Dexter
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dexter clear sky chart from 2005-11-06 to 2026-06-16.

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	18% 11% 4 8% 5% 4 4 3 5% 6% 32%	138145
	Night	19% 13% 4 9% 5% 4 4 3 5% 6% 27%	133862
Transparency	Day	56% 2 11% 21% 9% 1	141651
	Night	61% 3 9% 18% 9% 1	138445
Seeing	Day	27% 17% 29% 17% 7% 2	16566
	Night	27% 15% 27% 22% 8% 1	25760

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	16% 23% 8% 14% 5% 4 3 3 4 5% 16%	4661
	11th to 20th	Day	12% 22% 8% 22% 8% 5% 4 2 3 4 11%	4650
	21st to end	Day	12% 16% 8% 15% 10% 6% 5% 3 4 5% 15%	5559
February	1st to 10th	Day	17% 19% 5% 11% 6% 4 5% 2 5% 6% 20%	1890
	11th to 20th	Day	17% 16% 6% 10% 5% 5% 4 3 4 5% 24%	1864
	21st to end	Day	18% 19% 5% 10% 6% 5% 4 3 4 5% 22%	1730
March	1st to 10th	Day	21% 15% 5% 8% 4 3 3 2 4 5% 31%	4640
	11th to 20th	Day	13% 16% 4 9% 5% 5% 4 3 5% 6% 30%	5090
	21st to end	Day	21% 10% 3 7% 4 4 4 3 4 6% 35%	5862
April	1st to 10th	Day	21% 13% 4 6% 4 4 4 3 4 5% 33%	2520
	11th to 20th	Day	23% 9% 2 6% 4 3 4 3 4 6% 37%	2494
	21st to end	Day	23% 10% 3 6% 4 4 3 3 4 5% 34%	2579
May	1st to 10th	Day	26% 10% 3 7% 4 4 4 3 4 5% 30%	8237
	11th to 20th	Day	19% 8% 3 7% 4 4 4 3 5% 7% 34%	8221
	21st to end	Day	23% 8% 2 6% 4 4 4 4 5% 7% 32%	9060
June	1st to 10th	Day	19% 7% 3 6% 5% 5% 4 4 5% 7% 36%	2940
	11th to 20th	Day	16% 6% 2 6% 5% 4 5% 5% 6% 8% 38%	2870
	21st to end	Day	17% 7% 2 6% 4 5% 4 4 6% 8% 38%	2800
July	1st to 10th	Day	13% 5% 2 5% 4 5% 4 4 6% 9% 42%	6360
	11th to 20th	Day	12% 5% 2 6% 4 4 4 4 6% 7% 45%	6360
	21st to end	Day	13% 4 2 5% 4 4 5% 4 6% 8% 46%	6926
August	1st to 10th	Day	17% 7% 2 6% 4 4 4 3 5% 7% 40%	4370
	11th to 20th	Day	18% 6% 2 6% 3 4 4 4 6% 9% 37%	4086
	21st to end	Day	17% 5% 2 6% 4 3 4 4 6% 8% 41%	4312
September	1st to 10th	Day	15% 5% 2 5% 3 4 4 3 5% 8% 45%	2400
	11th to 20th	Day	13% 6% 2 5% 4 4 3 3 5% 7% 48%	2400
	21st to end	Day	19% 7% 2 6% 5% 4 4 4 6% 8% 37%	2132
October	1st to 10th	Day	22% 8% 3 7% 4 3 3 3 4 6% 36%	2000
	11th to 20th	Day	23% 9% 3 7% 5% 5% 4 3 5% 7% 29%	2000
	21st to end	Day	29% 9% 3 7% 4 4 4 3 5% 6% 25%	2080
November	1st to 10th	Day	17% 12% 3 8% 5% 5% 4 4 6% 7% 30%	1851
	11th to 20th	Day	16% 16% 4 9% 7% 4 4 3 5% 6% 26%	1727
	21st to end	Day	21% 21% 5% 9% 5% 4 4 3 5% 5% 18%	1680
December	1st to 10th	Day	21% 25% 5% 10% 5% 4 4 3 4 6% 12%	2680
	11th to 20th	Day	21% 21% 6% 12% 4 4 4 3 3 5% 16%	3066
	21st to end	Day	23% 17% 6% 10% 5% 5% 4 3 4 5% 19%	4048
January	1st to 10th	Night	17% 22% 7% 13% 6% 5% 4 3 3 4 16%	8234
	11th to 20th	Night	14% 23% 10% 20% 7% 5% 4 3 3 3 8%	8235
	21st to end	Night	14% 16% 8% 15% 9% 7% 5% 3 4 4 15%	8608
February	1st to 10th	Night	17% 17% 6% 14% 7% 5% 4 2 4 4 19%	2730
	11th to 20th	Night	17% 17% 6% 11% 5% 5% 3 3 4 5% 24%	2642
	21st to end	Night	18% 16% 5% 11% 5% 4 4 3 4 5% 24%	2076
March	1st to 10th	Night	20% 13% 4 10% 5% 4 4 3 4 4 30%	5419
	11th to 20th	Night	18% 15% 4 7% 4 3 4 3 5% 7% 31%	5089
	21st to end	Night	25% 12% 3 8% 5% 4 3 2 4 5% 30%	5312
April	1st to 10th	Night	22% 12% 3 7% 5% 3 3 3 4 5% 31%	2100
	11th to 20th	Night	24% 8% 3 6% 4 3 4 4 5% 6% 33%	2075
	21st to end	Night	23% 8% 3 7% 4 4 4 4 4 6% 34%	2056
May	1st to 10th	Night	30% 10% 3 8% 4 4 4 3 5% 6% 23%	4660
	11th to 20th	Night	21% 10% 3 7% 4 3 4 3 5% 7% 32%	4639
	21st to end	Night	21% 9% 2 6% 4 4 4 4 5% 7% 33%	5114
June	1st to 10th	Night	17% 7% 3 8% 5% 4 5% 4 5% 8% 34%	1680
	11th to 20th	Night	16% 5% 2 6% 4 5% 4 4 6% 9% 40%	1640
	21st to end	Night	17% 8% 3 6% 5% 4 5% 4 6% 7% 36%	1600
July	1st to 10th	Night	15% 5% 3 6% 5% 5% 5% 4 7% 9% 37%	3600
	11th to 20th	Night	15% 6% 2 6% 4 4 4 3 5% 7% 43%	3600
	21st to end	Night	12% 5% 2 5% 4 3 4 4 6% 8% 47%	3926
August	1st to 10th	Night	13% 8% 2 6% 5% 4 4 3 6% 7% 42%	2776
	11th to 20th	Night	14% 6% 3 7% 4 4 5% 4 6% 8% 38%	2928
	21st to end	Night	10% 5% 2 6% 5% 5% 5% 5% 7% 9% 41%	3586
September	1st to 10th	Night	15% 7% 2 5% 4 4 4 4 5% 7% 44%	2000
	11th to 20th	Night	13% 5% 2 5% 3 3 4 4 5% 7% 51%	2000
	21st to end	Night	18% 6% 2 6% 5% 4 4 3 5% 7% 40%	2265
October	1st to 10th	Night	21% 8% 3 7% 4 5% 5% 4 4 6% 35%	2400
	11th to 20th	Night	22% 9% 4 7% 5% 4 5% 4 5% 6% 30%	2400
	21st to end	Night	28% 10% 3 9% 5% 4 4 3 4 5% 26%	2759
November	1st to 10th	Night	21% 10% 3 7% 4 4 4 3 5% 5% 32%	2667
	11th to 20th	Night	19% 13% 4 9% 5% 4 3 3 5% 6% 29%	2888
	21st to end	Night	25% 19% 4 7% 4 4 4 3 5% 6% 18%	2940
December	1st to 10th	Night	20% 26% 6% 12% 5% 4 4 3 4 4 12%	4720
	11th to 20th	Night	23% 19% 6% 11% 5% 4 3 2 4 4 19%	5348
	21st to end	Night	28% 16% 5% 9% 4 4 4 3 3 5% 18%	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	77% 1 6% 12% 4	4662
	11th to 20th	Day	82% 1 4 6% 5% 1	4680
	21st to end	Day	75% 2 8% 9% 5% 1	5559
February	1st to 10th	Day	70% 4 8% 14% 4 1	1890
	11th to 20th	Day	68% 3 7% 16% 6% 1	1873
	21st to end	Day	68% 3 8% 13% 7%	1730
March	1st to 10th	Day	63% 1 8% 15% 11% 2	4643
	11th to 20th	Day	58% 2 16% 13% 9% 1	5090
	21st to end	Day	56% 1 5% 21% 15% 2	5862
April	1st to 10th	Day	57% 3 7% 19% 12% 2	2520
	11th to 20th	Day	52% 3 7% 22% 14% 2	2494
	21st to end	Day	54% 2 9% 19% 12% 3	2579
May	1st to 10th	Day	59% 2 7% 21% 10% 1	8249
	11th to 20th	Day	53% 2 10% 24% 10% 1	8225
	21st to end	Day	54% 2 11% 24% 9% 1	9061
June	1st to 10th	Day	50% 4 11% 22% 13% 1	2940
	11th to 20th	Day	45% 4 12% 26% 11% 1	2870
	21st to end	Day	47% 4 14% 23% 12% 1	2800
July	1st to 10th	Day	42% 2 13% 31% 12%	6290
	11th to 20th	Day	40% 2 14% 30% 12% 1	6285
	21st to end	Day	37% 3 13% 36% 9%	6728
August	1st to 10th	Day	45% 3 15% 25% 11%	4356
	11th to 20th	Day	47% 3 16% 25% 8% 1	4125
	21st to end	Day	43% 3 14% 32% 8%	4312
September	1st to 10th	Day	41% 4 13% 29% 12% 1	2400
	11th to 20th	Day	38% 3 10% 31% 17%	2400
	21st to end	Day	47% 4 12% 26% 10%	2132
October	1st to 10th	Day	47% 3 10% 30% 10%	3260
	11th to 20th	Day	50% 3 14% 25% 9%	3240
	21st to end	Day	53% 3 13% 23% 7% 1	3344
November	1st to 10th	Day	55% 5% 13% 18% 8% 1	1851
	11th to 20th	Day	61% 4 10% 16% 8% 2	1727
	21st to end	Day	71% 4 10% 8% 6%	1680
December	1st to 10th	Day	77% 3 12% 7% 1	2680
	11th to 20th	Day	75% 2 8% 11% 4	3066
	21st to end	Day	73% 2 7% 14% 4	4048
January	1st to 10th	Night	77% 1 7% 10% 4	8234
	11th to 20th	Night	86% 2 3 6% 3	8280
	21st to end	Night	77% 1 7% 8% 7% 1	8608
February	1st to 10th	Night	72% 4 7% 12% 5%	2730
	11th to 20th	Night	66% 4 7% 16% 6%	2644
	21st to end	Night	64% 4 10% 15% 7% 1	2076
March	1st to 10th	Night	62% 2 6% 16% 11% 2	5429
	11th to 20th	Night	56% 2 14% 17% 7% 3	5090
	21st to end	Night	62% 2 3 19% 12% 1	5312
April	1st to 10th	Night	57% 3 8% 19% 11% 2	2100
	11th to 20th	Night	54% 4 8% 19% 15% 1	2075
	21st to end	Night	52% 2 9% 20% 14% 2	2056
May	1st to 10th	Night	64% 2 7% 16% 9% 2	4666
	11th to 20th	Night	53% 2 11% 22% 11% 1	4640
	21st to end	Night	53% 2 9% 22% 13% 1	5115
June	1st to 10th	Night	49% 4 11% 23% 12% 1	1680
	11th to 20th	Night	43% 3 13% 21% 17% 2	1640
	21st to end	Night	46% 4 13% 23% 12% 1	1600
July	1st to 10th	Night	44% 2 15% 23% 15% 1	3560
	11th to 20th	Night	43% 2 11% 30% 13% 1	3552
	21st to end	Night	37% 3 11% 34% 14% 1	3809
August	1st to 10th	Night	44% 3 14% 27% 11% 1	2766
	11th to 20th	Night	47% 4 12% 28% 9%	2955
	21st to end	Night	39% 4 12% 35% 10% 1	3586
September	1st to 10th	Night	40% 5% 13% 28% 12% 1	2000
	11th to 20th	Night	35% 3 12% 32% 17% 1	2000
	21st to end	Night	45% 4 11% 27% 13% 1	2265
October	1st to 10th	Night	49% 3 8% 27% 13% 1	3920
	11th to 20th	Night	49% 3 13% 24% 11% 1	3899
	21st to end	Night	57% 3 10% 23% 7% 1	4445
November	1st to 10th	Night	55% 4 11% 19% 9% 2	2667
	11th to 20th	Night	57% 6% 9% 18% 8% 2	2888
	21st to end	Night	69% 5% 9% 13% 4	2940
December	1st to 10th	Night	79% 2 8% 9% 2	4720
	11th to 20th	Night	73% 3 6% 12% 5%	5348
	21st to end	Night	73% 2 7% 10% 7%	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	34% 23% 25% 14% 4	220
	11th to 20th	Day	35% 23% 26% 14% 2	220
	21st to end	Day	29% 28% 29% 11% 3	322
February	1st to 10th	Day	35% 26% 29% 9% 1	330
	11th to 20th	Day	35% 29% 28% 7%	351
	21st to end	Day	35% 26% 29% 9% 1	446
March	1st to 10th	Day	32% 22% 30% 13% 3	540
	11th to 20th	Day	35% 22% 29% 10% 3 1	540
	21st to end	Day	38% 21% 26% 9% 5%	594
April	1st to 10th	Day	37% 22% 25% 11% 4	540
	11th to 20th	Day	35% 23% 20% 15% 4 3	532
	21st to end	Day	33% 21% 29% 11% 5% 2	540
May	1st to 10th	Day	31% 19% 27% 15% 7% 2	543
	11th to 20th	Day	22% 15% 35% 20% 6% 1	567
	21st to end	Day	23% 16% 32% 18% 9% 1	617
June	1st to 10th	Day	26% 14% 34% 19% 6% 1	570
	11th to 20th	Day	21% 16% 33% 21% 8% 1	550
	21st to end	Day	24% 13% 35% 20% 7% 1	530
July	1st to 10th	Day	14% 12% 32% 27% 12% 2	525
	11th to 20th	Day	18% 9% 35% 25% 10% 3	524
	21st to end	Day	15% 11% 37% 27% 9% 1	576
August	1st to 10th	Day	15% 8% 33% 27% 12% 4	526
	11th to 20th	Day	18% 7% 29% 27% 13% 5%	519
	21st to end	Day	18% 11% 31% 22% 13% 4	583
September	1st to 10th	Day	17% 12% 28% 25% 12% 5%	530
	11th to 20th	Day	12% 10% 26% 23% 21% 9%	530
	21st to end	Day	20% 14% 27% 23% 12% 3	530
October	1st to 10th	Day	26% 15% 25% 19% 12% 3	530
	11th to 20th	Day	30% 19% 28% 15% 6% 2	530
	21st to end	Day	36% 18% 26% 15% 4	517
November	1st to 10th	Day	32% 20% 27% 14% 7%	425
	11th to 20th	Day	30% 21% 30% 12% 6% 1	267
	21st to end	Day	35% 30% 23% 9% 2	220
December	1st to 10th	Day	45% 14% 27% 12% 3	220
	11th to 20th	Day	35% 27% 32% 5% 1	220
	21st to end	Day	36% 22% 26% 13% 3	242
January	1st to 10th	Night	34% 22% 26% 15% 3	840
	11th to 20th	Night	32% 22% 27% 15% 3	840
	21st to end	Night	26% 21% 28% 20% 5%	924
February	1st to 10th	Night	30% 23% 27% 19% 2	840
	11th to 20th	Night	28% 21% 31% 16% 3	823
	21st to end	Night	30% 20% 29% 18% 3	692
March	1st to 10th	Night	28% 18% 31% 19% 3	840
	11th to 20th	Night	33% 20% 27% 16% 4	840
	21st to end	Night	29% 18% 28% 19% 5%	924
April	1st to 10th	Night	31% 17% 30% 20% 2	840
	11th to 20th	Night	30% 17% 26% 22% 5%	831
	21st to end	Night	30% 14% 26% 23% 7% 1	796
May	1st to 10th	Night	30% 10% 25% 28% 7% 1	420
	11th to 20th	Night	19% 10% 37% 28% 7%	414
	21st to end	Night	18% 8% 34% 29% 11%	455
June	1st to 10th	Night	22% 8% 29% 31% 9%	420
	11th to 20th	Night	18% 10% 29% 31% 12%	410
	21st to end	Night	18% 9% 33% 32% 8% 1	400
July	1st to 10th	Night	13% 6% 25% 39% 16% 1	390
	11th to 20th	Night	14% 5% 24% 37% 18% 2	388
	21st to end	Night	15% 5% 29% 38% 12% 1	438
August	1st to 10th	Night	15% 4 25% 38% 17% 1	510
	11th to 20th	Night	18% 5% 18% 34% 21% 3	621
	21st to end	Night	14% 8% 25% 33% 18% 2	880
September	1st to 10th	Night	17% 8% 25% 31% 16% 2	800
	11th to 20th	Night	16% 7% 22% 30% 21% 5%	800
	21st to end	Night	18% 13% 22% 27% 18% 2	800
October	1st to 10th	Night	26% 14% 24% 19% 15% 2	800
	11th to 20th	Night	28% 15% 26% 22% 8% 1	800
	21st to end	Night	33% 14% 29% 21% 3	880
November	1st to 10th	Night	30% 15% 27% 19% 8%	820
	11th to 20th	Night	28% 17% 30% 17% 7% 1	840
	21st to end	Night	37% 19% 24% 15% 5%	840
December	1st to 10th	Night	39% 20% 22% 15% 4	840
	11th to 20th	Night	34% 24% 27% 12% 2 1	840
	21st to end	Night	37% 19% 27% 15% 2	924

Page generated at 2026-06-13 02:31:43. Version ac07

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