Lavell Sky observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lavell Sky observatory clear sky chart from 2005-11-06 to 2024-01-15.

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% 9% 4 7% 6% 4 5% 5% 5% 7% 34%	74936
	Night	13% 10% 4 7% 6% 3 5% 5% 5% 7% 34%	74835
Transparency	Day	50% 4 13% 23% 10% 1	74632
	Night	50% 4 12% 22% 10% 1	74673
Seeing	Day	17% 10% 31% 26% 13% 4	14951
	Night	17% 7% 32% 32% 11% 1	24991

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	11% 11% 7% 10% 8% 4 5% 5% 6% 7% 25%	1328
	11th to 20th	Day	10% 16% 8% 13% 8% 5% 6% 5% 5% 7% 18%	1467
	21st to end	Day	10% 11% 6% 13% 12% 5% 8% 6% 6% 8% 15%	1683
February	1st to 10th	Day	8% 12% 7% 11% 7% 3 6% 7% 6% 7% 28%	1620
	11th to 20th	Day	8% 11% 5% 8% 8% 4 4 6% 6% 8% 32%	1574
	21st to end	Day	10% 11% 6% 10% 8% 4 5% 5% 5% 7% 31%	1375
March	1st to 10th	Day	11% 10% 5% 8% 7% 4 5% 4 5% 7% 33%	1883
	11th to 20th	Day	12% 9% 5% 9% 7% 4 3 4 6% 6% 35%	1980
	21st to end	Day	17% 11% 5% 7% 6% 4 4 4 4 5% 33%	2228
April	1st to 10th	Day	16% 12% 4 7% 7% 4 5% 4 5% 5% 31%	2160
	11th to 20th	Day	18% 11% 4 7% 5% 2 6% 5% 5% 7% 29%	2171
	21st to end	Day	21% 9% 4 6% 6% 3 5% 4 5% 5% 32%	2347
May	1st to 10th	Day	19% 9% 3 6% 6% 3 4 4 4 5% 36%	2520
	11th to 20th	Day	16% 6% 4 6% 5% 3 6% 5% 6% 7% 37%	2479
	21st to end	Day	17% 7% 2 6% 6% 3 4 5% 6% 9% 36%	2725
June	1st to 10th	Day	13% 6% 3 5% 5% 3 5% 5% 6% 9% 41%	2573
	11th to 20th	Day	16% 5% 3 5% 6% 4 5% 4 6% 8% 37%	2700
	21st to end	Day	14% 6% 3 6% 6% 3 5% 6% 7% 9% 35%	2700
July	1st to 10th	Day	8% 4 2 4 5% 3 5% 5% 6% 9% 49%	2700
	11th to 20th	Day	11% 5% 2 6% 5% 4 4 5% 6% 8% 43%	2602
	21st to end	Day	8% 4 2 5% 5% 3 6% 5% 7% 9% 46%	2743
August	1st to 10th	Day	8% 6% 3 6% 6% 4 4 5% 6% 9% 44%	2428
	11th to 20th	Day	13% 6% 2 5% 4 3 4 5% 6% 8% 42%	2301
	21st to end	Day	12% 5% 2 5% 4 3 5% 5% 6% 7% 46%	2484
September	1st to 10th	Day	11% 7% 2 6% 5% 3 5% 4 5% 10% 41%	2160
	11th to 20th	Day	16% 6% 3 6% 5% 3 5% 5% 4 8% 40%	2160
	21st to end	Day	18% 8% 3 6% 4 3 3 4 5% 7% 39%	1878
October	1st to 10th	Day	19% 9% 3 6% 5% 3 5% 5% 5% 6% 34%	1800
	11th to 20th	Day	18% 13% 4 6% 5% 3 5% 5% 5% 7% 29%	1800
	21st to end	Day	20% 14% 5% 7% 6% 3 4 4 5% 6% 27%	1883
November	1st to 10th	Day	13% 11% 7% 9% 7% 4 5% 5% 6% 6% 29%	1515
	11th to 20th	Day	13% 16% 8% 11% 7% 4 5% 4 4 5% 22%	1520
	21st to end	Day	16% 12% 7% 8% 8% 4 6% 5% 5% 6% 24%	1520
December	1st to 10th	Day	12% 12% 7% 11% 12% 6% 6% 6% 6% 6% 17%	1520
	11th to 20th	Day	12% 16% 7% 12% 8% 5% 5% 6% 5% 4 19%	1914
	21st to end	Day	23% 20% 7% 9% 9% 3 3 2 3 5% 15%	2495
January	1st to 10th	Night	9% 10% 5% 10% 9% 4 6% 7% 7% 8% 26%	2837
	11th to 20th	Night	11% 11% 6% 11% 9% 4 6% 5% 5% 7% 24%	2583
	21st to end	Night	11% 14% 7% 11% 7% 4 6% 5% 6% 7% 22%	2671
February	1st to 10th	Night	7% 12% 5% 8% 7% 4 7% 6% 5% 8% 31%	2340
	11th to 20th	Night	8% 9% 5% 8% 7% 4 7% 5% 5% 7% 36%	2273
	21st to end	Night	10% 12% 5% 7% 6% 4 5% 6% 6% 7% 31%	1880
March	1st to 10th	Night	11% 10% 6% 8% 6% 4 5% 5% 5% 6% 34%	2078
	11th to 20th	Night	12% 10% 4 7% 5% 3 4 5% 5% 6% 40%	1979
	21st to end	Night	15% 10% 4 8% 6% 3 4 5% 5% 6% 34%	2127
April	1st to 10th	Night	17% 10% 4 8% 6% 3 5% 3 5% 5% 34%	1800
	11th to 20th	Night	17% 10% 5% 6% 6% 4 5% 4 4 6% 34%	1737
	21st to end	Night	20% 10% 4 8% 5% 3 4 4 5% 6% 32%	1612
May	1st to 10th	Night	17% 9% 3 5% 5% 2 4 4 5% 7% 38%	1440
	11th to 20th	Night	16% 5% 3 5% 4 3 5% 5% 6% 9% 40%	1416
	21st to end	Night	15% 5% 2 5% 5% 3 5% 5% 5% 7% 42%	1551
June	1st to 10th	Night	13% 5% 3 5% 5% 3 5% 5% 7% 8% 41%	1382
	11th to 20th	Night	12% 5% 2 5% 4 3 5% 4 7% 7% 46%	1260
	21st to end	Night	8% 6% 3 5% 5% 3 4 5% 6% 9% 45%	1260
July	1st to 10th	Night	5% 3 1 3 3 3 4 5% 5% 12% 57%	1260
	11th to 20th	Night	8% 4 2 4 4 3 4 5% 5% 10% 53%	1354
	21st to end	Night	6% 3 1 3 4 2 4 4 7% 9% 56%	1575
August	1st to 10th	Night	7% 4 2 4 4 3 4 4 5% 8% 54%	1509
	11th to 20th	Night	12% 5% 2 4 4 2 4 4 6% 7% 52%	1600
	21st to end	Night	13% 5% 2 4 3 2 3 4 5% 9% 49%	1872
September	1st to 10th	Night	10% 6% 2 4 5% 3 5% 4 6% 8% 48%	1800
	11th to 20th	Night	11% 5% 3 4 4 3 4 5% 4 8% 50%	1800
	21st to end	Night	17% 7% 3 5% 5% 3 4 4 5% 7% 41%	2059
October	1st to 10th	Night	15% 8% 3 6% 5% 3 4 4 5% 6% 39%	2160
	11th to 20th	Night	16% 12% 4 6% 6% 3 4 4 5% 7% 33%	2160
	21st to end	Night	18% 10% 3 9% 6% 4 5% 5% 4 6% 28%	2471
November	1st to 10th	Night	13% 11% 4 7% 5% 3 5% 4 5% 7% 34%	2559
	11th to 20th	Night	15% 12% 7% 9% 7% 4 5% 5% 5% 7% 26%	2660
	21st to end	Night	13% 9% 5% 9% 8% 4 5% 5% 6% 7% 29%	2660
December	1st to 10th	Night	10% 12% 7% 12% 9% 4 7% 6% 5% 8% 20%	2660
	11th to 20th	Night	12% 14% 6% 11% 8% 5% 7% 5% 5% 6% 21%	3283
	21st to end	Night	24% 19% 7% 9% 6% 2 4 3 4 5% 16%	5167

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% 4 9% 19% 8%	1329
	11th to 20th	Day	68% 3 8% 14% 8%	1467
	21st to end	Day	66% 4 9% 14% 8%	1683
February	1st to 10th	Day	55% 3 11% 18% 11% 2	1620
	11th to 20th	Day	51% 4 13% 19% 11% 2	1583
	21st to end	Day	54% 3 11% 17% 12% 1	1375
March	1st to 10th	Day	51% 4 15% 22% 8% 1	1885
	11th to 20th	Day	51% 4 12% 21% 11% 1	1980
	21st to end	Day	54% 4 11% 21% 8% 1	2228
April	1st to 10th	Day	56% 2 8% 18% 13% 2	2160
	11th to 20th	Day	54% 4 12% 19% 10% 1	2171
	21st to end	Day	54% 3 9% 22% 11% 1	2347
May	1st to 10th	Day	52% 3 10% 23% 10% 2	2520
	11th to 20th	Day	47% 4 12% 25% 10% 2	2483
	21st to end	Day	46% 5% 12% 24% 12% 1	2725
June	1st to 10th	Day	41% 3 17% 29% 9% 1	2573
	11th to 20th	Day	45% 4 14% 24% 13%	2700
	21st to end	Day	45% 5% 15% 27% 8% 1	2700
July	1st to 10th	Day	31% 4 14% 35% 14% 1	2626
	11th to 20th	Day	39% 4 15% 28% 13% 1	2522
	21st to end	Day	35% 4 16% 31% 13% 1	2591
August	1st to 10th	Day	38% 4 14% 31% 10% 2	2413
	11th to 20th	Day	40% 3 19% 27% 10%	2301
	21st to end	Day	39% 4 14% 30% 12% 1	2484
September	1st to 10th	Day	41% 3 16% 30% 10%	2160
	11th to 20th	Day	44% 3 18% 27% 7%	2160
	21st to end	Day	47% 4 14% 29% 6%	1878
October	1st to 10th	Day	51% 3 15% 24% 7%	1800
	11th to 20th	Day	56% 4 12% 20% 8% 1	1800
	21st to end	Day	60% 3 12% 19% 6%	1883
November	1st to 10th	Day	56% 4 11% 20% 9% 1	1515
	11th to 20th	Day	66% 3 11% 13% 6% 1	1520
	21st to end	Day	62% 3 13% 16% 5% 1	1520
December	1st to 10th	Day	66% 4 11% 15% 3	1520
	11th to 20th	Day	68% 3 8% 16% 4 1	1915
	21st to end	Day	77% 2 3 11% 7%	2495
January	1st to 10th	Night	56% 4 10% 20% 10%	2837
	11th to 20th	Night	61% 5% 11% 17% 7% 1	2583
	21st to end	Night	63% 4 7% 17% 9%	2671
February	1st to 10th	Night	53% 4 10% 19% 13% 1	2340
	11th to 20th	Night	49% 4 11% 20% 15% 2	2274
	21st to end	Night	52% 3 10% 22% 11% 1	1880
March	1st to 10th	Night	52% 4 11% 19% 13% 1	2089
	11th to 20th	Night	46% 3 13% 22% 14% 1	1980
	21st to end	Night	51% 4 13% 20% 10% 2	2127
April	1st to 10th	Night	54% 3 8% 19% 15% 1	1800
	11th to 20th	Night	52% 3 9% 23% 13% 1	1737
	21st to end	Night	55% 2 6% 24% 12% 1	1612
May	1st to 10th	Night	47% 4 12% 25% 12% 1	1440
	11th to 20th	Night	42% 4 12% 27% 13% 3	1417
	21st to end	Night	42% 5% 12% 27% 12% 2	1552
June	1st to 10th	Night	40% 4 18% 26% 10% 2	1382
	11th to 20th	Night	37% 4 14% 27% 17% 2	1260
	21st to end	Night	35% 5% 18% 29% 11% 1	1260
July	1st to 10th	Night	22% 4 19% 37% 17% 1	1225
	11th to 20th	Night	30% 4 16% 31% 16% 2	1311
	21st to end	Night	25% 4 19% 35% 15% 2	1487
August	1st to 10th	Night	29% 4 17% 35% 12% 4	1500
	11th to 20th	Night	33% 4 19% 31% 12% 1	1600
	21st to end	Night	34% 3 17% 28% 17% 1	1872
September	1st to 10th	Night	35% 4 17% 30% 13% 1	1800
	11th to 20th	Night	34% 5% 21% 31% 10%	1800
	21st to end	Night	45% 3 14% 31% 7%	2059
October	1st to 10th	Night	47% 3 14% 27% 8% 1	2160
	11th to 20th	Night	51% 3 13% 25% 7%	2160
	21st to end	Night	58% 3 12% 19% 7%	2471
November	1st to 10th	Night	51% 3 12% 25% 8% 1	2559
	11th to 20th	Night	60% 3 14% 16% 8%	2660
	21st to end	Night	55% 4 17% 17% 6% 1	2660
December	1st to 10th	Night	64% 3 12% 17% 3	2660
	11th to 20th	Night	64% 3 10% 17% 5% 1	3281
	21st to end	Night	74% 2 6% 12% 6%	5167

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% 11% 31% 30% 12% 1	270
	11th to 20th	Day	17% 10% 36% 29% 8% 2	252
	21st to end	Day	13% 9% 36% 28% 14% 1	264
February	1st to 10th	Day	13% 12% 50% 19% 7%	240
	11th to 20th	Day	18% 15% 38% 19% 7% 4	240
	21st to end	Day	17% 11% 42% 24% 5% 1	198
March	1st to 10th	Day	13% 13% 38% 22% 12% 2	240
	11th to 20th	Day	16% 8% 40% 23% 9% 4	240
	21st to end	Day	22% 11% 32% 22% 10% 2	314
April	1st to 10th	Day	24% 13% 31% 23% 9% 1	420
	11th to 20th	Day	26% 9% 27% 26% 11% 1	449
	21st to end	Day	24% 10% 31% 23% 12% 1	600
May	1st to 10th	Day	22% 14% 29% 25% 8% 3	603
	11th to 20th	Day	19% 12% 28% 26% 12% 4	625
	21st to end	Day	20% 7% 29% 28% 13% 3	679
June	1st to 10th	Day	14% 8% 30% 30% 12% 6%	630
	11th to 20th	Day	16% 10% 36% 24% 10% 3	630
	21st to end	Day	15% 7% 33% 22% 15% 7%	630
July	1st to 10th	Day	9% 6% 24% 31% 19% 10%	621
	11th to 20th	Day	12% 8% 28% 27% 18% 7%	618
	21st to end	Day	9% 5% 27% 30% 21% 7%	684
August	1st to 10th	Day	9% 6% 24% 33% 21% 6%	626
	11th to 20th	Day	16% 5% 21% 32% 21% 6%	615
	21st to end	Day	16% 7% 24% 27% 21% 4	603
September	1st to 10th	Day	11% 7% 30% 31% 19% 2	450
	11th to 20th	Day	17% 7% 30% 26% 15% 4	450
	21st to end	Day	24% 12% 33% 17% 11% 4	276
October	1st to 10th	Day	22% 11% 31% 18% 12% 5%	270
	11th to 20th	Day	19% 16% 37% 23% 3 1	270
	21st to end	Day	28% 16% 34% 15% 6% 1	297
November	1st to 10th	Day	17% 13% 35% 26% 9%	270
	11th to 20th	Day	22% 16% 38% 19% 5%	270
	21st to end	Day	23% 16% 31% 24% 6%	270
December	1st to 10th	Day	16% 14% 37% 24% 8% 1	270
	11th to 20th	Day	20% 18% 33% 25% 5%	270
	21st to end	Day	24% 12% 34% 23% 4 2	297
January	1st to 10th	Night	14% 9% 34% 31% 11% 1	950
	11th to 20th	Night	18% 7% 37% 29% 8% 1	923
	21st to end	Night	17% 8% 36% 30% 8%	990
February	1st to 10th	Night	13% 8% 37% 32% 9% 1	900
	11th to 20th	Night	14% 9% 38% 28% 9% 2	879
	21st to end	Night	16% 7% 35% 29% 10% 2	696
March	1st to 10th	Night	16% 10% 34% 30% 10%	649
	11th to 20th	Night	16% 7% 38% 30% 8% 1	540
	21st to end	Night	19% 8% 30% 28% 13% 3	594
April	1st to 10th	Night	21% 8% 35% 29% 6% 1	540
	11th to 20th	Night	21% 8% 33% 29% 8% 1	533
	21st to end	Night	24% 9% 26% 30% 11% 1	540
May	1st to 10th	Night	20% 9% 33% 31% 7% 1	540
	11th to 20th	Night	19% 5% 31% 32% 11% 2	531
	21st to end	Night	17% 6% 28% 35% 13% 1	584
June	1st to 10th	Night	15% 4 27% 40% 13% 1	540
	11th to 20th	Night	13% 4 32% 41% 9%	540
	21st to end	Night	12% 5% 23% 39% 19% 1	540
July	1st to 10th	Night	6% 2 24% 44% 22% 1	525
	11th to 20th	Night	10% 3 28% 38% 20% 1	522
	21st to end	Night	6% 2 24% 47% 20% 2	591
August	1st to 10th	Night	8% 2 23% 44% 22% 1	537
	11th to 20th	Night	12% 3 21% 38% 22% 3	534
	21st to end	Night	14% 6% 22% 39% 18% 2	594
September	1st to 10th	Night	12% 4 24% 44% 15% 2	540
	11th to 20th	Night	13% 4 29% 35% 18% 1	540
	21st to end	Night	19% 9% 32% 27% 12% 2	629
October	1st to 10th	Night	19% 8% 31% 29% 12% 1	720
	11th to 20th	Night	21% 10% 32% 29% 7% 1	720
	21st to end	Night	23% 11% 33% 27% 6%	792
November	1st to 10th	Night	18% 8% 34% 31% 8% 1	893
	11th to 20th	Night	20% 10% 33% 27% 8% 1	950
	21st to end	Night	17% 12% 37% 27% 6%	950
December	1st to 10th	Night	17% 10% 34% 29% 10% 1	950
	11th to 20th	Night	21% 8% 36% 25% 9% 1	950
	21st to end	Night	24% 8% 34% 26% 7% 1	1045

Page generated at 2024-01-12 06:31:48. Version ac07

Copyright 2024 Attilla Danko