Bert and Jeanette Lynch Memorial Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bert and Jeanette Lynch Memorial Observatory clear sky chart from 2005-11-06 to 2025-01-22.

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	12% 7% 3 6% 4 4 4 4 5% 7% 43%	104909
	Night	13% 8% 3 6% 4 4 4 3 5% 6% 44%	104529
Transparency	Day	39% 4 11% 26% 18% 3	108544
	Night	39% 3 11% 25% 18% 4	109035
Seeing	Day	18% 12% 29% 24% 13% 4	15797
	Night	18% 13% 30% 25% 12% 2	25721

By Month

Percentage Cloud Cover SE (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	12% 11% 5% 10% 4 3 4 3 4 5% 38%	2607
	11th to 20th	Day	12% 9% 4 7% 4 4 4 3 4 5% 44%	2922
	21st to end	Day	20% 10% 4 7% 4 3 3 3 4 5% 37%	3144
February	1st to 10th	Day	15% 10% 4 7% 5% 4 4 3 5% 6% 37%	1710
	11th to 20th	Day	14% 10% 3 6% 4 4 4 4 6% 6% 39%	1838
	21st to end	Day	13% 12% 2 6% 5% 3 5% 4 5% 6% 38%	1570
March	1st to 10th	Day	17% 13% 4 6% 3 3 3 3 3 4 41%	3211
	11th to 20th	Day	12% 8% 2 4 3 3 3 3 5% 6% 51%	3480
	21st to end	Day	13% 9% 3 7% 5% 4 5% 3 5% 7% 38%	3995
April	1st to 10th	Day	9% 6% 2 7% 4 5% 5% 3 5% 7% 46%	2280
	11th to 20th	Day	16% 9% 3 6% 5% 3 4 3 4 6% 41%	2254
	21st to end	Day	18% 8% 3 6% 5% 4 4 4 4 7% 37%	2280
May	1st to 10th	Day	13% 7% 3 7% 6% 5% 5% 4 7% 9% 33%	3765
	11th to 20th	Day	17% 7% 3 7% 4 4 5% 3 5% 9% 37%	4314
	21st to end	Day	11% 7% 3 7% 6% 5% 5% 4 5% 7% 42%	4824
June	1st to 10th	Day	9% 5% 2 6% 5% 5% 5% 4 7% 8% 44%	2660
	11th to 20th	Day	6% 4 1 5% 5% 5% 5% 5% 7% 9% 49%	2660
	21st to end	Day	5% 4 1 4 5% 5% 6% 5% 8% 10% 47%	2660
July	1st to 10th	Day	13% 5% 2 6% 4 5% 5% 4 7% 10% 40%	4440
	11th to 20th	Day	4 3 2 5% 4 5% 6% 5% 7% 11% 48%	4417
	21st to end	Day	7% 6% 3 7% 6% 6% 7% 6% 7% 9% 35%	4465
August	1st to 10th	Day	6% 3 1 4 4 4 5% 4 6% 10% 52%	4056
	11th to 20th	Day	11% 5% 2 6% 4 5% 5% 4 6% 8% 44%	3729
	21st to end	Day	7% 5% 2 5% 3 3 4 4 6% 9% 52%	4180
September	1st to 10th	Day	12% 5% 2 5% 4 3 4 4 6% 8% 48%	2280
	11th to 20th	Day	10% 6% 2 6% 4 4 4 4 6% 9% 46%	2266
	21st to end	Day	11% 5% 1 4 4 3 4 4 4 7% 52%	2071
October	1st to 10th	Day	8% 4 2 5% 3 4 4 3 4 6% 57%	1900
	11th to 20th	Day	12% 7% 2 5% 3 3 4 2 4 6% 53%	1900
	21st to end	Day	17% 8% 3 5% 3 3 3 2 5% 5% 47%	2090
November	1st to 10th	Day	11% 6% 2 5% 4 4 3 4 4 5% 53%	1786
	11th to 20th	Day	12% 8% 3 6% 4 3 4 3 4 6% 47%	1800
	21st to end	Day	14% 11% 3 5% 4 5% 3 3 4 5% 43%	1755
December	1st to 10th	Day	9% 10% 2 5% 3 3 4 3 4 6% 50%	2610
	11th to 20th	Day	12% 12% 4 7% 5% 3 4 3 5% 6% 40%	3008
	21st to end	Day	17% 17% 6% 10% 5% 4 4 3 4 5% 26%	3982
January	1st to 10th	Night	14% 10% 5% 10% 5% 4 4 3 5% 5% 36%	4568
	11th to 20th	Night	12% 9% 4 11% 6% 4 5% 3 4 5% 36%	4250
	21st to end	Night	22% 13% 5% 7% 4 3 3 3 4 4 32%	4546
February	1st to 10th	Night	17% 11% 3 9% 4 4 3 3 5% 6% 36%	2470
	11th to 20th	Night	13% 8% 4 8% 4 4 4 3 4 5% 43%	2227
	21st to end	Night	15% 9% 3 7% 5% 4 4 3 4 5% 39%	1884
March	1st to 10th	Night	19% 11% 2 5% 3 3 3 2 3 5% 42%	3669
	11th to 20th	Night	13% 8% 2 4 3 4 4 3 5% 5% 49%	3480
	21st to end	Night	14% 9% 3 7% 5% 4 5% 4 6% 8% 36%	3635
April	1st to 10th	Night	9% 7% 2 5% 4 3 4 4 6% 8% 49%	1900
	11th to 20th	Night	13% 8% 2 6% 5% 4 4 4 4 6% 45%	1875
	21st to end	Night	18% 7% 3 7% 4 4 3 2 5% 6% 41%	1900
May	1st to 10th	Night	17% 8% 2 5% 4 3 4 3 5% 9% 41%	3130
	11th to 20th	Night	16% 8% 2 5% 3 3 3 3 5% 8% 45%	2581
	21st to end	Night	11% 8% 2 7% 5% 5% 5% 4 7% 8% 39%	2743
June	1st to 10th	Night	10% 5% 1 5% 4 4 5% 6% 7% 8% 48%	1520
	11th to 20th	Night	6% 4 1 3 2 3 4 4 6% 11% 57%	1520
	21st to end	Night	2 3 1 3 4 5% 4 4 7% 10% 56%	1520
July	1st to 10th	Night	12% 4 2 4 3 4 3 3 5% 10% 49%	2530
	11th to 20th	Night	6% 3 1 4 3 3 4 3 5% 9% 60%	2549
	21st to end	Night	6% 6% 3 8% 6% 5% 6% 5% 6% 9% 41%	3098
August	1st to 10th	Night	5% 3 1 4 4 4 4 4 6% 9% 58%	2866
	11th to 20th	Night	8% 5% 3 6% 4 4 4 3 6% 8% 48%	3100
	21st to end	Night	5% 4 2 4 3 3 4 4 5% 8% 57%	3476
September	1st to 10th	Night	11% 6% 2 5% 3 3 4 3 5% 6% 53%	1900
	11th to 20th	Night	8% 5% 2 6% 3 4 4 3 5% 7% 52%	1900
	21st to end	Night	10% 4 2 4 4 4 4 3 5% 7% 53%	2099
October	1st to 10th	Night	6% 4 1 4 3 3 2 3 4 5% 64%	2280
	11th to 20th	Night	13% 5% 2 4 3 2 3 3 4 6% 55%	2280
	21st to end	Night	18% 7% 2 5% 2 3 4 3 4 5% 48%	2508
November	1st to 10th	Night	10% 7% 2 4 3 3 2 2 4 6% 57%	2510
	11th to 20th	Night	12% 8% 2 5% 3 3 4 3 5% 6% 49%	2600
	21st to end	Night	16% 10% 2 5% 5% 2 3 2 3 5% 45%	2640
December	1st to 10th	Night	12% 9% 3 7% 4 3 3 2 4 5% 47%	4580
	11th to 20th	Night	11% 10% 3 7% 5% 3 4 3 4 5% 43%	5199
	21st to end	Night	19% 16% 5% 9% 5% 5% 4 3 5% 4 26%	6996

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% 3 7% 27% 12% 2	2608
	11th to 20th	Day	43% 2 8% 26% 17% 3	2922
	21st to end	Day	51% 2 9% 18% 15% 5%	3144
February	1st to 10th	Day	50% 2 11% 23% 13% 2	1710
	11th to 20th	Day	44% 4 12% 20% 15% 5%	1848
	21st to end	Day	46% 4 8% 24% 13% 6%	1570
March	1st to 10th	Day	49% 2 7% 20% 14% 8%	3211
	11th to 20th	Day	36% 3 10% 28% 17% 6%	3480
	21st to end	Day	46% 3 16% 22% 13% 1	3995
April	1st to 10th	Day	37% 3 12% 26% 20% 1	2280
	11th to 20th	Day	46% 2 10% 21% 17% 4	2254
	21st to end	Day	48% 3 10% 23% 14% 1	2280
May	1st to 10th	Day	47% 4 14% 23% 12% 1	3800
	11th to 20th	Day	46% 3 12% 26% 12% 1	4318
	21st to end	Day	42% 4 9% 23% 20% 1	4837
June	1st to 10th	Day	37% 4 14% 28% 17% 2	2660
	11th to 20th	Day	30% 5% 12% 29% 21% 3	2660
	21st to end	Day	30% 5% 18% 26% 16% 5%	2660
July	1st to 10th	Day	39% 4 12% 29% 13% 2	4371
	11th to 20th	Day	28% 5% 14% 35% 16% 2	4342
	21st to end	Day	41% 8% 14% 27% 9% 1	4325
August	1st to 10th	Day	26% 5% 16% 33% 20%	4042
	11th to 20th	Day	38% 4 12% 26% 17% 2	3765
	21st to end	Day	29% 4 14% 36% 14% 3	4179
September	1st to 10th	Day	33% 4 12% 29% 18% 5%	2280
	11th to 20th	Day	35% 5% 8% 27% 24% 2	2266
	21st to end	Day	32% 5% 7% 29% 24% 3	2071
October	1st to 10th	Day	18% 1 5% 20% 44% 11%	3160
	11th to 20th	Day	23% 2 5% 22% 37% 10%	3140
	21st to end	Day	31% 2 6% 30% 26% 5%	3428
November	1st to 10th	Day	35% 3 10% 25% 21% 6%	1786
	11th to 20th	Day	38% 3 7% 24% 20% 7%	1800
	21st to end	Day	45% 2 8% 25% 18% 2	1755
December	1st to 10th	Day	36% 3 7% 37% 16% 1	2610
	11th to 20th	Day	45% 3 7% 23% 19% 1	3005
	21st to end	Day	62% 2 11% 14% 9% 2	3982
January	1st to 10th	Night	50% 4 8% 24% 13% 2	4568
	11th to 20th	Night	50% 4 7% 23% 14% 2	4250
	21st to end	Night	56% 3 7% 22% 11% 1	4546
February	1st to 10th	Night	50% 3 8% 22% 15% 2	2470
	11th to 20th	Night	44% 3 11% 22% 18% 3	2228
	21st to end	Night	47% 2 7% 22% 16% 5%	1884
March	1st to 10th	Night	48% 2 8% 22% 16% 4	3669
	11th to 20th	Night	38% 3 12% 24% 19% 5%	3480
	21st to end	Night	47% 4 14% 27% 9%	3635
April	1st to 10th	Night	33% 4 13% 27% 20% 3	1900
	11th to 20th	Night	40% 3 9% 24% 19% 5%	1875
	21st to end	Night	46% 3 9% 25% 16% 2	1900
May	1st to 10th	Night	43% 4 17% 22% 13% 2	3160
	11th to 20th	Night	40% 4 15% 24% 16% 1	2582
	21st to end	Night	42% 5% 11% 25% 15% 1	2751
June	1st to 10th	Night	32% 5% 16% 26% 19% 2	1520
	11th to 20th	Night	22% 4 13% 35% 22% 4	1520
	21st to end	Night	21% 5% 18% 30% 19% 7%	1520
July	1st to 10th	Night	33% 4 15% 30% 15% 3	2490
	11th to 20th	Night	23% 4 11% 39% 20% 2	2501
	21st to end	Night	37% 7% 17% 24% 13% 2	2999
August	1st to 10th	Night	22% 5% 20% 32% 21% 1	2856
	11th to 20th	Night	33% 5% 16% 25% 17% 4	3130
	21st to end	Night	24% 5% 14% 38% 17% 3	3476
September	1st to 10th	Night	33% 4 9% 28% 20% 6%	1900
	11th to 20th	Night	31% 4 10% 27% 25% 2	1900
	21st to end	Night	32% 4 8% 26% 27% 4	2099
October	1st to 10th	Night	14% 1 7% 17% 48% 13%	3800
	11th to 20th	Night	23% 2 6% 21% 33% 15%	3779
	21st to end	Night	30% 3 7% 27% 27% 7%	4120
November	1st to 10th	Night	31% 2 10% 27% 23% 5%	2510
	11th to 20th	Night	37% 3 6% 24% 24% 6%	2600
	21st to end	Night	43% 2 7% 25% 20% 2	2640
December	1st to 10th	Night	41% 3 8% 30% 18% 1	4580
	11th to 20th	Night	44% 3 10% 22% 20% 1	5201
	21st to end	Night	61% 4 10% 16% 7% 1	6996

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	29% 23% 35% 11% 2	300
	11th to 20th	Day	30% 28% 34% 8%	300
	21st to end	Day	24% 29% 36% 10% 1	300
February	1st to 10th	Day	28% 24% 36% 10% 1	270
	11th to 20th	Day	33% 26% 31% 8% 1 1	270
	21st to end	Day	32% 24% 36% 7% 1	225
March	1st to 10th	Day	23% 24% 41% 10% 2	270
	11th to 20th	Day	31% 21% 36% 9% 2	270
	21st to end	Day	31% 22% 34% 10% 3	401
April	1st to 10th	Day	20% 23% 37% 15% 4	460
	11th to 20th	Day	28% 20% 29% 18% 5% 1	452
	21st to end	Day	24% 19% 35% 16% 5% 1	460
May	1st to 10th	Day	22% 16% 37% 17% 6% 1	463
	11th to 20th	Day	19% 13% 32% 24% 9% 4	621
	21st to end	Day	12% 11% 35% 26% 11% 5%	734
June	1st to 10th	Day	14% 6% 26% 28% 22% 5%	680
	11th to 20th	Day	7% 4 27% 38% 19% 4	680
	21st to end	Day	6% 6% 34% 33% 16% 4	680
July	1st to 10th	Day	12% 3 19% 31% 26% 10%	671
	11th to 20th	Day	5% 3 22% 40% 24% 5%	668
	21st to end	Day	9% 4 20% 37% 24% 6%	739
August	1st to 10th	Day	11% 2 19% 37% 24% 7%	654
	11th to 20th	Day	14% 3 23% 29% 23% 7%	479
	21st to end	Day	12% 3 15% 31% 28% 11%	539
September	1st to 10th	Day	14% 4 17% 37% 22% 7%	490
	11th to 20th	Day	11% 4 19% 32% 23% 11%	490
	21st to end	Day	15% 8% 24% 29% 18% 6%	471
October	1st to 10th	Day	12% 9% 33% 31% 12% 4	300
	11th to 20th	Day	23% 12% 40% 20% 3 1	300
	21st to end	Day	29% 21% 32% 15% 3	330
November	1st to 10th	Day	18% 14% 42% 19% 5% 2	300
	11th to 20th	Day	24% 20% 33% 17% 5% 1	300
	21st to end	Day	29% 20% 31% 17% 3 1	300
December	1st to 10th	Day	23% 24% 35% 12% 4 2	300
	11th to 20th	Day	29% 21% 33% 13% 3 1	300
	21st to end	Day	32% 25% 31% 10% 2	330
January	1st to 10th	Night	22% 24% 35% 16% 3	1000
	11th to 20th	Night	24% 29% 31% 13% 3	1000
	21st to end	Night	21% 25% 37% 16% 1	1051
February	1st to 10th	Night	26% 21% 36% 16% 1	950
	11th to 20th	Night	21% 22% 41% 14% 2	752
	21st to end	Night	26% 23% 35% 15% 2	628
March	1st to 10th	Night	26% 18% 36% 17% 2	722
	11th to 20th	Night	22% 18% 36% 20% 3	570
	21st to end	Night	29% 14% 34% 19% 5%	627
April	1st to 10th	Night	15% 20% 39% 23% 4	570
	11th to 20th	Night	21% 16% 30% 26% 7%	563
	21st to end	Night	23% 13% 37% 21% 6%	570
May	1st to 10th	Night	19% 10% 37% 25% 9%	570
	11th to 20th	Night	19% 7% 33% 27% 13% 1	561
	21st to end	Night	12% 8% 28% 32% 16% 3	617
June	1st to 10th	Night	12% 4 21% 38% 24% 2	570
	11th to 20th	Night	8% 1 24% 45% 20% 1	570
	21st to end	Night	4 3 29% 41% 22% 2	570
July	1st to 10th	Night	9% 2 12% 37% 32% 8%	555
	11th to 20th	Night	6% 2 14% 46% 27% 4	552
	21st to end	Night	8% 2 14% 43% 30% 3	624
August	1st to 10th	Night	8% 1 15% 38% 34% 4	567
	11th to 20th	Night	7% 3 16% 39% 31% 4	564
	21st to end	Night	8% 1 15% 36% 33% 7%	627
September	1st to 10th	Night	13% 2 15% 35% 29% 5%	570
	11th to 20th	Night	10% 3 15% 37% 29% 6%	570
	21st to end	Night	12% 6% 25% 27% 25% 4	755
October	1st to 10th	Night	8% 6% 28% 33% 21% 4	760
	11th to 20th	Night	17% 14% 31% 26% 11% 1	760
	21st to end	Night	24% 16% 33% 21% 6%	836
November	1st to 10th	Night	13% 13% 40% 25% 8% 1	780
	11th to 20th	Night	22% 16% 31% 24% 6% 1	800
	21st to end	Night	24% 20% 33% 17% 5%	840
December	1st to 10th	Night	24% 17% 37% 19% 4 1	1000
	11th to 20th	Night	24% 16% 37% 19% 3	1000
	21st to end	Night	27% 21% 34% 16% 2	1100

Page generated at 2025-01-19 02:06:44. Version ac07

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