Highland Meadows Observing Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Highland Meadows Observing Site clear sky chart from 2005-11-06 to 2024-11-28.

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% 10% 4 9% 6% 5% 5% 4 6% 7% 38%	105630
	Night	7% 12% 4 9% 6% 5% 5% 4 5% 7% 38%	102504
Transparency	Day	44% 10% 14% 19% 11% 4	105386
	Night	46% 10% 15% 18% 9% 3	102394
Seeing	Day	14% 15% 25% 26% 16% 4	15282
	Night	14% 9% 21% 36% 18% 2	24468

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	7% 24% 10% 19% 9% 6% 5% 4 5% 4 8%	2224
	11th to 20th	Day	10% 16% 6% 13% 8% 7% 7% 4 5% 5% 20%	2516
	21st to end	Day	11% 24% 7% 20% 7% 5% 4 3 4 4 11%	2794
February	1st to 10th	Day	8% 18% 6% 16% 7% 6% 5% 5% 5% 6% 17%	1558
	11th to 20th	Day	5% 17% 7% 13% 8% 8% 5% 5% 6% 7% 20%	1703
	21st to end	Day	6% 17% 7% 14% 8% 7% 6% 5% 5% 5% 20%	1570
March	1st to 10th	Day	4 16% 6% 11% 7% 6% 6% 5% 6% 8% 27%	3138
	11th to 20th	Day	5% 15% 3 8% 6% 5% 5% 4 5% 6% 39%	3443
	21st to end	Day	8% 20% 5% 13% 6% 6% 6% 5% 7% 6% 18%	3900
April	1st to 10th	Day	6% 15% 6% 11% 7% 8% 6% 5% 7% 8% 22%	2280
	11th to 20th	Day	9% 14% 4 11% 8% 7% 6% 5% 6% 6% 25%	2440
	21st to end	Day	10% 14% 4 11% 6% 6% 6% 5% 6% 6% 27%	2470
May	1st to 10th	Day	13% 14% 5% 11% 5% 6% 5% 4 5% 5% 28%	4131
	11th to 20th	Day	7% 8% 3 8% 5% 5% 6% 5% 8% 10% 33%	4518
	21st to end	Day	13% 10% 3 9% 7% 6% 6% 5% 7% 8% 26%	5161
June	1st to 10th	Day	16% 9% 2 8% 6% 5% 6% 4 6% 7% 30%	2850
	11th to 20th	Day	15% 9% 3 8% 7% 6% 5% 5% 6% 8% 27%	2850
	21st to end	Day	6% 4 2 6% 5% 5% 5% 5% 7% 9% 46%	2850
July	1st to 10th	Day	2 2 1 3 4 6% 5% 3 5% 6% 61%	4740
	11th to 20th	Day	2 1 1 2 2 2 2 3 3 4 78%	4651
	21st to end	Day	1 1 1 3 2 2 2 3 5% 7% 73%	4790
August	1st to 10th	Day	5% 3 1 3 3 3 4 4 7% 8% 58%	4351
	11th to 20th	Day	5% 3 1 4 4 4 4 3 6% 8% 58%	4028
	21st to end	Day	5% 3 1 5% 3 3 4 3 5% 7% 59%	4521
September	1st to 10th	Day	6% 4 1 5% 3 4 4 4 6% 7% 56%	2283
	11th to 20th	Day	7% 6% 2 6% 4 5% 5% 4 6% 9% 46%	2090
	21st to end	Day	8% 5% 2 6% 5% 6% 6% 4 6% 8% 45%	2090
October	1st to 10th	Day	6% 5% 2 5% 4 4 4 3 5% 6% 57%	3426
	11th to 20th	Day	7% 7% 2 7% 4 4 5% 4 7% 9% 43%	2940
	21st to end	Day	9% 13% 4 11% 7% 7% 6% 5% 6% 6% 26%	3101
November	1st to 10th	Day	11% 20% 5% 11% 7% 7% 5% 5% 5% 7% 18%	1764
	11th to 20th	Day	8% 16% 6% 13% 7% 7% 6% 4 6% 8% 20%	1606
	21st to end	Day	7% 18% 5% 12% 8% 7% 6% 4 7% 6% 19%	1399
December	1st to 10th	Day	7% 19% 8% 13% 8% 6% 6% 4 6% 5% 19%	1330
	11th to 20th	Day	10% 21% 7% 13% 8% 7% 6% 4 5% 5% 12%	1682
	21st to end	Day	8% 18% 7% 22% 12% 7% 5% 3 4 4 11%	2442
January	1st to 10th	Night	8% 26% 9% 18% 9% 5% 4 4 4 4 9%	4726
	11th to 20th	Night	8% 14% 6% 14% 8% 6% 5% 4 4 5% 26%	4405
	21st to end	Night	13% 26% 8% 14% 6% 4 5% 3 4 4 14%	4862
February	1st to 10th	Night	9% 17% 4 12% 7% 5% 6% 3 6% 6% 24%	2620
	11th to 20th	Night	6% 15% 6% 12% 8% 6% 5% 4 6% 5% 27%	2362
	21st to end	Night	4 15% 5% 12% 7% 6% 6% 5% 6% 7% 27%	1884
March	1st to 10th	Night	3 11% 4 9% 6% 6% 6% 5% 8% 8% 35%	3736
	11th to 20th	Night	4 10% 3 7% 5% 5% 5% 3 5% 6% 46%	3536
	21st to end	Night	8% 17% 5% 11% 7% 6% 6% 5% 6% 7% 22%	3750
April	1st to 10th	Night	6% 11% 3 8% 6% 6% 5% 4 7% 9% 36%	1900
	11th to 20th	Night	7% 12% 4 7% 6% 5% 5% 5% 5% 7% 36%	1691
	21st to end	Night	7% 11% 3 7% 5% 5% 6% 5% 5% 7% 38%	1710
May	1st to 10th	Night	11% 12% 4 9% 7% 5% 5% 4 6% 7% 31%	2836
	11th to 20th	Night	7% 7% 3 6% 5% 5% 5% 5% 7% 9% 42%	2372
	21st to end	Night	16% 11% 3 8% 5% 5% 5% 5% 5% 8% 30%	2414
June	1st to 10th	Night	12% 7% 4 6% 5% 5% 5% 4 6% 7% 39%	1330
	11th to 20th	Night	12% 6% 2 7% 6% 6% 6% 6% 6% 8% 36%	1330
	21st to end	Night	4 4 2 5% 4 3 4 4 6% 8% 56%	1330
July	1st to 10th	Night	2 1 1 3 3 4 4 3 5% 6% 68%	2220
	11th to 20th	Night	2 1 1 2 1 2 2 2 2 5% 79%	2306
	21st to end	Night	2 2 1 2 2 2 2 2 4 5% 76%	2762
August	1st to 10th	Night	3 3 1 3 2 3 3 3 4 7% 69%	2580
	11th to 20th	Night	3 2 1 5% 4 5% 5% 4 7% 8% 56%	2811
	21st to end	Night	3 3 1 2 3 2 4 3 6% 8% 64%	3146
September	1st to 10th	Night	4 3 2 5% 3 3 4 3 5% 7% 61%	1894
	11th to 20th	Night	5% 4 2 5% 3 5% 4 4 6% 8% 53%	2090
	21st to end	Night	6% 5% 2 5% 3 5% 4 4 6% 9% 52%	2090
October	1st to 10th	Night	4 4 2 5% 4 3 5% 4 6% 8% 56%	3552
	11th to 20th	Night	4 5% 2 5% 4 4 5% 4 6% 9% 52%	3986
	21st to end	Night	5% 8% 2 7% 5% 5% 5% 4 7% 9% 43%	4457
November	1st to 10th	Night	11% 14% 5% 9% 6% 5% 6% 5% 6% 8% 25%	2535
	11th to 20th	Night	8% 15% 5% 10% 7% 5% 5% 4 6% 6% 28%	2772
	21st to end	Night	9% 17% 6% 10% 7% 6% 5% 4 6% 6% 24%	2935
December	1st to 10th	Night	7% 20% 6% 11% 7% 6% 5% 4 5% 5% 23%	2850
	11th to 20th	Night	8% 20% 8% 13% 8% 7% 6% 4 5% 6% 16%	3510
	21st to end	Night	9% 16% 7% 16% 9% 7% 5% 3 5% 5% 18%	5214

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	82% 9% 6% 3 1	2224
	11th to 20th	Day	67% 9% 12% 8% 3 1	2540
	21st to end	Day	76% 10% 6% 6% 1	2794
February	1st to 10th	Day	67% 10% 12% 6% 3 1	1558
	11th to 20th	Day	62% 14% 14% 7% 4	1712
	21st to end	Day	66% 9% 11% 9% 4 1	1570
March	1st to 10th	Day	51% 11% 17% 14% 7%	3138
	11th to 20th	Day	42% 12% 26% 17% 2	3444
	21st to end	Day	61% 14% 12% 9% 3	3900
April	1st to 10th	Day	58% 12% 14% 14% 2	2280
	11th to 20th	Day	57% 10% 14% 16% 4	2440
	21st to end	Day	55% 10% 14% 15% 5% 1	2470
May	1st to 10th	Day	54% 8% 13% 19% 5%	4131
	11th to 20th	Day	37% 14% 21% 20% 7%	4522
	21st to end	Day	47% 16% 19% 14% 3	5162
June	1st to 10th	Day	52% 10% 14% 17% 7%	2850
	11th to 20th	Day	51% 11% 14% 16% 6% 2	2850
	21st to end	Day	31% 11% 17% 25% 15% 1	2850
July	1st to 10th	Day	21% 7% 9% 27% 26% 11%	4666
	11th to 20th	Day	11% 4 7% 15% 29% 33%	4570
	21st to end	Day	12% 4 7% 23% 34% 20%	4639
August	1st to 10th	Day	21% 6% 12% 31% 25% 5%	4334
	11th to 20th	Day	22% 8% 14% 38% 17% 2	4067
	21st to end	Day	24% 6% 15% 34% 20% 3	4520
September	1st to 10th	Day	26% 7% 12% 31% 18% 5%	2283
	11th to 20th	Day	33% 10% 17% 24% 14% 2	2090
	21st to end	Day	36% 10% 21% 23% 10% 1	2090
October	1st to 10th	Day	28% 5% 20% 36% 10%	3426
	11th to 20th	Day	36% 8% 23% 25% 7%	2940
	21st to end	Day	54% 9% 18% 16% 3	3101
November	1st to 10th	Day	65% 11% 13% 8% 3	1764
	11th to 20th	Day	64% 11% 14% 7% 4	1606
	21st to end	Day	65% 13% 13% 7% 3	1399
December	1st to 10th	Day	67% 10% 12% 9% 2	1330
	11th to 20th	Day	73% 10% 12% 5% 1	1684
	21st to end	Day	71% 12% 10% 6% 1	2442
January	1st to 10th	Night	77% 12% 5% 5% 1	4726
	11th to 20th	Night	61% 9% 11% 9% 5% 4	4443
	21st to end	Night	74% 11% 8% 6% 2	4862
February	1st to 10th	Night	62% 10% 12% 10% 4 1	2620
	11th to 20th	Night	59% 13% 14% 10% 4	2363
	21st to end	Night	56% 11% 14% 14% 4 1	1884
March	1st to 10th	Night	41% 14% 21% 17% 7%	3736
	11th to 20th	Night	37% 13% 26% 22% 2	3536
	21st to end	Night	56% 17% 14% 11% 3	3750
April	1st to 10th	Night	44% 14% 19% 19% 4	1900
	11th to 20th	Night	46% 10% 17% 19% 7% 1	1691
	21st to end	Night	44% 12% 18% 19% 6% 1	1710
May	1st to 10th	Night	49% 12% 15% 20% 5%	2836
	11th to 20th	Night	35% 12% 17% 27% 9%	2372
	21st to end	Night	49% 12% 20% 14% 5%	2414
June	1st to 10th	Night	42% 10% 20% 20% 8%	1330
	11th to 20th	Night	44% 11% 15% 21% 7% 2	1330
	21st to end	Night	25% 9% 18% 29% 18% 2	1330
July	1st to 10th	Night	16% 8% 10% 28% 26% 12%	2185
	11th to 20th	Night	12% 3 8% 15% 22% 40%	2264
	21st to end	Night	12% 5% 8% 21% 30% 25%	2674
August	1st to 10th	Night	15% 5% 12% 33% 25% 10%	2572
	11th to 20th	Night	22% 7% 13% 35% 18% 4	2838
	21st to end	Night	17% 5% 13% 36% 24% 4	3146
September	1st to 10th	Night	23% 7% 15% 30% 18% 8%	1894
	11th to 20th	Night	27% 8% 16% 31% 16% 3	2090
	21st to end	Night	29% 10% 22% 23% 14% 3	2090
October	1st to 10th	Night	26% 6% 19% 35% 13%	3552
	11th to 20th	Night	29% 10% 21% 28% 12%	3986
	21st to end	Night	38% 9% 24% 22% 7%	4457
November	1st to 10th	Night	59% 11% 14% 11% 4	2535
	11th to 20th	Night	58% 13% 16% 10% 4	2772
	21st to end	Night	61% 11% 14% 10% 3	2935
December	1st to 10th	Night	65% 10% 12% 10% 3	2850
	11th to 20th	Night	68% 12% 13% 5% 1	3507
	21st to end	Night	66% 12% 12% 7% 2	5214

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	17% 16% 18% 32% 12% 6%	180
	11th to 20th	Day	20% 11% 24% 27% 12% 6%	180
	21st to end	Day	17% 14% 27% 28% 11% 2	198
February	1st to 10th	Day	20% 19% 30% 24% 6% 1	198
	11th to 20th	Day	14% 18% 25% 29% 13% 1	308
	21st to end	Day	19% 18% 29% 25% 8% 1	382
March	1st to 10th	Day	17% 20% 30% 19% 12% 2	460
	11th to 20th	Day	16% 15% 25% 25% 14% 5%	460
	21st to end	Day	18% 20% 30% 21% 9% 3	506
April	1st to 10th	Day	17% 22% 32% 19% 8% 2	460
	11th to 20th	Day	18% 25% 28% 17% 10% 2	452
	21st to end	Day	18% 22% 26% 20% 11% 3	460
May	1st to 10th	Day	18% 15% 24% 29% 11% 3	463
	11th to 20th	Day	20% 11% 25% 24% 16% 5%	564
	21st to end	Day	21% 11% 17% 27% 19% 5%	734
June	1st to 10th	Day	17% 14% 26% 22% 18% 4	680
	11th to 20th	Day	18% 18% 27% 21% 15% 2	680
	21st to end	Day	10% 11% 25% 25% 23% 6%	680
July	1st to 10th	Day	5% 8% 23% 31% 28% 6%	671
	11th to 20th	Day	5% 11% 23% 33% 24% 4	618
	21st to end	Day	3 11% 26% 31% 24% 5%	531
August	1st to 10th	Day	8% 9% 26% 30% 21% 6%	487
	11th to 20th	Day	6% 9% 24% 27% 23% 10%	477
	21st to end	Day	9% 13% 23% 31% 18% 7%	539
September	1st to 10th	Day	9% 14% 25% 27% 18% 7%	490
	11th to 20th	Day	9% 13% 29% 24% 18% 6%	490
	21st to end	Day	12% 18% 26% 24% 16% 3	490
October	1st to 10th	Day	15% 12% 25% 29% 14% 5%	452
	11th to 20th	Day	16% 13% 22% 27% 14% 8%	300
	21st to end	Day	25% 13% 23% 24% 12% 2	330
November	1st to 10th	Day	20% 19% 24% 25% 11%	300
	11th to 20th	Day	17% 17% 25% 28% 11% 2	300
	21st to end	Day	16% 14% 27% 26% 14% 2	204
December	1st to 10th	Day	22% 17% 21% 19% 14% 8%	180
	11th to 20th	Day	16% 16% 26% 27% 14% 2	180
	21st to end	Day	13% 12% 24% 34% 14% 3	198
January	1st to 10th	Night	22% 12% 24% 30% 10% 2	950
	11th to 20th	Night	19% 9% 24% 33% 12% 2	770
	21st to end	Night	18% 11% 21% 39% 10% 1	836
February	1st to 10th	Night	18% 13% 25% 32% 11% 2	760
	11th to 20th	Night	16% 10% 27% 35% 11% 1	744
	21st to end	Night	16% 11% 22% 32% 16% 2	628
March	1st to 10th	Night	11% 12% 26% 36% 14% 1	760
	11th to 20th	Night	14% 11% 23% 34% 16% 2	760
	21st to end	Night	14% 11% 25% 31% 17% 2	836
April	1st to 10th	Night	13% 9% 25% 35% 18% 2	760
	11th to 20th	Night	12% 12% 28% 34% 13% 1	563
	21st to end	Night	12% 12% 25% 33% 16% 1	570
May	1st to 10th	Night	11% 8% 25% 36% 18% 2	559
	11th to 20th	Night	11% 6% 17% 34% 29% 3	374
	21st to end	Night	17% 5% 18% 30% 25% 4	411
June	1st to 10th	Night	14% 6% 20% 36% 22% 3	380
	11th to 20th	Night	14% 7% 28% 30% 19% 2	380
	21st to end	Night	7% 3 16% 39% 32% 4	380
July	1st to 10th	Night	3 2 11% 45% 36% 2	370
	11th to 20th	Night	4 3 12% 49% 30% 1	368
	21st to end	Night	2 2 12% 45% 35% 3	416
August	1st to 10th	Night	3 2 12% 40% 38% 4	403
	11th to 20th	Night	3 3 13% 39% 35% 6%	564
	21st to end	Night	6% 5% 17% 42% 28% 2	627
September	1st to 10th	Night	7% 1 15% 41% 29% 6%	740
	11th to 20th	Night	7% 5% 14% 36% 33% 5%	760
	21st to end	Night	9% 6% 18% 38% 24% 5%	760
October	1st to 10th	Night	10% 8% 17% 39% 23% 3	760
	11th to 20th	Night	11% 8% 18% 38% 22% 3	760
	21st to end	Night	16% 11% 23% 36% 13% 2	836
November	1st to 10th	Night	18% 11% 21% 38% 11% 1	780
	11th to 20th	Night	20% 15% 25% 29% 11%	972
	21st to end	Night	16% 12% 23% 33% 14% 1	986
December	1st to 10th	Night	17% 11% 21% 34% 14% 3	950
	11th to 20th	Night	19% 8% 26% 37% 10%	950
	21st to end	Night	21% 10% 24% 32% 13%	1045

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