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 2024-03-06.

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	5% 5% 2 5% 5% 3 4 4 5% 7% 53%	78533
	Night	7% 6% 3 5% 5% 3 5% 5% 5% 7% 49%	81002
Transparency	Day	31% 3 12% 23% 20% 12%	78239
	Night	35% 3 13% 23% 16% 9%	80818
Seeing	Day	9% 9% 23% 29% 21% 10%	13545
	Night	9% 5% 21% 42% 21% 2	23139

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% 5% 7% 8% 4 6% 5% 6% 8% 33%	2539
	11th to 20th	Day	8% 11% 6% 9% 10% 5% 6% 5% 5% 7% 27%	2540
	21st to end	Day	9% 10% 4 7% 7% 5% 5% 5% 6% 7% 33%	2837
February	1st to 10th	Day	6% 8% 3 6% 6% 4 5% 5% 6% 9% 41%	1719
	11th to 20th	Day	7% 9% 3 6% 6% 3 5% 4 6% 9% 41%	1850
	21st to end	Day	5% 7% 4 7% 6% 3 4 6% 7% 8% 41%	1570
March	1st to 10th	Day	7% 6% 3 7% 7% 4 6% 6% 6% 9% 38%	1851
	11th to 20th	Day	6% 8% 3 5% 5% 3 4 6% 7% 8% 44%	1953
	21st to end	Day	7% 7% 3 6% 6% 4 6% 6% 6% 9% 40%	2196
April	1st to 10th	Day	6% 7% 3 6% 6% 4 5% 5% 6% 9% 44%	2160
	11th to 20th	Day	5% 6% 3 6% 5% 3 4 5% 6% 7% 50%	2210
	21st to end	Day	6% 5% 3 5% 4 3 4 4 5% 8% 53%	2340
May	1st to 10th	Day	5% 4 2 5% 4 3 5% 4 6% 8% 54%	2340
	11th to 20th	Day	5% 4 2 5% 5% 3 4 5% 7% 8% 50%	2301
	21st to end	Day	6% 4 2 4 5% 3 6% 5% 6% 9% 49%	2663
June	1st to 10th	Day	6% 3 2 3 4 3 6% 4 7% 9% 53%	2520
	11th to 20th	Day	4 3 1 3 4 2 4 4 4 8% 63%	2520
	21st to end	Day	2 2 1 2 2 1 3 3 4 6% 74%	2520
July	1st to 10th	Day	2 2 1 2 3 2 3 4 5% 7% 71%	2520
	11th to 20th	Day	2 2 1 2 2 1 3 3 4 5% 75%	2520
	21st to end	Day	3 2 1 3 3 2 4 3 3 5% 69%	2715
August	1st to 10th	Day	4 3 1 3 3 2 3 4 4 6% 65%	2328
	11th to 20th	Day	1 2 2 3 1 3 4 5% 6% 74%	2299
	21st to end	Day	2 2 1 2 2 2 3 3 4 5% 74%	2449
September	1st to 10th	Day	1 2 1 2 3 1 2 3 4 4 76%	2119
	11th to 20th	Day	4 3 1 4 2 2 2 4 4 5% 69%	1980
	21st to end	Day	6% 2 1 2 3 2 3 3 4 7% 66%	1980
October	1st to 10th	Day	6% 4 2 4 4 2 4 4 4 7% 59%	1980
	11th to 20th	Day	5% 3 2 3 4 3 3 4 4 7% 63%	1785
	21st to end	Day	4 3 2 4 4 3 4 4 6% 9% 58%	1782
November	1st to 10th	Day	8% 6% 3 7% 5% 3 5% 4 4 8% 48%	1674
	11th to 20th	Day	7% 5% 3 4 6% 3 5% 6% 7% 8% 45%	1710
	21st to end	Day	6% 7% 3 6% 6% 3 4 5% 6% 10% 43%	1710
December	1st to 10th	Day	9% 8% 3 7% 7% 4 4 4 5% 6% 42%	1631
	11th to 20th	Day	8% 8% 4 8% 8% 5% 5% 6% 8% 9% 32%	1928
	21st to end	Day	7% 7% 4 9% 7% 4 5% 5% 7% 7% 37%	2794
January	1st to 10th	Night	9% 10% 3 9% 7% 4 6% 6% 7% 8% 33%	4406
	11th to 20th	Night	10% 13% 4 9% 8% 5% 6% 6% 6% 7% 25%	4420
	21st to end	Night	10% 11% 4 9% 6% 4 5% 5% 5% 6% 35%	4817
February	1st to 10th	Night	8% 8% 4 7% 7% 3 5% 5% 6% 8% 38%	2456
	11th to 20th	Night	7% 7% 3 5% 5% 3 5% 5% 5% 8% 47%	2218
	21st to end	Night	6% 8% 3 6% 5% 3 4 6% 7% 9% 42%	1884
March	1st to 10th	Night	6% 7% 4 6% 6% 3 5% 6% 7% 10% 41%	2225
	11th to 20th	Night	6% 6% 3 5% 6% 4 6% 5% 6% 9% 45%	2007
	21st to end	Night	8% 8% 3 7% 7% 4 6% 6% 5% 7% 40%	2158
April	1st to 10th	Night	8% 6% 2 5% 5% 4 5% 5% 6% 7% 47%	1800
	11th to 20th	Night	6% 8% 3 6% 5% 3 5% 5% 5% 6% 48%	1696
	21st to end	Night	4 4 2 5% 5% 3 4 5% 6% 8% 53%	1620
May	1st to 10th	Night	6% 4 2 5% 4 3 5% 5% 6% 8% 52%	1620
	11th to 20th	Night	6% 5% 1 5% 5% 3 4 5% 7% 10% 49%	1594
	21st to end	Night	8% 6% 2 5% 5% 3 6% 5% 7% 8% 44%	1608
June	1st to 10th	Night	6% 4 2 4 4 3 5% 5% 6% 9% 53%	1440
	11th to 20th	Night	4 2 2 4 3 2 3 4 4 9% 64%	1440
	21st to end	Night	1 1 1 2 3 2 3 4 5% 6% 73%	1440
July	1st to 10th	Night	1 2 1 2 3 2 4 4 5% 7% 68%	1440
	11th to 20th	Night	1 2 3 2 2 4 4 6% 77%	1440
	21st to end	Night	3 3 2 2 3 2 2 4 5% 6% 68%	1602
August	1st to 10th	Night	5% 3 1 3 4 2 4 4 5% 8% 63%	1611
	11th to 20th	Night	2 1 1 1 2 2 3 4 5% 7% 71%	1602
	21st to end	Night	2 2 1 2 3 2 4 4 4 6% 71%	1903
September	1st to 10th	Night	3 2 1 3 2 2 3 2 3 5% 74%	1840
	11th to 20th	Night	4 2 1 3 2 2 4 4 4 7% 66%	1980
	21st to end	Night	6% 2 1 3 4 2 2 3 4 5% 68%	1980
October	1st to 10th	Night	6% 3 1 4 3 2 4 3 5% 7% 62%	1980
	11th to 20th	Night	7% 3 1 4 5% 2 3 4 4 7% 60%	2172
	21st to end	Night	4 4 1 5% 4 2 4 5% 6% 9% 57%	2574
November	1st to 10th	Night	9% 5% 2 5% 5% 3 5% 5% 6% 8% 48%	2405
	11th to 20th	Night	8% 5% 3 6% 6% 3 4 5% 7% 9% 46%	2470
	21st to end	Night	6% 6% 3 5% 5% 3 6% 5% 6% 7% 48%	2470
December	1st to 10th	Night	10% 8% 3 7% 6% 3 4 5% 5% 9% 41%	2546
	11th to 20th	Night	11% 9% 5% 8% 7% 4 6% 5% 7% 9% 31%	3276
	21st to end	Night	9% 8% 4 7% 6% 3 5% 5% 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	42% 4 15% 26% 10% 2	1851
	11th to 20th	Day	36% 3 14% 32% 13% 2	1953
	21st to end	Day	41% 4 16% 27% 11% 2	2196
April	1st to 10th	Day	37% 3 12% 24% 19% 5%	2160
	11th to 20th	Day	32% 3 9% 30% 21% 4	2213
	21st to end	Day	30% 2 9% 30% 25% 4	2340
May	1st to 10th	Day	29% 2 6% 28% 28% 7%	2340
	11th to 20th	Day	30% 4 9% 31% 21% 6%	2304
	21st to end	Day	31% 4 13% 29% 19% 5%	2663
June	1st to 10th	Day	28% 3 12% 29% 24% 5%	2520
	11th to 20th	Day	22% 2 6% 22% 34% 14%	2520
	21st to end	Day	13% 1 3 19% 35% 29%	2520
July	1st to 10th	Day	14% 2 2 15% 32% 34%	2451
	11th to 20th	Day	12% 2 1 9% 28% 48%	2445
	21st to end	Day	18% 2 1 10% 24% 45%	2564
August	1st to 10th	Day	21% 2 4 16% 28% 30%	2313
	11th to 20th	Day	12% 3 2 16% 35% 32%	2299
	21st to end	Day	14% 2 2 16% 38% 28%	2449
September	1st to 10th	Day	14% 1 3 15% 32% 34%	2119
	11th to 20th	Day	19% 2 6% 26% 27% 21%	1980
	21st to end	Day	20% 2 5% 23% 37% 13%	1980
October	1st to 10th	Day	27% 2 9% 29% 24% 8%	1980
	11th to 20th	Day	23% 3 9% 37% 23% 5%	1785
	21st to end	Day	24% 2 17% 34% 20% 2	1782
November	1st to 10th	Day	37% 4 14% 28% 16% 2	1674
	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	37% 5% 16% 29% 11% 2	2225
	11th to 20th	Night	37% 3 12% 31% 15% 2	2007
	21st to end	Night	43% 4 14% 25% 12% 1	2158
April	1st to 10th	Night	37% 3 10% 26% 19% 6%	1800
	11th to 20th	Night	36% 3 8% 28% 22% 3	1696
	21st to end	Night	28% 3 10% 29% 26% 4	1620
May	1st to 10th	Night	30% 2 5% 23% 32% 7%	1620
	11th to 20th	Night	30% 3 9% 29% 25% 5%	1595
	21st to end	Night	36% 3 11% 25% 20% 4	1608
June	1st to 10th	Night	30% 2 10% 28% 25% 6%	1440
	11th to 20th	Night	21% 2 7% 20% 36% 14%	1440
	21st to end	Night	13% 2 3 17% 32% 32%	1440
July	1st to 10th	Night	16% 3 1 10% 31% 39%	1400
	11th to 20th	Night	12% 2 2 8% 21% 55%	1392
	21st to end	Night	18% 2 1 8% 22% 49%	1513
August	1st to 10th	Night	21% 3 3 15% 21% 37%	1602
	11th to 20th	Night	13% 2 2 13% 30% 40%	1602
	21st to end	Night	17% 2 2 12% 32% 35%	1903
September	1st to 10th	Night	15% 2 3 12% 29% 39%	1840
	11th to 20th	Night	20% 2 4 20% 29% 25%	1980
	21st to end	Night	22% 2 4 18% 35% 20%	1980
October	1st to 10th	Night	24% 2 8% 27% 28% 12%	1980
	11th to 20th	Night	26% 2 5% 32% 29% 6%	2172
	21st to end	Night	25% 3 12% 33% 24% 3	2574
November	1st to 10th	Night	35% 3 13% 28% 18% 3	2405
	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% 10% 34% 33% 11% 2	441
	11th to 20th	Day	8% 12% 31% 31% 15% 2	420
	21st to end	Day	11% 17% 34% 23% 12% 2	462
April	1st to 10th	Day	16% 16% 24% 22% 16% 6%	420
	11th to 20th	Day	12% 18% 30% 25% 11% 4	412
	21st to end	Day	10% 16% 32% 24% 16% 3	420
May	1st to 10th	Day	7% 15% 26% 31% 14% 8%	423
	11th to 20th	Day	13% 11% 23% 25% 18% 10%	448
	21st to end	Day	10% 7% 22% 23% 24% 14%	485
June	1st to 10th	Day	6% 8% 25% 26% 22% 13%	450
	11th to 20th	Day	7% 13% 28% 29% 17% 6%	450
	21st to end	Day	3 6% 24% 33% 23% 10%	450
July	1st to 10th	Day	4 3 20% 33% 27% 13%	446
	11th to 20th	Day	3 3 18% 37% 26% 13%	444
	21st to end	Day	3 2 11% 34% 34% 15%	487
August	1st to 10th	Day	6% 3 19% 30% 27% 15%	447
	11th to 20th	Day	2 4 13% 28% 31% 21%	437
	21st to end	Day	2 4 17% 30% 27% 20%	495
September	1st to 10th	Day	4 5% 16% 24% 30% 22%	450
	11th to 20th	Day	6% 3 18% 29% 27% 17%	450
	21st to end	Day	7% 9% 18% 26% 30% 11%	450
October	1st to 10th	Day	8% 7% 18% 24% 26% 17%	450
	11th to 20th	Day	6% 11% 21% 23% 27% 12%	302
	21st to end	Day	8% 9% 19% 39% 19% 6%	297
November	1st to 10th	Day	16% 6% 22% 34% 19% 4	270
	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	9% 6% 28% 44% 12% 1	742
	11th to 20th	Night	9% 5% 28% 40% 18% 2	720
	21st to end	Night	11% 9% 29% 36% 13% 1	792
April	1st to 10th	Night	12% 8% 22% 40% 16% 2	720
	11th to 20th	Night	10% 11% 29% 39% 10% 1	628
	21st to end	Night	6% 9% 27% 39% 17% 2	540
May	1st to 10th	Night	8% 8% 26% 37% 19% 2	540
	11th to 20th	Night	7% 6% 17% 41% 26% 3	531
	21st to end	Night	11% 7% 18% 31% 29% 4	446
June	1st to 10th	Night	8% 6% 15% 39% 28% 3	360
	11th to 20th	Night	5% 6% 23% 42% 24% 1	360
	21st to end	Night	3 3 21% 47% 25% 1	360
July	1st to 10th	Night	3 1 11% 55% 30% 1	350
	11th to 20th	Night	1 1 15% 56% 27%	348
	21st to end	Night	2 2 8% 51% 36% 1	420
August	1st to 10th	Night	6% 1 11% 52% 29% 1	537
	11th to 20th	Night	2 1 10% 52% 33% 1	534
	21st to end	Night	3 2 14% 47% 31% 3	715
September	1st to 10th	Night	4 2 12% 45% 33% 5%	720
	11th to 20th	Night	6% 3 12% 41% 34% 6%	720
	21st to end	Night	7% 4 12% 39% 32% 7%	720
October	1st to 10th	Night	7% 4 16% 43% 26% 4	720
	11th to 20th	Night	10% 4 17% 38% 28% 3	720
	21st to end	Night	7% 4 23% 40% 23% 3	792
November	1st to 10th	Night	13% 3 19% 42% 23% 1	740
	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 2024-03-03 04:28:55. Version ac07

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