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 2024-01-14.

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	8% 10% 4 8% 7% 4 6% 5% 6% 7% 34%	74615
	Night	7% 11% 5% 8% 7% 4 5% 5% 6% 7% 35%	75150
Transparency	Day	48% 10% 14% 17% 10% 2	74308
	Night	48% 11% 15% 16% 8% 2	74975
Seeing	Day	14% 14% 25% 26% 16% 4	14061
	Night	14% 9% 21% 35% 19% 2	23414

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	9% 20% 8% 12% 11% 6% 7% 5% 5% 5% 12%	1334
	11th to 20th	Day	9% 16% 8% 12% 9% 5% 7% 6% 6% 6% 15%	1464
	21st to end	Day	8% 17% 7% 13% 9% 5% 6% 5% 6% 6% 17%	1584
February	1st to 10th	Day	8% 16% 7% 13% 10% 4 6% 6% 5% 7% 18%	1476
	11th to 20th	Day	5% 15% 8% 12% 9% 5% 7% 6% 6% 7% 19%	1611
	21st to end	Day	6% 14% 9% 13% 9% 5% 7% 6% 6% 6% 20%	1480
March	1st to 10th	Day	7% 16% 8% 11% 9% 5% 7% 5% 5% 6% 21%	1800
	11th to 20th	Day	8% 16% 5% 9% 7% 4 6% 6% 5% 7% 25%	1946
	21st to end	Day	10% 18% 5% 11% 7% 4 6% 6% 6% 7% 20%	2215
April	1st to 10th	Day	7% 14% 6% 11% 8% 6% 7% 6% 6% 8% 21%	2160
	11th to 20th	Day	10% 12% 5% 10% 8% 5% 7% 6% 5% 6% 24%	2310
	21st to end	Day	10% 13% 4 9% 7% 4 6% 6% 6% 7% 27%	2340
May	1st to 10th	Day	9% 10% 4 9% 7% 4 6% 6% 6% 7% 33%	2348
	11th to 20th	Day	11% 8% 4 8% 7% 4 7% 6% 6% 9% 31%	2548
	21st to end	Day	16% 11% 5% 8% 7% 5% 6% 6% 6% 7% 24%	2917
June	1st to 10th	Day	17% 8% 3 7% 7% 4 6% 5% 6% 8% 29%	2700
	11th to 20th	Day	16% 8% 3 7% 8% 4 6% 6% 7% 8% 26%	2700
	21st to end	Day	6% 4 2 5% 6% 3 5% 6% 7% 9% 47%	2700
July	1st to 10th	Day	3 3 2 3 4 4 5% 5% 5% 7% 60%	2700
	11th to 20th	Day	3 3 1 3 4 2 3 4 5% 6% 64%	2653
	21st to end	Day	2 2 1 3 2 2 2 3 4 6% 73%	2741
August	1st to 10th	Day	4 3 1 3 3 2 4 5% 6% 8% 61%	2483
	11th to 20th	Day	6% 3 1 4 3 2 4 4 5% 8% 60%	2299
	21st to end	Day	6% 4 2 5% 5% 3 4 5% 4 8% 53%	2574
September	1st to 10th	Day	6% 4 2 4 4 4 4 5% 5% 7% 55%	2164
	11th to 20th	Day	7% 5% 2 5% 5% 3 5% 6% 6% 9% 47%	1980
	21st to end	Day	8% 5% 2 6% 6% 5% 6% 6% 5% 8% 44%	1980
October	1st to 10th	Day	10% 9% 4 7% 7% 4 5% 4 5% 5% 40%	1944
	11th to 20th	Day	9% 9% 3 7% 7% 4 5% 6% 6% 8% 35%	1679
	21st to end	Day	12% 12% 5% 8% 6% 4 5% 5% 6% 7% 29%	1782
November	1st to 10th	Day	12% 18% 6% 9% 9% 4 6% 5% 5% 8% 18%	1674
	11th to 20th	Day	8% 15% 7% 11% 8% 4 7% 5% 6% 7% 22%	1526
	21st to end	Day	8% 16% 6% 11% 9% 6% 7% 5% 7% 6% 20%	1349
December	1st to 10th	Day	7% 18% 9% 11% 9% 4 7% 5% 6% 6% 19%	1330
	11th to 20th	Day	10% 20% 8% 12% 9% 5% 7% 6% 5% 5% 13%	1682
	21st to end	Day	8% 17% 7% 19% 15% 6% 6% 4 4 4 11%	2442
January	1st to 10th	Night	10% 20% 8% 13% 10% 5% 5% 5% 5% 6% 14%	2836
	11th to 20th	Night	9% 15% 7% 12% 9% 4 5% 5% 5% 6% 23%	2584
	21st to end	Night	8% 15% 6% 10% 8% 4 6% 6% 6% 7% 24%	2772
February	1st to 10th	Night	9% 16% 5% 11% 8% 4 6% 5% 6% 6% 24%	2482
	11th to 20th	Night	7% 14% 6% 10% 10% 4 6% 6% 6% 5% 27%	2234
	21st to end	Night	5% 13% 6% 10% 8% 4 6% 6% 6% 7% 28%	1776
March	1st to 10th	Night	6% 13% 6% 10% 6% 5% 6% 5% 7% 7% 29%	2160
	11th to 20th	Night	6% 11% 4 6% 7% 5% 7% 7% 7% 8% 33%	2013
	21st to end	Night	6% 13% 5% 9% 7% 4 6% 7% 7% 9% 26%	2138
April	1st to 10th	Night	5% 9% 4 7% 7% 5% 6% 6% 7% 9% 37%	1800
	11th to 20th	Night	7% 11% 5% 6% 7% 5% 5% 6% 5% 7% 36%	1601
	21st to end	Night	7% 10% 3 7% 6% 4 6% 7% 5% 7% 39%	1620
May	1st to 10th	Night	6% 7% 4 6% 6% 4 7% 6% 7% 10% 38%	1610
	11th to 20th	Night	9% 7% 3 6% 6% 3 7% 6% 6% 9% 39%	1342
	21st to end	Night	14% 10% 3 6% 5% 3 5% 5% 4 8% 35%	1358
June	1st to 10th	Night	12% 7% 4 6% 5% 4 5% 5% 6% 7% 38%	1260
	11th to 20th	Night	13% 6% 3 6% 6% 4 6% 8% 6% 8% 36%	1260
	21st to end	Night	5% 3 2 5% 4 2 4 5% 6% 8% 56%	1260
July	1st to 10th	Night	2 1 1 2 2 2 3 4 6% 7% 71%	1260
	11th to 20th	Night	3 2 1 3 2 2 2 3 4 7% 71%	1304
	21st to end	Night	2 1 1 3 1 2 2 4 6% 76%	1576
August	1st to 10th	Night	3 2 1 2 3 2 2 3 4 8% 70%	1455
	11th to 20th	Night	4 2 1 3 3 2 3 4 5% 8% 65%	1602
	21st to end	Night	5% 4 1 3 4 2 4 4 6% 7% 60%	1782
September	1st to 10th	Night	4 3 2 5% 4 3 4 4 5% 6% 60%	1794
	11th to 20th	Night	5% 4 2 5% 4 3 5% 4 6% 8% 54%	1980
	21st to end	Night	7% 5% 2 4 4 3 5% 5% 6% 8% 51%	1980
October	1st to 10th	Night	7% 6% 3 6% 6% 3 5% 6% 6% 7% 46%	2016
	11th to 20th	Night	8% 6% 2 6% 6% 4 6% 5% 6% 9% 43%	2279
	21st to end	Night	9% 11% 4 6% 8% 4 5% 5% 5% 8% 35%	2574
November	1st to 10th	Night	12% 13% 6% 8% 7% 4 6% 5% 6% 8% 25%	2405
	11th to 20th	Night	9% 14% 6% 9% 8% 4 5% 5% 6% 7% 28%	2633
	21st to end	Night	9% 14% 8% 9% 7% 5% 5% 6% 6% 6% 25%	2830
December	1st to 10th	Night	7% 18% 8% 10% 8% 4 6% 5% 5% 6% 23%	2850
	11th to 20th	Night	8% 19% 8% 12% 10% 5% 6% 5% 5% 6% 17%	3510
	21st to end	Night	9% 16% 7% 14% 11% 6% 5% 4 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	76% 10% 8% 4 1	1334
	11th to 20th	Day	71% 12% 10% 4 1 1	1464
	21st to end	Day	69% 10% 10% 8% 2	1584
February	1st to 10th	Day	66% 10% 13% 6% 4 1	1476
	11th to 20th	Day	62% 14% 14% 7% 3	1620
	21st to end	Day	66% 9% 11% 9% 5% 1	1480
March	1st to 10th	Day	63% 10% 13% 10% 4	1800
	11th to 20th	Day	57% 11% 14% 14% 4	1947
	21st to end	Day	62% 12% 14% 10% 2	2215
April	1st to 10th	Day	59% 12% 14% 13% 2	2160
	11th to 20th	Day	58% 10% 13% 15% 4	2310
	21st to end	Day	55% 10% 15% 15% 4 1	2340
May	1st to 10th	Day	47% 9% 19% 19% 6%	2348
	11th to 20th	Day	47% 13% 17% 16% 7%	2552
	21st to end	Day	56% 11% 16% 12% 4	2918
June	1st to 10th	Day	53% 10% 15% 17% 6%	2700
	11th to 20th	Day	52% 12% 14% 16% 5% 1	2700
	21st to end	Day	31% 11% 17% 26% 14% 1	2700
July	1st to 10th	Day	23% 7% 12% 30% 22% 6%	2626
	11th to 20th	Day	19% 6% 11% 27% 30% 7%	2572
	21st to end	Day	13% 5% 9% 26% 39% 8%	2589
August	1st to 10th	Day	18% 8% 14% 29% 24% 7%	2466
	11th to 20th	Day	22% 7% 15% 31% 23% 3	2299
	21st to end	Day	28% 8% 12% 27% 21% 4	2574
September	1st to 10th	Day	27% 8% 13% 30% 18% 5%	2164
	11th to 20th	Day	32% 11% 16% 25% 15% 2	1980
	21st to end	Day	37% 10% 20% 22% 9% 1	1980
October	1st to 10th	Day	44% 8% 18% 24% 6%	1944
	11th to 20th	Day	46% 10% 20% 19% 4	1679
	21st to end	Day	54% 11% 17% 14% 4	1782
November	1st to 10th	Day	65% 11% 12% 8% 3	1674
	11th to 20th	Day	63% 12% 15% 6% 4 1	1526
	21st to end	Day	64% 13% 13% 7% 3	1349
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	74% 10% 7% 8% 2	2836
	11th to 20th	Night	64% 11% 13% 8% 2 2	2584
	21st to end	Night	61% 13% 12% 10% 3	2772
February	1st to 10th	Night	62% 11% 12% 10% 4 1	2482
	11th to 20th	Night	59% 13% 14% 10% 3	2235
	21st to end	Night	55% 11% 15% 14% 5% 1	1776
March	1st to 10th	Night	54% 12% 16% 13% 5%	2160
	11th to 20th	Night	47% 15% 17% 18% 3	2013
	21st to end	Night	53% 15% 17% 12% 4	2138
April	1st to 10th	Night	44% 14% 19% 19% 4	1800
	11th to 20th	Night	47% 10% 16% 19% 7% 1	1601
	21st to end	Night	44% 12% 19% 19% 6% 1	1620
May	1st to 10th	Night	37% 14% 21% 20% 7%	1610
	11th to 20th	Night	41% 10% 18% 23% 8%	1342
	21st to end	Night	47% 9% 21% 15% 8%	1358
June	1st to 10th	Night	42% 10% 19% 20% 8%	1260
	11th to 20th	Night	45% 12% 15% 20% 7% 1	1260
	21st to end	Night	24% 9% 18% 29% 18% 1	1260
July	1st to 10th	Night	13% 7% 13% 32% 28% 8%	1225
	11th to 20th	Night	15% 4 13% 26% 30% 12%	1262
	21st to end	Night	10% 5% 10% 24% 38% 13%	1488
August	1st to 10th	Night	14% 5% 14% 32% 24% 11%	1447
	11th to 20th	Night	17% 6% 13% 35% 23% 6%	1602
	21st to end	Night	22% 6% 12% 28% 27% 4	1782
September	1st to 10th	Night	24% 7% 15% 29% 18% 7%	1794
	11th to 20th	Night	27% 8% 15% 31% 17% 3	1980
	21st to end	Night	30% 11% 22% 22% 14% 2	1980
October	1st to 10th	Night	37% 10% 17% 26% 9%	2016
	11th to 20th	Night	38% 11% 20% 23% 7%	2279
	21st to end	Night	49% 11% 16% 17% 7%	2574
November	1st to 10th	Night	59% 11% 14% 11% 4	2405
	11th to 20th	Night	58% 13% 16% 9% 4	2633
	21st to end	Night	60% 11% 15% 10% 3	2830
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% 13% 25% 22% 13% 7%	166
	21st to end	Day	15% 14% 30% 28% 11% 2	176
February	1st to 10th	Day	20% 21% 31% 22% 5% 1	176
	11th to 20th	Day	15% 18% 25% 28% 13% 1	276
	21st to end	Day	16% 17% 29% 27% 9% 1	346
March	1st to 10th	Day	18% 20% 30% 18% 11% 2	420
	11th to 20th	Day	17% 16% 25% 26% 12% 4	420
	21st to end	Day	19% 20% 29% 21% 9% 3	462
April	1st to 10th	Day	17% 21% 32% 20% 9% 2	420
	11th to 20th	Day	20% 25% 27% 16% 10% 2	412
	21st to end	Day	18% 22% 27% 19% 11% 3	420
May	1st to 10th	Day	17% 15% 24% 30% 11% 3	423
	11th to 20th	Day	20% 10% 24% 24% 16% 6%	519
	21st to end	Day	22% 9% 17% 27% 20% 5%	679
June	1st to 10th	Day	17% 14% 25% 22% 19% 4	630
	11th to 20th	Day	17% 17% 27% 21% 15% 2	630
	21st to end	Day	9% 11% 23% 26% 24% 7%	630
July	1st to 10th	Day	5% 8% 22% 30% 29% 6%	621
	11th to 20th	Day	5% 12% 23% 31% 25% 4	571
	21st to end	Day	3 11% 26% 30% 25% 5%	487
August	1st to 10th	Day	7% 10% 25% 30% 21% 6%	447
	11th to 20th	Day	7% 9% 23% 27% 24% 11%	437
	21st to end	Day	9% 13% 23% 30% 18% 7%	495
September	1st to 10th	Day	10% 15% 26% 27% 17% 6%	450
	11th to 20th	Day	9% 11% 29% 25% 19% 7%	450
	21st to end	Day	13% 18% 26% 24% 17% 4	450
October	1st to 10th	Day	15% 13% 24% 29% 15% 5%	414
	11th to 20th	Day	17% 13% 22% 26% 13% 8%	270
	21st to end	Day	26% 13% 23% 24% 12% 2	297
November	1st to 10th	Day	21% 18% 24% 26% 11%	270
	11th to 20th	Day	18% 14% 25% 30% 11% 2	270
	21st to end	Day	15% 13% 27% 28% 15% 3	189
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	20% 10% 23% 33% 12% 2	746
	21st to end	Night	17% 10% 21% 40% 11% 1	792
February	1st to 10th	Night	18% 13% 26% 31% 11% 2	720
	11th to 20th	Night	16% 10% 26% 36% 11% 1	704
	21st to end	Night	15% 11% 23% 33% 17% 2	592
March	1st to 10th	Night	11% 12% 25% 37% 13% 1	720
	11th to 20th	Night	14% 11% 24% 34% 16% 2	720
	21st to end	Night	14% 10% 25% 32% 16% 2	792
April	1st to 10th	Night	11% 9% 24% 36% 18% 2	720
	11th to 20th	Night	12% 12% 29% 33% 13% 1	533
	21st to end	Night	13% 12% 25% 33% 16% 1	540
May	1st to 10th	Night	10% 8% 25% 36% 18% 2	530
	11th to 20th	Night	11% 5% 17% 34% 29% 3	354
	21st to end	Night	17% 5% 18% 30% 26% 4	389
June	1st to 10th	Night	13% 6% 20% 35% 23% 3	360
	11th to 20th	Night	15% 6% 28% 29% 20% 2	360
	21st to end	Night	7% 2 16% 37% 34% 4	360
July	1st to 10th	Night	3 3 11% 45% 37% 2	350
	11th to 20th	Night	4 3 13% 48% 31% 1	348
	21st to end	Night	3 2 11% 45% 36% 3	394
August	1st to 10th	Night	3 2 12% 39% 40% 4	381
	11th to 20th	Night	3 3 13% 39% 35% 6%	534
	21st to end	Night	6% 4 16% 42% 29% 3	594
September	1st to 10th	Night	7% 2 16% 42% 27% 6%	701
	11th to 20th	Night	7% 4 14% 35% 34% 5%	720
	21st to end	Night	10% 6% 17% 38% 25% 5%	720
October	1st to 10th	Night	10% 8% 17% 38% 24% 3	720
	11th to 20th	Night	11% 8% 17% 38% 22% 3	720
	21st to end	Night	17% 10% 22% 35% 14% 2	792
November	1st to 10th	Night	19% 11% 21% 37% 11% 1	740
	11th to 20th	Night	20% 14% 24% 30% 11%	923
	21st to end	Night	16% 12% 23% 33% 14% 1	950
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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