Warren
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Warren clear sky chart from 2005-11-06 to 2025-02-06.

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% 5% 10% 5% 5% 4 3 5% 6% 27%	108595
	Night	17% 14% 5% 11% 5% 4 4 3 4 5% 26%	109632
Transparency	Day	56% 6% 11% 18% 9% 1	112235
	Night	59% 5% 10% 17% 8% 1	114155
Seeing	Day	26% 17% 28% 17% 8% 3	14839
	Night	26% 16% 27% 22% 10% 1	24468

By Month

Percentage Cloud Cover NE (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% 21% 10% 26% 6% 4 3 2 2 3 10%	3671
	11th to 20th	Day	12% 23% 11% 22% 8% 7% 2 1 2 2 10%	4026
	21st to end	Day	19% 17% 9% 15% 8% 5% 5% 2 3 3 13%	4466
February	1st to 10th	Day	18% 20% 6% 14% 9% 6% 4 2 2 4 17%	1755
	11th to 20th	Day	15% 16% 7% 17% 6% 5% 4 4 4 4 17%	1663
	21st to end	Day	20% 16% 4 13% 7% 4 3 4 4 5% 22%	1517
March	1st to 10th	Day	21% 12% 7% 8% 5% 4 3 3 4 6% 27%	3432
	11th to 20th	Day	11% 21% 7% 11% 4 3 3 3 4 5% 27%	3480
	21st to end	Day	20% 12% 4 12% 5% 3 3 3 4 6% 28%	3815
April	1st to 10th	Day	17% 17% 4 8% 4 4 4 3 5% 6% 28%	2242
	11th to 20th	Day	20% 13% 3 6% 4 4 4 3 5% 6% 31%	2259
	21st to end	Day	21% 12% 3 7% 4 4 3 3 4 5% 33%	2470
May	1st to 10th	Day	25% 9% 3 7% 5% 4 4 3 4 6% 29%	4108
	11th to 20th	Day	19% 10% 3 9% 5% 5% 5% 4 6% 7% 25%	4260
	21st to end	Day	13% 6% 2 7% 5% 5% 5% 4 5% 8% 40%	4837
June	1st to 10th	Day	18% 8% 3 8% 5% 5% 5% 4 6% 7% 33%	2660
	11th to 20th	Day	15% 7% 2 7% 5% 5% 6% 4 7% 9% 32%	2660
	21st to end	Day	18% 7% 2 5% 5% 5% 5% 4 6% 9% 35%	2660
July	1st to 10th	Day	10% 6% 2 7% 5% 5% 6% 5% 7% 11% 36%	4440
	11th to 20th	Day	13% 7% 3 7% 5% 5% 6% 5% 7% 10% 34%	4320
	21st to end	Day	11% 7% 2 7% 5% 5% 6% 5% 6% 8% 37%	4466
August	1st to 10th	Day	18% 7% 3 8% 5% 6% 5% 4 7% 8% 28%	4104
	11th to 20th	Day	16% 7% 2 9% 5% 6% 7% 6% 8% 9% 26%	4044
	21st to end	Day	14% 6% 2 6% 5% 5% 6% 5% 7% 10% 35%	4281
September	1st to 10th	Day	19% 8% 2 6% 4 4 4 3 5% 6% 38%	2280
	11th to 20th	Day	15% 6% 2 7% 4 4 5% 3 6% 9% 38%	2176
	21st to end	Day	20% 8% 4 9% 5% 4 5% 3 5% 7% 30%	2043
October	1st to 10th	Day	19% 8% 3 6% 5% 5% 5% 4 6% 7% 32%	1900
	11th to 20th	Day	22% 10% 3 7% 5% 5% 4 3 5% 6% 29%	1900
	21st to end	Day	25% 14% 3 8% 5% 4 4 3 4 6% 24%	2090
November	1st to 10th	Day	15% 14% 4 7% 5% 4 4 3 5% 7% 32%	1824
	11th to 20th	Day	18% 20% 5% 9% 4 3 4 4 5% 6% 22%	1600
	21st to end	Day	21% 23% 6% 8% 5% 4 3 3 4 6% 17%	1600
December	1st to 10th	Day	19% 25% 16% 16% 4 2 2 2 2 3 8%	2600
	11th to 20th	Day	19% 22% 9% 12% 7% 4 3 2 3 3 15%	2986
	21st to end	Day	22% 25% 8% 11% 5% 4 4 2 3 4 12%	3960
January	1st to 10th	Night	13% 19% 10% 28% 9% 4 3 2 2 3 8%	6259
	11th to 20th	Night	11% 18% 11% 24% 9% 5% 4 3 3 4 8%	5859
	21st to end	Night	20% 18% 8% 17% 7% 5% 5% 2 3 3 12%	6490
February	1st to 10th	Night	18% 20% 6% 13% 8% 5% 3 3 3 3 17%	2536
	11th to 20th	Night	15% 16% 7% 16% 8% 5% 5% 3 4 4 17%	2403
	21st to end	Night	20% 14% 5% 15% 6% 4 3 3 4 4 21%	1930
March	1st to 10th	Night	21% 16% 4 10% 5% 4 3 2 3 5% 28%	3408
	11th to 20th	Night	18% 18% 8% 9% 4 3 3 3 4 5% 26%	3479
	21st to end	Night	16% 13% 5% 10% 5% 3 3 3 4 5% 33%	3817
April	1st to 10th	Night	18% 16% 4 7% 4 3 4 3 5% 6% 29%	1936
	11th to 20th	Night	20% 13% 3 5% 4 4 3 4 4 6% 35%	1875
	21st to end	Night	16% 12% 3 7% 4 5% 4 3 5% 8% 33%	1722
May	1st to 10th	Night	27% 10% 3 6% 4 3 4 3 5% 6% 30%	2833
	11th to 20th	Night	18% 11% 3 8% 4 4 4 4 4 6% 33%	2630
	21st to end	Night	14% 7% 2 6% 3 3 4 4 6% 9% 41%	2738
June	1st to 10th	Night	14% 7% 2 7% 5% 5% 3 5% 7% 8% 38%	1520
	11th to 20th	Night	13% 8% 2 6% 5% 4 4 4 6% 10% 39%	1520
	21st to end	Night	15% 7% 2 6% 4 4 4 3 5% 9% 40%	1520
July	1st to 10th	Night	14% 8% 3 7% 5% 4 4 3 6% 7% 39%	2520
	11th to 20th	Night	12% 7% 3 6% 4 4 4 3 6% 8% 43%	2637
	21st to end	Night	12% 6% 2 6% 4 4 5% 4 6% 8% 42%	3087
August	1st to 10th	Night	15% 9% 3 7% 5% 5% 4 4 6% 7% 36%	2825
	11th to 20th	Night	19% 7% 2 6% 4 4 4 4 6% 7% 37%	2785
	21st to end	Night	11% 6% 2 6% 4 4 4 4 6% 9% 44%	3343
September	1st to 10th	Night	15% 7% 2 6% 4 4 4 3 5% 7% 44%	1900
	11th to 20th	Night	12% 6% 3 5% 4 3 3 4 5% 7% 48%	2000
	21st to end	Night	19% 9% 4 7% 4 4 5% 3 5% 6% 33%	2137
October	1st to 10th	Night	18% 7% 2 6% 4 4 5% 3 4 7% 39%	2280
	11th to 20th	Night	22% 10% 3 7% 4 3 4 4 6% 6% 32%	2280
	21st to end	Night	27% 12% 2 6% 4 4 4 3 4 6% 28%	2508
November	1st to 10th	Night	15% 14% 3 7% 4 3 3 4 5% 7% 36%	2471
	11th to 20th	Night	19% 19% 4 8% 4 4 5% 3 5% 5% 23%	2800
	21st to end	Night	19% 20% 6% 10% 5% 4 4 2 5% 5% 19%	2800
December	1st to 10th	Night	16% 25% 12% 15% 5% 4 4 3 3 3 10%	4580
	11th to 20th	Night	21% 21% 9% 12% 5% 3 3 3 3 3 16%	5208
	21st to end	Night	21% 22% 8% 12% 7% 4 4 3 4 4 13%	6996

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	82% 3 6% 7% 3	3672
	11th to 20th	Day	84% 2 5% 8% 2	4060
	21st to end	Day	77% 4 7% 9% 3	4466
February	1st to 10th	Day	75% 3 8% 10% 4	1755
	11th to 20th	Day	70% 4 7% 13% 5%	1672
	21st to end	Day	64% 5% 10% 14% 5% 2	1517
March	1st to 10th	Day	59% 4 9% 23% 5%	3435
	11th to 20th	Day	59% 5% 15% 16% 5% 1	3480
	21st to end	Day	57% 5% 7% 20% 10% 1	3815
April	1st to 10th	Day	57% 4 10% 16% 11% 1	2242
	11th to 20th	Day	54% 6% 9% 19% 11% 2	2259
	21st to end	Day	54% 5% 9% 18% 12% 2	2470
May	1st to 10th	Day	56% 5% 8% 22% 8% 1	4120
	11th to 20th	Day	54% 8% 12% 18% 7% 1	4264
	21st to end	Day	40% 7% 12% 23% 15% 3	4837
June	1st to 10th	Day	48% 7% 12% 20% 13% 1	2660
	11th to 20th	Day	46% 9% 13% 21% 11% 1	2660
	21st to end	Day	45% 6% 13% 23% 12%	2660
July	1st to 10th	Day	40% 8% 13% 24% 14% 1	4370
	11th to 20th	Day	41% 7% 12% 22% 16%	4245
	21st to end	Day	42% 8% 13% 22% 14% 1	4324
August	1st to 10th	Day	50% 8% 13% 21% 7%	4091
	11th to 20th	Day	48% 10% 14% 21% 6% 1	4083
	21st to end	Day	42% 7% 12% 27% 11% 1	4281
September	1st to 10th	Day	46% 6% 11% 21% 15% 1	2280
	11th to 20th	Day	42% 6% 11% 25% 15% 1	2176
	21st to end	Day	52% 6% 10% 20% 10% 1	2043
October	1st to 10th	Day	43% 6% 13% 22% 16% 1	3160
	11th to 20th	Day	49% 5% 13% 16% 13% 4	3140
	21st to end	Day	49% 5% 14% 22% 10% 1	3428
November	1st to 10th	Day	52% 7% 11% 16% 12% 2	1824
	11th to 20th	Day	61% 5% 11% 14% 7% 2	1600
	21st to end	Day	69% 4 11% 11% 4 1	1600
December	1st to 10th	Day	83% 3 7% 6% 1	2600
	11th to 20th	Day	74% 4 9% 11% 2	2986
	21st to end	Day	78% 4 9% 7% 2	3960
January	1st to 10th	Night	84% 3 5% 6% 2	6259
	11th to 20th	Night	82% 3 8% 5% 2	5900
	21st to end	Night	78% 3 7% 7% 4 1	6490
February	1st to 10th	Night	73% 4 7% 12% 5%	2536
	11th to 20th	Night	71% 5% 8% 12% 4	2405
	21st to end	Night	68% 4 8% 13% 8% 1	1930
March	1st to 10th	Night	61% 4 9% 22% 4	3418
	11th to 20th	Night	60% 5% 12% 15% 7% 1	3480
	21st to end	Night	53% 4 8% 19% 14% 2	3817
April	1st to 10th	Night	56% 4 12% 17% 11% 1	1936
	11th to 20th	Night	50% 6% 12% 19% 12% 2	1875
	21st to end	Night	49% 6% 11% 20% 11% 2	1722
May	1st to 10th	Night	54% 5% 10% 18% 11% 2	2840
	11th to 20th	Night	50% 8% 13% 19% 9% 1	2631
	21st to end	Night	38% 8% 12% 24% 15% 5%	2739
June	1st to 10th	Night	42% 7% 13% 23% 14% 1	1520
	11th to 20th	Night	40% 7% 15% 22% 14% 2	1520
	21st to end	Night	40% 8% 13% 23% 14% 1	1520
July	1st to 10th	Night	45% 6% 10% 21% 16% 2	2480
	11th to 20th	Night	37% 5% 15% 27% 15% 1	2589
	21st to end	Night	39% 7% 13% 21% 20% 1	2988
August	1st to 10th	Night	46% 7% 12% 25% 9% 1	2814
	11th to 20th	Night	43% 7% 15% 27% 7%	2812
	21st to end	Night	35% 7% 15% 32% 10% 1	3343
September	1st to 10th	Night	40% 6% 12% 24% 15% 3	1900
	11th to 20th	Night	36% 5% 13% 26% 19% 1	2000
	21st to end	Night	51% 6% 12% 18% 12% 1	2137
October	1st to 10th	Night	43% 6% 10% 21% 19% 1	3800
	11th to 20th	Night	46% 5% 12% 17% 14% 5%	3779
	21st to end	Night	43% 4 15% 24% 13% 1	4120
November	1st to 10th	Night	48% 5% 12% 21% 11% 3	2471
	11th to 20th	Night	61% 5% 10% 14% 7% 3	2800
	21st to end	Night	67% 5% 10% 14% 3 1	2800
December	1st to 10th	Night	79% 5% 8% 7% 2	4580
	11th to 20th	Night	74% 3 9% 11% 3	5208
	21st to end	Night	76% 5% 8% 10% 2	6996

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	35% 29% 27% 7% 2	217
	11th to 20th	Day	38% 32% 22% 6% 2	300
	21st to end	Day	36% 28% 28% 8% 1	330
February	1st to 10th	Day	37% 27% 28% 7%	285
	11th to 20th	Day	40% 28% 27% 5%	270
	21st to end	Day	43% 25% 27% 6%	282
March	1st to 10th	Day	32% 25% 30% 11% 2	460
	11th to 20th	Day	34% 20% 33% 9% 2 2	460
	21st to end	Day	37% 22% 24% 13% 4 1	506
April	1st to 10th	Day	31% 25% 26% 14% 4 1	460
	11th to 20th	Day	33% 22% 23% 12% 8% 2	452
	21st to end	Day	30% 19% 33% 14% 3 1	460
May	1st to 10th	Day	31% 21% 25% 14% 7% 2	463
	11th to 20th	Day	25% 15% 30% 20% 8% 2	487
	21st to end	Day	17% 13% 29% 22% 14% 4	529
June	1st to 10th	Day	23% 15% 28% 23% 9% 2	490
	11th to 20th	Day	19% 15% 28% 26% 12% 2	490
	21st to end	Day	20% 13% 36% 22% 7% 2	490
July	1st to 10th	Day	13% 10% 28% 24% 18% 7%	485
	11th to 20th	Day	15% 10% 29% 25% 16% 6%	484
	21st to end	Day	14% 12% 30% 26% 14% 5%	532
August	1st to 10th	Day	13% 10% 26% 25% 18% 7%	486
	11th to 20th	Day	18% 9% 25% 25% 14% 9%	479
	21st to end	Day	17% 8% 27% 25% 15% 7%	539
September	1st to 10th	Day	21% 14% 20% 23% 15% 7%	490
	11th to 20th	Day	14% 4 24% 27% 21% 9%	490
	21st to end	Day	26% 13% 27% 18% 13% 3	490
October	1st to 10th	Day	21% 13% 31% 17% 14% 4	490
	11th to 20th	Day	29% 19% 29% 15% 6% 2	490
	21st to end	Day	36% 19% 27% 15% 4	539
November	1st to 10th	Day	28% 20% 29% 16% 5% 2	394
	11th to 20th	Day	40% 19% 30% 7% 5% 1	200
	21st to end	Day	39% 23% 31% 8% 1	200
December	1st to 10th	Day	38% 29% 24% 6% 2 2	200
	11th to 20th	Day	40% 25% 29% 7% 1	200
	21st to end	Day	39% 25% 28% 7% 1	220
January	1st to 10th	Night	31% 25% 32% 9% 3	800
	11th to 20th	Night	32% 26% 27% 13% 2	800
	21st to end	Night	29% 26% 29% 14% 2	880
February	1st to 10th	Night	34% 20% 31% 15%	781
	11th to 20th	Night	30% 27% 31% 11% 1	743
	21st to end	Night	32% 25% 27% 13% 2	628
March	1st to 10th	Night	29% 23% 30% 16% 3	760
	11th to 20th	Night	32% 21% 23% 18% 6%	760
	21st to end	Night	28% 19% 31% 17% 4 1	836
April	1st to 10th	Night	28% 17% 32% 19% 4	760
	11th to 20th	Night	28% 15% 29% 18% 8% 1	751
	21st to end	Night	23% 11% 34% 28% 4 1	582
May	1st to 10th	Night	26% 10% 25% 29% 11%	570
	11th to 20th	Night	20% 10% 30% 32% 8%	457
	21st to end	Night	15% 6% 29% 28% 20% 2	411
June	1st to 10th	Night	15% 4 31% 35% 14% 1	380
	11th to 20th	Night	14% 9% 27% 37% 12%	380
	21st to end	Night	16% 7% 30% 34% 13%	380
July	1st to 10th	Night	12% 4 22% 38% 20% 4	370
	11th to 20th	Night	12% 4 20% 39% 23% 2	433
	21st to end	Night	13% 5% 19% 39% 23% 1	624
August	1st to 10th	Night	12% 4 18% 37% 27% 2	567
	11th to 20th	Night	17% 4 17% 30% 29% 3	564
	21st to end	Night	14% 4 20% 32% 26% 3	755
September	1st to 10th	Night	19% 7% 22% 28% 21% 3	760
	11th to 20th	Night	14% 7% 18% 30% 27% 4	760
	21st to end	Night	24% 11% 21% 25% 16% 3	760
October	1st to 10th	Night	22% 9% 25% 25% 17% 2	760
	11th to 20th	Night	27% 14% 28% 21% 8% 1	760
	21st to end	Night	35% 13% 28% 20% 4	836
November	1st to 10th	Night	23% 16% 29% 24% 8%	780
	11th to 20th	Night	32% 17% 30% 16% 5% 1	800
	21st to end	Night	32% 22% 28% 14% 4	800
December	1st to 10th	Night	37% 24% 25% 12% 3	800
	11th to 20th	Night	34% 24% 25% 14% 3	800
	21st to end	Night	31% 25% 28% 14% 1	880

Page generated at 2025-02-03 03:05:53. Version ac07

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