Lolo Pass Visitor Center
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lolo Pass Visitor Center clear sky chart from 2005-11-06 to 2024-11-10.

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	6% 13% 4 9% 5% 4 4 3 5% 6% 39%	105280
	Night	5% 12% 5% 11% 5% 5% 5% 4 5% 6% 37%	102511
Transparency	Day	22% 48% 7% 12% 8% 4	105017
	Night	23% 48% 7% 12% 7% 3	102363
Seeing	Day	18% 20% 28% 21% 11% 3	15117
	Night	14% 15% 25% 30% 15% 2	24373

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	3 19% 13% 23% 6% 5% 4 3 5% 6% 14%	2421
	11th to 20th	Day	4 17% 7% 18% 8% 7% 4 4 5% 4 22%	2540
	21st to end	Day	4 24% 8% 11% 5% 5% 5% 4 5% 7% 22%	2794
February	1st to 10th	Day	6% 23% 8% 17% 8% 5% 4 3 4 4 17%	1615
	11th to 20th	Day	5% 21% 9% 16% 8% 5% 4 4 5% 5% 18%	1744
	21st to end	Day	4 21% 8% 18% 9% 6% 5% 3 3 4 18%	1570
March	1st to 10th	Day	3 14% 6% 17% 8% 7% 5% 4 6% 6% 25%	3138
	11th to 20th	Day	4 16% 7% 11% 5% 4 3 3 3 5% 40%	3449
	21st to end	Day	6% 25% 8% 16% 7% 7% 6% 4 5% 5% 11%	3876
April	1st to 10th	Day	9% 23% 7% 13% 6% 4 5% 3 6% 6% 18%	2280
	11th to 20th	Day	8% 22% 5% 10% 6% 5% 4 4 5% 5% 26%	2409
	21st to end	Day	13% 20% 5% 11% 5% 5% 4 3 4 5% 24%	2470
May	1st to 10th	Day	11% 22% 5% 9% 5% 4 5% 3 5% 5% 26%	4110
	11th to 20th	Day	8% 11% 3 8% 5% 4 5% 4 6% 8% 38%	4270
	21st to end	Day	14% 18% 5% 10% 6% 5% 5% 4 6% 7% 22%	5117
June	1st to 10th	Day	18% 12% 3 8% 6% 5% 4 4 6% 7% 25%	2850
	11th to 20th	Day	18% 12% 4 8% 5% 5% 4 4 5% 6% 29%	2850
	21st to end	Day	6% 6% 2 6% 5% 4 5% 4 6% 6% 52%	2850
July	1st to 10th	Day	2 2 1 3 3 3 4 3 5% 6% 68%	4726
	11th to 20th	Day	2 2 1 2 2 2 2 2 4 5% 77%	4420
	21st to end	Day	3 2 1 2 2 2 3 2 4 6% 73%	4790
August	1st to 10th	Day	3 3 1 3 3 3 4 4 7% 8% 60%	4256
	11th to 20th	Day	3 3 1 3 3 4 5% 4 7% 8% 57%	4028
	21st to end	Day	4 3 1 4 3 3 3 3 5% 6% 66%	4490
September	1st to 10th	Day	6% 4 2 5% 4 3 3 3 5% 6% 58%	2252
	11th to 20th	Day	8% 8% 2 7% 4 5% 5% 3 6% 7% 44%	2090
	21st to end	Day	9% 9% 3 6% 3 4 4 3 6% 7% 46%	2090
October	1st to 10th	Day	6% 10% 3 6% 4 3 3 2 4 6% 53%	3442
	11th to 20th	Day	7% 12% 3 7% 4 4 4 3 5% 7% 45%	2980
	21st to end	Day	6% 18% 6% 12% 6% 5% 4 2 4 5% 32%	3101
November	1st to 10th	Day	8% 21% 7% 13% 7% 5% 5% 3 4 5% 22%	1755
	11th to 20th	Day	7% 20% 5% 14% 6% 4 4 3 5% 6% 25%	1615
	21st to end	Day	5% 16% 7% 12% 6% 4 5% 5% 5% 7% 27%	1435
December	1st to 10th	Day	2 19% 6% 14% 7% 6% 6% 5% 5% 7% 22%	1330
	11th to 20th	Day	3 17% 10% 14% 9% 7% 5% 4 6% 7% 16%	1685
	21st to end	Day	3 15% 8% 16% 6% 5% 5% 3 5% 6% 29%	2442
January	1st to 10th	Night	3 20% 11% 21% 6% 5% 4 3 6% 6% 16%	4552
	11th to 20th	Night	4 15% 7% 20% 7% 5% 5% 4 4 6% 23%	4420
	21st to end	Night	4 19% 11% 15% 6% 5% 5% 4 5% 6% 21%	4862
February	1st to 10th	Night	7% 20% 8% 18% 7% 5% 4 4 4 5% 18%	2565
	11th to 20th	Night	3 18% 9% 16% 8% 5% 6% 4 4 5% 21%	2320
	21st to end	Night	4 17% 8% 16% 8% 6% 5% 4 6% 5% 21%	1884
March	1st to 10th	Night	2 10% 5% 14% 8% 6% 6% 5% 6% 6% 32%	3736
	11th to 20th	Night	2 14% 6% 9% 5% 5% 4 3 5% 5% 42%	3531
	21st to end	Night	7% 20% 9% 16% 7% 6% 5% 5% 5% 6% 15%	3775
April	1st to 10th	Night	7% 16% 5% 12% 7% 6% 5% 4 6% 7% 26%	1900
	11th to 20th	Night	7% 14% 4 10% 6% 6% 5% 4 6% 6% 32%	1718
	21st to end	Night	10% 14% 4 9% 5% 5% 5% 4 6% 6% 32%	1710
May	1st to 10th	Night	11% 19% 4 8% 4 4 4 3 5% 6% 32%	2860
	11th to 20th	Night	6% 8% 2 6% 5% 4 5% 4 6% 9% 45%	2624
	21st to end	Night	14% 14% 5% 9% 4 4 4 3 6% 7% 29%	2458
June	1st to 10th	Night	16% 9% 3 6% 6% 4 6% 4 7% 6% 33%	1330
	11th to 20th	Night	14% 11% 3 6% 4 4 5% 5% 6% 5% 36%	1330
	21st to end	Night	5% 5% 2 5% 3 5% 5% 3 6% 8% 54%	1330
July	1st to 10th	Night	1 1 2 2 2 2 3 4 6% 77%	2220
	11th to 20th	Night	3 1 1 3 2 2 2 2 3 4 75%	2536
	21st to end	Night	2 2 1 3 2 3 3 2 4 5% 74%	2761
August	1st to 10th	Night	3 2 1 3 2 3 4 3 6% 8% 63%	2678
	11th to 20th	Night	2 2 2 4 4 4 3 3 6% 7% 63%	2811
	21st to end	Night	4 3 1 3 2 3 3 3 4 6% 66%	3174
September	1st to 10th	Night	4 4 1 5% 3 3 3 3 5% 7% 61%	1928
	11th to 20th	Night	8% 6% 2 6% 3 4 5% 4 6% 7% 50%	2090
	21st to end	Night	8% 7% 2 6% 4 4 3 3 6% 6% 51%	2090
October	1st to 10th	Night	5% 9% 3 6% 4 4 3 3 4 6% 53%	3535
	11th to 20th	Night	6% 9% 2 7% 4 4 4 3 6% 7% 46%	3945
	21st to end	Night	6% 15% 6% 9% 5% 5% 5% 3 6% 7% 35%	4457
November	1st to 10th	Night	9% 15% 5% 11% 6% 5% 5% 4 5% 7% 28%	2528
	11th to 20th	Night	6% 18% 6% 11% 7% 6% 6% 4 5% 6% 26%	2543
	21st to end	Night	4 13% 6% 12% 6% 6% 5% 4 6% 8% 30%	2740
December	1st to 10th	Night	4 16% 7% 12% 6% 6% 6% 4 6% 7% 25%	2850
	11th to 20th	Night	3 15% 8% 16% 7% 7% 6% 5% 6% 7% 20%	3506
	21st to end	Night	3 13% 6% 15% 7% 6% 5% 5% 5% 7% 28%	5214

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	47% 40% 5% 6% 2	2421
	11th to 20th	Day	43% 38% 4 5% 9% 1	2540
	21st to end	Day	35% 42% 12% 9% 2	2794
February	1st to 10th	Day	26% 66% 4 2 1	1615
	11th to 20th	Day	24% 65% 5% 4 1	1753
	21st to end	Day	25% 65% 3 3 2 1	1570
March	1st to 10th	Day	28% 47% 5% 8% 12%	3138
	11th to 20th	Day	23% 40% 13% 23% 1	3449
	21st to end	Day	44% 45% 7% 3	3876
April	1st to 10th	Day	23% 66% 8% 3	2280
	11th to 20th	Day	19% 66% 5% 7% 2 1	2412
	21st to end	Day	22% 65% 3 8% 2	2470
May	1st to 10th	Day	35% 43% 8% 11% 3	4110
	11th to 20th	Day	21% 45% 12% 18% 4	4273
	21st to end	Day	32% 44% 10% 12% 1	5118
June	1st to 10th	Day	14% 66% 8% 10% 2	2850
	11th to 20th	Day	17% 66% 5% 6% 5% 1	2850
	21st to end	Day	14% 65% 4 8% 8% 1	2850
July	1st to 10th	Day	6% 37% 5% 10% 26% 15%	4652
	11th to 20th	Day	5% 36% 3 6% 13% 38%	4345
	21st to end	Day	6% 35% 3 15% 23% 17%	4639
August	1st to 10th	Day	11% 38% 6% 17% 19% 9%	4240
	11th to 20th	Day	11% 42% 9% 23% 14% 1	4067
	21st to end	Day	11% 38% 5% 25% 17% 4	4489
September	1st to 10th	Day	11% 60% 5% 13% 8% 2	2252
	11th to 20th	Day	18% 61% 6% 8% 7% 1	2090
	21st to end	Day	19% 61% 6% 9% 5% 1	2090
October	1st to 10th	Day	16% 37% 8% 25% 14%	3442
	11th to 20th	Day	19% 39% 12% 19% 11%	2980
	21st to end	Day	33% 38% 6% 16% 6% 2	3101
November	1st to 10th	Day	29% 58% 5% 7% 1	1755
	11th to 20th	Day	21% 61% 7% 7% 2 1	1615
	21st to end	Day	20% 61% 6% 7% 6% 1	1435
December	1st to 10th	Day	26% 61% 6% 4 2 1	1330
	11th to 20th	Day	31% 51% 7% 9% 1 1	1684
	21st to end	Day	26% 38% 11% 14% 6% 5%	2442
January	1st to 10th	Night	44% 39% 6% 8% 3	4552
	11th to 20th	Night	40% 38% 5% 9% 7% 1	4420
	21st to end	Night	39% 43% 9% 8% 2	4862
February	1st to 10th	Night	26% 66% 4 2 2	2565
	11th to 20th	Night	23% 65% 6% 5% 1	2321
	21st to end	Night	22% 65% 5% 5% 2 1	1884
March	1st to 10th	Night	23% 46% 5% 10% 15% 1	3736
	11th to 20th	Night	22% 41% 12% 23% 2	3531
	21st to end	Night	42% 44% 7% 5% 1	3775
April	1st to 10th	Night	17% 67% 9% 5% 2	1900
	11th to 20th	Night	16% 67% 7% 7% 3 1	1718
	21st to end	Night	18% 66% 4 9% 4	1710
May	1st to 10th	Night	31% 42% 8% 16% 3	2860
	11th to 20th	Night	19% 42% 10% 22% 6%	2624
	21st to end	Night	28% 44% 13% 13% 2	2458
June	1st to 10th	Night	11% 66% 7% 12% 3	1330
	11th to 20th	Night	14% 65% 5% 8% 5% 2	1330
	21st to end	Night	11% 65% 6% 9% 10% 1	1330
July	1st to 10th	Night	4 35% 3 15% 26% 16%	2185
	11th to 20th	Night	7% 36% 4 8% 9% 38%	2489
	21st to end	Night	8% 35% 4 14% 16% 24%	2674
August	1st to 10th	Night	10% 38% 5% 16% 20% 11%	2670
	11th to 20th	Night	11% 39% 7% 29% 13% 1	2838
	21st to end	Night	10% 38% 6% 25% 16% 5%	3174
September	1st to 10th	Night	11% 60% 6% 11% 9% 3	1928
	11th to 20th	Night	15% 60% 7% 10% 7% 1	2090
	21st to end	Night	15% 61% 8% 10% 5% 1	2090
October	1st to 10th	Night	18% 38% 6% 19% 19% 1	3535
	11th to 20th	Night	17% 41% 12% 18% 12%	3945
	21st to end	Night	24% 42% 10% 17% 7% 1	4457
November	1st to 10th	Night	26% 58% 7% 7% 2	2528
	11th to 20th	Night	21% 61% 8% 6% 2 1	2543
	21st to end	Night	17% 61% 6% 8% 7%	2740
December	1st to 10th	Night	22% 62% 6% 6% 4	2850
	11th to 20th	Night	30% 52% 6% 9% 2 1	3507
	21st to end	Night	28% 39% 10% 12% 6% 5%	5214

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% 23% 19% 26% 11% 3	180
	11th to 20th	Day	19% 26% 24% 16% 9% 7%	180
	21st to end	Day	22% 23% 28% 17% 8% 2	198
February	1st to 10th	Day	30% 31% 27% 11% 2	225
	11th to 20th	Day	25% 26% 31% 13% 6%	349
	21st to end	Day	26% 26% 29% 15% 5%	382
March	1st to 10th	Day	19% 31% 30% 15% 5% 1	460
	11th to 20th	Day	18% 21% 29% 23% 9%	460
	21st to end	Day	21% 26% 33% 13% 5% 1	506
April	1st to 10th	Day	24% 26% 30% 15% 4	460
	11th to 20th	Day	27% 22% 31% 13% 5% 2	452
	21st to end	Day	27% 24% 26% 15% 6% 2	460
May	1st to 10th	Day	17% 19% 29% 24% 10% 1	463
	11th to 20th	Day	25% 16% 25% 20% 12% 2	488
	21st to end	Day	23% 16% 21% 22% 14% 4	703
June	1st to 10th	Day	19% 17% 24% 22% 13% 5%	680
	11th to 20th	Day	25% 20% 25% 17% 11% 2	680
	21st to end	Day	10% 15% 28% 27% 18% 3	680
July	1st to 10th	Day	4 16% 28% 29% 19% 4	670
	11th to 20th	Day	8% 18% 38% 22% 12% 2	484
	21st to end	Day	4 13% 35% 32% 13% 3	531
August	1st to 10th	Day	6% 16% 30% 27% 17% 5%	487
	11th to 20th	Day	5% 12% 31% 32% 14% 6%	477
	21st to end	Day	10% 16% 33% 23% 14% 4	539
September	1st to 10th	Day	9% 17% 29% 25% 15% 6%	490
	11th to 20th	Day	15% 17% 30% 24% 11% 4	490
	21st to end	Day	19% 18% 28% 20% 13% 2	490
October	1st to 10th	Day	20% 15% 30% 21% 12% 2	468
	11th to 20th	Day	22% 17% 25% 18% 12% 6%	300
	21st to end	Day	24% 22% 30% 17% 5% 2	330
November	1st to 10th	Day	26% 21% 25% 20% 9%	297
	11th to 20th	Day	22% 20% 33% 14% 9% 2	270
	21st to end	Day	16% 27% 22% 27% 8% 1	230
December	1st to 10th	Day	21% 26% 24% 16% 9% 4	180
	11th to 20th	Day	23% 27% 26% 21% 3	180
	21st to end	Day	22% 25% 27% 17% 8% 2	198
January	1st to 10th	Night	18% 20% 24% 27% 10% 1	841
	11th to 20th	Night	15% 19% 29% 23% 11% 3	760
	21st to end	Night	14% 18% 30% 26% 10% 2	836
February	1st to 10th	Night	19% 24% 26% 23% 7% 1	760
	11th to 20th	Night	16% 22% 31% 22% 9% 2	744
	21st to end	Night	16% 20% 31% 22% 9% 2	628
March	1st to 10th	Night	11% 20% 28% 31% 9% 1	760
	11th to 20th	Night	13% 19% 25% 29% 13% 1	760
	21st to end	Night	16% 16% 28% 30% 9% 1	836
April	1st to 10th	Night	14% 16% 26% 29% 12% 2	760
	11th to 20th	Night	15% 17% 32% 24% 11% 1	590
	21st to end	Night	17% 15% 26% 29% 11% 2	570
May	1st to 10th	Night	15% 12% 24% 30% 18% 2	570
	11th to 20th	Night	13% 8% 21% 32% 22% 4	443
	21st to end	Night	19% 10% 18% 27% 25% 1	411
June	1st to 10th	Night	18% 7% 19% 31% 22% 3	380
	11th to 20th	Night	18% 12% 22% 33% 14% 1	380
	21st to end	Night	6% 5% 16% 43% 29% 1	380
July	1st to 10th	Night	2 3 17% 41% 35% 2	370
	11th to 20th	Night	5% 4 16% 51% 24% 1	368
	21st to end	Night	2 2 14% 47% 33% 1	416
August	1st to 10th	Night	4 4 15% 44% 32% 2	462
	11th to 20th	Night	3 2 19% 42% 29% 5%	564
	21st to end	Night	7% 6% 18% 40% 28% 1	642
September	1st to 10th	Night	6% 4 21% 36% 27% 5%	760
	11th to 20th	Night	10% 8% 17% 33% 27% 6%	760
	21st to end	Night	13% 8% 19% 32% 22% 5%	760
October	1st to 10th	Night	13% 10% 20% 37% 18% 2	760
	11th to 20th	Night	14% 10% 23% 31% 18% 4	760
	21st to end	Night	17% 16% 26% 25% 12% 4	836
November	1st to 10th	Night	17% 18% 27% 26% 10% 1	778
	11th to 20th	Night	20% 21% 27% 25% 7%	833
	21st to end	Night	15% 19% 26% 27% 11% 2	950
December	1st to 10th	Night	16% 21% 24% 27% 10% 2	950
	11th to 20th	Night	14% 21% 33% 24% 7% 1	950
	21st to end	Night	18% 24% 29% 21% 8% 1	1045

Page generated at 2024-11-07 03:55:48. Version ac07

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