Brockville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Brockville clear sky chart from 2005-11-06 to 2025-02-21.

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	17% 11% 4 8% 5% 4 4 3 5% 7% 31%	108699
	Night	18% 13% 4 9% 5% 4 4 3 5% 6% 29%	109861
Transparency	Day	51% 6% 12% 21% 9% 1	112225
	Night	55% 5% 11% 18% 9% 1	114499
Seeing	Day	25% 15% 29% 19% 9% 2	14803
	Night	25% 14% 29% 23% 8% 1	24068

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% 17% 6% 14% 6% 4 4 3 4 5% 19%	3597
	11th to 20th	Day	13% 18% 8% 17% 7% 5% 4 3 4 5% 16%	3570
	21st to end	Day	13% 19% 8% 13% 7% 6% 5% 3 4 4 17%	4190
February	1st to 10th	Day	17% 17% 5% 12% 7% 4 4 3 4 6% 21%	1800
	11th to 20th	Day	15% 16% 5% 12% 6% 5% 4 3 4 4 24%	1778
	21st to end	Day	20% 16% 5% 10% 7% 5% 4 4 4 5% 21%	1570
March	1st to 10th	Day	22% 13% 4 8% 5% 4 4 3 4 5% 28%	3116
	11th to 20th	Day	13% 17% 5% 10% 5% 5% 4 3 4 5% 29%	3475
	21st to end	Day	15% 8% 3 9% 5% 4 4 3 5% 5% 39%	4030
April	1st to 10th	Day	21% 13% 3 7% 5% 4 4 2 4 5% 32%	2280
	11th to 20th	Day	22% 9% 3 6% 4 4 3 3 4 5% 37%	2254
	21st to end	Day	23% 10% 3 7% 4 4 4 3 4 6% 31%	2365
May	1st to 10th	Day	20% 9% 3 8% 5% 4 4 4 5% 6% 31%	4426
	11th to 20th	Day	16% 9% 3 9% 5% 4 4 4 5% 8% 33%	4398
	21st to end	Day	14% 6% 2 6% 5% 4 4 4 7% 9% 38%	4837
June	1st to 10th	Day	21% 7% 3 7% 5% 5% 5% 4 6% 8% 31%	2660
	11th to 20th	Day	16% 6% 2 5% 5% 5% 4 4 6% 8% 37%	2660
	21st to end	Day	19% 8% 2 6% 5% 4 4 4 6% 7% 34%	2660
July	1st to 10th	Day	13% 6% 2 7% 5% 4 5% 5% 7% 10% 39%	4440
	11th to 20th	Day	14% 6% 2 5% 5% 4 5% 4 7% 9% 40%	4440
	21st to end	Day	12% 5% 2 6% 4 5% 5% 4 7% 9% 41%	4814
August	1st to 10th	Day	16% 8% 3 8% 4 4 4 4 6% 8% 35%	4310
	11th to 20th	Day	17% 6% 3 5% 4 4 4 4 6% 9% 38%	3956
	21st to end	Day	17% 5% 2 6% 4 3 4 4 6% 9% 40%	4180
September	1st to 10th	Day	14% 6% 2 6% 4 3 5% 4 6% 6% 44%	2280
	11th to 20th	Day	14% 6% 2 5% 4 3 4 3 5% 7% 48%	2275
	21st to end	Day	19% 7% 2 5% 4 4 5% 4 5% 8% 38%	2038
October	1st to 10th	Day	21% 9% 3 8% 4 4 4 3 5% 6% 33%	1900
	11th to 20th	Day	20% 11% 3 9% 6% 4 4 3 5% 7% 29%	1900
	21st to end	Day	27% 9% 2 8% 5% 4 5% 4 4 6% 27%	1948
November	1st to 10th	Day	16% 9% 4 8% 6% 5% 3 4 6% 7% 31%	1761
	11th to 20th	Day	16% 12% 4 10% 6% 5% 5% 4 5% 5% 30%	1645
	21st to end	Day	21% 17% 4 9% 5% 5% 4 3 5% 5% 21%	1600
December	1st to 10th	Day	22% 19% 5% 12% 6% 4 5% 3 5% 5% 14%	2600
	11th to 20th	Day	19% 18% 6% 11% 6% 5% 4 2 4 5% 21%	2986
	21st to end	Day	22% 17% 4 11% 5% 5% 4 3 4 4 22%	3960
January	1st to 10th	Night	16% 22% 7% 12% 6% 4 4 3 4 4 20%	6349
	11th to 20th	Night	12% 19% 8% 16% 8% 6% 5% 3 4 4 15%	6315
	21st to end	Night	17% 18% 7% 12% 7% 6% 5% 3 4 4 16%	6750
February	1st to 10th	Night	19% 16% 5% 12% 7% 4 5% 3 4 5% 20%	2600
	11th to 20th	Night	15% 14% 6% 11% 6% 4 5% 3 5% 5% 25%	2507
	21st to end	Night	18% 15% 5% 10% 6% 4 4 3 3 6% 25%	1885
March	1st to 10th	Night	20% 13% 4 7% 5% 4 3 3 4 5% 32%	3724
	11th to 20th	Night	21% 18% 4 7% 4 3 4 2 4 5% 26%	3480
	21st to end	Night	17% 12% 3 8% 5% 4 3 2 4 4 37%	3601
April	1st to 10th	Night	22% 11% 3 7% 5% 3 4 3 5% 5% 32%	1900
	11th to 20th	Night	22% 9% 2 7% 5% 3 4 3 4 6% 35%	1875
	21st to end	Night	23% 9% 3 7% 4 4 4 3 5% 5% 33%	1829
May	1st to 10th	Night	23% 9% 3 7% 5% 4 5% 4 5% 7% 27%	2514
	11th to 20th	Night	20% 10% 3 8% 4 4 4 3 4 6% 34%	2495
	21st to end	Night	15% 7% 2 6% 4 4 4 4 5% 8% 41%	2738
June	1st to 10th	Night	19% 7% 2 7% 6% 4 4 5% 6% 8% 32%	1520
	11th to 20th	Night	16% 5% 2 6% 4 4 5% 4 5% 8% 41%	1520
	21st to end	Night	19% 7% 3 6% 4 5% 5% 4 6% 8% 33%	1520
July	1st to 10th	Night	14% 8% 2 7% 4 5% 5% 4 6% 7% 38%	2520
	11th to 20th	Night	15% 7% 2 6% 4 4 4 3 5% 8% 42%	2520
	21st to end	Night	11% 7% 2 7% 4 5% 4 5% 6% 7% 42%	2739
August	1st to 10th	Night	15% 8% 3 6% 4 4 4 4 6% 9% 38%	2616
	11th to 20th	Night	15% 8% 2 7% 4 4 4 4 6% 7% 40%	2840
	21st to end	Night	10% 5% 3 7% 5% 5% 6% 4 7% 8% 41%	3476
September	1st to 10th	Night	14% 7% 2 6% 4 4 4 3 4 7% 45%	1900
	11th to 20th	Night	14% 6% 2 5% 4 3 2 2 5% 7% 49%	1905
	21st to end	Night	17% 7% 2 6% 4 4 4 4 6% 6% 40%	2139
October	1st to 10th	Night	20% 9% 3 6% 5% 4 5% 4 5% 6% 34%	2280
	11th to 20th	Night	20% 9% 3 8% 5% 4 4 4 5% 6% 33%	2280
	21st to end	Night	27% 9% 3 8% 5% 4 4 3 5% 6% 27%	2650
November	1st to 10th	Night	19% 10% 4 7% 4 4 3 3 5% 6% 34%	2537
	11th to 20th	Night	18% 11% 3 7% 5% 5% 4 4 5% 6% 31%	2753
	21st to end	Night	21% 15% 4 9% 5% 5% 4 4 5% 6% 22%	2800
December	1st to 10th	Night	21% 20% 6% 13% 6% 5% 4 3 4 4 13%	4580
	11th to 20th	Night	23% 16% 5% 9% 6% 3 3 3 3 4 25%	5208
	21st to end	Night	27% 15% 4 12% 5% 4 4 3 5% 4 17%	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	64% 6% 10% 15% 4 1	3598
	11th to 20th	Day	70% 4 11% 8% 6%	3600
	21st to end	Day	70% 4 9% 8% 8% 1	4190
February	1st to 10th	Day	65% 4 9% 16% 5% 1	1800
	11th to 20th	Day	63% 5% 10% 15% 8% 1	1787
	21st to end	Day	66% 5% 8% 12% 8% 1	1570
March	1st to 10th	Day	59% 5% 10% 18% 8% 1	3119
	11th to 20th	Day	56% 6% 13% 13% 10% 1	3475
	21st to end	Day	46% 4 10% 22% 14% 3	4030
April	1st to 10th	Day	56% 4 7% 18% 13% 3	2280
	11th to 20th	Day	50% 4 8% 19% 15% 3	2254
	21st to end	Day	54% 5% 8% 16% 13% 4	2365
May	1st to 10th	Day	53% 6% 10% 19% 10% 1	4440
	11th to 20th	Day	48% 9% 12% 22% 9% 1	4402
	21st to end	Day	41% 8% 13% 24% 13% 2	4837
June	1st to 10th	Day	51% 6% 11% 20% 12% 1	2660
	11th to 20th	Day	43% 7% 12% 25% 12% 2	2660
	21st to end	Day	48% 8% 13% 20% 11% 1	2660
July	1st to 10th	Day	39% 7% 13% 29% 12% 1	4370
	11th to 20th	Day	39% 6% 15% 30% 8%	4365
	21st to end	Day	38% 7% 15% 30% 10%	4661
August	1st to 10th	Day	45% 6% 15% 23% 10%	4296
	11th to 20th	Day	43% 7% 15% 27% 9%	3995
	21st to end	Day	41% 6% 15% 28% 10%	4180
September	1st to 10th	Day	39% 7% 14% 26% 12% 1	2280
	11th to 20th	Day	37% 5% 12% 30% 15%	2275
	21st to end	Day	45% 6% 12% 25% 11%	2038
October	1st to 10th	Day	47% 4 13% 27% 9%	3160
	11th to 20th	Day	49% 6% 15% 23% 7%	3140
	21st to end	Day	49% 5% 15% 24% 7%	3186
November	1st to 10th	Day	50% 6% 15% 21% 7% 1	1761
	11th to 20th	Day	56% 5% 12% 16% 9% 2	1645
	21st to end	Day	65% 6% 13% 10% 5%	1600
December	1st to 10th	Day	71% 6% 12% 9% 1	2600
	11th to 20th	Day	68% 4 10% 13% 5%	2986
	21st to end	Day	66% 5% 9% 16% 4	3960
January	1st to 10th	Night	68% 5% 12% 11% 4	6349
	11th to 20th	Night	73% 5% 9% 8% 4	6360
	21st to end	Night	71% 6% 7% 8% 7% 1	6750
February	1st to 10th	Night	67% 5% 10% 13% 5% 1	2600
	11th to 20th	Night	60% 5% 10% 17% 7%	2509
	21st to end	Night	61% 5% 9% 16% 8% 1	1885
March	1st to 10th	Night	55% 5% 9% 22% 8% 1	3734
	11th to 20th	Night	61% 4 14% 12% 8% 1	3481
	21st to end	Night	50% 3 7% 22% 15% 2	3601
April	1st to 10th	Night	53% 4 9% 19% 13% 2	1900
	11th to 20th	Night	51% 5% 9% 18% 15% 1	1875
	21st to end	Night	53% 4 10% 16% 14% 3	1829
May	1st to 10th	Night	55% 6% 11% 17% 9% 3	2520
	11th to 20th	Night	49% 7% 13% 20% 9% 2	2496
	21st to end	Night	40% 6% 13% 21% 18% 2	2739
June	1st to 10th	Night	47% 7% 13% 20% 11% 1	1520
	11th to 20th	Night	41% 7% 13% 21% 17% 2	1520
	21st to end	Night	46% 8% 12% 21% 13% 1	1520
July	1st to 10th	Night	43% 6% 11% 24% 14% 1	2480
	11th to 20th	Night	39% 6% 14% 33% 8%	2472
	21st to end	Night	39% 8% 14% 26% 12% 1	2651
August	1st to 10th	Night	42% 7% 14% 26% 11%	2606
	11th to 20th	Night	43% 6% 13% 29% 9% 1	2867
	21st to end	Night	38% 7% 15% 29% 11% 1	3476
September	1st to 10th	Night	40% 5% 13% 28% 13% 1	1900
	11th to 20th	Night	36% 6% 13% 30% 14% 1	1905
	21st to end	Night	43% 6% 12% 27% 12% 1	2139
October	1st to 10th	Night	44% 5% 13% 26% 11% 1	3800
	11th to 20th	Night	44% 6% 15% 25% 9%	3779
	21st to end	Night	50% 4 16% 22% 7%	4362
November	1st to 10th	Night	50% 6% 15% 19% 10% 1	2537
	11th to 20th	Night	52% 6% 13% 18% 9% 2	2753
	21st to end	Night	63% 6% 12% 14% 5%	2800
December	1st to 10th	Night	74% 5% 11% 9% 2	4580
	11th to 20th	Night	63% 5% 9% 14% 8%	5208
	21st to end	Night	69% 5% 8% 11% 7%	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	27% 22% 35% 12% 5% 1	200
	11th to 20th	Day	37% 17% 30% 14% 3 1	200
	21st to end	Day	25% 24% 33% 14% 4	270
February	1st to 10th	Day	35% 25% 30% 9% 1	300
	11th to 20th	Day	33% 25% 34% 8% 1	325
	21st to end	Day	37% 19% 30% 12% 2	382
March	1st to 10th	Day	28% 20% 31% 16% 5%	460
	11th to 20th	Day	30% 21% 30% 14% 3 1	460
	21st to end	Day	35% 19% 27% 13% 5% 1	506
April	1st to 10th	Day	36% 14% 30% 16% 4	460
	11th to 20th	Day	34% 19% 25% 13% 7% 3	452
	21st to end	Day	33% 18% 29% 12% 5% 2	460
May	1st to 10th	Day	25% 17% 29% 21% 6% 1	463
	11th to 20th	Day	20% 16% 35% 19% 8% 2	487
	21st to end	Day	19% 15% 30% 24% 10% 1	529
June	1st to 10th	Day	27% 12% 30% 22% 8% 1	490
	11th to 20th	Day	17% 12% 33% 24% 11% 2	490
	21st to end	Day	21% 18% 30% 19% 9% 2	490
July	1st to 10th	Day	15% 8% 31% 28% 16% 2	485
	11th to 20th	Day	16% 10% 30% 28% 13% 3	484
	21st to end	Day	14% 10% 32% 31% 11% 2	532
August	1st to 10th	Day	17% 9% 26% 30% 15% 4	486
	11th to 20th	Day	15% 7% 25% 30% 16% 6%	479
	21st to end	Day	16% 11% 31% 23% 14% 6%	539
September	1st to 10th	Day	17% 11% 30% 23% 12% 7%	490
	11th to 20th	Day	13% 9% 23% 24% 18% 13%	490
	21st to end	Day	21% 10% 26% 24% 16% 3	490
October	1st to 10th	Day	24% 16% 25% 18% 11% 5%	490
	11th to 20th	Day	27% 19% 29% 16% 7% 1	490
	21st to end	Day	34% 16% 27% 18% 5%	464
November	1st to 10th	Day	28% 19% 28% 17% 7% 1	395
	11th to 20th	Day	28% 16% 34% 15% 6% 2	245
	21st to end	Day	33% 21% 33% 12% 2	200
December	1st to 10th	Day	37% 19% 25% 16% 4 1	200
	11th to 20th	Day	33% 26% 32% 8% 3	200
	21st to end	Day	35% 19% 26% 15% 3 1	220
January	1st to 10th	Night	32% 18% 29% 18% 4	800
	11th to 20th	Night	31% 17% 29% 19% 4	800
	21st to end	Night	24% 18% 32% 21% 5%	880
February	1st to 10th	Night	29% 20% 32% 17% 2	800
	11th to 20th	Night	24% 19% 36% 17% 3	783
	21st to end	Night	28% 18% 30% 20% 3	629
March	1st to 10th	Night	28% 16% 30% 23% 4	760
	11th to 20th	Night	29% 18% 31% 18% 4 1	760
	21st to end	Night	27% 14% 32% 19% 7%	836
April	1st to 10th	Night	28% 15% 32% 23% 2	760
	11th to 20th	Night	28% 18% 29% 18% 6%	751
	21st to end	Night	27% 11% 32% 21% 8%	689
May	1st to 10th	Night	27% 9% 26% 28% 9% 1	380
	11th to 20th	Night	16% 10% 35% 31% 8%	374
	21st to end	Night	15% 9% 35% 30% 10% 1	411
June	1st to 10th	Night	20% 7% 28% 36% 8% 1	380
	11th to 20th	Night	15% 12% 28% 32% 12% 1	380
	21st to end	Night	19% 8% 27% 32% 13% 1	380
July	1st to 10th	Night	12% 6% 30% 38% 14%	370
	11th to 20th	Night	13% 5% 27% 36% 18% 1	368
	21st to end	Night	13% 5% 28% 41% 11% 2	416
August	1st to 10th	Night	14% 4 25% 37% 19%	436
	11th to 20th	Night	18% 4 19% 35% 21% 3	593
	21st to end	Night	14% 7% 27% 34% 15% 2	836
September	1st to 10th	Night	17% 8% 27% 31% 16% 1	760
	11th to 20th	Night	18% 6% 20% 29% 21% 6%	760
	21st to end	Night	18% 10% 26% 25% 18% 2	760
October	1st to 10th	Night	24% 12% 26% 21% 15% 1	760
	11th to 20th	Night	25% 14% 28% 23% 9% 1	760
	21st to end	Night	31% 14% 28% 22% 5%	836
November	1st to 10th	Night	27% 15% 30% 21% 8%	780
	11th to 20th	Night	25% 19% 30% 17% 9%	800
	21st to end	Night	35% 17% 26% 16% 6%	800
December	1st to 10th	Night	34% 18% 27% 17% 4	800
	11th to 20th	Night	31% 17% 32% 17% 2 1	800
	21st to end	Night	34% 16% 31% 16% 3	880

Page generated at 2025-02-18 03:26:31. Version ac07

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