 12% 22% 13% 2	1805
May	1st to 10th	Night	44% 8% 14% 17% 17%	2668
	11th to 20th	Night	35% 10% 12% 25% 17% 1	2507
	21st to end	Night	41% 8% 11% 19% 17% 4	2751
June	1st to 10th	Night	33% 8% 13% 27% 17% 1	1520
	11th to 20th	Night	35% 7% 10% 28% 19% 2	1520
	21st to end	Night	32% 7% 18% 26% 15% 3	1520
July	1st to 10th	Night	38% 5% 17% 22% 13% 4	2490
	11th to 20th	Night	23% 6% 16% 35% 18% 2	2482
	21st to end	Night	31% 8% 15% 22% 21% 3	2662
August	1st to 10th	Night	34% 6% 16% 23% 19% 1	2508
	11th to 20th	Night	37% 7% 11% 30% 14% 1	3018
	21st to end	Night	32% 6% 15% 25% 20% 3	3476
September	1st to 10th	Night	31% 6% 12% 27% 23% 1	1900
	11th to 20th	Night	31% 6% 12% 34% 16% 1	1949
	21st to end	Night	35% 6% 11% 31% 17% 1	2090
October	1st to 10th	Night	27% 3 6% 36% 26% 2	3722
	11th to 20th	Night	33% 5% 12% 30% 19% 2	3779
	21st to end	Night	45% 5% 10% 24% 16%	4460
November	1st to 10th	Night	41% 6% 11% 25% 15% 2	2470
	11th to 20th	Night	52% 6% 13% 17% 11% 1	2498
	21st to end	Night	48% 6% 14% 24% 7% 1	2660
December	1st to 10th	Night	54% 6% 13% 18% 8% 1	2660
	11th to 20th	Night	59% 6% 11% 16% 7% 1	3281
	21st to end	Night	66% 7% 9% 13% 5%	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	20% 9% 31% 27% 9% 4	270
	11th to 20th	Day	21% 10% 34% 27% 6% 2	270
	21st to end	Day	24% 5% 33% 29% 7%	297
February	1st to 10th	Day	14% 11% 41% 23% 9% 1	270
	11th to 20th	Day	19% 16% 36% 21% 7% 1	270
	21st to end	Day	18% 13% 43% 24% 2	225
March	1st to 10th	Day	22% 13% 35% 24% 5%	270
	11th to 20th	Day	21% 13% 34% 21% 6% 5%	270
	21st to end	Day	27% 8% 31% 23% 8% 2	486
April	1st to 10th	Day	27% 12% 32% 23% 6%	460
	11th to 20th	Day	29% 12% 28% 17% 11% 3	452
	21st to end	Day	22% 11% 30% 23% 12% 3	460
May	1st to 10th	Day	20% 8% 34% 26% 11% 1	558
	11th to 20th	Day	20% 8% 30% 25% 13% 4	675
	21st to end	Day	19% 8% 25% 28% 14% 6%	734
June	1st to 10th	Day	10% 9% 30% 30% 17% 4	680
	11th to 20th	Day	15% 7% 30% 28% 16% 4	680
	21st to end	Day	15% 7% 25% 29% 18% 5%	680
July	1st to 10th	Day	9% 3 18% 29% 29% 12%	671
	11th to 20th	Day	9% 4 25% 29% 24% 10%	668
	21st to end	Day	7% 2 24% 32% 25% 9%	739
August	1st to 10th	Day	8% 4 22% 30% 24% 12%	676
	11th to 20th	Day	14% 3 16% 28% 25% 14%	542
	21st to end	Day	14% 4 19% 30% 23% 8%	539
September	1st to 10th	Day	15% 5% 23% 29% 21% 8%	490
	11th to 20th	Day	14% 3 19% 30% 25% 10%	490
	21st to end	Day	17% 6% 27% 22% 21% 6%	490
October	1st to 10th	Day	16% 11% 24% 29% 18% 4	348
	11th to 20th	Day	24% 11% 33% 21% 9% 1	300
	21st to end	Day	24% 11% 35% 21% 7% 2	330
November	1st to 10th	Day	19% 11% 34% 24% 10% 2	282
	11th to 20th	Day	19% 14% 39% 21% 6% 1	270
	21st to end	Day	20% 15% 40% 20% 5%	270
December	1st to 10th	Day	19% 14% 39% 21% 6% 1	270
	11th to 20th	Day	20% 13% 37% 19% 10% 1	270
	21st to end	Day	26% 13% 40% 17% 4	297
January	1st to 10th	Night	18% 11% 35% 26% 9% 1	950
	11th to 20th	Night	22% 9% 34% 27% 6% 1	950
	21st to end	Night	22% 9% 32% 31% 7%	1045
February	1st to 10th	Night	18% 8% 37% 29% 7% 1	950
	11th to 20th	Night	17% 11% 36% 28% 8%	813
	21st to end	Night	23% 10% 36% 26% 4 1	628
March	1st to 10th	Night	21% 8% 34% 28% 8% 1	760
	11th to 20th	Night	18% 8% 37% 29% 8% 1	679
	21st to end	Night	24% 6% 30% 31% 7% 2	627
April	1st to 10th	Night	25% 8% 37% 24% 6%	570
	11th to 20th	Night	24% 9% 30% 31% 6% 1	563
	21st to end	Night	20% 8% 30% 34% 7% 1	570
May	1st to 10th	Night	21% 6% 33% 32% 7%	570
	11th to 20th	Night	18% 5% 33% 34% 9%	561
	21st to end	Night	14% 5% 27% 36% 17% 1	617
June	1st to 10th	Night	10% 3 29% 42% 14% 1	570
	11th to 20th	Night	12% 4 29% 42% 13% 1	570
	21st to end	Night	10% 4 27% 42% 17%	570
July	1st to 10th	Night	9% 3 17% 40% 28% 3	555
	11th to 20th	Night	8% 3 21% 42% 23% 2	552
	21st to end	Night	7% 2 15% 49% 25% 2	624
August	1st to 10th	Night	8% 2 16% 47% 25% 2	567
	11th to 20th	Night	11% 1 16% 41% 27% 5%	564
	21st to end	Night	12% 3 18% 42% 24% 2	627
September	1st to 10th	Night	11% 4 23% 36% 22% 4	570
	11th to 20th	Night	15% 4 21% 35% 22% 3	619
	21st to end	Night	14% 7% 24% 33% 20% 2	760
October	1st to 10th	Night	16% 6% 27% 33% 17% 1	760
	11th to 20th	Night	22% 10% 30% 29% 9%	760
	21st to end	Night	25% 7% 29% 31% 8% 1	836
November	1st to 10th	Night	17% 9% 36% 27% 11% 1	760
	11th to 20th	Night	22% 11% 39% 22% 6% 1	788
	21st to end	Night	22% 11% 35% 25% 7%	950
December	1st to 10th	Night	21% 11% 40% 21% 6%	950
	11th to 20th	Night	23% 10% 35% 26% 6% 1	950
	21st to end	Night	29% 10% 32% 25% 3	1045

Page generated at 2024-11-03 01:11:29. Version ac07

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