Lewiston Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lewiston Lake clear sky chart from 2005-11-06 to 2024-11-08.

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	10% 4 1 3 2 3 3 3 4 5% 61%	105284
	Night	12% 5% 1 4 3 3 3 3 4 5% 58%	102499
Transparency	Day	25% 5% 8% 19% 23% 19%	105039
	Night	28% 5% 10% 21% 22% 14%	102333
Seeing	Day	13% 12% 26% 29% 16% 4	15112
	Night	13% 5% 19% 35% 24% 3	24223

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	19% 8% 2 4 3 4 5% 4 6% 8% 38%	2539
	11th to 20th	Day	29% 10% 3 6% 4 3 3 2 3 5% 33%	2810
	21st to end	Day	31% 8% 2 4 2 3 3 3 4 6% 32%	3146
February	1st to 10th	Day	19% 6% 2 4 3 4 5% 4 6% 5% 42%	1710
	11th to 20th	Day	16% 9% 2 4 3 3 3 3 5% 7% 46%	1665
	21st to end	Day	16% 7% 3 4 4 3 4 4 6% 7% 42%	1559
March	1st to 10th	Day	21% 18% 3 7% 3 3 3 3 4 5% 29%	3384
	11th to 20th	Day	13% 6% 2 3 3 3 3 3 4 6% 56%	3490
	21st to end	Day	21% 11% 2 6% 4 4 4 3 5% 6% 33%	3855
April	1st to 10th	Day	18% 6% 2 4 4 4 3 4 5% 7% 42%	2280
	11th to 20th	Day	14% 6% 2 5% 4 3 4 3 5% 7% 48%	2249
	21st to end	Day	6% 4 1 5% 4 3 4 3 5% 9% 56%	2327
May	1st to 10th	Day	6% 3 1 3 3 3 3 3 4 5% 66%	4110
	11th to 20th	Day	5% 2 1 3 2 2 2 3 4 5% 73%	4334
	21st to end	Day	5% 2 1 2 2 2 2 3 4 7% 69%	4813
June	1st to 10th	Day	6% 4 1 4 3 3 4 3 6% 6% 59%	2660
	11th to 20th	Day	3 2 1 3 2 3 2 2 4 6% 73%	2660
	21st to end	Day	4 2 1 2 1 2 2 2 2 3 79%	2660
July	1st to 10th	Day	1 1 1 1 1 1 1 2 2 90%	4420
	11th to 20th	Day	2 2 1 2 1 2 2 1 3 3 83%	4376
	21st to end	Day	1 1 1 1 1 2 3 89%	4455
August	1st to 10th	Day	2 1 2 1 2 2 2 3 5% 79%	4091
	11th to 20th	Day	1 1 1 1 2 2 2 3 4 83%	4004
	21st to end	Day	2 1 1 1 1 1 2 2 3 5% 80%	4180
September	1st to 10th	Day	1 1 1 1 1 1 2 4 86%	2280
	11th to 20th	Day	4 2 1 2 2 3 3 3 5% 6% 68%	2271
	21st to end	Day	3 2 2 2 2 2 2 3 5% 76%	2001
October	1st to 10th	Day	4 2 1 2 2 2 3 2 3 4 76%	3180
	11th to 20th	Day	7% 2 1 3 2 3 3 4 5% 7% 63%	3161
	21st to end	Day	10% 5% 2 6% 4 4 5% 4 6% 8% 48%	3448
November	1st to 10th	Day	13% 6% 2 4 4 4 4 4 4 8% 48%	1827
	11th to 20th	Day	14% 6% 2 5% 3 4 4 4 7% 8% 43%	1577
	21st to end	Day	13% 4 1 4 4 4 4 4 4 6% 52%	1520
December	1st to 10th	Day	20% 7% 1 5% 2 3 4 3 4 6% 46%	1520
	11th to 20th	Day	31% 7% 3 5% 3 3 4 3 5% 6% 29%	1928
	21st to end	Day	27% 8% 2 5% 4 3 3 3 6% 7% 33%	2794
January	1st to 10th	Night	20% 9% 2 5% 4 3 4 5% 6% 8% 35%	4406
	11th to 20th	Night	26% 10% 3 7% 3 3 3 3 4 5% 33%	4141
	21st to end	Night	32% 9% 2 6% 4 3 3 3 3 5% 28%	4521
February	1st to 10th	Night	19% 7% 2 4 3 3 4 3 5% 6% 44%	2470
	11th to 20th	Night	17% 7% 2 5% 3 3 3 4 6% 7% 44%	2402
	21st to end	Night	14% 6% 2 5% 3 3 3 3 5% 8% 47%	1894
March	1st to 10th	Night	20% 11% 3 6% 4 3 4 4 5% 6% 34%	3478
	11th to 20th	Night	15% 6% 1 4 3 3 2 2 4 5% 56%	3490
	21st to end	Night	15% 8% 3 6% 5% 5% 4 4 5% 7% 38%	3784
April	1st to 10th	Night	15% 8% 2 5% 4 3 3 3 5% 7% 45%	1900
	11th to 20th	Night	10% 5% 2 4 3 3 3 3 5% 7% 54%	1879
	21st to end	Night	7% 5% 1 3 2 2 3 3 4 8% 62%	1849
May	1st to 10th	Night	6% 3 1 3 2 2 2 2 2 5% 71%	2860
	11th to 20th	Night	4 2 1 2 2 2 2 2 3 4 76%	2558
	21st to end	Night	5% 2 1 2 2 2 2 2 4 6% 74%	2762
June	1st to 10th	Night	7% 4 2 4 4 3 3 4 6% 6% 58%	1520
	11th to 20th	Night	4 3 1 2 1 1 2 1 3 4 79%	1520
	21st to end	Night	3 1 1 2 2 1 2 2 3 3 81%	1520
July	1st to 10th	Night	1 1 1 1 1 1 2 2 91%	2540
	11th to 20th	Night	1 1 1 2 1 2 2 2 3 3 83%	2568
	21st to end	Night	1 1 1 1 1 2 92%	3109
August	1st to 10th	Night	2 2 1 2 1 2 2 2 3 3 80%	2848
	11th to 20th	Night	1 1 1 1 1 2 1 2 3 88%	2834
	21st to end	Night	3 1 1 1 1 1 1 2 2 85%	3498
September	1st to 10th	Night	1 1 1 1 1 1 1 2 4 88%	1900
	11th to 20th	Night	3 2 1 1 1 2 2 2 4 6% 76%	1905
	21st to end	Night	3 2 1 2 2 2 3 2 4 5% 75%	2177
October	1st to 10th	Night	3 1 1 2 2 2 3 2 2 3 79%	3800
	11th to 20th	Night	6% 3 1 3 2 3 4 3 4 6% 65%	3777
	21st to end	Night	8% 2 1 4 3 4 5% 4 6% 8% 55%	4121
November	1st to 10th	Night	13% 4 2 6% 4 4 4 3 5% 7% 48%	2412
	11th to 20th	Night	14% 6% 1 4 3 4 4 5% 7% 9% 43%	2598
	21st to end	Night	13% 5% 2 4 3 3 4 3 5% 7% 51%	2660
December	1st to 10th	Night	23% 7% 1 4 2 2 3 3 5% 7% 44%	2660
	11th to 20th	Night	33% 6% 1 5% 3 3 3 3 5% 6% 33%	3276
	21st to end	Night	24% 11% 3 5% 4 3 3 3 4 5% 35%	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	44% 10% 15% 21% 7% 2	2539
	11th to 20th	Day	56% 5% 10% 14% 8% 7%	2810
	21st to end	Day	52% 7% 13% 12% 12% 4	3146
February	1st to 10th	Day	42% 7% 11% 19% 14% 7%	1710
	11th to 20th	Day	39% 6% 9% 23% 19% 4	1674
	21st to end	Day	40% 8% 12% 21% 15% 5%	1559
March	1st to 10th	Day	56% 8% 9% 12% 13% 2	3384
	11th to 20th	Day	31% 6% 11% 22% 27% 3	3490
	21st to end	Day	49% 9% 12% 21% 7% 2	3855
April	1st to 10th	Day	40% 7% 15% 19% 16% 3	2280
	11th to 20th	Day	34% 7% 13% 24% 17% 5%	2252
	21st to end	Day	24% 6% 14% 30% 21% 5%	2327
May	1st to 10th	Day	19% 7% 13% 26% 25% 11%	4110
	11th to 20th	Day	15% 3 7% 17% 40% 18%	4337
	21st to end	Day	16% 4 13% 39% 26% 3	4814
June	1st to 10th	Day	23% 7% 10% 28% 24% 8%	2660
	11th to 20th	Day	13% 3 9% 23% 35% 16%	2660
	21st to end	Day	13% 2 4 17% 34% 29%	2660
July	1st to 10th	Day	5% 1 3 9% 19% 63%	4351
	11th to 20th	Day	9% 2 3 9% 23% 54%	4301
	21st to end	Day	4 1 2 12% 33% 48%	4315
August	1st to 10th	Day	9% 1 3 12% 28% 46%	4076
	11th to 20th	Day	6% 2 4 23% 34% 31%	4043
	21st to end	Day	9% 3 5% 18% 38% 28%	4179
September	1st to 10th	Day	5% 2 3 12% 28% 50%	2280
	11th to 20th	Day	15% 6% 7% 20% 35% 17%	2271
	21st to end	Day	13% 3 6% 20% 33% 26%	2001
October	1st to 10th	Day	13% 3 5% 16% 23% 39%	3180
	11th to 20th	Day	20% 5% 9% 27% 26% 13%	3161
	21st to end	Day	31% 7% 9% 20% 22% 11%	3448
November	1st to 10th	Day	35% 6% 10% 22% 18% 9%	1827
	11th to 20th	Day	37% 8% 14% 19% 15% 8%	1577
	21st to end	Day	34% 5% 13% 18% 21% 10%	1520
December	1st to 10th	Day	41% 5% 8% 17% 20% 9%	1520
	11th to 20th	Day	57% 5% 8% 15% 12% 3	1928
	21st to end	Day	50% 7% 9% 19% 12% 3	2794
January	1st to 10th	Night	45% 10% 15% 19% 7% 3	4406
	11th to 20th	Night	54% 9% 8% 13% 11% 6%	4141
	21st to end	Night	58% 7% 7% 12% 12% 4	4521
February	1st to 10th	Night	41% 5% 10% 21% 16% 7%	2470
	11th to 20th	Night	39% 6% 10% 21% 18% 5%	2404
	21st to end	Night	36% 6% 14% 21% 19% 4	1894
March	1st to 10th	Night	47% 11% 13% 17% 11% 2	3478
	11th to 20th	Night	30% 5% 10% 28% 21% 5%	3490
	21st to end	Night	41% 11% 15% 23% 8% 2	3784
April	1st to 10th	Night	39% 7% 15% 19% 16% 3	1900
	11th to 20th	Night	29% 7% 16% 25% 18% 5%	1879
	21st to end	Night	21% 7% 17% 33% 19% 3	1849
May	1st to 10th	Night	18% 4 13% 29% 28% 8%	2860
	11th to 20th	Night	14% 4 9% 19% 41% 14%	2558
	21st to end	Night	13% 5% 18% 41% 22% 2	2762
June	1st to 10th	Night	24% 8% 13% 30% 21% 4	1520
	11th to 20th	Night	11% 4 10% 29% 37% 11%	1520
	21st to end	Night	11% 2 6% 22% 40% 20%	1520
July	1st to 10th	Night	4 1 3 13% 21% 59%	2500
	11th to 20th	Night	8% 2 3 11% 28% 49%	2520
	21st to end	Night	4 1 3 15% 38% 38%	3011
August	1st to 10th	Night	10% 1 4 15% 32% 39%	2839
	11th to 20th	Night	5% 2 5% 27% 38% 24%	2861
	21st to end	Night	8% 2 4 27% 39% 20%	3498
September	1st to 10th	Night	4 1 3 14% 30% 47%	1900
	11th to 20th	Night	11% 3 8% 25% 38% 15%	1905
	21st to end	Night	13% 4 6% 22% 31% 25%	2177
October	1st to 10th	Night	13% 3 5% 13% 31% 35%	3800
	11th to 20th	Night	19% 5% 9% 35% 20% 11%	3777
	21st to end	Night	25% 6% 10% 24% 23% 12%	4121
November	1st to 10th	Night	34% 7% 13% 20% 16% 9%	2412
	11th to 20th	Night	36% 9% 12% 21% 15% 7%	2598
	21st to end	Night	32% 6% 12% 19% 20% 11%	2660
December	1st to 10th	Night	41% 5% 8% 17% 21% 8%	2660
	11th to 20th	Night	52% 5% 8% 17% 16% 3	3276
	21st to end	Night	50% 7% 10% 16% 13% 3	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	37% 11% 23% 19% 8% 2	180
	11th to 20th	Day	29% 12% 22% 20% 13% 3	346
	21st to end	Day	23% 12% 25% 23% 14% 3	407
February	1st to 10th	Day	22% 15% 25% 23% 12% 2	370
	11th to 20th	Day	24% 16% 30% 21% 8% 1	365
	21st to end	Day	20% 18% 27% 25% 8% 1	377
March	1st to 10th	Day	32% 19% 26% 18% 5%	460
	11th to 20th	Day	25% 15% 25% 22% 10% 2	460
	21st to end	Day	25% 20% 30% 17% 7%	506
April	1st to 10th	Day	23% 17% 29% 22% 8% 1	460
	11th to 20th	Day	24% 19% 25% 20% 10% 2	452
	21st to end	Day	10% 23% 30% 21% 13% 3	460
May	1st to 10th	Day	13% 20% 29% 27% 8% 2	463
	11th to 20th	Day	13% 16% 29% 25% 14% 4	488
	21st to end	Day	9% 16% 26% 30% 14% 5%	529
June	1st to 10th	Day	9% 18% 23% 32% 16% 2	490
	11th to 20th	Day	5% 21% 30% 29% 13% 1	490
	21st to end	Day	3 11% 29% 34% 19% 4	490
July	1st to 10th	Day	3 7% 27% 40% 18% 6%	486
	11th to 20th	Day	1 5% 24% 43% 21% 6%	484
	21st to end	Day	3 22% 43% 22% 9%	531
August	1st to 10th	Day	1 3 25% 40% 23% 8%	487
	11th to 20th	Day	2 6% 25% 36% 22% 9%	477
	21st to end	Day	3 6% 22% 36% 27% 6%	539
September	1st to 10th	Day	2 6% 26% 38% 24% 4	490
	11th to 20th	Day	6% 9% 24% 38% 19% 4	490
	21st to end	Day	4 10% 28% 35% 20% 3	490
October	1st to 10th	Day	8% 11% 27% 30% 20% 4	490
	11th to 20th	Day	10% 9% 22% 32% 22% 4	490
	21st to end	Day	15% 11% 25% 28% 17% 4	539
November	1st to 10th	Day	16% 12% 22% 30% 17% 4	381
	11th to 20th	Day	14% 6% 26% 29% 19% 6%	207
	21st to end	Day	17% 11% 22% 30% 17% 3	180
December	1st to 10th	Day	27% 8% 22% 22% 14% 7%	180
	11th to 20th	Day	27% 6% 23% 26% 12% 6%	180
	21st to end	Day	24% 9% 27% 24% 15% 1	198
January	1st to 10th	Night	24% 4 24% 29% 15% 4	760
	11th to 20th	Night	22% 6% 22% 31% 16% 3	760
	21st to end	Night	22% 5% 20% 31% 18% 4	836
February	1st to 10th	Night	21% 4 21% 35% 18% 1	760
	11th to 20th	Night	21% 6% 21% 34% 15% 2	744
	21st to end	Night	18% 10% 24% 36% 11% 1	628
March	1st to 10th	Night	25% 9% 22% 29% 13% 3	760
	11th to 20th	Night	21% 8% 20% 31% 19% 1	760
	21st to end	Night	20% 11% 26% 31% 11%	836
April	1st to 10th	Night	18% 10% 26% 29% 15% 2	760
	11th to 20th	Night	14% 10% 26% 31% 16% 3	751
	21st to end	Night	9% 8% 30% 33% 20% 1	709
May	1st to 10th	Night	8% 6% 32% 34% 18% 1	570
	11th to 20th	Night	6% 6% 24% 38% 25% 1	403
	21st to end	Night	9% 4 22% 36% 27% 1	411
June	1st to 10th	Night	9% 6% 23% 37% 25% 1	380
	11th to 20th	Night	5% 6% 26% 41% 23% 1	380
	21st to end	Night	2 2 15% 49% 31% 1	380
July	1st to 10th	Night	1 1 9% 45% 41% 2	370
	11th to 20th	Night	1 10% 43% 44% 2	383
	21st to end	Night	1 4 40% 50% 5%	624
August	1st to 10th	Night	1 1 5% 39% 49% 5%	567
	11th to 20th	Night	2 1 9% 41% 43% 5%	573
	21st to end	Night	3 1 8% 39% 45% 5%	836
September	1st to 10th	Night	1 2 11% 42% 41% 3	760
	11th to 20th	Night	4 3 11% 38% 40% 5%	760
	21st to end	Night	4 4 15% 38% 36% 4	760
October	1st to 10th	Night	5% 4 18% 38% 32% 3	760
	11th to 20th	Night	8% 4 17% 36% 31% 4	760
	21st to end	Night	13% 5% 16% 37% 24% 5%	836
November	1st to 10th	Night	13% 4 19% 37% 21% 5%	770
	11th to 20th	Night	16% 4 19% 38% 20% 3	760
	21st to end	Night	15% 5% 23% 35% 18% 4	760
December	1st to 10th	Night	26% 3 18% 32% 16% 5%	760
	11th to 20th	Night	27% 4 19% 33% 12% 4	760
	21st to end	Night	25% 7% 27% 31% 9% 1	836

Page generated at 2024-11-05 05:15:47. Version ac07

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