Grande Cache
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Grande Cache clear sky chart from 2005-11-06 to 2024-02-10.

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	9% 10% 4 9% 8% 4 6% 6% 6% 8% 29%	77401
	Night	6% 9% 4 8% 7% 4 6% 6% 7% 9% 33%	81512
Transparency	Day	51% 12% 16% 14% 6% 1	77094
	Night	45% 13% 18% 17% 7% 1	81399
Seeing	Day	21% 21% 29% 19% 9% 2	15202
	Night	15% 19% 30% 24% 10% 1	23590

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	2 8% 5% 10% 12% 6% 8% 6% 7% 10% 26%	1899
	11th to 20th	Day	3 9% 5% 9% 8% 4 5% 6% 11% 9% 31%	2071
	21st to end	Day	3 9% 4 9% 8% 4 5% 6% 8% 9% 34%	2673
February	1st to 10th	Day	3 10% 5% 14% 9% 4 8% 6% 7% 8% 27%	1512
	11th to 20th	Day	3 11% 8% 14% 8% 5% 7% 7% 6% 7% 25%	1492
	21st to end	Day	1 8% 6% 12% 12% 5% 7% 8% 7% 7% 26%	1415
March	1st to 10th	Day	1 10% 4 9% 10% 6% 8% 7% 8% 9% 29%	1800
	11th to 20th	Day	2 10% 4 9% 8% 5% 7% 8% 8% 9% 31%	1850
	21st to end	Day	4 14% 7% 13% 11% 5% 6% 6% 7% 7% 20%	2367
April	1st to 10th	Day	3 13% 6% 11% 10% 5% 8% 9% 7% 7% 20%	2160
	11th to 20th	Day	6% 17% 6% 10% 10% 5% 6% 4 6% 7% 24%	2258
	21st to end	Day	7% 13% 6% 9% 8% 4 7% 7% 6% 7% 26%	2520
May	1st to 10th	Day	10% 14% 7% 10% 8% 4 6% 6% 6% 6% 24%	2520
	11th to 20th	Day	11% 11% 4 7% 6% 5% 5% 6% 6% 7% 32%	2588
	21st to end	Day	20% 11% 4 8% 6% 4 6% 5% 5% 7% 25%	3054
June	1st to 10th	Day	18% 10% 4 7% 7% 4 6% 5% 6% 7% 26%	2880
	11th to 20th	Day	21% 12% 5% 10% 8% 4 6% 6% 6% 6% 17%	2880
	21st to end	Day	14% 8% 4 9% 8% 5% 6% 6% 6% 7% 27%	2880
July	1st to 10th	Day	17% 8% 3 7% 9% 4 5% 5% 5% 7% 28%	2880
	11th to 20th	Day	14% 6% 4 7% 9% 5% 7% 6% 6% 7% 29%	2880
	21st to end	Day	10% 7% 3 7% 7% 4 8% 6% 7% 8% 34%	2879
August	1st to 10th	Day	11% 8% 3 8% 7% 5% 5% 7% 7% 7% 32%	2507
	11th to 20th	Day	12% 7% 2 6% 7% 5% 5% 5% 6% 9% 36%	2475
	21st to end	Day	14% 8% 3 7% 9% 5% 6% 6% 6% 8% 29%	2577
September	1st to 10th	Day	13% 9% 3 8% 6% 4 5% 5% 5% 7% 35%	2160
	11th to 20th	Day	12% 10% 3 6% 5% 4 5% 5% 5% 8% 37%	2137
	21st to end	Day	11% 9% 4 7% 6% 3 5% 6% 6% 7% 36%	1962
October	1st to 10th	Day	10% 13% 4 7% 7% 4 6% 5% 5% 7% 32%	1800
	11th to 20th	Day	6% 9% 5% 8% 6% 4 7% 6% 7% 9% 33%	1679
	21st to end	Day	8% 11% 4 8% 7% 4 5% 6% 6% 9% 31%	1778
November	1st to 10th	Day	6% 13% 6% 8% 7% 4 7% 7% 7% 8% 28%	1488
	11th to 20th	Day	3 10% 4 9% 7% 6% 6% 6% 7% 8% 34%	1330
	21st to end	Day	3 10% 6% 8% 8% 4 6% 6% 7% 12% 30%	1330
December	1st to 10th	Day	4 9% 7% 11% 7% 4 7% 5% 6% 7% 33%	1188
	11th to 20th	Day	4 12% 4 8% 7% 5% 7% 6% 7% 8% 32%	1442
	21st to end	Day	1 8% 4 9% 7% 5% 6% 5% 7% 9% 40%	2090
January	1st to 10th	Night	2 8% 4 13% 10% 4 6% 6% 7% 9% 30%	5046
	11th to 20th	Night	3 9% 4 7% 7% 4 8% 9% 10% 9% 29%	4858
	21st to end	Night	3 9% 4 10% 8% 4 7% 6% 8% 9% 32%	4982
February	1st to 10th	Night	4 12% 5% 9% 8% 5% 6% 7% 8% 8% 28%	2652
	11th to 20th	Night	3 12% 7% 11% 8% 5% 7% 6% 7% 9% 25%	2351
	21st to end	Night	2 9% 5% 12% 11% 4 7% 7% 6% 7% 29%	1841
March	1st to 10th	Night	2 9% 5% 11% 9% 5% 6% 5% 6% 8% 34%	2160
	11th to 20th	Night	2 9% 5% 8% 6% 4 6% 7% 8% 9% 37%	2105
	21st to end	Night	3 10% 6% 11% 8% 4 6% 6% 7% 9% 29%	1989
April	1st to 10th	Night	5% 11% 5% 8% 8% 4 6% 7% 8% 9% 29%	1800
	11th to 20th	Night	7% 13% 5% 8% 8% 3 5% 7% 6% 8% 31%	1651
	21st to end	Night	9% 11% 5% 8% 6% 3 5% 4 6% 8% 34%	1440
May	1st to 10th	Night	8% 13% 6% 9% 7% 3 6% 6% 8% 6% 28%	1440
	11th to 20th	Night	9% 8% 3 7% 5% 4 6% 6% 7% 8% 38%	1303
	21st to end	Night	15% 9% 5% 6% 5% 3 6% 4 7% 9% 32%	1217
June	1st to 10th	Night	14% 9% 4 7% 6% 3 4 5% 6% 6% 36%	1080
	11th to 20th	Night	19% 10% 5% 7% 6% 5% 7% 7% 6% 7% 22%	1080
	21st to end	Night	11% 8% 3 6% 8% 4 5% 7% 7% 7% 37%	1080
July	1st to 10th	Night	15% 7% 2 5% 5% 4 5% 5% 7% 9% 37%	1080
	11th to 20th	Night	13% 6% 2 5% 6% 3 5% 6% 7% 9% 37%	1080
	21st to end	Night	8% 6% 3 6% 5% 3 7% 5% 7% 9% 41%	1435
August	1st to 10th	Night	11% 9% 3 6% 5% 3 5% 5% 6% 8% 38%	1432
	11th to 20th	Night	11% 4 2 5% 5% 3 5% 6% 7% 9% 44%	1424
	21st to end	Night	12% 7% 3 6% 8% 4 6% 6% 6% 9% 33%	1776
September	1st to 10th	Night	14% 8% 4 7% 6% 3 5% 5% 7% 6% 36%	1800
	11th to 20th	Night	11% 10% 4 5% 5% 3 4 4 7% 7% 40%	1822
	21st to end	Night	9% 8% 3 6% 5% 4 5% 6% 7% 9% 39%	1995
October	1st to 10th	Night	9% 13% 5% 7% 6% 4 5% 5% 5% 8% 33%	2160
	11th to 20th	Night	7% 9% 3 7% 6% 4 5% 6% 7% 10% 36%	2281
	21st to end	Night	5% 10% 6% 10% 8% 4 5% 6% 8% 8% 31%	2578
November	1st to 10th	Night	6% 12% 6% 9% 6% 3 5% 5% 6% 10% 32%	2590
	11th to 20th	Night	3 10% 5% 9% 7% 4 5% 5% 7% 10% 34%	2831
	21st to end	Night	3 11% 5% 8% 8% 5% 7% 6% 8% 9% 30%	2850
December	1st to 10th	Night	4 7% 5% 10% 8% 4 6% 5% 6% 8% 36%	2987
	11th to 20th	Night	4 11% 5% 9% 7% 5% 6% 7% 7% 8% 30%	3750
	21st to end	Night	1 8% 4 7% 7% 4 7% 7% 7% 10% 39%	5566

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	49% 13% 22% 13% 2 1	1899
	11th to 20th	Day	44% 10% 13% 12% 16% 6%	2092
	21st to end	Day	40% 17% 26% 10% 6%	2673
February	1st to 10th	Day	53% 11% 12% 11% 10% 2	1512
	11th to 20th	Day	58% 9% 13% 12% 7%	1500
	21st to end	Day	54% 12% 12% 13% 7% 2	1415
March	1st to 10th	Day	49% 13% 16% 12% 8% 1	1800
	11th to 20th	Day	46% 13% 15% 18% 7% 1	1850
	21st to end	Day	62% 13% 12% 9% 4	2367
April	1st to 10th	Day	59% 14% 15% 9% 3	2160
	11th to 20th	Day	60% 9% 13% 13% 5%	2258
	21st to end	Day	55% 12% 13% 15% 4	2520
May	1st to 10th	Day	59% 12% 13% 12% 4	2520
	11th to 20th	Day	50% 11% 15% 16% 8%	2592
	21st to end	Day	58% 10% 14% 14% 4 1	3055
June	1st to 10th	Day	56% 11% 12% 15% 5% 1	2880
	11th to 20th	Day	65% 12% 12% 9% 2	2880
	21st to end	Day	54% 12% 15% 13% 5% 1	2880
July	1st to 10th	Day	53% 11% 16% 13% 6% 1	2801
	11th to 20th	Day	52% 14% 16% 14% 3	2793
	21st to end	Day	43% 16% 18% 18% 5%	2719
August	1st to 10th	Day	49% 15% 15% 16% 5% 1	2490
	11th to 20th	Day	44% 13% 18% 20% 5% 1	2475
	21st to end	Day	51% 12% 17% 14% 5% 1	2577
September	1st to 10th	Day	49% 11% 17% 16% 5% 2	2160
	11th to 20th	Day	45% 12% 15% 19% 7% 1	2137
	21st to end	Day	45% 12% 17% 15% 9% 2	1962
October	1st to 10th	Day	51% 12% 15% 16% 6% 1	1800
	11th to 20th	Day	45% 13% 18% 19% 5%	1679
	21st to end	Day	48% 13% 16% 16% 6% 1	1778
November	1st to 10th	Day	52% 11% 16% 15% 5% 1	1488
	11th to 20th	Day	45% 14% 20% 14% 6% 2	1330
	21st to end	Day	45% 14% 23% 10% 5% 4	1330
December	1st to 10th	Day	50% 13% 12% 16% 8% 1	1188
	11th to 20th	Day	47% 12% 19% 17% 5% 1	1444
	21st to end	Day	36% 13% 18% 19% 12% 2	2090
January	1st to 10th	Night	47% 13% 16% 14% 8% 2	5046
	11th to 20th	Night	42% 12% 14% 12% 17% 2	4899
	21st to end	Night	42% 16% 25% 11% 5% 1	4982
February	1st to 10th	Night	51% 11% 15% 12% 9% 2	2652
	11th to 20th	Night	53% 13% 14% 13% 6% 1	2353
	21st to end	Night	51% 9% 13% 18% 8% 1	1841
March	1st to 10th	Night	46% 12% 14% 18% 10% 1	2160
	11th to 20th	Night	41% 13% 17% 22% 6% 1	2106
	21st to end	Night	47% 14% 18% 15% 6%	1989
April	1st to 10th	Night	47% 13% 19% 16% 5%	1800
	11th to 20th	Night	48% 12% 18% 16% 6%	1651
	21st to end	Night	46% 12% 15% 21% 6% 1	1440
May	1st to 10th	Night	52% 12% 14% 16% 6%	1440
	11th to 20th	Night	41% 12% 17% 21% 9%	1303
	21st to end	Night	46% 13% 17% 18% 5% 1	1217
June	1st to 10th	Night	48% 11% 15% 19% 8%	1080
	11th to 20th	Night	57% 13% 15% 13% 2	1080
	21st to end	Night	43% 13% 20% 20% 3 1	1080
July	1st to 10th	Night	39% 14% 20% 20% 6% 1	1050
	11th to 20th	Night	41% 17% 21% 18% 2	1044
	21st to end	Night	35% 12% 23% 24% 6% 1	1355
August	1st to 10th	Night	42% 13% 22% 19% 4	1424
	11th to 20th	Night	35% 13% 24% 22% 5%	1424
	21st to end	Night	47% 13% 19% 16% 5%	1776
September	1st to 10th	Night	45% 12% 19% 17% 5% 1	1800
	11th to 20th	Night	41% 11% 18% 22% 8% 1	1822
	21st to end	Night	39% 16% 20% 16% 9%	1995
October	1st to 10th	Night	47% 13% 16% 19% 5%	2160
	11th to 20th	Night	40% 15% 19% 22% 4	2281
	21st to end	Night	48% 14% 17% 14% 6%	2578
November	1st to 10th	Night	47% 11% 18% 16% 6% 1	2590
	11th to 20th	Night	46% 14% 18% 14% 6% 1	2831
	21st to end	Night	47% 15% 19% 11% 6% 2	2850
December	1st to 10th	Night	46% 11% 17% 15% 9% 1	2987
	11th to 20th	Night	48% 13% 15% 18% 4	3747
	21st to end	Night	35% 14% 20% 23% 7% 1	5566

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	14% 20% 31% 23% 9% 2	180
	11th to 20th	Day	17% 22% 26% 24% 10% 1	180
	21st to end	Day	23% 23% 30% 18% 5% 1	198
February	1st to 10th	Day	21% 24% 28% 16% 10% 1	178
	11th to 20th	Day	23% 28% 27% 16% 6%	252
	21st to end	Day	17% 23% 38% 16% 6% 1	318
March	1st to 10th	Day	17% 24% 31% 17% 9% 1	420
	11th to 20th	Day	18% 26% 33% 15% 6% 3	420
	21st to end	Day	22% 25% 27% 17% 8% 2	462
April	1st to 10th	Day	21% 24% 31% 16% 7% 1	420
	11th to 20th	Day	21% 21% 31% 15% 10% 1	412
	21st to end	Day	19% 25% 30% 16% 7% 3	420
May	1st to 10th	Day	20% 24% 30% 19% 7%	423
	11th to 20th	Day	18% 12% 30% 24% 13% 3	559
	21st to end	Day	22% 12% 23% 23% 16% 3	816
June	1st to 10th	Day	21% 21% 29% 20% 8% 1	810
	11th to 20th	Day	26% 20% 27% 18% 8% 1	810
	21st to end	Day	20% 17% 27% 22% 12% 3	810
July	1st to 10th	Day	22% 13% 30% 21% 13% 2	796
	11th to 20th	Day	17% 18% 31% 22% 10% 2	792
	21st to end	Day	15% 18% 30% 24% 11% 3	625
August	1st to 10th	Day	17% 15% 33% 22% 11% 3	447
	11th to 20th	Day	19% 21% 32% 19% 7% 2	437
	21st to end	Day	18% 25% 29% 17% 10% 1	495
September	1st to 10th	Day	24% 21% 30% 17% 6% 2	450
	11th to 20th	Day	25% 25% 26% 16% 6% 2	450
	21st to end	Day	28% 28% 22% 15% 6% 1	450
October	1st to 10th	Day	28% 22% 25% 14% 9% 2	450
	11th to 20th	Day	23% 26% 24% 19% 5% 2	329
	21st to end	Day	20% 26% 30% 16% 6% 1	295
November	1st to 10th	Day	28% 26% 30% 8% 6% 1	180
	11th to 20th	Day	21% 26% 35% 14% 3 1	180
	21st to end	Day	30% 20% 26% 16% 6% 3	180
December	1st to 10th	Day	14% 28% 29% 17% 8% 2	180
	11th to 20th	Day	21% 24% 29% 20% 6% 1	180
	21st to end	Day	16% 21% 30% 22% 8% 3	198
January	1st to 10th	Night	14% 22% 35% 23% 4 1	1040
	11th to 20th	Night	16% 22% 34% 21% 6% 1	944
	21st to end	Night	19% 24% 30% 20% 6% 1	868
February	1st to 10th	Night	19% 17% 28% 23% 12% 1	758
	11th to 20th	Night	12% 24% 31% 25% 7% 1	704
	21st to end	Night	10% 17% 37% 22% 13% 1	592
March	1st to 10th	Night	11% 21% 31% 26% 10% 1	720
	11th to 20th	Night	8% 23% 37% 23% 9% 1	720
	21st to end	Night	11% 19% 26% 30% 14% 1	792
April	1st to 10th	Night	12% 20% 30% 26% 12% 1	720
	11th to 20th	Night	15% 15% 29% 27% 14% 1	583
	21st to end	Night	16% 14% 27% 30% 11% 1	360
May	1st to 10th	Night	12% 12% 29% 33% 14% 1	360
	11th to 20th	Night	11% 5% 27% 41% 15% 1	354
	21st to end	Night	17% 11% 21% 24% 24% 3	389
June	1st to 10th	Night	18% 12% 24% 31% 14% 1	360
	11th to 20th	Night	23% 11% 24% 27% 14% 1	360
	21st to end	Night	13% 9% 28% 28% 19% 3	360
July	1st to 10th	Night	17% 9% 23% 33% 18% 1	350
	11th to 20th	Night	17% 12% 18% 31% 20% 1	348
	21st to end	Night	11% 10% 20% 30% 27% 2	394
August	1st to 10th	Night	15% 9% 21% 26% 26% 3	358
	11th to 20th	Night	12% 10% 26% 32% 19% 1	356
	21st to end	Night	17% 12% 28% 28% 14% 1	588
September	1st to 10th	Night	20% 14% 24% 28% 12% 1	720
	11th to 20th	Night	16% 16% 23% 26% 16% 1	720
	21st to end	Night	19% 23% 25% 22% 10% 2	720
October	1st to 10th	Night	20% 20% 24% 24% 10% 1	720
	11th to 20th	Night	16% 23% 29% 26% 6% 1	720
	21st to end	Night	19% 21% 34% 19% 6% 1	792
November	1st to 10th	Night	19% 27% 30% 17% 7%	740
	11th to 20th	Night	17% 29% 33% 18% 3	931
	21st to end	Night	19% 27% 33% 17% 3 1	950
December	1st to 10th	Night	15% 25% 32% 19% 8%	1015
	11th to 20th	Night	13% 24% 36% 20% 6%	1040
	21st to end	Night	14% 21% 37% 20% 7% 1	1144

Page generated at 2024-02-07 04:11:55. Version ac07

Copyright 2024 Attilla Danko