Mt. Baldy
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mt. Baldy 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	17% 13% 4 10% 6% 5% 5% 4 6% 7% 23%	106679
	Night	15% 14% 4 10% 6% 5% 5% 4 6% 7% 23%	101485
Transparency	Day	61% 11% 11% 11% 5% 1	106369
	Night	56% 8% 10% 14% 9% 3	101444
Seeing	Day	22% 13% 24% 24% 14% 3	18071
	Night	20% 11% 23% 25% 17% 3	22480

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% 11% 3 9% 8% 7% 7% 4 10% 10% 22%	1269
	11th to 20th	Day	9% 13% 3 7% 5% 4 5% 5% 7% 9% 33%	1658
	21st to end	Day	7% 14% 5% 10% 8% 9% 6% 4 6% 5% 24%	2090
February	1st to 10th	Day	8% 16% 5% 9% 4 3 5% 4 5% 9% 30%	1299
	11th to 20th	Day	11% 23% 4 11% 6% 6% 5% 5% 4 5% 18%	1479
	21st to end	Day	8% 13% 6% 10% 5% 5% 6% 4 4 7% 31%	1356
March	1st to 10th	Day	6% 17% 7% 13% 8% 6% 4 3 5% 5% 26%	3074
	11th to 20th	Day	8% 10% 4 11% 7% 6% 7% 4 8% 8% 27%	3253
	21st to end	Day	12% 22% 6% 11% 6% 5% 4 4 4 5% 21%	4155
April	1st to 10th	Day	8% 15% 6% 10% 7% 7% 5% 4 6% 7% 25%	2322
	11th to 20th	Day	6% 12% 4 8% 5% 6% 6% 5% 6% 7% 34%	2626
	21st to end	Day	9% 14% 4 8% 6% 6% 6% 6% 7% 7% 28%	2693
May	1st to 10th	Day	18% 20% 6% 12% 7% 6% 5% 3 4 5% 14%	5002
	11th to 20th	Day	9% 12% 4 11% 6% 5% 5% 4 6% 7% 29%	5023
	21st to end	Day	20% 13% 4 10% 5% 5% 6% 4 6% 6% 22%	5974
June	1st to 10th	Day	14% 9% 4 9% 6% 6% 7% 5% 8% 9% 24%	3420
	11th to 20th	Day	14% 9% 3 9% 6% 6% 7% 6% 7% 8% 24%	3420
	21st to end	Day	16% 9% 4 9% 6% 5% 6% 6% 7% 9% 23%	3420
July	1st to 10th	Day	24% 11% 4 10% 7% 6% 5% 4 6% 5% 18%	5700
	11th to 20th	Day	27% 13% 4 9% 6% 5% 5% 3 5% 6% 16%	5576
	21st to end	Day	24% 10% 3 8% 5% 4 5% 4 6% 7% 25%	5504
August	1st to 10th	Day	28% 10% 4 10% 5% 5% 5% 4 5% 6% 19%	5029
	11th to 20th	Day	29% 10% 3 8% 5% 4 4 3 5% 6% 22%	4418
	21st to end	Day	24% 11% 4 8% 6% 5% 5% 4 6% 7% 20%	4884
September	1st to 10th	Day	28% 11% 4 10% 5% 5% 6% 4 5% 5% 17%	2348
	11th to 20th	Day	31% 13% 4 9% 5% 4 4 3 4 4 19%	2280
	21st to end	Day	22% 13% 5% 8% 5% 5% 4 3 6% 6% 23%	2024
October	1st to 10th	Day	18% 11% 3 9% 7% 7% 7% 5% 7% 6% 20%	3129
	11th to 20th	Day	11% 11% 3 9% 4 4 5% 3 5% 8% 37%	2813
	21st to end	Day	18% 11% 4 6% 4 4 5% 4 6% 10% 28%	2667
November	1st to 10th	Day	12% 16% 5% 11% 7% 6% 8% 5% 6% 5% 20%	1371
	11th to 20th	Day	10% 13% 4 10% 7% 5% 7% 8% 10% 9% 17%	1202
	21st to end	Day	11% 18% 6% 12% 9% 6% 5% 5% 6% 10% 13%	1005
December	1st to 10th	Day	16% 15% 5% 11% 6% 6% 7% 6% 9% 9% 11%	832
	11th to 20th	Day	5% 21% 6% 15% 8% 7% 5% 6% 7% 7% 13%	967
	21st to end	Day	5% 11% 4 11% 9% 9% 6% 9% 11% 9% 17%	1397
January	1st to 10th	Night	9% 13% 5% 10% 7% 7% 7% 6% 8% 8% 21%	5686
	11th to 20th	Night	9% 14% 4 8% 5% 4 4 3 5% 10% 32%	5254
	21st to end	Night	7% 14% 4 9% 6% 7% 6% 4 5% 7% 30%	5577
February	1st to 10th	Night	9% 15% 4 9% 5% 4 5% 5% 7% 7% 29%	2879
	11th to 20th	Night	14% 19% 6% 12% 6% 6% 4 3 5% 6% 19%	2588
	21st to end	Night	8% 14% 4 12% 7% 5% 5% 4 5% 8% 27%	2096
March	1st to 10th	Night	6% 18% 6% 13% 5% 4 4 3 5% 7% 29%	3780
	11th to 20th	Night	7% 12% 5% 11% 6% 6% 6% 4 6% 8% 29%	3702
	21st to end	Night	9% 22% 6% 10% 5% 4 4 4 6% 5% 25%	3476
April	1st to 10th	Night	9% 19% 6% 10% 7% 6% 5% 3 4 5% 26%	1857
	11th to 20th	Night	8% 13% 3 10% 6% 6% 5% 4 6% 5% 32%	1503
	21st to end	Night	10% 13% 5% 10% 8% 4 5% 3 5% 6% 32%	1487
May	1st to 10th	Night	17% 21% 5% 12% 5% 5% 5% 4 5% 4 16%	1965
	11th to 20th	Night	14% 15% 6% 10% 6% 5% 6% 4 5% 6% 23%	1882
	21st to end	Night	26% 13% 5% 7% 4 4 5% 3 6% 7% 21%	1603
June	1st to 10th	Night	19% 13% 3 10% 6% 6% 6% 3 6% 7% 21%	760
	11th to 20th	Night	16% 12% 4 10% 7% 5% 5% 4 6% 7% 23%	760
	21st to end	Night	20% 10% 4 10% 7% 7% 7% 2 4 7% 22%	760
July	1st to 10th	Night	32% 11% 4 8% 5% 5% 4 4 6% 5% 16%	1270
	11th to 20th	Night	37% 11% 3 7% 5% 4 4 3 4 4 18%	1395
	21st to end	Night	29% 10% 3 8% 5% 5% 4 4 4 6% 22%	2060
August	1st to 10th	Night	31% 11% 3 8% 5% 4 4 3 4 6% 20%	1910
	11th to 20th	Night	32% 9% 3 8% 4 4 4 3 5% 6% 22%	2420
	21st to end	Night	30% 12% 4 9% 6% 5% 4 3 5% 4 18%	2783
September	1st to 10th	Night	32% 11% 4 10% 5% 5% 5% 4 5% 4 15%	1830
	11th to 20th	Night	31% 12% 3 9% 5% 4 5% 3 4 4 19%	1900
	21st to end	Night	26% 11% 4 8% 5% 4 5% 3 5% 5% 23%	2156
October	1st to 10th	Night	20% 13% 4 11% 6% 6% 5% 4 6% 6% 17%	3832
	11th to 20th	Night	13% 11% 3 8% 5% 5% 5% 4 6% 8% 33%	4113
	21st to end	Night	17% 14% 4 9% 5% 5% 6% 3 4 8% 23%	4892
November	1st to 10th	Night	13% 17% 4 11% 6% 7% 5% 4 5% 6% 21%	2927
	11th to 20th	Night	9% 13% 3 8% 6% 6% 8% 8% 8% 10% 22%	3195
	21st to end	Night	10% 18% 5% 13% 7% 5% 6% 6% 6% 8% 15%	3329
December	1st to 10th	Night	16% 17% 5% 11% 6% 7% 6% 5% 7% 7% 13%	3348
	11th to 20th	Night	7% 22% 6% 13% 7% 6% 6% 5% 7% 7% 13%	4240
	21st to end	Night	7% 14% 4 12% 8% 7% 7% 7% 9% 10% 14%	6270

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	46% 9% 13% 15% 13% 4	1269
	11th to 20th	Day	44% 8% 10% 13% 18% 8%	1673
	21st to end	Day	54% 7% 5% 9% 16% 9%	2090
February	1st to 10th	Day	48% 8% 9% 16% 12% 8%	1299
	11th to 20th	Day	64% 9% 8% 11% 6% 2	1486
	21st to end	Day	54% 7% 7% 16% 13% 3	1356
March	1st to 10th	Day	57% 7% 5% 11% 12% 7%	3074
	11th to 20th	Day	50% 11% 7% 15% 14% 3	3253
	21st to end	Day	66% 9% 8% 7% 7% 2	4155
April	1st to 10th	Day	62% 12% 8% 12% 6% 1	2322
	11th to 20th	Day	52% 13% 10% 18% 8%	2626
	21st to end	Day	58% 9% 9% 15% 8% 1	2693
May	1st to 10th	Day	74% 8% 7% 9% 3	5002
	11th to 20th	Day	53% 14% 8% 20% 4	5026
	21st to end	Day	62% 13% 9% 14% 3	5975
June	1st to 10th	Day	61% 14% 12% 12% 1	3420
	11th to 20th	Day	60% 13% 13% 11% 3	3420
	21st to end	Day	61% 13% 17% 8%	3420
July	1st to 10th	Day	69% 13% 12% 6%	5611
	11th to 20th	Day	71% 11% 15% 3	5477
	21st to end	Day	59% 12% 20% 9%	5330
August	1st to 10th	Day	69% 10% 14% 6% 1	5010
	11th to 20th	Day	63% 11% 14% 11% 1	4461
	21st to end	Day	64% 12% 13% 9% 1	4883
September	1st to 10th	Day	72% 10% 8% 8% 1	2348
	11th to 20th	Day	71% 8% 10% 10% 1	2280
	21st to end	Day	65% 10% 9% 13% 3	2024
October	1st to 10th	Day	59% 10% 13% 15% 3	3129
	11th to 20th	Day	47% 8% 12% 19% 14%	2813
	21st to end	Day	49% 10% 10% 22% 7% 1	2667
November	1st to 10th	Day	57% 8% 10% 12% 9% 3	1371
	11th to 20th	Day	49% 6% 8% 23% 12% 1	1202
	21st to end	Day	60% 4 10% 11% 12% 3	1005
December	1st to 10th	Day	60% 9% 11% 9% 9% 2	832
	11th to 20th	Day	63% 9% 9% 11% 7% 1	970
	21st to end	Day	46% 6% 9% 17% 13% 10%	1397
January	1st to 10th	Night	48% 9% 12% 16% 11% 4	5686
	11th to 20th	Night	47% 6% 9% 13% 20% 5%	5302
	21st to end	Night	47% 7% 5% 12% 19% 10%	5577
February	1st to 10th	Night	48% 7% 7% 17% 12% 7%	2879
	11th to 20th	Night	64% 8% 8% 10% 8% 2	2592
	21st to end	Night	55% 9% 8% 13% 13% 2	2096
March	1st to 10th	Night	53% 8% 6% 10% 13% 9%	3780
	11th to 20th	Night	47% 7% 8% 16% 18% 3	3704
	21st to end	Night	58% 9% 9% 11% 10% 2	3476
April	1st to 10th	Night	60% 8% 10% 15% 6%	1857
	11th to 20th	Night	51% 9% 12% 19% 9%	1503
	21st to end	Night	52% 7% 11% 18% 11%	1487
May	1st to 10th	Night	66% 8% 9% 14% 3	1965
	11th to 20th	Night	59% 7% 10% 20% 5%	1883
	21st to end	Night	59% 9% 15% 15% 2	1603
June	1st to 10th	Night	62% 10% 15% 11% 1	760
	11th to 20th	Night	59% 14% 14% 10% 3	760
	21st to end	Night	63% 10% 18% 8%	760
July	1st to 10th	Night	67% 12% 15% 6%	1250
	11th to 20th	Night	69% 8% 19% 4	1371
	21st to end	Night	61% 9% 22% 7%	1995
August	1st to 10th	Night	65% 9% 19% 7%	1904
	11th to 20th	Night	62% 12% 13% 11% 2	2443
	21st to end	Night	69% 9% 12% 9% 2	2783
September	1st to 10th	Night	73% 9% 8% 8% 2	1830
	11th to 20th	Night	69% 9% 10% 10% 2	1900
	21st to end	Night	64% 8% 12% 12% 4	2156
October	1st to 10th	Night	63% 8% 10% 16% 3	3832
	11th to 20th	Night	47% 8% 13% 19% 13%	4113
	21st to end	Night	56% 7% 11% 18% 8% 1	4892
November	1st to 10th	Night	59% 7% 9% 13% 8% 2	2927
	11th to 20th	Night	47% 9% 8% 21% 13% 1	3195
	21st to end	Night	59% 6% 10% 12% 10% 4	3329
December	1st to 10th	Night	63% 8% 9% 9% 9% 1	3348
	11th to 20th	Night	63% 7% 8% 13% 8% 1	4236
	21st to end	Night	50% 6% 8% 16% 14% 6%	6270

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	3 20% 20% 30% 19% 8%	90
	11th to 20th	Day	13% 16% 26% 27% 11% 7%	270
	21st to end	Day	16% 14% 21% 26% 15% 7%	308
February	1st to 10th	Day	13% 12% 25% 25% 14% 11%	283
	11th to 20th	Day	20% 20% 26% 21% 11% 2	365
	21st to end	Day	17% 17% 30% 20% 9% 7%	307
March	1st to 10th	Day	16% 11% 31% 25% 14% 4	370
	11th to 20th	Day	10% 14% 33% 21% 19% 4	424
	21st to end	Day	12% 15% 27% 27% 16% 3	616
April	1st to 10th	Day	13% 18% 29% 24% 13% 2	574
	11th to 20th	Day	12% 13% 21% 32% 20% 3	640
	21st to end	Day	16% 11% 25% 30% 16% 3	650
May	1st to 10th	Day	20% 20% 25% 23% 11% 1	653
	11th to 20th	Day	17% 14% 25% 26% 14% 3	675
	21st to end	Day	25% 15% 22% 26% 11% 1	822
June	1st to 10th	Day	18% 13% 25% 22% 17% 4	870
	11th to 20th	Day	19% 11% 25% 27% 15% 3	870
	21st to end	Day	18% 10% 25% 25% 17% 4	870
July	1st to 10th	Day	24% 11% 20% 28% 16% 2	856
	11th to 20th	Day	27% 10% 23% 23% 14% 3	852
	21st to end	Day	26% 10% 24% 21% 16% 4	744
August	1st to 10th	Day	31% 10% 23% 21% 13% 3	676
	11th to 20th	Day	29% 14% 25% 18% 12% 2	665
	21st to end	Day	31% 12% 22% 20% 14% 2	748
September	1st to 10th	Day	33% 14% 22% 19% 10% 2	603
	11th to 20th	Day	36% 12% 17% 20% 13% 2	580
	21st to end	Day	28% 13% 18% 21% 16% 4	390
October	1st to 10th	Day	32% 13% 22% 21% 12% 2	390
	11th to 20th	Day	24% 9% 25% 25% 13% 4	390
	21st to end	Day	21% 14% 22% 22% 16% 4	429
November	1st to 10th	Day	20% 12% 25% 19% 16% 8%	395
	11th to 20th	Day	15% 8% 26% 22% 22% 7%	300
	21st to end	Day	14% 20% 17% 29% 12% 9%	117
December	1st to 10th	Day	26% 13% 14% 26% 16% 6%	90
	11th to 20th	Day	12% 16% 30% 28% 9% 6%	90
	21st to end	Day	15% 18% 31% 20% 10% 5%	99
January	1st to 10th	Night	10% 13% 24% 30% 20% 4	940
	11th to 20th	Night	17% 14% 28% 24% 13% 4	907
	21st to end	Night	19% 11% 27% 24% 15% 4	935
February	1st to 10th	Night	13% 12% 26% 31% 14% 4	850
	11th to 20th	Night	20% 18% 28% 24% 9% 1	834
	21st to end	Night	12% 14% 32% 26% 11% 4	601
March	1st to 10th	Night	13% 14% 27% 28% 16% 2	660
	11th to 20th	Night	10% 11% 25% 32% 17% 5%	660
	21st to end	Night	13% 10% 25% 25% 20% 6%	631
April	1st to 10th	Night	17% 11% 24% 26% 18% 3	570
	11th to 20th	Night	13% 11% 17% 26% 27% 6%	563
	21st to end	Night	13% 8% 25% 34% 18% 2	570
May	1st to 10th	Night	18% 11% 22% 28% 18% 2	419
	11th to 20th	Night	18% 8% 18% 29% 25% 1	374
	21st to end	Night	19% 8% 18% 35% 19% 1	228
June	1st to 10th	Night	24% 11% 14% 31% 20% 1	190
	11th to 20th	Night	21% 5% 22% 32% 20% 1	190
	21st to end	Night	21% 4 17% 32% 25% 1	190
July	1st to 10th	Night	27% 8% 15% 23% 28%	185
	11th to 20th	Night	35% 7% 11% 20% 25% 2	257
	21st to end	Night	32% 6% 15% 21% 21% 5%	416
August	1st to 10th	Night	33% 8% 16% 24% 18% 2	378
	11th to 20th	Night	37% 9% 19% 19% 14% 2	520
	21st to end	Night	35% 7% 17% 20% 18% 2	627
September	1st to 10th	Night	36% 10% 19% 20% 13% 2	570
	11th to 20th	Night	35% 10% 16% 18% 18% 3	570
	21st to end	Night	32% 8% 15% 22% 18% 4	605
October	1st to 10th	Night	33% 12% 17% 20% 16% 3	689
	11th to 20th	Night	22% 10% 20% 25% 20% 4	860
	21st to end	Night	22% 10% 22% 27% 16% 3	946
November	1st to 10th	Night	21% 10% 25% 27% 15% 2	880
	11th to 20th	Night	14% 10% 26% 32% 16% 3	900
	21st to end	Night	16% 15% 26% 23% 15% 5%	885
December	1st to 10th	Night	23% 12% 24% 23% 13% 4	906
	11th to 20th	Night	14% 11% 31% 25% 15% 5%	940
	21st to end	Night	16% 18% 27% 20% 13% 6%	1034

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

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