Bloomfield
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bloomfield clear sky chart from 2005-11-06 to 2026-04-17.

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	14% 9% 3 7% 5% 4 4 4 6% 7% 37%	131171
	Night	15% 9% 3 7% 4 4 4 3 5% 7% 38%	131183
Transparency	Day	44% 6% 11% 23% 14% 2	134776
	Night	45% 5% 10% 22% 15% 2	135653
Seeing	Day	18% 12% 26% 23% 15% 5%	17437
	Night	19% 10% 27% 29% 14% 2	27361

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	14% 13% 6% 11% 4 4 5% 3 5% 6% 28%	4691
	11th to 20th	Day	10% 14% 5% 14% 7% 5% 5% 4 4 5% 28%	4710
	21st to end	Day	19% 15% 5% 11% 6% 5% 4 3 4 4 24%	5556
February	1st to 10th	Day	19% 11% 6% 8% 4 3 3 4 5% 5% 31%	2100
	11th to 20th	Day	17% 11% 4 9% 5% 4 3 3 6% 6% 33%	2048
	21st to end	Day	16% 12% 4 10% 4 3 4 4 4 5% 34%	1730
March	1st to 10th	Day	20% 11% 4 7% 3 3 3 2 3 3 39%	4580
	11th to 20th	Day	12% 9% 3 7% 3 3 4 4 6% 8% 42%	4826
	21st to end	Day	16% 11% 3 7% 5% 5% 4 4 5% 7% 32%	5973
April	1st to 10th	Day	17% 9% 3 6% 6% 4 4 3 5% 7% 37%	2520
	11th to 20th	Day	18% 9% 3 6% 4 3 4 4 6% 6% 39%	2446
	21st to end	Day	20% 7% 3 7% 5% 4 3 3 4 7% 38%	2505
May	1st to 10th	Day	19% 10% 3 7% 5% 4 5% 5% 7% 9% 27%	5862
	11th to 20th	Day	18% 8% 3 7% 5% 5% 5% 4 5% 7% 34%	5861
	21st to end	Day	14% 8% 3 8% 5% 5% 6% 5% 7% 9% 31%	6632
June	1st to 10th	Day	12% 6% 2 6% 4 4 4 4 6% 8% 44%	2800
	11th to 20th	Day	9% 6% 2 6% 4 5% 5% 4 6% 9% 45%	2800
	21st to end	Day	9% 6% 2 5% 5% 5% 5% 4 6% 10% 43%	2800
July	1st to 10th	Day	11% 5% 2 6% 4 4 4 4 6% 11% 43%	6360
	11th to 20th	Day	9% 5% 3 7% 5% 5% 6% 5% 8% 11% 36%	6360
	21st to end	Day	10% 7% 3 8% 6% 6% 7% 5% 8% 10% 32%	6789
August	1st to 10th	Day	7% 5% 2 6% 4 4 4 3 7% 11% 48%	4214
	11th to 20th	Day	9% 5% 2 7% 4 6% 6% 4 7% 10% 40%	3849
	21st to end	Day	5% 4 2 5% 3 3 4 4 7% 10% 54%	4312
September	1st to 10th	Day	11% 6% 2 6% 5% 4 5% 3 5% 7% 47%	2400
	11th to 20th	Day	9% 5% 2 5% 5% 4 4 4 6% 8% 50%	2200
	21st to end	Day	12% 5% 1 5% 4 3 4 3 5% 7% 50%	2200
October	1st to 10th	Day	11% 5% 2 5% 3 4 4 3 4 7% 53%	2200
	11th to 20th	Day	14% 7% 2 6% 3 3 4 3 5% 7% 45%	2052
	21st to end	Day	20% 9% 2 5% 4 4 4 3 4 5% 40%	1980
November	1st to 10th	Day	10% 6% 2 6% 4 3 3 3 5% 6% 52%	1852
	11th to 20th	Day	17% 9% 3 6% 4 3 3 3 4 6% 41%	1890
	21st to end	Day	21% 12% 4 6% 3 3 3 3 4 5% 37%	1890
December	1st to 10th	Day	15% 11% 4 7% 4 3 3 3 4 5% 42%	3020
	11th to 20th	Day	16% 14% 5% 9% 5% 4 6% 4 4 5% 28%	3093
	21st to end	Day	27% 19% 6% 8% 5% 4 4 3 3 4 17%	4070
January	1st to 10th	Night	17% 13% 6% 11% 5% 4 4 3 5% 5% 27%	8232
	11th to 20th	Night	13% 16% 5% 12% 6% 5% 5% 3 4 4 27%	8280
	21st to end	Night	18% 12% 4 8% 5% 4 4 3 5% 6% 31%	8643
February	1st to 10th	Night	19% 11% 4 9% 5% 5% 4 4 5% 6% 27%	2520
	11th to 20th	Night	17% 11% 3 9% 6% 4 3 3 4 7% 32%	2458
	21st to end	Night	19% 12% 3 8% 4 4 4 3 5% 5% 34%	2076
March	1st to 10th	Night	21% 13% 4 7% 4 3 3 2 3 5% 36%	5493
	11th to 20th	Night	14% 7% 2 6% 3 3 4 3 4 7% 46%	5340
	21st to end	Night	18% 9% 3 9% 5% 5% 5% 3 5% 6% 32%	5242
April	1st to 10th	Night	15% 10% 2 7% 4 4 4 2 5% 8% 40%	2100
	11th to 20th	Night	17% 7% 2 6% 4 3 4 3 5% 7% 41%	2035
	21st to end	Night	16% 7% 3 6% 5% 4 5% 4 6% 7% 37%	1893
May	1st to 10th	Night	18% 10% 3 8% 5% 5% 4 4 6% 9% 29%	4033
	11th to 20th	Night	16% 7% 3 7% 4 5% 5% 5% 6% 8% 35%	4032
	21st to end	Night	15% 6% 2 7% 5% 5% 5% 4 6% 9% 35%	4214
June	1st to 10th	Night	10% 7% 2 6% 4 4 3 4 6% 9% 47%	1600
	11th to 20th	Night	9% 4 1 6% 3 4 5% 4 6% 9% 48%	1600
	21st to end	Night	6% 3 1 5% 4 5% 5% 4 8% 10% 49%	1600
July	1st to 10th	Night	8% 6% 3 7% 4 4 5% 3 5% 8% 47%	3618
	11th to 20th	Night	7% 5% 2 6% 5% 5% 5% 4 8% 9% 44%	3617
	21st to end	Night	8% 7% 2 7% 5% 6% 5% 5% 8% 10% 37%	4074
August	1st to 10th	Night	7% 5% 2 6% 4 4 4 3 5% 9% 52%	2931
	11th to 20th	Night	6% 5% 2 6% 5% 4 5% 4 6% 9% 48%	3200
	21st to end	Night	3 3 2 5% 3 4 4 4 6% 9% 57%	3586
September	1st to 10th	Night	9% 6% 2 5% 4 5% 4 4 5% 6% 51%	2000
	11th to 20th	Night	7% 4 2 5% 4 3 5% 3 5% 7% 56%	2180
	21st to end	Night	12% 6% 2 5% 3 3 3 4 5% 7% 49%	2200
October	1st to 10th	Night	8% 4 2 4 4 3 4 3 5% 6% 58%	2200
	11th to 20th	Night	15% 6% 2 5% 3 3 3 3 4 6% 50%	2341
	21st to end	Night	19% 8% 3 6% 3 3 3 3 5% 6% 41%	2860
November	1st to 10th	Night	11% 8% 2 6% 4 3 4 3 4 6% 49%	2666
	11th to 20th	Night	14% 9% 3 6% 4 4 3 3 5% 6% 43%	2730
	21st to end	Night	21% 11% 4 6% 4 3 3 3 4 6% 36%	2730
December	1st to 10th	Night	19% 10% 4 8% 5% 3 3 2 3 5% 40%	4380
	11th to 20th	Night	19% 11% 4 9% 4 4 4 3 5% 5% 31%	5329
	21st to end	Night	29% 18% 4 8% 4 4 3 3 3 4 19%	7150

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	56% 4 11% 21% 7% 1	4692
	11th to 20th	Day	58% 3 11% 17% 9% 2	4710
	21st to end	Day	63% 4 8% 17% 5% 3	5556
February	1st to 10th	Day	54% 5% 9% 21% 8% 2	2100
	11th to 20th	Day	52% 5% 10% 21% 11% 1	2058
	21st to end	Day	52% 4 9% 22% 10% 3	1730
March	1st to 10th	Day	51% 3 5% 20% 17% 4	4580
	11th to 20th	Day	40% 4 9% 30% 14% 2	4826
	21st to end	Day	49% 7% 11% 22% 10% 1	5975
April	1st to 10th	Day	46% 6% 12% 21% 14% 1	2520
	11th to 20th	Day	45% 5% 11% 24% 12% 3	2446
	21st to end	Day	48% 5% 10% 24% 10% 3	2505
May	1st to 10th	Day	50% 8% 13% 18% 11%	5897
	11th to 20th	Day	47% 8% 10% 24% 10%	5865
	21st to end	Day	45% 8% 14% 19% 13% 2	6646
June	1st to 10th	Day	36% 8% 11% 24% 17% 3	2800
	11th to 20th	Day	34% 8% 13% 22% 19% 4	2800
	21st to end	Day	36% 8% 15% 20% 17% 4	2800
July	1st to 10th	Day	36% 6% 10% 26% 20% 2	6291
	11th to 20th	Day	38% 9% 13% 26% 13% 1	6285
	21st to end	Day	44% 9% 14% 22% 10% 1	6595
August	1st to 10th	Day	30% 6% 14% 33% 15% 1	4201
	11th to 20th	Day	37% 8% 12% 26% 16% 1	3885
	21st to end	Day	25% 6% 15% 34% 16% 4	4311
September	1st to 10th	Day	36% 5% 11% 24% 20% 4	2400
	11th to 20th	Day	32% 5% 12% 27% 21% 3	2200
	21st to end	Day	34% 5% 10% 24% 25% 3	2200
October	1st to 10th	Day	21% 4 6% 28% 39% 2	3590
	11th to 20th	Day	29% 4 8% 27% 31% 2	3320
	21st to end	Day	37% 4 7% 24% 26% 2	3180
November	1st to 10th	Day	33% 4 10% 30% 17% 5%	1852
	11th to 20th	Day	45% 5% 9% 22% 16% 4	1890
	21st to end	Day	51% 4 8% 21% 15% 1	1890
December	1st to 10th	Day	46% 3 11% 27% 12%	3020
	11th to 20th	Day	59% 4 8% 21% 7% 1	3090
	21st to end	Day	70% 5% 10% 10% 5%	4070
January	1st to 10th	Night	58% 5% 11% 20% 6%	8233
	11th to 20th	Night	61% 3 8% 13% 12% 3	8280
	21st to end	Night	54% 3 11% 22% 10% 1	8643
February	1st to 10th	Night	57% 5% 12% 18% 7% 1	2520
	11th to 20th	Night	53% 3 11% 20% 12% 1	2459
	21st to end	Night	53% 5% 11% 20% 11% 2	2076
March	1st to 10th	Night	53% 3 5% 22% 13% 4	5493
	11th to 20th	Night	38% 5% 10% 25% 22% 1	5340
	21st to end	Night	52% 5% 9% 24% 8% 1	5242
April	1st to 10th	Night	43% 5% 10% 26% 14% 2	2100
	11th to 20th	Night	42% 4 11% 20% 18% 5%	2035
	21st to end	Night	46% 6% 10% 23% 13% 3	1893
May	1st to 10th	Night	50% 10% 12% 19% 8% 1	4060
	11th to 20th	Night	45% 8% 12% 24% 11%	4033
	21st to end	Night	43% 9% 14% 20% 12% 3	4222
June	1st to 10th	Night	34% 7% 10% 24% 21% 4	1600
	11th to 20th	Night	32% 8% 11% 23% 20% 6%	1600
	21st to end	Night	27% 10% 14% 23% 20% 6%	1600
July	1st to 10th	Night	36% 6% 9% 25% 21% 3	3580
	11th to 20th	Night	32% 9% 15% 28% 15% 2	3572
	21st to end	Night	39% 8% 16% 23% 12% 1	3957
August	1st to 10th	Night	28% 7% 14% 37% 12% 2	2920
	11th to 20th	Night	31% 7% 15% 29% 18% 1	3230
	21st to end	Night	23% 7% 13% 30% 23% 4	3586
September	1st to 10th	Night	32% 7% 9% 26% 20% 6%	2000
	11th to 20th	Night	27% 5% 11% 25% 28% 4	2180
	21st to end	Night	34% 6% 10% 21% 24% 5%	2200
October	1st to 10th	Night	18% 4 7% 19% 47% 4	3590
	11th to 20th	Night	25% 3 7% 26% 36% 3	3812
	21st to end	Night	35% 4 7% 22% 26% 6%	4610
November	1st to 10th	Night	36% 4 9% 25% 21% 4	2666
	11th to 20th	Night	41% 4 10% 23% 19% 3	2730
	21st to end	Night	51% 4 10% 22% 13% 1	2730
December	1st to 10th	Night	49% 3 9% 24% 13%	4380
	11th to 20th	Night	54% 5% 12% 19% 10% 1	5331
	21st to end	Night	70% 4 8% 12% 5% 1	7150

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	26% 22% 29% 17% 5%	330
	11th to 20th	Day	30% 24% 32% 12% 1	330
	21st to end	Day	31% 24% 31% 11% 3	363
February	1st to 10th	Day	26% 25% 34% 13% 2	330
	11th to 20th	Day	28% 26% 32% 12% 2 1	330
	21st to end	Day	29% 21% 37% 11% 2	273
March	1st to 10th	Day	24% 27% 33% 14% 2	330
	11th to 20th	Day	29% 23% 32% 12% 3 1	419
	21st to end	Day	29% 20% 31% 16% 4	594
April	1st to 10th	Day	23% 21% 31% 19% 6% 1	540
	11th to 20th	Day	23% 22% 24% 21% 8% 1	516
	21st to end	Day	23% 21% 31% 15% 8% 1	500
May	1st to 10th	Day	22% 15% 29% 25% 7% 3	503
	11th to 20th	Day	21% 9% 27% 25% 13% 5%	527
	21st to end	Day	14% 7% 29% 24% 17% 8%	655
June	1st to 10th	Day	13% 5% 26% 29% 21% 5%	730
	11th to 20th	Day	12% 6% 24% 32% 21% 5%	730
	21st to end	Day	13% 5% 27% 27% 20% 7%	730
July	1st to 10th	Day	11% 4 17% 28% 25% 15%	721
	11th to 20th	Day	8% 4 20% 33% 23% 11%	718
	21st to end	Day	11% 3 18% 30% 30% 8%	734
August	1st to 10th	Day	10% 3 16% 29% 29% 12%	526
	11th to 20th	Day	12% 3 19% 29% 30% 7%	519
	21st to end	Day	8% 1 15% 31% 31% 14%	583
September	1st to 10th	Day	10% 5% 17% 32% 28% 8%	530
	11th to 20th	Day	8% 2 13% 32% 32% 12%	530
	21st to end	Day	16% 8% 21% 25% 21% 8%	530
October	1st to 10th	Day	10% 5% 27% 32% 20% 5%	530
	11th to 20th	Day	16% 13% 34% 22% 11% 4	410
	21st to end	Day	29% 15% 35% 18% 2	363
November	1st to 10th	Day	12% 18% 34% 25% 8% 3	330
	11th to 20th	Day	23% 21% 30% 18% 7% 2	330
	21st to end	Day	33% 9% 32% 19% 5%	330
December	1st to 10th	Day	23% 21% 36% 14% 5% 1	330
	11th to 20th	Day	27% 19% 35% 15% 4 1	330
	21st to end	Day	33% 17% 34% 13% 2 1	363
January	1st to 10th	Night	23% 16% 34% 23% 4	1050
	11th to 20th	Night	27% 18% 33% 19% 3	1050
	21st to end	Night	22% 17% 36% 23% 2	1102
February	1st to 10th	Night	26% 12% 38% 22% 2	840
	11th to 20th	Night	25% 16% 36% 21% 2	823
	21st to end	Night	27% 15% 37% 20% 1	692
March	1st to 10th	Night	28% 15% 30% 24% 3	840
	11th to 20th	Night	24% 13% 35% 22% 6% 1	840
	21st to end	Night	25% 12% 31% 27% 5%	772
April	1st to 10th	Night	20% 13% 33% 28% 6%	630
	11th to 20th	Night	19% 12% 31% 28% 9% 1	611
	21st to end	Night	19% 9% 35% 29% 8% 1	600
May	1st to 10th	Night	19% 8% 32% 31% 11%	600
	11th to 20th	Night	18% 5% 24% 34% 17% 2	591
	21st to end	Night	12% 4 22% 36% 23% 3	650
June	1st to 10th	Night	12% 3 21% 40% 23% 1	600
	11th to 20th	Night	11% 3 19% 43% 23% 1	600
	21st to end	Night	8% 3 21% 38% 29% 1	600
July	1st to 10th	Night	10% 2 12% 34% 34% 9%	585
	11th to 20th	Night	8% 3 13% 38% 34% 4	582
	21st to end	Night	9% 3 14% 37% 34% 4	657
August	1st to 10th	Night	9% 3 9% 39% 36% 5%	597
	11th to 20th	Night	7% 2 11% 39% 37% 5%	594
	21st to end	Night	6% 2 12% 36% 39% 5%	660
September	1st to 10th	Night	12% 3 12% 37% 33% 4	600
	11th to 20th	Night	8% 3 14% 35% 34% 6%	780
	21st to end	Night	14% 7% 20% 31% 25% 4	800
October	1st to 10th	Night	10% 4 21% 38% 23% 4	800
	11th to 20th	Night	18% 9% 28% 29% 15% 1	800
	21st to end	Night	23% 12% 33% 25% 8%	880
November	1st to 10th	Night	15% 9% 34% 30% 11% 1	820
	11th to 20th	Night	19% 15% 30% 28% 8%	840
	21st to end	Night	27% 14% 27% 25% 8%	840
December	1st to 10th	Night	25% 11% 36% 23% 5%	840
	11th to 20th	Night	27% 11% 32% 24% 5% 1	1040
	21st to end	Night	33% 14% 32% 19% 3	1155

Page generated at 2026-04-14 02:44:29. Version ac07

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