Grand Falls-Windsor
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Grand Falls-Windsor clear sky chart from 2005-11-06 to 2025-07-06.

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	21% 14% 5% 9% 5% 5% 4 3 5% 6% 24%	119978
	Night	19% 13% 5% 10% 5% 5% 4 4 5% 6% 24%	119040
Transparency	Day	64% 3 9% 17% 7% 1	123461
	Night	63% 3 10% 16% 8% 1	123740
Seeing	Day	31% 12% 28% 20% 8% 2	19007
	Night	29% 11% 31% 22% 6% 1	25827

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	19% 20% 7% 11% 6% 5% 5% 2 3 3 18%	3278
	11th to 20th	Day	14% 19% 9% 17% 6% 5% 4 3 4 4 15%	3591
	21st to end	Day	8% 12% 6% 11% 8% 7% 6% 4 6% 6% 26%	3982
February	1st to 10th	Day	18% 14% 4 10% 9% 6% 5% 4 5% 6% 20%	1600
	11th to 20th	Day	17% 21% 6% 10% 7% 4 5% 4 5% 4 16%	1822
	21st to end	Day	12% 15% 6% 13% 7% 6% 5% 4 4 5% 23%	1650
March	1st to 10th	Day	19% 16% 4 12% 8% 5% 5% 3 4 5% 21%	4474
	11th to 20th	Day	20% 19% 8% 12% 6% 4 4 2 3 3 19%	4791
	21st to end	Day	25% 21% 8% 11% 5% 4 3 2 3 4 16%	5756
April	1st to 10th	Day	19% 21% 7% 12% 7% 5% 4 3 4 4 14%	2400
	11th to 20th	Day	22% 18% 5% 9% 4 3 3 3 4 6% 24%	2530
	21st to end	Day	23% 22% 6% 8% 4 4 3 2 4 4 20%	2600
May	1st to 10th	Day	27% 19% 5% 8% 5% 4 4 3 3 4 17%	6151
	11th to 20th	Day	19% 16% 4 9% 5% 4 4 3 4 5% 26%	6400
	21st to end	Day	25% 17% 3 6% 4 3 4 3 4 6% 24%	7428
June	1st to 10th	Day	32% 16% 3 7% 5% 4 3 3 4 5% 17%	3000
	11th to 20th	Day	26% 11% 4 8% 5% 4 5% 4 5% 6% 23%	3000
	21st to end	Day	25% 11% 3 8% 6% 5% 4 4 5% 5% 23%	3000
July	1st to 10th	Day	21% 11% 4 9% 5% 6% 5% 4 5% 6% 24%	4825
	11th to 20th	Day	16% 9% 3 8% 6% 5% 6% 5% 7% 8% 27%	4599
	21st to end	Day	15% 7% 2 7% 4 5% 5% 4 6% 9% 37%	4815
August	1st to 10th	Day	22% 9% 3 8% 6% 5% 5% 4 6% 7% 24%	4424
	11th to 20th	Day	18% 9% 3 7% 4 4 4 3 5% 6% 37%	4080
	21st to end	Day	20% 8% 3 8% 5% 4 4 4 5% 7% 32%	4476
September	1st to 10th	Day	19% 9% 3 8% 5% 3 4 4 5% 7% 32%	2280
	11th to 20th	Day	25% 10% 4 7% 5% 4 4 3 5% 6% 28%	2103
	21st to end	Day	18% 11% 4 9% 5% 4 4 4 5% 7% 29%	2090
October	1st to 10th	Day	20% 12% 3 7% 5% 4 4 4 4 6% 31%	2071
	11th to 20th	Day	22% 14% 4 8% 6% 5% 4 3 5% 6% 23%	1710
	21st to end	Day	24% 15% 3 9% 6% 5% 4 3 4 4 22%	1881
November	1st to 10th	Day	24% 14% 5% 9% 6% 5% 5% 4 4 4 20%	1760
	11th to 20th	Day	22% 15% 6% 9% 5% 4 4 3 3 5% 24%	1595
	21st to end	Day	23% 17% 5% 8% 6% 5% 4 3 4 5% 21%	1400
December	1st to 10th	Day	13% 14% 4 9% 5% 5% 4 5% 5% 6% 30%	2290
	11th to 20th	Day	25% 12% 4 10% 4 5% 5% 4 5% 6% 21%	2628
	21st to end	Day	19% 16% 5% 11% 5% 4 4 5% 6% 6% 18%	3498
January	1st to 10th	Night	17% 20% 6% 12% 6% 5% 4 3 4 4 19%	6684
	11th to 20th	Night	12% 16% 8% 15% 7% 5% 5% 5% 5% 5% 16%	6314
	21st to end	Night	8% 10% 4 10% 5% 7% 6% 5% 7% 9% 30%	6996
February	1st to 10th	Night	17% 12% 4 13% 8% 5% 5% 4 5% 6% 21%	2800
	11th to 20th	Night	17% 17% 5% 11% 6% 5% 6% 4 5% 5% 20%	2462
	21st to end	Night	12% 13% 4 10% 7% 4 5% 4 5% 6% 29%	1980
March	1st to 10th	Night	18% 14% 4 10% 6% 5% 5% 4 6% 6% 21%	5366
	11th to 20th	Night	17% 15% 7% 13% 7% 6% 5% 4 4 4 18%	5168
	21st to end	Night	22% 19% 6% 11% 6% 4 3 3 4 5% 18%	5173
April	1st to 10th	Night	23% 19% 6% 9% 4 3 3 2 4 5% 21%	2000
	11th to 20th	Night	21% 16% 5% 8% 4 4 4 2 4 4 28%	1819
	21st to end	Night	22% 19% 5% 8% 4 4 3 3 4 6% 22%	1800
May	1st to 10th	Night	28% 19% 5% 10% 4 4 4 3 3 5% 16%	3805
	11th to 20th	Night	23% 14% 5% 11% 5% 5% 4 3 3 5% 22%	3514
	21st to end	Night	27% 15% 3 6% 3 3 4 3 4 6% 25%	3468
June	1st to 10th	Night	32% 14% 4 7% 3 4 4 4 3 5% 19%	1400
	11th to 20th	Night	25% 10% 2 7% 5% 4 5% 3 7% 7% 26%	1400
	21st to end	Night	27% 11% 3 7% 5% 5% 4 4 4 4 26%	1400
July	1st to 10th	Night	25% 10% 2 7% 4 4 4 3 5% 7% 27%	2256
	11th to 20th	Night	15% 10% 3 8% 5% 4 6% 4 6% 8% 30%	2368
	21st to end	Night	15% 8% 3 7% 5% 4 4 3 5% 6% 39%	2750
August	1st to 10th	Night	13% 9% 3 7% 5% 5% 4 4 6% 8% 35%	2516
	11th to 20th	Night	18% 8% 2 7% 4 4 4 4 5% 5% 39%	2756
	21st to end	Night	21% 7% 2 6% 4 4 4 3 5% 6% 38%	3187
September	1st to 10th	Night	20% 8% 3 8% 6% 4 3 3 4 6% 36%	1900
	11th to 20th	Night	22% 10% 2 6% 5% 4 3 3 5% 6% 33%	2076
	21st to end	Night	21% 9% 3 9% 4 4 3 4 6% 7% 30%	2090
October	1st to 10th	Night	21% 10% 3 8% 4 4 5% 3 5% 6% 30%	2108
	11th to 20th	Night	22% 11% 3 8% 4 5% 4 3 5% 6% 29%	2466
	21st to end	Night	26% 13% 3 7% 4 4 4 3 4 5% 26%	2717
November	1st to 10th	Night	22% 14% 4 8% 6% 5% 5% 4 6% 6% 20%	2538
	11th to 20th	Night	25% 13% 5% 8% 6% 4 4 4 5% 5% 21%	2802
	21st to end	Night	21% 16% 6% 10% 6% 5% 4 4 5% 5% 19%	3000
December	1st to 10th	Night	15% 12% 4 9% 5% 4 5% 3 6% 6% 31%	4900
	11th to 20th	Night	25% 13% 4 10% 6% 5% 5% 4 4 5% 20%	5581
	21st to end	Night	17% 13% 6% 15% 6% 5% 5% 4 5% 6% 18%	7480

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	73% 2 5% 12% 7% 2	3279
	11th to 20th	Day	75% 2 7% 10% 6%	3620
	21st to end	Day	59% 4 6% 17% 11% 3	3982
February	1st to 10th	Day	66% 3 9% 12% 7% 2	1600
	11th to 20th	Day	72% 2 6% 12% 7% 1	1829
	21st to end	Day	66% 2 5% 15% 11% 1	1650
March	1st to 10th	Day	68% 3 5% 12% 10% 2	4478
	11th to 20th	Day	73% 2 5% 12% 7% 3	4791
	21st to end	Day	75% 2 4 12% 7%	5756
April	1st to 10th	Day	75% 2 6% 10% 6% 1	2400
	11th to 20th	Day	65% 1 7% 15% 10% 1	2530
	21st to end	Day	70% 2 6% 13% 9% 1	2600
May	1st to 10th	Day	74% 2 7% 13% 4 1	6163
	11th to 20th	Day	63% 2 9% 19% 7% 1	6404
	21st to end	Day	64% 2 9% 19% 6%	7428
June	1st to 10th	Day	72% 2 6% 14% 6%	3000
	11th to 20th	Day	63% 3 10% 19% 5% 1	3000
	21st to end	Day	63% 3 10% 16% 7% 1	3000
July	1st to 10th	Day	61% 3 12% 18% 6%	4750
	11th to 20th	Day	55% 4 17% 19% 4	4517
	21st to end	Day	45% 3 20% 26% 6% 1	4662
August	1st to 10th	Day	58% 4 13% 21% 4	4410
	11th to 20th	Day	49% 3 14% 23% 10% 1	4120
	21st to end	Day	52% 3 14% 26% 5%	4476
September	1st to 10th	Day	53% 3 11% 23% 9% 2	2280
	11th to 20th	Day	59% 2 12% 19% 7%	2103
	21st to end	Day	56% 3 14% 19% 8% 1	2090
October	1st to 10th	Day	59% 4 10% 18% 8%	3449
	11th to 20th	Day	59% 6% 11% 18% 6%	2832
	21st to end	Day	62% 4 9% 16% 9% 1	3092
November	1st to 10th	Day	68% 3 11% 12% 5%	1760
	11th to 20th	Day	66% 2 9% 13% 8% 1	1595
	21st to end	Day	68% 3 10% 9% 8% 1	1400
December	1st to 10th	Day	56% 5% 8% 20% 10%	2290
	11th to 20th	Day	66% 4 15% 9% 6%	2627
	21st to end	Day	68% 3 7% 17% 3	3498
January	1st to 10th	Night	72% 1 5% 11% 7% 3	6684
	11th to 20th	Night	72% 4 6% 11% 6% 1	6360
	21st to end	Night	52% 6% 10% 13% 16% 3	6996
February	1st to 10th	Night	66% 2 7% 14% 9% 1	2800
	11th to 20th	Night	70% 2 8% 12% 7% 1	2466
	21st to end	Night	57% 2 8% 18% 13% 1	1980
March	1st to 10th	Night	64% 4 7% 14% 9% 3	5375
	11th to 20th	Night	71% 3 7% 10% 8% 1	5169
	21st to end	Night	70% 2 8% 14% 6%	5173
April	1st to 10th	Night	70% 2 4 12% 11% 1	2000
	11th to 20th	Night	63% 1 7% 18% 10%	1819
	21st to end	Night	66% 3 7% 14% 10% 1	1800
May	1st to 10th	Night	75% 2 7% 13% 3	3810
	11th to 20th	Night	68% 2 8% 15% 7%	3515
	21st to end	Night	63% 2 9% 20% 5%	3469
June	1st to 10th	Night	69% 3 9% 13% 6%	1400
	11th to 20th	Night	59% 3 14% 19% 6%	1400
	21st to end	Night	61% 3 10% 18% 7% 1	1400
July	1st to 10th	Night	58% 3 15% 20% 4	2222
	11th to 20th	Night	55% 5% 16% 18% 7%	2326
	21st to end	Night	47% 4 16% 28% 5%	2663
August	1st to 10th	Night	49% 5% 20% 23% 4	2505
	11th to 20th	Night	47% 3 17% 25% 7% 1	2782
	21st to end	Night	48% 3 16% 28% 5%	3186
September	1st to 10th	Night	51% 3 12% 24% 10%	1900
	11th to 20th	Night	54% 3 13% 19% 10% 1	2076
	21st to end	Night	54% 3 13% 20% 9% 1	2090
October	1st to 10th	Night	59% 4 15% 16% 6% 1	3511
	11th to 20th	Night	54% 6% 13% 18% 8%	4093
	21st to end	Night	58% 4 12% 17% 9% 1	4467
November	1st to 10th	Night	66% 4 10% 15% 6%	2538
	11th to 20th	Night	66% 3 9% 16% 6%	2802
	21st to end	Night	69% 3 8% 12% 8%	3000
December	1st to 10th	Night	55% 5% 7% 22% 12%	4900
	11th to 20th	Night	69% 4 11% 11% 5%	5583
	21st to end	Night	69% 3 8% 16% 3	7480

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	30% 16% 30% 16% 6% 2	400
	11th to 20th	Day	29% 17% 28% 21% 5% 1	400
	21st to end	Day	29% 15% 31% 20% 5%	440
February	1st to 10th	Day	30% 18% 30% 15% 7% 1	400
	11th to 20th	Day	31% 20% 31% 14% 3 1	396
	21st to end	Day	23% 18% 35% 16% 5% 2	331
March	1st to 10th	Day	30% 19% 32% 14% 6% 1	400
	11th to 20th	Day	30% 15% 24% 18% 10% 3	400
	21st to end	Day	38% 15% 25% 16% 5% 2	502
April	1st to 10th	Day	35% 17% 29% 15% 4	500
	11th to 20th	Day	35% 12% 27% 20% 5% 1	648
	21st to end	Day	37% 11% 28% 17% 5% 1	700
May	1st to 10th	Day	41% 12% 20% 17% 8% 2	703
	11th to 20th	Day	31% 11% 24% 22% 9% 3	724
	21st to end	Day	37% 10% 28% 18% 6% 1	790
June	1st to 10th	Day	42% 9% 23% 16% 8% 2	730
	11th to 20th	Day	34% 9% 27% 19% 10% 2	730
	21st to end	Day	30% 10% 28% 19% 9% 5%	730
July	1st to 10th	Day	32% 8% 27% 20% 12% 2	695
	11th to 20th	Day	27% 7% 26% 27% 12% 1	668
	21st to end	Day	27% 6% 25% 30% 11% 1	740
August	1st to 10th	Day	24% 9% 29% 24% 12% 2	675
	11th to 20th	Day	27% 4 25% 26% 14% 4	667
	21st to end	Day	26% 7% 24% 26% 14% 3	718
September	1st to 10th	Day	21% 12% 33% 22% 8% 3	490
	11th to 20th	Day	37% 9% 28% 20% 5% 2	396
	21st to end	Day	22% 14% 36% 20% 7% 2	390
October	1st to 10th	Day	26% 13% 32% 22% 5% 2	390
	11th to 20th	Day	34% 8% 27% 19% 9% 3	390
	21st to end	Day	32% 14% 28% 16% 8% 2	429
November	1st to 10th	Day	38% 13% 26% 16% 5% 1	395
	11th to 20th	Day	33% 16% 26% 19% 6% 1	400
	21st to end	Day	39% 18% 29% 12% 4	400
December	1st to 10th	Day	28% 13% 33% 18% 9%	400
	11th to 20th	Day	29% 19% 30% 18% 4	400
	21st to end	Day	26% 15% 30% 20% 6% 3	440
January	1st to 10th	Night	28% 14% 30% 20% 6% 1	900
	11th to 20th	Night	26% 17% 32% 20% 4 1	900
	21st to end	Night	23% 16% 36% 21% 4	990
February	1st to 10th	Night	26% 16% 37% 17% 3	900
	11th to 20th	Night	30% 17% 33% 17% 2 1	831
	21st to end	Night	21% 12% 37% 22% 6% 2	660
March	1st to 10th	Night	26% 19% 34% 17% 4	800
	11th to 20th	Night	24% 13% 30% 26% 7%	685
	21st to end	Night	33% 13% 30% 18% 5%	660
April	1st to 10th	Night	34% 16% 28% 17% 4 1	600
	11th to 20th	Night	31% 9% 34% 20% 5% 1	594
	21st to end	Night	34% 10% 30% 21% 4	600
May	1st to 10th	Night	36% 6% 29% 20% 7% 1	600
	11th to 20th	Night	32% 7% 30% 23% 8%	592
	21st to end	Night	36% 9% 29% 21% 5%	649
June	1st to 10th	Night	41% 8% 25% 22% 4	600
	11th to 20th	Night	34% 7% 26% 25% 8%	600
	21st to end	Night	33% 7% 30% 21% 8% 1	600
July	1st to 10th	Night	28% 8% 32% 24% 8% 1	572
	11th to 20th	Night	22% 7% 34% 32% 5%	552
	21st to end	Night	26% 6% 33% 29% 7%	623
August	1st to 10th	Night	22% 5% 28% 34% 11% 1	568
	11th to 20th	Night	25% 5% 28% 30% 12%	562
	21st to end	Night	22% 6% 28% 33% 10% 1	627
September	1st to 10th	Night	26% 4 33% 29% 7%	570
	11th to 20th	Night	31% 9% 29% 27% 4	570
	21st to end	Night	28% 8% 34% 26% 5%	570
October	1st to 10th	Night	30% 8% 32% 25% 5%	580
	11th to 20th	Night	32% 8% 28% 23% 8% 1	856
	21st to end	Night	35% 11% 27% 20% 7%	946
November	1st to 10th	Night	33% 13% 29% 20% 4 1	880
	11th to 20th	Night	33% 11% 30% 19% 5% 1	900
	21st to end	Night	31% 18% 29% 20% 2	900
December	1st to 10th	Night	29% 14% 28% 21% 7% 1	900
	11th to 20th	Night	34% 16% 29% 17% 4	900
	21st to end	Night	25% 12% 32% 23% 7% 1	990

Page generated at 2025-07-03 02:30:15. Version ac07

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