Southwest Corner Mountain
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Southwest Corner Mountain clear sky chart from 2005-11-06 to 2024-01-14.

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	7% 7% 3 6% 5% 3 5% 5% 6% 8% 45%	74787
	Night	9% 9% 3 6% 5% 3 5% 5% 6% 8% 42%	75001
Transparency	Day	37% 7% 13% 22% 16% 5%	74490
	Night	41% 7% 14% 21% 13% 4	74816
Seeing	Day	10% 8% 25% 33% 19% 5%	13172
	Night	12% 3 20% 41% 21% 2	22291

By Month

Percentage Cloud Cover NW (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% 21% 5% 9% 7% 4 5% 5% 6% 6% 19%	1519
	11th to 20th	Day	12% 15% 8% 8% 7% 2 6% 4 5% 8% 24%	1464
	21st to end	Day	11% 15% 6% 11% 6% 4 5% 4 5% 8% 27%	1584
February	1st to 10th	Day	8% 12% 4 9% 7% 3 7% 5% 6% 7% 31%	1536
	11th to 20th	Day	8% 14% 4 6% 4 3 4 5% 6% 8% 38%	1575
	21st to end	Day	5% 11% 5% 9% 6% 4 6% 7% 6% 9% 33%	1480
March	1st to 10th	Day	9% 9% 4 6% 5% 4 5% 5% 7% 10% 38%	1800
	11th to 20th	Day	8% 8% 3 6% 5% 3 7% 6% 7% 10% 38%	1896
	21st to end	Day	6% 8% 3 7% 7% 4 6% 8% 7% 9% 33%	2340
April	1st to 10th	Day	8% 6% 3 6% 7% 4 6% 7% 7% 9% 35%	2160
	11th to 20th	Day	5% 6% 4 7% 6% 5% 6% 6% 8% 9% 38%	2132
	21st to end	Day	6% 6% 3 6% 6% 4 6% 6% 6% 10% 42%	2404
May	1st to 10th	Day	5% 4 3 5% 6% 3 5% 6% 7% 9% 47%	2520
	11th to 20th	Day	8% 6% 3 6% 7% 3 5% 6% 7% 9% 41%	2477
	21st to end	Day	9% 6% 3 6% 7% 4 6% 6% 7% 9% 39%	2723
June	1st to 10th	Day	9% 6% 3 5% 5% 4 6% 7% 7% 8% 40%	2520
	11th to 20th	Day	7% 4 3 5% 5% 4 6% 6% 6% 8% 44%	2520
	21st to end	Day	5% 4 2 4 4 3 5% 5% 6% 8% 55%	2520
July	1st to 10th	Day	2 2 1 4 4 3 4 4 5% 7% 63%	2520
	11th to 20th	Day	2 3 2 3 3 2 3 4 4 6% 68%	2520
	21st to end	Day	2 1 2 2 2 3 2 4 5% 78%	2741
August	1st to 10th	Day	3 2 1 2 3 2 3 3 5% 8% 68%	2507
	11th to 20th	Day	2 2 1 3 4 2 2 3 4 7% 71%	2406
	21st to end	Day	2 2 1 4 4 3 4 5% 6% 8% 62%	2381
September	1st to 10th	Day	3 2 1 2 4 2 3 4 5% 8% 67%	2160
	11th to 20th	Day	4 3 2 4 5% 3 5% 6% 5% 9% 53%	2147
	21st to end	Day	7% 4 2 3 5% 2 4 6% 6% 6% 56%	1960
October	1st to 10th	Day	6% 4 2 4 4 3 6% 5% 6% 8% 51%	1800
	11th to 20th	Day	7% 4 3 5% 5% 3 5% 6% 6% 9% 47%	1782
	21st to end	Day	12% 8% 3 6% 5% 3 4 5% 5% 8% 42%	1782
November	1st to 10th	Day	13% 9% 4 5% 6% 4 5% 6% 6% 9% 33%	1632
	11th to 20th	Day	9% 13% 5% 7% 6% 3 5% 6% 5% 7% 35%	1520
	21st to end	Day	9% 13% 6% 9% 6% 3 6% 5% 6% 7% 29%	1520
December	1st to 10th	Day	13% 13% 5% 8% 6% 3 5% 3 6% 6% 30%	1520
	11th to 20th	Day	16% 17% 7% 11% 6% 2 4 4 6% 5% 22%	1925
	21st to end	Day	13% 20% 6% 11% 7% 4 5% 5% 4 5% 19%	2794
January	1st to 10th	Night	13% 19% 6% 10% 6% 4 5% 5% 5% 6% 20%	2646
	11th to 20th	Night	14% 17% 6% 8% 7% 2 5% 4 5% 8% 23%	2574
	21st to end	Night	11% 14% 7% 10% 8% 4 5% 6% 6% 6% 23%	2772
February	1st to 10th	Night	10% 10% 4 8% 7% 3 6% 5% 6% 9% 32%	2421
	11th to 20th	Night	9% 9% 3 7% 6% 3 5% 6% 8% 9% 37%	2271
	21st to end	Night	8% 11% 4 7% 6% 4 5% 5% 7% 9% 34%	1776
March	1st to 10th	Night	10% 10% 4 6% 6% 3 6% 6% 7% 10% 34%	2160
	11th to 20th	Night	6% 7% 3 5% 6% 4 7% 6% 7% 9% 40%	2061
	21st to end	Night	9% 7% 3 5% 6% 4 7% 7% 7% 10% 34%	2016
April	1st to 10th	Night	6% 7% 3 7% 6% 3 7% 6% 7% 9% 39%	1800
	11th to 20th	Night	5% 8% 3 5% 5% 3 5% 5% 6% 8% 47%	1779
	21st to end	Night	6% 6% 3 4 5% 2 5% 5% 6% 8% 48%	1554
May	1st to 10th	Night	4 4 2 5% 4 3 5% 6% 7% 8% 52%	1440
	11th to 20th	Night	9% 5% 2 6% 5% 2 5% 6% 7% 9% 45%	1416
	21st to end	Night	9% 4 3 6% 4 3 5% 6% 7% 9% 46%	1552
June	1st to 10th	Night	8% 4 2 5% 6% 3 5% 5% 7% 8% 47%	1440
	11th to 20th	Night	6% 4 2 6% 4 3 5% 5% 7% 8% 50%	1440
	21st to end	Night	3 3 2 3 3 2 5% 5% 5% 7% 62%	1440
July	1st to 10th	Night	2 2 1 3 4 2 3 4 6% 7% 66%	1440
	11th to 20th	Night	2 1 1 2 3 2 3 3 5% 6% 72%	1440
	21st to end	Night	1 1 1 1 1 2 3 4 5% 80%	1576
August	1st to 10th	Night	2 2 1 2 2 2 2 3 3 6% 75%	1432
	11th to 20th	Night	1 2 1 2 2 1 2 4 5% 8% 72%	1490
	21st to end	Night	3 2 1 3 3 2 4 4 5% 8% 66%	1975
September	1st to 10th	Night	2 2 1 2 4 2 3 5% 5% 6% 67%	1800
	11th to 20th	Night	5% 4 2 4 4 2 3 4 5% 7% 61%	1813
	21st to end	Night	6% 5% 1 3 3 2 4 4 6% 10% 57%	1998
October	1st to 10th	Night	8% 6% 2 4 5% 3 4 5% 6% 7% 52%	2160
	11th to 20th	Night	5% 6% 2 6% 5% 3 5% 5% 6% 8% 50%	2178
	21st to end	Night	13% 7% 2 5% 5% 3 4 5% 6% 8% 43%	2574
November	1st to 10th	Night	15% 9% 4 5% 5% 3 4 5% 7% 8% 37%	2445
	11th to 20th	Night	11% 11% 3 6% 6% 3 5% 6% 6% 8% 34%	2660
	21st to end	Night	11% 16% 6% 8% 5% 3 4 5% 6% 8% 28%	2660
December	1st to 10th	Night	13% 13% 5% 8% 5% 3 5% 4 6% 8% 29%	2660
	11th to 20th	Night	14% 16% 8% 13% 7% 4 6% 5% 5% 6% 17%	3280
	21st to end	Night	17% 22% 5% 9% 7% 4 4 4 5% 5% 20%	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	67% 8% 10% 10% 4 1	1519
	11th to 20th	Day	60% 9% 15% 13% 2 1	1464
	21st to end	Day	58% 7% 15% 16% 4	1584
February	1st to 10th	Day	51% 9% 19% 15% 5% 1	1536
	11th to 20th	Day	45% 8% 19% 18% 9% 1	1584
	21st to end	Day	47% 10% 17% 17% 8%	1480
March	1st to 10th	Day	42% 9% 18% 20% 10% 1	1800
	11th to 20th	Day	41% 9% 17% 22% 11%	1896
	21st to end	Day	44% 10% 19% 19% 6% 1	2340
April	1st to 10th	Day	42% 9% 16% 22% 10% 2	2160
	11th to 20th	Day	39% 8% 17% 21% 12% 3	2132
	21st to end	Day	37% 9% 13% 23% 15% 4	2404
May	1st to 10th	Day	30% 8% 14% 30% 15% 4	2520
	11th to 20th	Day	36% 7% 16% 27% 12% 1	2480
	21st to end	Day	39% 9% 13% 25% 13% 2	2724
June	1st to 10th	Day	38% 8% 12% 22% 15% 5%	2520
	11th to 20th	Day	34% 8% 12% 26% 16% 4	2520
	21st to end	Day	24% 8% 11% 27% 23% 7%	2520
July	1st to 10th	Day	20% 5% 9% 24% 28% 13%	2451
	11th to 20th	Day	17% 4 7% 20% 31% 20%	2445
	21st to end	Day	10% 4 5% 22% 40% 20%	2589
August	1st to 10th	Day	15% 5% 8% 25% 32% 15%	2490
	11th to 20th	Day	14% 4 9% 28% 34% 10%	2406
	21st to end	Day	18% 7% 10% 32% 27% 6%	2381
September	1st to 10th	Day	16% 5% 11% 29% 30% 8%	2160
	11th to 20th	Day	27% 6% 12% 24% 24% 6%	2147
	21st to end	Day	27% 7% 17% 27% 17% 5%	1960
October	1st to 10th	Day	31% 6% 14% 31% 17% 2	1800
	11th to 20th	Day	34% 8% 20% 25% 13% 1	1782
	21st to end	Day	42% 7% 16% 24% 11% 1	1782
November	1st to 10th	Day	48% 9% 15% 18% 9% 1	1632
	11th to 20th	Day	49% 10% 16% 15% 8% 2	1520
	21st to end	Day	55% 10% 15% 12% 6% 2	1520
December	1st to 10th	Day	55% 7% 16% 16% 6%	1520
	11th to 20th	Day	66% 9% 13% 8% 5%	1928
	21st to end	Day	68% 7% 10% 10% 5%	2794
January	1st to 10th	Night	66% 8% 12% 10% 4 1	2646
	11th to 20th	Night	61% 8% 14% 14% 3	2574
	21st to end	Night	62% 8% 15% 12% 4 1	2772
February	1st to 10th	Night	50% 10% 19% 15% 5% 2	2421
	11th to 20th	Night	44% 8% 20% 20% 7% 1	2273
	21st to end	Night	43% 11% 15% 20% 9% 1	1776
March	1st to 10th	Night	45% 8% 17% 20% 9% 1	2160
	11th to 20th	Night	40% 9% 15% 24% 11% 1	2062
	21st to end	Night	44% 8% 18% 22% 6% 1	2016
April	1st to 10th	Night	39% 8% 15% 26% 10% 2	1800
	11th to 20th	Night	34% 8% 15% 24% 17% 3	1779
	21st to end	Night	32% 6% 14% 30% 16% 3	1554
May	1st to 10th	Night	27% 6% 14% 32% 16% 4	1440
	11th to 20th	Night	32% 8% 15% 27% 15% 2	1416
	21st to end	Night	32% 7% 14% 31% 14% 2	1552
June	1st to 10th	Night	32% 7% 13% 26% 18% 5%	1440
	11th to 20th	Night	28% 7% 16% 29% 17% 4	1440
	21st to end	Night	22% 5% 14% 30% 25% 6%	1440
July	1st to 10th	Night	18% 5% 10% 25% 30% 14%	1400
	11th to 20th	Night	13% 4 8% 25% 30% 20%	1392
	21st to end	Night	7% 3 5% 24% 36% 25%	1488
August	1st to 10th	Night	12% 4 8% 25% 32% 19%	1424
	11th to 20th	Night	11% 4 11% 28% 36% 11%	1490
	21st to end	Night	16% 6% 9% 26% 35% 8%	1975
September	1st to 10th	Night	17% 5% 10% 28% 31% 9%	1800
	11th to 20th	Night	22% 6% 11% 26% 27% 8%	1813
	21st to end	Night	23% 5% 16% 33% 16% 6%	1998
October	1st to 10th	Night	32% 6% 12% 30% 19% 2	2160
	11th to 20th	Night	32% 7% 17% 28% 16% 2	2178
	21st to end	Night	39% 7% 14% 28% 11% 1	2574
November	1st to 10th	Night	45% 8% 19% 16% 9% 2	2445
	11th to 20th	Night	48% 10% 16% 16% 7% 3	2660
	21st to end	Night	56% 8% 15% 14% 7% 1	2660
December	1st to 10th	Night	55% 7% 16% 19% 3	2660
	11th to 20th	Night	67% 10% 11% 8% 3	3276
	21st to end	Night	67% 6% 9% 11% 6% 1	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	26% 4 14% 38% 12% 6%	180
	11th to 20th	Day	25% 7% 16% 28% 19% 5%	166
	21st to end	Day	26% 1 17% 36% 18% 3	176
February	1st to 10th	Day	10% 5% 31% 39% 13% 2	256
	11th to 20th	Day	16% 5% 32% 31% 12% 4	335
	21st to end	Day	8% 5% 32% 36% 16% 2	346
March	1st to 10th	Day	14% 8% 32% 30% 13% 4	420
	11th to 20th	Day	14% 11% 26% 25% 19% 5%	420
	21st to end	Day	10% 13% 33% 27% 13% 3	462
April	1st to 10th	Day	15% 15% 29% 26% 13% 3	420
	11th to 20th	Day	9% 18% 30% 26% 12% 5%	412
	21st to end	Day	8% 14% 31% 28% 16% 3	420
May	1st to 10th	Day	6% 14% 30% 32% 16% 2	423
	11th to 20th	Day	15% 9% 21% 30% 19% 6%	448
	21st to end	Day	11% 7% 24% 30% 20% 8%	485
June	1st to 10th	Day	10% 11% 28% 32% 16% 4	450
	11th to 20th	Day	8% 13% 32% 28% 16% 3	450
	21st to end	Day	6% 6% 22% 36% 25% 6%	450
July	1st to 10th	Day	5% 6% 21% 42% 22% 4	446
	11th to 20th	Day	3 8% 24% 34% 23% 7%	444
	21st to end	Day	2 4 23% 36% 26% 8%	487
August	1st to 10th	Day	5% 4 19% 36% 29% 8%	447
	11th to 20th	Day	2 3 18% 35% 32% 11%	437
	21st to end	Day	2 8% 21% 37% 23% 8%	495
September	1st to 10th	Day	4 5% 24% 34% 23% 9%	450
	11th to 20th	Day	6% 7% 20% 34% 26% 8%	450
	21st to end	Day	9% 9% 23% 33% 22% 5%	450
October	1st to 10th	Day	9% 8% 24% 30% 22% 6%	450
	11th to 20th	Day	9% 8% 25% 29% 22% 7%	432
	21st to end	Day	17% 5% 27% 34% 13% 4	297
November	1st to 10th	Day	17% 7% 23% 36% 15% 1	250
	11th to 20th	Day	21% 4 27% 25% 17% 6%	180
	21st to end	Day	17% 3 22% 34% 17% 6%	180
December	1st to 10th	Day	24% 5% 12% 31% 17% 12%	180
	11th to 20th	Day	19% 3 20% 43% 13% 2	180
	21st to end	Day	18% 3 13% 42% 18% 6%	198
January	1st to 10th	Night	23% 5% 21% 34% 16% 1	760
	11th to 20th	Night	22% 3 16% 38% 18% 3	736
	21st to end	Night	19% 2 16% 39% 20% 3	792
February	1st to 10th	Night	16% 3 22% 43% 15% 2	720
	11th to 20th	Night	14% 2 23% 42% 17% 2	704
	21st to end	Night	11% 4 22% 42% 18% 3	592
March	1st to 10th	Night	15% 4 20% 41% 17% 2	720
	11th to 20th	Night	10% 4 23% 43% 19% 1	720
	21st to end	Night	11% 6% 23% 41% 17% 1	792
April	1st to 10th	Night	10% 5% 20% 42% 22% 1	720
	11th to 20th	Night	9% 6% 25% 38% 20% 2	711
	21st to end	Night	8% 5% 27% 43% 15% 2	474
May	1st to 10th	Night	5% 4 30% 38% 23%	360
	11th to 20th	Night	11% 3 17% 39% 27% 2	354
	21st to end	Night	10% 4 14% 41% 27% 4	389
June	1st to 10th	Night	10% 4 24% 39% 22% 2	360
	11th to 20th	Night	6% 6% 25% 39% 23% 1	360
	21st to end	Night	3 4 20% 48% 24% 1	360
July	1st to 10th	Night	3 3 19% 44% 29% 2	350
	11th to 20th	Night	2 1 23% 46% 26% 1	348
	21st to end	Night	1 2 15% 47% 34% 1	394
August	1st to 10th	Night	3 2 14% 39% 38% 4	358
	11th to 20th	Night	2 2 11% 40% 41% 5%	422
	21st to end	Night	4 4 16% 42% 32% 3	787
September	1st to 10th	Night	3 3 16% 46% 28% 4	720
	11th to 20th	Night	7% 3 14% 32% 38% 7%	720
	21st to end	Night	8% 3 15% 45% 26% 3	720
October	1st to 10th	Night	11% 4 15% 43% 26% 2	720
	11th to 20th	Night	8% 3 23% 41% 21% 3	720
	21st to end	Night	17% 4 20% 40% 17% 3	792
November	1st to 10th	Night	20% 4 19% 44% 13% 1	740
	11th to 20th	Night	17% 3 25% 38% 14% 3	760
	21st to end	Night	21% 3 20% 38% 15% 4	760
December	1st to 10th	Night	18% 2 18% 39% 20% 3	760
	11th to 20th	Night	22% 3 19% 40% 15% 1	760
	21st to end	Night	26% 2 19% 43% 9% 1	836

Page generated at 2024-01-11 10:32:00. Version ac07

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