Big Stump
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Big Stump clear sky chart from 2005-11-06 to 2024-03-08.

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	8% 6% 2 3 3 2 3 3 4 6% 61%	78681
	Night	8% 5% 2 3 3 2 3 3 4 6% 61%	80901
Transparency	Day	25% 4 8% 21% 26% 15%	78391
	Night	25% 4 9% 23% 26% 14%	80713
Seeing	Day	10% 12% 32% 33% 11% 2	14322
	Night	9% 3 21% 41% 24% 1	24014

By Month

Percentage Cloud Cover SW (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% 10% 3 5% 3 3 3 4 5% 7% 47%	2539
	11th to 20th	Day	12% 7% 3 6% 6% 4 6% 5% 7% 7% 38%	2677
	21st to end	Day	16% 9% 2 6% 5% 3 5% 5% 6% 8% 36%	3146
February	1st to 10th	Day	14% 9% 3 3 3 1 3 4 5% 5% 49%	1867
	11th to 20th	Day	11% 12% 3 5% 4 2 3 3 4 5% 47%	1850
	21st to end	Day	16% 12% 4 5% 4 3 3 2 4 5% 41%	1570
March	1st to 10th	Day	16% 13% 3 6% 4 2 4 4 4 6% 38%	1871
	11th to 20th	Day	12% 11% 3 5% 5% 2 4 4 5% 8% 42%	1888
	21st to end	Day	14% 13% 3 4 4 3 3 3 5% 6% 43%	2358
April	1st to 10th	Day	11% 9% 3 4 4 2 3 3 4 7% 49%	2160
	11th to 20th	Day	12% 8% 2 5% 4 2 4 3 4 6% 50%	2129
	21st to end	Day	10% 7% 2 3 3 2 4 4 5% 7% 53%	2160
May	1st to 10th	Day	9% 7% 2 3 3 2 2 2 4 6% 61%	2246
	11th to 20th	Day	7% 4 1 2 4 2 3 3 4 7% 62%	2301
	21st to end	Day	9% 4 2 3 3 2 3 4 5% 7% 58%	2652
June	1st to 10th	Day	4 3 1 3 3 2 3 4 4 7% 65%	2520
	11th to 20th	Day	2 1 1 2 1 1 1 2 3 4 82%	2520
	21st to end	Day	1 1 1 2 1 1 2 2 2 3 84%	2520
July	1st to 10th	Day	1 1 1 2 2 1 2 2 3 4 83%	2520
	11th to 20th	Day	2 1 1 2 2 2 3 3 3 4 79%	2520
	21st to end	Day	2 2 1 2 2 2 3 3 4 5% 75%	2637
August	1st to 10th	Day	1 2 1 2 2 1 2 2 2 3 82%	2153
	11th to 20th	Day	1 1 1 1 2 1 2 2 3 3 83%	2122
	21st to end	Day	1 1 1 1 1 1 2 3 4 84%	2376
September	1st to 10th	Day	2 1 2 2 1 1 2 3 4 83%	2160
	11th to 20th	Day	2 1 1 2 2 1 2 2 2 4 82%	2080
	21st to end	Day	2 2 1 2 2 1 2 2 2 4 79%	1980
October	1st to 10th	Day	6% 4 1 2 3 1 3 3 4 5% 69%	1931
	11th to 20th	Day	4 2 1 3 2 2 4 3 3 4 72%	1800
	21st to end	Day	5% 2 1 3 3 2 2 3 4 5% 71%	1935
November	1st to 10th	Day	6% 9% 2 3 3 2 3 3 5% 5% 58%	1674
	11th to 20th	Day	7% 4 2 2 3 2 3 3 5% 6% 64%	1710
	21st to end	Day	8% 6% 2 4 3 2 4 4 5% 6% 57%	1710
December	1st to 10th	Day	12% 4 2 4 3 2 3 4 5% 6% 55%	1677
	11th to 20th	Day	18% 8% 3 6% 5% 3 4 3 4 6% 38%	1928
	21st to end	Day	11% 10% 3 5% 5% 3 4 5% 5% 9% 39%	2794
January	1st to 10th	Night	12% 9% 2 4 3 2 3 4 5% 6% 50%	4406
	11th to 20th	Night	15% 10% 3 6% 5% 3 3 4 5% 7% 40%	4282
	21st to end	Night	15% 9% 3 4 5% 3 5% 5% 6% 9% 37%	4521
February	1st to 10th	Night	13% 8% 2 4 3 2 4 3 4 6% 50%	2309
	11th to 20th	Night	12% 7% 2 3 3 2 3 3 4 6% 53%	2218
	21st to end	Night	14% 9% 4 4 3 2 3 3 4 5% 49%	1884
March	1st to 10th	Night	14% 10% 3 4 4 3 3 5% 5% 6% 43%	2249
	11th to 20th	Night	11% 8% 2 4 4 2 3 4 6% 8% 47%	2069
	21st to end	Night	13% 8% 2 3 3 3 3 4 4 6% 51%	1996
April	1st to 10th	Night	10% 6% 1 3 3 2 4 4 4 7% 57%	1800
	11th to 20th	Night	9% 5% 2 3 4 2 4 4 4 5% 59%	1779
	21st to end	Night	7% 4 1 2 3 2 3 3 4 8% 63%	1800
May	1st to 10th	Night	6% 4 1 3 3 2 3 3 4 8% 64%	1710
	11th to 20th	Night	6% 3 2 3 2 1 2 3 3 5% 71%	1594
	21st to end	Night	6% 3 1 3 2 2 2 3 3 5% 70%	1619
June	1st to 10th	Night	5% 2 2 3 2 1 2 2 3 6% 72%	1440
	11th to 20th	Night	1 1 1 1 2 1 2 2 2 5% 82%	1440
	21st to end	Night	1 1 1 1 1 2 2 2 2 87%	1440
July	1st to 10th	Night	1 1 1 1 1 2 3 3 86%	1440
	11th to 20th	Night	1 2 1 2 2 1 2 3 3 4 80%	1440
	21st to end	Night	2 1 1 2 3 1 3 3 3 4 76%	1676
August	1st to 10th	Night	2 1 1 2 2 1 1 1 3 3 84%	1785
	11th to 20th	Night	1 1 1 1 2 2 2 3 87%	1780
	21st to end	Night	1 1 1 2 1 2 2 2 2 86%	1980
September	1st to 10th	Night	1 1 1 1 1 1 2 2 3 88%	1800
	11th to 20th	Night	1 1 1 1 2 2 2 3 3 84%	1879
	21st to end	Night	2 1 1 2 2 1 1 3 3 4 81%	1980
October	1st to 10th	Night	4 3 1 2 3 1 3 3 3 5% 73%	2024
	11th to 20th	Night	4 2 1 2 3 2 3 3 3 4 73%	2160
	21st to end	Night	5% 2 1 2 2 1 2 2 3 4 77%	2420
November	1st to 10th	Night	7% 5% 1 2 3 2 3 3 4 5% 64%	2405
	11th to 20th	Night	7% 3 1 3 3 1 3 3 5% 8% 63%	2470
	21st to end	Night	8% 6% 2 4 3 1 3 4 4 6% 58%	2470
December	1st to 10th	Night	12% 5% 1 4 3 2 3 3 4 8% 54%	2498
	11th to 20th	Night	20% 7% 2 4 4 2 4 4 5% 7% 40%	3276
	21st to end	Night	10% 7% 3 6% 6% 3 4 6% 6% 9% 41%	4862

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	36% 4 12% 30% 15% 2	2539
	11th to 20th	Day	40% 6% 14% 22% 11% 7%	2677
	21st to end	Day	42% 5% 15% 22% 13% 4	3146
February	1st to 10th	Day	35% 5% 8% 24% 20% 7%	1867
	11th to 20th	Day	38% 4 9% 20% 22% 7%	1860
	21st to end	Day	45% 4 8% 25% 15% 2	1570
March	1st to 10th	Day	44% 6% 11% 18% 17% 4	1871
	11th to 20th	Day	40% 6% 11% 22% 16% 5%	1888
	21st to end	Day	41% 5% 16% 22% 13% 3	2358
April	1st to 10th	Day	36% 5% 12% 25% 19% 3	2160
	11th to 20th	Day	35% 5% 12% 24% 20% 4	2132
	21st to end	Day	29% 6% 13% 34% 17% 1	2160
May	1st to 10th	Day	25% 4 10% 33% 24% 3	2246
	11th to 20th	Day	23% 6% 9% 33% 24% 4	2304
	21st to end	Day	26% 6% 10% 35% 22% 2	2652
June	1st to 10th	Day	19% 4 12% 25% 31% 8%	2520
	11th to 20th	Day	9% 3 7% 21% 40% 19%	2520
	21st to end	Day	9% 2 3 14% 42% 29%	2520
July	1st to 10th	Day	8% 3 3 10% 32% 43%	2451
	11th to 20th	Day	11% 4 4 14% 35% 33%	2445
	21st to end	Day	13% 4 5% 18% 30% 30%	2490
August	1st to 10th	Day	10% 2 4 10% 35% 39%	2138
	11th to 20th	Day	8% 3 3 15% 38% 34%	2122
	21st to end	Day	7% 2 2 12% 41% 36%	2376
September	1st to 10th	Day	7% 2 4 11% 36% 40%	2160
	11th to 20th	Day	10% 3 4 20% 38% 26%	2080
	21st to end	Day	12% 3 3 19% 40% 22%	1980
October	1st to 10th	Day	19% 3 4 20% 27% 26%	1931
	11th to 20th	Day	17% 3 5% 22% 31% 24%	1800
	21st to end	Day	16% 3 5% 22% 31% 22%	1935
November	1st to 10th	Day	26% 3 8% 21% 27% 15%	1674
	11th to 20th	Day	21% 3 9% 23% 31% 13%	1710
	21st to end	Day	27% 4 9% 17% 28% 15%	1710
December	1st to 10th	Day	29% 5% 8% 20% 24% 13%	1677
	11th to 20th	Day	46% 6% 9% 16% 16% 7%	1928
	21st to end	Day	40% 5% 10% 23% 16% 5%	2794
January	1st to 10th	Night	34% 3 17% 26% 18% 3	4406
	11th to 20th	Night	41% 4 10% 26% 13% 6%	4282
	21st to end	Night	40% 7% 12% 21% 15% 5%	4521
February	1st to 10th	Night	36% 3 7% 26% 20% 9%	2309
	11th to 20th	Night	31% 3 10% 23% 26% 7%	2219
	21st to end	Night	36% 3 11% 27% 18% 5%	1884
March	1st to 10th	Night	39% 6% 10% 22% 19% 5%	2249
	11th to 20th	Night	33% 5% 13% 23% 20% 5%	2069
	21st to end	Night	35% 7% 14% 28% 13% 3	1996
April	1st to 10th	Night	28% 6% 14% 30% 16% 7%	1800
	11th to 20th	Night	27% 6% 13% 28% 21% 6%	1779
	21st to end	Night	20% 5% 16% 40% 18% 1	1800
May	1st to 10th	Night	20% 5% 11% 34% 26% 4	1710
	11th to 20th	Night	19% 3 10% 37% 27% 4	1595
	21st to end	Night	18% 5% 13% 33% 29% 3	1619
June	1st to 10th	Night	16% 3 12% 27% 34% 8%	1440
	11th to 20th	Night	8% 3 8% 22% 39% 19%	1440
	21st to end	Night	7% 2 4 15% 43% 30%	1440
July	1st to 10th	Night	6% 2 3 13% 32% 44%	1400
	11th to 20th	Night	9% 3 6% 15% 35% 32%	1392
	21st to end	Night	12% 3 6% 17% 32% 30%	1583
August	1st to 10th	Night	9% 1 4 14% 35% 37%	1776
	11th to 20th	Night	5% 2 3 17% 40% 35%	1780
	21st to end	Night	8% 1 2 12% 43% 34%	1980
September	1st to 10th	Night	6% 2 2 12% 33% 45%	1800
	11th to 20th	Night	7% 2 4 21% 41% 24%	1879
	21st to end	Night	9% 3 4 20% 40% 24%	1980
October	1st to 10th	Night	15% 4 6% 21% 31% 24%	2024
	11th to 20th	Night	14% 4 5% 19% 33% 24%	2160
	21st to end	Night	13% 3 4 24% 35% 21%	2420
November	1st to 10th	Night	23% 3 8% 23% 27% 16%	2405
	11th to 20th	Night	21% 3 9% 21% 31% 15%	2470
	21st to end	Night	26% 4 9% 17% 30% 13%	2470
December	1st to 10th	Night	30% 4 10% 21% 23% 13%	2498
	11th to 20th	Night	42% 6% 9% 19% 17% 6%	3276
	21st to end	Night	37% 5% 10% 26% 16% 5%	4862

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	28% 9% 33% 20% 8% 2	180
	11th to 20th	Day	17% 13% 30% 25% 13% 2	265
	21st to end	Day	19% 10% 33% 27% 10% 1	407
February	1st to 10th	Day	20% 13% 31% 25% 9% 2	445
	11th to 20th	Day	18% 18% 35% 22% 6%	455
	21st to end	Day	20% 19% 38% 18% 4	382
March	1st to 10th	Day	25% 16% 35% 19% 4	449
	11th to 20th	Day	18% 21% 30% 22% 9%	420
	21st to end	Day	23% 21% 31% 21% 3	462
April	1st to 10th	Day	17% 19% 33% 25% 7%	420
	11th to 20th	Day	21% 19% 32% 24% 4	412
	21st to end	Day	12% 17% 33% 25% 11% 2	420
May	1st to 10th	Day	13% 20% 34% 24% 9% 1	423
	11th to 20th	Day	13% 13% 33% 27% 12% 1	448
	21st to end	Day	14% 13% 30% 29% 12% 2	485
June	1st to 10th	Day	4 15% 28% 37% 14% 2	450
	11th to 20th	Day	4 14% 32% 37% 11% 2	450
	21st to end	Day	1 10% 34% 38% 15% 2	450
July	1st to 10th	Day	1 3 32% 43% 17% 3	446
	11th to 20th	Day	2 2 21% 52% 17% 6%	444
	21st to end	Day	2 1 25% 50% 16% 5%	487
August	1st to 10th	Day	2 6% 39% 38% 12% 3	447
	11th to 20th	Day	2 5% 29% 46% 13% 6%	437
	21st to end	Day	2 2 30% 48% 14% 4	495
September	1st to 10th	Day	3 4 34% 43% 15% 1	450
	11th to 20th	Day	3 10% 38% 39% 10%	450
	21st to end	Day	4 12% 32% 39% 12%	450
October	1st to 10th	Day	5% 16% 30% 38% 11%	450
	11th to 20th	Day	4 12% 34% 39% 11%	450
	21st to end	Day	5% 11% 32% 38% 13%	450
November	1st to 10th	Day	10% 10% 32% 34% 13% 1	270
	11th to 20th	Day	6% 10% 33% 36% 14% 1	270
	21st to end	Day	10% 13% 29% 32% 16% 1	270
December	1st to 10th	Day	15% 8% 38% 27% 11% 1	255
	11th to 20th	Day	15% 12% 35% 22% 16% 1	180
	21st to end	Day	22% 12% 31% 22% 11% 2	198
January	1st to 10th	Night	19% 3 28% 32% 16% 2	760
	11th to 20th	Night	11% 6% 28% 39% 15% 1	760
	21st to end	Night	18% 4 30% 33% 14% 1	836
February	1st to 10th	Night	17% 4 29% 35% 14% 1	760
	11th to 20th	Night	15% 5% 28% 34% 16% 1	744
	21st to end	Night	19% 7% 30% 35% 9% 1	628
March	1st to 10th	Night	18% 7% 26% 39% 10% 1	750
	11th to 20th	Night	14% 5% 24% 35% 20% 1	720
	21st to end	Night	16% 5% 28% 39% 12%	792
April	1st to 10th	Night	13% 3 27% 44% 13%	720
	11th to 20th	Night	10% 6% 26% 42% 16%	711
	21st to end	Night	7% 4 25% 41% 21% 1	720
May	1st to 10th	Night	7% 3 26% 44% 20% 1	630
	11th to 20th	Night	8% 2 20% 45% 24% 1	531
	21st to end	Night	7% 4 23% 39% 26% 1	457
June	1st to 10th	Night	4 1 17% 46% 29% 3	360
	11th to 20th	Night	1 1 17% 49% 30% 2	360
	21st to end	Night	1 2 11% 48% 37% 1	360
July	1st to 10th	Night	7% 43% 49% 1	350
	11th to 20th	Night	1 3 43% 50% 3	348
	21st to end	Night	2 1 7% 38% 49% 4	494
August	1st to 10th	Night	2 9% 46% 41% 1	711
	11th to 20th	Night	1 7% 46% 45% 1	712
	21st to end	Night	2 6% 39% 51% 2	792
September	1st to 10th	Night	1 1 8% 44% 44% 1	720
	11th to 20th	Night	1 1 12% 51% 33% 2	720
	21st to end	Night	2 1 16% 47% 33% 2	720
October	1st to 10th	Night	3 2 19% 51% 23% 1	720
	11th to 20th	Night	4 2 20% 46% 27% 2	720
	21st to end	Night	5% 2 20% 38% 30% 5%	792
November	1st to 10th	Night	9% 3 18% 42% 25% 3	740
	11th to 20th	Night	8% 3 22% 45% 20% 2	760
	21st to end	Night	10% 3 28% 40% 17% 2	760
December	1st to 10th	Night	13% 4 28% 39% 14% 2	760
	11th to 20th	Night	19% 4 28% 36% 11% 1	760
	21st to end	Night	18% 5% 33% 33% 11% 1	836

Page generated at 2024-03-05 04:24:03. Version ac07

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