Red Top
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Red Top clear sky chart from 2005-11-06 to 2024-04-25.

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	12% 9% 4 7% 6% 4 5% 5% 5% 7% 35%	83635
	Night	12% 10% 4 8% 6% 3 5% 5% 5% 6% 36%	85461
Transparency	Day	47% 7% 13% 23% 10% 1	83328
	Night	47% 6% 13% 22% 11% 1	85289
Seeing	Day	15% 7% 28% 30% 16% 4	15235
	Night	16% 7% 31% 32% 12% 1	25331

By Month

Percentage Cloud Cover SE (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% 15% 7% 13% 9% 4 5% 4 4 7% 22%	2384
	11th to 20th	Day	6% 8% 5% 12% 12% 8% 10% 10% 7% 6% 17%	2530
	21st to end	Day	6% 17% 10% 15% 7% 4 5% 5% 5% 6% 20%	3078
February	1st to 10th	Day	8% 12% 5% 9% 7% 4 6% 5% 6% 7% 32%	1710
	11th to 20th	Day	8% 10% 4 8% 7% 4 5% 5% 5% 7% 37%	1664
	21st to end	Day	9% 11% 4 9% 7% 4 6% 5% 4 8% 33%	1448
March	1st to 10th	Day	11% 10% 4 8% 7% 4 4 5% 4 7% 36%	3357
	11th to 20th	Day	9% 8% 4 8% 7% 3 4 5% 6% 7% 39%	3480
	21st to end	Day	19% 13% 5% 9% 6% 4 4 5% 5% 6% 25%	3863
April	1st to 10th	Day	15% 11% 3 7% 6% 4 4 5% 5% 6% 33%	2280
	11th to 20th	Day	18% 11% 5% 7% 6% 3 4 4 5% 6% 31%	2299
	21st to end	Day	21% 9% 4 6% 5% 4 5% 4 4 6% 32%	2394
May	1st to 10th	Day	16% 9% 4 6% 6% 4 4 4 5% 6% 35%	2467
	11th to 20th	Day	16% 7% 3 6% 6% 3 4 5% 5% 8% 37%	2479
	21st to end	Day	15% 6% 2 6% 6% 3 5% 5% 5% 8% 38%	2725
June	1st to 10th	Day	10% 5% 3 5% 5% 3 5% 5% 6% 9% 45%	2520
	11th to 20th	Day	13% 6% 3 6% 5% 3 5% 5% 6% 8% 41%	2695
	21st to end	Day	8% 5% 2 6% 6% 3 6% 6% 8% 10% 39%	2700
July	1st to 10th	Day	6% 4 2 4 4 3 5% 5% 6% 10% 52%	2700
	11th to 20th	Day	8% 6% 2 4 4 4 5% 5% 7% 8% 48%	2556
	21st to end	Day	7% 3 2 4 5% 3 5% 5% 6% 10% 50%	2743
August	1st to 10th	Day	9% 4 3 5% 5% 4 5% 6% 6% 8% 45%	2346
	11th to 20th	Day	12% 6% 2 5% 4 3 4 5% 5% 8% 45%	2301
	21st to end	Day	11% 6% 2 4 4 2 4 4 5% 8% 49%	2489
September	1st to 10th	Day	9% 6% 3 5% 5% 3 4 5% 6% 10% 45%	2160
	11th to 20th	Day	12% 5% 3 6% 5% 3 5% 5% 5% 7% 45%	2130
	21st to end	Day	15% 8% 2 5% 4 4 4 5% 5% 8% 41%	1896
October	1st to 10th	Day	17% 10% 3 7% 5% 2 4 5% 5% 7% 36%	1800
	11th to 20th	Day	15% 13% 4 7% 5% 4 5% 3 4 6% 34%	1800
	21st to end	Day	19% 11% 4 8% 5% 3 4 5% 4 5% 32%	1936
November	1st to 10th	Day	13% 12% 6% 7% 7% 3 5% 4 4 5% 33%	1519
	11th to 20th	Day	12% 14% 8% 12% 9% 3 4 5% 4 5% 24%	1520
	21st to end	Day	14% 11% 5% 8% 6% 5% 5% 5% 5% 7% 29%	1520
December	1st to 10th	Day	10% 14% 6% 10% 10% 5% 6% 6% 5% 5% 23%	1520
	11th to 20th	Day	10% 14% 6% 12% 9% 4 6% 5% 4 5% 24%	1918
	21st to end	Day	22% 18% 7% 12% 8% 3 3 3 4 5% 16%	2708
January	1st to 10th	Night	12% 10% 4 13% 9% 3 5% 5% 5% 5% 29%	4528
	11th to 20th	Night	6% 10% 6% 11% 10% 6% 9% 7% 6% 7% 21%	4440
	21st to end	Night	9% 18% 9% 13% 6% 3 5% 5% 5% 5% 23%	4587
February	1st to 10th	Night	6% 9% 5% 9% 8% 4 6% 5% 5% 7% 36%	2470
	11th to 20th	Night	6% 10% 4 8% 7% 4 6% 4 6% 7% 37%	2403
	21st to end	Night	11% 10% 4 8% 7% 4 5% 5% 5% 8% 33%	2004
March	1st to 10th	Night	8% 8% 3 6% 6% 3 4 5% 4 6% 46%	3524
	11th to 20th	Night	8% 8% 3 9% 7% 4 5% 5% 5% 6% 39%	3480
	21st to end	Night	22% 13% 4 9% 6% 3 3 3 3 4 29%	3767
April	1st to 10th	Night	17% 10% 3 6% 5% 2 5% 4 5% 6% 36%	1900
	11th to 20th	Night	19% 11% 4 6% 4 3 3 3 4 5% 37%	1827
	21st to end	Night	18% 8% 3 7% 5% 3 4 4 4 7% 35%	1665
May	1st to 10th	Night	13% 10% 3 6% 6% 3 5% 4 4 7% 38%	1490
	11th to 20th	Night	14% 6% 3 6% 4 2 4 6% 6% 7% 41%	1416
	21st to end	Night	14% 5% 2 6% 5% 3 5% 5% 7% 8% 41%	1551
June	1st to 10th	Night	11% 4 2 5% 5% 3 5% 5% 7% 8% 44%	1440
	11th to 20th	Night	10% 6% 2 5% 6% 3 4 5% 5% 8% 46%	1260
	21st to end	Night	9% 6% 2 5% 5% 3 5% 5% 6% 6% 49%	1260
July	1st to 10th	Night	3 4 2 3 4 3 5% 5% 6% 8% 58%	1260
	11th to 20th	Night	8% 4 2 3 4 3 5% 4 5% 7% 55%	1402
	21st to end	Night	4 2 2 4 4 3 3 4 6% 9% 60%	1575
August	1st to 10th	Night	6% 4 2 4 4 3 4 5% 7% 9% 52%	1590
	11th to 20th	Night	13% 4 2 4 4 2 3 3 5% 7% 53%	1600
	21st to end	Night	10% 5% 2 4 4 3 3 4 5% 7% 53%	1867
September	1st to 10th	Night	8% 4 2 5% 4 3 4 5% 5% 8% 53%	1800
	11th to 20th	Night	8% 4 2 5% 4 3 4 4 5% 8% 51%	1826
	21st to end	Night	15% 5% 2 5% 4 2 4 4 5% 7% 47%	2045
October	1st to 10th	Night	15% 7% 3 5% 5% 2 4 4 5% 7% 43%	2160
	11th to 20th	Night	16% 10% 4 7% 4 4 3 4 5% 6% 37%	2160
	21st to end	Night	18% 10% 4 9% 5% 3 4 4 5% 6% 33%	2420
November	1st to 10th	Night	14% 10% 3 8% 6% 3 5% 5% 5% 6% 36%	2559
	11th to 20th	Night	15% 10% 5% 9% 6% 5% 6% 5% 5% 6% 29%	2660
	21st to end	Night	12% 8% 4 7% 7% 4 6% 5% 6% 7% 34%	2660
December	1st to 10th	Night	9% 12% 6% 12% 8% 4 5% 5% 6% 7% 24%	2660
	11th to 20th	Night	9% 15% 5% 11% 8% 4 6% 6% 5% 7% 23%	3279
	21st to end	Night	23% 18% 5% 8% 7% 3 4 3 4 5% 20%	4926

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	62% 4 11% 16% 5% 1	2385
	11th to 20th	Day	62% 8% 10% 15% 5%	2530
	21st to end	Day	62% 8% 10% 15% 6%	3078
February	1st to 10th	Day	51% 4 11% 23% 10% 2	1710
	11th to 20th	Day	46% 6% 13% 24% 10% 1	1673
	21st to end	Day	50% 5% 10% 20% 13% 1	1448
March	1st to 10th	Day	47% 7% 13% 22% 11% 1	3357
	11th to 20th	Day	41% 5% 14% 29% 11% 1	3480
	21st to end	Day	57% 8% 9% 21% 5% 1	3863
April	1st to 10th	Day	50% 5% 12% 18% 13% 2	2280
	11th to 20th	Day	53% 5% 10% 19% 12% 1	2299
	21st to end	Day	52% 6% 11% 20% 11%	2394
May	1st to 10th	Day	48% 7% 11% 23% 9% 2	2467
	11th to 20th	Day	44% 8% 14% 23% 10% 2	2483
	21st to end	Day	44% 8% 12% 25% 11% 1	2725
June	1st to 10th	Day	34% 8% 17% 31% 9% 1	2520
	11th to 20th	Day	40% 8% 15% 23% 14% 1	2695
	21st to end	Day	36% 10% 16% 27% 10% 1	2700
July	1st to 10th	Day	26% 8% 16% 33% 16% 1	2626
	11th to 20th	Day	32% 9% 14% 28% 15% 2	2479
	21st to end	Day	27% 9% 18% 29% 16% 1	2591
August	1st to 10th	Day	34% 9% 14% 31% 10% 3	2331
	11th to 20th	Day	36% 8% 16% 29% 11% 1	2301
	21st to end	Day	32% 7% 15% 30% 15% 1	2489
September	1st to 10th	Day	34% 7% 15% 34% 9%	2160
	11th to 20th	Day	37% 8% 18% 29% 8%	2130
	21st to end	Day	42% 7% 14% 30% 7%	1896
October	1st to 10th	Day	47% 7% 13% 24% 8% 1	1800
	11th to 20th	Day	52% 6% 11% 20% 10% 1	1800
	21st to end	Day	53% 5% 12% 21% 8%	1936
November	1st to 10th	Day	54% 5% 11% 19% 10% 1	1519
	11th to 20th	Day	62% 6% 14% 12% 5% 1	1520
	21st to end	Day	54% 8% 17% 15% 4 2	1520
December	1st to 10th	Day	63% 8% 12% 13% 4	1520
	11th to 20th	Day	61% 6% 13% 16% 5%	1915
	21st to end	Day	71% 4 9% 9% 6%	2708
January	1st to 10th	Night	54% 6% 13% 20% 7% 1	4528
	11th to 20th	Night	59% 7% 14% 14% 5% 1	4440
	21st to end	Night	61% 6% 10% 17% 5% 1	4587
February	1st to 10th	Night	47% 5% 12% 23% 12% 1	2470
	11th to 20th	Night	45% 5% 13% 24% 11% 2	2404
	21st to end	Night	48% 5% 13% 21% 12% 1	2004
March	1st to 10th	Night	39% 5% 15% 23% 17% 2	3524
	11th to 20th	Night	43% 4 13% 25% 15%	3480
	21st to end	Night	61% 4 8% 17% 9% 1	3767
April	1st to 10th	Night	48% 5% 10% 20% 16% 2	1900
	11th to 20th	Night	51% 3 8% 21% 15% 1	1827
	21st to end	Night	49% 6% 8% 21% 14% 2	1665
May	1st to 10th	Night	46% 6% 13% 22% 13% 1	1490
	11th to 20th	Night	40% 6% 14% 24% 14% 3	1417
	21st to end	Night	38% 8% 14% 24% 14% 2	1552
June	1st to 10th	Night	35% 8% 18% 27% 10% 3	1440
	11th to 20th	Night	36% 7% 15% 24% 17% 2	1260
	21st to end	Night	33% 8% 16% 28% 13% 2	1260
July	1st to 10th	Night	23% 7% 18% 34% 18% 1	1225
	11th to 20th	Night	28% 7% 14% 29% 18% 4	1357
	21st to end	Night	21% 6% 19% 33% 19% 3	1487
August	1st to 10th	Night	26% 8% 16% 34% 12% 4	1581
	11th to 20th	Night	31% 6% 16% 31% 15% 1	1600
	21st to end	Night	31% 6% 12% 31% 18% 2	1867
September	1st to 10th	Night	29% 7% 16% 34% 13% 1	1800
	11th to 20th	Night	31% 7% 16% 33% 12%	1826
	21st to end	Night	38% 6% 13% 33% 10%	2045
October	1st to 10th	Night	40% 6% 13% 28% 12% 1	2160
	11th to 20th	Night	46% 6% 13% 23% 11% 1	2160
	21st to end	Night	53% 6% 12% 20% 9% 1	2420
November	1st to 10th	Night	49% 6% 13% 22% 9% 2	2559
	11th to 20th	Night	56% 7% 14% 14% 9%	2660
	21st to end	Night	50% 9% 17% 18% 5% 1	2660
December	1st to 10th	Night	58% 7% 15% 14% 5% 1	2660
	11th to 20th	Night	59% 6% 12% 15% 6% 2	3281
	21st to end	Night	66% 5% 9% 14% 6%	4926

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	13% 10% 32% 29% 13% 3	270
	11th to 20th	Day	13% 9% 36% 36% 6%	270
	21st to end	Day	14% 6% 36% 26% 17% 1	297
February	1st to 10th	Day	14% 11% 39% 29% 6% 1	270
	11th to 20th	Day	14% 16% 36% 26% 6% 2	270
	21st to end	Day	16% 10% 39% 31% 5%	225
March	1st to 10th	Day	16% 12% 34% 29% 8% 2	270
	11th to 20th	Day	17% 7% 33% 28% 13% 2	270
	21st to end	Day	21% 12% 25% 26% 12% 3	321
April	1st to 10th	Day	20% 13% 28% 30% 7% 1	460
	11th to 20th	Day	26% 9% 25% 26% 13% 1	497
	21st to end	Day	23% 6% 31% 24% 13% 4	622
May	1st to 10th	Day	18% 6% 30% 31% 12% 2	603
	11th to 20th	Day	17% 8% 26% 30% 15% 4	625
	21st to end	Day	17% 5% 24% 27% 22% 4	679
June	1st to 10th	Day	10% 3 25% 30% 27% 4	630
	11th to 20th	Day	13% 4 29% 35% 17% 1	630
	21st to end	Day	11% 5% 24% 33% 19% 8%	630
July	1st to 10th	Day	9% 2 18% 33% 28% 11%	621
	11th to 20th	Day	9% 4 21% 35% 22% 9%	618
	21st to end	Day	8% 3 22% 35% 23% 9%	684
August	1st to 10th	Day	10% 3 19% 34% 27% 6%	626
	11th to 20th	Day	13% 4 19% 31% 27% 7%	615
	21st to end	Day	12% 7% 22% 31% 23% 5%	608
September	1st to 10th	Day	11% 5% 28% 31% 20% 4	450
	11th to 20th	Day	11% 5% 24% 34% 22% 3	420
	21st to end	Day	21% 10% 27% 24% 12% 6%	270
October	1st to 10th	Day	21% 4 29% 25% 14% 7%	270
	11th to 20th	Day	16% 17% 31% 27% 8%	270
	21st to end	Day	25% 9% 39% 19% 7%	297
November	1st to 10th	Day	20% 11% 29% 31% 9% 1	270
	11th to 20th	Day	17% 14% 40% 23% 5%	270
	21st to end	Day	20% 14% 38% 24% 4	270
December	1st to 10th	Day	14% 11% 39% 25% 11%	270
	11th to 20th	Day	17% 15% 36% 25% 7%	270
	21st to end	Day	28% 10% 32% 25% 3 1	297
January	1st to 10th	Night	13% 8% 37% 32% 9% 1	950
	11th to 20th	Night	15% 6% 38% 31% 8% 1	950
	21st to end	Night	15% 8% 37% 31% 9% 1	1045
February	1st to 10th	Night	10% 7% 40% 32% 10% 1	950
	11th to 20th	Night	11% 10% 41% 27% 9% 1	929
	21st to end	Night	15% 9% 35% 30% 10% 1	748
March	1st to 10th	Night	15% 9% 36% 29% 10% 1	641
	11th to 20th	Night	15% 9% 39% 27% 8%	570
	21st to end	Night	20% 8% 29% 30% 10% 3	627
April	1st to 10th	Night	21% 8% 36% 29% 6% 1	570
	11th to 20th	Night	25% 8% 27% 32% 7% 1	563
	21st to end	Night	22% 6% 27% 33% 11% 1	555
May	1st to 10th	Night	16% 8% 33% 31% 10% 1	540
	11th to 20th	Night	17% 6% 29% 35% 11% 2	531
	21st to end	Night	15% 5% 25% 37% 18% 1	584
June	1st to 10th	Night	12% 3 23% 42% 18% 1	540
	11th to 20th	Night	11% 3 30% 42% 13%	540
	21st to end	Night	11% 5% 20% 40% 23% 1	540
July	1st to 10th	Night	5% 2 17% 44% 29% 3	525
	11th to 20th	Night	9% 2 23% 39% 23% 3	522
	21st to end	Night	5% 2 19% 46% 24% 3	591
August	1st to 10th	Night	7% 2 16% 51% 21% 4	537
	11th to 20th	Night	14% 3 20% 34% 25% 4	534
	21st to end	Night	10% 4 21% 38% 25% 2	594
September	1st to 10th	Night	10% 5% 22% 39% 21% 3	540
	11th to 20th	Night	11% 4 27% 35% 21% 1	540
	21st to end	Night	17% 8% 32% 29% 13% 2	605
October	1st to 10th	Night	19% 8% 29% 29% 13% 1	720
	11th to 20th	Night	21% 11% 33% 28% 7% 1	720
	21st to end	Night	25% 11% 30% 28% 6%	792
November	1st to 10th	Night	19% 11% 29% 31% 10%	893
	11th to 20th	Night	19% 12% 34% 26% 8% 1	950
	21st to end	Night	16% 13% 38% 25% 8%	950
December	1st to 10th	Night	15% 11% 34% 30% 9% 1	950
	11th to 20th	Night	20% 8% 36% 27% 8% 1	950
	21st to end	Night	25% 8% 33% 26% 6% 1	1045

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