Upsala
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Upsala clear sky chart from 2005-11-06 to 2026-07-01.

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	13% 11% 4 10% 6% 5% 5% 4 6% 7% 31%	138564
	Night	12% 12% 5% 11% 6% 5% 5% 4 5% 6% 28%	134033
Transparency	Day	51% 6% 11% 21% 10% 1	141975
	Night	56% 5% 11% 19% 9% 1	138708
Seeing	Day	20% 16% 34% 21% 8% 2	18429
	Night	19% 13% 34% 25% 9% 1	28435

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	7% 12% 6% 19% 8% 8% 7% 5% 6% 5% 17%	4422
	11th to 20th	Day	5% 15% 7% 18% 8% 7% 7% 9% 9% 4 11%	4679
	21st to end	Day	6% 11% 8% 20% 8% 7% 6% 5% 8% 7% 14%	5156
February	1st to 10th	Day	7% 13% 6% 12% 8% 8% 8% 6% 7% 7% 19%	1815
	11th to 20th	Day	7% 11% 4 12% 8% 7% 5% 4 7% 6% 28%	1844
	21st to end	Day	6% 12% 7% 15% 8% 6% 5% 4 5% 6% 26%	1683
March	1st to 10th	Day	10% 13% 4 10% 6% 5% 4 3 4 6% 35%	4578
	11th to 20th	Day	8% 13% 7% 13% 5% 6% 5% 3 4 5% 30%	4993
	21st to end	Day	16% 17% 4 10% 6% 5% 4 2 4 5% 28%	5954
April	1st to 10th	Day	13% 14% 5% 10% 6% 5% 4 4 4 5% 30%	2520
	11th to 20th	Day	16% 16% 3 9% 4 4 4 3 5% 6% 30%	2494
	21st to end	Day	17% 12% 5% 8% 5% 4 4 4 5% 5% 31%	2861
May	1st to 10th	Day	13% 13% 4 7% 4 4 4 3 4 7% 37%	8241
	11th to 20th	Day	17% 10% 3 6% 5% 4 4 3 5% 7% 37%	8222
	21st to end	Day	13% 6% 2 5% 4 4 5% 3 6% 8% 45%	9061
June	1st to 10th	Day	19% 7% 2 7% 4 5% 4 4 5% 8% 35%	2959
	11th to 20th	Day	17% 6% 3 8% 6% 5% 6% 4 5% 7% 34%	3150
	21st to end	Day	18% 7% 2 7% 5% 5% 5% 4 6% 8% 34%	3150
July	1st to 10th	Day	12% 6% 2 6% 5% 6% 6% 5% 7% 9% 37%	6800
	11th to 20th	Day	14% 6% 2 6% 4 5% 4 4 6% 8% 41%	6433
	21st to end	Day	13% 7% 3 6% 4 4 5% 4 6% 8% 39%	6926
August	1st to 10th	Day	15% 7% 3 8% 5% 5% 5% 4 7% 8% 32%	4563
	11th to 20th	Day	12% 5% 1 5% 4 4 5% 3 6% 9% 45%	4347
	21st to end	Day	13% 7% 3 7% 4 4 5% 5% 6% 8% 39%	4393
September	1st to 10th	Day	15% 6% 3 8% 5% 5% 5% 4 5% 6% 37%	2400
	11th to 20th	Day	19% 10% 3 6% 4 3 4 3 6% 8% 34%	2392
	21st to end	Day	20% 10% 4 7% 4 4 4 3 5% 6% 32%	2137
October	1st to 10th	Day	18% 14% 3 8% 6% 5% 5% 4 4 6% 28%	2000
	11th to 20th	Day	18% 21% 4 10% 5% 5% 4 3 5% 5% 21%	1972
	21st to end	Day	20% 21% 5% 10% 4 5% 3 2 4 4 22%	1980
November	1st to 10th	Day	15% 17% 6% 12% 6% 5% 5% 3 4 6% 21%	1737
	11th to 20th	Day	16% 19% 7% 16% 7% 5% 4 2 3 5% 17%	1680
	21st to end	Day	16% 18% 7% 19% 8% 5% 4 3 4 4 14%	1680
December	1st to 10th	Day	10% 16% 7% 22% 14% 5% 4 3 3 4 11%	2588
	11th to 20th	Day	8% 14% 7% 17% 7% 7% 7% 4 6% 5% 19%	2937
	21st to end	Day	16% 21% 7% 17% 6% 4 3 3 4 5% 14%	3817
January	1st to 10th	Night	5% 14% 7% 17% 9% 8% 7% 4 5% 5% 20%	8480
	11th to 20th	Night	5% 13% 8% 18% 11% 9% 9% 7% 7% 3 10%	8236
	21st to end	Night	5% 12% 8% 16% 8% 8% 8% 5% 8% 8% 14%	9058
February	1st to 10th	Night	8% 12% 5% 11% 8% 8% 9% 6% 7% 7% 20%	2803
	11th to 20th	Night	8% 12% 4 9% 7% 7% 8% 5% 7% 6% 26%	2663
	21st to end	Night	6% 13% 5% 14% 9% 7% 7% 4 5% 5% 23%	2123
March	1st to 10th	Night	11% 10% 4 8% 6% 6% 6% 4 5% 6% 34%	5482
	11th to 20th	Night	9% 15% 5% 14% 8% 6% 5% 3 5% 6% 24%	5230
	21st to end	Night	16% 16% 5% 10% 5% 5% 4 3 5% 5% 26%	5218
April	1st to 10th	Night	14% 14% 4 9% 5% 4 4 3 4 5% 32%	2100
	11th to 20th	Night	15% 14% 5% 8% 4 4 4 4 5% 7% 31%	2075
	21st to end	Night	17% 11% 4 8% 5% 3 4 3 6% 6% 32%	1755
May	1st to 10th	Night	13% 10% 3 5% 3 3 4 4 6% 6% 43%	4688
	11th to 20th	Night	17% 9% 3 7% 4 4 3 3 4 6% 39%	4670
	21st to end	Night	15% 4 2 5% 3 3 4 3 5% 7% 48%	5148
June	1st to 10th	Night	17% 8% 2 6% 4 4 5% 4 7% 6% 36%	1655
	11th to 20th	Night	14% 5% 2 6% 4 4 5% 5% 7% 9% 39%	1470
	21st to end	Night	14% 7% 3 7% 5% 3 4 5% 6% 7% 38%	1470
July	1st to 10th	Night	12% 7% 2 6% 4 4 4 3 6% 9% 44%	3180
	11th to 20th	Night	14% 7% 2 5% 4 4 4 3 5% 7% 44%	3532
	21st to end	Night	15% 6% 2 6% 4 4 4 3 5% 8% 43%	3948
August	1st to 10th	Night	16% 5% 1 4 4 4 4 4 7% 7% 43%	2597
	11th to 20th	Night	12% 4 2 5% 4 4 5% 4 8% 8% 45%	2695
	21st to end	Night	17% 7% 2 5% 4 3 4 3 5% 7% 44%	3507
September	1st to 10th	Night	13% 7% 3 6% 5% 4 5% 3 5% 7% 42%	2000
	11th to 20th	Night	18% 8% 3 5% 4 4 3 4 6% 8% 38%	2000
	21st to end	Night	21% 10% 3 7% 4 3 3 3 5% 5% 36%	2247
October	1st to 10th	Night	18% 14% 3 8% 4 4 3 4 4 5% 33%	2400
	11th to 20th	Night	19% 17% 4 7% 4 4 4 3 4 6% 28%	2427
	21st to end	Night	20% 18% 5% 10% 5% 4 4 3 5% 6% 21%	2860
November	1st to 10th	Night	16% 18% 5% 11% 5% 5% 4 3 5% 5% 22%	2778
	11th to 20th	Night	17% 18% 6% 15% 7% 5% 5% 3 3 5% 17%	2940
	21st to end	Night	13% 19% 8% 18% 7% 5% 4 3 5% 4 15%	2940
December	1st to 10th	Night	11% 19% 9% 20% 11% 6% 4 3 4 3 10%	4805
	11th to 20th	Night	10% 14% 6% 16% 8% 7% 7% 5% 5% 5% 17%	5461
	21st to end	Night	17% 20% 7% 15% 7% 4 4 3 3 5% 14%	7392

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	68% 4 6% 12% 9% 1	4423
	11th to 20th	Day	70% 3 6% 17% 4	4710
	21st to end	Day	67% 3 7% 13% 10%	5156
February	1st to 10th	Day	61% 5% 8% 16% 9% 1	1815
	11th to 20th	Day	54% 5% 10% 21% 9% 1	1853
	21st to end	Day	58% 5% 9% 15% 12% 1	1683
March	1st to 10th	Day	52% 4 10% 17% 14% 4	4580
	11th to 20th	Day	55% 5% 8% 19% 12% 1	4993
	21st to end	Day	58% 4 8% 16% 13% 2	5954
April	1st to 10th	Day	55% 5% 9% 18% 13% 2	2520
	11th to 20th	Day	55% 4 10% 20% 9% 2	2494
	21st to end	Day	53% 6% 8% 19% 12% 2	2861
May	1st to 10th	Day	45% 5% 10% 24% 16% 1	8250
	11th to 20th	Day	45% 6% 9% 21% 17% 2	8226
	21st to end	Day	36% 7% 11% 25% 19% 3	9061
June	1st to 10th	Day	47% 7% 11% 22% 12% 1	2959
	11th to 20th	Day	48% 7% 10% 22% 12% 1	3150
	21st to end	Day	47% 7% 13% 23% 9% 1	3150
July	1st to 10th	Day	40% 9% 14% 28% 9% 1	6727
	11th to 20th	Day	38% 7% 20% 30% 5%	6356
	21st to end	Day	41% 6% 16% 29% 7%	6728
August	1st to 10th	Day	46% 8% 14% 26% 6%	4548
	11th to 20th	Day	35% 7% 22% 28% 8%	4389
	21st to end	Day	40% 7% 16% 29% 7%	4392
September	1st to 10th	Day	46% 6% 14% 26% 8%	2400
	11th to 20th	Day	47% 7% 20% 21% 5%	2392
	21st to end	Day	52% 5% 13% 21% 7% 1	2137
October	1st to 10th	Day	48% 5% 13% 26% 8%	3260
	11th to 20th	Day	56% 4 14% 20% 5%	3188
	21st to end	Day	63% 6% 13% 16% 2	3180
November	1st to 10th	Day	65% 6% 12% 11% 5% 1	1737
	11th to 20th	Day	72% 5% 8% 11% 4	1680
	21st to end	Day	75% 5% 8% 7% 4	1680
December	1st to 10th	Day	78% 3 9% 7% 3	2588
	11th to 20th	Day	66% 5% 7% 12% 10% 1	2938
	21st to end	Day	74% 3 4 13% 7%	3817
January	1st to 10th	Night	66% 4 7% 12% 9% 2	8480
	11th to 20th	Night	73% 4 5% 11% 6%	8280
	21st to end	Night	66% 4 8% 15% 8%	9058
February	1st to 10th	Night	60% 5% 9% 16% 9% 1	2803
	11th to 20th	Night	54% 5% 12% 19% 9%	2664
	21st to end	Night	62% 5% 8% 15% 9% 1	2123
March	1st to 10th	Night	50% 5% 9% 13% 18% 4	5493
	11th to 20th	Night	60% 6% 9% 15% 8% 1	5231
	21st to end	Night	59% 4 8% 17% 11% 1	5218
April	1st to 10th	Night	53% 5% 8% 21% 13% 1	2100
	11th to 20th	Night	52% 5% 11% 20% 11% 1	2075
	21st to end	Night	50% 6% 9% 20% 13% 2	1755
May	1st to 10th	Night	40% 6% 10% 28% 15% 1	4695
	11th to 20th	Night	46% 6% 10% 24% 12% 2	4671
	21st to end	Night	35% 6% 12% 29% 18% 1	5149
June	1st to 10th	Night	45% 7% 11% 24% 12% 1	1655
	11th to 20th	Night	40% 8% 13% 24% 14% 1	1470
	21st to end	Night	43% 7% 16% 23% 10% 1	1470
July	1st to 10th	Night	37% 7% 17% 30% 10%	3145
	11th to 20th	Night	38% 6% 20% 30% 6%	3486
	21st to end	Night	39% 5% 15% 33% 7%	3832
August	1st to 10th	Night	38% 7% 16% 31% 7% 1	2588
	11th to 20th	Night	34% 8% 19% 31% 9%	2719
	21st to end	Night	39% 6% 18% 29% 7%	3507
September	1st to 10th	Night	41% 7% 16% 27% 9% 1	2000
	11th to 20th	Night	44% 8% 20% 25% 4	2000
	21st to end	Night	50% 6% 13% 25% 5% 1	2247
October	1st to 10th	Night	43% 5% 11% 31% 10%	3920
	11th to 20th	Night	55% 4 11% 21% 7%	3950
	21st to end	Night	63% 5% 16% 13% 3	4610
November	1st to 10th	Night	64% 6% 11% 14% 5%	2778
	11th to 20th	Night	71% 5% 9% 11% 4	2940
	21st to end	Night	73% 5% 9% 9% 3	2940
December	1st to 10th	Night	80% 5% 7% 7% 2	4805
	11th to 20th	Night	68% 5% 9% 13% 5%	5459
	21st to end	Night	74% 3 5% 13% 5%	7392

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	16% 15% 41% 24% 4	330
	11th to 20th	Day	14% 14% 39% 26% 7%	330
	21st to end	Day	13% 15% 44% 21% 5% 1	363
February	1st to 10th	Day	15% 22% 43% 15% 4 1	330
	11th to 20th	Day	13% 22% 40% 19% 5% 1	330
	21st to end	Day	16% 25% 43% 14% 3	273
March	1st to 10th	Day	18% 20% 41% 16% 5%	330
	11th to 20th	Day	16% 26% 39% 13% 5% 1	330
	21st to end	Day	21% 18% 34% 19% 6% 2	525
April	1st to 10th	Day	20% 19% 34% 19% 8% 1	540
	11th to 20th	Day	28% 16% 27% 19% 9% 1	532
	21st to end	Day	23% 16% 33% 18% 8% 2	710
May	1st to 10th	Day	23% 18% 31% 20% 5% 2	753
	11th to 20th	Day	22% 16% 34% 19% 7% 2	775
	21st to end	Day	21% 15% 33% 22% 7% 2	844
June	1st to 10th	Day	22% 15% 31% 23% 7% 3	780
	11th to 20th	Day	20% 18% 35% 18% 8% 1	780
	21st to end	Day	20% 14% 31% 23% 8% 3	780
July	1st to 10th	Day	13% 11% 35% 25% 11% 4	722
	11th to 20th	Day	16% 14% 31% 24% 11% 3	718
	21st to end	Day	12% 13% 34% 26% 11% 5%	794
August	1st to 10th	Day	16% 12% 33% 27% 10% 3	726
	11th to 20th	Day	16% 10% 26% 29% 14% 4	715
	21st to end	Day	20% 13% 28% 27% 11% 2	638
September	1st to 10th	Day	18% 11% 31% 25% 13% 3	530
	11th to 20th	Day	25% 11% 29% 23% 10% 2	530
	21st to end	Day	26% 14% 28% 21% 10% 1	467
October	1st to 10th	Day	27% 20% 29% 15% 6% 2	330
	11th to 20th	Day	26% 23% 30% 18% 2 1	330
	21st to end	Day	32% 20% 33% 11% 3 1	363
November	1st to 10th	Day	27% 18% 36% 15% 4	330
	11th to 20th	Day	30% 23% 33% 10% 3 1	330
	21st to end	Day	25% 23% 35% 14% 3	330
December	1st to 10th	Day	20% 15% 41% 20% 3 1	297
	11th to 20th	Day	20% 17% 43% 14% 5%	281
	21st to end	Day	20% 17% 35% 22% 3 2	363
January	1st to 10th	Night	16% 15% 42% 22% 6%	1050
	11th to 20th	Night	16% 14% 42% 22% 5% 1	1050
	21st to end	Night	14% 14% 43% 23% 6%	1155
February	1st to 10th	Night	15% 16% 39% 23% 7%	1050
	11th to 20th	Night	13% 16% 37% 23% 10% 1	1029
	21st to end	Night	13% 15% 38% 26% 7% 1	739
March	1st to 10th	Night	14% 16% 38% 24% 8%	840
	11th to 20th	Night	17% 17% 37% 20% 8% 1	693
	21st to end	Night	22% 11% 29% 25% 11% 3	693
April	1st to 10th	Night	20% 11% 34% 27% 8% 1	630
	11th to 20th	Night	21% 12% 32% 28% 7% 1	623
	21st to end	Night	20% 9% 30% 31% 9% 1	630
May	1st to 10th	Night	22% 12% 30% 29% 7% 1	630
	11th to 20th	Night	21% 14% 31% 25% 7% 1	621
	21st to end	Night	20% 8% 31% 32% 9%	683
June	1st to 10th	Night	21% 8% 31% 30% 11%	630
	11th to 20th	Night	15% 11% 34% 32% 8%	630
	21st to end	Night	17% 8% 28% 33% 13% 1	630
July	1st to 10th	Night	10% 7% 31% 35% 16% 1	585
	11th to 20th	Night	14% 9% 30% 29% 16% 1	582
	21st to end	Night	10% 7% 27% 38% 17% 1	657
August	1st to 10th	Night	14% 5% 31% 33% 15% 1	597
	11th to 20th	Night	16% 6% 24% 30% 21% 3	594
	21st to end	Night	18% 9% 27% 30% 16%	660
September	1st to 10th	Night	16% 9% 26% 31% 16% 1	600
	11th to 20th	Night	22% 9% 32% 25% 11% 1	600
	21st to end	Night	26% 9% 28% 27% 9% 1	787
October	1st to 10th	Night	27% 12% 30% 22% 7% 1	800
	11th to 20th	Night	30% 12% 32% 20% 6% 1	800
	21st to end	Night	28% 13% 33% 20% 7%	880
November	1st to 10th	Night	26% 14% 33% 20% 5% 1	932
	11th to 20th	Night	26% 15% 32% 19% 6% 1	1050
	21st to end	Night	25% 18% 35% 19% 3	1050
December	1st to 10th	Night	17% 16% 39% 21% 6% 1	1050
	11th to 20th	Night	19% 17% 38% 17% 7% 1	1050
	21st to end	Night	24% 14% 32% 23% 6% 1	1155

Page generated at 2026-06-28 02:10:48. Version ac07

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