Tamiment
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tamiment clear sky chart from 2005-11-06 to 2024-11-28.

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% 8% 3 6% 5% 4 4 4 5% 7% 37%	101594
	Night	17% 8% 2 6% 4 4 4 3 5% 6% 40%	97957
Transparency	Day	25% 46% 7% 13% 8% 1	105114
	Night	24% 47% 7% 13% 8% 1	102526
Seeing	Day	24% 16% 29% 19% 9% 3	14968
	Night	22% 15% 29% 25% 9% 1	24182

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% 11% 3 6% 4 4 4 3 4 5% 41%	2517
	11th to 20th	Day	15% 11% 5% 10% 6% 5% 4 3 4 5% 31%	2520
	21st to end	Day	21% 11% 4 7% 5% 5% 4 3 4 5% 31%	3092
February	1st to 10th	Day	16% 9% 3 8% 5% 5% 5% 3 6% 6% 34%	1710
	11th to 20th	Day	13% 8% 4 7% 4 5% 5% 4 5% 5% 39%	1792
	21st to end	Day	19% 10% 3 7% 5% 3 4 3 5% 6% 35%	1570
March	1st to 10th	Day	25% 11% 3 6% 5% 3 3 3 4 5% 33%	3116
	11th to 20th	Day	9% 8% 3 8% 5% 4 5% 4 6% 8% 40%	3443
	21st to end	Day	20% 9% 2 5% 4 3 3 3 4 5% 41%	4063
April	1st to 10th	Day	17% 9% 3 7% 4 4 4 4 5% 6% 37%	2280
	11th to 20th	Day	18% 7% 3 6% 4 5% 4 3 6% 6% 39%	2254
	21st to end	Day	18% 6% 2 6% 4 5% 5% 5% 6% 5% 38%	2280
May	1st to 10th	Day	27% 8% 2 6% 4 4 4 3 5% 6% 31%	4185
	11th to 20th	Day	23% 9% 3 8% 6% 5% 4 4 5% 6% 28%	4398
	21st to end	Day	13% 5% 2 5% 4 4 5% 4 6% 10% 42%	4837
June	1st to 10th	Day	15% 5% 2 7% 5% 5% 5% 5% 6% 9% 36%	2660
	11th to 20th	Day	16% 6% 2 6% 5% 5% 5% 4 7% 9% 34%	2660
	21st to end	Day	12% 6% 2 7% 5% 5% 5% 5% 6% 9% 38%	2660
July	1st to 10th	Day	9% 6% 3 7% 6% 5% 6% 5% 6% 10% 36%	4440
	11th to 20th	Day	11% 6% 2 6% 5% 5% 5% 5% 7% 10% 38%	4440
	21st to end	Day	15% 8% 3 7% 5% 5% 5% 4 6% 7% 33%	4814
August	1st to 10th	Day	22% 5% 3 6% 5% 5% 5% 4 6% 8% 31%	4143
	11th to 20th	Day	14% 6% 2 6% 4 4 5% 4 6% 8% 39%	3762
	21st to end	Day	15% 5% 2 5% 3 3 4 3 6% 9% 45%	4180
September	1st to 10th	Day	16% 6% 2 5% 3 4 4 4 5% 8% 41%	2280
	11th to 20th	Day	14% 4 2 5% 3 4 4 3 4 7% 50%	2242
	21st to end	Day	19% 7% 3 7% 4 4 4 4 5% 6% 39%	2090
October	1st to 10th	Day	20% 7% 2 6% 4 3 4 3 4 7% 39%	1910
	11th to 20th	Day	15% 6% 3 6% 4 4 4 3 5% 7% 44%	1900
	21st to end	Day	21% 6% 2 6% 3 4 4 3 6% 6% 38%	1986
November	1st to 10th	Day	14% 6% 2 5% 3 2 2 3 4 6% 52%	1761
	11th to 20th	Day	19% 7% 2 5% 3 3 4 3 6% 6% 44%	1800
	21st to end	Day	17% 8% 2 5% 4 5% 5% 4 6% 6% 37%	1611
December	1st to 10th	Day	18% 10% 4 7% 5% 4 5% 3 4 5% 34%	1520
	11th to 20th	Day	21% 8% 2 6% 4 4 4 3 6% 6% 35%	1906
	21st to end	Day	19% 13% 5% 10% 6% 5% 5% 3 5% 6% 24%	2772
January	1st to 10th	Night	16% 7% 3 6% 5% 4 4 4 5% 6% 40%	4429
	11th to 20th	Night	15% 9% 4 10% 5% 5% 4 3 5% 5% 35%	4440
	21st to end	Night	23% 11% 2 7% 5% 3 4 3 5% 5% 32%	4560
February	1st to 10th	Night	16% 9% 3 6% 5% 4 4 3 5% 6% 40%	2470
	11th to 20th	Night	15% 8% 2 6% 5% 5% 5% 4 6% 6% 39%	2274
	21st to end	Night	18% 8% 3 6% 5% 4 4 3 5% 6% 39%	1884
March	1st to 10th	Night	22% 11% 3 6% 3 3 3 3 4 5% 35%	3724
	11th to 20th	Night	11% 8% 2 6% 4 4 5% 4 6% 7% 44%	3511
	21st to end	Night	16% 9% 3 7% 4 4 3 3 4 5% 42%	3568
April	1st to 10th	Night	17% 10% 2 7% 6% 4 4 4 5% 7% 34%	1900
	11th to 20th	Night	19% 7% 2 6% 4 4 4 3 6% 7% 39%	1875
	21st to end	Night	19% 7% 3 5% 4 2 4 4 5% 6% 41%	1900
May	1st to 10th	Night	27% 9% 2 7% 4 4 4 3 5% 6% 30%	2782
	11th to 20th	Night	25% 9% 3 6% 5% 4 4 3 4 6% 32%	2495
	21st to end	Night	13% 6% 2 6% 5% 4 5% 4 6% 9% 40%	2738
June	1st to 10th	Night	17% 6% 2 5% 4 4 3 3 5% 8% 43%	1520
	11th to 20th	Night	14% 6% 1 5% 5% 3 5% 5% 6% 8% 42%	1520
	21st to end	Night	13% 4 2 5% 4 4 4 3 7% 9% 45%	1520
July	1st to 10th	Night	10% 5% 2 7% 5% 5% 6% 5% 6% 9% 41%	2520
	11th to 20th	Night	12% 6% 2 6% 4 4 5% 5% 8% 10% 39%	2520
	21st to end	Night	18% 6% 2 5% 3 4 5% 4 6% 7% 39%	2739
August	1st to 10th	Night	22% 6% 2 6% 4 4 5% 3 6% 8% 34%	2783
	11th to 20th	Night	16% 7% 3 6% 4 4 5% 3 5% 6% 42%	3033
	21st to end	Night	14% 4 2 4 3 3 3 3 5% 8% 51%	3476
September	1st to 10th	Night	16% 5% 2 5% 3 4 4 3 4 8% 46%	1900
	11th to 20th	Night	13% 6% 2 4 3 3 3 3 4 7% 52%	1938
	21st to end	Night	18% 6% 3 6% 4 3 3 3 5% 5% 44%	2090
October	1st to 10th	Night	23% 6% 2 5% 3 4 3 2 4 6% 43%	2266
	11th to 20th	Night	17% 6% 2 5% 3 3 3 3 4 5% 48%	2280
	21st to end	Night	22% 7% 2 4 3 3 3 2 5% 7% 42%	2612
November	1st to 10th	Night	13% 6% 2 4 3 3 4 4 5% 5% 50%	2537
	11th to 20th	Night	19% 6% 3 5% 3 3 3 3 5% 5% 45%	2600
	21st to end	Night	14% 7% 2 6% 4 5% 4 3 6% 7% 43%	2721
December	1st to 10th	Night	19% 7% 3 7% 4 5% 5% 3 6% 7% 34%	2660
	11th to 20th	Night	18% 9% 2 6% 4 5% 5% 4 5% 6% 36%	3288
	21st to end	Night	21% 12% 4 7% 4 4 4 3 5% 5% 32%	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	29% 37% 9% 18% 5% 2	2518
	11th to 20th	Day	36% 37% 6% 13% 6% 1	2520
	21st to end	Day	37% 40% 7% 11% 4 1	3092
February	1st to 10th	Day	18% 66% 6% 7% 3	1710
	11th to 20th	Day	15% 64% 3 9% 8% 1	1801
	21st to end	Day	18% 65% 4 8% 4 1	1570
March	1st to 10th	Day	37% 41% 5% 13% 4 1	3119
	11th to 20th	Day	20% 42% 11% 20% 5% 1	3443
	21st to end	Day	27% 40% 6% 7% 16% 4	4063
April	1st to 10th	Day	20% 65% 3 6% 5% 1	2280
	11th to 20th	Day	16% 65% 4 8% 7%	2254
	21st to end	Day	17% 66% 3 8% 5% 1	2280
May	1st to 10th	Day	35% 42% 8% 10% 5%	4199
	11th to 20th	Day	39% 41% 8% 10% 2	4402
	21st to end	Day	20% 42% 7% 18% 11% 2	4837
June	1st to 10th	Day	17% 66% 4 8% 6%	2660
	11th to 20th	Day	14% 66% 5% 9% 6%	2660
	21st to end	Day	15% 64% 4 10% 7%	2660
July	1st to 10th	Day	27% 39% 9% 14% 10% 1	4370
	11th to 20th	Day	28% 37% 12% 15% 8%	4365
	21st to end	Day	34% 35% 7% 12% 10% 1	4661
August	1st to 10th	Day	36% 37% 9% 13% 4	4129
	11th to 20th	Day	26% 37% 10% 21% 6%	3799
	21st to end	Day	20% 37% 8% 25% 9% 1	4180
September	1st to 10th	Day	15% 61% 6% 11% 7%	2280
	11th to 20th	Day	16% 60% 4 9% 11% 1	2242
	21st to end	Day	20% 60% 5% 8% 6% 1	2090
October	1st to 10th	Day	27% 37% 3 11% 18% 3	3170
	11th to 20th	Day	18% 36% 4 20% 18% 4	3140
	21st to end	Day	12% 37% 13% 20% 16% 2	3250
November	1st to 10th	Day	18% 56% 6% 11% 7% 2	1761
	11th to 20th	Day	14% 57% 4 12% 11% 2	1800
	21st to end	Day	18% 59% 7% 12% 3 1	1611
December	1st to 10th	Day	23% 60% 6% 4 6% 1	1520
	11th to 20th	Day	26% 49% 7% 13% 4	1906
	21st to end	Day	43% 38% 4 11% 3	2772
January	1st to 10th	Night	28% 37% 9% 18% 5% 3	4429
	11th to 20th	Night	32% 39% 8% 14% 7% 1	4440
	21st to end	Night	37% 41% 6% 11% 5% 1	4560
February	1st to 10th	Night	15% 65% 7% 9% 3 1	2470
	11th to 20th	Night	16% 63% 4 9% 7% 1	2276
	21st to end	Night	16% 65% 5% 8% 5% 2	1884
March	1st to 10th	Night	36% 42% 4 11% 6% 1	3734
	11th to 20th	Night	18% 43% 10% 19% 9% 1	3512
	21st to end	Night	28% 40% 3 10% 14% 4	3568
April	1st to 10th	Night	19% 65% 3 8% 5%	1900
	11th to 20th	Night	14% 66% 4 9% 7%	1875
	21st to end	Night	15% 65% 4 9% 6% 1	1900
May	1st to 10th	Night	36% 41% 7% 14% 2	2788
	11th to 20th	Night	38% 42% 10% 8% 3	2496
	21st to end	Night	26% 43% 8% 15% 8% 1	2739
June	1st to 10th	Night	14% 65% 3 10% 8%	1520
	11th to 20th	Night	13% 66% 6% 9% 6%	1520
	21st to end	Night	13% 65% 4 11% 7%	1520
July	1st to 10th	Night	26% 39% 11% 12% 12% 1	2480
	11th to 20th	Night	26% 37% 11% 18% 8%	2472
	21st to end	Night	31% 36% 9% 10% 13% 1	2651
August	1st to 10th	Night	36% 38% 11% 11% 3	2773
	11th to 20th	Night	27% 37% 9% 20% 6%	3062
	21st to end	Night	18% 37% 7% 27% 11%	3476
September	1st to 10th	Night	14% 60% 6% 12% 8% 1	1900
	11th to 20th	Night	13% 60% 4 9% 12% 2	1938
	21st to end	Night	20% 59% 4 9% 7% 1	2090
October	1st to 10th	Night	27% 36% 7% 15% 13% 1	3786
	11th to 20th	Night	15% 36% 6% 19% 21% 4	3779
	21st to end	Night	16% 36% 10% 22% 14% 1	4298
November	1st to 10th	Night	17% 57% 6% 11% 8% 1	2537
	11th to 20th	Night	16% 57% 4 10% 11% 1	2600
	21st to end	Night	17% 58% 7% 12% 5% 1	2721
December	1st to 10th	Night	21% 60% 5% 9% 4	2660
	11th to 20th	Night	26% 51% 5% 9% 8% 1	3288
	21st to end	Night	36% 39% 8% 14% 4	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	34% 24% 26% 13% 3	180
	11th to 20th	Day	41% 24% 27% 7% 2	180
	21st to end	Day	26% 31% 29% 9% 4 1	288
February	1st to 10th	Day	31% 30% 29% 8% 2	270
	11th to 20th	Day	35% 26% 29% 9% 1	400
	21st to end	Day	34% 24% 27% 12% 2	382
March	1st to 10th	Day	32% 20% 30% 15% 3	460
	11th to 20th	Day	30% 25% 28% 13% 3 1	460
	21st to end	Day	33% 23% 28% 11% 5% 1	506
April	1st to 10th	Day	31% 24% 27% 14% 5%	460
	11th to 20th	Day	28% 24% 25% 14% 7% 2	452
	21st to end	Day	27% 20% 33% 13% 5% 2	460
May	1st to 10th	Day	34% 19% 27% 12% 7% 2	463
	11th to 20th	Day	23% 19% 30% 18% 8% 2	487
	21st to end	Day	18% 12% 30% 23% 15% 2	529
June	1st to 10th	Day	20% 14% 30% 22% 11% 2	490
	11th to 20th	Day	19% 13% 29% 26% 12% 1	490
	21st to end	Day	16% 14% 33% 25% 10% 2	490
July	1st to 10th	Day	14% 8% 28% 26% 18% 5%	485
	11th to 20th	Day	12% 6% 28% 31% 20% 3	484
	21st to end	Day	15% 9% 33% 27% 12% 3	532
August	1st to 10th	Day	14% 6% 29% 31% 14% 6%	486
	11th to 20th	Day	15% 7% 23% 33% 16% 6%	479
	21st to end	Day	14% 10% 30% 23% 15% 8%	539
September	1st to 10th	Day	21% 11% 24% 23% 14% 6%	490
	11th to 20th	Day	13% 9% 29% 22% 16% 10%	490
	21st to end	Day	25% 10% 28% 22% 11% 4	490
October	1st to 10th	Day	27% 11% 24% 20% 13% 5%	490
	11th to 20th	Day	20% 16% 31% 22% 9% 2	490
	21st to end	Day	27% 15% 30% 18% 7% 1	484
November	1st to 10th	Day	22% 18% 28% 21% 10% 2	395
	11th to 20th	Day	28% 19% 30% 18% 5% 1	400
	21st to end	Day	29% 21% 31% 16% 3	229
December	1st to 10th	Day	29% 27% 29% 9% 6%	180
	11th to 20th	Day	37% 23% 27% 11% 3	180
	21st to end	Day	31% 20% 33% 12% 4 1	198
January	1st to 10th	Night	24% 22% 35% 16% 3	760
	11th to 20th	Night	28% 20% 30% 20% 2	760
	21st to end	Night	20% 24% 35% 19% 2	836
February	1st to 10th	Night	25% 19% 35% 19% 2	760
	11th to 20th	Night	26% 25% 37% 12%	743
	21st to end	Night	30% 20% 31% 17% 2	628
March	1st to 10th	Night	26% 21% 32% 18% 3	760
	11th to 20th	Night	25% 22% 30% 18% 4	760
	21st to end	Night	22% 24% 33% 15% 5%	836
April	1st to 10th	Night	24% 22% 31% 20% 3	760
	11th to 20th	Night	24% 18% 32% 21% 7%	751
	21st to end	Night	24% 17% 30% 24% 5%	760
May	1st to 10th	Night	27% 13% 29% 25% 6%	544
	11th to 20th	Night	20% 10% 34% 28% 8% 1	374
	21st to end	Night	16% 7% 26% 39% 13%	411
June	1st to 10th	Night	18% 8% 22% 37% 15%	380
	11th to 20th	Night	16% 5% 32% 36% 12%	380
	21st to end	Night	14% 5% 25% 43% 12% 1	380
July	1st to 10th	Night	15% 4 21% 41% 17% 2	370
	11th to 20th	Night	11% 4 21% 45% 17% 2	368
	21st to end	Night	13% 5% 20% 43% 17% 1	416
August	1st to 10th	Night	14% 2 20% 39% 24% 2	538
	11th to 20th	Night	16% 5% 17% 36% 25% 1	710
	21st to end	Night	16% 5% 20% 34% 23% 2	836
September	1st to 10th	Night	18% 5% 25% 32% 18% 2	760
	11th to 20th	Night	17% 4 24% 30% 20% 6%	760
	21st to end	Night	21% 7% 24% 29% 17% 2	760
October	1st to 10th	Night	26% 9% 21% 26% 16% 1	760
	11th to 20th	Night	20% 13% 28% 31% 8%	760
	21st to end	Night	27% 13% 29% 22% 8%	836
November	1st to 10th	Night	18% 18% 29% 26% 9% 1	780
	11th to 20th	Night	27% 17% 26% 23% 6% 1	800
	21st to end	Night	21% 21% 30% 23% 5%	789
December	1st to 10th	Night	26% 19% 32% 19% 5%	760
	11th to 20th	Night	25% 19% 31% 22% 3	760
	21st to end	Night	26% 18% 33% 20% 2	836

Page generated at 2024-11-25 00:22:18. Version ac07

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