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 2024-11-06.

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	16% 10% 3 9% 5% 5% 5% 4 5% 7% 32%	101618
	Night	17% 12% 4 9% 5% 5% 4 3 5% 6% 30%	97448
Transparency	Day	50% 6% 12% 21% 10% 1	105140
	Night	53% 7% 12% 19% 9% 1	102015
Seeing	Day	21% 13% 29% 22% 11% 4	14382
	Night	22% 11% 28% 28% 11% 1	23511

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	17% 16% 6% 15% 7% 5% 4 3 3 3 21%	2517
	11th to 20th	Day	13% 13% 5% 18% 8% 6% 4 3 4 5% 20%	2520
	21st to end	Day	14% 20% 7% 15% 6% 5% 4 3 4 4 19%	2973
February	1st to 10th	Day	11% 17% 6% 14% 7% 5% 5% 4 5% 5% 21%	1710
	11th to 20th	Day	12% 15% 5% 10% 7% 5% 4 4 5% 7% 25%	1663
	21st to end	Day	17% 15% 4 9% 6% 6% 5% 4 4 6% 25%	1508
March	1st to 10th	Day	21% 15% 4 8% 5% 4 3 3 4 5% 28%	3234
	11th to 20th	Day	11% 15% 6% 12% 6% 5% 5% 3 4 5% 27%	3480
	21st to end	Day	13% 8% 3 7% 5% 4 4 3 5% 6% 44%	3938
April	1st to 10th	Day	21% 13% 2 6% 5% 4 4 4 5% 5% 30%	2280
	11th to 20th	Day	22% 10% 2 6% 5% 4 4 3 4 5% 35%	2254
	21st to end	Day	21% 9% 3 8% 4 4 4 3 5% 5% 33%	2453
May	1st to 10th	Day	19% 9% 3 8% 5% 5% 5% 3 6% 7% 32%	4425
	11th to 20th	Day	17% 8% 3 7% 4 4 4 4 5% 7% 36%	4398
	21st to end	Day	15% 8% 2 7% 5% 4 4 3 5% 7% 38%	4837
June	1st to 10th	Day	20% 8% 3 8% 5% 5% 4 5% 5% 8% 30%	2660
	11th to 20th	Day	14% 5% 3 6% 5% 5% 5% 5% 6% 8% 39%	2660
	21st to end	Day	16% 8% 3 7% 6% 5% 6% 4 6% 7% 33%	2660
July	1st to 10th	Day	12% 6% 3 7% 5% 6% 6% 4 8% 9% 35%	4440
	11th to 20th	Day	11% 5% 2 5% 5% 6% 5% 5% 8% 8% 39%	4440
	21st to end	Day	10% 5% 2 6% 4 4 4 3 6% 8% 46%	4814
August	1st to 10th	Day	12% 6% 3 8% 6% 6% 6% 5% 6% 9% 34%	4242
	11th to 20th	Day	16% 7% 2 6% 4 5% 5% 4 6% 8% 37%	4044
	21st to end	Day	9% 6% 2 7% 4 5% 5% 5% 7% 10% 40%	4245
September	1st to 10th	Day	14% 5% 3 7% 4 4 4 4 6% 7% 41%	2280
	11th to 20th	Day	13% 6% 2 6% 5% 4 4 3 5% 7% 45%	2280
	21st to end	Day	18% 7% 2 7% 4 5% 5% 4 5% 7% 35%	1999
October	1st to 10th	Day	18% 9% 3 7% 5% 5% 5% 4 4 6% 33%	1900
	11th to 20th	Day	23% 12% 3 9% 5% 4 5% 3 4 6% 26%	1900
	21st to end	Day	25% 10% 3 9% 5% 4 5% 4 5% 6% 23%	1990
November	1st to 10th	Day	16% 10% 4 7% 5% 5% 5% 4 5% 7% 32%	1636
	11th to 20th	Day	18% 14% 4 10% 6% 5% 5% 4 5% 5% 24%	1520
	21st to end	Day	24% 17% 5% 10% 6% 5% 4 4 5% 4 16%	1520
December	1st to 10th	Day	21% 19% 5% 9% 6% 5% 5% 4 5% 4 16%	1520
	11th to 20th	Day	20% 17% 5% 12% 5% 5% 4 4 4 5% 21%	1906
	21st to end	Day	27% 19% 6% 14% 3 2 3 1 2 4 18%	2772
January	1st to 10th	Night	16% 19% 7% 13% 6% 5% 4 3 4 4 17%	4429
	11th to 20th	Night	13% 13% 4 14% 8% 6% 6% 4 5% 6% 20%	4440
	21st to end	Night	13% 21% 7% 12% 7% 6% 4 3 4 4 19%	4678
February	1st to 10th	Night	13% 15% 6% 14% 7% 5% 5% 3 5% 5% 21%	2470
	11th to 20th	Night	13% 14% 6% 12% 7% 5% 5% 3 4 6% 26%	2403
	21st to end	Night	15% 14% 4 10% 7% 5% 4 4 5% 5% 27%	1946
March	1st to 10th	Night	20% 12% 4 10% 5% 4 4 2 4 4 31%	3601
	11th to 20th	Night	16% 17% 5% 10% 5% 4 4 4 5% 6% 24%	3479
	21st to end	Night	14% 8% 3 9% 5% 5% 4 3 5% 6% 36%	3693
April	1st to 10th	Night	19% 12% 3 9% 5% 4 4 4 4 6% 30%	1900
	11th to 20th	Night	20% 10% 3 6% 4 4 4 3 5% 5% 36%	1875
	21st to end	Night	21% 10% 3 9% 5% 4 4 3 5% 6% 32%	1743
May	1st to 10th	Night	20% 10% 3 7% 5% 4 4 3 5% 7% 31%	2514
	11th to 20th	Night	18% 8% 2 7% 5% 4 5% 3 5% 7% 34%	2495
	21st to end	Night	13% 7% 2 8% 5% 5% 5% 4 5% 6% 40%	2738
June	1st to 10th	Night	16% 7% 3 8% 6% 5% 4 5% 6% 7% 34%	1520
	11th to 20th	Night	14% 6% 2 6% 4 4 5% 5% 6% 8% 42%	1520
	21st to end	Night	17% 9% 2 4 6% 4 5% 4 6% 8% 35%	1520
July	1st to 10th	Night	12% 6% 3 9% 6% 6% 5% 5% 7% 7% 35%	2520
	11th to 20th	Night	13% 7% 2 6% 4 6% 5% 4 5% 8% 40%	2520
	21st to end	Night	9% 5% 2 6% 4 5% 4 4 6% 8% 47%	2739
August	1st to 10th	Night	12% 4 2 7% 5% 4 5% 4 7% 8% 42%	2684
	11th to 20th	Night	15% 6% 2 6% 4 4 4 4 6% 8% 41%	2785
	21st to end	Night	12% 6% 2 5% 5% 5% 5% 4 6% 9% 42%	3378
September	1st to 10th	Night	12% 5% 2 7% 4 4 4 4 5% 7% 46%	1900
	11th to 20th	Night	15% 5% 2 6% 3 3 3 3 5% 7% 47%	1900
	21st to end	Night	18% 7% 3 7% 4 4 3 3 4 6% 41%	2179
October	1st to 10th	Night	20% 7% 2 6% 4 4 3 3 5% 6% 38%	2280
	11th to 20th	Night	21% 11% 3 8% 6% 5% 4 4 4 6% 29%	2280
	21st to end	Night	23% 12% 4 8% 5% 5% 5% 3 4 6% 26%	2608
November	1st to 10th	Night	18% 11% 3 7% 5% 5% 5% 3 5% 6% 31%	2559
	11th to 20th	Night	18% 12% 4 10% 7% 5% 4 3 5% 6% 26%	2660
	21st to end	Night	23% 16% 4 11% 5% 4 4 3 5% 5% 19%	2660
December	1st to 10th	Night	22% 19% 5% 11% 6% 5% 4 3 4 5% 17%	2660
	11th to 20th	Night	20% 19% 5% 9% 5% 4 4 3 4 5% 22%	3288
	21st to end	Night	28% 19% 5% 12% 4 3 3 2 3 3 16%	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	66% 8% 11% 9% 6%	2518
	11th to 20th	Day	66% 6% 9% 12% 6% 1	2520
	21st to end	Day	70% 4 9% 10% 5% 1	2973
February	1st to 10th	Day	64% 6% 9% 16% 5% 1	1710
	11th to 20th	Day	58% 6% 13% 13% 8% 1	1672
	21st to end	Day	60% 5% 9% 15% 10% 1	1508
March	1st to 10th	Day	59% 5% 9% 16% 10% 1	3237
	11th to 20th	Day	58% 6% 11% 14% 9% 1	3480
	21st to end	Day	41% 4 10% 23% 18% 4	3938
April	1st to 10th	Day	55% 4 8% 19% 11% 3	2280
	11th to 20th	Day	52% 4 7% 22% 14% 2	2254
	21st to end	Day	53% 5% 7% 16% 16% 3	2453
May	1st to 10th	Day	49% 7% 9% 21% 11% 3	4439
	11th to 20th	Day	44% 8% 13% 23% 11% 1	4402
	21st to end	Day	45% 7% 11% 19% 16% 3	4837
June	1st to 10th	Day	51% 7% 11% 19% 12% 1	2660
	11th to 20th	Day	42% 7% 12% 23% 14% 2	2660
	21st to end	Day	47% 8% 12% 20% 12% 1	2660
July	1st to 10th	Day	42% 7% 14% 26% 10% 1	4370
	11th to 20th	Day	38% 8% 15% 30% 9%	4365
	21st to end	Day	35% 7% 13% 34% 11%	4661
August	1st to 10th	Day	46% 7% 14% 24% 10%	4228
	11th to 20th	Day	43% 6% 18% 25% 7%	4083
	21st to end	Day	36% 7% 16% 30% 11% 1	4245
September	1st to 10th	Day	39% 7% 15% 27% 12%	2280
	11th to 20th	Day	38% 7% 12% 31% 11% 1	2280
	21st to end	Day	47% 8% 13% 24% 9%	1999
October	1st to 10th	Day	52% 6% 9% 25% 7%	3160
	11th to 20th	Day	53% 5% 13% 23% 6%	3140
	21st to end	Day	56% 6% 18% 15% 4	3254
November	1st to 10th	Day	49% 7% 14% 22% 6%	1636
	11th to 20th	Day	60% 7% 13% 13% 6% 1	1520
	21st to end	Day	70% 7% 10% 8% 5%	1520
December	1st to 10th	Day	71% 6% 10% 9% 4	1520
	11th to 20th	Day	65% 8% 7% 13% 7%	1906
	21st to end	Day	74% 3 7% 13% 3	2772
January	1st to 10th	Night	69% 9% 12% 9% 3	4429
	11th to 20th	Night	62% 9% 13% 12% 4	4440
	21st to end	Night	69% 5% 9% 10% 6%	4678
February	1st to 10th	Night	64% 6% 10% 14% 6% 1	2470
	11th to 20th	Night	60% 4 11% 18% 6%	2405
	21st to end	Night	57% 6% 9% 18% 9% 1	1946
March	1st to 10th	Night	56% 5% 13% 16% 8% 1	3611
	11th to 20th	Night	58% 6% 13% 14% 8% 1	3480
	21st to end	Night	45% 6% 10% 20% 15% 3	3693
April	1st to 10th	Night	56% 5% 7% 18% 12% 2	1900
	11th to 20th	Night	50% 5% 8% 21% 14% 2	1875
	21st to end	Night	53% 5% 7% 16% 16% 2	1743
May	1st to 10th	Night	48% 9% 11% 20% 10% 2	2520
	11th to 20th	Night	45% 9% 12% 21% 11% 2	2496
	21st to end	Night	42% 9% 11% 21% 15% 2	2739
June	1st to 10th	Night	46% 8% 12% 23% 10% 1	1520
	11th to 20th	Night	37% 9% 11% 25% 16% 2	1520
	21st to end	Night	45% 8% 13% 20% 13% 1	1520
July	1st to 10th	Night	44% 7% 15% 20% 13% 1	2480
	11th to 20th	Night	41% 6% 13% 31% 9%	2472
	21st to end	Night	34% 7% 14% 32% 14%	2651
August	1st to 10th	Night	39% 6% 14% 27% 14%	2674
	11th to 20th	Night	40% 7% 16% 28% 9%	2812
	21st to end	Night	38% 7% 16% 26% 12% 2	3378
September	1st to 10th	Night	37% 7% 12% 29% 14% 1	1900
	11th to 20th	Night	36% 6% 16% 31% 10%	1900
	21st to end	Night	43% 8% 13% 27% 10%	2179
October	1st to 10th	Night	41% 5% 13% 30% 11%	3800
	11th to 20th	Night	50% 4 16% 21% 8%	3779
	21st to end	Night	53% 6% 18% 17% 7%	4294
November	1st to 10th	Night	52% 7% 14% 18% 8%	2559
	11th to 20th	Night	58% 7% 12% 14% 7% 1	2660
	21st to end	Night	65% 7% 11% 13% 3	2660
December	1st to 10th	Night	70% 6% 9% 11% 4	2660
	11th to 20th	Night	64% 6% 10% 14% 7%	3288
	21st to end	Night	74% 4 7% 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	25% 13% 34% 22% 6% 1	180
	11th to 20th	Day	28% 14% 34% 18% 3 2	180
	21st to end	Day	25% 15% 31% 19% 9% 1	256
February	1st to 10th	Day	25% 19% 36% 16% 4 1	270
	11th to 20th	Day	23% 24% 39% 13%	270
	21st to end	Day	30% 17% 33% 18% 2	320
March	1st to 10th	Day	24% 15% 35% 21% 4 1	460
	11th to 20th	Day	23% 17% 32% 22% 5% 1	460
	21st to end	Day	27% 17% 29% 19% 6% 1	506
April	1st to 10th	Day	28% 17% 30% 14% 9% 1	460
	11th to 20th	Day	33% 15% 22% 17% 10% 4	452
	21st to end	Day	29% 15% 30% 17% 7% 3	460
May	1st to 10th	Day	25% 12% 27% 24% 8% 3	463
	11th to 20th	Day	19% 15% 28% 23% 12% 3	487
	21st to end	Day	18% 12% 34% 21% 12% 3	529
June	1st to 10th	Day	23% 10% 31% 23% 12% 1	490
	11th to 20th	Day	16% 12% 29% 24% 14% 6%	490
	21st to end	Day	19% 11% 30% 22% 14% 3	490
July	1st to 10th	Day	11% 7% 25% 37% 15% 4	485
	11th to 20th	Day	12% 8% 31% 29% 17% 4	484
	21st to end	Day	13% 7% 28% 30% 17% 5%	532
August	1st to 10th	Day	14% 7% 25% 29% 19% 6%	486
	11th to 20th	Day	15% 4 23% 29% 21% 8%	479
	21st to end	Day	13% 9% 28% 26% 16% 8%	539
September	1st to 10th	Day	14% 8% 28% 25% 18% 8%	490
	11th to 20th	Day	14% 8% 21% 23% 20% 14%	490
	21st to end	Day	17% 11% 27% 22% 16% 7%	490
October	1st to 10th	Day	25% 13% 23% 20% 15% 4	490
	11th to 20th	Day	28% 18% 28% 17% 8% 1	490
	21st to end	Day	30% 15% 26% 22% 7% 1	486
November	1st to 10th	Day	24% 16% 32% 21% 7% 1	300
	11th to 20th	Day	23% 21% 37% 11% 7% 1	180
	21st to end	Day	33% 22% 30% 10% 3 3	180
December	1st to 10th	Day	28% 12% 38% 16% 6% 1	180
	11th to 20th	Day	27% 19% 34% 14% 3 2	180
	21st to end	Day	28% 22% 27% 19% 3 2	198
January	1st to 10th	Night	26% 14% 31% 24% 4	760
	11th to 20th	Night	28% 13% 28% 24% 7%	760
	21st to end	Night	20% 11% 32% 29% 8%	836
February	1st to 10th	Night	21% 14% 36% 24% 5% 1	760
	11th to 20th	Night	21% 13% 36% 25% 5%	743
	21st to end	Night	23% 15% 30% 27% 5%	628
March	1st to 10th	Night	24% 13% 32% 26% 5%	760
	11th to 20th	Night	24% 16% 30% 23% 6% 1	760
	21st to end	Night	21% 12% 32% 26% 8%	836
April	1st to 10th	Night	26% 13% 29% 26% 6%	760
	11th to 20th	Night	26% 13% 31% 23% 8%	751
	21st to end	Night	26% 10% 26% 27% 10% 1	603
May	1st to 10th	Night	23% 5% 29% 32% 10% 1	380
	11th to 20th	Night	20% 9% 28% 34% 8% 1	374
	21st to end	Night	15% 7% 33% 33% 11%	411
June	1st to 10th	Night	18% 5% 28% 40% 8% 1	380
	11th to 20th	Night	14% 8% 27% 36% 14% 1	380
	21st to end	Night	20% 7% 24% 34% 13% 1	380
July	1st to 10th	Night	11% 4 27% 42% 15% 1	370
	11th to 20th	Night	14% 4 22% 42% 18% 1	368
	21st to end	Night	10% 4 24% 44% 17% 1	416
August	1st to 10th	Night	11% 3 20% 39% 26% 1	478
	11th to 20th	Night	12% 3 16% 39% 27% 3	564
	21st to end	Night	13% 6% 22% 37% 19% 2	777
September	1st to 10th	Night	14% 5% 27% 31% 21% 2	760
	11th to 20th	Night	17% 6% 19% 29% 24% 5%	760
	21st to end	Night	21% 8% 21% 27% 20% 2	760
October	1st to 10th	Night	24% 7% 27% 25% 15% 2	760
	11th to 20th	Night	28% 11% 29% 21% 10% 1	760
	21st to end	Night	30% 12% 25% 26% 6% 1	836
November	1st to 10th	Night	24% 15% 24% 28% 8% 1	764
	11th to 20th	Night	23% 17% 31% 19% 9% 1	760
	21st to end	Night	32% 15% 23% 24% 6%	760
December	1st to 10th	Night	30% 15% 29% 19% 6%	760
	11th to 20th	Night	28% 14% 30% 23% 5% 1	760
	21st to end	Night	34% 13% 26% 22% 4	836

Page generated at 2024-11-03 13:19:04. Version ac07

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