Blue Mountain
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Blue Mountain clear sky chart from 2005-11-06 to 2024-11-04.

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	28% 13% 3 6% 4 3 3 3 4 5% 29%	105812
	Night	32% 13% 3 5% 3 3 3 2 4 4 28%	101775
Transparency	Day	59% 5% 10% 16% 8% 1	105570
	Night	61% 5% 10% 15% 8% 2	101663
Seeing	Day	35% 11% 22% 22% 8% 2	14996
	Night	40% 7% 17% 23% 12% 1	23348

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	42% 24% 4 6% 3 2 2 1 2 2 10%	2356
	11th to 20th	Day	30% 14% 6% 7% 3 4 3 2 4 6% 22%	2516
	21st to end	Day	52% 16% 2 5% 2 2 2 2 2 3 12%	2801
February	1st to 10th	Day	36% 16% 3 8% 4 4 3 3 3 3 14%	1710
	11th to 20th	Day	34% 21% 4 6% 3 3 3 2 3 4 19%	1665
	21st to end	Day	29% 24% 4 7% 4 3 2 2 3 3 18%	1496
March	1st to 10th	Day	26% 22% 4 9% 4 4 3 3 4 4 17%	3159
	11th to 20th	Day	24% 18% 3 6% 3 3 2 1 2 3 35%	3490
	21st to end	Day	33% 22% 4 7% 4 4 4 3 4 4 13%	3996
April	1st to 10th	Day	32% 22% 3 6% 5% 4 5% 3 4 4 13%	2280
	11th to 20th	Day	30% 19% 3 7% 5% 3 3 3 3 4 18%	2252
	21st to end	Day	34% 17% 4 8% 4 4 4 3 3 4 14%	2549
May	1st to 10th	Day	24% 16% 2 6% 4 4 4 4 4 5% 26%	4420
	11th to 20th	Day	25% 12% 3 6% 4 3 4 3 4 8% 28%	4377
	21st to end	Day	42% 15% 3 7% 4 4 3 2 3 3 14%	4813
June	1st to 10th	Day	35% 10% 2 6% 4 4 4 3 4 5% 21%	2676
	11th to 20th	Day	39% 12% 3 7% 5% 4 4 4 4 4 14%	2850
	21st to end	Day	24% 9% 3 7% 4 4 5% 4 6% 6% 30%	2850
July	1st to 10th	Day	13% 5% 1 4 3 3 3 3 4 4 57%	4740
	11th to 20th	Day	10% 5% 1 3 3 2 2 3 3 5% 63%	4485
	21st to end	Day	17% 6% 2 4 3 3 3 3 4 6% 50%	4790
August	1st to 10th	Day	10% 4 1 4 3 3 3 3 4 6% 58%	4401
	11th to 20th	Day	19% 9% 3 8% 5% 4 5% 3 5% 6% 33%	4030
	21st to end	Day	22% 8% 3 7% 3 3 3 3 4 6% 38%	4306
September	1st to 10th	Day	17% 7% 3 5% 4 3 4 3 4 6% 44%	2280
	11th to 20th	Day	22% 8% 3 7% 4 4 4 4 4 5% 35%	2280
	21st to end	Day	27% 8% 2 6% 2 3 4 2 3 5% 37%	2019
October	1st to 10th	Day	26% 7% 2 4 3 3 4 3 6% 8% 34%	3180
	11th to 20th	Day	41% 9% 2 4 3 2 2 2 3 4 25%	3161
	21st to end	Day	40% 12% 4 6% 4 3 3 3 4 5% 18%	3200
November	1st to 10th	Day	45% 13% 2 5% 5% 3 3 3 3 3 15%	1574
	11th to 20th	Day	44% 15% 3 6% 2 2 2 2 3 3 19%	1520
	21st to end	Day	40% 17% 3 6% 3 2 3 2 3 4 18%	1520
December	1st to 10th	Day	37% 15% 2 5% 4 2 2 2 3 3 24%	1520
	11th to 20th	Day	37% 18% 3 6% 3 3 3 3 2 3 19%	1925
	21st to end	Day	32% 21% 4 9% 5% 3 3 2 4 4 13%	2625
January	1st to 10th	Night	42% 21% 4 6% 3 3 3 2 3 3 11%	4566
	11th to 20th	Night	33% 15% 4 5% 3 2 3 2 4 6% 22%	4382
	21st to end	Night	47% 14% 3 6% 3 3 3 2 3 4 13%	4853
February	1st to 10th	Night	35% 18% 3 6% 5% 4 4 3 3 3 18%	2470
	11th to 20th	Night	31% 20% 3 6% 3 3 4 3 3 4 20%	2402
	21st to end	Night	31% 21% 3 6% 3 3 3 3 3 4 19%	1957
March	1st to 10th	Night	24% 23% 4 8% 4 4 5% 4 4 5% 17%	3711
	11th to 20th	Night	27% 15% 3 4 2 2 2 2 2 5% 36%	3489
	21st to end	Night	37% 21% 3 7% 3 3 2 2 3 3 15%	3657
April	1st to 10th	Night	32% 19% 3 7% 4 3 4 4 5% 5% 15%	1900
	11th to 20th	Night	30% 16% 2 6% 4 3 3 3 4 5% 23%	1876
	21st to end	Night	36% 14% 3 6% 5% 4 3 3 5% 5% 18%	1630
May	1st to 10th	Night	26% 12% 2 6% 3 2 2 2 4 3 39%	2540
	11th to 20th	Night	26% 10% 2 4 3 2 3 3 4 5% 37%	2516
	21st to end	Night	42% 10% 3 7% 4 3 3 4 4 4 17%	2762
June	1st to 10th	Night	33% 9% 2 7% 4 4 4 3 4 5% 26%	1499
	11th to 20th	Night	36% 10% 3 6% 3 5% 3 2 5% 5% 21%	1330
	21st to end	Night	22% 6% 2 7% 4 3 5% 3 5% 6% 38%	1330
July	1st to 10th	Night	12% 4 2 4 3 2 2 2 3 3 63%	2220
	11th to 20th	Night	8% 3 1 2 2 2 2 2 3 5% 70%	2471
	21st to end	Night	17% 5% 2 4 2 2 2 2 4 4 55%	2762
August	1st to 10th	Night	7% 2 1 3 2 3 3 2 5% 6% 66%	2529
	11th to 20th	Night	21% 7% 2 5% 2 3 3 2 5% 5% 44%	2805
	21st to end	Night	26% 6% 2 4 3 2 2 2 3 3 46%	3367
September	1st to 10th	Night	17% 6% 2 4 3 3 3 2 3 5% 52%	1900
	11th to 20th	Night	26% 9% 2 6% 4 3 3 2 4 5% 36%	1900
	21st to end	Night	27% 8% 2 5% 2 3 3 3 4 5% 37%	2157
October	1st to 10th	Night	24% 7% 2 5% 4 4 4 3 6% 7% 35%	3800
	11th to 20th	Night	40% 7% 2 4 2 2 3 3 4 5% 28%	3777
	21st to end	Night	42% 13% 2 5% 3 2 2 2 4 3 21%	4361
November	1st to 10th	Night	43% 12% 3 6% 4 3 3 2 4 4 16%	2574
	11th to 20th	Night	44% 12% 3 5% 3 3 3 2 2 3 21%	2660
	21st to end	Night	40% 15% 3 5% 3 2 3 2 3 4 19%	2660
December	1st to 10th	Night	34% 14% 2 5% 5% 3 3 3 4 3 23%	2660
	11th to 20th	Night	39% 17% 4 5% 3 3 2 2 4 4 16%	3280
	21st to end	Night	34% 21% 3 7% 4 4 4 2 4 3 12%	5022

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	83% 2 3 8% 2 2	2356
	11th to 20th	Day	65% 4 7% 14% 8% 2	2540
	21st to end	Day	80% 4 5% 6% 5%	2801
February	1st to 10th	Day	75% 5% 7% 8% 3 1	1710
	11th to 20th	Day	73% 5% 6% 9% 6% 2	1674
	21st to end	Day	72% 5% 7% 11% 4	1496
March	1st to 10th	Day	69% 6% 9% 11% 5%	3159
	11th to 20th	Day	58% 3 9% 26% 2	3490
	21st to end	Day	77% 5% 10% 7% 1	3996
April	1st to 10th	Day	75% 7% 10% 7% 1	2280
	11th to 20th	Day	70% 6% 8% 11% 5% 1	2252
	21st to end	Day	76% 5% 7% 8% 4 1	2549
May	1st to 10th	Day	59% 7% 11% 17% 7%	4420
	11th to 20th	Day	56% 8% 21% 14% 2	4380
	21st to end	Day	77% 6% 10% 7%	4814
June	1st to 10th	Day	66% 6% 14% 9% 5%	2676
	11th to 20th	Day	73% 7% 10% 8% 2	2850
	21st to end	Day	53% 8% 14% 18% 6% 1	2850
July	1st to 10th	Day	30% 5% 8% 22% 24% 10%	4666
	11th to 20th	Day	25% 4 8% 27% 33% 2	4407
	21st to end	Day	34% 5% 14% 32% 12% 2	4639
August	1st to 10th	Day	27% 5% 11% 40% 16% 1	4384
	11th to 20th	Day	49% 8% 16% 19% 7% 1	4069
	21st to end	Day	48% 4 11% 25% 11% 1	4305
September	1st to 10th	Day	40% 7% 12% 23% 13% 5%	2280
	11th to 20th	Day	52% 6% 9% 17% 14% 3	2280
	21st to end	Day	51% 5% 15% 15% 10% 3	2019
October	1st to 10th	Day	48% 5% 12% 28% 6%	3180
	11th to 20th	Day	64% 3 9% 14% 9% 1	3161
	21st to end	Day	70% 4 9% 8% 8% 1	3200
November	1st to 10th	Day	75% 5% 8% 7% 5%	1574
	11th to 20th	Day	73% 4 6% 8% 7% 2	1520
	21st to end	Day	73% 4 4 8% 9% 3	1520
December	1st to 10th	Day	68% 5% 6% 12% 9% 1	1520
	11th to 20th	Day	71% 5% 9% 9% 5% 1	1928
	21st to end	Day	73% 7% 7% 9% 4	2625
January	1st to 10th	Night	81% 4 4 7% 2 2	4566
	11th to 20th	Night	66% 3 5% 14% 10% 2	4420
	21st to end	Night	77% 5% 6% 6% 5% 1	4853
February	1st to 10th	Night	72% 5% 7% 10% 4 1	2470
	11th to 20th	Night	69% 7% 7% 9% 7% 2	2404
	21st to end	Night	71% 4 8% 12% 4 1	1957
March	1st to 10th	Night	68% 5% 9% 11% 6%	3711
	11th to 20th	Night	54% 4 13% 26% 3 1	3490
	21st to end	Night	75% 5% 10% 9% 1	3657
April	1st to 10th	Night	71% 7% 12% 9% 1	1900
	11th to 20th	Night	65% 5% 10% 11% 7% 2	1876
	21st to end	Night	68% 7% 9% 10% 4 1	1630
May	1st to 10th	Night	53% 4 15% 21% 7%	2540
	11th to 20th	Night	52% 6% 19% 18% 4	2516
	21st to end	Night	72% 8% 12% 7% 1	2762
June	1st to 10th	Night	61% 5% 15% 13% 5%	1499
	11th to 20th	Night	65% 8% 13% 11% 3	1330
	21st to end	Night	48% 8% 19% 17% 6% 3	1330
July	1st to 10th	Night	29% 4 9% 23% 19% 16%	2185
	11th to 20th	Night	21% 3 9% 25% 39% 2	2426
	21st to end	Night	33% 6% 11% 28% 19% 3	2674
August	1st to 10th	Night	20% 5% 15% 39% 20% 2	2521
	11th to 20th	Night	44% 6% 20% 20% 8% 2	2832
	21st to end	Night	45% 4 12% 27% 12% 1	3367
September	1st to 10th	Night	36% 5% 14% 24% 15% 5%	1900
	11th to 20th	Night	51% 6% 8% 17% 14% 4	1900
	21st to end	Night	51% 6% 12% 18% 11% 3	2157
October	1st to 10th	Night	48% 5% 12% 28% 6%	3800
	11th to 20th	Night	60% 4 9% 15% 11% 1	3777
	21st to end	Night	69% 3 7% 11% 9% 1	4361
November	1st to 10th	Night	73% 5% 8% 9% 4 1	2574
	11th to 20th	Night	72% 4 7% 9% 7% 2	2660
	21st to end	Night	71% 3 5% 9% 9% 2	2660
December	1st to 10th	Night	67% 4 8% 10% 8% 2	2660
	11th to 20th	Night	73% 4 8% 10% 4 1	3276
	21st to end	Night	76% 6% 7% 8% 3	5022

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	50% 14% 16% 10% 8% 1	180
	11th to 20th	Day	48% 11% 19% 15% 7%	180
	21st to end	Day	56% 8% 14% 17% 6%	205
February	1st to 10th	Day	49% 11% 19% 16% 3 1	370
	11th to 20th	Day	53% 11% 19% 15% 3	365
	21st to end	Day	44% 12% 25% 16% 3	348
March	1st to 10th	Day	40% 15% 25% 16% 5%	460
	11th to 20th	Day	39% 12% 21% 19% 8% 1	460
	21st to end	Day	49% 12% 20% 15% 3	506
April	1st to 10th	Day	46% 13% 21% 15% 4 1	460
	11th to 20th	Day	42% 17% 19% 15% 6% 1	452
	21st to end	Day	43% 14% 21% 17% 5%	460
May	1st to 10th	Day	33% 12% 27% 23% 5%	463
	11th to 20th	Day	38% 13% 19% 20% 7% 2	488
	21st to end	Day	41% 13% 17% 21% 7% 2	529
June	1st to 10th	Day	34% 14% 22% 21% 8% 2	506
	11th to 20th	Day	37% 12% 26% 18% 5% 1	680
	21st to end	Day	25% 11% 25% 30% 7% 2	680
July	1st to 10th	Day	20% 10% 27% 32% 10% 2	671
	11th to 20th	Day	17% 12% 27% 29% 11% 3	520
	21st to end	Day	18% 7% 25% 32% 15% 4	531
August	1st to 10th	Day	17% 6% 26% 31% 15% 5%	487
	11th to 20th	Day	14% 10% 22% 34% 15% 5%	477
	21st to end	Day	22% 11% 23% 30% 11% 3	539
September	1st to 10th	Day	22% 13% 25% 28% 11% 2	490
	11th to 20th	Day	25% 13% 22% 27% 11% 2	490
	21st to end	Day	28% 11% 25% 22% 11% 2	490
October	1st to 10th	Day	36% 7% 21% 24% 11% 2	490
	11th to 20th	Day	42% 8% 20% 18% 11% 2	490
	21st to end	Day	46% 9% 21% 15% 8% 2	392
November	1st to 10th	Day	53% 9% 19% 16% 4	219
	11th to 20th	Day	52% 11% 13% 14% 8% 2	180
	21st to end	Day	52% 6% 19% 11% 8% 4	180
December	1st to 10th	Day	59% 7% 9% 14% 7% 4	180
	11th to 20th	Day	51% 10% 21% 13% 4	180
	21st to end	Day	49% 7% 24% 16% 4 1	198
January	1st to 10th	Night	57% 8% 17% 14% 4	804
	11th to 20th	Night	46% 10% 22% 16% 5% 1	760
	21st to end	Night	48% 8% 22% 19% 3	836
February	1st to 10th	Night	47% 9% 24% 16% 5%	760
	11th to 20th	Night	46% 7% 23% 21% 4	744
	21st to end	Night	47% 8% 21% 19% 5%	628
March	1st to 10th	Night	43% 10% 19% 21% 8%	760
	11th to 20th	Night	47% 6% 21% 20% 6% 1	760
	21st to end	Night	50% 8% 18% 18% 5% 1	836
April	1st to 10th	Night	44% 8% 16% 22% 8% 2	760
	11th to 20th	Night	39% 12% 18% 23% 7% 1	748
	21st to end	Night	44% 7% 17% 23% 7% 1	490
May	1st to 10th	Night	31% 7% 15% 31% 16%	380
	11th to 20th	Night	33% 3 13% 31% 18% 1	374
	21st to end	Night	35% 8% 10% 25% 20% 2	411
June	1st to 10th	Night	37% 7% 10% 26% 18% 2	380
	11th to 20th	Night	38% 7% 13% 27% 14% 1	380
	21st to end	Night	23% 4 14% 32% 25% 2	380
July	1st to 10th	Night	16% 4 9% 32% 34% 4	370
	11th to 20th	Night	14% 5% 7% 38% 32% 3	368
	21st to end	Night	15% 3 6% 33% 38% 5%	416
August	1st to 10th	Night	13% 2 4 33% 43% 6%	378
	11th to 20th	Night	15% 4 8% 30% 36% 7%	557
	21st to end	Night	22% 4 10% 33% 29% 1	757
September	1st to 10th	Night	19% 4 12% 36% 24% 4	760
	11th to 20th	Night	29% 5% 12% 26% 24% 4	760
	21st to end	Night	32% 4 13% 34% 16% 1	760
October	1st to 10th	Night	30% 6% 19% 29% 14% 1	760
	11th to 20th	Night	40% 5% 21% 24% 11% 1	760
	21st to end	Night	46% 5% 23% 21% 5% 1	836
November	1st to 10th	Night	51% 7% 23% 16% 2	754
	11th to 20th	Night	52% 10% 17% 16% 4	760
	21st to end	Night	49% 9% 21% 17% 3	760
December	1st to 10th	Night	42% 9% 23% 19% 6% 1	760
	11th to 20th	Night	53% 8% 24% 11% 3 1	760
	21st to end	Night	57% 8% 20% 13% 2	881

Page generated at 2024-11-01 19:47:32. Version ac07

Copyright © 2024 Attilla Danko.