Doug Firebaugh Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Doug Firebaugh Observatory clear sky chart from 2005-11-06 to 2024-11-05.

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	13% 9% 3 8% 5% 5% 5% 4 5% 7% 38%	101450
	Night	13% 9% 3 8% 5% 4 4 3 5% 6% 39%	97686
Transparency	Day	45% 4 12% 24% 14% 1	104989
	Night	45% 3 11% 24% 15% 2	102287
Seeing	Day	16% 10% 28% 26% 14% 5%	15864
	Night	17% 9% 31% 30% 11% 1	25699

By Month

Percentage Cloud Cover SE (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	11% 13% 9% 14% 6% 5% 4 4 4 4 26%	2527
	11th to 20th	Day	11% 10% 5% 15% 6% 5% 5% 8% 8% 6% 19%	2530
	21st to end	Day	15% 20% 9% 12% 5% 4 3 3 4 5% 20%	2984
February	1st to 10th	Day	11% 14% 5% 9% 6% 5% 5% 4 4 6% 31%	1710
	11th to 20th	Day	12% 11% 4 8% 5% 5% 5% 3 5% 7% 36%	1786
	21st to end	Day	12% 14% 5% 10% 5% 4 4 3 5% 6% 32%	1570
March	1st to 10th	Day	13% 9% 3 6% 5% 4 4 3 5% 7% 41%	3120
	11th to 20th	Day	10% 7% 3 7% 4 4 4 4 5% 7% 43%	3402
	21st to end	Day	21% 12% 4 11% 5% 6% 5% 3 5% 5% 23%	4094
April	1st to 10th	Day	18% 13% 3 7% 5% 4 5% 3 5% 7% 31%	2280
	11th to 20th	Day	17% 9% 3 7% 4 5% 5% 4 4 7% 34%	2254
	21st to end	Day	20% 8% 3 8% 4 4 4 3 5% 7% 34%	2308
May	1st to 10th	Day	16% 8% 3 8% 5% 4 4 4 5% 7% 35%	4203
	11th to 20th	Day	15% 7% 2 6% 4 4 4 3 5% 6% 42%	4399
	21st to end	Day	12% 6% 2 6% 5% 5% 4 4 6% 9% 40%	4824
June	1st to 10th	Day	10% 6% 2 6% 5% 5% 5% 5% 5% 9% 42%	2660
	11th to 20th	Day	10% 6% 2 6% 4 4 4 4 6% 9% 45%	2660
	21st to end	Day	11% 7% 2 7% 5% 4 5% 5% 7% 9% 38%	2660
July	1st to 10th	Day	10% 8% 3 8% 6% 6% 5% 5% 7% 9% 34%	4440
	11th to 20th	Day	5% 4 1 5% 4 4 5% 4 6% 10% 51%	4440
	21st to end	Day	8% 6% 3 8% 5% 5% 6% 4 7% 9% 40%	4813
August	1st to 10th	Day	9% 5% 3 6% 5% 5% 6% 5% 7% 9% 41%	4273
	11th to 20th	Day	10% 5% 2 5% 4 4 4 4 6% 9% 47%	3802
	21st to end	Day	9% 6% 2 6% 3 4 4 4 5% 8% 48%	4180
September	1st to 10th	Day	12% 5% 3 5% 4 4 5% 3 5% 7% 47%	2280
	11th to 20th	Day	12% 4 1 4 3 3 4 3 5% 8% 52%	2228
	21st to end	Day	12% 7% 2 7% 4 3 4 3 5% 7% 46%	2090
October	1st to 10th	Day	13% 6% 2 5% 4 4 4 3 4 6% 50%	1928
	11th to 20th	Day	17% 9% 3 7% 4 5% 4 3 5% 6% 38%	1900
	21st to end	Day	18% 9% 2 6% 5% 3 4 3 4 6% 40%	1941
November	1st to 10th	Day	11% 8% 3 7% 4 4 4 3 5% 6% 44%	1708
	11th to 20th	Day	14% 12% 3 7% 6% 5% 4 3 5% 6% 34%	1710
	21st to end	Day	14% 13% 4 7% 3 5% 3 3 5% 5% 37%	1525
December	1st to 10th	Day	13% 14% 4 9% 5% 4 5% 3 4 5% 33%	1520
	11th to 20th	Day	13% 14% 4 9% 7% 5% 5% 3 5% 6% 30%	1918
	21st to end	Day	22% 20% 8% 12% 5% 4 4 3 4 4 14%	2783
January	1st to 10th	Night	13% 13% 8% 13% 5% 4 4 3 4 5% 30%	4428
	11th to 20th	Night	13% 17% 6% 13% 6% 4 4 5% 7% 5% 20%	4440
	21st to end	Night	17% 18% 7% 11% 6% 4 4 3 4 4 22%	4678
February	1st to 10th	Night	12% 14% 5% 9% 6% 5% 3 3 5% 5% 33%	2470
	11th to 20th	Night	12% 10% 3 9% 5% 4 4 3 5% 5% 40%	2279
	21st to end	Night	16% 11% 3 8% 3 4 4 3 5% 6% 36%	1884
March	1st to 10th	Night	18% 9% 3 5% 4 4 3 3 4 5% 42%	3733
	11th to 20th	Night	9% 6% 3 7% 5% 5% 4 4 5% 7% 47%	3588
	21st to end	Night	24% 12% 5% 10% 5% 4 4 3 4 5% 26%	3536
April	1st to 10th	Night	16% 10% 3 6% 4 4 4 3 5% 6% 38%	1900
	11th to 20th	Night	17% 8% 3 7% 4 4 3 4 3 6% 40%	1875
	21st to end	Night	17% 7% 2 7% 4 5% 4 4 6% 8% 36%	1872
May	1st to 10th	Night	17% 7% 3 7% 6% 5% 4 4 7% 6% 35%	2692
	11th to 20th	Night	13% 7% 2 6% 4 4 5% 5% 6% 5% 41%	2506
	21st to end	Night	9% 6% 2 6% 4 4 4 4 6% 9% 45%	2743
June	1st to 10th	Night	8% 4 2 6% 4 4 6% 5% 6% 9% 46%	1520
	11th to 20th	Night	10% 4 2 4 5% 5% 3 4 6% 10% 46%	1520
	21st to end	Night	9% 6% 2 8% 3 4 4 5% 7% 8% 44%	1520
July	1st to 10th	Night	14% 7% 2 6% 5% 4 4 3 6% 8% 40%	2530
	11th to 20th	Night	5% 3 2 4 3 3 5% 3 6% 8% 57%	2530
	21st to end	Night	6% 4 2 6% 5% 5% 5% 5% 7% 8% 48%	2750
August	1st to 10th	Night	6% 4 2 5% 4 4 4 3 7% 8% 53%	2664
	11th to 20th	Night	8% 5% 2 5% 4 4 5% 4 5% 7% 52%	3029
	21st to end	Night	9% 5% 2 5% 3 4 4 4 6% 9% 51%	3476
September	1st to 10th	Night	10% 6% 1 4 3 3 4 2 4 6% 57%	1900
	11th to 20th	Night	10% 4 2 6% 3 4 4 4 5% 8% 51%	1933
	21st to end	Night	10% 5% 2 5% 4 4 4 4 5% 7% 50%	2090
October	1st to 10th	Night	11% 6% 2 5% 3 4 4 3 4 6% 52%	2250
	11th to 20th	Night	16% 7% 2 5% 4 3 3 3 4 6% 45%	2280
	21st to end	Night	19% 9% 2 6% 4 5% 4 4 4 6% 37%	2655
November	1st to 10th	Night	12% 7% 3 6% 3 3 3 3 4 5% 50%	2470
	11th to 20th	Night	14% 11% 3 8% 5% 4 4 4 4 6% 37%	2470
	21st to end	Night	17% 10% 2 7% 5% 3 4 3 4 6% 39%	2652
December	1st to 10th	Night	15% 12% 4 10% 5% 5% 5% 4 5% 6% 31%	2660
	11th to 20th	Night	14% 12% 4 9% 5% 5% 4 3 5% 6% 31%	3279
	21st to end	Night	21% 17% 6% 11% 6% 4 5% 3 4 4 19%	4884

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	63% 3 12% 16% 6%	2528
	11th to 20th	Day	59% 3 15% 13% 10% 1	2530
	21st to end	Day	67% 4 9% 14% 5% 1	2984
February	1st to 10th	Day	55% 3 12% 18% 11% 1	1710
	11th to 20th	Day	49% 3 11% 25% 10% 2	1795
	21st to end	Day	52% 5% 10% 22% 10% 2	1570
March	1st to 10th	Day	45% 2 13% 27% 11% 3	3120
	11th to 20th	Day	41% 3 12% 32% 12% 1	3402
	21st to end	Day	64% 4 13% 15% 4 1	4094
April	1st to 10th	Day	54% 4 10% 22% 10%	2280
	11th to 20th	Day	50% 3 10% 23% 12% 2	2254
	21st to end	Day	52% 4 12% 18% 13% 1	2308
May	1st to 10th	Day	49% 3 10% 22% 15% 1	4241
	11th to 20th	Day	42% 3 10% 30% 14%	4403
	21st to end	Day	40% 4 11% 24% 15% 5%	4837
June	1st to 10th	Day	38% 4 14% 27% 16% 1	2660
	11th to 20th	Day	36% 5% 13% 25% 20% 2	2660
	21st to end	Day	42% 6% 14% 24% 12% 2	2660
July	1st to 10th	Day	45% 5% 14% 25% 10% 2	4371
	11th to 20th	Day	28% 4 17% 33% 17% 1	4365
	21st to end	Day	40% 5% 16% 19% 19% 2	4662
August	1st to 10th	Day	38% 5% 16% 27% 13% 1	4258
	11th to 20th	Day	33% 4 14% 33% 15% 1	3839
	21st to end	Day	35% 4 12% 32% 15% 2	4179
September	1st to 10th	Day	37% 4 9% 28% 20% 2	2280
	11th to 20th	Day	31% 4 11% 31% 20% 2	2228
	21st to end	Day	38% 3 9% 29% 20% 1	2090
October	1st to 10th	Day	24% 3 6% 37% 30% 1	3201
	11th to 20th	Day	34% 2 9% 26% 26% 2	3140
	21st to end	Day	43% 2 9% 29% 14% 3	3179
November	1st to 10th	Day	41% 3 15% 25% 14% 2	1708
	11th to 20th	Day	52% 3 13% 21% 10% 1	1710
	21st to end	Day	50% 4 15% 22% 8% 1	1525
December	1st to 10th	Day	53% 3 15% 19% 8% 2	1520
	11th to 20th	Day	57% 3 14% 16% 9% 2	1915
	21st to end	Day	75% 3 8% 9% 5%	2783
January	1st to 10th	Night	58% 2 11% 19% 9% 1	4428
	11th to 20th	Night	64% 2 10% 14% 9%	4440
	21st to end	Night	67% 3 9% 15% 6% 1	4678
February	1st to 10th	Night	55% 2 9% 20% 12% 2	2470
	11th to 20th	Night	47% 3 11% 24% 14% 1	2280
	21st to end	Night	49% 3 12% 22% 12% 4	1884
March	1st to 10th	Night	46% 2 13% 24% 12% 4	3733
	11th to 20th	Night	37% 3 10% 31% 17% 2	3588
	21st to end	Night	63% 3 8% 19% 6% 1	3536
April	1st to 10th	Night	48% 3 11% 22% 14% 2	1900
	11th to 20th	Night	47% 3 6% 22% 18% 4	1875
	21st to end	Night	47% 4 11% 24% 13% 2	1872
May	1st to 10th	Night	50% 4 11% 17% 16% 2	2719
	11th to 20th	Night	43% 4 13% 26% 14% 1	2507
	21st to end	Night	35% 5% 11% 25% 21% 3	2751
June	1st to 10th	Night	33% 6% 14% 26% 20% 1	1520
	11th to 20th	Night	33% 5% 10% 24% 24% 3	1520
	21st to end	Night	37% 6% 14% 22% 17% 4	1520
July	1st to 10th	Night	43% 3 16% 24% 11% 3	2490
	11th to 20th	Night	24% 4 14% 36% 19% 2	2482
	21st to end	Night	32% 6% 17% 20% 19% 5%	2662
August	1st to 10th	Night	30% 3 15% 32% 18% 2	2655
	11th to 20th	Night	32% 3 13% 32% 18% 1	3058
	21st to end	Night	31% 5% 12% 32% 17% 4	3476
September	1st to 10th	Night	30% 4 11% 28% 25% 3	1900
	11th to 20th	Night	32% 4 11% 31% 19% 3	1933
	21st to end	Night	33% 4 9% 31% 20% 3	2090
October	1st to 10th	Night	24% 2 6% 36% 30% 2	3757
	11th to 20th	Night	33% 2 7% 25% 29% 3	3779
	21st to end	Night	45% 2 8% 26% 16% 3	4367
November	1st to 10th	Night	37% 3 10% 27% 19% 3	2470
	11th to 20th	Night	49% 2 12% 22% 13% 1	2470
	21st to end	Night	48% 4 11% 24% 11% 1	2652
December	1st to 10th	Night	55% 4 11% 22% 8% 1	2660
	11th to 20th	Night	52% 3 14% 20% 9% 1	3281
	21st to end	Night	69% 3 8% 15% 5%	4884

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	16% 14% 30% 29% 10% 1	270
	11th to 20th	Day	18% 13% 42% 21% 5% 1	270
	21st to end	Day	19% 11% 37% 26% 7% 1	297
February	1st to 10th	Day	20% 14% 37% 21% 8%	270
	11th to 20th	Day	20% 19% 30% 25% 6%	270
	21st to end	Day	22% 16% 43% 16% 4	225
March	1st to 10th	Day	14% 21% 41% 18% 6%	270
	11th to 20th	Day	19% 17% 36% 19% 7% 1	270
	21st to end	Day	29% 14% 33% 18% 6% 1	461
April	1st to 10th	Day	25% 14% 35% 19% 6% 1	460
	11th to 20th	Day	22% 16% 30% 21% 9% 1	452
	21st to end	Day	25% 12% 29% 23% 9% 2	460
May	1st to 10th	Day	20% 13% 33% 23% 9% 2	532
	11th to 20th	Day	22% 10% 27% 26% 12% 3	675
	21st to end	Day	17% 10% 26% 24% 17% 6%	734
June	1st to 10th	Day	10% 8% 27% 31% 18% 6%	680
	11th to 20th	Day	11% 8% 33% 29% 14% 5%	680
	21st to end	Day	14% 9% 28% 31% 15% 4	680
July	1st to 10th	Day	9% 3 18% 31% 25% 14%	671
	11th to 20th	Day	9% 4 25% 29% 23% 9%	668
	21st to end	Day	8% 4 19% 37% 24% 7%	739
August	1st to 10th	Day	7% 4 20% 33% 25% 11%	676
	11th to 20th	Day	13% 4 18% 31% 21% 13%	528
	21st to end	Day	12% 3 18% 34% 24% 9%	539
September	1st to 10th	Day	15% 6% 20% 32% 21% 6%	490
	11th to 20th	Day	10% 4 20% 33% 23% 10%	490
	21st to end	Day	15% 10% 28% 24% 17% 7%	490
October	1st to 10th	Day	16% 11% 26% 27% 16% 4	328
	11th to 20th	Day	24% 19% 30% 19% 8%	300
	21st to end	Day	25% 17% 30% 21% 5% 1	330
November	1st to 10th	Day	16% 15% 36% 21% 10% 2	282
	11th to 20th	Day	21% 17% 34% 18% 8% 1	270
	21st to end	Day	24% 13% 36% 22% 4	270
December	1st to 10th	Day	17% 15% 41% 19% 8% 1	270
	11th to 20th	Day	16% 12% 38% 26% 7% 1	270
	21st to end	Day	23% 18% 40% 17% 2	297
January	1st to 10th	Night	18% 12% 39% 24% 5% 1	950
	11th to 20th	Night	19% 11% 40% 24% 6%	950
	21st to end	Night	20% 10% 36% 29% 5%	1045
February	1st to 10th	Night	20% 12% 38% 25% 5%	950
	11th to 20th	Night	16% 13% 40% 26% 5%	804
	21st to end	Night	22% 14% 40% 20% 4	628
March	1st to 10th	Night	22% 10% 37% 25% 6%	760
	11th to 20th	Night	16% 11% 36% 30% 7%	639
	21st to end	Night	24% 11% 33% 24% 6% 1	627
April	1st to 10th	Night	21% 12% 38% 24% 5%	570
	11th to 20th	Night	21% 12% 31% 28% 7%	563
	21st to end	Night	20% 9% 33% 29% 8% 1	570
May	1st to 10th	Night	18% 8% 36% 29% 8% 1	570
	11th to 20th	Night	20% 6% 29% 34% 10% 1	561
	21st to end	Night	11% 6% 32% 35% 15% 1	617
June	1st to 10th	Night	10% 4 27% 44% 15% 1	570
	11th to 20th	Night	12% 4 30% 41% 12% 1	570
	21st to end	Night	10% 5% 27% 42% 15% 1	570
July	1st to 10th	Night	9% 2 12% 42% 32% 4	555
	11th to 20th	Night	9% 2 18% 43% 25% 3	552
	21st to end	Night	8% 2 17% 45% 26% 2	624
August	1st to 10th	Night	6% 2 16% 44% 29% 4	567
	11th to 20th	Night	9% 2 12% 40% 31% 6%	564
	21st to end	Night	10% 1 16% 44% 26% 3	627
September	1st to 10th	Night	12% 4 18% 39% 23% 5%	570
	11th to 20th	Night	10% 5% 21% 35% 25% 4	603
	21st to end	Night	13% 8% 26% 34% 18% 1	760
October	1st to 10th	Night	14% 6% 29% 32% 17% 1	760
	11th to 20th	Night	20% 11% 30% 28% 9%	760
	21st to end	Night	23% 11% 32% 26% 7%	836
November	1st to 10th	Night	17% 9% 39% 24% 10% 1	760
	11th to 20th	Night	19% 15% 37% 24% 6%	760
	21st to end	Night	20% 12% 35% 26% 7%	942
December	1st to 10th	Night	19% 12% 40% 24% 5%	950
	11th to 20th	Night	22% 9% 38% 25% 6%	950
	21st to end	Night	27% 13% 35% 22% 3	1045

Page generated at 2024-11-03 01:11:23. Version ac07

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