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 2025-02-21.

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% 7% 32%	108747
	Night	19% 13% 5% 9% 5% 4 4 3 5% 6% 27%	109827
Transparency	Day	55% 3 11% 22% 9% 1	112299
	Night	60% 3 9% 18% 9% 1	114439
Seeing	Day	26% 18% 29% 18% 7% 2	14836
	Night	27% 15% 27% 22% 8% 1	24143

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 4 18%	3597
	11th to 20th	Day	12% 20% 8% 22% 7% 4 4 3 4 4 12%	3570
	21st to end	Day	15% 17% 8% 14% 9% 6% 4 3 4 6% 14%	4300
February	1st to 10th	Day	18% 19% 5% 11% 6% 4 5% 2 5% 6% 19%	1800
	11th to 20th	Day	17% 15% 6% 10% 5% 5% 5% 3 4 5% 25%	1773
	21st to end	Day	18% 18% 5% 9% 6% 5% 4 3 4 5% 23%	1570
March	1st to 10th	Day	23% 15% 4 7% 4 3 3 2 4 5% 30%	3165
	11th to 20th	Day	13% 19% 4 9% 5% 5% 3 3 4 6% 28%	3480
	21st to end	Day	16% 9% 3 7% 4 4 4 3 5% 7% 39%	4001
April	1st to 10th	Day	21% 13% 3 5% 4 4 4 3 4 5% 34%	2280
	11th to 20th	Day	22% 8% 2 5% 4 3 4 3 4 6% 38%	2254
	21st to end	Day	23% 10% 3 6% 4 4 3 4 4 6% 34%	2333
May	1st to 10th	Day	23% 10% 3 7% 4 4 4 3 5% 6% 32%	4426
	11th to 20th	Day	16% 8% 3 8% 4 5% 5% 4 6% 8% 33%	4398
	21st to end	Day	15% 5% 2 6% 4 4 5% 4 6% 9% 40%	4837
June	1st to 10th	Day	20% 7% 2 6% 5% 5% 5% 4 5% 7% 34%	2660
	11th to 20th	Day	16% 6% 2 5% 5% 4 4 5% 6% 8% 39%	2660
	21st to end	Day	17% 7% 2 6% 4 5% 4 4 6% 8% 37%	2660
July	1st to 10th	Day	13% 5% 2 5% 4 5% 4 4 6% 9% 43%	4440
	11th to 20th	Day	14% 6% 2 5% 3 4 4 4 6% 8% 45%	4440
	21st to end	Day	12% 4 2 6% 4 4 5% 4 7% 9% 42%	4814
August	1st to 10th	Day	18% 7% 2 6% 4 4 4 3 5% 7% 39%	4236
	11th to 20th	Day	18% 6% 2 6% 3 4 4 4 6% 9% 36%	3959
	21st to end	Day	17% 5% 2 6% 4 3 4 3 6% 8% 41%	4180
September	1st to 10th	Day	15% 6% 2 5% 4 4 4 4 5% 7% 44%	2280
	11th to 20th	Day	14% 6% 2 5% 4 3 4 3 5% 7% 47%	2280
	21st to end	Day	19% 7% 2 5% 5% 4 4 4 6% 8% 37%	2026
October	1st to 10th	Day	23% 8% 3 7% 4 3 3 3 4 6% 34%	1900
	11th to 20th	Day	23% 10% 3 7% 5% 5% 4 3 4 7% 29%	1900
	21st to end	Day	29% 9% 3 7% 4 4 4 3 5% 6% 25%	1976
November	1st to 10th	Day	16% 12% 3 8% 5% 5% 4 4 6% 7% 30%	1761
	11th to 20th	Day	17% 15% 4 9% 7% 4 4 3 6% 6% 27%	1645
	21st to end	Day	21% 21% 5% 9% 5% 4 4 3 5% 5% 17%	1600
December	1st to 10th	Day	22% 25% 5% 10% 5% 4 4 3 4 6% 12%	2600
	11th to 20th	Day	21% 21% 6% 12% 4 3 4 3 3 5% 16%	2986
	21st to end	Day	23% 17% 5% 10% 5% 5% 4 3 4 5% 19%	3960
January	1st to 10th	Night	16% 23% 7% 13% 6% 4 4 3 3 4 17%	6349
	11th to 20th	Night	12% 22% 11% 20% 7% 6% 4 3 3 3 9%	6315
	21st to end	Night	16% 19% 9% 14% 9% 6% 4 3 4 4 14%	6655
February	1st to 10th	Night	18% 18% 6% 14% 7% 5% 4 2 4 4 19%	2600
	11th to 20th	Night	17% 16% 6% 11% 5% 4 4 3 4 5% 25%	2513
	21st to end	Night	19% 15% 5% 11% 5% 4 4 3 4 5% 26%	1885
March	1st to 10th	Night	19% 12% 4 8% 5% 4 4 3 4 4 32%	3674
	11th to 20th	Night	23% 19% 4 8% 4 3 3 3 4 5% 25%	3479
	21st to end	Night	20% 10% 3 7% 5% 4 3 2 4 5% 37%	3631
April	1st to 10th	Night	22% 12% 3 7% 5% 3 3 3 4 5% 32%	1900
	11th to 20th	Night	23% 8% 3 6% 5% 4 4 4 5% 6% 33%	1875
	21st to end	Night	23% 8% 3 7% 4 4 4 4 4 6% 33%	1860
May	1st to 10th	Night	26% 10% 3 7% 4 4 3 4 5% 6% 28%	2514
	11th to 20th	Night	21% 10% 3 7% 4 4 4 4 5% 6% 32%	2495
	21st to end	Night	15% 7% 2 5% 4 4 4 4 6% 8% 41%	2738
June	1st to 10th	Night	17% 7% 3 8% 5% 4 5% 4 6% 8% 34%	1520
	11th to 20th	Night	15% 5% 2 6% 4 5% 4 4 6% 9% 41%	1520
	21st to end	Night	17% 9% 3 6% 5% 4 5% 4 6% 7% 36%	1520
July	1st to 10th	Night	15% 6% 3 6% 5% 5% 5% 4 6% 7% 39%	2520
	11th to 20th	Night	14% 7% 2 6% 5% 3 4 3 6% 7% 43%	2520
	21st to end	Night	14% 6% 2 5% 4 3 4 5% 6% 8% 43%	2739
August	1st to 10th	Night	14% 8% 2 6% 4 4 4 3 6% 7% 41%	2690
	11th to 20th	Night	14% 6% 3 8% 4 4 5% 4 6% 8% 37%	2836
	21st to end	Night	10% 5% 2 6% 5% 5% 5% 5% 7% 9% 41%	3476
September	1st to 10th	Night	16% 7% 2 5% 4 4 4 4 5% 6% 44%	1900
	11th to 20th	Night	14% 5% 2 5% 3 3 3 3 5% 6% 51%	1900
	21st to end	Night	18% 6% 2 6% 5% 4 4 3 5% 8% 40%	2151
October	1st to 10th	Night	21% 9% 3 7% 4 5% 5% 4 4 6% 33%	2280
	11th to 20th	Night	22% 9% 4 7% 5% 4 5% 4 5% 5% 30%	2280
	21st to end	Night	29% 10% 3 9% 5% 4 4 3 4 5% 25%	2621
November	1st to 10th	Night	21% 11% 3 7% 5% 4 4 3 6% 5% 32%	2537
	11th to 20th	Night	19% 12% 4 9% 5% 4 4 3 5% 6% 29%	2750
	21st to end	Night	25% 19% 4 7% 4 4 4 3 5% 6% 19%	2800
December	1st to 10th	Night	20% 26% 6% 12% 5% 4 4 3 4 4 11%	4580
	11th to 20th	Night	24% 19% 5% 11% 5% 4 3 2 4 4 19%	5208
	21st to end	Night	28% 16% 5% 9% 4 4 4 3 4 5% 18%	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	75% 1 5% 13% 4 1	3598
	11th to 20th	Day	81% 2 5% 8% 4 1	3600
	21st to end	Day	76% 2 8% 8% 6% 1	4300
February	1st to 10th	Day	71% 4 7% 14% 4 1	1800
	11th to 20th	Day	67% 3 7% 16% 7% 1	1782
	21st to end	Day	67% 3 8% 14% 8%	1570
March	1st to 10th	Day	62% 1 8% 19% 8% 1	3168
	11th to 20th	Day	61% 3 14% 13% 8% 1	3480
	21st to end	Day	50% 2 7% 27% 13% 2	4001
April	1st to 10th	Day	56% 3 7% 20% 12% 2	2280
	11th to 20th	Day	50% 3 8% 23% 14% 2	2254
	21st to end	Day	54% 3 9% 19% 12% 3	2333
May	1st to 10th	Day	56% 3 9% 22% 9% 1	4440
	11th to 20th	Day	52% 3 12% 24% 9% 1	4402
	21st to end	Day	44% 3 13% 27% 12% 1	4837
June	1st to 10th	Day	51% 4 11% 21% 12% 1	2660
	11th to 20th	Day	45% 4 13% 26% 11% 2	2660
	21st to end	Day	47% 5% 13% 23% 11% 1	2660
July	1st to 10th	Day	40% 3 13% 31% 13% 1	4370
	11th to 20th	Day	39% 3 16% 34% 9%	4365
	21st to end	Day	40% 4 16% 30% 10%	4661
August	1st to 10th	Day	46% 3 15% 24% 11%	4222
	11th to 20th	Day	47% 3 17% 25% 8%	3998
	21st to end	Day	43% 3 14% 31% 8%	4180
September	1st to 10th	Day	42% 4 13% 28% 12% 1	2280
	11th to 20th	Day	39% 3 10% 31% 16%	2280
	21st to end	Day	47% 4 12% 27% 10%	2026
October	1st to 10th	Day	48% 3 10% 30% 9%	3160
	11th to 20th	Day	50% 2 14% 25% 9%	3140
	21st to end	Day	53% 3 14% 23% 7%	3240
November	1st to 10th	Day	55% 5% 13% 19% 8% 1	1761
	11th to 20th	Day	60% 4 10% 16% 8% 2	1645
	21st to end	Day	71% 4 10% 9% 5%	1600
December	1st to 10th	Day	77% 3 12% 7% 1	2600
	11th to 20th	Day	75% 2 8% 11% 4	2986
	21st to end	Day	73% 2 7% 15% 4	3960
January	1st to 10th	Night	77% 1 7% 10% 4	6349
	11th to 20th	Night	84% 3 3 6% 3	6360
	21st to end	Night	80% 2 6% 7% 6%	6655
February	1st to 10th	Night	73% 4 7% 11% 5%	2600
	11th to 20th	Night	65% 4 7% 17% 7%	2515
	21st to end	Night	62% 4 10% 16% 7% 1	1885
March	1st to 10th	Night	58% 2 8% 22% 9% 1	3684
	11th to 20th	Night	65% 2 10% 15% 8%	3480
	21st to end	Night	54% 2 4 22% 15% 2	3631
April	1st to 10th	Night	56% 3 8% 20% 10% 2	1900
	11th to 20th	Night	53% 4 8% 19% 15% 1	1875
	21st to end	Night	53% 2 9% 19% 14% 2	1860
May	1st to 10th	Night	58% 2 9% 18% 11% 2	2520
	11th to 20th	Night	53% 3 12% 22% 9% 2	2496
	21st to end	Night	43% 3 11% 23% 19% 2	2739
June	1st to 10th	Night	49% 4 12% 23% 10% 1	1520
	11th to 20th	Night	42% 4 13% 22% 17% 2	1520
	21st to end	Night	47% 4 13% 23% 12% 1	1520
July	1st to 10th	Night	44% 3 11% 23% 17% 1	2480
	11th to 20th	Night	43% 3 12% 32% 10%	2472
	21st to end	Night	39% 4 13% 29% 13% 1	2651
August	1st to 10th	Night	45% 3 14% 27% 11% 1	2680
	11th to 20th	Night	47% 4 12% 28% 8%	2863
	21st to end	Night	39% 4 11% 35% 10% 1	3476
September	1st to 10th	Night	41% 5% 13% 27% 12% 1	1900
	11th to 20th	Night	36% 3 12% 31% 17% 1	1900
	21st to end	Night	45% 4 11% 28% 12% 1	2151
October	1st to 10th	Night	50% 3 8% 26% 12% 1	3800
	11th to 20th	Night	49% 3 13% 24% 11% 1	3779
	21st to end	Night	57% 3 10% 23% 6% 1	4307
November	1st to 10th	Night	55% 4 12% 18% 9% 2	2537
	11th to 20th	Night	57% 6% 9% 18% 8% 2	2750
	21st to end	Night	68% 6% 9% 13% 4	2800
December	1st to 10th	Night	80% 2 8% 9% 1	4580
	11th to 20th	Night	73% 3 6% 12% 5%	5208
	21st to end	Night	73% 2 7% 10% 7%	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	32% 25% 26% 14% 4	200
	11th to 20th	Day	32% 25% 26% 15% 2 1	200
	21st to end	Day	29% 28% 29% 11% 2	293
February	1st to 10th	Day	38% 28% 27% 7%	300
	11th to 20th	Day	36% 31% 28% 6%	320
	21st to end	Day	34% 26% 28% 10% 1	382
March	1st to 10th	Day	30% 23% 30% 13% 4	460
	11th to 20th	Day	33% 23% 30% 10% 3 1	460
	21st to end	Day	36% 21% 27% 10% 5%	506
April	1st to 10th	Day	35% 23% 26% 12% 4	460
	11th to 20th	Day	34% 23% 21% 15% 4 3	452
	21st to end	Day	33% 21% 27% 12% 5% 2	460
May	1st to 10th	Day	28% 20% 27% 16% 8% 2	463
	11th to 20th	Day	20% 15% 34% 22% 7% 2	487
	21st to end	Day	19% 16% 33% 20% 11% 1	529
June	1st to 10th	Day	27% 14% 33% 18% 6% 2	490
	11th to 20th	Day	19% 14% 35% 22% 8% 2	490
	21st to end	Day	23% 14% 34% 20% 7% 1	490
July	1st to 10th	Day	14% 12% 31% 28% 13% 2	485
	11th to 20th	Day	18% 10% 35% 24% 10% 3	484
	21st to end	Day	15% 11% 37% 27% 9% 1	532
August	1st to 10th	Day	17% 9% 33% 26% 12% 4	486
	11th to 20th	Day	18% 8% 28% 28% 13% 5%	479
	21st to end	Day	18% 11% 31% 22% 13% 5%	539
September	1st to 10th	Day	17% 12% 30% 25% 11% 5%	490
	11th to 20th	Day	13% 11% 26% 21% 21% 8%	490
	21st to end	Day	19% 15% 27% 24% 12% 3	490
October	1st to 10th	Day	28% 16% 25% 17% 11% 3	490
	11th to 20th	Day	31% 19% 27% 15% 6% 2	490
	21st to end	Day	36% 18% 26% 15% 4	479
November	1st to 10th	Day	31% 19% 27% 15% 7% 1	395
	11th to 20th	Day	29% 21% 31% 11% 5% 2	245
	21st to end	Day	33% 32% 24% 9% 3	200
December	1st to 10th	Day	45% 14% 25% 14% 3	200
	11th to 20th	Day	34% 28% 32% 6% 2	200
	21st to end	Day	35% 21% 27% 13% 4	220
January	1st to 10th	Night	33% 23% 26% 15% 4	800
	11th to 20th	Night	31% 22% 27% 16% 3	800
	21st to end	Night	26% 21% 28% 20% 5%	880
February	1st to 10th	Night	31% 24% 26% 17% 2	800
	11th to 20th	Night	28% 21% 31% 16% 3	783
	21st to end	Night	30% 20% 28% 19% 3	629
March	1st to 10th	Night	27% 18% 31% 20% 4	760
	11th to 20th	Night	33% 21% 26% 16% 4	760
	21st to end	Night	28% 17% 29% 19% 6%	836
April	1st to 10th	Night	31% 18% 29% 21% 3	760
	11th to 20th	Night	28% 18% 27% 22% 5%	751
	21st to end	Night	31% 14% 24% 22% 8% 1	720
May	1st to 10th	Night	27% 10% 26% 29% 8% 1	380
	11th to 20th	Night	17% 10% 37% 29% 7%	374
	21st to end	Night	16% 8% 33% 30% 12%	411
June	1st to 10th	Night	22% 9% 28% 31% 9% 1	380
	11th to 20th	Night	17% 9% 29% 32% 13%	380
	21st to end	Night	19% 8% 32% 33% 8% 1	380
July	1st to 10th	Night	13% 6% 24% 40% 16% 1	370
	11th to 20th	Night	14% 5% 24% 36% 18% 2	368
	21st to end	Night	15% 6% 28% 38% 13% 1	416
August	1st to 10th	Night	16% 4 25% 37% 17% 1	484
	11th to 20th	Night	19% 5% 18% 34% 21% 3	589
	21st to end	Night	14% 8% 25% 33% 18% 2	836
September	1st to 10th	Night	18% 8% 26% 31% 16% 2	760
	11th to 20th	Night	16% 7% 22% 29% 21% 5%	760
	21st to end	Night	18% 13% 22% 27% 18% 2	760
October	1st to 10th	Night	27% 14% 24% 19% 15% 2	760
	11th to 20th	Night	28% 16% 25% 22% 8% 1	760
	21st to end	Night	34% 15% 28% 20% 3	836
November	1st to 10th	Night	29% 16% 28% 19% 8% 1	780
	11th to 20th	Night	28% 18% 30% 16% 8% 1	800
	21st to end	Night	37% 19% 24% 15% 5%	800
December	1st to 10th	Night	40% 20% 22% 15% 4	800
	11th to 20th	Night	34% 24% 27% 13% 3 1	800
	21st to end	Night	36% 19% 27% 15% 2	880

Page generated at 2025-02-18 03:26:32. Version ac07

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