McCleary
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the McCleary 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	22% 10% 3 8% 5% 4 4 3 5% 6% 29%	105826
	Night	24% 12% 3 7% 4 4 4 3 4 5% 30%	102318
Transparency	Day	54% 8% 12% 16% 9% 2	105581
	Night	54% 7% 13% 17% 7% 1	102209
Seeing	Day	25% 12% 23% 23% 13% 3	15322
	Night	27% 9% 20% 28% 15% 1	23676

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	39% 13% 4 10% 5% 5% 4 3 4 4 9%	2219
	11th to 20th	Day	32% 15% 4 8% 5% 4 3 2 4 4 19%	2450
	21st to end	Day	45% 15% 4 8% 4 4 3 2 3 3 8%	2990
February	1st to 10th	Day	33% 14% 3 10% 6% 4 5% 3 5% 5% 12%	1710
	11th to 20th	Day	34% 16% 3 8% 5% 4 4 3 4 4 16%	1665
	21st to end	Day	31% 16% 4 9% 6% 4 3 3 4 5% 15%	1444
March	1st to 10th	Day	23% 14% 5% 11% 8% 7% 5% 3 5% 5% 15%	3310
	11th to 20th	Day	25% 11% 3 7% 4 3 3 2 3 5% 32%	3490
	21st to end	Day	27% 16% 6% 10% 5% 5% 4 3 4 5% 15%	3885
April	1st to 10th	Day	31% 13% 4 10% 5% 5% 4 4 5% 5% 14%	2280
	11th to 20th	Day	27% 12% 4 9% 6% 5% 4 3 4 5% 21%	2311
	21st to end	Day	24% 12% 4 9% 7% 5% 4 4 5% 6% 20%	2470
May	1st to 10th	Day	20% 9% 3 7% 5% 4 4 3 5% 6% 34%	4389
	11th to 20th	Day	13% 8% 3 7% 5% 4 5% 5% 6% 10% 33%	4377
	21st to end	Day	26% 11% 3 10% 6% 6% 5% 4 6% 5% 17%	4813
June	1st to 10th	Day	23% 11% 3 8% 5% 5% 4 3 5% 8% 25%	2741
	11th to 20th	Day	20% 12% 4 10% 5% 5% 6% 5% 7% 6% 21%	2850
	21st to end	Day	16% 8% 3 8% 5% 5% 4 4 6% 6% 35%	2850
July	1st to 10th	Day	7% 5% 2 5% 3 3 2 3 4 5% 62%	4740
	11th to 20th	Day	7% 7% 2 5% 3 3 3 3 4 6% 58%	4594
	21st to end	Day	13% 8% 3 5% 3 3 3 3 4 6% 49%	4790
August	1st to 10th	Day	7% 9% 2 4 3 3 4 3 5% 7% 52%	4194
	11th to 20th	Day	12% 8% 3 8% 5% 5% 5% 4 7% 8% 35%	4026
	21st to end	Day	18% 8% 3 5% 4 3 4 3 4 6% 42%	4377
September	1st to 10th	Day	11% 8% 2 7% 4 4 4 3 5% 7% 45%	2280
	11th to 20th	Day	16% 9% 4 8% 5% 5% 4 3 5% 7% 34%	2256
	21st to end	Day	20% 8% 3 7% 4 4 5% 3 4 6% 36%	2012
October	1st to 10th	Day	18% 7% 2 6% 4 4 5% 4 6% 10% 34%	3180
	11th to 20th	Day	31% 9% 3 6% 5% 4 3 3 5% 8% 23%	3161
	21st to end	Day	28% 9% 4 8% 6% 4 5% 4 5% 6% 20%	3340
November	1st to 10th	Day	38% 12% 3 8% 5% 5% 5% 3 4 5% 12%	1578
	11th to 20th	Day	36% 11% 3 8% 6% 5% 5% 3 5% 4 15%	1600
	21st to end	Day	33% 11% 4 8% 5% 4 4 2 4 5% 18%	1576
December	1st to 10th	Day	31% 12% 3 10% 5% 5% 3 3 4 4 20%	1520
	11th to 20th	Day	37% 12% 4 9% 5% 5% 5% 3 5% 5% 8%	1916
	21st to end	Day	31% 17% 6% 11% 6% 5% 4 3 4 4 9%	2442
January	1st to 10th	Night	38% 18% 4 9% 5% 4 3 2 3 3 10%	4726
	11th to 20th	Night	31% 13% 3 7% 4 4 3 3 5% 6% 21%	4444
	21st to end	Night	43% 14% 3 8% 4 3 3 2 3 4 11%	4670
February	1st to 10th	Night	32% 14% 4 7% 4 4 4 3 4 6% 18%	2470
	11th to 20th	Night	28% 16% 3 8% 5% 4 3 3 4 4 22%	2402
	21st to end	Night	28% 16% 3 8% 5% 4 4 3 5% 5% 20%	2009
March	1st to 10th	Night	22% 16% 5% 10% 7% 5% 4 3 5% 6% 17%	3562
	11th to 20th	Night	21% 12% 3 6% 3 3 2 2 4 5% 38%	3489
	21st to end	Night	29% 20% 4 10% 5% 4 3 2 3 4 16%	3767
April	1st to 10th	Night	26% 13% 4 9% 5% 5% 4 4 4 5% 21%	1900
	11th to 20th	Night	20% 11% 3 9% 5% 5% 4 4 5% 7% 26%	1815
	21st to end	Night	22% 11% 3 8% 5% 5% 4 3 5% 6% 27%	1710
May	1st to 10th	Night	21% 9% 2 4 4 3 2 2 4 5% 44%	2572
	11th to 20th	Night	11% 8% 2 7% 4 4 4 4 5% 7% 43%	2516
	21st to end	Night	13% 19% 4 8% 5% 4 4 4 5% 7% 28%	2762
June	1st to 10th	Night	19% 8% 2 7% 5% 4 4 4 6% 7% 34%	1435
	11th to 20th	Night	14% 8% 2 7% 6% 4 5% 5% 7% 9% 33%	1330
	21st to end	Night	10% 9% 2 8% 4 3 3 3 5% 8% 44%	1330
July	1st to 10th	Night	5% 6% 2 5% 3 2 2 2 3 3 67%	2220
	11th to 20th	Night	4 5% 3 5% 4 3 4 2 4 6% 58%	2366
	21st to end	Night	8% 9% 2 5% 3 2 2 2 4 6% 57%	2762
August	1st to 10th	Night	4 10% 4 7% 4 3 3 3 4 7% 51%	2741
	11th to 20th	Night	11% 13% 3 8% 3 3 3 2 4 5% 46%	2812
	21st to end	Night	17% 9% 2 5% 3 3 2 2 4 5% 47%	3293
September	1st to 10th	Night	8% 6% 3 6% 3 3 2 2 4 6% 55%	1900
	11th to 20th	Night	16% 9% 3 6% 4 4 4 4 5% 7% 39%	1919
	21st to end	Night	17% 8% 4 7% 4 3 3 3 4 7% 40%	2167
October	1st to 10th	Night	15% 7% 3 6% 4 3 4 3 5% 8% 42%	3800
	11th to 20th	Night	29% 11% 3 6% 3 3 3 3 4 5% 29%	3777
	21st to end	Night	28% 10% 3 7% 4 4 4 3 5% 5% 26%	4224
November	1st to 10th	Night	35% 11% 3 6% 4 4 4 3 5% 5% 19%	2716
	11th to 20th	Night	35% 12% 3 7% 5% 3 4 3 4 4 20%	2800
	21st to end	Night	30% 10% 3 7% 5% 5% 5% 4 5% 4 21%	2758
December	1st to 10th	Night	31% 11% 3 7% 5% 5% 3 3 4 5% 23%	2660
	11th to 20th	Night	33% 13% 4 8% 5% 5% 4 4 4 5% 14%	3280
	21st to end	Night	32% 16% 6% 10% 5% 4 4 3 3 3 14%	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	79% 8% 5% 5% 2 1	2219
	11th to 20th	Day	68% 7% 8% 13% 3 1	2474
	21st to end	Day	82% 5% 6% 5% 2	2990
February	1st to 10th	Day	73% 8% 9% 6% 3	1710
	11th to 20th	Day	73% 6% 8% 8% 4 1	1674
	21st to end	Day	71% 6% 8% 9% 5% 1	1444
March	1st to 10th	Day	69% 9% 12% 9% 2	3310
	11th to 20th	Day	54% 6% 12% 26% 2 1	3490
	21st to end	Day	69% 8% 12% 10% 1	3885
April	1st to 10th	Day	69% 7% 13% 9% 1	2280
	11th to 20th	Day	65% 6% 10% 11% 7% 1	2311
	21st to end	Day	63% 7% 13% 12% 4 1	2470
May	1st to 10th	Day	47% 8% 16% 19% 10%	4389
	11th to 20th	Day	41% 13% 23% 19% 5%	4380
	21st to end	Day	62% 11% 15% 9% 2	4814
June	1st to 10th	Day	58% 7% 16% 13% 6%	2741
	11th to 20th	Day	60% 9% 14% 14% 4	2850
	21st to end	Day	46% 9% 17% 19% 7% 2	2850
July	1st to 10th	Day	25% 5% 9% 19% 25% 17%	4666
	11th to 20th	Day	23% 5% 12% 26% 31% 4	4513
	21st to end	Day	31% 7% 13% 31% 15% 2	4639
August	1st to 10th	Day	26% 7% 13% 30% 21% 3	4177
	11th to 20th	Day	41% 11% 20% 19% 7% 2	4065
	21st to end	Day	42% 7% 11% 25% 14% 1	4376
September	1st to 10th	Day	38% 6% 15% 21% 15% 5%	2280
	11th to 20th	Day	49% 7% 12% 17% 13% 2	2256
	21st to end	Day	50% 7% 14% 17% 11% 1	2012
October	1st to 10th	Day	43% 7% 13% 30% 7%	3180
	11th to 20th	Day	58% 8% 13% 14% 7%	3161
	21st to end	Day	61% 8% 11% 11% 8% 1	3340
November	1st to 10th	Day	73% 8% 8% 8% 4	1578
	11th to 20th	Day	72% 7% 7% 8% 5% 1	1600
	21st to end	Day	69% 7% 7% 10% 8%	1576
December	1st to 10th	Day	69% 5% 7% 11% 8%	1520
	11th to 20th	Day	76% 8% 7% 7% 2	1919
	21st to end	Day	78% 8% 7% 5% 3	2442
January	1st to 10th	Night	78% 8% 6% 5% 2 1	4726
	11th to 20th	Night	62% 8% 10% 16% 3 1	4482
	21st to end	Night	78% 6% 6% 6% 3 1	4670
February	1st to 10th	Night	68% 7% 11% 8% 5%	2470
	11th to 20th	Night	66% 7% 11% 9% 7%	2404
	21st to end	Night	67% 6% 11% 11% 5%	2009
March	1st to 10th	Night	65% 7% 13% 12% 3	3562
	11th to 20th	Night	47% 6% 17% 25% 3 1	3490
	21st to end	Night	72% 8% 10% 9% 1	3767
April	1st to 10th	Night	63% 7% 14% 14% 2	1900
	11th to 20th	Night	56% 6% 15% 14% 7% 1	1815
	21st to end	Night	55% 8% 14% 15% 7% 1	1710
May	1st to 10th	Night	42% 7% 15% 28% 8%	2572
	11th to 20th	Night	33% 10% 25% 21% 10%	2516
	21st to end	Night	50% 13% 21% 15% 2	2762
June	1st to 10th	Night	46% 7% 19% 21% 6% 1	1435
	11th to 20th	Night	45% 10% 23% 20% 2	1330
	21st to end	Night	35% 8% 26% 22% 7% 3	1330
July	1st to 10th	Night	19% 6% 14% 25% 20% 16%	2185
	11th to 20th	Night	19% 7% 15% 30% 28% 2	2324
	21st to end	Night	24% 5% 15% 34% 18% 4	2674
August	1st to 10th	Night	21% 9% 17% 29% 21% 3	2733
	11th to 20th	Night	36% 9% 23% 20% 9% 3	2839
	21st to end	Night	39% 5% 14% 26% 15% 2	3293
September	1st to 10th	Night	27% 7% 18% 25% 17% 6%	1900
	11th to 20th	Night	40% 7% 14% 19% 15% 4	1919
	21st to end	Night	42% 7% 14% 22% 13% 2	2167
October	1st to 10th	Night	38% 6% 15% 34% 7%	3800
	11th to 20th	Night	56% 5% 13% 21% 5%	3777
	21st to end	Night	57% 8% 12% 15% 8% 1	4224
November	1st to 10th	Night	66% 8% 10% 12% 4	2716
	11th to 20th	Night	69% 6% 9% 9% 5% 2	2800
	21st to end	Night	63% 8% 11% 9% 8% 1	2758
December	1st to 10th	Night	65% 7% 9% 13% 6%	2660
	11th to 20th	Night	70% 9% 10% 8% 3	3276
	21st to end	Night	74% 8% 8% 8% 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	44% 11% 18% 18% 8% 1	180
	11th to 20th	Day	43% 11% 20% 18% 7% 1	180
	21st to end	Day	42% 12% 17% 20% 8% 1	316
February	1st to 10th	Day	39% 15% 17% 21% 7% 1	370
	11th to 20th	Day	42% 10% 27% 14% 7%	365
	21st to end	Day	38% 20% 18% 17% 6% 1	323
March	1st to 10th	Day	34% 16% 23% 20% 7% 1	460
	11th to 20th	Day	31% 12% 25% 17% 11% 4	460
	21st to end	Day	33% 16% 26% 15% 8% 2	506
April	1st to 10th	Day	35% 16% 23% 15% 8% 2	460
	11th to 20th	Day	30% 18% 24% 15% 10% 3	452
	21st to end	Day	29% 18% 27% 17% 8% 1	460
May	1st to 10th	Day	22% 12% 25% 25% 13% 2	463
	11th to 20th	Day	27% 11% 20% 21% 15% 5%	488
	21st to end	Day	21% 10% 26% 28% 10% 4	529
June	1st to 10th	Day	25% 13% 25% 22% 12% 3	571
	11th to 20th	Day	21% 18% 33% 19% 7% 2	680
	21st to end	Day	14% 14% 27% 26% 15% 3	680
July	1st to 10th	Day	11% 10% 28% 34% 15% 3	671
	11th to 20th	Day	8% 8% 27% 31% 20% 6%	587
	21st to end	Day	8% 6% 22% 30% 24% 10%	531
August	1st to 10th	Day	11% 8% 21% 29% 22% 9%	487
	11th to 20th	Day	8% 6% 20% 30% 29% 8%	477
	21st to end	Day	15% 11% 24% 27% 16% 7%	539
September	1st to 10th	Day	14% 9% 24% 30% 17% 6%	490
	11th to 20th	Day	18% 11% 21% 27% 19% 3	490
	21st to end	Day	21% 10% 22% 30% 16% 2	490
October	1st to 10th	Day	27% 9% 21% 20% 19% 4	490
	11th to 20th	Day	30% 10% 20% 24% 15% 2	490
	21st to end	Day	31% 19% 21% 18% 9% 2	480
November	1st to 10th	Day	39% 15% 19% 19% 7% 2	205
	11th to 20th	Day	42% 16% 17% 16% 10% 1	200
	21st to end	Day	35% 12% 16% 23% 13% 2	194
December	1st to 10th	Day	42% 15% 18% 17% 7% 1	180
	11th to 20th	Day	43% 14% 22% 14% 6% 1	180
	21st to end	Day	42% 12% 22% 19% 5% 1	198
January	1st to 10th	Night	48% 11% 16% 17% 8%	850
	11th to 20th	Night	39% 7% 14% 28% 12%	776
	21st to end	Night	37% 7% 15% 27% 13% 1	836
February	1st to 10th	Night	37% 11% 15% 25% 11% 1	760
	11th to 20th	Night	34% 13% 19% 23% 11%	744
	21st to end	Night	34% 13% 20% 22% 10% 1	628
March	1st to 10th	Night	33% 10% 19% 22% 13% 2	760
	11th to 20th	Night	34% 9% 20% 25% 11% 1	760
	21st to end	Night	33% 12% 22% 22% 9% 1	836
April	1st to 10th	Night	30% 12% 22% 24% 12% 1	760
	11th to 20th	Night	22% 13% 22% 28% 14% 1	687
	21st to end	Night	25% 11% 22% 31% 11%	570
May	1st to 10th	Night	19% 9% 23% 35% 13% 1	399
	11th to 20th	Night	20% 7% 27% 30% 14% 2	374
	21st to end	Night	17% 9% 28% 30% 15% 1	411
June	1st to 10th	Night	18% 10% 26% 35% 11%	380
	11th to 20th	Night	14% 11% 36% 28% 12%	380
	21st to end	Night	11% 7% 31% 33% 17% 1	380
July	1st to 10th	Night	6% 5% 29% 42% 17% 1	370
	11th to 20th	Night	7% 5% 26% 44% 17% 1	368
	21st to end	Night	5% 4 31% 39% 19% 2	416
August	1st to 10th	Night	8% 4 21% 37% 26% 3	499
	11th to 20th	Night	7% 3 16% 35% 34% 5%	564
	21st to end	Night	13% 6% 26% 32% 21% 3	709
September	1st to 10th	Night	10% 5% 22% 32% 28% 3	760
	11th to 20th	Night	15% 7% 18% 31% 25% 3	760
	21st to end	Night	19% 8% 21% 31% 19% 2	760
October	1st to 10th	Night	20% 7% 16% 31% 24% 3	760
	11th to 20th	Night	29% 5% 16% 27% 20% 3	760
	21st to end	Night	32% 8% 20% 25% 14% 1	836
November	1st to 10th	Night	37% 8% 18% 27% 9% 1	780
	11th to 20th	Night	38% 11% 18% 25% 8% 1	800
	21st to end	Night	33% 8% 19% 26% 12% 2	788
December	1st to 10th	Night	34% 7% 19% 28% 12% 1	760
	11th to 20th	Night	42% 7% 17% 25% 8% 1	760
	21st to end	Night	43% 11% 19% 19% 8%	935

Page generated at 2024-11-24 21:22:20. Version ac07

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