Glencoe
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Glencoe clear sky chart from 2005-11-06 to 2024-11-05.

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	13% 8% 3 7% 5% 4 5% 4 6% 7% 38%	101293
	Night	15% 10% 3 7% 5% 4 4 4 5% 7% 37%	97811
Transparency	Day	43% 7% 13% 22% 13% 2	104863
	Night	45% 6% 12% 21% 14% 2	102382
Seeing	Day	15% 6% 24% 33% 17% 4	15825
	Night	18% 8% 27% 30% 15% 2	25663

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	13% 12% 7% 10% 7% 5% 5% 4 5% 6% 26%	2527
	11th to 20th	Day	13% 14% 7% 13% 4 3 6% 9% 8% 5% 17%	2530
	21st to end	Day	19% 21% 6% 9% 5% 4 4 3 4 5% 21%	2815
February	1st to 10th	Day	13% 13% 5% 9% 7% 5% 5% 4 6% 7% 27%	1761
	11th to 20th	Day	13% 10% 4 7% 5% 5% 6% 4 5% 5% 35%	1848
	21st to end	Day	11% 13% 3 12% 5% 4 5% 4 5% 7% 30%	1570
March	1st to 10th	Day	15% 11% 3 7% 5% 4 5% 4 5% 6% 37%	3120
	11th to 20th	Day	10% 6% 2 6% 5% 5% 6% 5% 7% 8% 40%	3248
	21st to end	Day	19% 11% 5% 11% 6% 6% 5% 4 5% 5% 23%	4165
April	1st to 10th	Day	16% 10% 3 8% 5% 5% 5% 4 6% 6% 33%	2280
	11th to 20th	Day	15% 7% 2 6% 6% 4 6% 4 6% 7% 36%	2254
	21st to end	Day	18% 8% 3 7% 5% 5% 4 4 5% 7% 34%	2406
May	1st to 10th	Day	15% 8% 3 6% 5% 4 6% 4 6% 7% 36%	4082
	11th to 20th	Day	15% 6% 2 5% 4 4 5% 4 6% 8% 41%	4288
	21st to end	Day	10% 6% 2 6% 4 4 4 4 6% 9% 45%	4824
June	1st to 10th	Day	9% 6% 2 6% 4 5% 5% 5% 6% 7% 46%	2660
	11th to 20th	Day	10% 5% 2 5% 4 4 4 4 6% 9% 46%	2660
	21st to end	Day	10% 6% 2 6% 4 5% 5% 4 7% 9% 41%	2660
July	1st to 10th	Day	11% 7% 3 7% 5% 5% 5% 5% 8% 9% 36%	4440
	11th to 20th	Day	6% 4 1 4 4 4 5% 4 6% 9% 54%	4440
	21st to end	Day	7% 6% 2 6% 5% 5% 5% 4 7% 7% 46%	4813
August	1st to 10th	Day	11% 4 2 5% 4 4 5% 4 6% 9% 46%	4309
	11th to 20th	Day	9% 5% 2 5% 3 4 4 4 6% 8% 50%	3799
	21st to end	Day	7% 5% 2 6% 5% 4 4 4 6% 8% 50%	4180
September	1st to 10th	Day	11% 6% 3 6% 3 4 4 4 5% 7% 49%	2280
	11th to 20th	Day	11% 5% 2 4 3 3 4 3 6% 8% 52%	2146
	21st to end	Day	12% 5% 2 7% 5% 4 4 4 7% 8% 42%	2090
October	1st to 10th	Day	13% 6% 3 7% 5% 4 4 3 5% 6% 45%	2058
	11th to 20th	Day	18% 8% 3 8% 4 5% 5% 3 5% 7% 35%	1867
	21st to end	Day	19% 8% 3 6% 5% 5% 5% 3 5% 7% 34%	1881
November	1st to 10th	Day	12% 10% 2 7% 4 4 3 3 5% 7% 43%	1708
	11th to 20th	Day	14% 12% 4 9% 5% 5% 3 4 6% 7% 32%	1710
	21st to end	Day	18% 11% 3 8% 5% 5% 5% 4 3 4 35%	1653
December	1st to 10th	Day	17% 14% 4 9% 7% 7% 5% 4 4 6% 23%	1520
	11th to 20th	Day	12% 12% 5% 10% 7% 6% 4 5% 6% 6% 27%	1918
	21st to end	Day	20% 20% 5% 12% 7% 4 4 3 3 5% 15%	2783
January	1st to 10th	Night	15% 14% 7% 10% 6% 4 4 3 4 5% 27%	4428
	11th to 20th	Night	16% 17% 6% 13% 6% 4 4 6% 7% 5% 16%	4440
	21st to end	Night	22% 18% 7% 9% 5% 3 3 3 4 5% 20%	4848
February	1st to 10th	Night	15% 15% 5% 8% 5% 5% 4 2 4 6% 31%	2418
	11th to 20th	Night	13% 10% 4 8% 5% 5% 4 3 5% 6% 36%	2218
	21st to end	Night	19% 10% 3 9% 4 4 4 2 4 5% 36%	1884
March	1st to 10th	Night	18% 11% 2 7% 4 3 4 2 4 6% 39%	3733
	11th to 20th	Night	9% 7% 2 6% 4 4 5% 4 5% 7% 46%	3722
	21st to end	Night	21% 11% 7% 9% 5% 4 4 3 4 5% 27%	3471
April	1st to 10th	Night	16% 9% 2 6% 6% 4 5% 3 5% 7% 38%	1900
	11th to 20th	Night	19% 9% 3 6% 4 4 5% 3 5% 5% 38%	1875
	21st to end	Night	19% 8% 3 6% 5% 3 4 4 5% 7% 38%	1772
May	1st to 10th	Night	16% 7% 3 7% 5% 5% 5% 4 5% 7% 35%	2813
	11th to 20th	Night	16% 6% 2 6% 4 4 5% 5% 7% 8% 37%	2612
	21st to end	Night	13% 7% 2 8% 4 4 4 3 5% 7% 44%	2743
June	1st to 10th	Night	10% 5% 2 6% 5% 5% 5% 3 6% 7% 46%	1520
	11th to 20th	Night	10% 6% 2 6% 3 5% 4 4 6% 9% 45%	1520
	21st to end	Night	9% 6% 3 7% 5% 5% 5% 4 6% 9% 41%	1520
July	1st to 10th	Night	12% 5% 2 6% 5% 6% 5% 5% 6% 9% 39%	2530
	11th to 20th	Night	6% 4 1 5% 4 3 4 4 7% 8% 54%	2530
	21st to end	Night	5% 4 2 6% 5% 5% 6% 6% 8% 7% 46%	2750
August	1st to 10th	Night	8% 5% 1 5% 4 5% 5% 4 6% 9% 49%	2624
	11th to 20th	Night	8% 5% 1 5% 4 4 5% 3 6% 7% 51%	3028
	21st to end	Night	8% 4 2 6% 4 4 4 4 5% 9% 50%	3476
September	1st to 10th	Night	11% 5% 2 6% 4 3 4 3 5% 7% 51%	1900
	11th to 20th	Night	11% 4 2 4 2 3 4 4 6% 8% 52%	2014
	21st to end	Night	13% 5% 3 7% 4 4 4 3 5% 8% 44%	2090
October	1st to 10th	Night	14% 6% 2 5% 3 4 4 4 5% 6% 48%	2118
	11th to 20th	Night	18% 8% 3 6% 4 4 3 3 4 5% 42%	2312
	21st to end	Night	21% 8% 3 6% 4 4 3 3 5% 7% 36%	2717
November	1st to 10th	Night	12% 9% 2 6% 5% 3 4 4 4 6% 45%	2470
	11th to 20th	Night	15% 11% 4 8% 5% 4 4 4 5% 7% 34%	2470
	21st to end	Night	17% 9% 4 7% 5% 4 4 3 5% 6% 35%	2522
December	1st to 10th	Night	17% 12% 4 9% 7% 5% 5% 5% 6% 6% 24%	2660
	11th to 20th	Night	15% 14% 4 9% 5% 5% 4 4 6% 6% 28%	3279
	21st to end	Night	23% 17% 6% 10% 6% 5% 4 3 4 5% 18%	4884

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	58% 8% 13% 15% 6%	2528
	11th to 20th	Day	63% 8% 14% 11% 4	2530
	21st to end	Day	67% 4 8% 17% 5%	2815
February	1st to 10th	Day	55% 7% 14% 14% 10% 2	1761
	11th to 20th	Day	50% 6% 11% 22% 10% 1	1858
	21st to end	Day	53% 8% 12% 17% 9% 2	1570
March	1st to 10th	Day	48% 7% 12% 20% 11% 2	3120
	11th to 20th	Day	38% 9% 14% 28% 10% 1	3248
	21st to end	Day	62% 8% 13% 12% 4	4165
April	1st to 10th	Day	50% 7% 12% 19% 11%	2280
	11th to 20th	Day	47% 7% 10% 21% 12% 3	2254
	21st to end	Day	49% 8% 12% 17% 12% 2	2406
May	1st to 10th	Day	44% 8% 12% 22% 12% 1	4120
	11th to 20th	Day	38% 8% 13% 27% 13% 1	4292
	21st to end	Day	34% 9% 13% 21% 19% 4	4837
June	1st to 10th	Day	36% 7% 13% 23% 18% 3	2660
	11th to 20th	Day	34% 8% 13% 23% 20% 3	2660
	21st to end	Day	38% 8% 15% 22% 13% 3	2660
July	1st to 10th	Day	43% 7% 14% 22% 12% 2	4371
	11th to 20th	Day	27% 7% 17% 31% 17% 1	4365
	21st to end	Day	36% 8% 18% 17% 20% 2	4662
August	1st to 10th	Day	35% 6% 17% 27% 13% 1	4294
	11th to 20th	Day	32% 6% 13% 33% 15% 1	3837
	21st to end	Day	32% 6% 14% 26% 20% 2	4179
September	1st to 10th	Day	35% 6% 14% 23% 18% 3	2280
	11th to 20th	Day	29% 6% 14% 30% 18% 3	2146
	21st to end	Day	38% 8% 12% 24% 17% 1	2090
October	1st to 10th	Day	27% 4 7% 38% 23% 1	3422
	11th to 20th	Day	36% 6% 11% 27% 20%	3083
	21st to end	Day	44% 4 10% 26% 12% 3	3081
November	1st to 10th	Day	41% 5% 14% 22% 16% 2	1708
	11th to 20th	Day	51% 8% 12% 20% 9% 1	1710
	21st to end	Day	53% 6% 11% 22% 8%	1653
December	1st to 10th	Day	58% 9% 13% 14% 6% 1	1520
	11th to 20th	Day	53% 7% 16% 18% 5% 1	1915
	21st to end	Day	72% 7% 8% 10% 3	2783
January	1st to 10th	Night	58% 7% 13% 15% 6% 1	4428
	11th to 20th	Night	67% 6% 12% 9% 4	4440
	21st to end	Night	67% 4 10% 14% 5%	4848
February	1st to 10th	Night	54% 5% 11% 16% 12% 1	2418
	11th to 20th	Night	49% 5% 12% 20% 12% 1	2219
	21st to end	Night	52% 4 11% 19% 10% 4	1884
March	1st to 10th	Night	48% 5% 13% 23% 9% 3	3733
	11th to 20th	Night	36% 6% 12% 26% 18% 2	3722
	21st to end	Night	59% 6% 10% 17% 7% 1	3471
April	1st to 10th	Night	46% 6% 13% 22% 13% 1	1900
	11th to 20th	Night	47% 6% 7% 19% 18% 4	1875
	21st to end	Night	45% 6% 11% 21% 13% 2	1772
May	1st to 10th	Night	46% 8% 11% 19% 14% 2	2840
	11th to 20th	Night	40% 10% 14% 25% 10% 1	2613
	21st to end	Night	39% 7% 10% 18% 20% 6%	2751
June	1st to 10th	Night	34% 7% 13% 25% 19% 3	1520
	11th to 20th	Night	34% 6% 12% 24% 22% 2	1520
	21st to end	Night	37% 9% 14% 21% 17% 2	1520
July	1st to 10th	Night	39% 7% 16% 20% 11% 6%	2490
	11th to 20th	Night	27% 7% 14% 32% 18% 2	2482
	21st to end	Night	31% 9% 16% 18% 23% 3	2662
August	1st to 10th	Night	32% 7% 15% 28% 17% 1	2615
	11th to 20th	Night	30% 7% 13% 30% 19% 1	3056
	21st to end	Night	30% 6% 12% 32% 18% 3	3476
September	1st to 10th	Night	32% 6% 12% 26% 22% 3	1900
	11th to 20th	Night	29% 5% 8% 31% 25% 2	2014
	21st to end	Night	39% 6% 10% 28% 16% 2	2090
October	1st to 10th	Night	23% 4 8% 38% 25% 2	3534
	11th to 20th	Night	37% 5% 9% 22% 25% 2	3835
	21st to end	Night	41% 5% 9% 25% 18% 2	4467
November	1st to 10th	Night	39% 6% 10% 25% 17% 3	2470
	11th to 20th	Night	47% 7% 12% 21% 11% 1	2470
	21st to end	Night	50% 5% 14% 21% 9%	2522
December	1st to 10th	Night	54% 11% 13% 15% 7% 1	2660
	11th to 20th	Night	53% 8% 14% 17% 8% 1	3281
	21st to end	Night	68% 6% 11% 11% 4	4884

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% 10% 34% 31% 6% 1	270
	11th to 20th	Day	20% 11% 34% 27% 6% 1	270
	21st to end	Day	23% 7% 32% 31% 7%	297
February	1st to 10th	Day	18% 8% 41% 27% 4 1	270
	11th to 20th	Day	20% 14% 32% 28% 6%	270
	21st to end	Day	17% 10% 42% 26% 4	225
March	1st to 10th	Day	17% 11% 38% 31% 3	270
	11th to 20th	Day	19% 12% 33% 28% 7% 1	308
	21st to end	Day	25% 11% 30% 25% 7% 2	506
April	1st to 10th	Day	20% 10% 32% 30% 8%	460
	11th to 20th	Day	16% 8% 35% 25% 12% 3	452
	21st to end	Day	21% 6% 30% 29% 13% 2	460
May	1st to 10th	Day	21% 5% 27% 34% 11% 2	463
	11th to 20th	Day	19% 3 23% 38% 15% 2	603
	21st to end	Day	15% 3 20% 34% 22% 6%	734
June	1st to 10th	Day	12% 3 20% 38% 23% 4	680
	11th to 20th	Day	11% 3 22% 37% 23% 4	680
	21st to end	Day	12% 4 22% 39% 19% 4	680
July	1st to 10th	Day	9% 2 13% 37% 27% 12%	671
	11th to 20th	Day	11% 1 17% 39% 24% 7%	668
	21st to end	Day	8% 3 14% 42% 28% 5%	739
August	1st to 10th	Day	9% 2 12% 38% 30% 10%	614
	11th to 20th	Day	12% 3 15% 35% 28% 8%	479
	21st to end	Day	7% 4 12% 37% 32% 8%	539
September	1st to 10th	Day	14% 4 16% 32% 28% 5%	490
	11th to 20th	Day	9% 3 12% 33% 30% 11%	490
	21st to end	Day	15% 7% 22% 28% 21% 7%	490
October	1st to 10th	Day	17% 5% 22% 32% 18% 5%	458
	11th to 20th	Day	21% 13% 25% 28% 12% 1	300
	21st to end	Day	28% 10% 27% 31% 5%	330
November	1st to 10th	Day	15% 12% 26% 32% 14% 2	282
	11th to 20th	Day	21% 14% 32% 23% 9% 1	270
	21st to end	Day	25% 10% 31% 31% 4	270
December	1st to 10th	Day	17% 14% 36% 26% 6%	270
	11th to 20th	Day	16% 14% 40% 24% 7%	270
	21st to end	Day	25% 16% 36% 21% 3	297
January	1st to 10th	Night	19% 14% 38% 24% 5%	950
	11th to 20th	Night	22% 14% 35% 24% 5% 1	950
	21st to end	Night	22% 10% 35% 27% 5%	1045
February	1st to 10th	Night	22% 8% 37% 25% 8%	898
	11th to 20th	Night	18% 11% 35% 31% 5%	743
	21st to end	Night	24% 9% 38% 25% 4	628
March	1st to 10th	Night	21% 8% 34% 27% 9%	760
	11th to 20th	Night	16% 7% 32% 35% 9% 1	760
	21st to end	Night	23% 7% 28% 30% 11% 1	632
April	1st to 10th	Night	21% 9% 30% 31% 8% 1	570
	11th to 20th	Night	24% 6% 28% 29% 13% 1	563
	21st to end	Night	22% 5% 26% 32% 14% 1	570
May	1st to 10th	Night	18% 3 25% 38% 14% 1	570
	11th to 20th	Night	18% 4 18% 34% 23% 2	561
	21st to end	Night	14% 2 17% 35% 27% 5%	617
June	1st to 10th	Night	12% 2 14% 42% 28% 3	570
	11th to 20th	Night	13% 2 18% 40% 24% 2	570
	21st to end	Night	10% 3 17% 38% 29% 3	570
July	1st to 10th	Night	8% 3 7% 37% 36% 8%	555
	11th to 20th	Night	9% 2 11% 39% 32% 7%	552
	21st to end	Night	6% 2 11% 42% 35% 4	624
August	1st to 10th	Night	7% 2 9% 41% 35% 7%	567
	11th to 20th	Night	8% 2 12% 35% 34% 9%	564
	21st to end	Night	9% 2 13% 34% 36% 5%	627
September	1st to 10th	Night	13% 3 15% 32% 31% 7%	570
	11th to 20th	Night	12% 4 14% 32% 30% 8%	684
	21st to end	Night	14% 6% 22% 28% 22% 7%	760
October	1st to 10th	Night	16% 6% 21% 31% 21% 4	760
	11th to 20th	Night	21% 9% 29% 28% 10% 1	760
	21st to end	Night	24% 11% 29% 26% 9% 1	836
November	1st to 10th	Night	17% 11% 34% 24% 13% 1	760
	11th to 20th	Night	19% 17% 32% 24% 6% 1	760
	21st to end	Night	20% 12% 36% 25% 7%	812
December	1st to 10th	Night	22% 14% 35% 23% 5%	950
	11th to 20th	Night	22% 13% 35% 25% 4	950
	21st to end	Night	29% 12% 35% 21% 2	1045

Page generated at 2024-11-03 01:11:28. Version ac07

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