Oregon Trail Overlook
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Oregon Trail Overlook clear sky chart from 2005-11-06 to 2024-11-02.

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	5% 5% 2 5% 4 4 4 3 5% 7% 57%	101189
	Night	6% 6% 2 6% 4 4 4 4 5% 7% 52%	97947
Transparency	Day	28% 3 10% 22% 21% 16%	100935
	Night	33% 3 12% 22% 18% 13%	97791
Seeing	Day	8% 9% 24% 29% 21% 10%	14487
	Night	9% 5% 21% 42% 21% 2	23903

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	6% 11% 4 9% 7% 5% 6% 4 7% 8% 33%	2539
	11th to 20th	Day	8% 11% 6% 11% 8% 6% 6% 4 5% 7% 27%	2540
	21st to end	Day	9% 11% 4 9% 6% 6% 5% 4 6% 7% 32%	2837
February	1st to 10th	Day	6% 8% 3 7% 5% 5% 4 4 6% 9% 41%	1719
	11th to 20th	Day	7% 10% 3 7% 5% 4 5% 3 6% 9% 41%	1850
	21st to end	Day	5% 8% 4 8% 6% 4 5% 5% 7% 8% 41%	1570
March	1st to 10th	Day	7% 9% 3 10% 6% 5% 6% 4 7% 9% 35%	3138
	11th to 20th	Day	4 7% 2 5% 4 3 3 3 5% 6% 59%	3450
	21st to end	Day	6% 7% 3 8% 6% 6% 6% 5% 7% 9% 38%	3855
April	1st to 10th	Day	6% 8% 2 6% 5% 5% 4 4 6% 9% 44%	2280
	11th to 20th	Day	5% 6% 2 6% 4 4 4 5% 6% 8% 51%	2335
	21st to end	Day	6% 5% 3 5% 4 4 3 3 6% 8% 53%	2470
May	1st to 10th	Day	6% 6% 2 7% 4 4 4 3 5% 7% 52%	4110
	11th to 20th	Day	3 3 1 4 3 3 3 3 5% 6% 68%	4071
	21st to end	Day	5% 3 1 4 3 3 5% 3 6% 8% 58%	4714
June	1st to 10th	Day	6% 3 1 4 4 4 5% 4 7% 9% 53%	2660
	11th to 20th	Day	4 3 1 4 3 3 3 4 4 8% 64%	2660
	21st to end	Day	2 2 1 2 2 2 3 2 4 6% 74%	2660
July	1st to 10th	Day	1 1 1 2 2 1 2 2 3 4 81%	4420
	11th to 20th	Day	2 2 1 3 2 2 3 3 4 5% 73%	4420
	21st to end	Day	2 2 1 3 2 3 3 3 4 5% 72%	4740
August	1st to 10th	Day	3 3 1 4 3 3 4 3 5% 7% 64%	4092
	11th to 20th	Day	1 1 1 2 2 2 3 2 4 5% 77%	4028
	21st to end	Day	2 3 1 3 2 2 2 2 3 4 77%	4305
September	1st to 10th	Day	1 2 1 3 3 2 3 2 4 4 75%	2236
	11th to 20th	Day	3 3 1 4 2 2 3 3 4 5% 68%	2090
	21st to end	Day	6% 3 1 3 2 3 2 3 4 6% 68%	2090
October	1st to 10th	Day	6% 4 2 4 3 3 3 3 4 6% 61%	2090
	11th to 20th	Day	4 3 2 3 4 4 3 3 4 7% 64%	1883
	21st to end	Day	4 3 1 4 3 4 4 3 6% 9% 58%	1881
November	1st to 10th	Day	8% 7% 2 7% 5% 5% 4 3 5% 8% 47%	1683
	11th to 20th	Day	7% 5% 3 5% 5% 5% 5% 5% 7% 8% 45%	1710
	21st to end	Day	6% 8% 3 7% 6% 5% 3 4 6% 9% 43%	1710
December	1st to 10th	Day	9% 8% 3 8% 6% 5% 4 3 6% 6% 42%	1631
	11th to 20th	Day	8% 9% 4 9% 7% 6% 5% 4 8% 9% 32%	1928
	21st to end	Day	7% 8% 4 10% 6% 5% 5% 4 8% 7% 37%	2794
January	1st to 10th	Night	8% 11% 3 10% 6% 5% 6% 5% 7% 8% 32%	4406
	11th to 20th	Night	10% 13% 4 10% 7% 6% 6% 5% 6% 7% 24%	4420
	21st to end	Night	10% 12% 4 10% 5% 5% 4 4 5% 6% 34%	4817
February	1st to 10th	Night	8% 9% 4 8% 6% 4 5% 4 6% 8% 38%	2456
	11th to 20th	Night	7% 8% 3 6% 4 5% 4 4 5% 8% 47%	2218
	21st to end	Night	6% 10% 3 6% 5% 3 4 5% 8% 9% 42%	1884
March	1st to 10th	Night	7% 9% 3 7% 5% 4 5% 5% 7% 8% 39%	3736
	11th to 20th	Night	5% 6% 2 5% 4 4 4 3 5% 6% 56%	3530
	21st to end	Night	6% 7% 2 7% 6% 6% 6% 5% 7% 8% 40%	3783
April	1st to 10th	Night	7% 7% 2 6% 5% 5% 4 4 6% 7% 47%	1900
	11th to 20th	Night	5% 8% 2 5% 5% 4 4 4 5% 6% 50%	1791
	21st to end	Night	4 5% 2 5% 4 4 4 4 7% 8% 52%	1710
May	1st to 10th	Night	9% 5% 2 5% 3 3 4 4 7% 8% 49%	2860
	11th to 20th	Night	3 3 1 3 3 2 3 3 5% 7% 67%	2834
	21st to end	Night	5% 5% 2 5% 4 3 5% 3 6% 7% 55%	2860
June	1st to 10th	Night	6% 4 2 5% 4 5% 4 4 6% 8% 52%	1520
	11th to 20th	Night	3 3 2 4 3 3 3 3 4 8% 65%	1520
	21st to end	Night	1 1 1 2 2 2 3 3 5% 6% 73%	1520
July	1st to 10th	Night	1 1 1 2 2 3 2 3 4 79%	2540
	11th to 20th	Night	1 1 2 3 2 3 3 4 6% 76%	2540
	21st to end	Night	2 3 1 4 2 2 3 4 5% 7% 67%	2813
August	1st to 10th	Night	3 3 1 4 3 4 4 3 5% 7% 62%	2847
	11th to 20th	Night	2 1 1 2 2 3 3 3 4 6% 73%	2811
	21st to end	Night	2 2 1 3 2 3 3 2 3 4 74%	3365
September	1st to 10th	Night	3 2 1 3 2 3 3 2 3 5% 74%	1943
	11th to 20th	Night	4 3 1 3 2 4 4 3 4 7% 65%	2090
	21st to end	Night	5% 2 1 4 3 2 3 2 4 4 70%	2090
October	1st to 10th	Night	6% 3 1 4 2 3 3 2 5% 6% 64%	2090
	11th to 20th	Night	7% 3 2 4 4 3 4 3 5% 7% 60%	2294
	21st to end	Night	4 4 1 5% 3 4 4 4 6% 9% 57%	2717
November	1st to 10th	Night	9% 6% 2 5% 4 4 5% 4 6% 7% 48%	2418
	11th to 20th	Night	7% 5% 2 7% 5% 4 4 4 7% 8% 46%	2470
	21st to end	Night	6% 6% 3 6% 4 5% 5% 4 6% 7% 48%	2470
December	1st to 10th	Night	9% 9% 3 8% 5% 4 4 4 5% 9% 40%	2546
	11th to 20th	Night	11% 10% 4 9% 6% 5% 5% 4 7% 8% 31%	3276
	21st to end	Night	8% 9% 4 9% 5% 5% 5% 4 5% 7% 41%	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	49% 4 20% 21% 4	2539
	11th to 20th	Day	57% 5% 20% 15% 3	2540
	21st to end	Day	51% 3 24% 17% 5%	2837
February	1st to 10th	Day	40% 5% 23% 24% 6% 1	1719
	11th to 20th	Day	40% 5% 19% 26% 10% 1	1860
	21st to end	Day	40% 4 16% 27% 12% 1	1570
March	1st to 10th	Day	46% 3 12% 27% 11% 1	3138
	11th to 20th	Day	28% 2 11% 39% 19% 2	3450
	21st to end	Day	43% 2 13% 30% 11% 1	3855
April	1st to 10th	Day	37% 3 12% 26% 18% 5%	2280
	11th to 20th	Day	31% 3 10% 30% 21% 5%	2338
	21st to end	Day	30% 2 9% 30% 25% 4	2470
May	1st to 10th	Day	34% 1 5% 25% 28% 7%	4110
	11th to 20th	Day	18% 2 5% 28% 33% 13%	4074
	21st to end	Day	25% 2 9% 31% 28% 5%	4714
June	1st to 10th	Day	28% 3 12% 29% 24% 5%	2660
	11th to 20th	Day	21% 2 6% 22% 34% 15%	2660
	21st to end	Day	13% 1 3 18% 35% 29%	2660
July	1st to 10th	Day	9% 1 1 9% 19% 61%	4351
	11th to 20th	Day	14% 2 1 6% 20% 57%	4345
	21st to end	Day	15% 2 1 8% 28% 46%	4590
August	1st to 10th	Day	20% 3 3 12% 25% 37%	4078
	11th to 20th	Day	11% 2 2 12% 35% 39%	4067
	21st to end	Day	13% 2 1 12% 36% 35%	4304
September	1st to 10th	Day	14% 2 3 15% 32% 34%	2236
	11th to 20th	Day	20% 2 6% 26% 27% 19%	2090
	21st to end	Day	19% 2 5% 23% 38% 14%	2090
October	1st to 10th	Day	26% 2 9% 28% 26% 9%	2090
	11th to 20th	Day	22% 3 9% 37% 23% 6%	1883
	21st to end	Day	24% 2 16% 34% 21% 3	1881
November	1st to 10th	Day	37% 4 14% 28% 16% 2	1683
	11th to 20th	Day	35% 4 20% 32% 8% 1	1710
	21st to end	Day	38% 2 19% 31% 9%	1710
December	1st to 10th	Day	42% 5% 21% 22% 9% 1	1631
	11th to 20th	Day	48% 4 27% 19% 2	1928
	21st to end	Day	45% 3 20% 24% 8%	2794
January	1st to 10th	Night	49% 4 20% 21% 5%	4406
	11th to 20th	Night	58% 4 18% 17% 3	4420
	21st to end	Night	51% 4 21% 20% 4	4817
February	1st to 10th	Night	44% 5% 22% 23% 5% 1	2456
	11th to 20th	Night	36% 4 21% 28% 11% 1	2219
	21st to end	Night	37% 4 18% 29% 11% 1	1884
March	1st to 10th	Night	41% 3 14% 29% 11% 1	3736
	11th to 20th	Night	30% 2 12% 34% 20% 1	3530
	21st to end	Night	41% 3 14% 31% 11% 1	3783
April	1st to 10th	Night	37% 3 11% 27% 18% 5%	1900
	11th to 20th	Night	35% 3 7% 28% 22% 4	1791
	21st to end	Night	28% 3 10% 28% 26% 4	1710
May	1st to 10th	Night	33% 1 5% 25% 25% 10%	2860
	11th to 20th	Night	18% 1 5% 22% 39% 14%	2835
	21st to end	Night	29% 2 8% 22% 35% 4	2860
June	1st to 10th	Night	30% 2 9% 28% 25% 6%	1520
	11th to 20th	Night	20% 2 6% 19% 37% 15%	1520
	21st to end	Night	13% 2 3 16% 32% 34%	1520
July	1st to 10th	Night	11% 2 1 6% 18% 62%	2500
	11th to 20th	Night	11% 2 2 5% 17% 63%	2492
	21st to end	Night	17% 2 1 7% 30% 43%	2725
August	1st to 10th	Night	21% 3 3 10% 21% 43%	2838
	11th to 20th	Night	12% 3 2 13% 28% 42%	2838
	21st to end	Night	15% 2 2 10% 32% 39%	3365
September	1st to 10th	Night	15% 1 3 12% 31% 38%	1943
	11th to 20th	Night	21% 2 4 21% 29% 23%	2090
	21st to end	Night	20% 1 3 18% 35% 21%	2090
October	1st to 10th	Night	23% 2 7% 25% 29% 14%	2090
	11th to 20th	Night	26% 2 5% 31% 29% 6%	2294
	21st to end	Night	25% 3 12% 33% 23% 3	2717
November	1st to 10th	Night	35% 3 13% 28% 18% 3	2418
	11th to 20th	Night	35% 3 16% 32% 13% 1	2470
	21st to end	Night	34% 3 19% 33% 10%	2470
December	1st to 10th	Night	42% 4 24% 21% 8% 1	2546
	11th to 20th	Night	50% 4 21% 23% 2	3276
	21st to end	Night	45% 2 20% 25% 8%	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	18% 8% 28% 28% 14% 3	180
	11th to 20th	Day	8% 4 38% 28% 16% 6%	180
	21st to end	Day	14% 7% 25% 29% 22% 4	213
February	1st to 10th	Day	16% 11% 33% 27% 13% 1	279
	11th to 20th	Day	13% 13% 30% 27% 14% 4	455
	21st to end	Day	11% 16% 32% 30% 10% 1	382
March	1st to 10th	Day	10% 11% 33% 32% 11% 2	460
	11th to 20th	Day	8% 12% 31% 30% 16% 3	460
	21st to end	Day	11% 16% 33% 25% 12% 2	506
April	1st to 10th	Day	16% 16% 24% 22% 16% 6%	460
	11th to 20th	Day	11% 18% 31% 24% 12% 4	452
	21st to end	Day	10% 15% 32% 25% 15% 3	460
May	1st to 10th	Day	8% 15% 27% 29% 14% 7%	463
	11th to 20th	Day	13% 11% 23% 25% 18% 10%	488
	21st to end	Day	9% 8% 22% 24% 23% 14%	529
June	1st to 10th	Day	6% 8% 24% 27% 23% 12%	490
	11th to 20th	Day	7% 13% 29% 28% 17% 6%	490
	21st to end	Day	3 6% 24% 34% 23% 10%	490
July	1st to 10th	Day	3 4 21% 33% 27% 13%	486
	11th to 20th	Day	2 3 17% 36% 27% 14%	484
	21st to end	Day	3 2 12% 34% 34% 16%	531
August	1st to 10th	Day	6% 3 18% 32% 26% 14%	487
	11th to 20th	Day	2 4 14% 29% 30% 20%	477
	21st to end	Day	3 5% 17% 29% 26% 20%	539
September	1st to 10th	Day	3 4 16% 23% 32% 22%	490
	11th to 20th	Day	6% 3 19% 29% 27% 17%	490
	21st to end	Day	6% 8% 19% 26% 30% 12%	490
October	1st to 10th	Day	8% 7% 17% 24% 27% 18%	490
	11th to 20th	Day	6% 11% 21% 21% 27% 14%	333
	21st to end	Day	8% 8% 20% 39% 19% 5%	330
November	1st to 10th	Day	16% 5% 22% 34% 19% 4	273
	11th to 20th	Day	8% 8% 20% 37% 20% 7%	270
	21st to end	Day	13% 7% 20% 33% 21% 7%	270
December	1st to 10th	Day	16% 7% 23% 31% 16% 7%	232
	11th to 20th	Day	14% 9% 28% 29% 16% 4	180
	21st to end	Day	16% 10% 23% 32% 14% 6%	198
January	1st to 10th	Night	13% 4 23% 41% 17% 1	760
	11th to 20th	Night	13% 5% 23% 39% 18% 2	760
	21st to end	Night	13% 5% 19% 42% 19% 2	836
February	1st to 10th	Night	12% 5% 30% 40% 13% 1	760
	11th to 20th	Night	10% 6% 25% 42% 16% 1	744
	21st to end	Night	11% 9% 26% 39% 15%	628
March	1st to 10th	Night	10% 6% 28% 44% 12% 1	760
	11th to 20th	Night	8% 4 28% 39% 18% 2	760
	21st to end	Night	11% 9% 30% 37% 13% 1	836
April	1st to 10th	Night	12% 8% 22% 40% 16% 2	760
	11th to 20th	Night	10% 10% 30% 39% 10% 1	663
	21st to end	Night	6% 9% 27% 39% 17% 2	570
May	1st to 10th	Night	9% 8% 27% 36% 18% 2	570
	11th to 20th	Night	7% 7% 18% 41% 25% 3	561
	21st to end	Night	11% 7% 18% 32% 29% 3	471
June	1st to 10th	Night	8% 5% 16% 40% 28% 3	380
	11th to 20th	Night	5% 6% 23% 43% 23% 1	380
	21st to end	Night	3 3 21% 48% 25% 1	380
July	1st to 10th	Night	2 1 11% 55% 30% 1	370
	11th to 20th	Night	1 1 14% 56% 28%	368
	21st to end	Night	2 2 8% 51% 36% 1	444
August	1st to 10th	Night	5% 1 11% 52% 29% 1	567
	11th to 20th	Night	2 1 12% 52% 31% 1	564
	21st to end	Night	3 2 15% 46% 31% 3	755
September	1st to 10th	Night	3 2 12% 45% 34% 5%	760
	11th to 20th	Night	6% 3 12% 41% 33% 5%	760
	21st to end	Night	7% 4 12% 39% 32% 6%	760
October	1st to 10th	Night	7% 4 16% 43% 27% 4	760
	11th to 20th	Night	10% 4 17% 38% 28% 3	760
	21st to end	Night	8% 4 23% 40% 23% 3	836
November	1st to 10th	Night	13% 3 19% 42% 23% 1	744
	11th to 20th	Night	11% 5% 25% 40% 17% 2	760
	21st to end	Night	10% 5% 22% 38% 22% 3	760
December	1st to 10th	Night	13% 5% 24% 41% 16% 2	760
	11th to 20th	Night	18% 5% 18% 42% 16% 2	760
	21st to end	Night	18% 7% 25% 39% 10% 1	836

Page generated at 2024-10-29 23:22:59. Version ac07

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