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 2024-02-05.

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	15% 11% 5% 9% 7% 4 5% 5% 5% 6% 28%	78190
	Night	13% 12% 5% 9% 8% 4 5% 5% 5% 6% 26%	80657
Transparency	Day	55% 6% 11% 19% 8% 1	77889
	Night	57% 6% 11% 18% 7% 1	80492
Seeing	Day	20% 15% 33% 21% 8% 2	15022
	Night	19% 12% 34% 25% 9% 1	25182

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	10% 12% 6% 14% 13% 7% 8% 6% 6% 6% 14%	2373
	11th to 20th	Day	6% 10% 5% 13% 12% 7% 9% 8% 6% 6% 17%	2530
	21st to end	Day	10% 14% 10% 21% 10% 5% 5% 5% 6% 4 10%	2783
February	1st to 10th	Day	7% 11% 6% 10% 9% 5% 8% 9% 7% 7% 21%	1587
	11th to 20th	Day	8% 11% 4 10% 8% 5% 6% 6% 7% 7% 28%	1574
	21st to end	Day	6% 11% 7% 13% 9% 5% 5% 5% 5% 6% 27%	1440
March	1st to 10th	Day	9% 12% 5% 10% 7% 5% 6% 6% 4 6% 31%	1798
	11th to 20th	Day	12% 14% 5% 10% 7% 3 4 4 4 5% 33%	1941
	21st to end	Day	15% 10% 4 8% 7% 4 5% 4 5% 7% 30%	2316
April	1st to 10th	Day	13% 14% 5% 8% 7% 4 5% 5% 4 6% 30%	2160
	11th to 20th	Day	17% 14% 4 8% 5% 3 4 4 4 6% 32%	2134
	21st to end	Day	17% 12% 5% 7% 5% 3 5% 5% 5% 5% 32%	2451
May	1st to 10th	Day	17% 13% 5% 7% 6% 3 5% 5% 4 6% 29%	2520
	11th to 20th	Day	17% 10% 4 6% 7% 3 5% 5% 5% 7% 32%	2479
	21st to end	Day	21% 7% 3 5% 5% 3 4 4 5% 8% 35%	2725
June	1st to 10th	Day	20% 6% 2 6% 6% 3 5% 5% 4 9% 34%	2536
	11th to 20th	Day	17% 6% 3 7% 6% 4 5% 5% 5% 7% 36%	2700
	21st to end	Day	18% 6% 3 6% 5% 3 4 5% 5% 8% 35%	2700
July	1st to 10th	Day	11% 6% 3 5% 6% 4 6% 5% 7% 8% 39%	2700
	11th to 20th	Day	15% 6% 3 5% 6% 3 5% 5% 6% 8% 37%	2554
	21st to end	Day	14% 6% 2 6% 6% 3 5% 6% 6% 7% 39%	2743
August	1st to 10th	Day	12% 6% 3 6% 7% 4 5% 6% 7% 9% 35%	2507
	11th to 20th	Day	13% 6% 2 6% 6% 3 6% 5% 6% 9% 40%	2404
	21st to end	Day	15% 7% 3 6% 4 3 4 5% 5% 7% 39%	2426
September	1st to 10th	Day	16% 6% 3 7% 7% 3 5% 5% 5% 6% 38%	2160
	11th to 20th	Day	20% 10% 3 5% 5% 3 4 4 6% 8% 32%	2154
	21st to end	Day	22% 11% 4 6% 5% 3 4 4 5% 6% 29%	1924
October	1st to 10th	Day	20% 15% 4 8% 6% 4 4 5% 4 6% 25%	1800
	11th to 20th	Day	19% 20% 5% 8% 7% 4 4 4 5% 5% 21%	1776
	21st to end	Day	21% 20% 6% 9% 5% 4 3 3 4 4 21%	1782
November	1st to 10th	Day	16% 16% 7% 10% 7% 4 5% 4 5% 6% 20%	1569
	11th to 20th	Day	17% 16% 8% 15% 9% 4 4 3 3 4 16%	1520
	21st to end	Day	17% 17% 7% 16% 10% 3 5% 4 4 4 14%	1520
December	1st to 10th	Day	8% 14% 7% 16% 14% 5% 6% 5% 4 6% 14%	1463
	11th to 20th	Day	12% 14% 8% 12% 8% 4 6% 6% 5% 6% 19%	1827
	21st to end	Day	20% 21% 8% 10% 9% 3 3 3 3 3 15%	2614
January	1st to 10th	Night	7% 16% 6% 12% 12% 5% 7% 6% 6% 6% 17%	4573
	11th to 20th	Night	6% 11% 6% 13% 14% 8% 10% 9% 5% 5% 12%	4440
	21st to end	Night	9% 16% 12% 17% 8% 4 5% 6% 6% 5% 13%	4884
February	1st to 10th	Night	8% 11% 5% 10% 9% 6% 9% 8% 7% 7% 21%	2466
	11th to 20th	Night	9% 11% 4 7% 8% 5% 8% 8% 7% 6% 27%	2273
	21st to end	Night	7% 13% 6% 12% 11% 6% 6% 5% 5% 5% 25%	1816
March	1st to 10th	Night	8% 11% 6% 9% 8% 5% 7% 6% 4 6% 30%	2149
	11th to 20th	Night	11% 13% 5% 8% 6% 3 4 4 5% 5% 35%	2033
	21st to end	Night	13% 11% 4 8% 6% 5% 5% 4 5% 6% 33%	2039
April	1st to 10th	Night	15% 11% 5% 9% 6% 3 5% 4 5% 6% 32%	1800
	11th to 20th	Night	16% 14% 4 7% 5% 2 4 5% 5% 7% 30%	1775
	21st to end	Night	16% 11% 4 7% 5% 2 4 5% 6% 7% 33%	1505
May	1st to 10th	Night	17% 12% 4 5% 5% 3 4 5% 5% 7% 33%	1440
	11th to 20th	Night	18% 7% 4 6% 5% 3 5% 4 5% 6% 37%	1416
	21st to end	Night	18% 6% 3 5% 5% 3 5% 4 5% 8% 37%	1551
June	1st to 10th	Night	18% 6% 3 5% 5% 3 6% 5% 7% 6% 35%	1419
	11th to 20th	Night	14% 5% 2 5% 5% 3 5% 5% 6% 9% 40%	1260
	21st to end	Night	14% 6% 3 6% 5% 3 4 5% 6% 8% 39%	1260
July	1st to 10th	Night	9% 4 1 4 4 4 4 6% 7% 9% 48%	1260
	11th to 20th	Night	13% 5% 3 4 4 3 4 5% 5% 9% 45%	1404
	21st to end	Night	9% 5% 2 5% 5% 3 5% 6% 5% 8% 47%	1575
August	1st to 10th	Night	11% 6% 2 5% 5% 3 5% 5% 6% 6% 47%	1432
	11th to 20th	Night	13% 5% 3 5% 4 3 4 4 7% 7% 45%	1494
	21st to end	Night	15% 7% 3 5% 5% 3 4 4 5% 8% 42%	1930
September	1st to 10th	Night	13% 7% 2 6% 6% 3 4 5% 4 7% 43%	1800
	11th to 20th	Night	19% 8% 2 4 4 3 3 5% 6% 8% 38%	1800
	21st to end	Night	23% 10% 3 6% 5% 2 3 3 5% 5% 34%	2021
October	1st to 10th	Night	19% 14% 3 7% 5% 3 3 5% 4 5% 31%	2160
	11th to 20th	Night	19% 16% 5% 6% 5% 3 4 4 4 6% 27%	2183
	21st to end	Night	20% 17% 5% 10% 6% 3 4 3 4 7% 21%	2574
November	1st to 10th	Night	17% 16% 7% 10% 7% 4 4 5% 5% 6% 21%	2506
	11th to 20th	Night	17% 15% 7% 14% 9% 5% 5% 4 3 5% 17%	2660
	21st to end	Night	14% 18% 8% 15% 9% 4 5% 4 4 5% 15%	2660
December	1st to 10th	Night	10% 13% 7% 16% 12% 5% 7% 5% 5% 5% 15%	2701
	11th to 20th	Night	12% 14% 6% 12% 10% 5% 6% 6% 6% 7% 16%	3355
	21st to end	Night	20% 20% 7% 11% 9% 3 4 4 3 4 14%	5043

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	70% 5% 7% 12% 6%	2374
	11th to 20th	Day	64% 4 9% 19% 3	2530
	21st to end	Day	76% 4 6% 9% 5%	2783
February	1st to 10th	Day	58% 5% 9% 17% 9% 1	1587
	11th to 20th	Day	54% 5% 10% 20% 9% 1	1583
	21st to end	Day	56% 5% 9% 16% 13% 1	1440
March	1st to 10th	Day	53% 6% 10% 17% 11% 3	1800
	11th to 20th	Day	54% 5% 10% 19% 11% 2	1941
	21st to end	Day	54% 5% 12% 15% 12% 2	2316
April	1st to 10th	Day	55% 5% 9% 18% 12% 2	2160
	11th to 20th	Day	54% 4 10% 21% 10% 2	2134
	21st to end	Day	52% 6% 8% 18% 13% 2	2451
May	1st to 10th	Day	56% 6% 9% 20% 8% 1	2520
	11th to 20th	Day	50% 7% 11% 21% 9% 1	2483
	21st to end	Day	47% 8% 12% 19% 13% 1	2725
June	1st to 10th	Day	48% 7% 11% 22% 11% 1	2536
	11th to 20th	Day	48% 6% 10% 22% 13% 1	2700
	21st to end	Day	46% 7% 13% 24% 9%	2700
July	1st to 10th	Day	39% 8% 12% 28% 11% 1	2626
	11th to 20th	Day	41% 8% 13% 28% 9%	2477
	21st to end	Day	41% 8% 16% 27% 8% 1	2591
August	1st to 10th	Day	42% 10% 17% 25% 5% 1	2492
	11th to 20th	Day	40% 8% 17% 26% 9%	2404
	21st to end	Day	42% 8% 15% 25% 9% 1	2426
September	1st to 10th	Day	46% 6% 13% 26% 9%	2160
	11th to 20th	Day	49% 7% 19% 20% 5%	2154
	21st to end	Day	55% 6% 14% 20% 6%	1924
October	1st to 10th	Day	60% 6% 11% 19% 4	1800
	11th to 20th	Day	65% 5% 10% 16% 3 1	1776
	21st to end	Day	69% 6% 8% 14% 4	1782
November	1st to 10th	Day	65% 6% 12% 11% 5% 1	1569
	11th to 20th	Day	74% 5% 8% 9% 4	1520
	21st to end	Day	75% 6% 8% 7% 4	1520
December	1st to 10th	Day	71% 5% 9% 10% 4 1	1463
	11th to 20th	Day	64% 6% 8% 13% 6% 2	1828
	21st to end	Day	76% 3 4 12% 4 1	2614
January	1st to 10th	Night	66% 6% 10% 14% 4	4573
	11th to 20th	Night	72% 6% 9% 11% 3	4440
	21st to end	Night	72% 5% 8% 10% 5%	4884
February	1st to 10th	Night	59% 5% 9% 16% 10% 1	2466
	11th to 20th	Night	54% 5% 13% 19% 9%	2274
	21st to end	Night	61% 5% 8% 15% 10% 1	1816
March	1st to 10th	Night	55% 6% 10% 17% 10% 2	2160
	11th to 20th	Night	51% 5% 11% 19% 12% 2	2034
	21st to end	Night	52% 5% 11% 19% 10% 3	2039
April	1st to 10th	Night	52% 6% 8% 21% 13% 1	1800
	11th to 20th	Night	52% 5% 11% 19% 11% 2	1775
	21st to end	Night	50% 6% 10% 19% 14% 2	1505
May	1st to 10th	Night	51% 6% 12% 20% 12%	1440
	11th to 20th	Night	47% 6% 11% 24% 10% 2	1417
	21st to end	Night	46% 7% 11% 22% 12% 2	1552
June	1st to 10th	Night	46% 7% 12% 23% 11% 1	1419
	11th to 20th	Night	39% 8% 13% 23% 15% 1	1260
	21st to end	Night	42% 8% 17% 22% 10% 1	1260
July	1st to 10th	Night	30% 8% 14% 36% 11%	1225
	11th to 20th	Night	34% 7% 16% 33% 10%	1358
	21st to end	Night	35% 7% 17% 29% 11% 1	1487
August	1st to 10th	Night	35% 9% 17% 31% 7% 2	1423
	11th to 20th	Night	36% 9% 17% 29% 9%	1494
	21st to end	Night	39% 8% 17% 26% 10% 1	1930
September	1st to 10th	Night	40% 7% 15% 26% 10% 1	1800
	11th to 20th	Night	44% 8% 19% 25% 4	1800
	21st to end	Night	53% 6% 13% 24% 4	2021
October	1st to 10th	Night	55% 6% 13% 20% 5%	2160
	11th to 20th	Night	57% 7% 13% 19% 3	2183
	21st to end	Night	64% 6% 14% 12% 4	2574
November	1st to 10th	Night	65% 7% 11% 13% 5%	2506
	11th to 20th	Night	72% 5% 9% 10% 3	2660
	21st to end	Night	72% 5% 10% 10% 4	2660
December	1st to 10th	Night	70% 7% 8% 11% 3	2701
	11th to 20th	Night	64% 7% 10% 14% 4	3353
	21st to end	Night	75% 3 5% 13% 3	5043

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	17% 14% 41% 23% 5%	270
	11th to 20th	Day	13% 14% 39% 28% 7%	270
	21st to end	Day	14% 14% 45% 19% 6% 1	297
February	1st to 10th	Day	15% 18% 44% 17% 4 1	252
	11th to 20th	Day	15% 24% 40% 15% 5% 2	240
	21st to end	Day	13% 29% 40% 14% 4	198
March	1st to 10th	Day	12% 20% 42% 20% 6%	240
	11th to 20th	Day	16% 24% 38% 15% 6% 1	240
	21st to end	Day	18% 17% 34% 21% 6% 3	402
April	1st to 10th	Day	20% 18% 34% 18% 9% 1	420
	11th to 20th	Day	26% 15% 27% 20% 10% 1	412
	21st to end	Day	22% 16% 32% 20% 8% 2	565
May	1st to 10th	Day	24% 16% 33% 20% 5% 2	603
	11th to 20th	Day	21% 15% 33% 20% 8% 3	625
	21st to end	Day	23% 14% 32% 22% 7% 1	679
June	1st to 10th	Day	22% 14% 31% 22% 8% 3	630
	11th to 20th	Day	18% 19% 35% 18% 9% 1	630
	21st to end	Day	19% 12% 31% 25% 9% 3	630
July	1st to 10th	Day	13% 11% 37% 25% 11% 4	621
	11th to 20th	Day	17% 15% 31% 23% 11% 3	618
	21st to end	Day	11% 12% 33% 27% 10% 5%	684
August	1st to 10th	Day	15% 11% 34% 27% 10% 3	626
	11th to 20th	Day	17% 10% 27% 29% 14% 4	615
	21st to end	Day	21% 12% 28% 26% 12% 2	545
September	1st to 10th	Day	17% 11% 32% 25% 12% 2	450
	11th to 20th	Day	28% 12% 30% 20% 8% 2	450
	21st to end	Day	29% 14% 27% 21% 8% 1	394
October	1st to 10th	Day	27% 19% 29% 16% 7% 3	270
	11th to 20th	Day	25% 23% 29% 19% 3 1	270
	21st to end	Day	36% 19% 34% 10% 1	297
November	1st to 10th	Day	26% 19% 35% 17% 4	270
	11th to 20th	Day	28% 24% 33% 10% 3 1	270
	21st to end	Day	26% 23% 34% 13% 4	270
December	1st to 10th	Day	21% 16% 39% 20% 3 1	243
	11th to 20th	Day	21% 17% 43% 14% 5%	229
	21st to end	Day	20% 18% 34% 22% 3 3	297
January	1st to 10th	Night	15% 14% 44% 21% 6%	950
	11th to 20th	Night	16% 14% 42% 23% 5% 1	950
	21st to end	Night	15% 14% 42% 24% 6%	1045
February	1st to 10th	Night	13% 15% 40% 24% 8%	923
	11th to 20th	Night	14% 15% 37% 22% 10% 1	879
	21st to end	Night	13% 14% 38% 26% 8% 1	632
March	1st to 10th	Night	13% 15% 37% 25% 10%	720
	11th to 20th	Night	18% 16% 36% 20% 9% 1	594
	21st to end	Night	21% 10% 29% 26% 11% 3	594
April	1st to 10th	Night	20% 11% 34% 27% 8% 1	540
	11th to 20th	Night	22% 10% 31% 29% 8% 1	533
	21st to end	Night	19% 8% 30% 32% 10% 1	540
May	1st to 10th	Night	23% 12% 31% 26% 7% 1	540
	11th to 20th	Night	20% 14% 29% 27% 8% 2	531
	21st to end	Night	21% 8% 30% 32% 9%	584
June	1st to 10th	Night	21% 7% 29% 31% 11%	540
	11th to 20th	Night	15% 11% 34% 31% 9%	540
	21st to end	Night	18% 7% 27% 33% 14% 1	540
July	1st to 10th	Night	10% 7% 32% 36% 15% 1	525
	11th to 20th	Night	14% 9% 31% 29% 17% 1	522
	21st to end	Night	10% 6% 27% 39% 17% 1	591
August	1st to 10th	Night	14% 5% 32% 32% 15% 1	537
	11th to 20th	Night	15% 7% 23% 32% 21% 3	534
	21st to end	Night	18% 9% 28% 29% 16%	594
September	1st to 10th	Night	16% 8% 27% 32% 16% 1	540
	11th to 20th	Night	24% 9% 31% 25% 11% 1	540
	21st to end	Night	27% 10% 28% 26% 8% 1	707
October	1st to 10th	Night	28% 11% 29% 22% 8% 1	720
	11th to 20th	Night	29% 12% 32% 20% 6%	720
	21st to end	Night	28% 14% 31% 20% 7%	792
November	1st to 10th	Night	25% 14% 33% 21% 6% 1	840
	11th to 20th	Night	25% 15% 33% 19% 6% 1	950
	21st to end	Night	25% 18% 35% 18% 3	950
December	1st to 10th	Night	17% 15% 40% 20% 7% 1	950
	11th to 20th	Night	20% 17% 37% 17% 7% 1	950
	21st to end	Night	24% 14% 31% 23% 7% 1	1045

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