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 2024-01-12.

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	11% 4 1 3 3 2 3 3 4 6% 59%	74706
	Night	13% 5% 2 3 3 2 3 3 4 6% 56%	75028
Transparency	Day	27% 5% 9% 20% 23% 16%	74421
	Night	30% 5% 10% 21% 22% 12%	74834
Seeing	Day	13% 12% 26% 30% 16% 4	13954
	Night	13% 5% 19% 35% 24% 3	23204

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	23% 7% 2 3 3 3 5% 6% 6% 7% 34%	1519
	11th to 20th	Day	22% 5% 2 3 3 2 4 3 4 7% 45%	1609
	21st to end	Day	17% 8% 3 4 3 2 3 4 4 7% 44%	1782
February	1st to 10th	Day	19% 5% 2 3 4 3 6% 5% 5% 6% 43%	1620
	11th to 20th	Day	14% 7% 2 4 4 2 3 4 5% 7% 48%	1575
	21st to end	Day	17% 7% 3 4 4 2 3 5% 5% 7% 42%	1470
March	1st to 10th	Day	21% 10% 3 6% 5% 2 4 4 5% 7% 32%	1944
	11th to 20th	Day	20% 7% 2 4 4 3 3 4 5% 8% 40%	1980
	21st to end	Day	20% 8% 2 4 5% 2 5% 4 5% 6% 39%	2196
April	1st to 10th	Day	20% 6% 3 4 4 3 4 4 5% 8% 41%	2160
	11th to 20th	Day	13% 5% 2 4 5% 2 4 4 6% 7% 48%	2129
	21st to end	Day	6% 4 2 3 5% 2 3 4 4 8% 57%	2204
May	1st to 10th	Day	8% 4 1 3 3 2 4 4 4 7% 60%	2340
	11th to 20th	Day	8% 4 1 4 4 2 3 4 5% 7% 57%	2447
	21st to end	Day	9% 3 2 3 4 2 4 4 5% 8% 54%	2723
June	1st to 10th	Day	7% 3 2 4 3 2 4 4 6% 7% 58%	2520
	11th to 20th	Day	3 2 1 2 2 2 3 3 4 6% 73%	2520
	21st to end	Day	4 2 1 2 2 1 2 2 2 3 79%	2520
July	1st to 10th	Day	1 1 1 1 2 1 2 2 3 4 82%	2520
	11th to 20th	Day	2 1 1 1 1 1 2 2 3 3 83%	2502
	21st to end	Day	1 1 2 1 2 3 4 4 83%	2546
August	1st to 10th	Day	2 1 1 1 1 2 2 3 4 81%	2328
	11th to 20th	Day	1 1 1 1 1 1 2 2 2 3 86%	2289
	21st to end	Day	2 1 1 1 1 1 2 2 4 85%	2376
September	1st to 10th	Day	1 1 1 1 1 2 2 4 86%	2160
	11th to 20th	Day	4 2 1 2 2 2 3 4 5% 6% 69%	2152
	21st to end	Day	3 2 1 2 2 1 2 2 3 5% 75%	1896
October	1st to 10th	Day	6% 2 1 2 2 2 3 2 3 5% 72%	1800
	11th to 20th	Day	10% 3 1 2 2 2 3 4 4 6% 64%	1800
	21st to end	Day	11% 5% 2 3 3 2 2 4 5% 8% 56%	1980
November	1st to 10th	Day	13% 5% 2 4 4 3 4 5% 4 8% 48%	1760
	11th to 20th	Day	15% 6% 2 4 3 3 4 5% 6% 9% 43%	1577
	21st to end	Day	13% 4 1 3 4 3 4 5% 4 6% 52%	1520
December	1st to 10th	Day	20% 6% 1 4 3 2 4 3 4 5% 46%	1520
	11th to 20th	Day	31% 7% 3 5% 4 2 4 4 5% 6% 29%	1928
	21st to end	Day	27% 7% 2 4 5% 3 3 4 6% 7% 33%	2794
January	1st to 10th	Night	21% 9% 2 5% 4 3 4 5% 5% 8% 35%	2646
	11th to 20th	Night	21% 5% 2 5% 4 2 3 4 4 6% 44%	2385
	21st to end	Night	17% 7% 2 4 4 3 3 4 4 7% 44%	2574
February	1st to 10th	Night	18% 6% 2 4 3 2 4 4 5% 7% 45%	2340
	11th to 20th	Night	16% 6% 1 4 4 2 4 4 5% 7% 46%	2272
	21st to end	Night	14% 5% 2 4 4 2 3 4 5% 9% 48%	1785
March	1st to 10th	Night	22% 8% 2 5% 4 3 4 3 4 7% 37%	2015
	11th to 20th	Night	19% 7% 2 4 5% 3 4 4 5% 8% 39%	1980
	21st to end	Night	18% 6% 2 3 3 3 3 4 5% 7% 45%	2159
April	1st to 10th	Night	15% 7% 3 4 5% 3 3 4 4 7% 44%	1800
	11th to 20th	Night	10% 5% 2 4 3 2 4 4 5% 7% 54%	1779
	21st to end	Night	8% 5% 1 2 2 1 3 3 4 8% 62%	1752
May	1st to 10th	Night	6% 4 2 3 3 2 3 3 3 7% 63%	1620
	11th to 20th	Night	6% 3 1 4 4 3 4 4 5% 7% 58%	1444
	21st to end	Night	9% 3 2 2 3 2 3 3 4 8% 61%	1552
June	1st to 10th	Night	7% 3 2 3 4 2 4 5% 5% 7% 57%	1440
	11th to 20th	Night	4 2 1 2 2 1 2 2 3 4 78%	1440
	21st to end	Night	3 1 1 2 2 1 1 3 3 4 80%	1440
July	1st to 10th	Night	1 1 1 1 1 1 2 2 3 4 84%	1440
	11th to 20th	Night	1 1 2 1 1 2 2 3 3 84%	1454
	21st to end	Night	1 1 1 1 1 2 2 1 3 88%	1773
August	1st to 10th	Night	2 1 1 1 1 1 1 2 3 4 83%	1611
	11th to 20th	Night	1 1 1 1 2 2 2 2 3 86%	1610
	21st to end	Night	1 1 1 1 1 1 2 2 3 88%	1980
September	1st to 10th	Night	1 1 1 1 1 2 4 88%	1800
	11th to 20th	Night	3 2 1 2 1 2 2 4 6% 78%	1804
	21st to end	Night	3 2 1 2 2 2 2 3 4 5% 74%	2062
October	1st to 10th	Night	5% 2 1 2 3 1 2 2 3 4 74%	2160
	11th to 20th	Night	7% 2 1 2 3 1 2 3 4 6% 69%	2160
	21st to end	Night	11% 3 1 2 2 2 3 3 4 7% 62%	2376
November	1st to 10th	Night	13% 4 2 5% 4 3 5% 4 5% 8% 48%	2319
	11th to 20th	Night	14% 6% 1 4 3 3 4 6% 7% 9% 44%	2598
	21st to end	Night	13% 4 2 4 4 3 4 4 5% 7% 51%	2660
December	1st to 10th	Night	23% 6% 2 3 2 2 3 3 5% 7% 44%	2660
	11th to 20th	Night	33% 6% 2 4 4 2 3 3 5% 6% 33%	3276
	21st to end	Night	24% 10% 3 5% 5% 2 3 4 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	48% 8% 11% 21% 7% 4	1519
	11th to 20th	Day	42% 5% 10% 17% 14% 12%	1609
	21st to end	Day	42% 5% 8% 16% 21% 8%	1782
February	1st to 10th	Day	42% 6% 11% 19% 15% 8%	1620
	11th to 20th	Day	36% 6% 10% 23% 21% 4	1584
	21st to end	Day	40% 7% 11% 21% 15% 5%	1470
March	1st to 10th	Day	51% 7% 12% 14% 13% 3	1944
	11th to 20th	Day	43% 6% 11% 18% 19% 4	1980
	21st to end	Day	45% 6% 13% 21% 11% 3	2196
April	1st to 10th	Day	42% 7% 14% 18% 16% 3	2160
	11th to 20th	Day	34% 7% 13% 24% 17% 6%	2132
	21st to end	Day	25% 6% 14% 29% 21% 5%	2204
May	1st to 10th	Day	24% 6% 13% 26% 25% 8%	2340
	11th to 20th	Day	26% 5% 12% 26% 23% 8%	2450
	21st to end	Day	27% 6% 13% 31% 19% 4	2724
June	1st to 10th	Day	24% 7% 10% 28% 23% 8%	2520
	11th to 20th	Day	13% 4 9% 24% 35% 15%	2520
	21st to end	Day	14% 2 4 17% 34% 29%	2520
July	1st to 10th	Day	8% 2 5% 16% 30% 38%	2451
	11th to 20th	Day	8% 3 4 14% 31% 41%	2427
	21st to end	Day	6% 2 4 11% 32% 45%	2405
August	1st to 10th	Day	8% 2 6% 20% 34% 31%	2312
	11th to 20th	Day	7% 2 3 15% 35% 38%	2289
	21st to end	Day	6% 2 3 16% 37% 35%	2376
September	1st to 10th	Day	5% 2 4 12% 28% 50%	2160
	11th to 20th	Day	15% 5% 7% 20% 35% 18%	2152
	21st to end	Day	13% 3 6% 20% 32% 25%	1896
October	1st to 10th	Day	18% 4 7% 22% 27% 23%	1800
	11th to 20th	Day	21% 5% 10% 19% 27% 19%	1800
	21st to end	Day	27% 5% 10% 21% 19% 19%	1980
November	1st to 10th	Day	35% 6% 10% 22% 18% 10%	1760
	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	48% 8% 12% 18% 10% 4	2646
	11th to 20th	Night	42% 6% 10% 17% 14% 11%	2385
	21st to end	Night	42% 4 9% 17% 21% 7%	2574
February	1st to 10th	Night	40% 4 10% 22% 16% 8%	2340
	11th to 20th	Night	37% 6% 11% 21% 19% 5%	2274
	21st to end	Night	35% 6% 13% 21% 19% 5%	1785
March	1st to 10th	Night	48% 7% 10% 17% 15% 3	2015
	11th to 20th	Night	44% 6% 11% 19% 17% 4	1980
	21st to end	Night	40% 7% 16% 23% 11% 3	2159
April	1st to 10th	Night	41% 7% 15% 18% 16% 3	1800
	11th to 20th	Night	29% 7% 16% 24% 19% 5%	1779
	21st to end	Night	22% 7% 17% 32% 19% 3	1752
May	1st to 10th	Night	21% 6% 12% 29% 27% 5%	1620
	11th to 20th	Night	24% 6% 16% 28% 19% 6%	1444
	21st to end	Night	23% 7% 16% 37% 15% 3	1552
June	1st to 10th	Night	24% 8% 14% 29% 21% 4	1440
	11th to 20th	Night	12% 4 10% 29% 34% 11%	1440
	21st to end	Night	11% 2 6% 23% 39% 20%	1440
July	1st to 10th	Night	7% 2 5% 23% 30% 34%	1400
	11th to 20th	Night	7% 2 4 17% 35% 34%	1406
	21st to end	Night	6% 1 3 14% 33% 42%	1674
August	1st to 10th	Night	7% 2 5% 24% 39% 23%	1602
	11th to 20th	Night	7% 2 5% 18% 40% 29%	1610
	21st to end	Night	6% 1 4 21% 37% 31%	1980
September	1st to 10th	Night	4 1 3 15% 29% 47%	1800
	11th to 20th	Night	10% 3 8% 23% 40% 16%	1804
	21st to end	Night	13% 4 7% 22% 29% 25%	2062
October	1st to 10th	Night	16% 3 8% 20% 29% 23%	2160
	11th to 20th	Night	18% 4 8% 24% 27% 19%	2160
	21st to end	Night	24% 5% 10% 22% 22% 18%	2376
November	1st to 10th	Night	35% 6% 13% 20% 16% 10%	2319
	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	28% 11% 24% 21% 13% 4	321
	21st to end	Day	21% 12% 26% 23% 15% 3	374
February	1st to 10th	Day	21% 14% 25% 25% 13% 2	340
	11th to 20th	Day	22% 16% 31% 22% 8% 1	335
	21st to end	Day	20% 19% 29% 24% 8% 1	342
March	1st to 10th	Day	31% 19% 27% 18% 5%	420
	11th to 20th	Day	26% 15% 26% 23% 8% 2	420
	21st to end	Day	24% 20% 30% 18% 8%	462
April	1st to 10th	Day	25% 18% 30% 20% 7% 1	420
	11th to 20th	Day	24% 20% 26% 19% 9% 2	412
	21st to end	Day	10% 24% 30% 22% 11% 3	420
May	1st to 10th	Day	13% 19% 29% 29% 9% 3	423
	11th to 20th	Day	14% 17% 29% 23% 13% 4	448
	21st to end	Day	10% 16% 26% 29% 14% 5%	485
June	1st to 10th	Day	10% 18% 22% 31% 16% 3	450
	11th to 20th	Day	5% 20% 31% 30% 13% 1	450
	21st to end	Day	3 10% 29% 35% 20% 4	450
July	1st to 10th	Day	3 7% 28% 40% 17% 4	446
	11th to 20th	Day	1 4 24% 44% 22% 5%	444
	21st to end	Day	3 22% 45% 22% 8%	487
August	1st to 10th	Day	1 4 25% 40% 22% 8%	447
	11th to 20th	Day	1 5% 23% 37% 24% 9%	437
	21st to end	Day	2 5% 23% 37% 27% 5%	495
September	1st to 10th	Day	2 6% 26% 38% 24% 4	450
	11th to 20th	Day	5% 8% 24% 38% 20% 4	450
	21st to end	Day	4 10% 29% 36% 18% 3	450
October	1st to 10th	Day	8% 11% 27% 30% 20% 4	450
	11th to 20th	Day	10% 9% 22% 33% 22% 5%	450
	21st to end	Day	15% 10% 25% 28% 18% 4	495
November	1st to 10th	Day	16% 12% 21% 30% 17% 4	356
	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% 4	728
	21st to end	Night	20% 5% 20% 32% 19% 4	792
February	1st to 10th	Night	21% 3 21% 36% 18% 2	720
	11th to 20th	Night	20% 6% 21% 35% 15% 3	704
	21st to end	Night	18% 10% 24% 36% 11% 1	592
March	1st to 10th	Night	24% 8% 21% 30% 13% 3	720
	11th to 20th	Night	22% 7% 20% 31% 19% 2	720
	21st to end	Night	20% 10% 25% 32% 12% 1	792
April	1st to 10th	Night	19% 9% 27% 29% 14% 2	720
	11th to 20th	Night	14% 10% 26% 31% 16% 3	711
	21st to end	Night	9% 8% 29% 33% 20% 1	672
May	1st to 10th	Night	8% 6% 31% 35% 19% 1	540
	11th to 20th	Night	7% 6% 25% 37% 25% 1	382
	21st to end	Night	10% 4 22% 36% 27% 2	389
June	1st to 10th	Night	9% 6% 23% 36% 25% 1	360
	11th to 20th	Night	5% 5% 26% 40% 24% 1	360
	21st to end	Night	3 1 15% 48% 32% 1	360
July	1st to 10th	Night	1 1 9% 46% 40% 2	350
	11th to 20th	Night	1 10% 43% 44% 2	362
	21st to end	Night	1 4 41% 49% 5%	591
August	1st to 10th	Night	1 1 6% 39% 49% 5%	537
	11th to 20th	Night	2 1 8% 40% 44% 5%	542
	21st to end	Night	2 1 7% 40% 45% 5%	792
September	1st to 10th	Night	1 2 12% 40% 42% 3	720
	11th to 20th	Night	4 2 11% 38% 41% 5%	720
	21st to end	Night	4 4 15% 37% 36% 4	720
October	1st to 10th	Night	6% 4 19% 38% 31% 3	720
	11th to 20th	Night	8% 4 17% 36% 31% 4	720
	21st to end	Night	13% 5% 15% 36% 25% 6%	792
November	1st to 10th	Night	13% 4 19% 37% 21% 5%	740
	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 2024-01-09 13:24:22. Version ac07

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