PICO
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the PICO 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	13% 7% 3 6% 5% 3 5% 5% 5% 8% 40%	74809
	Night	14% 8% 3 6% 5% 3 4 4 5% 7% 42%	74987
Transparency	Day	43% 4 12% 24% 14% 2	74510
	Night	43% 3 11% 24% 16% 3	74807
Seeing	Day	16% 9% 25% 26% 18% 6%	14494
	Night	17% 9% 29% 30% 14% 1	24446

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	14% 10% 6% 9% 7% 4 5% 4 5% 5% 30%	1517
	11th to 20th	Day	17% 13% 6% 10% 7% 4 4 4 4 5% 26%	1472
	21st to end	Day	14% 13% 7% 10% 6% 3 4 4 4 6% 30%	1778
February	1st to 10th	Day	17% 11% 6% 9% 7% 3 5% 4 5% 6% 29%	1670
	11th to 20th	Day	14% 10% 4 7% 8% 3 6% 5% 5% 8% 30%	1748
	21st to end	Day	17% 12% 4 7% 6% 3 4 3 5% 5% 32%	1480
March	1st to 10th	Day	16% 9% 4 5% 5% 4 4 5% 4 6% 37%	1800
	11th to 20th	Day	16% 11% 4 7% 6% 2 4 4 5% 7% 34%	1903
	21st to end	Day	21% 12% 5% 8% 5% 3 4 4 5% 6% 28%	2355
April	1st to 10th	Day	13% 6% 4 6% 6% 3 5% 5% 6% 9% 38%	2160
	11th to 20th	Day	17% 9% 3 6% 5% 3 4 4 4 6% 40%	2134
	21st to end	Day	20% 7% 2 5% 6% 4 4 4 5% 7% 37%	2160
May	1st to 10th	Day	17% 6% 3 6% 5% 3 6% 5% 7% 9% 34%	2322
	11th to 20th	Day	18% 7% 3 4 6% 3 5% 4 6% 8% 37%	2377
	21st to end	Day	9% 5% 4 6% 5% 5% 7% 6% 7% 10% 37%	2725
June	1st to 10th	Day	8% 4 2 4 5% 3 5% 5% 7% 9% 46%	2520
	11th to 20th	Day	8% 5% 3 4 5% 3 4 5% 6% 9% 48%	2520
	21st to end	Day	7% 4 3 6% 5% 4 6% 6% 7% 10% 42%	2520
July	1st to 10th	Day	9% 3 2 4 5% 3 6% 6% 7% 10% 42%	2520
	11th to 20th	Day	5% 4 2 4 5% 4 6% 6% 8% 10% 46%	2520
	21st to end	Day	9% 3 2 4 5% 3 5% 6% 7% 10% 47%	2743
August	1st to 10th	Day	9% 4 2 4 4 3 4 6% 7% 11% 45%	2278
	11th to 20th	Day	8% 4 2 5% 6% 4 5% 7% 6% 10% 42%	2125
	21st to end	Day	7% 4 2 5% 4 3 4 5% 6% 10% 50%	2376
September	1st to 10th	Day	13% 5% 2 5% 4 3 4 4 5% 8% 46%	2160
	11th to 20th	Day	9% 5% 3 4 4 3 6% 4 5% 6% 50%	2079
	21st to end	Day	8% 5% 2 4 4 3 4 4 5% 7% 54%	1980
October	1st to 10th	Day	11% 4 2 4 4 3 3 4 5% 7% 52%	1893
	11th to 20th	Day	15% 7% 3 5% 4 2 4 4 5% 6% 46%	1800
	21st to end	Day	18% 7% 3 6% 5% 2 3 4 5% 5% 42%	1866
November	1st to 10th	Day	10% 6% 2 4 4 2 4 3 5% 7% 53%	1672
	11th to 20th	Day	16% 8% 4 4 4 2 3 4 5% 7% 42%	1710
	21st to end	Day	15% 11% 4 6% 6% 3 4 3 4 5% 39%	1705
December	1st to 10th	Day	14% 12% 6% 7% 6% 3 4 4 4 7% 33%	1520
	11th to 20th	Day	15% 11% 5% 9% 5% 4 5% 5% 5% 8% 28%	1918
	21st to end	Day	21% 17% 6% 13% 5% 2 4 4 4 5% 19%	2783
January	1st to 10th	Night	12% 11% 4 9% 7% 4 5% 4 4 6% 35%	2648
	11th to 20th	Night	16% 11% 5% 10% 7% 3 4 3 3 5% 32%	2577
	21st to end	Night	14% 9% 5% 9% 7% 3 4 5% 4 6% 32%	2576
February	1st to 10th	Night	18% 11% 5% 8% 6% 3 5% 4 4 5% 30%	2290
	11th to 20th	Night	15% 8% 4 8% 6% 2 5% 5% 4 5% 38%	2098
	21st to end	Night	20% 8% 3 8% 5% 3 3 3 4 6% 36%	1776
March	1st to 10th	Night	16% 10% 4 6% 5% 4 4 4 4 5% 39%	2160
	11th to 20th	Night	18% 7% 3 5% 6% 2 5% 4 6% 6% 38%	2072
	21st to end	Night	20% 10% 3 7% 5% 3 4 5% 5% 6% 32%	2000
April	1st to 10th	Night	13% 7% 3 5% 5% 3 4 4 4 7% 45%	1800
	11th to 20th	Night	16% 7% 2 5% 4 2 4 4 4 7% 45%	1775
	21st to end	Night	19% 7% 3 6% 6% 3 4 4 4 6% 38%	1800
May	1st to 10th	Night	16% 7% 3 6% 5% 3 4 5% 5% 7% 40%	1638
	11th to 20th	Night	14% 6% 2 6% 5% 4 5% 5% 5% 6% 42%	1514
	21st to end	Night	9% 7% 2 6% 6% 3 6% 5% 7% 10% 39%	1551
June	1st to 10th	Night	7% 4 2 5% 5% 2 5% 4 7% 8% 50%	1440
	11th to 20th	Night	6% 4 2 4 4 3 4 5% 6% 9% 52%	1440
	21st to end	Night	7% 4 3 5% 4 3 4 5% 7% 10% 48%	1440
July	1st to 10th	Night	9% 4 2 5% 4 3 4 4 6% 8% 51%	1440
	11th to 20th	Night	6% 3 2 4 4 3 4 4 5% 11% 55%	1440
	21st to end	Night	6% 4 2 4 4 3 4 5% 6% 10% 53%	1575
August	1st to 10th	Night	7% 5% 1 3 4 3 4 5% 7% 10% 51%	1654
	11th to 20th	Night	6% 4 2 5% 5% 4 5% 5% 7% 8% 50%	1776
	21st to end	Night	6% 2 2 3 4 3 4 5% 5% 9% 57%	1980
September	1st to 10th	Night	11% 5% 2 5% 3 2 4 4 4 8% 52%	1800
	11th to 20th	Night	7% 4 2 5% 4 2 3 4 5% 8% 55%	1862
	21st to end	Night	8% 5% 2 4 3 2 4 4 5% 7% 55%	1980
October	1st to 10th	Night	9% 4 1 4 5% 2 4 4 4 7% 55%	2064
	11th to 20th	Night	15% 5% 3 4 4 2 3 3 4 6% 51%	2160
	21st to end	Night	18% 8% 2 5% 5% 2 4 4 4 6% 42%	2488
November	1st to 10th	Night	10% 6% 3 4 4 2 3 4 4 5% 54%	2406
	11th to 20th	Night	13% 8% 3 6% 4 2 4 3 5% 6% 48%	2470
	21st to end	Night	18% 8% 4 5% 5% 2 3 4 4 6% 41%	2474
December	1st to 10th	Night	16% 9% 4 7% 6% 3 5% 5% 5% 7% 33%	2660
	11th to 20th	Night	17% 8% 4 7% 5% 3 3 4 4 5% 39%	3279
	21st to end	Night	24% 17% 6% 8% 7% 3 4 4 4 4 20%	4884

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	56% 3 9% 19% 12% 1	1518
	11th to 20th	Day	61% 2 10% 19% 7%	1472
	21st to end	Day	56% 3 12% 21% 8% 1	1778
February	1st to 10th	Day	56% 3 13% 18% 9% 1	1670
	11th to 20th	Day	52% 4 11% 22% 10% 1	1758
	21st to end	Day	54% 3 8% 23% 10% 2	1480
March	1st to 10th	Day	48% 5% 10% 25% 11% 1	1800
	11th to 20th	Day	50% 4 14% 21% 10% 1	1903
	21st to end	Day	58% 4 11% 19% 7% 1	2355
April	1st to 10th	Day	43% 4 14% 25% 14% 1	2160
	11th to 20th	Day	47% 3 11% 25% 12% 2	2134
	21st to end	Day	48% 4 12% 23% 11% 2	2160
May	1st to 10th	Day	46% 6% 16% 23% 8% 1	2322
	11th to 20th	Day	46% 6% 14% 20% 14% 1	2381
	21st to end	Day	41% 7% 16% 21% 14% 2	2725
June	1st to 10th	Day	32% 6% 15% 27% 17% 3	2520
	11th to 20th	Day	33% 6% 11% 27% 21% 3	2520
	21st to end	Day	36% 6% 15% 23% 16% 3	2520
July	1st to 10th	Day	35% 6% 12% 29% 14% 3	2451
	11th to 20th	Day	30% 7% 15% 29% 16% 3	2445
	21st to end	Day	32% 6% 13% 31% 16% 2	2591
August	1st to 10th	Day	32% 6% 14% 33% 14% 1	2263
	11th to 20th	Day	35% 6% 16% 27% 14% 2	2125
	21st to end	Day	29% 5% 13% 27% 20% 6%	2376
September	1st to 10th	Day	36% 4 11% 26% 18% 4	2160
	11th to 20th	Day	34% 4 8% 27% 25% 3	2079
	21st to end	Day	30% 4 8% 29% 24% 4	1980
October	1st to 10th	Day	32% 4 13% 27% 22% 3	1893
	11th to 20th	Day	40% 3 9% 23% 23% 3	1800
	21st to end	Day	44% 3 9% 26% 16% 2	1866
November	1st to 10th	Day	32% 4 13% 28% 19% 5%	1672
	11th to 20th	Day	42% 2 9% 26% 16% 4	1710
	21st to end	Day	50% 2 10% 25% 12% 1	1705
December	1st to 10th	Day	51% 3 14% 21% 10% 1	1520
	11th to 20th	Day	55% 4 7% 26% 7% 2	1915
	21st to end	Day	68% 2 10% 13% 6% 1	2783
January	1st to 10th	Night	51% 2 9% 22% 14% 1	2648
	11th to 20th	Night	56% 3 10% 23% 9%	2577
	21st to end	Night	53% 4 11% 21% 10% 1	2576
February	1st to 10th	Night	56% 3 11% 18% 10% 2	2290
	11th to 20th	Night	48% 4 10% 22% 14% 2	2099
	21st to end	Night	51% 2 9% 23% 11% 3	1776
March	1st to 10th	Night	48% 3 8% 24% 16% 1	2160
	11th to 20th	Night	47% 3 13% 22% 13% 2	2072
	21st to end	Night	53% 3 11% 22% 9% 2	2000
April	1st to 10th	Night	40% 3 11% 27% 17% 2	1800
	11th to 20th	Night	40% 2 11% 25% 18% 4	1775
	21st to end	Night	48% 4 9% 21% 15% 3	1800
May	1st to 10th	Night	43% 4 13% 26% 13% 2	1638
	11th to 20th	Night	43% 6% 12% 23% 15% 1	1515
	21st to end	Night	40% 5% 14% 20% 16% 4	1552
June	1st to 10th	Night	31% 5% 13% 29% 19% 3	1440
	11th to 20th	Night	28% 4 11% 27% 24% 5%	1440
	21st to end	Night	31% 6% 15% 24% 18% 6%	1440
July	1st to 10th	Night	33% 4 14% 28% 17% 5%	1400
	11th to 20th	Night	25% 5% 13% 33% 20% 4	1392
	21st to end	Night	27% 5% 13% 29% 22% 3	1487
August	1st to 10th	Night	28% 5% 15% 32% 18% 2	1645
	11th to 20th	Night	32% 5% 11% 31% 21% 2	1776
	21st to end	Night	25% 5% 13% 28% 22% 7%	1980
September	1st to 10th	Night	32% 3 10% 28% 21% 7%	1800
	11th to 20th	Night	28% 5% 8% 29% 26% 4	1862
	21st to end	Night	29% 4 9% 25% 28% 5%	1980
October	1st to 10th	Night	30% 4 11% 25% 25% 5%	2064
	11th to 20th	Night	36% 2 6% 28% 23% 4	2160
	21st to end	Night	44% 3 8% 23% 18% 3	2488
November	1st to 10th	Night	33% 4 11% 26% 21% 6%	2406
	11th to 20th	Night	39% 2 9% 27% 20% 3	2470
	21st to end	Night	45% 3 10% 25% 16% 1	2474
December	1st to 10th	Night	50% 3 12% 22% 12% 1	2660
	11th to 20th	Night	48% 2 11% 26% 12% 1	3281
	21st to end	Night	70% 2 7% 13% 7% 1	4884

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	20% 17% 34% 21% 6% 1	270
	11th to 20th	Day	31% 15% 33% 18% 4	252
	21st to end	Day	19% 21% 38% 18% 4	264
February	1st to 10th	Day	28% 16% 40% 14% 3	240
	11th to 20th	Day	26% 20% 30% 19% 4 1	240
	21st to end	Day	28% 11% 43% 16% 3	198
March	1st to 10th	Day	22% 18% 38% 18% 5%	240
	11th to 20th	Day	28% 15% 36% 16% 4 1	240
	21st to end	Day	32% 14% 30% 18% 6%	441
April	1st to 10th	Day	16% 15% 35% 26% 8% 1	420
	11th to 20th	Day	22% 16% 28% 21% 11% 2	412
	21st to end	Day	22% 12% 34% 21% 9% 2	420
May	1st to 10th	Day	21% 11% 30% 26% 9% 2	423
	11th to 20th	Day	19% 8% 26% 27% 16% 3	523
	21st to end	Day	10% 7% 28% 32% 16% 8%	679
June	1st to 10th	Day	9% 5% 22% 30% 24% 9%	630
	11th to 20th	Day	10% 5% 20% 34% 24% 6%	630
	21st to end	Day	8% 5% 26% 32% 21% 8%	630
July	1st to 10th	Day	11% 3 11% 28% 28% 19%	621
	11th to 20th	Day	6% 3 18% 35% 28% 11%	618
	21st to end	Day	11% 2 14% 31% 32% 10%	684
August	1st to 10th	Day	10% 1 13% 33% 31% 12%	558
	11th to 20th	Day	10% 3 15% 30% 27% 16%	439
	21st to end	Day	8% 1 12% 29% 37% 13%	495
September	1st to 10th	Day	13% 4 16% 28% 26% 12%	450
	11th to 20th	Day	8% 2 12% 32% 32% 13%	450
	21st to end	Day	9% 8% 24% 24% 24% 11%	450
October	1st to 10th	Day	12% 7% 23% 32% 21% 4	363
	11th to 20th	Day	16% 17% 33% 24% 8% 1	270
	21st to end	Day	28% 15% 31% 22% 4	297
November	1st to 10th	Day	14% 13% 31% 24% 13% 4	270
	11th to 20th	Day	20% 17% 33% 20% 9% 2	270
	21st to end	Day	25% 15% 30% 21% 7%	270
December	1st to 10th	Day	15% 18% 40% 19% 5% 3	270
	11th to 20th	Day	20% 15% 34% 26% 4	270
	21st to end	Day	26% 21% 35% 11% 7%	297
January	1st to 10th	Night	18% 16% 37% 25% 4	950
	11th to 20th	Night	21% 15% 37% 21% 5%	921
	21st to end	Night	19% 14% 38% 25% 3	990
February	1st to 10th	Night	24% 13% 37% 23% 3	850
	11th to 20th	Night	19% 17% 37% 25% 2	703
	21st to end	Night	26% 15% 36% 21% 2	592
March	1st to 10th	Night	21% 14% 37% 24% 4	720
	11th to 20th	Night	22% 12% 33% 26% 6%	632
	21st to end	Night	26% 10% 31% 27% 6%	594
April	1st to 10th	Night	17% 13% 34% 29% 6%	540
	11th to 20th	Night	18% 9% 35% 27% 10%	533
	21st to end	Night	22% 9% 32% 28% 7% 1	540
May	1st to 10th	Night	18% 7% 33% 32% 10% 1	540
	11th to 20th	Night	17% 5% 27% 33% 16% 2	531
	21st to end	Night	11% 4 24% 36% 21% 4	584
June	1st to 10th	Night	9% 3 19% 42% 26%	540
	11th to 20th	Night	8% 2 22% 44% 24% 2	540
	21st to end	Night	8% 3 24% 35% 28% 1	540
July	1st to 10th	Night	10% 2 10% 31% 41% 6%	525
	11th to 20th	Night	6% 3 11% 46% 31% 4	522
	21st to end	Night	7% 1 12% 41% 35% 3	591
August	1st to 10th	Night	9% 2 9% 43% 33% 4	537
	11th to 20th	Night	6% 1 11% 41% 36% 5%	534
	21st to end	Night	6% 1 12% 37% 39% 5%	594
September	1st to 10th	Night	13% 3 13% 36% 31% 4	540
	11th to 20th	Night	8% 3 14% 37% 33% 5%	602
	21st to end	Night	10% 4 22% 31% 28% 5%	720
October	1st to 10th	Night	12% 3 24% 35% 22% 4	720
	11th to 20th	Night	17% 12% 29% 28% 13% 1	720
	21st to end	Night	22% 12% 32% 28% 6%	792
November	1st to 10th	Night	13% 7% 38% 31% 10% 1	740
	11th to 20th	Night	17% 14% 34% 27% 8% 1	760
	21st to end	Night	23% 11% 31% 28% 6%	764
December	1st to 10th	Night	21% 12% 35% 25% 6% 1	950
	11th to 20th	Night	23% 8% 34% 30% 6%	950
	21st to end	Night	28% 15% 33% 22% 3	1045

Page generated at 2024-01-11 21:33:46. Version ac07

Copyright 2024 Attilla Danko