Pembroke
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Pembroke clear sky chart from 2005-11-06 to 2025-11-03.

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	15% 10% 4 9% 5% 5% 5% 4 5% 7% 32%	127219
	Night	16% 12% 4 10% 5% 5% 4 3 5% 6% 29%	122813
Transparency	Day	51% 6% 11% 21% 10% 1	130723
	Night	54% 6% 11% 18% 9% 1	127396
Seeing	Day	21% 13% 29% 22% 11% 3	15632
	Night	22% 11% 28% 28% 10% 1	24737

By Month

Percentage Cloud Cover NE (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	14% 15% 6% 18% 8% 6% 4 2 3 4 19%	3597
	11th to 20th	Day	11% 16% 6% 16% 9% 6% 4 3 4 5% 19%	3570
	21st to end	Day	11% 19% 8% 15% 6% 5% 4 3 4 5% 20%	4259
February	1st to 10th	Day	11% 17% 6% 14% 7% 6% 5% 4 5% 5% 21%	1800
	11th to 20th	Day	12% 15% 5% 10% 8% 6% 4 4 5% 7% 24%	1753
	21st to end	Day	17% 15% 4 9% 6% 6% 5% 4 4 6% 24%	1585
March	1st to 10th	Day	20% 13% 4 10% 6% 4 4 3 5% 6% 25%	4650
	11th to 20th	Day	12% 12% 5% 11% 6% 5% 5% 4 6% 7% 28%	4980
	21st to end	Day	17% 12% 3 8% 5% 4 3 3 4 5% 37%	5644
April	1st to 10th	Day	21% 13% 2 7% 5% 4 4 4 5% 5% 31%	2400
	11th to 20th	Day	22% 10% 2 6% 5% 4 4 3 4 5% 35%	2374
	21st to end	Day	21% 9% 3 8% 5% 4 4 3 5% 5% 33%	2582
May	1st to 10th	Day	20% 9% 3 8% 5% 5% 4 3 5% 6% 32%	6345
	11th to 20th	Day	15% 8% 3 7% 5% 5% 5% 4 6% 7% 36%	6318
	21st to end	Day	19% 9% 2 8% 5% 5% 4 3 5% 6% 34%	6949
June	1st to 10th	Day	20% 8% 3 8% 5% 5% 4 5% 4 8% 31%	2800
	11th to 20th	Day	14% 5% 3 6% 5% 5% 5% 5% 6% 8% 39%	2800
	21st to end	Day	16% 8% 3 7% 6% 5% 6% 4 6% 7% 33%	2800
July	1st to 10th	Day	14% 6% 3 7% 5% 5% 6% 4 8% 9% 34%	6360
	11th to 20th	Day	10% 5% 2 5% 5% 5% 5% 4 7% 8% 44%	6360
	21st to end	Day	8% 5% 2 5% 4 4 5% 4 7% 10% 47%	6926
August	1st to 10th	Day	12% 6% 3 8% 6% 6% 6% 5% 7% 9% 35%	4376
	11th to 20th	Day	16% 6% 2 6% 4 5% 5% 4 6% 8% 37%	4174
	21st to end	Day	9% 5% 2 7% 4 5% 5% 5% 7% 10% 41%	4379
September	1st to 10th	Day	14% 5% 3 7% 4 4 4 4 6% 8% 41%	2400
	11th to 20th	Day	12% 6% 2 6% 5% 4 4 3 5% 7% 45%	2400
	21st to end	Day	18% 7% 2 7% 5% 5% 5% 4 5% 7% 36%	2104
October	1st to 10th	Day	18% 9% 3 7% 4 5% 5% 4 4 7% 35%	2000
	11th to 20th	Day	22% 12% 3 9% 5% 4 5% 3 4 6% 26%	2000
	21st to end	Day	25% 11% 4 9% 5% 4 4 3 5% 6% 23%	2094
November	1st to 10th	Day	15% 10% 4 8% 5% 5% 5% 4 5% 7% 32%	1694
	11th to 20th	Day	18% 14% 4 10% 6% 5% 5% 4 5% 5% 24%	1600
	21st to end	Day	24% 17% 5% 10% 7% 5% 4 4 5% 4 16%	1600
December	1st to 10th	Day	19% 21% 5% 11% 7% 6% 6% 3 4 3 14%	2600
	11th to 20th	Day	16% 16% 7% 14% 5% 5% 4 3 3 4 23%	2986
	21st to end	Day	21% 18% 5% 15% 5% 4 5% 3 3 4 18%	3960
January	1st to 10th	Night	13% 20% 8% 17% 6% 5% 4 3 3 4 17%	6349
	11th to 20th	Night	11% 14% 6% 15% 8% 6% 6% 4 5% 5% 19%	6315
	21st to end	Night	10% 19% 8% 13% 7% 7% 5% 3 4 5% 19%	6692
February	1st to 10th	Night	13% 15% 6% 14% 7% 5% 6% 3 5% 5% 22%	2600
	11th to 20th	Night	13% 14% 6% 12% 7% 6% 5% 3 4 6% 25%	2533
	21st to end	Night	14% 14% 5% 10% 7% 5% 4 4 5% 5% 27%	2045
March	1st to 10th	Night	19% 16% 4 10% 4 4 4 2 4 4 28%	5185
	11th to 20th	Night	12% 13% 4 9% 6% 5% 6% 5% 7% 8% 27%	4979
	21st to end	Night	16% 11% 4 10% 5% 5% 4 3 5% 6% 31%	5287
April	1st to 10th	Night	19% 12% 4 9% 5% 4 4 4 4 6% 30%	2000
	11th to 20th	Night	20% 10% 3 7% 4 4 3 3 4 5% 36%	1975
	21st to end	Night	21% 10% 3 8% 5% 4 4 3 5% 6% 32%	1835
May	1st to 10th	Night	22% 9% 3 7% 4 4 4 4 6% 7% 28%	3594
	11th to 20th	Night	15% 6% 2 7% 5% 4 5% 3 5% 7% 41%	3575
	21st to end	Night	18% 8% 2 7% 5% 6% 5% 4 5% 6% 34%	3926
June	1st to 10th	Night	16% 8% 2 8% 6% 5% 4 5% 6% 7% 35%	1600
	11th to 20th	Night	14% 6% 2 6% 4 4 4 5% 6% 8% 43%	1600
	21st to end	Night	17% 9% 2 4 6% 4 5% 5% 6% 8% 35%	1600
July	1st to 10th	Night	14% 5% 2 8% 5% 5% 5% 4 8% 8% 35%	3600
	11th to 20th	Night	11% 6% 2 6% 4 5% 5% 4 5% 8% 44%	3600
	21st to end	Night	8% 5% 2 6% 4 4 4 4 6% 8% 49%	3926
August	1st to 10th	Night	11% 4 2 7% 5% 4 5% 4 7% 8% 42%	2770
	11th to 20th	Night	15% 6% 2 6% 4 3 4 4 6% 8% 42%	2875
	21st to end	Night	13% 6% 2 5% 5% 5% 5% 4 6% 8% 42%	3485
September	1st to 10th	Night	11% 5% 2 7% 4 4 4 4 5% 7% 45%	2000
	11th to 20th	Night	14% 5% 2 6% 3 3 3 3 5% 8% 48%	2000
	21st to end	Night	17% 7% 2 7% 4 4 3 3 4 6% 41%	2294
October	1st to 10th	Night	19% 7% 2 6% 4 4 3 3 5% 6% 40%	2400
	11th to 20th	Night	20% 11% 3 8% 6% 5% 4 4 4 6% 30%	2400
	21st to end	Night	23% 12% 4 8% 5% 5% 5% 3 4 6% 27%	2745
November	1st to 10th	Night	18% 11% 3 7% 5% 5% 5% 3 5% 6% 31%	2644
	11th to 20th	Night	18% 12% 4 10% 7% 5% 4 3 5% 6% 26%	2800
	21st to end	Night	22% 16% 4 11% 5% 5% 4 3 5% 5% 19%	2800
December	1st to 10th	Night	19% 19% 5% 12% 6% 5% 4 4 5% 5% 14%	4580
	11th to 20th	Night	19% 17% 5% 11% 6% 4 4 3 4 5% 22%	5208
	21st to end	Night	25% 18% 4 13% 6% 4 4 2 4 4 18%	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	69% 6% 8% 10% 6%	3598
	11th to 20th	Day	68% 5% 8% 11% 7%	3600
	21st to end	Day	66% 4 9% 13% 8% 1	4259
February	1st to 10th	Day	64% 5% 9% 16% 5% 1	1800
	11th to 20th	Day	59% 6% 13% 13% 8% 1	1762
	21st to end	Day	61% 5% 9% 15% 9% 1	1585
March	1st to 10th	Day	60% 4 8% 12% 13% 2	4653
	11th to 20th	Day	54% 6% 16% 14% 9% 1	4980
	21st to end	Day	50% 3 8% 20% 16% 3	5644
April	1st to 10th	Day	54% 4 8% 19% 12% 3	2400
	11th to 20th	Day	52% 4 7% 21% 14% 2	2374
	21st to end	Day	53% 5% 7% 16% 16% 3	2582
May	1st to 10th	Day	50% 6% 9% 20% 10% 5%	6356
	11th to 20th	Day	45% 7% 11% 22% 13% 1	6322
	21st to end	Day	50% 6% 11% 19% 13% 2	6949
June	1st to 10th	Day	51% 6% 10% 19% 12% 1	2800
	11th to 20th	Day	41% 7% 12% 24% 14% 2	2800
	21st to end	Day	47% 8% 12% 20% 12% 1	2800
July	1st to 10th	Day	43% 7% 14% 27% 9%	6290
	11th to 20th	Day	35% 7% 13% 32% 12%	6285
	21st to end	Day	32% 6% 16% 36% 11%	6728
August	1st to 10th	Day	45% 7% 15% 24% 10%	4362
	11th to 20th	Day	43% 6% 18% 26% 7%	4213
	21st to end	Day	36% 7% 16% 30% 10% 1	4379
September	1st to 10th	Day	39% 7% 16% 27% 11%	2400
	11th to 20th	Day	38% 7% 12% 32% 11% 1	2400
	21st to end	Day	47% 7% 13% 23% 10%	2104
October	1st to 10th	Day	51% 6% 9% 26% 7%	3260
	11th to 20th	Day	53% 5% 13% 23% 7%	3240
	21st to end	Day	56% 6% 18% 15% 4 1	3358
November	1st to 10th	Day	50% 7% 14% 22% 6%	1694
	11th to 20th	Day	60% 6% 13% 13% 6% 1	1600
	21st to end	Day	70% 6% 10% 8% 5%	1600
December	1st to 10th	Day	75% 5% 10% 8% 2	2600
	11th to 20th	Day	65% 6% 5% 15% 8%	2986
	21st to end	Day	71% 4 7% 13% 4	3960
January	1st to 10th	Night	72% 6% 9% 10% 3	6349
	11th to 20th	Night	65% 7% 10% 12% 6%	6360
	21st to end	Night	68% 4 8% 9% 11%	6692
February	1st to 10th	Night	63% 6% 10% 14% 6% 1	2600
	11th to 20th	Night	61% 4 11% 18% 6%	2535
	21st to end	Night	57% 6% 9% 19% 8% 1	2045
March	1st to 10th	Night	60% 4 10% 13% 10% 3	5195
	11th to 20th	Night	52% 7% 17% 15% 8% 1	4980
	21st to end	Night	52% 5% 9% 19% 12% 3	5287
April	1st to 10th	Night	56% 5% 7% 18% 12% 2	2000
	11th to 20th	Night	50% 5% 8% 22% 14% 2	1975
	21st to end	Night	53% 5% 7% 17% 16% 2	1835
May	1st to 10th	Night	51% 7% 9% 20% 9% 4	3600
	11th to 20th	Night	40% 8% 14% 19% 16% 3	3576
	21st to end	Night	48% 7% 12% 18% 13% 2	3927
June	1st to 10th	Night	46% 8% 12% 23% 10% 1	1600
	11th to 20th	Night	37% 8% 11% 26% 16% 2	1600
	21st to end	Night	45% 8% 13% 21% 13% 1	1600
July	1st to 10th	Night	44% 7% 15% 22% 11% 1	3560
	11th to 20th	Night	37% 6% 13% 31% 12%	3552
	21st to end	Night	32% 6% 12% 37% 13%	3809
August	1st to 10th	Night	38% 6% 15% 27% 14%	2760
	11th to 20th	Night	40% 7% 16% 28% 9%	2902
	21st to end	Night	38% 7% 16% 26% 11% 2	3485
September	1st to 10th	Night	37% 7% 13% 30% 13% 1	2000
	11th to 20th	Night	35% 6% 16% 33% 11%	2000
	21st to end	Night	43% 8% 13% 27% 11%	2294
October	1st to 10th	Night	40% 5% 13% 31% 12%	3920
	11th to 20th	Night	49% 4 16% 21% 8%	3899
	21st to end	Night	52% 6% 17% 17% 7%	4431
November	1st to 10th	Night	52% 7% 14% 19% 8%	2644
	11th to 20th	Night	58% 7% 12% 15% 7% 1	2800
	21st to end	Night	65% 7% 11% 14% 3	2800
December	1st to 10th	Night	72% 5% 11% 10% 2	4580
	11th to 20th	Night	65% 4 9% 12% 11%	5208
	21st to end	Night	71% 3 6% 11% 8%	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	24% 14% 34% 23% 5% 1	200
	11th to 20th	Day	28% 14% 35% 19% 3 2	200
	21st to end	Day	25% 15% 32% 19% 8% 1	285
February	1st to 10th	Day	26% 20% 35% 14% 4 1	300
	11th to 20th	Day	23% 26% 38% 12%	300
	21st to end	Day	28% 16% 35% 19% 2	349
March	1st to 10th	Day	25% 16% 34% 20% 4 1	500
	11th to 20th	Day	23% 18% 32% 21% 5% 1	500
	21st to end	Day	29% 17% 29% 19% 5% 1	550
April	1st to 10th	Day	29% 17% 30% 14% 9% 1	500
	11th to 20th	Day	31% 16% 24% 16% 10% 3	492
	21st to end	Day	29% 14% 32% 16% 6% 2	500
May	1st to 10th	Day	24% 12% 29% 23% 8% 3	503
	11th to 20th	Day	19% 14% 30% 23% 11% 3	527
	21st to end	Day	19% 12% 33% 22% 11% 3	573
June	1st to 10th	Day	24% 11% 32% 22% 12% 1	530
	11th to 20th	Day	16% 12% 30% 24% 13% 5%	530
	21st to end	Day	19% 11% 32% 21% 14% 3	530
July	1st to 10th	Day	12% 7% 26% 37% 15% 3	525
	11th to 20th	Day	12% 9% 30% 29% 16% 4	524
	21st to end	Day	12% 8% 30% 29% 17% 5%	576
August	1st to 10th	Day	13% 6% 24% 30% 21% 6%	526
	11th to 20th	Day	16% 3 22% 31% 21% 8%	519
	21st to end	Day	13% 9% 28% 26% 16% 8%	583
September	1st to 10th	Day	15% 8% 27% 24% 18% 8%	530
	11th to 20th	Day	13% 7% 21% 23% 21% 15%	530
	21st to end	Day	17% 11% 28% 22% 16% 6%	530
October	1st to 10th	Day	24% 13% 23% 21% 16% 4	530
	11th to 20th	Day	27% 18% 29% 17% 8% 1	530
	21st to end	Day	30% 15% 26% 23% 6% 1	524
November	1st to 10th	Day	25% 16% 31% 20% 8% 1	316
	11th to 20th	Day	23% 20% 37% 13% 8% 1	200
	21st to end	Day	34% 21% 30% 12% 3 3	200
December	1st to 10th	Day	28% 12% 38% 17% 5% 1	200
	11th to 20th	Day	26% 20% 35% 14% 4 2	200
	21st to end	Day	26% 20% 27% 21% 4 2	220
January	1st to 10th	Night	26% 14% 33% 23% 4	800
	11th to 20th	Night	27% 12% 28% 25% 8% 1	800
	21st to end	Night	20% 11% 32% 28% 8%	880
February	1st to 10th	Night	20% 14% 37% 24% 5% 1	800
	11th to 20th	Night	21% 14% 36% 24% 5%	783
	21st to end	Night	23% 15% 30% 27% 6%	660
March	1st to 10th	Night	24% 13% 32% 26% 5%	800
	11th to 20th	Night	23% 16% 31% 24% 6% 1	800
	21st to end	Night	22% 12% 31% 26% 8%	880
April	1st to 10th	Night	26% 14% 29% 26% 6%	800
	11th to 20th	Night	26% 13% 30% 23% 8%	791
	21st to end	Night	26% 10% 26% 27% 10% 1	635
May	1st to 10th	Night	24% 5% 29% 31% 11% 1	400
	11th to 20th	Night	20% 9% 29% 34% 8% 1	394
	21st to end	Night	16% 7% 32% 33% 12%	433
June	1st to 10th	Night	18% 6% 29% 40% 8% 1	400
	11th to 20th	Night	15% 8% 27% 36% 14% 1	400
	21st to end	Night	20% 7% 25% 35% 13% 1	400
July	1st to 10th	Night	11% 4 28% 42% 15% 1	390
	11th to 20th	Night	14% 4 22% 42% 18% 1	388
	21st to end	Night	10% 4 24% 45% 16% 1	438
August	1st to 10th	Night	11% 3 19% 40% 26% 1	504
	11th to 20th	Night	12% 3 16% 39% 26% 3	594
	21st to end	Night	14% 6% 22% 36% 19% 2	818
September	1st to 10th	Night	14% 5% 27% 31% 21% 2	800
	11th to 20th	Night	17% 6% 18% 30% 24% 5%	800
	21st to end	Night	20% 8% 21% 28% 20% 3	800
October	1st to 10th	Night	23% 7% 27% 27% 15% 2	800
	11th to 20th	Night	27% 10% 30% 22% 9% 1	800
	21st to end	Night	29% 12% 25% 27% 6% 1	880
November	1st to 10th	Night	24% 15% 24% 28% 8% 1	789
	11th to 20th	Night	23% 17% 32% 19% 9% 1	800
	21st to end	Night	32% 16% 22% 24% 6%	800
December	1st to 10th	Night	30% 15% 30% 20% 6%	800
	11th to 20th	Night	28% 14% 30% 23% 5% 1	800
	21st to end	Night	33% 12% 26% 22% 5%	880

Page generated at 2025-10-31 02:02:39. Version ac07

Copyright © 2025 Attilla Danko.