Gimli
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Gimli clear sky chart from 2005-11-06 to 2025-10-04.

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	10% 8% 3 8% 5% 5% 5% 4 6% 8% 36%	130816
	Night	9% 10% 4 10% 6% 5% 5% 4 6% 7% 34%	127335
Transparency	Day	44% 7% 16% 24% 8% 1	130512
	Night	48% 7% 13% 21% 9% 1	127220
Seeing	Day	13% 5% 20% 34% 23% 6%	17596
	Night	15% 4 24% 36% 17% 3	27432

By Month

Percentage Cloud Cover NW (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	6% 16% 7% 12% 7% 7% 8% 5% 7% 6% 19%	3179
	11th to 20th	Day	5% 11% 5% 16% 9% 8% 8% 8% 10% 8% 13%	3159
	21st to end	Day	5% 14% 7% 14% 8% 7% 7% 5% 6% 7% 19%	3894
February	1st to 10th	Day	9% 11% 6% 12% 8% 7% 8% 5% 8% 7% 19%	1694
	11th to 20th	Day	7% 10% 4 10% 6% 7% 7% 6% 8% 9% 27%	1754
	21st to end	Day	5% 13% 4 10% 8% 6% 8% 5% 7% 8% 26%	1543
March	1st to 10th	Day	9% 10% 5% 10% 6% 6% 6% 5% 8% 9% 27%	4619
	11th to 20th	Day	8% 11% 5% 13% 9% 7% 6% 4 6% 7% 24%	4978
	21st to end	Day	8% 11% 4 10% 6% 6% 7% 4 6% 6% 32%	5464
April	1st to 10th	Day	10% 10% 3 9% 5% 5% 4 4 6% 7% 37%	2451
	11th to 20th	Day	11% 9% 4 7% 6% 4 6% 5% 5% 7% 36%	2572
	21st to end	Day	13% 8% 3 7% 6% 5% 5% 4 6% 7% 37%	2600
May	1st to 10th	Day	11% 7% 3 6% 4 4 4 3 5% 7% 46%	6175
	11th to 20th	Day	17% 8% 3 7% 5% 5% 5% 4 6% 7% 32%	6701
	21st to end	Day	14% 5% 2 5% 4 4 4 3 5% 7% 48%	7428
June	1st to 10th	Day	16% 7% 2 7% 5% 5% 4 4 5% 8% 37%	3000
	11th to 20th	Day	13% 7% 3 7% 5% 5% 5% 4 6% 8% 36%	3000
	21st to end	Day	12% 5% 3 7% 6% 5% 5% 4 7% 9% 37%	3000
July	1st to 10th	Day	8% 5% 2 6% 5% 5% 5% 5% 8% 9% 43%	6800
	11th to 20th	Day	9% 5% 2 6% 4 4 5% 4 6% 10% 45%	6800
	21st to end	Day	6% 4 2 6% 4 4 5% 4 7% 10% 47%	7400
August	1st to 10th	Day	7% 4 2 6% 5% 5% 5% 4 8% 9% 45%	4451
	11th to 20th	Day	10% 5% 2 6% 5% 5% 5% 4 5% 8% 46%	4171
	21st to end	Day	12% 7% 2 6% 4 4 4 4 6% 8% 44%	4675
September	1st to 10th	Day	11% 5% 2 6% 4 4 5% 4 6% 8% 46%	2503
	11th to 20th	Day	14% 8% 3 8% 5% 6% 4 3 6% 8% 36%	2200
	21st to end	Day	14% 7% 2 6% 4 4 4 3 6% 9% 41%	2200
October	1st to 10th	Day	13% 9% 3 6% 4 5% 4 4 5% 7% 40%	3231
	11th to 20th	Day	9% 10% 3 8% 5% 5% 5% 4 7% 8% 36%	3061
	21st to end	Day	13% 12% 4 9% 5% 5% 5% 3 6% 9% 30%	3075
November	1st to 10th	Day	16% 15% 4 12% 6% 4 4 3 5% 5% 27%	1567
	11th to 20th	Day	11% 16% 5% 12% 6% 6% 5% 5% 5% 6% 25%	1600
	21st to end	Day	12% 16% 5% 11% 7% 5% 5% 4 5% 7% 24%	1444
December	1st to 10th	Day	11% 14% 5% 14% 9% 7% 7% 4 7% 8% 14%	2290
	11th to 20th	Day	10% 13% 5% 13% 8% 4 5% 5% 6% 8% 24%	2639
	21st to end	Day	6% 14% 6% 17% 8% 7% 5% 4 5% 6% 22%	3498
January	1st to 10th	Night	5% 13% 6% 15% 8% 8% 7% 5% 6% 7% 21%	6787
	11th to 20th	Night	5% 13% 7% 14% 9% 9% 9% 8% 7% 5% 14%	6759
	21st to end	Night	7% 16% 7% 14% 7% 6% 6% 4 7% 6% 20%	7069
February	1st to 10th	Night	8% 12% 5% 11% 7% 7% 7% 5% 6% 6% 26%	2705
	11th to 20th	Night	6% 9% 4 8% 5% 5% 7% 6% 7% 8% 34%	2533
	21st to end	Night	5% 13% 3 10% 5% 6% 6% 5% 5% 7% 33%	2105
March	1st to 10th	Night	8% 12% 4 9% 6% 6% 5% 5% 7% 8% 31%	5248
	11th to 20th	Night	6% 9% 3 8% 6% 5% 6% 5% 6% 8% 39%	4980
	21st to end	Night	10% 12% 4 8% 5% 4 4 4 5% 6% 39%	5467
April	1st to 10th	Night	12% 6% 2 6% 4 4 5% 4 6% 9% 42%	1943
	11th to 20th	Night	13% 10% 4 8% 6% 3 5% 4 5% 6% 37%	1779
	21st to end	Night	10% 8% 3 7% 6% 5% 6% 4 6% 6% 38%	1800
May	1st to 10th	Night	13% 7% 3 7% 4 5% 4 4 5% 6% 42%	3804
	11th to 20th	Night	17% 6% 3 7% 5% 5% 5% 4 6% 8% 35%	3214
	21st to end	Night	12% 5% 2 6% 3 3 3 3 5% 7% 52%	3470
June	1st to 10th	Night	14% 7% 2 7% 6% 5% 4 4 6% 7% 39%	1400
	11th to 20th	Night	15% 6% 2 5% 5% 4 5% 4 6% 10% 40%	1400
	21st to end	Night	12% 5% 2 6% 4 5% 5% 5% 8% 9% 41%	1400
July	1st to 10th	Night	8% 3 2 5% 3 4 4 4 6% 10% 51%	3180
	11th to 20th	Night	8% 4 2 5% 4 5% 5% 4 6% 9% 47%	3180
	21st to end	Night	5% 4 2 5% 4 4 4 5% 7% 10% 52%	3466
August	1st to 10th	Night	8% 4 1 5% 4 4 5% 5% 7% 9% 48%	2692
	11th to 20th	Night	8% 3 1 4 3 4 4 4 7% 11% 51%	2888
	21st to end	Night	9% 5% 2 5% 4 5% 4 3 5% 8% 49%	3234
September	1st to 10th	Night	10% 5% 3 5% 4 3 4 4 6% 7% 50%	1895
	11th to 20th	Night	14% 5% 3 7% 4 4 3 3 6% 8% 44%	2200
	21st to end	Night	14% 6% 2 6% 4 4 4 3 5% 9% 43%	2200
October	1st to 10th	Night	14% 8% 2 5% 3 4 4 3 5% 8% 43%	3762
	11th to 20th	Night	10% 8% 3 8% 5% 5% 4 3 6% 8% 39%	3859
	21st to end	Night	9% 9% 3 9% 6% 6% 5% 4 6% 7% 37%	4482
November	1st to 10th	Night	14% 14% 3 9% 5% 6% 6% 4 6% 6% 28%	2731
	11th to 20th	Night	11% 15% 6% 13% 7% 5% 4 3 5% 6% 25%	2800
	21st to end	Night	13% 14% 6% 13% 7% 5% 5% 3 5% 6% 22%	2955
December	1st to 10th	Night	9% 16% 6% 15% 11% 8% 6% 4 4 5% 15%	4900
	11th to 20th	Night	8% 13% 6% 13% 7% 5% 5% 5% 6% 6% 26%	5568
	21st to end	Night	7% 11% 5% 18% 9% 7% 5% 4 5% 5% 23%	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	63% 6% 10% 14% 6%	3179
	11th to 20th	Day	63% 5% 9% 19% 4	3180
	21st to end	Day	62% 9% 12% 14% 4	3894
February	1st to 10th	Day	59% 6% 13% 13% 8% 1	1694
	11th to 20th	Day	49% 6% 15% 22% 8%	1763
	21st to end	Day	52% 8% 12% 19% 8% 1	1543
March	1st to 10th	Day	49% 8% 16% 18% 9% 1	4619
	11th to 20th	Day	51% 8% 15% 18% 8%	4980
	21st to end	Day	45% 7% 15% 24% 9% 1	5464
April	1st to 10th	Day	44% 6% 13% 25% 11% 1	2451
	11th to 20th	Day	44% 5% 13% 22% 13% 2	2572
	21st to end	Day	43% 6% 15% 26% 8% 2	2600
May	1st to 10th	Day	35% 5% 14% 28% 18% 1	6175
	11th to 20th	Day	47% 7% 11% 24% 10% 1	6705
	21st to end	Day	34% 6% 9% 22% 21% 6%	7428
June	1st to 10th	Day	43% 7% 14% 24% 11% 1	3000
	11th to 20th	Day	42% 8% 16% 22% 11% 1	3000
	21st to end	Day	40% 9% 19% 23% 8%	3000
July	1st to 10th	Day	33% 9% 24% 27% 7%	6726
	11th to 20th	Day	32% 7% 23% 33% 4	6719
	21st to end	Day	30% 8% 25% 32% 5%	7193
August	1st to 10th	Day	31% 8% 21% 32% 9%	4434
	11th to 20th	Day	34% 7% 23% 30% 5%	4210
	21st to end	Day	36% 7% 25% 27% 5%	4674
September	1st to 10th	Day	35% 8% 18% 31% 8% 1	2503
	11th to 20th	Day	46% 7% 19% 24% 4	2200
	21st to end	Day	40% 7% 18% 28% 7%	2200
October	1st to 10th	Day	43% 6% 16% 28% 7%	3231
	11th to 20th	Day	43% 8% 13% 26% 9%	3061
	21st to end	Day	50% 7% 19% 20% 3	3075
November	1st to 10th	Day	60% 7% 12% 17% 3 1	1567
	11th to 20th	Day	62% 10% 11% 14% 3	1600
	21st to end	Day	61% 9% 15% 12% 2	1444
December	1st to 10th	Day	68% 11% 9% 8% 4	2290
	11th to 20th	Day	58% 5% 14% 16% 7%	2640
	21st to end	Day	62% 9% 8% 16% 5%	3498
January	1st to 10th	Night	61% 8% 9% 13% 9%	6787
	11th to 20th	Night	68% 6% 7% 16% 4	6800
	21st to end	Night	62% 6% 12% 15% 6%	7069
February	1st to 10th	Night	56% 7% 12% 15% 9% 1	2705
	11th to 20th	Night	44% 7% 17% 22% 9%	2534
	21st to end	Night	50% 6% 11% 22% 10%	2105
March	1st to 10th	Night	49% 6% 12% 17% 10% 5%	5248
	11th to 20th	Night	39% 8% 13% 26% 13% 1	4980
	21st to end	Night	46% 5% 9% 26% 13% 1	5467
April	1st to 10th	Night	39% 5% 10% 25% 17% 3	1943
	11th to 20th	Night	47% 5% 9% 22% 15% 3	1779
	21st to end	Night	43% 7% 11% 24% 14% 2	1800
May	1st to 10th	Night	41% 6% 9% 24% 19%	3804
	11th to 20th	Night	45% 6% 11% 26% 10% 2	3214
	21st to end	Night	33% 6% 7% 22% 26% 5%	3470
June	1st to 10th	Night	42% 8% 13% 24% 12% 1	1400
	11th to 20th	Night	39% 8% 17% 22% 13% 2	1400
	21st to end	Night	35% 9% 21% 26% 9% 1	1400
July	1st to 10th	Night	29% 8% 19% 34% 9% 1	3145
	11th to 20th	Night	32% 7% 18% 36% 6% 1	3138
	21st to end	Night	26% 8% 24% 32% 9%	3368
August	1st to 10th	Night	31% 8% 18% 31% 12%	2685
	11th to 20th	Night	26% 8% 27% 32% 7%	2915
	21st to end	Night	32% 8% 21% 31% 8%	3234
September	1st to 10th	Night	33% 8% 17% 31% 11%	1895
	11th to 20th	Night	40% 8% 18% 25% 9% 1	2200
	21st to end	Night	41% 6% 15% 28% 9% 1	2200
October	1st to 10th	Night	40% 6% 13% 29% 13%	3762
	11th to 20th	Night	43% 7% 13% 28% 10%	3859
	21st to end	Night	46% 7% 17% 26% 4	4482
November	1st to 10th	Night	59% 7% 14% 15% 5% 1	2731
	11th to 20th	Night	62% 9% 13% 11% 4	2800
	21st to end	Night	64% 8% 13% 10% 4	2955
December	1st to 10th	Night	72% 7% 11% 7% 3	4900
	11th to 20th	Night	57% 6% 12% 13% 11%	5566
	21st to end	Night	61% 7% 9% 16% 7%	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	9% 3 26% 37% 21% 5%	300
	11th to 20th	Day	8% 6% 19% 43% 20% 3	300
	21st to end	Day	14% 5% 23% 34% 19% 4	330
February	1st to 10th	Day	13% 4 27% 35% 18% 3	300
	11th to 20th	Day	9% 3 28% 34% 20% 7%	300
	21st to end	Day	5% 4 24% 42% 22% 2	249
March	1st to 10th	Day	12% 4 23% 31% 24% 6%	300
	11th to 20th	Day	9% 6% 24% 36% 20% 4	300
	21st to end	Day	10% 4 21% 32% 26% 6%	330
April	1st to 10th	Day	12% 3 20% 38% 21% 5%	551
	11th to 20th	Day	15% 5% 21% 33% 22% 4	690
	21st to end	Day	14% 4 18% 36% 24% 5%	700
May	1st to 10th	Day	11% 4 21% 35% 25% 4	703
	11th to 20th	Day	15% 6% 17% 31% 24% 6%	725
	21st to end	Day	17% 4 14% 28% 30% 7%	789
June	1st to 10th	Day	17% 5% 18% 31% 22% 7%	730
	11th to 20th	Day	13% 6% 22% 36% 19% 4	730
	21st to end	Day	12% 5% 15% 35% 25% 9%	730
July	1st to 10th	Day	9% 2 17% 31% 29% 11%	721
	11th to 20th	Day	11% 4 19% 32% 25% 9%	718
	21st to end	Day	6% 4 15% 35% 30% 10%	794
August	1st to 10th	Day	8% 3 18% 33% 27% 11%	726
	11th to 20th	Day	10% 3 16% 31% 29% 11%	715
	21st to end	Day	13% 4 18% 31% 25% 9%	803
September	1st to 10th	Day	11% 4 23% 35% 23% 4	633
	11th to 20th	Day	16% 7% 22% 34% 17% 4	330
	21st to end	Day	18% 5% 21% 34% 21% 2	330
October	1st to 10th	Day	21% 6% 21% 33% 16% 4	309
	11th to 20th	Day	13% 9% 25% 38% 13% 2	300
	21st to end	Day	20% 7% 27% 29% 13% 3	330
November	1st to 10th	Day	21% 3 23% 32% 18% 3	300
	11th to 20th	Day	19% 5% 33% 29% 12% 2	300
	21st to end	Day	22% 7% 25% 36% 10%	300
December	1st to 10th	Day	17% 3 24% 34% 18% 3	300
	11th to 20th	Day	17% 7% 27% 36% 11% 2	300
	21st to end	Day	10% 4 23% 35% 23% 5%	330
January	1st to 10th	Night	13% 4 28% 36% 17% 3	1000
	11th to 20th	Night	13% 6% 25% 41% 15% 2	1000
	21st to end	Night	15% 4 24% 40% 16% 2	1100
February	1st to 10th	Night	13% 3 25% 40% 17% 2	1000
	11th to 20th	Night	10% 3 24% 37% 22% 4	979
	21st to end	Night	10% 4 26% 37% 20% 2	785
March	1st to 10th	Night	14% 3 23% 37% 20% 3	752
	11th to 20th	Night	12% 2 30% 40% 13% 3	600
	21st to end	Night	17% 4 22% 36% 17% 4	660
April	1st to 10th	Night	14% 3 23% 41% 16% 3	600
	11th to 20th	Night	15% 5% 20% 39% 19% 2	593
	21st to end	Night	13% 3 22% 43% 16% 3	600
May	1st to 10th	Night	19% 3 21% 39% 16% 2	600
	11th to 20th	Night	17% 5% 17% 37% 21% 4	591
	21st to end	Night	17% 3 19% 36% 22% 2	650
June	1st to 10th	Night	16% 3 21% 33% 24% 3	600
	11th to 20th	Night	18% 4 18% 38% 20% 3	600
	21st to end	Night	14% 4 14% 38% 27% 4	600
July	1st to 10th	Night	8% 2 16% 40% 29% 5%	585
	11th to 20th	Night	10% 4 18% 38% 25% 5%	582
	21st to end	Night	7% 3 16% 39% 28% 6%	657
August	1st to 10th	Night	9% 2 16% 42% 26% 5%	597
	11th to 20th	Night	9% 3 15% 39% 27% 6%	594
	21st to end	Night	11% 5% 18% 37% 25% 3	660
September	1st to 10th	Night	14% 4 24% 37% 18% 4	600
	11th to 20th	Night	18% 5% 21% 39% 15% 2	600
	21st to end	Night	16% 5% 27% 33% 16% 2	600
October	1st to 10th	Night	22% 6% 28% 32% 11% 1	724
	11th to 20th	Night	20% 7% 28% 32% 12% 1	803
	21st to end	Night	21% 8% 27% 33% 10% 1	1045
November	1st to 10th	Night	21% 6% 31% 27% 14% 1	975
	11th to 20th	Night	18% 7% 32% 31% 8% 3	1000
	21st to end	Night	20% 6% 33% 32% 9% 1	1000
December	1st to 10th	Night	12% 5% 27% 38% 16% 3	1000
	11th to 20th	Night	15% 5% 31% 36% 11% 2	1000
	21st to end	Night	18% 4 27% 32% 17% 2	1100

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