TamyMartOffgrid
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the TamyMartOffgrid clear sky chart from 2005-11-06 to 2025-12-03.

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% 10% 4 8% 5% 5% 4 3 5% 7% 32%	127401
	Night	16% 12% 4 9% 5% 4 4 3 5% 6% 30%	123253
Transparency	Day	33% 38% 8% 14% 6% 1	130879
	Night	35% 38% 7% 13% 6% 1	127862
Seeing	Day	23% 16% 30% 19% 8% 2	15758
	Night	22% 14% 29% 25% 9% 1	24877

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	13% 18% 7% 14% 8% 6% 4 3 4 3 20%	3597
	11th to 20th	Day	12% 16% 6% 15% 8% 5% 5% 3 5% 5% 20%	3570
	21st to end	Day	9% 17% 8% 15% 7% 6% 5% 3 4 6% 20%	4172
February	1st to 10th	Day	13% 16% 5% 13% 8% 5% 4 4 5% 5% 23%	1800
	11th to 20th	Day	12% 16% 6% 12% 6% 5% 4 3 5% 5% 26%	1753
	21st to end	Day	18% 14% 4 9% 5% 6% 4 4 6% 4 25%	1628
March	1st to 10th	Day	19% 15% 4 11% 5% 4 4 3 4 6% 24%	4540
	11th to 20th	Day	13% 13% 5% 10% 5% 5% 4 4 5% 7% 28%	4980
	21st to end	Day	18% 11% 3 7% 5% 4 3 3 4 5% 37%	5730
April	1st to 10th	Day	22% 13% 3 7% 5% 4 4 3 4 6% 31%	2400
	11th to 20th	Day	22% 11% 3 6% 4 4 3 2 4 5% 35%	2374
	21st to end	Day	22% 10% 3 8% 5% 4 4 3 3 5% 32%	2559
May	1st to 10th	Day	22% 9% 3 8% 5% 5% 4 3 6% 7% 28%	6346
	11th to 20th	Day	16% 9% 3 8% 5% 4 5% 3 5% 8% 33%	6318
	21st to end	Day	21% 8% 3 8% 4 4 4 4 5% 7% 33%	6949
June	1st to 10th	Day	22% 8% 3 7% 5% 4 5% 4 5% 7% 30%	2800
	11th to 20th	Day	15% 6% 3 6% 5% 4 5% 4 6% 7% 39%	2800
	21st to end	Day	18% 8% 2 7% 5% 5% 5% 5% 6% 6% 33%	2800
July	1st to 10th	Day	14% 6% 3 7% 5% 5% 5% 4 7% 10% 34%	6360
	11th to 20th	Day	12% 5% 2 6% 5% 4 5% 4 6% 8% 44%	6360
	21st to end	Day	10% 5% 2 5% 4 4 4 4 7% 10% 46%	6926
August	1st to 10th	Day	14% 6% 3 7% 6% 6% 6% 4 6% 8% 35%	4447
	11th to 20th	Day	17% 6% 2 6% 4 5% 4 4 7% 8% 36%	4160
	21st to end	Day	13% 5% 2 6% 4 5% 5% 4 7% 10% 39%	4312
September	1st to 10th	Day	14% 5% 2 6% 4 4 5% 4 7% 7% 42%	2400
	11th to 20th	Day	12% 5% 2 6% 4 4 4 4 5% 7% 46%	2400
	21st to end	Day	19% 6% 2 6% 4 4 4 4 5% 7% 39%	2121
October	1st to 10th	Day	21% 7% 3 6% 4 4 5% 3 5% 6% 36%	2000
	11th to 20th	Day	23% 10% 3 7% 6% 4 5% 3 4 7% 28%	2000
	21st to end	Day	26% 10% 3 8% 5% 5% 4 2 4 6% 27%	2057
November	1st to 10th	Day	17% 10% 4 6% 5% 4 6% 5% 5% 6% 33%	1820
	11th to 20th	Day	18% 14% 5% 9% 5% 5% 5% 3 5% 5% 25%	1680
	21st to end	Day	22% 17% 4 11% 5% 5% 5% 3 3 5% 18%	1680
December	1st to 10th	Day	21% 22% 6% 10% 6% 6% 5% 4 4 5% 13%	2616
	11th to 20th	Day	17% 18% 6% 11% 6% 5% 4 3 4 4 24%	2986
	21st to end	Day	22% 20% 5% 11% 4 4 3 3 3 5% 19%	3960
January	1st to 10th	Night	14% 20% 8% 15% 6% 5% 4 3 4 4 18%	6349
	11th to 20th	Night	11% 14% 6% 16% 8% 6% 5% 3 4 5% 21%	6315
	21st to end	Night	11% 18% 6% 14% 8% 7% 5% 3 4 4 21%	6769
February	1st to 10th	Night	12% 14% 6% 13% 7% 6% 5% 3 5% 6% 23%	2600
	11th to 20th	Night	12% 16% 5% 12% 7% 4 4 3 4 5% 28%	2533
	21st to end	Night	15% 13% 4 10% 8% 5% 4 4 4 6% 27%	2000
March	1st to 10th	Night	21% 15% 4 10% 5% 4 4 2 3 4 29%	5284
	11th to 20th	Night	11% 13% 4 9% 5% 4 5% 4 7% 8% 28%	4979
	21st to end	Night	17% 11% 4 9% 5% 4 4 2 4 6% 33%	5202
April	1st to 10th	Night	20% 12% 4 7% 5% 4 4 4 4 6% 31%	2000
	11th to 20th	Night	19% 10% 3 7% 5% 3 5% 3 4 5% 35%	1975
	21st to end	Night	21% 10% 3 7% 4 4 4 3 4 6% 32%	1859
May	1st to 10th	Night	21% 10% 3 7% 4 5% 5% 4 6% 7% 27%	3594
	11th to 20th	Night	17% 7% 2 6% 5% 4 5% 4 5% 6% 39%	3575
	21st to end	Night	19% 8% 3 8% 5% 4 5% 4 6% 7% 32%	3926
June	1st to 10th	Night	17% 7% 2 7% 5% 6% 4 4 7% 8% 34%	1600
	11th to 20th	Night	13% 7% 3 5% 4 4 4 4 6% 8% 43%	1600
	21st to end	Night	18% 7% 3 5% 5% 5% 5% 4 5% 8% 36%	1600
July	1st to 10th	Night	14% 6% 2 8% 6% 5% 6% 4 6% 8% 35%	3600
	11th to 20th	Night	13% 5% 2 7% 4 4 4 3 6% 7% 45%	3600
	21st to end	Night	10% 5% 2 5% 4 4 5% 4 6% 8% 48%	3926
August	1st to 10th	Night	12% 6% 3 7% 4 5% 5% 4 6% 8% 40%	2698
	11th to 20th	Night	15% 7% 2 6% 4 3 4 4 6% 7% 41%	2875
	21st to end	Night	15% 5% 2 6% 4 4 4 4 5% 7% 43%	3553
September	1st to 10th	Night	11% 5% 3 6% 4 4 5% 4 6% 7% 47%	2000
	11th to 20th	Night	15% 5% 1 4 3 3 4 3 5% 7% 50%	2000
	21st to end	Night	17% 8% 2 7% 4 4 3 3 4 6% 43%	2274
October	1st to 10th	Night	18% 8% 2 5% 4 4 4 3 4 6% 42%	2400
	11th to 20th	Night	21% 8% 3 8% 6% 5% 5% 4 4 6% 31%	2400
	21st to end	Night	22% 12% 3 9% 4 5% 4 3 5% 6% 28%	2781
November	1st to 10th	Night	18% 13% 3 7% 5% 4 4 3 6% 6% 31%	2693
	11th to 20th	Night	20% 12% 4 8% 5% 6% 4 3 4 5% 28%	2940
	21st to end	Night	21% 16% 4 11% 5% 4 4 3 5% 6% 21%	2940
December	1st to 10th	Night	19% 19% 5% 12% 6% 5% 5% 4 5% 5% 14%	4609
	11th to 20th	Night	23% 16% 5% 10% 5% 4 3 2 4 4 25%	5208
	21st to end	Night	24% 19% 4 11% 4 4 3 2 3 4 22%	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	53% 27% 7% 9% 4	3598
	11th to 20th	Day	51% 27% 8% 9% 6%	3600
	21st to end	Day	50% 29% 7% 9% 5% 1	4172
February	1st to 10th	Day	26% 62% 3 6% 3 1	1800
	11th to 20th	Day	24% 61% 4 7% 4	1762
	21st to end	Day	24% 62% 4 4 5% 1	1628
March	1st to 10th	Day	47% 29% 5% 8% 10% 2	4543
	11th to 20th	Day	39% 30% 12% 11% 7% 1	4980
	21st to end	Day	38% 28% 4 16% 13% 1	5730
April	1st to 10th	Day	23% 62% 3 5% 6% 1	2400
	11th to 20th	Day	22% 62% 2 8% 6% 1	2374
	21st to end	Day	22% 62% 3 7% 6%	2559
May	1st to 10th	Day	42% 31% 5% 15% 6% 1	6357
	11th to 20th	Day	37% 30% 10% 15% 8%	6322
	21st to end	Day	40% 29% 8% 14% 8%	6949
June	1st to 10th	Day	20% 61% 4 10% 5% 1	2800
	11th to 20th	Day	17% 62% 5% 9% 5% 1	2800
	21st to end	Day	18% 61% 5% 10% 5% 1	2800
July	1st to 10th	Day	34% 28% 12% 20% 6%	6290
	11th to 20th	Day	27% 27% 10% 28% 8%	6285
	21st to end	Day	23% 27% 13% 30% 7%	6728
August	1st to 10th	Day	30% 37% 11% 16% 6%	4433
	11th to 20th	Day	30% 37% 9% 19% 4	4199
	21st to end	Day	24% 38% 12% 18% 7%	4312
September	1st to 10th	Day	17% 58% 7% 12% 5%	2400
	11th to 20th	Day	14% 57% 5% 18% 6%	2400
	21st to end	Day	16% 58% 7% 12% 8%	2121
October	1st to 10th	Day	31% 37% 7% 20% 4	3260
	11th to 20th	Day	28% 37% 10% 18% 7%	3240
	21st to end	Day	32% 37% 13% 14% 3	3295
November	1st to 10th	Day	30% 54% 6% 8% 2	1820
	11th to 20th	Day	28% 55% 5% 9% 3	1680
	21st to end	Day	33% 55% 5% 3 4	1680
December	1st to 10th	Day	51% 36% 6% 6% 1	2616
	11th to 20th	Day	46% 32% 6% 10% 6%	2986
	21st to end	Day	51% 27% 5% 13% 3	3960
January	1st to 10th	Night	53% 26% 9% 9% 3	6349
	11th to 20th	Night	49% 27% 10% 10% 3	6360
	21st to end	Night	52% 28% 6% 5% 8%	6769
February	1st to 10th	Night	23% 62% 4 7% 3	2600
	11th to 20th	Night	23% 61% 2 9% 4	2535
	21st to end	Night	22% 62% 4 7% 6%	2000
March	1st to 10th	Night	45% 29% 5% 10% 8% 3	5294
	11th to 20th	Night	38% 31% 12% 11% 6% 2	4980
	21st to end	Night	39% 30% 5% 16% 8% 2	5202
April	1st to 10th	Night	22% 62% 3 8% 5% 1	2000
	11th to 20th	Night	19% 62% 3 9% 7% 1	1975
	21st to end	Night	20% 62% 3 7% 7% 1	1859
May	1st to 10th	Night	42% 31% 7% 15% 5% 1	3600
	11th to 20th	Night	33% 31% 11% 14% 10% 1	3576
	21st to end	Night	41% 30% 8% 12% 8%	3927
June	1st to 10th	Night	17% 62% 4 12% 5% 1	1600
	11th to 20th	Night	15% 63% 4 10% 8% 1	1600
	21st to end	Night	19% 61% 4 10% 7% 1	1600
July	1st to 10th	Night	37% 28% 12% 15% 8%	3560
	11th to 20th	Night	28% 28% 10% 26% 9%	3552
	21st to end	Night	24% 28% 9% 29% 10%	3809
August	1st to 10th	Night	27% 38% 10% 18% 8%	2688
	11th to 20th	Night	30% 38% 9% 19% 4	2902
	21st to end	Night	26% 37% 10% 17% 8% 2	3553
September	1st to 10th	Night	14% 59% 7% 15% 6%	2000
	11th to 20th	Night	13% 58% 5% 18% 5% 1	2000
	21st to end	Night	16% 57% 5% 13% 8%	2274
October	1st to 10th	Night	22% 36% 10% 22% 9%	3920
	11th to 20th	Night	26% 37% 12% 18% 7%	3899
	21st to end	Night	32% 37% 12% 13% 6%	4493
November	1st to 10th	Night	28% 54% 7% 8% 3	2693
	11th to 20th	Night	27% 55% 5% 10% 3	2940
	21st to end	Night	30% 55% 6% 6% 3	2940
December	1st to 10th	Night	47% 37% 9% 7% 1	4609
	11th to 20th	Night	46% 31% 4 10% 9%	5208
	21st to end	Night	52% 26% 3 10% 9%	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	21% 24% 36% 17% 3	200
	11th to 20th	Day	25% 17% 39% 16% 4 1	200
	21st to end	Day	22% 22% 34% 19% 4	267
February	1st to 10th	Day	30% 26% 30% 11% 2	300
	11th to 20th	Day	29% 27% 36% 7% 1	300
	21st to end	Day	32% 22% 32% 13% 2	392
March	1st to 10th	Day	28% 19% 35% 14% 4	500
	11th to 20th	Day	27% 21% 34% 14% 3 1	500
	21st to end	Day	31% 21% 29% 14% 5% 1	550
April	1st to 10th	Day	34% 23% 24% 15% 5% 1	500
	11th to 20th	Day	35% 19% 22% 13% 9% 2	492
	21st to end	Day	30% 21% 31% 12% 5% 1	500
May	1st to 10th	Day	28% 16% 32% 15% 6% 3	503
	11th to 20th	Day	20% 17% 32% 21% 8% 2	527
	21st to end	Day	23% 17% 30% 20% 9% 2	573
June	1st to 10th	Day	25% 15% 31% 21% 8% 1	530
	11th to 20th	Day	18% 15% 32% 23% 9% 3	530
	21st to end	Day	21% 14% 32% 22% 9% 2	530
July	1st to 10th	Day	12% 8% 33% 34% 11% 2	525
	11th to 20th	Day	14% 10% 34% 26% 13% 3	524
	21st to end	Day	13% 11% 34% 28% 12% 3	576
August	1st to 10th	Day	13% 8% 28% 32% 14% 4	526
	11th to 20th	Day	17% 7% 24% 31% 14% 7%	519
	21st to end	Day	17% 11% 29% 25% 14% 5%	583
September	1st to 10th	Day	18% 11% 30% 21% 14% 6%	530
	11th to 20th	Day	12% 10% 23% 25% 20% 10%	530
	21st to end	Day	20% 13% 28% 22% 12% 5%	530
October	1st to 10th	Day	24% 15% 25% 22% 12% 3	530
	11th to 20th	Day	28% 20% 30% 15% 6% 1	530
	21st to end	Day	30% 18% 28% 19% 4	503
November	1st to 10th	Day	29% 17% 31% 17% 6% 1	394
	11th to 20th	Day	26% 22% 33% 14% 4	220
	21st to end	Day	31% 24% 32% 10% 2 1	220
December	1st to 10th	Day	32% 13% 38% 14% 3	204
	11th to 20th	Day	31% 25% 34% 9% 2 1	200
	21st to end	Day	31% 18% 37% 11% 3	220
January	1st to 10th	Night	27% 14% 36% 19% 3	800
	11th to 20th	Night	27% 19% 28% 21% 5%	800
	21st to end	Night	18% 16% 38% 22% 5%	880
February	1st to 10th	Night	20% 19% 35% 23% 3	800
	11th to 20th	Night	22% 19% 37% 18% 3	783
	21st to end	Night	23% 20% 29% 23% 5%	660
March	1st to 10th	Night	26% 16% 33% 22% 4	800
	11th to 20th	Night	23% 19% 34% 19% 6%	800
	21st to end	Night	24% 18% 33% 19% 7%	880
April	1st to 10th	Night	28% 16% 30% 22% 5%	800
	11th to 20th	Night	25% 18% 28% 21% 7% 1	791
	21st to end	Night	27% 16% 28% 23% 6%	659
May	1st to 10th	Night	25% 8% 29% 28% 9% 1	400
	11th to 20th	Night	24% 9% 28% 30% 8%	394
	21st to end	Night	16% 9% 36% 28% 11%	433
June	1st to 10th	Night	19% 9% 30% 36% 7%	400
	11th to 20th	Night	16% 7% 30% 33% 14% 1	400
	21st to end	Night	19% 7% 28% 33% 13%	400
July	1st to 10th	Night	10% 4 29% 42% 15% 1	390
	11th to 20th	Night	12% 5% 22% 44% 16% 1	388
	21st to end	Night	11% 6% 25% 44% 13% 1	438
August	1st to 10th	Night	11% 5% 22% 39% 22%	458
	11th to 20th	Night	12% 5% 20% 37% 24% 3	594
	21st to end	Night	14% 7% 25% 35% 17% 2	860
September	1st to 10th	Night	13% 8% 28% 31% 19% 1	800
	11th to 20th	Night	16% 7% 23% 28% 23% 3	800
	21st to end	Night	20% 9% 25% 26% 18% 2	800
October	1st to 10th	Night	22% 12% 26% 24% 16% 1	800
	11th to 20th	Night	26% 14% 29% 23% 7% 1	800
	21st to end	Night	26% 16% 30% 24% 4	880
November	1st to 10th	Night	26% 16% 26% 25% 6% 1	820
	11th to 20th	Night	26% 17% 32% 16% 9%	840
	21st to end	Night	31% 18% 26% 21% 5%	840
December	1st to 10th	Night	29% 18% 31% 19% 4	809
	11th to 20th	Night	29% 17% 31% 19% 4 1	800
	21st to end	Night	34% 16% 29% 17% 4	880

Page generated at 2025-11-30 01:00:54. Version ac07

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