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 2025-02-25.

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	14% 11% 4 10% 6% 5% 5% 4 5% 7% 30%	108928
	Night	13% 13% 5% 11% 6% 5% 5% 4 5% 6% 27%	109863
Transparency	Day	53% 6% 12% 20% 9% 1	112387
	Night	57% 5% 11% 19% 8% 1	114566
Seeing	Day	20% 16% 33% 21% 8% 2	16483
	Night	19% 12% 34% 25% 9% 1	26664

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% 11% 6% 18% 8% 8% 7% 5% 6% 6% 18%	3411
	11th to 20th	Day	5% 12% 6% 18% 8% 7% 7% 8% 10% 5% 13%	3589
	21st to end	Day	7% 14% 11% 23% 8% 6% 4 4 5% 4 13%	3982
February	1st to 10th	Day	7% 12% 6% 12% 8% 8% 8% 7% 7% 7% 19%	1728
	11th to 20th	Day	7% 12% 4 12% 8% 7% 5% 4 7% 6% 27%	1754
	21st to end	Day	6% 12% 7% 15% 8% 6% 4 4 5% 6% 27%	1565
March	1st to 10th	Day	10% 12% 4 9% 5% 4 4 3 4 6% 39%	3118
	11th to 20th	Day	7% 13% 8% 14% 5% 6% 5% 3 4 5% 31%	3413
	21st to end	Day	16% 16% 5% 10% 5% 4 4 2 4 5% 28%	4063
April	1st to 10th	Day	13% 15% 4 10% 6% 5% 4 4 4 5% 30%	2280
	11th to 20th	Day	17% 15% 3 9% 4 4 4 3 5% 6% 31%	2254
	21st to end	Day	17% 12% 5% 8% 5% 4 4 4 5% 5% 32%	2589
May	1st to 10th	Day	17% 12% 3 7% 5% 4 5% 4 4 7% 33%	4428
	11th to 20th	Day	15% 9% 3 7% 6% 5% 5% 4 6% 7% 34%	4399
	21st to end	Day	20% 8% 3 6% 5% 4 4 3 5% 6% 36%	4837
June	1st to 10th	Day	20% 7% 2 7% 4 5% 4 4 5% 8% 34%	2677
	11th to 20th	Day	17% 6% 3 8% 6% 5% 5% 4 5% 7% 34%	2850
	21st to end	Day	19% 6% 2 7% 5% 5% 4 4 5% 8% 35%	2850
July	1st to 10th	Day	11% 6% 2 7% 6% 6% 6% 5% 8% 9% 34%	4750
	11th to 20th	Day	12% 5% 2 5% 4 4 4 4 6% 8% 45%	4487
	21st to end	Day	14% 7% 3 6% 5% 4 5% 4 6% 8% 40%	4814
August	1st to 10th	Day	16% 7% 3 8% 5% 5% 5% 5% 7% 8% 32%	4423
	11th to 20th	Day	12% 5% 1 5% 4 4 5% 3 6% 9% 45%	4211
	21st to end	Day	13% 7% 3 7% 4 4 5% 5% 6% 8% 39%	4258
September	1st to 10th	Day	15% 6% 3 8% 5% 5% 5% 4 5% 6% 38%	2280
	11th to 20th	Day	19% 10% 3 6% 4 3 4 3 6% 8% 33%	2273
	21st to end	Day	20% 11% 4 7% 4 4 4 3 5% 6% 31%	2030
October	1st to 10th	Day	19% 15% 3 8% 6% 4 5% 3 4 6% 27%	1900
	11th to 20th	Day	18% 21% 4 10% 5% 5% 4 3 5% 5% 21%	1874
	21st to end	Day	20% 21% 5% 10% 4 5% 3 2 4 4 22%	1881
November	1st to 10th	Day	16% 18% 5% 11% 6% 5% 4 3 4 6% 21%	1653
	11th to 20th	Day	16% 19% 7% 16% 7% 5% 4 2 3 5% 16%	1600
	21st to end	Day	17% 18% 7% 19% 8% 4 4 3 4 4 14%	1600
December	1st to 10th	Day	11% 17% 7% 22% 14% 5% 4 3 3 4 11%	2511
	11th to 20th	Day	8% 15% 7% 17% 6% 7% 6% 4 6% 5% 19%	2861
	21st to end	Day	16% 21% 7% 17% 6% 4 3 3 4 4 14%	3735
January	1st to 10th	Night	5% 15% 6% 16% 10% 7% 6% 4 5% 5% 19%	6545
	11th to 20th	Night	6% 11% 7% 18% 11% 9% 8% 7% 8% 4 11%	6316
	21st to end	Night	6% 15% 10% 19% 7% 6% 6% 4 6% 5% 14%	6996
February	1st to 10th	Night	8% 11% 5% 11% 8% 8% 9% 6% 7% 7% 20%	2670
	11th to 20th	Night	8% 11% 4 9% 7% 7% 9% 6% 7% 6% 26%	2533
	21st to end	Night	6% 13% 5% 14% 9% 7% 6% 4 5% 5% 24%	1984
March	1st to 10th	Night	12% 12% 4 9% 6% 5% 5% 4 5% 6% 34%	3722
	11th to 20th	Night	9% 16% 5% 13% 6% 6% 5% 3 5% 5% 27%	3575
	21st to end	Night	16% 15% 5% 10% 5% 6% 4 3 5% 5% 27%	3567
April	1st to 10th	Night	14% 13% 3 9% 5% 5% 4 3 5% 5% 32%	1900
	11th to 20th	Night	16% 14% 4 8% 4 4 4 4 5% 7% 30%	1875
	21st to end	Night	16% 12% 4 8% 5% 3 4 3 6% 6% 33%	1587
May	1st to 10th	Night	15% 11% 4 6% 4 4 4 4 6% 6% 37%	2523
	11th to 20th	Night	13% 8% 4 7% 5% 4 5% 4 5% 6% 38%	2506
	21st to end	Night	23% 6% 2 5% 3 3 4 3 5% 7% 40%	2750
June	1st to 10th	Night	18% 7% 2 6% 5% 5% 5% 4 7% 6% 34%	1497
	11th to 20th	Night	14% 5% 2 6% 5% 4 5% 5% 7% 9% 40%	1330
	21st to end	Night	14% 7% 3 7% 5% 3 4 5% 7% 8% 38%	1330
July	1st to 10th	Night	11% 7% 2 5% 4 3 5% 4 6% 9% 42%	2220
	11th to 20th	Night	10% 6% 2 5% 4 4 4 3 5% 8% 48%	2468
	21st to end	Night	12% 5% 2 5% 4 4 3 4 5% 9% 47%	2750
August	1st to 10th	Night	16% 5% 1 4 4 4 4 4 7% 7% 42%	2517
	11th to 20th	Night	12% 4 2 5% 4 4 5% 4 8% 8% 45%	2611
	21st to end	Night	17% 7% 2 5% 4 4 3 3 5% 7% 44%	3400
September	1st to 10th	Night	13% 7% 2 6% 5% 4 4 4 5% 7% 43%	1900
	11th to 20th	Night	19% 8% 2 5% 4 4 4 4 6% 8% 38%	1900
	21st to end	Night	22% 11% 3 7% 4 3 3 3 4 5% 35%	2134
October	1st to 10th	Night	19% 14% 3 8% 4 4 3 4 4 5% 32%	2280
	11th to 20th	Night	18% 17% 4 7% 4 4 4 3 4 6% 28%	2305
	21st to end	Night	20% 18% 5% 10% 5% 4 4 3 5% 6% 21%	2717
November	1st to 10th	Night	16% 18% 5% 10% 6% 5% 4 3 5% 6% 21%	2642
	11th to 20th	Night	17% 18% 6% 15% 7% 6% 5% 3 3 5% 17%	2800
	21st to end	Night	13% 19% 8% 18% 7% 5% 4 3 5% 4 15%	2800
December	1st to 10th	Night	11% 20% 9% 20% 11% 6% 4 3 3 3 10%	4663
	11th to 20th	Night	10% 14% 6% 16% 8% 7% 7% 5% 5% 5% 17%	5317
	21st to end	Night	18% 20% 7% 15% 7% 4 4 3 3 5% 14%	7233

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	66% 5% 6% 12% 10% 2	3412
	11th to 20th	Day	66% 3 7% 21% 2	3620
	21st to end	Day	73% 4 5% 11% 8%	3982
February	1st to 10th	Day	61% 5% 9% 16% 9% 1	1728
	11th to 20th	Day	55% 5% 10% 20% 9% 1	1763
	21st to end	Day	57% 5% 9% 15% 13% 1	1565
March	1st to 10th	Day	46% 5% 9% 21% 16% 2	3120
	11th to 20th	Day	55% 6% 9% 20% 9% 1	3413
	21st to end	Day	58% 4 9% 15% 13% 1	4063
April	1st to 10th	Day	55% 5% 8% 17% 13% 2	2280
	11th to 20th	Day	54% 4 10% 21% 10% 2	2254
	21st to end	Day	52% 6% 8% 19% 13% 2	2589
May	1st to 10th	Day	47% 7% 10% 20% 15% 1	4440
	11th to 20th	Day	45% 9% 12% 22% 12% 1	4403
	21st to end	Day	46% 8% 12% 16% 15% 2	4837
June	1st to 10th	Day	48% 7% 11% 22% 11% 1	2677
	11th to 20th	Day	48% 6% 10% 22% 13% 1	2850
	21st to end	Day	47% 7% 13% 24% 9%	2850
July	1st to 10th	Day	41% 10% 15% 26% 8% 1	4676
	11th to 20th	Day	34% 7% 20% 32% 7%	4410
	21st to end	Day	41% 6% 14% 31% 7% 1	4662
August	1st to 10th	Day	46% 8% 13% 26% 6%	4408
	11th to 20th	Day	35% 7% 21% 28% 8%	4253
	21st to end	Day	41% 7% 17% 29% 7%	4257
September	1st to 10th	Day	45% 6% 14% 26% 8%	2280
	11th to 20th	Day	48% 7% 20% 20% 5%	2273
	21st to end	Day	54% 6% 13% 20% 7% 1	2030
October	1st to 10th	Day	48% 5% 13% 26% 8%	3160
	11th to 20th	Day	56% 4 15% 20% 5%	3090
	21st to end	Day	63% 6% 14% 15% 2	3081
November	1st to 10th	Day	65% 6% 12% 11% 5% 1	1653
	11th to 20th	Day	73% 5% 9% 10% 4	1600
	21st to end	Day	76% 5% 8% 7% 4	1600
December	1st to 10th	Day	79% 3 9% 7% 2	2511
	11th to 20th	Day	65% 5% 7% 12% 10% 1	2862
	21st to end	Day	74% 3 4 13% 7%	3735
January	1st to 10th	Night	66% 4 8% 12% 9% 1	6545
	11th to 20th	Night	71% 5% 6% 13% 5%	6360
	21st to end	Night	70% 4 7% 13% 7%	6996
February	1st to 10th	Night	60% 6% 9% 16% 9% 1	2670
	11th to 20th	Night	54% 5% 13% 19% 9%	2534
	21st to end	Night	61% 5% 8% 16% 10% 1	1984
March	1st to 10th	Night	51% 6% 10% 17% 16% 2	3733
	11th to 20th	Night	58% 6% 9% 17% 8% 1	3576
	21st to end	Night	57% 5% 9% 16% 11% 2	3567
April	1st to 10th	Night	52% 6% 8% 21% 13% 1	1900
	11th to 20th	Night	52% 5% 11% 20% 11% 1	1875
	21st to end	Night	50% 6% 9% 20% 13% 2	1587
May	1st to 10th	Night	44% 7% 12% 24% 13%	2530
	11th to 20th	Night	44% 8% 12% 26% 8% 2	2507
	21st to end	Night	43% 6% 12% 23% 14% 1	2751
June	1st to 10th	Night	46% 7% 12% 23% 11% 1	1497
	11th to 20th	Night	39% 8% 14% 24% 15% 1	1330
	21st to end	Night	42% 8% 17% 23% 10% 1	1330
July	1st to 10th	Night	37% 8% 19% 26% 10%	2185
	11th to 20th	Night	32% 6% 18% 35% 9%	2422
	21st to end	Night	35% 6% 15% 36% 7% 1	2662
August	1st to 10th	Night	39% 7% 15% 31% 7% 1	2508
	11th to 20th	Night	33% 8% 19% 31% 9%	2635
	21st to end	Night	39% 6% 18% 29% 7%	3400
September	1st to 10th	Night	39% 7% 16% 27% 10% 1	1900
	11th to 20th	Night	44% 8% 20% 25% 4	1900
	21st to end	Night	51% 6% 13% 24% 5% 1	2134
October	1st to 10th	Night	43% 5% 11% 31% 10%	3800
	11th to 20th	Night	55% 4 12% 22% 7%	3828
	21st to end	Night	63% 5% 16% 13% 3	4467
November	1st to 10th	Night	64% 7% 11% 13% 5%	2642
	11th to 20th	Night	72% 5% 10% 10% 3	2800
	21st to end	Night	73% 5% 9% 9% 3	2800
December	1st to 10th	Night	80% 5% 7% 6% 2	4663
	11th to 20th	Night	67% 5% 9% 13% 5%	5315
	21st to end	Night	74% 3 5% 14% 5%	7233

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	15% 13% 42% 25% 5%	300
	11th to 20th	Day	13% 14% 37% 29% 6%	300
	21st to end	Day	15% 16% 45% 18% 6% 1	330
February	1st to 10th	Day	15% 20% 44% 16% 4 1	300
	11th to 20th	Day	13% 22% 41% 18% 5% 1	300
	21st to end	Day	14% 28% 41% 13% 3	237
March	1st to 10th	Day	15% 19% 41% 19% 6%	270
	11th to 20th	Day	15% 25% 39% 15% 6% 1	270
	21st to end	Day	20% 16% 35% 20% 6% 3	443
April	1st to 10th	Day	20% 18% 35% 18% 8% 1	460
	11th to 20th	Day	27% 17% 27% 19% 10% 1	452
	21st to end	Day	22% 16% 32% 20% 8% 2	614
May	1st to 10th	Day	24% 18% 32% 19% 5% 2	653
	11th to 20th	Day	22% 15% 33% 20% 8% 2	675
	21st to end	Day	23% 15% 32% 21% 7% 1	734
June	1st to 10th	Day	23% 14% 30% 22% 8% 3	680
	11th to 20th	Day	19% 19% 35% 17% 8% 1	680
	21st to end	Day	20% 13% 31% 24% 8% 3	680
July	1st to 10th	Day	13% 11% 35% 25% 11% 4	671
	11th to 20th	Day	16% 14% 31% 24% 12% 3	668
	21st to end	Day	12% 12% 32% 27% 11% 5%	739
August	1st to 10th	Day	16% 11% 34% 26% 10% 3	676
	11th to 20th	Day	17% 9% 26% 30% 15% 4	665
	21st to end	Day	20% 13% 28% 26% 12% 2	591
September	1st to 10th	Day	17% 12% 31% 26% 13% 2	490
	11th to 20th	Day	26% 12% 30% 21% 10% 2	490
	21st to end	Day	27% 14% 29% 20% 8% 1	430
October	1st to 10th	Day	28% 20% 28% 15% 7% 3	300
	11th to 20th	Day	25% 23% 31% 18% 3 1	300
	21st to end	Day	34% 21% 34% 9% 2	330
November	1st to 10th	Day	27% 18% 35% 16% 4	300
	11th to 20th	Day	29% 22% 34% 10% 3 1	300
	21st to end	Day	25% 23% 34% 14% 3	300
December	1st to 10th	Day	20% 15% 40% 21% 3 1	270
	11th to 20th	Day	20% 17% 43% 15% 5%	255
	21st to end	Day	19% 17% 35% 22% 4 3	330
January	1st to 10th	Night	15% 14% 43% 22% 6%	1000
	11th to 20th	Night	17% 13% 42% 23% 5% 1	1000
	21st to end	Night	15% 14% 42% 23% 6%	1100
February	1st to 10th	Night	14% 16% 40% 23% 7%	1000
	11th to 20th	Night	13% 15% 37% 23% 10% 1	979
	21st to end	Night	13% 14% 37% 27% 7% 1	692
March	1st to 10th	Night	13% 16% 37% 24% 9%	760
	11th to 20th	Night	18% 16% 36% 20% 9% 1	627
	21st to end	Night	21% 10% 29% 26% 11% 3	627
April	1st to 10th	Night	20% 11% 34% 27% 8% 1	570
	11th to 20th	Night	21% 12% 31% 28% 7% 1	563
	21st to end	Night	19% 9% 31% 31% 10% 1	570
May	1st to 10th	Night	22% 13% 31% 27% 7% 1	570
	11th to 20th	Night	20% 14% 31% 26% 8% 1	561
	21st to end	Night	21% 8% 30% 31% 9%	617
June	1st to 10th	Night	21% 8% 30% 30% 11%	570
	11th to 20th	Night	15% 11% 34% 31% 8%	570
	21st to end	Night	18% 7% 27% 33% 14% 1	570
July	1st to 10th	Night	10% 7% 31% 35% 16% 1	555
	11th to 20th	Night	14% 9% 30% 30% 17% 1	552
	21st to end	Night	10% 7% 27% 38% 18% 1	624
August	1st to 10th	Night	14% 5% 32% 33% 15% 1	567
	11th to 20th	Night	16% 6% 22% 31% 22% 3	564
	21st to end	Night	18% 9% 28% 29% 16%	627
September	1st to 10th	Night	16% 9% 26% 32% 16% 1	570
	11th to 20th	Night	23% 9% 32% 25% 11% 1	570
	21st to end	Night	27% 9% 28% 27% 8% 1	747
October	1st to 10th	Night	28% 12% 29% 22% 7% 1	760
	11th to 20th	Night	29% 12% 33% 20% 6%	760
	21st to end	Night	28% 14% 32% 20% 6%	836
November	1st to 10th	Night	26% 15% 32% 21% 5% 1	886
	11th to 20th	Night	26% 15% 33% 19% 6% 1	1000
	21st to end	Night	25% 18% 36% 19% 3	1000
December	1st to 10th	Night	18% 15% 39% 21% 7% 1	1000
	11th to 20th	Night	19% 17% 38% 18% 8% 1	1000
	21st to end	Night	24% 14% 31% 23% 7% 1	1100

Page generated at 2025-02-22 06:51:40. Version ac07

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