Grasslands National Park (West)
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Grasslands National Park (West) clear sky chart from 2005-11-06 to 2026-02-01.

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	7% 7% 3 8% 5% 5% 5% 4 6% 8% 43%	136700
	Night	6% 7% 3 8% 5% 5% 5% 4 6% 8% 42%	132661
Transparency	Day	39% 6% 15% 26% 12% 2	131321
	Night	39% 6% 15% 25% 13% 2	129060
Seeing	Day	12% 9% 29% 30% 16% 4	17372
	Night	10% 8% 32% 36% 13% 1	26919

By Month

Percentage Cloud Cover SW (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	4 13% 6% 15% 9% 7% 6% 4 5% 6% 24%	3249
	11th to 20th	Day	2 7% 5% 12% 8% 5% 8% 5% 6% 7% 34%	3270
	21st to end	Day	4 9% 4 10% 6% 5% 5% 5% 5% 7% 42%	4163
February	1st to 10th	Day	8% 13% 5% 12% 7% 6% 6% 4 7% 7% 26%	1800
	11th to 20th	Day	6% 10% 5% 14% 8% 6% 5% 5% 8% 8% 25%	1755
	21st to end	Day	4 12% 4 11% 9% 6% 7% 6% 6% 7% 27%	1513
March	1st to 10th	Day	4 9% 4 12% 7% 5% 5% 4 6% 8% 36%	4628
	11th to 20th	Day	5% 7% 3 8% 6% 6% 6% 5% 7% 10% 36%	5000
	21st to end	Day	7% 16% 7% 15% 7% 6% 5% 4 5% 7% 21%	5651
April	1st to 10th	Day	8% 9% 3 10% 6% 6% 5% 5% 6% 8% 35%	2400
	11th to 20th	Day	12% 14% 4 8% 6% 5% 5% 5% 6% 6% 31%	2453
	21st to end	Day	12% 10% 3 7% 6% 4 5% 4 6% 8% 36%	2670
May	1st to 10th	Day	13% 10% 3 6% 4 3 3 3 5% 7% 42%	6340
	11th to 20th	Day	15% 9% 3 8% 6% 6% 5% 4 6% 8% 30%	6298
	21st to end	Day	12% 6% 2 7% 5% 5% 5% 5% 6% 8% 39%	7004
June	1st to 10th	Day	13% 6% 3 6% 5% 5% 5% 5% 6% 9% 38%	3000
	11th to 20th	Day	14% 6% 2 6% 5% 5% 6% 4 7% 8% 37%	3000
	21st to end	Day	6% 4 2 5% 4 4 5% 4 8% 8% 50%	3000
July	1st to 10th	Day	3 3 1 5% 4 5% 6% 4 7% 9% 53%	6779
	11th to 20th	Day	4 3 1 4 4 4 5% 4 7% 9% 55%	6780
	21st to end	Day	4 4 2 5% 3 3 3 3 5% 7% 61%	6973
August	1st to 10th	Day	8% 6% 2 6% 4 4 5% 4 6% 8% 48%	6200
	11th to 20th	Day	3 3 1 4 3 3 4 4 6% 9% 60%	5798
	21st to end	Day	7% 3 1 4 3 2 3 3 4 6% 63%	6297
September	1st to 10th	Day	9% 5% 2 5% 4 4 4 3 6% 6% 52%	2400
	11th to 20th	Day	10% 6% 2 5% 4 4 3 3 6% 7% 49%	2400
	21st to end	Day	11% 6% 2 5% 3 3 3 3 5% 6% 53%	2110
October	1st to 10th	Day	7% 6% 2 5% 4 3 4 3 6% 7% 54%	3270
	11th to 20th	Day	5% 6% 2 6% 3 3 5% 3 5% 11% 52%	3250
	21st to end	Day	4 7% 2 5% 4 4 5% 4 7% 8% 50%	3246
November	1st to 10th	Day	9% 13% 4 7% 5% 4 4 4 5% 7% 37%	1648
	11th to 20th	Day	5% 8% 4 9% 6% 5% 5% 5% 6% 7% 39%	1680
	21st to end	Day	6% 11% 4 9% 6% 5% 5% 5% 6% 8% 35%	1680
December	1st to 10th	Day	4 8% 5% 13% 10% 9% 7% 5% 5% 7% 27%	2700
	11th to 20th	Day	7% 11% 6% 15% 6% 6% 4 4 5% 6% 28%	2720
	21st to end	Day	4 7% 3 11% 7% 5% 5% 5% 6% 8% 38%	3575
January	1st to 10th	Night	3 9% 4 12% 8% 7% 7% 6% 8% 8% 27%	6916
	11th to 20th	Night	3 7% 5% 14% 8% 6% 6% 5% 8% 8% 29%	6908
	21st to end	Night	2 7% 4 12% 6% 5% 6% 4 6% 8% 39%	7100
February	1st to 10th	Night	5% 11% 4 10% 7% 6% 6% 4 6% 7% 33%	2600
	11th to 20th	Night	4 10% 4 11% 7% 7% 6% 4 6% 9% 33%	2532
	21st to end	Night	4 10% 4 11% 7% 6% 5% 5% 6% 8% 35%	2116
March	1st to 10th	Night	5% 8% 3 9% 7% 5% 5% 4 7% 10% 37%	5248
	11th to 20th	Night	6% 7% 3 8% 5% 4 4 4 6% 10% 42%	5000
	21st to end	Night	9% 14% 6% 15% 8% 6% 5% 4 5% 6% 20%	5315
April	1st to 10th	Night	7% 8% 3 7% 6% 6% 5% 5% 7% 7% 39%	2000
	11th to 20th	Night	11% 11% 4 8% 5% 4 4 5% 7% 7% 34%	1892
	21st to end	Night	10% 8% 3 8% 6% 5% 6% 4 6% 7% 37%	1730
May	1st to 10th	Night	12% 7% 3 5% 4 3 4 3 5% 7% 47%	3640
	11th to 20th	Night	15% 8% 2 7% 5% 5% 5% 5% 7% 9% 32%	3617
	21st to end	Night	10% 6% 2 6% 4 4 4 4 6% 8% 46%	3885
June	1st to 10th	Night	12% 6% 2 5% 5% 5% 5% 3 7% 9% 43%	1400
	11th to 20th	Night	14% 4 2 5% 3 4 5% 5% 7% 8% 44%	1400
	21st to end	Night	5% 4 1 4 5% 3 4 4 5% 8% 56%	1400
July	1st to 10th	Night	4 3 1 4 3 3 4 4 6% 9% 58%	3180
	11th to 20th	Night	6% 4 1 5% 3 3 4 4 6% 8% 55%	3180
	21st to end	Night	6% 3 1 4 3 4 4 4 6% 8% 57%	3894
August	1st to 10th	Night	10% 5% 2 5% 3 4 4 4 7% 8% 49%	3597
	11th to 20th	Night	3 2 1 4 3 4 5% 4 7% 9% 57%	4051
	21st to end	Night	9% 4 2 5% 3 3 3 3 4 6% 59%	4679
September	1st to 10th	Night	9% 3 2 4 3 3 3 3 5% 7% 58%	2000
	11th to 20th	Night	9% 6% 2 5% 4 3 4 3 5% 8% 52%	2000
	21st to end	Night	8% 5% 1 5% 3 3 3 3 5% 9% 55%	2288
October	1st to 10th	Night	7% 5% 2 5% 3 3 3 3 5% 8% 55%	3920
	11th to 20th	Night	5% 5% 2 5% 3 3 4 3 5% 9% 56%	3898
	21st to end	Night	5% 6% 2 6% 4 4 5% 4 7% 8% 48%	4506
November	1st to 10th	Night	10% 11% 4 8% 6% 4 5% 3 5% 6% 38%	2870
	11th to 20th	Night	4 9% 4 9% 7% 5% 5% 4 6% 7% 40%	2940
	21st to end	Night	5% 10% 4 11% 5% 5% 4 5% 6% 8% 37%	2940
December	1st to 10th	Night	6% 12% 5% 14% 9% 6% 5% 4 6% 8% 26%	4710
	11th to 20th	Night	5% 12% 6% 14% 7% 5% 5% 5% 6% 8% 27%	5686
	21st to end	Night	4 8% 3 8% 6% 5% 5% 4 5% 7% 45%	7623

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	59% 7% 14% 14% 4	3249
	11th to 20th	Day	47% 6% 15% 17% 14% 1	3270
	21st to end	Day	41% 6% 24% 24% 4	4163
February	1st to 10th	Day	56% 6% 12% 16% 9%	1800
	11th to 20th	Day	53% 6% 16% 14% 10% 1	1764
	21st to end	Day	53% 7% 16% 14% 8%	1513
March	1st to 10th	Day	45% 6% 18% 24% 7%	4628
	11th to 20th	Day	40% 6% 19% 27% 8%	5000
	21st to end	Day	61% 8% 15% 12% 4	5651
April	1st to 10th	Day	46% 8% 15% 22% 10% 1	2400
	11th to 20th	Day	52% 6% 13% 21% 7% 1	2456
	21st to end	Day	45% 6% 14% 26% 9% 1	2670
May	1st to 10th	Day	41% 5% 10% 27% 15% 2	6340
	11th to 20th	Day	50% 7% 12% 23% 9%	6302
	21st to end	Day	38% 8% 15% 26% 12% 1	7005
June	1st to 10th	Day	41% 9% 16% 23% 11% 1	3000
	11th to 20th	Day	42% 7% 14% 23% 12% 1	3000
	21st to end	Day	29% 7% 15% 34% 13% 1	3000
July	1st to 10th	Day	26% 7% 19% 23% 19% 6%	6706
	11th to 20th	Day	25% 7% 16% 30% 18% 4	6699
	21st to end	Day	24% 5% 11% 29% 23% 9%	6773
August	1st to 10th	Day	27% 5% 11% 33% 21% 3	4517
	11th to 20th	Day	23% 5% 17% 35% 17% 2	4197
	21st to end	Day	23% 4 12% 38% 19% 3	4540
September	1st to 10th	Day	31% 5% 11% 30% 17% 6%	2400
	11th to 20th	Day	33% 6% 16% 29% 13% 3	2400
	21st to end	Day	32% 4 12% 31% 18% 3	2110
October	1st to 10th	Day	30% 3 12% 35% 16% 3	3270
	11th to 20th	Day	29% 4 13% 39% 12% 3	3250
	21st to end	Day	30% 5% 16% 37% 12%	3246
November	1st to 10th	Day	46% 5% 16% 23% 8% 2	1648
	11th to 20th	Day	43% 7% 18% 24% 7% 1	1680
	21st to end	Day	46% 7% 20% 19% 7% 1	1680
December	1st to 10th	Day	55% 8% 17% 17% 3	2700
	11th to 20th	Day	56% 6% 19% 16% 2	2719
	21st to end	Day	42% 6% 13% 21% 13% 5%	3575
January	1st to 10th	Night	49% 9% 18% 17% 7%	6916
	11th to 20th	Night	49% 5% 15% 13% 16% 1	6908
	21st to end	Night	41% 6% 22% 26% 5%	7100
February	1st to 10th	Night	48% 6% 16% 19% 11% 1	2600
	11th to 20th	Night	46% 8% 16% 17% 11% 1	2533
	21st to end	Night	45% 7% 14% 23% 11% 1	2116
March	1st to 10th	Night	40% 6% 19% 22% 13%	5248
	11th to 20th	Night	37% 6% 21% 28% 9%	5000
	21st to end	Night	62% 7% 13% 11% 6%	5315
April	1st to 10th	Night	42% 7% 15% 25% 11% 1	2000
	11th to 20th	Night	46% 7% 12% 22% 10% 2	1892
	21st to end	Night	44% 6% 13% 24% 12%	1730
May	1st to 10th	Night	35% 6% 10% 30% 18% 1	3640
	11th to 20th	Night	46% 7% 15% 22% 9%	3618
	21st to end	Night	33% 8% 15% 30% 11% 2	3885
June	1st to 10th	Night	38% 7% 16% 24% 14% 2	1400
	11th to 20th	Night	36% 6% 15% 27% 15% 2	1400
	21st to end	Night	26% 6% 17% 32% 17% 2	1400
July	1st to 10th	Night	21% 6% 20% 27% 22% 4	3145
	11th to 20th	Night	27% 5% 17% 29% 16% 6%	3138
	21st to end	Night	24% 4 14% 28% 24% 6%	3782
August	1st to 10th	Night	25% 3 11% 32% 24% 4	2617
	11th to 20th	Night	23% 5% 16% 34% 19% 2	2928
	21st to end	Night	28% 5% 11% 34% 19% 4	3367
September	1st to 10th	Night	27% 4 10% 31% 20% 8%	2000
	11th to 20th	Night	32% 5% 13% 28% 18% 5%	2000
	21st to end	Night	27% 4 12% 32% 22% 3	2288
October	1st to 10th	Night	29% 5% 10% 34% 21% 1	3920
	11th to 20th	Night	26% 4 12% 40% 17% 1	3898
	21st to end	Night	32% 6% 12% 37% 13% 1	4506
November	1st to 10th	Night	46% 6% 15% 21% 10% 2	2870
	11th to 20th	Night	41% 6% 19% 23% 10% 1	2940
	21st to end	Night	45% 6% 21% 20% 8%	2940
December	1st to 10th	Night	55% 7% 19% 14% 5%	4710
	11th to 20th	Night	54% 7% 20% 16% 3	5687
	21st to end	Night	38% 5% 11% 26% 15% 4	7623

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	9% 9% 34% 30% 13% 6%	220
	11th to 20th	Day	8% 13% 34% 25% 17% 3	225
	21st to end	Day	10% 11% 32% 31% 14% 1	363
February	1st to 10th	Day	16% 9% 39% 27% 8% 1	300
	11th to 20th	Day	8% 9% 35% 33% 13% 2	300
	21st to end	Day	11% 6% 35% 35% 9% 5%	249
March	1st to 10th	Day	10% 10% 34% 30% 14% 2	350
	11th to 20th	Day	8% 11% 38% 27% 13% 3	500
	21st to end	Day	12% 12% 31% 26% 16% 3	550
April	1st to 10th	Day	11% 14% 37% 29% 8% 1	500
	11th to 20th	Day	16% 17% 32% 25% 9% 2	492
	21st to end	Day	18% 12% 28% 29% 11% 2	570
May	1st to 10th	Day	17% 9% 23% 29% 18% 4	703
	11th to 20th	Day	15% 8% 26% 28% 18% 5%	725
	21st to end	Day	16% 9% 24% 26% 19% 6%	789
June	1st to 10th	Day	15% 12% 24% 28% 18% 3	730
	11th to 20th	Day	16% 12% 34% 23% 12% 3	730
	21st to end	Day	10% 7% 26% 31% 20% 5%	730
July	1st to 10th	Day	5% 3 26% 39% 22% 5%	721
	11th to 20th	Day	5% 6% 27% 37% 20% 5%	718
	21st to end	Day	5% 4 25% 36% 25% 5%	794
August	1st to 10th	Day	8% 5% 21% 37% 23% 7%	720
	11th to 20th	Day	9% 5% 22% 34% 21% 9%	517
	21st to end	Day	8% 7% 23% 35% 20% 6%	583
September	1st to 10th	Day	12% 8% 28% 34% 14% 4	530
	11th to 20th	Day	13% 6% 25% 31% 21% 3	530
	21st to end	Day	13% 10% 27% 30% 16% 4	425
October	1st to 10th	Day	21% 10% 22% 22% 22% 4	330
	11th to 20th	Day	11% 8% 37% 27% 15% 3	330
	21st to end	Day	11% 14% 38% 26% 9% 2	363
November	1st to 10th	Day	18% 13% 33% 26% 10%	330
	11th to 20th	Day	11% 15% 35% 28% 10% 1	330
	21st to end	Day	11% 9% 35% 29% 12% 3	330
December	1st to 10th	Day	10% 10% 38% 32% 8% 2	330
	11th to 20th	Day	11% 13% 35% 32% 8% 2	223
	21st to end	Day	9% 7% 33% 31% 17% 3	242
January	1st to 10th	Night	8% 9% 36% 35% 11% 1	1050
	11th to 20th	Night	10% 12% 36% 33% 8% 2	1050
	21st to end	Night	7% 12% 39% 30% 10% 1	1140
February	1st to 10th	Night	8% 7% 34% 34% 15% 1	800
	11th to 20th	Night	9% 6% 36% 39% 10% 1	784
	21st to end	Night	7% 7% 29% 37% 17% 3	660
March	1st to 10th	Night	10% 8% 34% 35% 12% 1	800
	11th to 20th	Night	10% 7% 35% 35% 11% 2	800
	21st to end	Night	13% 7% 32% 34% 12% 2	809
April	1st to 10th	Night	10% 6% 36% 38% 9% 1	600
	11th to 20th	Night	19% 7% 34% 32% 8%	593
	21st to end	Night	13% 9% 30% 38% 10%	600
May	1st to 10th	Night	14% 6% 25% 40% 13% 1	600
	11th to 20th	Night	13% 5% 27% 38% 16% 1	591
	21st to end	Night	17% 7% 25% 33% 17% 2	615
June	1st to 10th	Night	15% 8% 23% 35% 17% 1	400
	11th to 20th	Night	16% 6% 30% 37% 11%	400
	21st to end	Night	8% 6% 24% 44% 18% 1	400
July	1st to 10th	Night	6% 4 22% 49% 19% 1	390
	11th to 20th	Night	6% 3 28% 49% 14% 1	388
	21st to end	Night	4 3 25% 49% 18% 1	620
August	1st to 10th	Night	7% 3 23% 46% 18% 2	597
	11th to 20th	Night	7% 3 22% 47% 21% 1	594
	21st to end	Night	9% 5% 24% 42% 19% 1	660
September	1st to 10th	Night	10% 3 25% 41% 20% 1	600
	11th to 20th	Night	11% 5% 27% 39% 18% 1	600
	21st to end	Night	11% 5% 30% 37% 16% 1	783
October	1st to 10th	Night	12% 7% 28% 36% 16% 1	800
	11th to 20th	Night	11% 9% 31% 35% 13% 1	800
	21st to end	Night	12% 10% 36% 35% 7% 1	1015
November	1st to 10th	Night	16% 11% 35% 29% 9%	1025
	11th to 20th	Night	8% 12% 39% 30% 10% 1	1050
	21st to end	Night	10% 10% 39% 31% 9%	1050
December	1st to 10th	Night	9% 10% 35% 32% 13% 1	1050
	11th to 20th	Night	10% 10% 37% 33% 9% 1	1050
	21st to end	Night	12% 6% 34% 35% 11% 1	1155

Page generated at 2026-01-29 00:21:44. Version ac07

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