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 2024-01-12.

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% 4 7% 7% 4 5% 5% 6% 8% 35%	74651
	Night	11% 9% 4 8% 7% 4 5% 5% 6% 7% 34%	75090
Transparency	Day	46% 7% 16% 22% 8% 1	74332
	Night	48% 7% 14% 21% 9% 1	74928
Seeing	Day	13% 4 19% 34% 23% 6%	15076
	Night	15% 4 24% 37% 18% 3	25149

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	8% 13% 7% 9% 7% 6% 8% 7% 7% 6% 22%	1329
	11th to 20th	Day	9% 14% 6% 13% 8% 5% 6% 4 9% 7% 19%	1267
	21st to end	Day	10% 15% 7% 10% 9% 5% 7% 6% 7% 8% 15%	1544
February	1st to 10th	Day	10% 9% 7% 10% 9% 5% 8% 7% 7% 8% 20%	1525
	11th to 20th	Day	8% 10% 5% 8% 7% 6% 7% 7% 7% 10% 26%	1574
	21st to end	Day	6% 12% 5% 9% 10% 4 7% 7% 7% 8% 26%	1384
March	1st to 10th	Day	12% 10% 6% 8% 9% 5% 7% 7% 5% 7% 24%	1841
	11th to 20th	Day	8% 10% 4 10% 8% 4 6% 5% 6% 7% 31%	1978
	21st to end	Day	11% 9% 4 9% 7% 4 5% 5% 5% 7% 32%	2178
April	1st to 10th	Day	10% 10% 3 8% 6% 3 5% 5% 6% 6% 37%	2204
	11th to 20th	Day	11% 8% 4 6% 6% 3 7% 6% 5% 7% 37%	2312
	21st to end	Day	13% 7% 3 6% 7% 4 6% 5% 6% 7% 37%	2340
May	1st to 10th	Day	13% 8% 4 6% 5% 4 3 4 5% 7% 40%	2447
	11th to 20th	Day	16% 8% 3 6% 5% 3 5% 4 6% 7% 38%	2627
	21st to end	Day	19% 7% 3 5% 6% 3 5% 5% 5% 8% 35%	2918
June	1st to 10th	Day	16% 6% 2 6% 6% 4 4 5% 5% 8% 37%	2700
	11th to 20th	Day	14% 6% 3 6% 6% 4 6% 5% 6% 8% 36%	2700
	21st to end	Day	12% 5% 3 6% 6% 4 5% 5% 6% 9% 37%	2700
July	1st to 10th	Day	8% 4 2 5% 5% 3 6% 5% 7% 8% 47%	2700
	11th to 20th	Day	11% 4 2 4 5% 3 5% 5% 7% 9% 44%	2700
	21st to end	Day	6% 5% 2 5% 5% 3 5% 6% 6% 10% 48%	2939
August	1st to 10th	Day	8% 3 2 5% 5% 4 5% 6% 7% 9% 46%	2461
	11th to 20th	Day	11% 4 2 4 6% 3 4 5% 6% 8% 47%	2301
	21st to end	Day	13% 5% 2 5% 5% 3 4 5% 6% 7% 45%	2574
September	1st to 10th	Day	11% 5% 2 5% 5% 3 4 5% 5% 7% 48%	2255
	11th to 20th	Day	13% 8% 3 6% 6% 4 5% 4 5% 8% 37%	1980
	21st to end	Day	15% 7% 2 5% 5% 3 4 4 6% 9% 38%	1980
October	1st to 10th	Day	18% 12% 4 5% 5% 4 5% 4 5% 6% 31%	1826
	11th to 20th	Day	12% 13% 4 7% 6% 4 6% 6% 6% 6% 30%	1758
	21st to end	Day	15% 14% 5% 8% 8% 4 6% 5% 5% 7% 23%	1779
November	1st to 10th	Day	16% 14% 4 11% 7% 3 4 4 5% 5% 26%	1487
	11th to 20th	Day	10% 14% 6% 11% 7% 4 5% 6% 5% 6% 26%	1520
	21st to end	Day	12% 14% 6% 9% 8% 4 5% 5% 5% 7% 25%	1372
December	1st to 10th	Day	9% 13% 5% 12% 12% 6% 7% 6% 7% 7% 17%	1330
	11th to 20th	Day	10% 14% 7% 11% 10% 3 6% 6% 6% 7% 21%	1679
	21st to end	Day	8% 11% 4 9% 8% 5% 6% 6% 6% 7% 28%	2442
January	1st to 10th	Night	8% 12% 6% 10% 10% 6% 8% 7% 6% 7% 21%	2837
	11th to 20th	Night	9% 14% 6% 10% 9% 5% 6% 7% 7% 7% 20%	2722
	21st to end	Night	10% 13% 6% 11% 9% 4 7% 7% 7% 8% 20%	2811
February	1st to 10th	Night	7% 10% 5% 10% 8% 5% 8% 7% 7% 7% 27%	2434
	11th to 20th	Night	7% 9% 5% 8% 6% 4 7% 6% 7% 8% 33%	2273
	21st to end	Night	6% 11% 4 9% 6% 4 7% 6% 5% 7% 34%	1888
March	1st to 10th	Night	10% 11% 4 9% 6% 5% 6% 5% 6% 8% 32%	2118
	11th to 20th	Night	8% 9% 3 6% 6% 4 4 5% 5% 8% 43%	1980
	21st to end	Night	13% 10% 4 7% 5% 4 3 4 4 8% 37%	2178
April	1st to 10th	Night	12% 6% 2 6% 4 3 5% 5% 6% 8% 42%	1750
	11th to 20th	Night	13% 9% 4 6% 6% 3 5% 5% 5% 6% 37%	1599
	21st to end	Night	9% 8% 4 7% 7% 5% 6% 5% 6% 6% 38%	1620
May	1st to 10th	Night	16% 8% 4 6% 5% 3 4 5% 5% 6% 37%	1512
	11th to 20th	Night	14% 6% 2 6% 6% 3 4 4 5% 8% 43%	1268
	21st to end	Night	18% 5% 2 5% 5% 2 5% 4 5% 8% 41%	1358
June	1st to 10th	Night	15% 7% 3 7% 6% 3 4 4 5% 8% 39%	1260
	11th to 20th	Night	15% 5% 2 5% 5% 3 5% 4 6% 9% 41%	1260
	21st to end	Night	12% 4 2 5% 5% 3 6% 5% 8% 10% 41%	1260
July	1st to 10th	Night	7% 3 1 3 2 3 4 5% 5% 11% 57%	1260
	11th to 20th	Night	8% 3 1 4 4 4 5% 4 5% 10% 51%	1260
	21st to end	Night	7% 3 2 4 4 3 3 5% 6% 9% 55%	1379
August	1st to 10th	Night	8% 3 1 3 4 3 6% 5% 6% 8% 53%	1475
	11th to 20th	Night	9% 3 2 3 4 3 4 4 7% 9% 53%	1600
	21st to end	Night	12% 6% 2 4 5% 3 4 4 4 7% 51%	1782
September	1st to 10th	Night	11% 5% 3 5% 4 3 3 5% 6% 6% 50%	1704
	11th to 20th	Night	14% 5% 3 6% 5% 3 3 4 6% 8% 45%	1980
	21st to end	Night	15% 7% 2 6% 5% 3 4 4 5% 9% 40%	1980
October	1st to 10th	Night	17% 9% 3 6% 5% 4 5% 5% 5% 7% 35%	2115
	11th to 20th	Night	16% 10% 4 7% 7% 4 4 4 5% 7% 33%	2200
	21st to end	Night	15% 12% 3 8% 6% 3 5% 4 5% 8% 30%	2576
November	1st to 10th	Night	15% 13% 4 8% 6% 4 6% 5% 6% 6% 27%	2591
	11th to 20th	Night	10% 14% 7% 11% 8% 4 5% 4 5% 6% 25%	2660
	21st to end	Night	13% 13% 6% 12% 8% 3 5% 4 5% 6% 23%	2807
December	1st to 10th	Night	7% 10% 6% 12% 12% 6% 8% 5% 5% 7% 23%	2850
	11th to 20th	Night	9% 15% 7% 9% 8% 4 5% 6% 6% 6% 24%	3518
	21st to end	Night	8% 10% 5% 11% 10% 5% 6% 5% 6% 7% 28%	5225

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% 8% 14% 15% 4	1329
	11th to 20th	Day	62% 5% 11% 17% 5%	1267
	21st to end	Day	66% 6% 6% 14% 8%	1544
February	1st to 10th	Day	58% 6% 14% 14% 8% 1	1525
	11th to 20th	Day	50% 6% 15% 21% 8%	1583
	21st to end	Day	53% 7% 12% 20% 7%	1384
March	1st to 10th	Day	57% 7% 12% 16% 7%	1841
	11th to 20th	Day	48% 8% 16% 20% 7%	1980
	21st to end	Day	48% 7% 16% 19% 9% 1	2178
April	1st to 10th	Day	45% 6% 13% 24% 11% 1	2204
	11th to 20th	Day	43% 5% 14% 22% 14% 2	2312
	21st to end	Day	43% 6% 16% 25% 8% 2	2340
May	1st to 10th	Day	41% 5% 16% 24% 13% 1	2447
	11th to 20th	Day	43% 5% 12% 25% 14% 1	2631
	21st to end	Day	45% 7% 13% 20% 13% 1	2918
June	1st to 10th	Day	43% 7% 15% 23% 11% 1	2700
	11th to 20th	Day	43% 8% 15% 22% 12% 1	2700
	21st to end	Day	40% 9% 19% 23% 8% 1	2700
July	1st to 10th	Day	29% 8% 22% 29% 12%	2626
	11th to 20th	Day	33% 8% 20% 28% 9% 1	2619
	21st to end	Day	31% 8% 21% 31% 9%	2776
August	1st to 10th	Day	31% 8% 22% 32% 7%	2444
	11th to 20th	Day	34% 8% 22% 30% 6%	2301
	21st to end	Day	36% 7% 19% 30% 8%	2574
September	1st to 10th	Day	34% 8% 18% 31% 8% 1	2255
	11th to 20th	Day	45% 8% 18% 25% 4	1980
	21st to end	Day	42% 7% 18% 26% 6%	1980
October	1st to 10th	Day	53% 7% 16% 19% 5%	1826
	11th to 20th	Day	52% 10% 13% 20% 4 1	1758
	21st to end	Day	59% 9% 15% 13% 3	1779
November	1st to 10th	Day	60% 7% 11% 17% 4 1	1487
	11th to 20th	Day	62% 11% 10% 14% 3	1520
	21st to end	Day	61% 10% 15% 12% 2	1372
December	1st to 10th	Day	66% 8% 12% 11% 3	1330
	11th to 20th	Day	62% 6% 15% 12% 4	1680
	21st to end	Day	51% 12% 11% 19% 7%	2442
January	1st to 10th	Night	60% 9% 10% 16% 4	2837
	11th to 20th	Night	60% 7% 10% 17% 4	2722
	21st to end	Night	60% 6% 10% 17% 7%	2811
February	1st to 10th	Night	54% 7% 12% 16% 10% 1	2434
	11th to 20th	Night	46% 7% 17% 21% 10%	2274
	21st to end	Night	49% 6% 10% 23% 10%	1888
March	1st to 10th	Night	51% 6% 12% 20% 10% 1	2118
	11th to 20th	Night	40% 7% 13% 28% 11% 2	1980
	21st to end	Night	47% 6% 13% 20% 12% 2	2178
April	1st to 10th	Night	40% 5% 11% 24% 17% 3	1750
	11th to 20th	Night	46% 5% 9% 21% 15% 4	1599
	21st to end	Night	43% 7% 11% 24% 13% 2	1620
May	1st to 10th	Night	46% 6% 10% 24% 13% 1	1512
	11th to 20th	Night	40% 4 12% 27% 14% 3	1268
	21st to end	Night	43% 7% 12% 20% 16% 2	1358
June	1st to 10th	Night	43% 8% 14% 24% 10% 1	1260
	11th to 20th	Night	39% 8% 17% 22% 14% 2	1260
	21st to end	Night	34% 9% 22% 26% 8% 1	1260
July	1st to 10th	Night	22% 7% 18% 36% 15% 1	1225
	11th to 20th	Night	31% 7% 19% 30% 11% 2	1218
	21st to end	Night	26% 7% 17% 37% 12% 1	1302
August	1st to 10th	Night	28% 8% 18% 34% 11% 1	1468
	11th to 20th	Night	26% 9% 23% 32% 10%	1600
	21st to end	Night	33% 7% 17% 32% 11% 1	1782
September	1st to 10th	Night	33% 8% 16% 31% 11%	1704
	11th to 20th	Night	38% 7% 19% 25% 9% 1	1980
	21st to end	Night	43% 7% 15% 27% 8%	1980
October	1st to 10th	Night	49% 8% 14% 22% 8%	2115
	11th to 20th	Night	53% 7% 12% 23% 6%	2200
	21st to end	Night	54% 8% 16% 18% 3	2576
November	1st to 10th	Night	60% 8% 13% 14% 5% 1	2591
	11th to 20th	Night	61% 9% 13% 11% 5%	2660
	21st to end	Night	63% 8% 14% 11% 4	2807
December	1st to 10th	Night	62% 8% 16% 11% 3	2850
	11th to 20th	Night	58% 8% 14% 14% 6%	3516
	21st to end	Night	53% 9% 11% 17% 9% 1	5225

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	10% 3 26% 37% 19% 5%	270
	11th to 20th	Day	9% 6% 19% 42% 21% 4	243
	21st to end	Day	18% 3 20% 35% 19% 5%	264
February	1st to 10th	Day	13% 4 26% 40% 15% 3	240
	11th to 20th	Day	11% 3 30% 30% 18% 8%	240
	21st to end	Day	5% 1 23% 44% 26% 2	198
March	1st to 10th	Day	13% 3 21% 31% 25% 7%	240
	11th to 20th	Day	10% 3 20% 38% 23% 5%	240
	21st to end	Day	13% 3 19% 31% 28% 6%	264
April	1st to 10th	Day	13% 3 20% 39% 19% 5%	464
	11th to 20th	Day	15% 4 20% 33% 24% 4	590
	21st to end	Day	14% 3 18% 37% 23% 4	600
May	1st to 10th	Day	12% 4 19% 35% 26% 4	603
	11th to 20th	Day	16% 5% 14% 31% 27% 7%	625
	21st to end	Day	18% 4 15% 28% 28% 7%	679
June	1st to 10th	Day	17% 4 17% 32% 22% 8%	630
	11th to 20th	Day	14% 5% 20% 36% 20% 4	630
	21st to end	Day	12% 4 12% 35% 27% 11%	630
July	1st to 10th	Day	9% 2 17% 33% 29% 10%	621
	11th to 20th	Day	11% 4 19% 31% 26% 9%	618
	21st to end	Day	6% 4 15% 33% 31% 11%	684
August	1st to 10th	Day	8% 3 18% 33% 26% 12%	626
	11th to 20th	Day	9% 4 15% 32% 28% 11%	615
	21st to end	Day	14% 4 17% 31% 26% 9%	693
September	1st to 10th	Day	11% 3 23% 36% 22% 4	545
	11th to 20th	Day	15% 6% 21% 35% 19% 4	270
	21st to end	Day	20% 4 20% 33% 21% 1	270
October	1st to 10th	Day	23% 5% 19% 33% 16% 4	270
	11th to 20th	Day	13% 9% 24% 39% 14% 2	270
	21st to end	Day	21% 7% 27% 29% 13% 2	297
November	1st to 10th	Day	21% 3 22% 34% 16% 3	270
	11th to 20th	Day	18% 4 34% 29% 13% 2	270
	21st to end	Day	21% 7% 26% 36% 9%	270
December	1st to 10th	Day	15% 3 24% 35% 19% 4	270
	11th to 20th	Day	16% 7% 27% 36% 12% 2	270
	21st to end	Day	10% 3 22% 36% 24% 5%	297
January	1st to 10th	Night	12% 4 28% 36% 18% 3	950
	11th to 20th	Night	13% 5% 24% 41% 14% 2	908
	21st to end	Night	16% 3 24% 41% 15% 2	990
February	1st to 10th	Night	12% 3 24% 41% 17% 2	900
	11th to 20th	Night	11% 3 24% 37% 21% 4	879
	21st to end	Night	10% 3 25% 38% 22% 2	704
March	1st to 10th	Night	15% 3 21% 38% 21% 3	678
	11th to 20th	Night	13% 3 28% 39% 14% 3	540
	21st to end	Night	18% 3 21% 36% 18% 5%	594
April	1st to 10th	Night	14% 2 24% 42% 15% 3	540
	11th to 20th	Night	15% 4 20% 39% 21% 2	533
	21st to end	Night	13% 2 22% 44% 16% 2	540
May	1st to 10th	Night	20% 2 19% 40% 16% 2	540
	11th to 20th	Night	16% 4 16% 38% 22% 4	531
	21st to end	Night	18% 3 18% 35% 22% 2	584
June	1st to 10th	Night	17% 3 19% 32% 26% 3	540
	11th to 20th	Night	17% 4 17% 38% 21% 3	540
	21st to end	Night	13% 3 12% 39% 29% 5%	540
July	1st to 10th	Night	8% 2 16% 41% 28% 4	525
	11th to 20th	Night	10% 4 19% 38% 25% 5%	522
	21st to end	Night	8% 3 15% 38% 29% 7%	591
August	1st to 10th	Night	10% 2 16% 41% 26% 5%	537
	11th to 20th	Night	9% 3 15% 39% 27% 7%	534
	21st to end	Night	12% 5% 16% 38% 26% 3	594
September	1st to 10th	Night	14% 3 23% 37% 18% 4	540
	11th to 20th	Night	18% 5% 20% 40% 15% 2	540
	21st to end	Night	17% 5% 27% 34% 15% 1	540
October	1st to 10th	Night	23% 6% 28% 31% 11% 1	675
	11th to 20th	Night	21% 7% 26% 33% 12% 1	760
	21st to end	Night	22% 8% 26% 33% 10% 2	990
November	1st to 10th	Night	21% 6% 31% 27% 14% 2	925
	11th to 20th	Night	17% 7% 33% 31% 8% 3	950
	21st to end	Night	20% 6% 33% 32% 8% 1	950
December	1st to 10th	Night	11% 3 27% 40% 16% 3	950
	11th to 20th	Night	15% 5% 30% 36% 12% 2	950
	21st to end	Night	18% 4 27% 32% 17% 2	1045

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