Renfrew
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Renfrew 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	15% 11% 4 9% 6% 5% 4 4 5% 7% 32%	108779
	Night	16% 12% 4 10% 6% 5% 4 3 5% 6% 30%	109871
Transparency	Day	50% 7% 12% 20% 10% 1	112331
	Night	53% 7% 12% 18% 9% 1	114483
Seeing	Day	22% 17% 31% 19% 9% 3	14687
	Night	22% 14% 30% 24% 9% 1	23991

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	13% 16% 6% 15% 9% 6% 5% 3 4 4 20%	3597
	11th to 20th	Day	12% 16% 6% 16% 8% 5% 5% 3 5% 6% 19%	3570
	21st to end	Day	11% 19% 8% 14% 7% 6% 4 2 4 5% 20%	4236
February	1st to 10th	Day	13% 14% 6% 14% 8% 4 5% 4 5% 4 22%	1800
	11th to 20th	Day	11% 16% 5% 11% 6% 5% 5% 3 5% 6% 26%	1753
	21st to end	Day	18% 12% 5% 10% 7% 5% 5% 4 4 5% 24%	1570
March	1st to 10th	Day	20% 15% 5% 10% 5% 4 3 2 4 6% 27%	3202
	11th to 20th	Day	11% 15% 6% 12% 7% 5% 4 3 4 5% 28%	3480
	21st to end	Day	12% 8% 3 7% 5% 4 4 3 5% 6% 43%	3967
April	1st to 10th	Day	21% 14% 3 7% 5% 4 4 3 4 6% 31%	2280
	11th to 20th	Day	22% 10% 3 7% 4 4 4 3 4 4 36%	2254
	21st to end	Day	22% 10% 3 9% 5% 4 3 3 4 6% 32%	2427
May	1st to 10th	Day	20% 8% 3 8% 5% 5% 4 4 5% 7% 31%	4426
	11th to 20th	Day	16% 10% 3 7% 5% 4 4 4 6% 8% 34%	4398
	21st to end	Day	15% 7% 3 7% 5% 4 5% 4 5% 7% 38%	4837
June	1st to 10th	Day	20% 8% 3 7% 5% 5% 5% 4 5% 7% 30%	2660
	11th to 20th	Day	15% 7% 2 6% 4 5% 5% 4 6% 8% 39%	2660
	21st to end	Day	17% 7% 3 6% 5% 5% 6% 5% 6% 8% 32%	2660
July	1st to 10th	Day	11% 7% 3 8% 5% 5% 6% 5% 7% 9% 34%	4440
	11th to 20th	Day	11% 5% 2 6% 5% 5% 5% 4 7% 9% 39%	4440
	21st to end	Day	9% 5% 2 7% 4 4 4 4 6% 9% 45%	4814
August	1st to 10th	Day	14% 7% 3 8% 5% 5% 5% 4 6% 7% 35%	4268
	11th to 20th	Day	17% 6% 3 7% 5% 4 5% 4 5% 7% 37%	4044
	21st to end	Day	10% 6% 2 6% 4 4 5% 5% 6% 10% 40%	4194
September	1st to 10th	Day	13% 6% 2 6% 5% 4 4 4 5% 7% 42%	2280
	11th to 20th	Day	12% 6% 2 6% 5% 5% 4 3 5% 8% 45%	2280
	21st to end	Day	17% 7% 2 6% 4 4 5% 3 6% 7% 38%	2006
October	1st to 10th	Day	20% 9% 2 7% 5% 5% 4 4 5% 6% 34%	1900
	11th to 20th	Day	20% 10% 3 9% 6% 4 5% 3 5% 6% 28%	1900
	21st to end	Day	24% 13% 3 9% 4 4 4 3 5% 5% 25%	1976
November	1st to 10th	Day	15% 10% 4 8% 6% 4 5% 4 5% 7% 34%	1714
	11th to 20th	Day	17% 14% 4 8% 6% 6% 5% 3 6% 6% 26%	1600
	21st to end	Day	21% 15% 5% 10% 7% 6% 5% 3 5% 6% 18%	1600
December	1st to 10th	Day	20% 22% 6% 13% 6% 6% 4 3 4 5% 12%	2600
	11th to 20th	Day	16% 17% 6% 13% 6% 5% 4 2 3 4 24%	2986
	21st to end	Day	22% 17% 5% 14% 5% 5% 4 2 3 4 19%	3960
January	1st to 10th	Night	13% 19% 9% 17% 7% 4 4 2 4 3 18%	6349
	11th to 20th	Night	11% 14% 6% 15% 9% 6% 5% 4 5% 5% 21%	6315
	21st to end	Night	11% 18% 7% 13% 7% 7% 5% 3 4 5% 20%	6702
February	1st to 10th	Night	12% 15% 5% 13% 7% 6% 6% 4 5% 5% 23%	2600
	11th to 20th	Night	12% 14% 6% 11% 7% 6% 4 3 5% 5% 27%	2533
	21st to end	Night	15% 13% 4 11% 6% 5% 4 3 6% 6% 28%	1977
March	1st to 10th	Night	20% 13% 4 8% 6% 5% 4 3 4 4 31%	3636
	11th to 20th	Night	14% 17% 5% 11% 5% 4 5% 4 5% 6% 24%	3479
	21st to end	Night	13% 9% 3 9% 5% 5% 4 3 4 7% 37%	3664
April	1st to 10th	Night	20% 11% 3 9% 5% 4 4 3 5% 5% 32%	1900
	11th to 20th	Night	19% 10% 3 7% 5% 4 3 3 5% 6% 35%	1875
	21st to end	Night	21% 9% 4 8% 5% 4 4 2 5% 5% 33%	1768
May	1st to 10th	Night	20% 9% 3 9% 4 4 4 4 5% 6% 31%	2514
	11th to 20th	Night	17% 8% 3 7% 4 5% 4 4 6% 7% 34%	2495
	21st to end	Night	12% 7% 3 8% 4 5% 5% 4 6% 6% 40%	2738
June	1st to 10th	Night	15% 7% 2 9% 5% 5% 5% 5% 6% 8% 33%	1520
	11th to 20th	Night	13% 6% 3 7% 4 3 4 4 6% 8% 43%	1520
	21st to end	Night	17% 7% 3 6% 5% 4 4 4 6% 8% 36%	1520
July	1st to 10th	Night	11% 7% 3 10% 6% 6% 6% 4 6% 7% 36%	2520
	11th to 20th	Night	12% 6% 2 6% 4 5% 5% 4 6% 7% 43%	2520
	21st to end	Night	9% 5% 2 7% 5% 4 4 4 7% 8% 45%	2739
August	1st to 10th	Night	11% 6% 2 7% 5% 4 6% 4 7% 8% 40%	2657
	11th to 20th	Night	14% 7% 2 6% 4 4 4 4 6% 8% 42%	2785
	21st to end	Night	13% 6% 2 6% 4 4 5% 4 6% 9% 42%	3430
September	1st to 10th	Night	10% 7% 2 6% 5% 4 4 4 6% 6% 46%	1900
	11th to 20th	Night	14% 6% 1 5% 4 3 4 3 4 7% 50%	1900
	21st to end	Night	16% 6% 3 6% 4 4 4 4 5% 5% 43%	2167
October	1st to 10th	Night	18% 7% 2 7% 5% 3 4 4 5% 5% 39%	2280
	11th to 20th	Night	20% 10% 3 8% 6% 4 5% 3 5% 6% 30%	2280
	21st to end	Night	22% 10% 3 7% 5% 5% 5% 3 5% 7% 26%	2622
November	1st to 10th	Night	18% 11% 4 7% 5% 4 4 3 5% 6% 33%	2582
	11th to 20th	Night	18% 13% 3 8% 6% 5% 4 4 5% 6% 28%	2800
	21st to end	Night	21% 14% 5% 11% 6% 5% 4 3 5% 6% 21%	2800
December	1st to 10th	Night	19% 18% 5% 13% 7% 5% 5% 4 4 5% 14%	4580
	11th to 20th	Night	20% 15% 5% 12% 6% 4 4 3 4 4 24%	5208
	21st to end	Night	24% 18% 4 12% 5% 4 4 2 4 4 19%	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	66% 8% 9% 11% 6%	3598
	11th to 20th	Day	65% 7% 9% 11% 8%	3600
	21st to end	Day	66% 6% 8% 11% 8% 1	4236
February	1st to 10th	Day	63% 6% 10% 15% 5% 1	1800
	11th to 20th	Day	57% 7% 12% 14% 8% 1	1762
	21st to end	Day	60% 6% 11% 13% 9% 2	1570
March	1st to 10th	Day	59% 5% 9% 16% 9% 1	3205
	11th to 20th	Day	56% 8% 11% 15% 9% 1	3480
	21st to end	Day	40% 6% 9% 24% 18% 4	3967
April	1st to 10th	Day	55% 5% 8% 18% 12% 3	2280
	11th to 20th	Day	51% 5% 8% 21% 14% 2	2254
	21st to end	Day	54% 5% 8% 14% 15% 4	2427
May	1st to 10th	Day	49% 8% 10% 20% 11% 2	4440
	11th to 20th	Day	44% 11% 14% 19% 10% 1	4402
	21st to end	Day	43% 8% 12% 20% 16% 2	4837
June	1st to 10th	Day	52% 8% 10% 19% 11% 1	2660
	11th to 20th	Day	42% 8% 12% 23% 14% 2	2660
	21st to end	Day	47% 8% 13% 20% 11% 1	2660
July	1st to 10th	Day	42% 7% 15% 25% 10% 1	4370
	11th to 20th	Day	37% 8% 16% 28% 10%	4365
	21st to end	Day	35% 8% 14% 32% 11%	4661
August	1st to 10th	Day	46% 8% 14% 23% 9%	4254
	11th to 20th	Day	44% 8% 15% 26% 7%	4083
	21st to end	Day	36% 8% 17% 28% 11% 1	4194
September	1st to 10th	Day	40% 8% 14% 27% 11%	2280
	11th to 20th	Day	36% 7% 14% 29% 13%	2280
	21st to end	Day	44% 7% 15% 25% 9%	2006
October	1st to 10th	Day	48% 7% 11% 27% 6%	3160
	11th to 20th	Day	47% 6% 15% 22% 9%	3140
	21st to end	Day	51% 6% 19% 18% 5%	3240
November	1st to 10th	Day	48% 8% 15% 22% 6% 1	1714
	11th to 20th	Day	56% 8% 13% 14% 8% 1	1600
	21st to end	Day	66% 7% 13% 8% 5% 1	1600
December	1st to 10th	Day	75% 7% 10% 7% 2	2600
	11th to 20th	Day	64% 6% 9% 13% 8%	2986
	21st to end	Day	71% 4 7% 14% 4	3960
January	1st to 10th	Night	68% 7% 10% 11% 3	6349
	11th to 20th	Night	63% 8% 11% 13% 5%	6360
	21st to end	Night	66% 6% 8% 9% 10% 1	6702
February	1st to 10th	Night	61% 7% 11% 15% 6% 1	2600
	11th to 20th	Night	58% 6% 10% 19% 6% 1	2535
	21st to end	Night	55% 7% 10% 18% 9% 1	1977
March	1st to 10th	Night	56% 6% 11% 19% 8% 1	3646
	11th to 20th	Night	56% 9% 12% 14% 7% 1	3480
	21st to end	Night	43% 8% 11% 21% 15% 3	3664
April	1st to 10th	Night	53% 5% 9% 18% 13% 2	1900
	11th to 20th	Night	49% 5% 8% 22% 14% 2	1875
	21st to end	Night	53% 5% 8% 16% 16% 2	1768
May	1st to 10th	Night	48% 9% 11% 20% 9% 3	2520
	11th to 20th	Night	43% 12% 14% 20% 10% 2	2496
	21st to end	Night	39% 10% 13% 20% 16% 2	2739
June	1st to 10th	Night	44% 9% 14% 23% 9% 1	1520
	11th to 20th	Night	38% 7% 13% 24% 16% 2	1520
	21st to end	Night	44% 9% 14% 20% 12% 1	1520
July	1st to 10th	Night	44% 9% 15% 18% 13% 1	2480
	11th to 20th	Night	37% 8% 14% 32% 9%	2472
	21st to end	Night	35% 9% 14% 28% 14%	2651
August	1st to 10th	Night	38% 9% 15% 24% 13% 1	2647
	11th to 20th	Night	39% 8% 16% 29% 8%	2812
	21st to end	Night	37% 7% 16% 27% 11% 2	3430
September	1st to 10th	Night	36% 9% 13% 27% 14% 1	1900
	11th to 20th	Night	34% 7% 15% 34% 10% 1	1900
	21st to end	Night	42% 6% 13% 28% 10%	2167
October	1st to 10th	Night	39% 6% 13% 30% 12%	3800
	11th to 20th	Night	46% 7% 16% 22% 9%	3779
	21st to end	Night	50% 7% 18% 18% 7%	4308
November	1st to 10th	Night	51% 6% 15% 19% 9%	2582
	11th to 20th	Night	56% 7% 12% 17% 7% 1	2800
	21st to end	Night	63% 6% 12% 15% 3	2800
December	1st to 10th	Night	70% 7% 12% 9% 2	4580
	11th to 20th	Night	64% 5% 8% 13% 9% 1	5208
	21st to end	Night	69% 5% 6% 12% 9%	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	21% 23% 34% 19% 4 1	200
	11th to 20th	Day	30% 16% 36% 15% 4	200
	21st to end	Day	21% 22% 35% 16% 5% 1	280
February	1st to 10th	Day	26% 29% 30% 11% 4	300
	11th to 20th	Day	29% 28% 36% 6% 1	300
	21st to end	Day	32% 23% 34% 10% 1	358
March	1st to 10th	Day	25% 22% 35% 15% 2	460
	11th to 20th	Day	24% 21% 34% 17% 3 1	460
	21st to end	Day	29% 22% 30% 13% 5%	506
April	1st to 10th	Day	33% 18% 28% 14% 6%	460
	11th to 20th	Day	34% 20% 20% 15% 8% 2	452
	21st to end	Day	29% 20% 30% 13% 6% 1	460
May	1st to 10th	Day	25% 16% 30% 19% 8% 2	463
	11th to 20th	Day	19% 17% 31% 22% 8% 3	487
	21st to end	Day	20% 17% 31% 21% 9% 2	529
June	1st to 10th	Day	24% 13% 32% 22% 8% 1	490
	11th to 20th	Day	17% 16% 31% 21% 11% 3	490
	21st to end	Day	19% 15% 32% 21% 11% 2	490
July	1st to 10th	Day	9% 8% 32% 35% 12% 3	485
	11th to 20th	Day	11% 10% 35% 26% 13% 4	484
	21st to end	Day	13% 9% 35% 29% 12% 4	532
August	1st to 10th	Day	14% 8% 30% 29% 14% 6%	486
	11th to 20th	Day	14% 7% 27% 31% 16% 6%	479
	21st to end	Day	14% 12% 29% 27% 13% 6%	539
September	1st to 10th	Day	16% 11% 30% 22% 14% 8%	490
	11th to 20th	Day	11% 13% 22% 24% 19% 11%	490
	21st to end	Day	18% 14% 29% 20% 13% 6%	490
October	1st to 10th	Day	24% 16% 25% 20% 11% 4	490
	11th to 20th	Day	24% 21% 34% 13% 7% 1	490
	21st to end	Day	30% 21% 26% 18% 5% 1	479
November	1st to 10th	Day	26% 18% 32% 16% 7% 1	348
	11th to 20th	Day	25% 20% 37% 12% 5% 2	200
	21st to end	Day	29% 28% 32% 8% 3 1	200
December	1st to 10th	Day	31% 18% 38% 13% 2	200
	11th to 20th	Day	33% 24% 32% 8% 4 1	200
	21st to end	Day	28% 21% 31% 15% 4	220
January	1st to 10th	Night	26% 18% 36% 16% 4	800
	11th to 20th	Night	26% 20% 27% 21% 6% 1	800
	21st to end	Night	18% 16% 37% 23% 5% 1	880
February	1st to 10th	Night	20% 19% 39% 20% 3	800
	11th to 20th	Night	20% 20% 39% 18% 3	783
	21st to end	Night	22% 21% 29% 24% 3	647
March	1st to 10th	Night	25% 17% 33% 21% 4	760
	11th to 20th	Night	21% 22% 32% 18% 6%	760
	21st to end	Night	21% 17% 34% 20% 7%	836
April	1st to 10th	Night	27% 16% 32% 21% 4	760
	11th to 20th	Night	25% 19% 30% 20% 7%	751
	21st to end	Night	25% 14% 29% 22% 8%	628
May	1st to 10th	Night	22% 9% 30% 28% 10% 1	380
	11th to 20th	Night	21% 10% 32% 29% 7%	374
	21st to end	Night	14% 10% 36% 29% 10%	411
June	1st to 10th	Night	15% 9% 34% 34% 7%	380
	11th to 20th	Night	14% 8% 34% 32% 11% 1	380
	21st to end	Night	19% 9% 27% 32% 13%	380
July	1st to 10th	Night	9% 8% 30% 39% 13% 1	370
	11th to 20th	Night	12% 6% 28% 39% 14% 1	368
	21st to end	Night	9% 4 29% 44% 12% 2	416
August	1st to 10th	Night	10% 5% 25% 42% 18% 1	464
	11th to 20th	Night	11% 3 25% 38% 20% 3	564
	21st to end	Night	14% 7% 28% 32% 17% 2	803
September	1st to 10th	Night	14% 7% 31% 28% 18% 2	760
	11th to 20th	Night	17% 6% 21% 31% 21% 4	760
	21st to end	Night	19% 10% 24% 25% 20% 2	760
October	1st to 10th	Night	21% 12% 27% 25% 14% 1	760
	11th to 20th	Night	24% 16% 30% 21% 9% 1	760
	21st to end	Night	28% 15% 29% 23% 5%	836
November	1st to 10th	Night	25% 15% 28% 25% 6% 1	780
	11th to 20th	Night	25% 18% 32% 16% 9% 1	800
	21st to end	Night	32% 17% 25% 21% 5%	800
December	1st to 10th	Night	30% 18% 29% 19% 4	800
	11th to 20th	Night	27% 20% 31% 19% 4 1	800
	21st to end	Night	31% 16% 30% 17% 4	880

Page generated at 2025-02-22 06:51:37. Version ac07

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