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 2024-01-31.

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	19% 10% 4 6% 5% 3 4 4 5% 7% 33%	74880
	Night	20% 12% 4 7% 6% 3 4 4 5% 6% 30%	75245
Transparency	Day	54% 4 11% 21% 10% 1	74585
	Night	58% 4 10% 18% 9% 1	75074
Seeing	Day	26% 18% 29% 18% 7% 2	13497
	Night	26% 15% 27% 22% 8% 1	22806

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	20% 20% 6% 11% 7% 4 4 3 4 5% 17%	1517
	11th to 20th	Day	21% 18% 5% 12% 6% 3 4 3 3 5% 19%	1520
	21st to end	Day	14% 17% 7% 11% 8% 4 5% 5% 5% 5% 18%	1800
February	1st to 10th	Day	19% 18% 6% 10% 8% 3 5% 4 5% 6% 17%	1620
	11th to 20th	Day	19% 15% 6% 10% 6% 4 5% 3 3 4 25%	1591
	21st to end	Day	20% 18% 6% 8% 6% 3 5% 3 4 5% 23%	1480
March	1st to 10th	Day	16% 15% 6% 9% 6% 3 4 2 4 5% 28%	1818
	11th to 20th	Day	19% 13% 5% 8% 6% 4 4 4 4 6% 28%	1980
	21st to end	Day	23% 10% 4 5% 5% 2 4 3 4 5% 37%	2281
April	1st to 10th	Day	21% 12% 4 4 4 3 4 4 4 5% 34%	2160
	11th to 20th	Day	21% 7% 3 4 3 2 4 4 4 6% 40%	2134
	21st to end	Day	23% 9% 3 6% 5% 3 4 4 4 6% 34%	2209
May	1st to 10th	Day	20% 8% 3 5% 5% 4 5% 4 4 7% 35%	2520
	11th to 20th	Day	16% 6% 3 5% 4 3 5% 5% 5% 9% 40%	2478
	21st to end	Day	15% 5% 3 5% 5% 3 5% 5% 5% 9% 39%	2725
June	1st to 10th	Day	20% 7% 3 5% 5% 4 5% 5% 5% 7% 36%	2520
	11th to 20th	Day	17% 6% 2 4 4 3 5% 6% 6% 8% 40%	2520
	21st to end	Day	17% 7% 2 5% 4 3 5% 4 6% 8% 38%	2520
July	1st to 10th	Day	12% 5% 2 4 5% 3 4 4 6% 9% 46%	2520
	11th to 20th	Day	14% 5% 2 5% 4 3 4 5% 6% 8% 44%	2520
	21st to end	Day	13% 5% 2 4 5% 3 6% 5% 7% 9% 41%	2744
August	1st to 10th	Day	12% 5% 2 5% 5% 3 5% 5% 6% 8% 43%	2403
	11th to 20th	Day	14% 6% 2 5% 4 3 5% 5% 6% 9% 41%	2260
	21st to end	Day	15% 5% 2 5% 5% 3 4 5% 6% 8% 42%	2376
September	1st to 10th	Day	15% 5% 3 5% 4 3 4 5% 5% 7% 44%	2160
	11th to 20th	Day	15% 6% 2 4 4 3 4 4 5% 7% 46%	2160
	21st to end	Day	19% 6% 2 5% 5% 3 4 4 6% 8% 38%	1920
October	1st to 10th	Day	24% 8% 3 7% 5% 3 3 4 4 7% 33%	1800
	11th to 20th	Day	24% 9% 3 7% 6% 4 5% 4 4 7% 27%	1800
	21st to end	Day	31% 9% 3 6% 5% 3 5% 4 4 6% 24%	1872
November	1st to 10th	Day	17% 11% 4 7% 6% 3 5% 5% 6% 7% 30%	1671
	11th to 20th	Day	18% 14% 5% 8% 8% 3 4 4 5% 6% 26%	1563
	21st to end	Day	21% 19% 6% 8% 6% 4 4 4 4 6% 18%	1520
December	1st to 10th	Day	25% 23% 5% 9% 6% 3 3 4 3 5% 13%	1520
	11th to 20th	Day	22% 21% 7% 9% 5% 3 5% 4 4 5% 16%	1906
	21st to end	Day	28% 18% 7% 10% 6% 3 4 3 3 4 15%	2772
January	1st to 10th	Night	21% 20% 7% 11% 6% 3 4 3 3 4 17%	2649
	11th to 20th	Night	19% 20% 6% 12% 6% 4 5% 4 4 5% 16%	2660
	21st to end	Night	15% 18% 6% 11% 7% 4 4 4 4 5% 23%	2782
February	1st to 10th	Night	19% 16% 7% 14% 8% 4 4 4 4 4 17%	2340
	11th to 20th	Night	18% 15% 7% 9% 6% 4 4 4 4 5% 24%	2255
	21st to end	Night	19% 14% 6% 10% 6% 3 4 4 4 6% 25%	1776
March	1st to 10th	Night	17% 14% 6% 8% 7% 3 5% 5% 4 4 27%	2128
	11th to 20th	Night	21% 12% 5% 7% 5% 3 3 3 4 6% 31%	1979
	21st to end	Night	21% 10% 4 7% 6% 3 3 3 4 5% 34%	2075
April	1st to 10th	Night	22% 11% 4 6% 5% 3 3 4 4 5% 33%	1800
	11th to 20th	Night	23% 7% 3 6% 5% 3 4 6% 5% 6% 33%	1775
	21st to end	Night	24% 8% 3 6% 5% 2 5% 5% 4 6% 32%	1763
May	1st to 10th	Night	23% 7% 3 6% 5% 2 5% 4 5% 6% 34%	1440
	11th to 20th	Night	15% 7% 2 5% 5% 3 4 4 6% 7% 40%	1415
	21st to end	Night	12% 6% 2 5% 5% 4 4 6% 6% 7% 42%	1550
June	1st to 10th	Night	17% 7% 3 6% 6% 3 4 5% 6% 9% 35%	1440
	11th to 20th	Night	16% 5% 2 5% 4 3 5% 5% 6% 9% 41%	1440
	21st to end	Night	16% 8% 2 5% 5% 4 5% 5% 6% 7% 37%	1440
July	1st to 10th	Night	11% 4 3 5% 4 3 5% 5% 6% 8% 46%	1440
	11th to 20th	Night	12% 5% 2 5% 6% 3 4 5% 6% 9% 44%	1440
	21st to end	Night	13% 5% 2 5% 5% 2 4 6% 6% 8% 43%	1574
August	1st to 10th	Night	12% 6% 2 4 6% 4 4 5% 6% 8% 44%	1532
	11th to 20th	Night	14% 5% 3 6% 5% 3 5% 4 6% 8% 41%	1621
	21st to end	Night	12% 5% 3 5% 6% 3 4 5% 6% 8% 43%	1980
September	1st to 10th	Night	16% 6% 2 4 5% 2 5% 5% 5% 7% 43%	1800
	11th to 20th	Night	15% 5% 2 4 3 2 3 4 4 7% 50%	1800
	21st to end	Night	17% 6% 3 5% 6% 3 4 4 5% 7% 40%	2037
October	1st to 10th	Night	22% 8% 3 7% 5% 3 5% 5% 4 6% 32%	2160
	11th to 20th	Night	23% 9% 4 6% 6% 3 5% 5% 5% 6% 29%	2160
	21st to end	Night	30% 10% 3 8% 6% 3 4 3 4 5% 24%	2483
November	1st to 10th	Night	21% 10% 3 7% 5% 3 4 4 5% 5% 32%	2407
	11th to 20th	Night	19% 11% 5% 8% 5% 3 4 4 5% 6% 29%	2612
	21st to end	Night	25% 17% 4 7% 5% 3 4 4 5% 7% 19%	2660
December	1st to 10th	Night	24% 22% 5% 8% 5% 3 5% 4 4 4 15%	2660
	11th to 20th	Night	23% 18% 5% 9% 6% 3 4 3 5% 4 21%	3288
	21st to end	Night	31% 16% 7% 8% 5% 3 3 4 4 6% 14%	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	74% 3 7% 12% 3	1518
	11th to 20th	Day	72% 4 6% 11% 6% 1	1520
	21st to end	Day	70% 4 8% 12% 6% 1	1800
February	1st to 10th	Day	72% 4 7% 12% 3 1	1620
	11th to 20th	Day	68% 3 7% 15% 7% 1	1600
	21st to end	Day	68% 3 8% 13% 8%	1480
March	1st to 10th	Day	64% 2 9% 16% 8% 1	1821
	11th to 20th	Day	61% 3 10% 14% 10% 2	1980
	21st to end	Day	54% 2 7% 20% 14% 4	2281
April	1st to 10th	Day	55% 3 8% 20% 13% 2	2160
	11th to 20th	Day	49% 3 8% 24% 14% 2	2134
	21st to end	Day	54% 3 9% 18% 12% 3	2209
May	1st to 10th	Day	52% 4 8% 20% 13% 3	2520
	11th to 20th	Day	43% 5% 9% 26% 14% 2	2482
	21st to end	Day	43% 5% 16% 22% 12% 2	2725
June	1st to 10th	Day	50% 4 12% 21% 12% 1	2520
	11th to 20th	Day	44% 4 12% 26% 12% 2	2520
	21st to end	Day	46% 5% 14% 23% 12% 1	2520
July	1st to 10th	Day	36% 4 13% 29% 16% 1	2450
	11th to 20th	Day	39% 4 16% 31% 9%	2445
	21st to end	Day	41% 6% 17% 25% 12%	2591
August	1st to 10th	Day	40% 5% 17% 28% 10%	2389
	11th to 20th	Day	42% 6% 17% 26% 9%	2260
	21st to end	Day	43% 5% 13% 29% 10% 1	2376
September	1st to 10th	Day	42% 4 13% 28% 12% 1	2160
	11th to 20th	Day	40% 3 10% 30% 16% 1	2160
	21st to end	Day	46% 4 12% 27% 10%	1920
October	1st to 10th	Day	54% 4 9% 22% 11%	1800
	11th to 20th	Day	58% 4 13% 19% 5% 1	1800
	21st to end	Day	63% 4 9% 15% 8% 1	1872
November	1st to 10th	Day	54% 6% 13% 18% 8% 1	1671
	11th to 20th	Day	61% 4 10% 15% 8% 2	1563
	21st to end	Day	71% 4 10% 9% 6%	1520
December	1st to 10th	Day	76% 5% 9% 9% 1	1520
	11th to 20th	Day	74% 4 9% 10% 3	1906
	21st to end	Day	78% 2 5% 12% 2	2772
January	1st to 10th	Night	74% 3 7% 12% 4	2649
	11th to 20th	Night	73% 4 7% 10% 5% 1	2660
	21st to end	Night	67% 4 7% 13% 8% 1	2782
February	1st to 10th	Night	74% 4 7% 10% 5%	2340
	11th to 20th	Night	66% 4 7% 16% 7%	2257
	21st to end	Night	63% 4 10% 16% 7% 1	1776
March	1st to 10th	Night	62% 3 9% 16% 8% 1	2138
	11th to 20th	Night	58% 3 9% 19% 10% 1	1980
	21st to end	Night	55% 2 6% 18% 14% 3	2075
April	1st to 10th	Night	56% 3 9% 20% 10% 2	1800
	11th to 20th	Night	53% 4 8% 19% 15% 1	1775
	21st to end	Night	54% 2 9% 19% 14% 2	1763
May	1st to 10th	Night	51% 3 9% 18% 15% 4	1440
	11th to 20th	Night	44% 4 10% 24% 15% 3	1416
	21st to end	Night	42% 4 15% 22% 16% 2	1551
June	1st to 10th	Night	48% 4 12% 24% 10% 1	1440
	11th to 20th	Night	42% 4 13% 22% 18% 2	1440
	21st to end	Night	45% 5% 14% 24% 12% 1	1440
July	1st to 10th	Night	35% 4 14% 27% 19% 2	1400
	11th to 20th	Night	38% 4 12% 32% 13% 1	1392
	21st to end	Night	38% 6% 14% 29% 12% 1	1486
August	1st to 10th	Night	39% 5% 16% 29% 10% 1	1522
	11th to 20th	Night	43% 5% 12% 26% 13%	1621
	21st to end	Night	39% 6% 13% 31% 10%	1980
September	1st to 10th	Night	41% 6% 13% 27% 12% 2	1800
	11th to 20th	Night	36% 3 13% 31% 16% 1	1800
	21st to end	Night	44% 5% 11% 28% 12% 1	2037
October	1st to 10th	Night	55% 4 9% 20% 11% 1	2160
	11th to 20th	Night	57% 5% 13% 18% 7% 1	2160
	21st to end	Night	66% 5% 9% 12% 7% 1	2483
November	1st to 10th	Night	55% 4 12% 18% 9% 2	2407
	11th to 20th	Night	57% 6% 9% 18% 7% 2	2612
	21st to end	Night	67% 6% 9% 13% 4	2660
December	1st to 10th	Night	77% 4 8% 10% 2	2660
	11th to 20th	Night	70% 5% 9% 11% 5%	3288
	21st to end	Night	76% 3 9% 10% 2	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	32% 24% 24% 15% 4	180
	11th to 20th	Day	31% 26% 26% 14% 2 1	180
	21st to end	Day	29% 26% 29% 12% 3	260
February	1st to 10th	Day	39% 30% 24% 7%	240
	11th to 20th	Day	34% 32% 30% 5%	258
	21st to end	Day	35% 26% 27% 11% 1	346
March	1st to 10th	Day	29% 24% 30% 13% 4	420
	11th to 20th	Day	33% 23% 30% 10% 3 1	420
	21st to end	Day	36% 20% 27% 10% 6%	462
April	1st to 10th	Day	34% 23% 26% 13% 5%	420
	11th to 20th	Day	33% 22% 21% 16% 5% 4	412
	21st to end	Day	32% 21% 28% 12% 5% 2	420
May	1st to 10th	Day	27% 20% 27% 16% 8% 2	423
	11th to 20th	Day	21% 15% 34% 22% 6% 2	447
	21st to end	Day	19% 16% 33% 20% 11% 1	485
June	1st to 10th	Day	26% 14% 34% 18% 6% 1	450
	11th to 20th	Day	20% 14% 35% 21% 8% 2	450
	21st to end	Day	22% 13% 35% 21% 8% 1	450
July	1st to 10th	Day	14% 11% 30% 29% 13% 3	445
	11th to 20th	Day	18% 9% 34% 25% 11% 3	444
	21st to end	Day	15% 11% 37% 28% 8% 1	488
August	1st to 10th	Day	15% 9% 33% 27% 13% 4	446
	11th to 20th	Day	17% 8% 28% 29% 13% 6%	439
	21st to end	Day	17% 12% 31% 22% 13% 5%	495
September	1st to 10th	Day	16% 13% 30% 25% 11% 5%	450
	11th to 20th	Day	14% 12% 28% 21% 18% 6%	450
	21st to end	Day	18% 16% 28% 23% 12% 4	450
October	1st to 10th	Day	28% 17% 24% 17% 11% 3	450
	11th to 20th	Day	32% 20% 27% 15% 5% 2	450
	21st to end	Day	39% 17% 26% 14% 4	441
November	1st to 10th	Day	30% 20% 27% 15% 8% 1	365
	11th to 20th	Day	30% 22% 30% 11% 5% 2	223
	21st to end	Day	30% 33% 25% 9% 3	180
December	1st to 10th	Day	46% 13% 25% 13% 3	180
	11th to 20th	Day	33% 28% 32% 6% 1	180
	21st to end	Day	35% 23% 29% 11% 1 1	198
January	1st to 10th	Night	33% 23% 24% 15% 4	760
	11th to 20th	Night	32% 22% 27% 16% 3	760
	21st to end	Night	26% 21% 28% 20% 5%	835
February	1st to 10th	Night	30% 24% 28% 16% 2	720
	11th to 20th	Night	28% 21% 31% 16% 3	703
	21st to end	Night	30% 20% 29% 19% 3	592
March	1st to 10th	Night	27% 18% 31% 20% 3	720
	11th to 20th	Night	32% 20% 27% 16% 4	720
	21st to end	Night	27% 17% 30% 19% 6% 1	792
April	1st to 10th	Night	30% 18% 29% 20% 3	720
	11th to 20th	Night	28% 17% 27% 22% 5%	711
	21st to end	Night	31% 13% 25% 22% 8% 1	683
May	1st to 10th	Night	27% 9% 26% 29% 8% 1	360
	11th to 20th	Night	17% 10% 38% 29% 6%	354
	21st to end	Night	16% 7% 33% 31% 12% 1	389
June	1st to 10th	Night	23% 8% 27% 31% 10% 1	360
	11th to 20th	Night	17% 9% 29% 31% 14%	360
	21st to end	Night	17% 9% 32% 34% 8% 1	360
July	1st to 10th	Night	12% 6% 24% 40% 17% 1	350
	11th to 20th	Night	14% 6% 24% 35% 18% 2	348
	21st to end	Night	15% 6% 29% 37% 12% 1	394
August	1st to 10th	Night	15% 4 24% 37% 17% 2	458
	11th to 20th	Night	17% 5% 18% 34% 21% 4	557
	21st to end	Night	14% 8% 26% 33% 18% 2	792
September	1st to 10th	Night	18% 8% 26% 30% 16% 2	720
	11th to 20th	Night	17% 7% 23% 29% 19% 4	720
	21st to end	Night	18% 14% 22% 27% 18% 2	720
October	1st to 10th	Night	27% 15% 23% 18% 15% 2	720
	11th to 20th	Night	28% 16% 26% 21% 8% 1	720
	21st to end	Night	35% 15% 27% 20% 3	792
November	1st to 10th	Night	29% 16% 28% 19% 8% 1	740
	11th to 20th	Night	28% 18% 30% 15% 8% 1	760
	21st to end	Night	36% 20% 24% 15% 5%	760
December	1st to 10th	Night	40% 19% 22% 15% 4	760
	11th to 20th	Night	33% 24% 27% 13% 3 1	760
	21st to end	Night	36% 20% 27% 14% 1	836

Page generated at 2024-01-28 05:26:33. Version ac07

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