Barrhead
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Barrhead clear sky chart from 2005-11-06 to 2025-02-25.

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% 9% 3 8% 6% 5% 5% 4 6% 8% 34%	112207
	Night	9% 10% 4 10% 6% 6% 5% 4 6% 8% 32%	115078
Transparency	Day	45% 7% 18% 22% 8%	111942
	Night	48% 6% 16% 20% 8% 1	114989
Seeing	Day	13% 6% 23% 31% 20% 7%	16356
	Night	13% 5% 26% 37% 17% 2	25032

By Month

Percentage Cloud Cover NW (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	6% 14% 4 11% 8% 5% 6% 5% 6% 8% 27%	2876
	11th to 20th	Day	4 12% 3 11% 6% 6% 5% 5% 7% 9% 31%	3159
	21st to end	Day	8% 13% 3 7% 5% 5% 5% 4 6% 7% 38%	3792
February	1st to 10th	Day	8% 13% 5% 10% 7% 6% 7% 6% 8% 8% 22%	1600
	11th to 20th	Day	5% 13% 5% 12% 7% 6% 7% 5% 7% 7% 26%	1652
	21st to end	Day	5% 12% 5% 11% 8% 7% 7% 5% 5% 8% 28%	1526
March	1st to 10th	Day	3 13% 6% 13% 7% 5% 6% 4 5% 8% 29%	3138
	11th to 20th	Day	5% 11% 3 7% 6% 6% 5% 4 7% 8% 39%	3413
	21st to end	Day	7% 15% 6% 17% 6% 5% 6% 4 5% 7% 22%	3943
April	1st to 10th	Day	8% 12% 4 8% 7% 6% 7% 6% 7% 7% 28%	2353
	11th to 20th	Day	9% 12% 3 9% 6% 5% 5% 5% 7% 8% 31%	2440
	21st to end	Day	12% 11% 3 8% 7% 5% 6% 4 7% 7% 30%	2498
May	1st to 10th	Day	17% 9% 3 8% 6% 5% 5% 4 6% 7% 32%	4661
	11th to 20th	Day	12% 10% 3 8% 6% 6% 5% 5% 7% 8% 30%	4694
	21st to end	Day	12% 8% 3 9% 7% 6% 6% 5% 7% 10% 27%	5161
June	1st to 10th	Day	16% 8% 3 8% 6% 5% 5% 5% 7% 7% 31%	2921
	11th to 20th	Day	18% 8% 3 8% 7% 6% 6% 5% 7% 7% 24%	3040
	21st to end	Day	10% 6% 3 7% 5% 6% 6% 5% 7% 9% 36%	3040
July	1st to 10th	Day	9% 5% 2 6% 5% 5% 5% 4 6% 8% 45%	5060
	11th to 20th	Day	8% 4 2 6% 4 4 5% 4 7% 8% 47%	4814
	21st to end	Day	12% 5% 3 6% 4 4 4 4 6% 9% 43%	5138
August	1st to 10th	Day	13% 6% 2 5% 4 4 5% 4 6% 9% 42%	4499
	11th to 20th	Day	9% 5% 2 6% 5% 5% 5% 4 7% 9% 43%	4221
	21st to end	Day	12% 5% 2 6% 4 5% 5% 4 6% 8% 41%	4521
September	1st to 10th	Day	11% 6% 3 7% 4 5% 5% 4 6% 8% 41%	2395
	11th to 20th	Day	14% 6% 2 6% 4 4 5% 4 6% 8% 41%	2112
	21st to end	Day	9% 7% 2 8% 5% 4 5% 4 5% 9% 42%	2090
October	1st to 10th	Day	10% 8% 3 9% 5% 5% 5% 4 6% 8% 38%	3307
	11th to 20th	Day	12% 10% 4 8% 5% 4 4 3 5% 8% 35%	2842
	21st to end	Day	8% 12% 5% 9% 6% 5% 5% 3 6% 7% 36%	3080
November	1st to 10th	Day	11% 14% 5% 10% 7% 6% 5% 4 6% 7% 25%	1543
	11th to 20th	Day	7% 12% 6% 11% 7% 4 4 5% 5% 7% 31%	1400
	21st to end	Day	6% 12% 6% 13% 7% 5% 5% 5% 7% 7% 28%	1400
December	1st to 10th	Day	11% 14% 5% 12% 8% 6% 5% 4 5% 7% 23%	2290
	11th to 20th	Day	9% 15% 5% 11% 7% 7% 6% 5% 7% 6% 22%	2596
	21st to end	Day	4 7% 3 10% 6% 6% 6% 4 6% 9% 40%	2992
January	1st to 10th	Night	4 11% 5% 16% 9% 7% 6% 4 7% 7% 24%	7065
	11th to 20th	Night	4 9% 4 10% 7% 6% 6% 4 6% 7% 36%	6739
	21st to end	Night	8% 15% 4 10% 6% 5% 5% 3 6% 7% 33%	7210
February	1st to 10th	Night	6% 12% 5% 13% 9% 6% 6% 5% 7% 6% 26%	2800
	11th to 20th	Night	5% 12% 4 12% 8% 8% 6% 5% 6% 8% 28%	2633
	21st to end	Night	5% 12% 4 11% 7% 6% 6% 5% 6% 7% 30%	2022
March	1st to 10th	Night	3 8% 6% 14% 7% 6% 6% 4 7% 9% 29%	3736
	11th to 20th	Night	5% 9% 3 9% 6% 6% 5% 5% 7% 9% 35%	3566
	21st to end	Night	8% 12% 6% 16% 7% 6% 5% 4 6% 6% 23%	3706
April	1st to 10th	Night	8% 10% 4 11% 6% 7% 7% 5% 7% 8% 28%	1827
	11th to 20th	Night	10% 10% 4 9% 7% 6% 6% 4 6% 8% 29%	1691
	21st to end	Night	11% 10% 4 7% 6% 5% 6% 4 6% 8% 33%	1678
May	1st to 10th	Night	20% 10% 4 8% 6% 6% 4 4 5% 5% 29%	2298
	11th to 20th	Night	11% 11% 3 9% 7% 5% 6% 5% 7% 8% 28%	2199
	21st to end	Night	13% 8% 3 10% 8% 5% 6% 4 7% 9% 26%	2414
June	1st to 10th	Night	16% 9% 4 7% 5% 5% 5% 5% 7% 7% 32%	1255
	11th to 20th	Night	14% 11% 3 10% 6% 5% 7% 7% 9% 8% 19%	1140
	21st to end	Night	10% 6% 2 7% 5% 6% 7% 6% 7% 8% 36%	1140
July	1st to 10th	Night	10% 4 1 6% 4 5% 4 5% 6% 7% 47%	1900
	11th to 20th	Night	9% 5% 2 6% 6% 5% 5% 5% 8% 11% 40%	2146
	21st to end	Night	14% 6% 2 5% 5% 4 5% 4 6% 9% 40%	2414
August	1st to 10th	Night	11% 7% 2 6% 5% 5% 5% 4 6% 8% 41%	2428
	11th to 20th	Night	14% 7% 3 7% 5% 5% 4 4 6% 9% 37%	2609
	21st to end	Night	13% 5% 2 7% 4 4 4 4 7% 9% 43%	3146
September	1st to 10th	Night	12% 5% 3 6% 4 4 4 3 5% 8% 45%	1782
	11th to 20th	Night	13% 7% 2 5% 4 4 4 4 6% 8% 43%	2067
	21st to end	Night	10% 9% 2 6% 4 5% 5% 4 7% 8% 42%	2090
October	1st to 10th	Night	8% 7% 3 8% 6% 6% 6% 5% 7% 8% 36%	3666
	11th to 20th	Night	10% 7% 3 8% 5% 5% 5% 4 6% 8% 39%	4086
	21st to end	Night	9% 9% 4 8% 5% 6% 5% 4 7% 9% 34%	4457
November	1st to 10th	Night	13% 16% 5% 10% 6% 4 4 4 5% 6% 27%	2740
	11th to 20th	Night	8% 14% 5% 12% 6% 6% 5% 5% 5% 7% 27%	3000
	21st to end	Night	6% 14% 5% 12% 7% 6% 5% 4 5% 8% 27%	3000
December	1st to 10th	Night	10% 16% 5% 12% 6% 5% 5% 4 5% 7% 25%	4890
	11th to 20th	Night	11% 15% 6% 12% 7% 7% 6% 5% 6% 7% 19%	5574
	21st to end	Night	3 7% 3 11% 6% 5% 5% 4 6% 8% 41%	7964

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	53% 5% 15% 16% 10% 1	2876
	11th to 20th	Day	48% 6% 13% 14% 19% 1	3180
	21st to end	Day	45% 5% 24% 20% 6%	3792
February	1st to 10th	Day	55% 8% 15% 14% 8%	1600
	11th to 20th	Day	53% 8% 15% 17% 8%	1660
	21st to end	Day	51% 8% 16% 18% 7%	1526
March	1st to 10th	Day	52% 7% 14% 22% 5%	3138
	11th to 20th	Day	41% 7% 21% 22% 10%	3414
	21st to end	Day	58% 7% 14% 17% 3	3943
April	1st to 10th	Day	50% 10% 17% 16% 7% 1	2353
	11th to 20th	Day	48% 7% 15% 22% 8% 1	2440
	21st to end	Day	51% 7% 14% 21% 6% 1	2498
May	1st to 10th	Day	50% 7% 10% 23% 10% 1	4661
	11th to 20th	Day	46% 8% 12% 26% 8% 1	4698
	21st to end	Day	48% 8% 18% 16% 9% 1	5162
June	1st to 10th	Day	49% 8% 15% 20% 7% 1	2921
	11th to 20th	Day	55% 9% 15% 16% 4	3040
	21st to end	Day	41% 9% 21% 22% 6% 1	3040
July	1st to 10th	Day	35% 7% 16% 28% 13% 1	4981
	11th to 20th	Day	33% 8% 18% 29% 12%	4730
	21st to end	Day	37% 7% 23% 23% 10%	4976
August	1st to 10th	Day	37% 7% 22% 31% 2	4481
	11th to 20th	Day	35% 8% 23% 26% 8%	4263
	21st to end	Day	39% 8% 28% 22% 4	4520
September	1st to 10th	Day	40% 8% 21% 23% 7% 1	2395
	11th to 20th	Day	40% 7% 22% 24% 7%	2112
	21st to end	Day	39% 8% 17% 27% 8% 2	2090
October	1st to 10th	Day	43% 5% 25% 21% 6%	3307
	11th to 20th	Day	47% 5% 15% 26% 7%	2842
	21st to end	Day	48% 5% 19% 25% 3	3080
November	1st to 10th	Day	56% 7% 15% 15% 6% 1	1543
	11th to 20th	Day	51% 6% 18% 19% 6%	1400
	21st to end	Day	53% 8% 16% 17% 5% 1	1400
December	1st to 10th	Day	60% 6% 17% 12% 4 1	2290
	11th to 20th	Day	59% 7% 16% 13% 4	2598
	21st to end	Day	40% 6% 15% 27% 12% 1	2992
January	1st to 10th	Night	57% 5% 12% 16% 9% 1	7065
	11th to 20th	Night	45% 5% 14% 16% 19% 1	6780
	21st to end	Night	51% 4 21% 18% 6%	7210
February	1st to 10th	Night	56% 7% 12% 15% 9% 1	2800
	11th to 20th	Night	52% 7% 15% 16% 10% 1	2635
	21st to end	Night	50% 7% 14% 20% 8% 1	2022
March	1st to 10th	Night	49% 6% 18% 20% 6%	3736
	11th to 20th	Night	42% 7% 22% 19% 10% 1	3566
	21st to end	Night	57% 8% 13% 17% 6%	3706
April	1st to 10th	Night	48% 9% 14% 18% 10% 1	1827
	11th to 20th	Night	50% 7% 12% 18% 11% 2	1691
	21st to end	Night	47% 7% 9% 23% 12% 1	1678
May	1st to 10th	Night	54% 6% 8% 19% 11% 1	2298
	11th to 20th	Night	47% 10% 12% 22% 9% 1	2199
	21st to end	Night	51% 6% 18% 14% 10% 1	2414
June	1st to 10th	Night	49% 6% 15% 20% 10%	1255
	11th to 20th	Night	56% 9% 14% 17% 4	1140
	21st to end	Night	40% 10% 22% 21% 7%	1140
July	1st to 10th	Night	34% 8% 17% 27% 14% 1	1870
	11th to 20th	Night	35% 8% 17% 27% 12%	2107
	21st to end	Night	38% 7% 21% 27% 8%	2337
August	1st to 10th	Night	39% 9% 21% 29% 1	2421
	11th to 20th	Night	42% 7% 19% 21% 11%	2633
	21st to end	Night	36% 6% 27% 25% 5%	3146
September	1st to 10th	Night	37% 6% 18% 29% 8% 2	1782
	11th to 20th	Night	38% 6% 18% 29% 9% 1	2067
	21st to end	Night	39% 7% 15% 26% 11% 2	2090
October	1st to 10th	Night	43% 6% 21% 23% 7%	3666
	11th to 20th	Night	42% 5% 16% 30% 7%	4086
	21st to end	Night	45% 6% 24% 21% 4	4457
November	1st to 10th	Night	57% 6% 12% 20% 5%	2740
	11th to 20th	Night	56% 8% 12% 18% 6% 1	3000
	21st to end	Night	55% 7% 16% 17% 4 1	3000
December	1st to 10th	Night	59% 6% 14% 15% 6% 1	4890
	11th to 20th	Night	62% 6% 16% 12% 4	5571
	21st to end	Night	40% 5% 15% 28% 11% 1	7964

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	12% 6% 19% 37% 20% 8%	200
	11th to 20th	Day	11% 10% 28% 28% 18% 6%	200
	21st to end	Day	12% 9% 30% 30% 15% 5%	220
February	1st to 10th	Day	13% 8% 25% 30% 21% 6%	200
	11th to 20th	Day	11% 5% 30% 32% 15% 8%	247
	21st to end	Day	6% 5% 29% 36% 18% 5%	314
March	1st to 10th	Day	10% 10% 23% 35% 19% 3	460
	11th to 20th	Day	10% 5% 26% 36% 18% 6%	460
	21st to end	Day	18% 8% 25% 30% 16% 4	506
April	1st to 10th	Day	10% 10% 28% 35% 13% 3	460
	11th to 20th	Day	14% 6% 23% 32% 20% 5%	452
	21st to end	Day	16% 9% 27% 28% 14% 5%	460
May	1st to 10th	Day	14% 9% 23% 30% 19% 5%	600
	11th to 20th	Day	11% 5% 23% 34% 21% 5%	675
	21st to end	Day	16% 5% 19% 30% 22% 7%	734
June	1st to 10th	Day	18% 8% 23% 30% 16% 4	751
	11th to 20th	Day	19% 5% 18% 28% 22% 7%	870
	21st to end	Day	11% 4 18% 28% 29% 10%	870
July	1st to 10th	Day	12% 3 16% 36% 25% 8%	856
	11th to 20th	Day	12% 4 18% 31% 25% 10%	713
	21st to end	Day	12% 3 17% 31% 26% 12%	739
August	1st to 10th	Day	11% 4 17% 30% 21% 17%	546
	11th to 20th	Day	7% 6% 22% 34% 22% 9%	477
	21st to end	Day	14% 6% 18% 30% 23% 9%	539
September	1st to 10th	Day	16% 7% 26% 23% 20% 8%	490
	11th to 20th	Day	18% 5% 22% 31% 18% 6%	490
	21st to end	Day	12% 9% 29% 29% 17% 4	490
October	1st to 10th	Day	16% 8% 22% 32% 18% 5%	400
	11th to 20th	Day	16% 6% 28% 31% 15% 5%	300
	21st to end	Day	15% 9% 35% 26% 12% 4	330
November	1st to 10th	Day	17% 8% 21% 32% 19% 2	287
	11th to 20th	Day	11% 3 34% 34% 14% 6%	200
	21st to end	Day	9% 4 31% 37% 14% 7%	200
December	1st to 10th	Day	8% 6% 25% 44% 12% 7%	200
	11th to 20th	Day	12% 7% 26% 35% 18% 3	200
	21st to end	Day	7% 2 23% 29% 32% 7%	220
January	1st to 10th	Night	12% 4 29% 37% 15% 3	1065
	11th to 20th	Night	11% 7% 29% 38% 13% 2	1000
	21st to end	Night	15% 8% 33% 31% 10% 2	995
February	1st to 10th	Night	10% 7% 24% 37% 19% 4	800
	11th to 20th	Night	10% 5% 29% 37% 19% 1	784
	21st to end	Night	8% 4 25% 41% 19% 4	646
March	1st to 10th	Night	9% 4 30% 36% 19% 2	760
	11th to 20th	Night	12% 4 28% 38% 15% 3	760
	21st to end	Night	14% 4 23% 39% 17% 3	836
April	1st to 10th	Night	10% 6% 24% 40% 18% 2	687
	11th to 20th	Night	16% 5% 27% 36% 15% 2	563
	21st to end	Night	17% 7% 25% 36% 15% 1	538
May	1st to 10th	Night	15% 6% 24% 36% 17% 2	380
	11th to 20th	Night	13% 4 24% 37% 20% 2	374
	21st to end	Night	20% 3 20% 35% 21% 1	411
June	1st to 10th	Night	19% 6% 20% 39% 15% 1	380
	11th to 20th	Night	18% 5% 18% 32% 23% 3	380
	21st to end	Night	12% 2 15% 39% 27% 3	380
July	1st to 10th	Night	14% 2 14% 39% 30% 1	370
	11th to 20th	Night	12% 4 16% 41% 26% 2	368
	21st to end	Night	12% 4 14% 40% 26% 3	416
August	1st to 10th	Night	11% 4 15% 33% 32% 4	378
	11th to 20th	Night	12% 3 17% 40% 26% 2	436
	21st to end	Night	15% 3 18% 41% 23% 1	627
September	1st to 10th	Night	14% 3 18% 40% 23% 2	642
	11th to 20th	Night	15% 3 17% 41% 22% 1	760
	21st to end	Night	14% 4 30% 36% 14% 2	760
October	1st to 10th	Night	16% 4 24% 38% 17% 1	760
	11th to 20th	Night	14% 4 28% 38% 15% 2	760
	21st to end	Night	14% 7% 30% 36% 12% 1	836
November	1st to 10th	Night	20% 5% 28% 31% 13% 2	964
	11th to 20th	Night	14% 5% 35% 33% 11% 2	1000
	21st to end	Night	10% 4 34% 41% 10% 2	1000
December	1st to 10th	Night	12% 5% 31% 34% 15% 3	1000
	11th to 20th	Night	14% 5% 30% 35% 15% 2	1006
	21st to end	Night	11% 3 25% 40% 18% 4	1210

Page generated at 2025-02-22 04:51:34. Version ac07

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