Grand River
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Grand River 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	12% 8% 3 7% 5% 4 4 4 6% 7% 40%	101326
	Night	11% 8% 3 8% 4 4 4 3 5% 6% 44%	97832
Transparency	Day	40% 6% 12% 24% 15% 2	104968
	Night	39% 5% 12% 24% 17% 3	102330
Seeing	Day	15% 10% 29% 28% 14% 4	15795
	Night	15% 10% 33% 31% 11% 1	25627

By Month

Percentage Cloud Cover SE (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	12% 11% 5% 15% 6% 6% 5% 4 5% 6% 24%	2657
	11th to 20th	Day	9% 13% 5% 10% 7% 4 8% 3 5% 6% 29%	2850
	21st to end	Day	13% 15% 8% 16% 5% 5% 4 4 4 5% 21%	3135
February	1st to 10th	Day	12% 11% 4 12% 7% 5% 4 3 5% 7% 30%	1710
	11th to 20th	Day	11% 9% 4 9% 6% 4 5% 4 5% 7% 36%	1664
	21st to end	Day	13% 8% 3 7% 5% 4 4 3 5% 7% 39%	1549
March	1st to 10th	Day	17% 10% 3 8% 4 4 3 3 4 4 41%	3436
	11th to 20th	Day	10% 8% 3 6% 5% 4 4 3 5% 7% 45%	3480
	21st to end	Day	20% 14% 6% 8% 5% 4 4 4 5% 7% 23%	3814
April	1st to 10th	Day	16% 10% 3 6% 4 4 4 4 6% 6% 39%	2245
	11th to 20th	Day	15% 9% 3 7% 5% 4 4 4 5% 7% 38%	2254
	21st to end	Day	20% 8% 3 9% 3 4 4 3 5% 7% 36%	2413
May	1st to 10th	Day	15% 8% 3 7% 5% 5% 5% 4 6% 8% 34%	4082
	11th to 20th	Day	16% 7% 3 7% 5% 4 5% 3 6% 7% 37%	4199
	21st to end	Day	14% 7% 2 5% 5% 4 4 3 5% 7% 44%	4824
June	1st to 10th	Day	8% 6% 2 7% 5% 5% 5% 4 6% 8% 45%	2660
	11th to 20th	Day	8% 5% 2 5% 4 3 4 5% 7% 10% 46%	2660
	21st to end	Day	8% 5% 2 6% 6% 5% 6% 5% 7% 9% 43%	2660
July	1st to 10th	Day	10% 6% 3 6% 5% 5% 6% 5% 7% 9% 37%	4440
	11th to 20th	Day	6% 3 1 5% 4 4 5% 4 6% 8% 54%	4224
	21st to end	Day	5% 4 1 5% 4 5% 5% 5% 8% 11% 48%	4465
August	1st to 10th	Day	6% 4 2 5% 5% 5% 5% 4 8% 11% 46%	4104
	11th to 20th	Day	13% 6% 2 5% 4 4 5% 4 6% 9% 42%	4041
	21st to end	Day	7% 5% 2 6% 5% 4 4 4 6% 8% 49%	4258
September	1st to 10th	Day	13% 4 1 5% 3 3 3 3 5% 6% 54%	2280
	11th to 20th	Day	9% 5% 1 5% 4 3 3 4 6% 9% 50%	2182
	21st to end	Day	10% 5% 2 5% 3 3 3 3 5% 8% 52%	2038
October	1st to 10th	Day	14% 7% 2 5% 3 3 3 2 5% 7% 48%	1900
	11th to 20th	Day	12% 8% 3 5% 2 3 3 3 4 6% 51%	1900
	21st to end	Day	13% 9% 3 5% 4 4 4 4 5% 5% 44%	2090
November	1st to 10th	Day	11% 6% 2 5% 4 3 4 3 4 7% 52%	1851
	11th to 20th	Day	12% 9% 3 7% 4 3 4 4 4 6% 45%	1520
	21st to end	Day	16% 10% 3 6% 4 3 3 3 5% 6% 39%	1520
December	1st to 10th	Day	10% 10% 3 8% 5% 4 4 3 6% 8% 38%	1520
	11th to 20th	Day	9% 11% 4 11% 5% 4 4 3 5% 7% 35%	1918
	21st to end	Day	20% 14% 6% 15% 5% 4 4 3 4 5% 20%	2783
January	1st to 10th	Night	9% 9% 4 20% 7% 5% 4 3 4 6% 29%	4296
	11th to 20th	Night	11% 11% 5% 11% 5% 5% 6% 4 8% 6% 29%	4120
	21st to end	Night	13% 15% 6% 13% 4 5% 4 3 4 5% 27%	4532
February	1st to 10th	Night	12% 11% 4 9% 6% 4 4 4 5% 5% 36%	2470
	11th to 20th	Night	11% 10% 4 6% 5% 4 3 3 6% 6% 42%	2403
	21st to end	Night	11% 8% 3 8% 5% 4 4 3 5% 5% 44%	1920
March	1st to 10th	Night	13% 7% 3 8% 4 3 4 3 4 5% 46%	3419
	11th to 20th	Night	12% 7% 2 5% 3 3 3 3 4 5% 53%	3480
	21st to end	Night	17% 11% 5% 13% 6% 4 4 4 5% 5% 27%	3817
April	1st to 10th	Night	11% 7% 2 6% 4 4 3 3 6% 6% 47%	1934
	11th to 20th	Night	13% 7% 3 7% 4 4 4 3 5% 5% 44%	1875
	21st to end	Night	17% 7% 3 6% 4 5% 4 2 4 6% 42%	1762
May	1st to 10th	Night	16% 7% 2 6% 5% 4 4 4 6% 7% 40%	2823
	11th to 20th	Night	14% 7% 2 7% 4 4 3 3 5% 6% 45%	2704
	21st to end	Night	11% 5% 2 6% 5% 5% 4 3 5% 7% 47%	2743
June	1st to 10th	Night	6% 4 2 5% 3 3 4 4 7% 8% 54%	1520
	11th to 20th	Night	7% 5% 1 4 4 3 4 3 8% 11% 50%	1520
	21st to end	Night	6% 4 1 6% 3 4 5% 3 7% 9% 51%	1520
July	1st to 10th	Night	9% 4 2 5% 4 4 5% 4 6% 8% 48%	2530
	11th to 20th	Night	3 2 2 3 3 3 4 3 5% 8% 64%	2742
	21st to end	Night	5% 3 1 5% 4 4 5% 4 7% 9% 51%	3098
August	1st to 10th	Night	4 3 1 4 3 4 4 4 7% 8% 58%	2836
	11th to 20th	Night	11% 6% 2 4 3 4 3 3 5% 7% 52%	2798
	21st to end	Night	6% 4 2 5% 3 3 4 3 5% 9% 58%	3400
September	1st to 10th	Night	10% 4 2 4 2 3 3 3 5% 6% 58%	1900
	11th to 20th	Night	9% 5% 1 5% 3 3 4 3 6% 6% 54%	1994
	21st to end	Night	9% 4 1 4 3 3 3 3 5% 7% 58%	2123
October	1st to 10th	Night	12% 7% 2 6% 2 3 3 3 4 6% 53%	2280
	11th to 20th	Night	11% 6% 2 5% 4 4 3 2 3 5% 54%	2280
	21st to end	Night	14% 8% 3 6% 4 3 3 2 4 5% 48%	2508
November	1st to 10th	Night	9% 4 1 5% 3 3 4 3 6% 7% 56%	2342
	11th to 20th	Night	11% 6% 2 6% 4 3 3 3 5% 7% 49%	2660
	21st to end	Night	14% 10% 3 6% 3 3 3 3 4 5% 44%	2660
December	1st to 10th	Night	10% 10% 3 8% 5% 4 5% 3 5% 7% 40%	2660
	11th to 20th	Night	11% 9% 3 10% 5% 4 4 3 4 5% 42%	3279
	21st to end	Night	17% 17% 7% 13% 4 4 3 3 4 4 24%	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	57% 6% 15% 14% 8% 1	2658
	11th to 20th	Day	55% 5% 11% 20% 8%	2850
	21st to end	Day	64% 5% 11% 14% 5% 1	3135
February	1st to 10th	Day	55% 4 11% 19% 10% 2	1710
	11th to 20th	Day	47% 6% 11% 22% 13% 2	1673
	21st to end	Day	44% 5% 13% 22% 14% 2	1549
March	1st to 10th	Day	46% 5% 9% 21% 19% 1	3436
	11th to 20th	Day	39% 5% 12% 24% 18% 2	3480
	21st to end	Day	58% 10% 14% 13% 5% 1	3814
April	1st to 10th	Day	46% 6% 11% 25% 11% 1	2245
	11th to 20th	Day	46% 6% 11% 23% 13% 1	2254
	21st to end	Day	49% 5% 11% 22% 12% 1	2413
May	1st to 10th	Day	45% 8% 13% 20% 14% 1	4120
	11th to 20th	Day	44% 7% 10% 27% 12%	4203
	21st to end	Day	38% 7% 11% 25% 17% 2	4837
June	1st to 10th	Day	35% 9% 15% 26% 13% 3	2660
	11th to 20th	Day	31% 9% 13% 26% 19% 2	2660
	21st to end	Day	35% 9% 15% 24% 15% 2	2660
July	1st to 10th	Day	40% 7% 15% 25% 10% 2	4371
	11th to 20th	Day	27% 6% 14% 33% 18% 2	4151
	21st to end	Day	27% 10% 18% 30% 15% 1	4325
August	1st to 10th	Day	30% 6% 15% 31% 17% 1	4090
	11th to 20th	Day	38% 6% 13% 26% 16% 1	4080
	21st to end	Day	32% 5% 16% 28% 14% 4	4257
September	1st to 10th	Day	31% 5% 12% 28% 20% 5%	2280
	11th to 20th	Day	30% 6% 12% 30% 20% 1	2182
	21st to end	Day	31% 5% 10% 32% 21% 1	2038
October	1st to 10th	Day	23% 3 6% 20% 47% 2	3160
	11th to 20th	Day	23% 2 7% 30% 30% 8%	3140
	21st to end	Day	36% 4 10% 27% 20% 3	3428
November	1st to 10th	Day	33% 5% 13% 26% 20% 3	1851
	11th to 20th	Day	40% 4 13% 25% 17% 1	1520
	21st to end	Day	46% 4 13% 23% 14%	1520
December	1st to 10th	Day	44% 5% 14% 25% 11% 1	1520
	11th to 20th	Day	47% 5% 15% 26% 6% 1	1915
	21st to end	Day	66% 4 10% 14% 6% 1	2783
January	1st to 10th	Night	56% 5% 10% 18% 10% 1	4296
	11th to 20th	Night	53% 4 13% 18% 12% 1	4120
	21st to end	Night	59% 4 12% 15% 7% 2	4532
February	1st to 10th	Night	50% 5% 11% 20% 12% 3	2470
	11th to 20th	Night	42% 5% 10% 26% 15% 2	2404
	21st to end	Night	42% 5% 10% 21% 18% 5%	1920
March	1st to 10th	Night	41% 4 9% 24% 20% 2	3419
	11th to 20th	Night	33% 5% 9% 31% 16% 5%	3480
	21st to end	Night	57% 7% 17% 13% 5% 1	3817
April	1st to 10th	Night	37% 5% 12% 26% 17% 3	1934
	11th to 20th	Night	42% 5% 11% 25% 14% 3	1875
	21st to end	Night	44% 6% 11% 23% 14% 2	1762
May	1st to 10th	Night	41% 7% 13% 19% 18% 1	2850
	11th to 20th	Night	39% 8% 10% 26% 17% 1	2705
	21st to end	Night	36% 8% 11% 23% 20% 2	2751
June	1st to 10th	Night	25% 8% 18% 30% 16% 3	1520
	11th to 20th	Night	26% 7% 15% 26% 21% 4	1520
	21st to end	Night	28% 7% 16% 27% 19% 4	1520
July	1st to 10th	Night	33% 6% 13% 28% 16% 4	2490
	11th to 20th	Night	20% 5% 18% 35% 22% 2	2692
	21st to end	Night	27% 8% 19% 26% 18% 2	2999
August	1st to 10th	Night	22% 6% 15% 34% 21% 1	2826
	11th to 20th	Night	33% 5% 13% 28% 20% 2	2825
	21st to end	Night	25% 6% 17% 30% 18% 6%	3400
September	1st to 10th	Night	27% 6% 10% 26% 24% 7%	1900
	11th to 20th	Night	29% 5% 10% 32% 21% 2	1994
	21st to end	Night	27% 5% 9% 31% 25% 3	2123
October	1st to 10th	Night	22% 3 5% 19% 47% 3	3800
	11th to 20th	Night	26% 3 8% 25% 31% 8%	3779
	21st to end	Night	40% 3 8% 25% 22% 2	4120
November	1st to 10th	Night	27% 5% 16% 26% 21% 4	2342
	11th to 20th	Night	35% 4 11% 30% 17% 3	2660
	21st to end	Night	41% 5% 9% 27% 16% 2	2660
December	1st to 10th	Night	44% 6% 12% 25% 12% 1	2660
	11th to 20th	Night	44% 4 12% 29% 10% 1	3281
	21st to end	Night	64% 5% 8% 15% 8% 1	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	24% 13% 33% 22% 7% 1	270
	11th to 20th	Day	20% 19% 37% 21% 4	270
	21st to end	Day	19% 13% 41% 24% 3	297
February	1st to 10th	Day	19% 18% 38% 21% 3 1	270
	11th to 20th	Day	18% 16% 40% 20% 6% 1	270
	21st to end	Day	19% 15% 44% 17% 4 1	225
March	1st to 10th	Day	20% 17% 43% 17% 3	270
	11th to 20th	Day	25% 14% 33% 22% 6%	270
	21st to end	Day	37% 20% 27% 14% 2	297
April	1st to 10th	Day	26% 16% 34% 18% 5%	425
	11th to 20th	Day	20% 16% 35% 21% 8% 1	452
	21st to end	Day	23% 15% 35% 18% 8% 1	593
May	1st to 10th	Day	20% 14% 32% 26% 6% 2	653
	11th to 20th	Day	21% 12% 29% 25% 11% 2	675
	21st to end	Day	17% 8% 28% 30% 15% 3	734
June	1st to 10th	Day	8% 6% 23% 32% 25% 7%	680
	11th to 20th	Day	9% 4 30% 35% 18% 4	680
	21st to end	Day	8% 9% 32% 34% 14% 3	680
July	1st to 10th	Day	9% 5% 18% 34% 24% 11%	671
	11th to 20th	Day	6% 3 25% 38% 22% 7%	668
	21st to end	Day	8% 2 21% 39% 24% 5%	739
August	1st to 10th	Day	8% 3 19% 39% 25% 5%	676
	11th to 20th	Day	12% 4 18% 37% 24% 5%	665
	21st to end	Day	11% 2 18% 35% 27% 7%	591
September	1st to 10th	Day	13% 3 21% 29% 27% 7%	490
	11th to 20th	Day	10% 3 19% 38% 23% 7%	392
	21st to end	Day	13% 7% 29% 30% 15% 5%	300
October	1st to 10th	Day	19% 8% 30% 24% 14% 5%	300
	11th to 20th	Day	14% 22% 36% 19% 7% 2	300
	21st to end	Day	18% 18% 32% 21% 9% 2	330
November	1st to 10th	Day	16% 10% 46% 18% 9% 2	285
	11th to 20th	Day	17% 19% 37% 19% 6% 1	270
	21st to end	Day	23% 12% 37% 21% 6% 1	270
December	1st to 10th	Day	10% 17% 39% 25% 8% 3	270
	11th to 20th	Day	15% 14% 35% 28% 6% 1	270
	21st to end	Day	26% 19% 36% 18% 2	297
January	1st to 10th	Night	12% 13% 41% 25% 8%	950
	11th to 20th	Night	16% 15% 39% 23% 6%	950
	21st to end	Night	16% 13% 38% 27% 5%	1045
February	1st to 10th	Night	19% 12% 39% 25% 5%	950
	11th to 20th	Night	17% 13% 38% 27% 5%	929
	21st to end	Night	17% 14% 44% 20% 4 1	664
March	1st to 10th	Night	16% 13% 40% 25% 7%	570
	11th to 20th	Night	20% 12% 36% 26% 6%	570
	21st to end	Night	25% 13% 37% 20% 5%	627
April	1st to 10th	Night	15% 16% 41% 24% 4	570
	11th to 20th	Night	17% 15% 37% 25% 6%	563
	21st to end	Night	20% 10% 37% 25% 8%	570
May	1st to 10th	Night	15% 11% 35% 32% 6% 1	570
	11th to 20th	Night	15% 10% 30% 33% 11% 1	561
	21st to end	Night	15% 6% 30% 34% 14%	617
June	1st to 10th	Night	8% 4 27% 38% 22% 1	570
	11th to 20th	Night	8% 5% 26% 44% 16% 1	570
	21st to end	Night	8% 3 32% 42% 15%	570
July	1st to 10th	Night	6% 2 17% 40% 32% 3	555
	11th to 20th	Night	5% 2 18% 50% 24% 2	552
	21st to end	Night	6% 1 17% 50% 24% 2	624
August	1st to 10th	Night	5% 2 22% 45% 24% 2	567
	11th to 20th	Night	9% 2 17% 42% 27% 3	564
	21st to end	Night	7% 2 17% 41% 29% 3	627
September	1st to 10th	Night	12% 2 21% 36% 26% 3	570
	11th to 20th	Night	12% 2 23% 37% 24% 2	570
	21st to end	Night	9% 5% 28% 37% 20% 1	603
October	1st to 10th	Night	16% 8% 27% 33% 15% 2	760
	11th to 20th	Night	15% 12% 38% 28% 8%	760
	21st to end	Night	20% 11% 36% 25% 7% 1	836
November	1st to 10th	Night	11% 11% 38% 31% 8% 1	778
	11th to 20th	Night	13% 16% 40% 24% 6% 1	950
	21st to end	Night	19% 13% 37% 25% 7%	950
December	1st to 10th	Night	16% 13% 38% 27% 7% 1	950
	11th to 20th	Night	20% 9% 37% 29% 6%	950
	21st to end	Night	22% 14% 37% 23% 3	1045

Page generated at 2024-11-03 12:19:05. Version ac07

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