Tomstown
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tomstown clear sky chart from 2005-11-06 to 2024-11-05.

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	14% 7% 3 7% 5% 4 5% 4 6% 8% 38%	101273
	Night	14% 7% 3 7% 5% 4 4 4 6% 7% 39%	97705
Transparency	Day	23% 48% 7% 14% 8% 1	104912
	Night	23% 48% 6% 13% 8% 1	102205
Seeing	Day	22% 17% 27% 20% 10% 4	14895
	Night	19% 16% 27% 26% 11% 1	24367

By Month

Percentage Cloud Cover SE (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	15% 8% 3 9% 5% 5% 4 3 4 6% 37%	2558
	11th to 20th	Day	13% 13% 5% 10% 5% 6% 5% 4 5% 5% 29%	2840
	21st to end	Day	16% 13% 4 9% 5% 4 4 4 5% 6% 30%	3124
February	1st to 10th	Day	14% 10% 3 8% 6% 5% 5% 4 5% 6% 34%	1710
	11th to 20th	Day	14% 9% 2 8% 7% 5% 4 3 5% 6% 36%	1679
	21st to end	Day	18% 11% 3 7% 4 4 4 2 5% 5% 36%	1570
March	1st to 10th	Day	21% 8% 2 6% 5% 5% 5% 3 6% 6% 33%	3400
	11th to 20th	Day	10% 8% 3 7% 5% 5% 5% 3 5% 7% 43%	3480
	21st to end	Day	18% 9% 2 7% 4 3 4 3 5% 6% 39%	3864
April	1st to 10th	Day	14% 9% 3 7% 5% 5% 5% 4 6% 7% 35%	2280
	11th to 20th	Day	14% 7% 3 6% 5% 4 3 4 5% 6% 42%	2254
	21st to end	Day	18% 7% 2 7% 4 4 5% 4 5% 6% 39%	2294
May	1st to 10th	Day	26% 7% 2 7% 4 4 4 4 5% 7% 29%	4082
	11th to 20th	Day	23% 8% 3 7% 5% 5% 5% 4 6% 7% 28%	4297
	21st to end	Day	10% 6% 2 6% 4 4 5% 5% 7% 9% 41%	4823
June	1st to 10th	Day	12% 6% 2 5% 5% 5% 5% 4 7% 10% 39%	2660
	11th to 20th	Day	12% 6% 3 6% 5% 5% 5% 5% 6% 10% 38%	2660
	21st to end	Day	10% 5% 2 5% 4 5% 5% 4 7% 9% 43%	2660
July	1st to 10th	Day	6% 4 2 6% 5% 5% 6% 6% 8% 11% 41%	4440
	11th to 20th	Day	7% 5% 2 6% 4 5% 6% 5% 8% 11% 41%	4328
	21st to end	Day	10% 8% 3 8% 5% 5% 5% 4 7% 9% 36%	4466
August	1st to 10th	Day	14% 8% 2 7% 5% 5% 5% 5% 6% 9% 33%	4104
	11th to 20th	Day	10% 6% 2 7% 5% 5% 5% 5% 7% 9% 39%	3930
	21st to end	Day	10% 6% 2 6% 4 4 5% 4 6% 7% 46%	4180
September	1st to 10th	Day	16% 5% 2 5% 4 4 4 3 5% 5% 46%	2280
	11th to 20th	Day	12% 5% 2 5% 4 4 4 3 6% 8% 47%	2280
	21st to end	Day	19% 8% 3 6% 4 4 4 3 6% 6% 37%	1986
October	1st to 10th	Day	15% 5% 2 6% 5% 4 5% 3 5% 6% 45%	1900
	11th to 20th	Day	15% 6% 2 5% 4 4 3 4 5% 7% 45%	1900
	21st to end	Day	14% 7% 2 6% 4 3 3 4 5% 7% 45%	2090
November	1st to 10th	Day	11% 6% 4 5% 3 3 3 3 6% 7% 48%	1799
	11th to 20th	Day	15% 6% 2 6% 5% 4 4 3 6% 6% 43%	1633
	21st to end	Day	15% 8% 2 6% 5% 4 4 4 5% 7% 39%	1520
December	1st to 10th	Day	18% 8% 3 7% 5% 4 4 5% 7% 8% 30%	1520
	11th to 20th	Day	15% 10% 3 8% 5% 4 4 4 5% 7% 35%	1910
	21st to end	Day	17% 9% 3 9% 5% 6% 6% 5% 6% 7% 28%	2772
January	1st to 10th	Night	12% 9% 3 9% 6% 5% 4 4 6% 7% 35%	4383
	11th to 20th	Night	16% 9% 3 8% 5% 4 4 4 4 5% 37%	4120
	21st to end	Night	20% 11% 4 8% 5% 4 4 3 5% 6% 31%	4532
February	1st to 10th	Night	15% 8% 3 8% 5% 4 4 4 6% 7% 37%	2470
	11th to 20th	Night	16% 9% 3 7% 4 5% 5% 4 5% 7% 35%	2385
	21st to end	Night	16% 11% 3 7% 4 4 5% 3 6% 6% 35%	1884
March	1st to 10th	Night	20% 9% 2 6% 4 4 4 3 5% 5% 37%	3449
	11th to 20th	Night	11% 6% 3 7% 5% 3 4 4 5% 7% 45%	3480
	21st to end	Night	13% 9% 3 7% 4 4 3 3 4 5% 46%	3768
April	1st to 10th	Night	15% 8% 3 8% 7% 5% 4 4 6% 6% 34%	1900
	11th to 20th	Night	12% 7% 2 7% 4 4 4 3 7% 8% 42%	1875
	21st to end	Night	15% 6% 3 5% 4 4 5% 4 7% 6% 41%	1900
May	1st to 10th	Night	25% 8% 3 7% 4 4 3 3 5% 7% 30%	2814
	11th to 20th	Night	22% 10% 4 7% 5% 4 4 3 5% 6% 30%	2593
	21st to end	Night	11% 5% 2 7% 4 5% 5% 4 8% 9% 39%	2732
June	1st to 10th	Night	11% 6% 1 5% 4 3 4 5% 6% 8% 46%	1520
	11th to 20th	Night	12% 5% 3 7% 4 5% 5% 4 7% 9% 39%	1520
	21st to end	Night	8% 5% 2 6% 5% 5% 5% 4 6% 11% 44%	1520
July	1st to 10th	Night	7% 4 2 6% 4 5% 6% 5% 7% 11% 42%	2520
	11th to 20th	Night	6% 5% 2 7% 6% 5% 6% 5% 8% 11% 40%	2614
	21st to end	Night	12% 7% 3 6% 5% 5% 5% 4 6% 9% 40%	3087
August	1st to 10th	Night	13% 8% 3 8% 5% 5% 5% 4 6% 9% 34%	2825
	11th to 20th	Night	10% 6% 3 8% 5% 5% 5% 5% 6% 8% 41%	2866
	21st to end	Night	11% 6% 2 6% 5% 4 4 3 5% 9% 46%	3476
September	1st to 10th	Night	14% 5% 2 5% 4 4 3 4 5% 6% 47%	1900
	11th to 20th	Night	10% 6% 2 6% 3 3 4 2 5% 7% 52%	1900
	21st to end	Night	18% 7% 3 5% 3 4 4 3 5% 6% 41%	2190
October	1st to 10th	Night	17% 6% 3 6% 4 4 3 3 5% 6% 44%	2280
	11th to 20th	Night	12% 5% 2 5% 4 4 4 3 4 5% 49%	2280
	21st to end	Night	16% 5% 2 5% 4 4 4 4 5% 7% 45%	2508
November	1st to 10th	Night	9% 6% 2 5% 4 4 4 4 5% 6% 52%	2379
	11th to 20th	Night	13% 7% 2 5% 5% 4 4 3 5% 7% 43%	2546
	21st to end	Night	13% 6% 2 7% 5% 5% 4 4 5% 8% 40%	2660
December	1st to 10th	Night	15% 9% 3 8% 5% 5% 4 4 5% 7% 34%	2660
	11th to 20th	Night	17% 7% 3 6% 5% 5% 5% 4 6% 6% 36%	3285
	21st to end	Night	16% 9% 2 7% 5% 5% 6% 5% 7% 8% 29%	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	30% 37% 8% 15% 6% 3	2559
	11th to 20th	Day	37% 39% 5% 10% 8% 2	2840
	21st to end	Day	35% 41% 5% 14% 3 1	3124
February	1st to 10th	Day	19% 65% 6% 6% 3	1710
	11th to 20th	Day	18% 64% 3 8% 6% 1	1688
	21st to end	Day	18% 65% 4 8% 5% 1	1570
March	1st to 10th	Day	36% 42% 5% 12% 5% 1	3400
	11th to 20th	Day	21% 42% 6% 20% 9% 1	3480
	21st to end	Day	27% 41% 7% 13% 11% 2	3864
April	1st to 10th	Day	19% 66% 4 6% 5% 1	2280
	11th to 20th	Day	14% 67% 5% 9% 5% 1	2254
	21st to end	Day	17% 65% 4 9% 6%	2294
May	1st to 10th	Day	36% 42% 5% 12% 5%	4120
	11th to 20th	Day	34% 43% 9% 12% 2	4301
	21st to end	Day	20% 43% 8% 15% 12% 1	4837
June	1st to 10th	Day	15% 66% 4 9% 5%	2660
	11th to 20th	Day	14% 67% 4 8% 6%	2660
	21st to end	Day	14% 64% 5% 11% 6%	2660
July	1st to 10th	Day	22% 41% 11% 17% 6% 3	4370
	11th to 20th	Day	22% 40% 12% 18% 8%	4253
	21st to end	Day	28% 38% 7% 15% 12% 1	4324
August	1st to 10th	Day	31% 40% 9% 16% 4	4091
	11th to 20th	Day	23% 41% 8% 21% 7%	3969
	21st to end	Day	20% 39% 8% 19% 14%	4180
September	1st to 10th	Day	15% 61% 6% 9% 8% 1	2280
	11th to 20th	Day	15% 60% 5% 11% 8% 1	2280
	21st to end	Day	20% 61% 4 9% 6% 1	1986
October	1st to 10th	Day	22% 37% 4 14% 18% 4	3160
	11th to 20th	Day	14% 38% 8% 19% 12% 8%	3140
	21st to end	Day	12% 37% 9% 21% 20% 2	3428
November	1st to 10th	Day	18% 58% 6% 8% 7% 3	1799
	11th to 20th	Day	13% 60% 4 11% 11% 1	1633
	21st to end	Day	16% 60% 7% 13% 4 1	1520
December	1st to 10th	Day	22% 61% 5% 7% 4 1	1520
	11th to 20th	Day	27% 48% 5% 16% 4 1	1906
	21st to end	Day	34% 40% 10% 10% 6%	2772
January	1st to 10th	Night	31% 37% 7% 15% 8% 2	4383
	11th to 20th	Night	31% 38% 8% 15% 7% 2	4120
	21st to end	Night	37% 40% 4 14% 4 1	4532
February	1st to 10th	Night	16% 66% 6% 9% 3	2470
	11th to 20th	Night	17% 64% 3 8% 8% 1	2387
	21st to end	Night	16% 65% 4 7% 5% 2	1884
March	1st to 10th	Night	34% 42% 4 16% 4 1	3449
	11th to 20th	Night	20% 42% 5% 24% 9% 1	3480
	21st to end	Night	23% 41% 5% 14% 15% 2	3768
April	1st to 10th	Night	17% 66% 3 8% 5% 1	1900
	11th to 20th	Night	14% 67% 5% 9% 5% 1	1875
	21st to end	Night	15% 65% 4 9% 6% 1	1900
May	1st to 10th	Night	37% 41% 4 10% 7% 1	2841
	11th to 20th	Night	35% 44% 6% 12% 3	2594
	21st to end	Night	23% 44% 10% 17% 5% 1	2739
June	1st to 10th	Night	14% 66% 4 9% 7%	1520
	11th to 20th	Night	14% 66% 4 10% 6%	1520
	21st to end	Night	13% 65% 6% 10% 6%	1520
July	1st to 10th	Night	21% 41% 14% 11% 9% 4	2480
	11th to 20th	Night	23% 40% 11% 16% 10%	2566
	21st to end	Night	30% 38% 7% 12% 12% 1	2988
August	1st to 10th	Night	32% 40% 10% 14% 3	2814
	11th to 20th	Night	23% 40% 8% 20% 8%	2893
	21st to end	Night	20% 39% 8% 22% 11%	3476
September	1st to 10th	Night	14% 61% 6% 10% 7% 1	1900
	11th to 20th	Night	14% 60% 5% 11% 9% 1	1900
	21st to end	Night	20% 61% 4 9% 6%	2190
October	1st to 10th	Night	23% 39% 7% 15% 16% 1	3800
	11th to 20th	Night	13% 38% 6% 17% 19% 7%	3779
	21st to end	Night	12% 37% 8% 21% 18% 4	4120
November	1st to 10th	Night	16% 58% 6% 11% 6% 2	2379
	11th to 20th	Night	16% 59% 3 10% 11% 1	2546
	21st to end	Night	16% 60% 6% 11% 6% 1	2660
December	1st to 10th	Night	22% 61% 6% 7% 5%	2660
	11th to 20th	Night	24% 49% 5% 12% 9% 1	3288
	21st to end	Night	32% 41% 9% 11% 6%	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	33% 28% 28% 8% 2 2	193
	11th to 20th	Day	38% 27% 29% 6% 1	270
	21st to end	Day	27% 34% 29% 8% 2	297
February	1st to 10th	Day	31% 31% 29% 6% 2	270
	11th to 20th	Day	41% 28% 28% 3 1	286
	21st to end	Day	34% 27% 24% 14% 1	382
March	1st to 10th	Day	31% 24% 27% 14% 4	460
	11th to 20th	Day	31% 27% 25% 12% 4 1	460
	21st to end	Day	31% 23% 29% 13% 4 1	506
April	1st to 10th	Day	28% 24% 30% 13% 4 1	460
	11th to 20th	Day	22% 22% 29% 15% 9% 3	452
	21st to end	Day	28% 19% 32% 12% 7% 2	460
May	1st to 10th	Day	29% 22% 27% 12% 7% 3	463
	11th to 20th	Day	25% 18% 28% 17% 10% 2	487
	21st to end	Day	18% 11% 25% 26% 16% 5%	529
June	1st to 10th	Day	16% 16% 28% 20% 16% 4	490
	11th to 20th	Day	19% 11% 29% 26% 13% 3	490
	21st to end	Day	13% 13% 32% 24% 14% 3	490
July	1st to 10th	Day	11% 6% 28% 28% 18% 9%	485
	11th to 20th	Day	8% 6% 27% 31% 21% 7%	484
	21st to end	Day	14% 6% 26% 32% 15% 6%	532
August	1st to 10th	Day	12% 6% 23% 30% 20% 8%	486
	11th to 20th	Day	13% 8% 22% 31% 18% 9%	479
	21st to end	Day	11% 7% 24% 31% 17% 9%	539
September	1st to 10th	Day	20% 8% 19% 28% 17% 8%	490
	11th to 20th	Day	14% 6% 21% 32% 19% 8%	490
	21st to end	Day	29% 13% 23% 20% 11% 4	490
October	1st to 10th	Day	20% 10% 26% 24% 14% 4	490
	11th to 20th	Day	20% 19% 26% 23% 10% 2	490
	21st to end	Day	19% 18% 37% 18% 7% 1	539
November	1st to 10th	Day	18% 18% 28% 23% 10% 2	425
	11th to 20th	Day	26% 23% 27% 17% 6%	293
	21st to end	Day	26% 25% 34% 11% 4	180
December	1st to 10th	Day	31% 30% 27% 8% 4 1	180
	11th to 20th	Day	31% 25% 29% 13% 3	180
	21st to end	Day	26% 28% 29% 15% 3	198
January	1st to 10th	Night	19% 29% 33% 16% 3	760
	11th to 20th	Night	23% 22% 31% 21% 3	760
	21st to end	Night	20% 26% 34% 18% 2	836
February	1st to 10th	Night	21% 22% 33% 22% 2	760
	11th to 20th	Night	27% 29% 31% 13% 1	743
	21st to end	Night	26% 25% 30% 16% 2	628
March	1st to 10th	Night	23% 23% 33% 18% 3	760
	11th to 20th	Night	27% 22% 28% 18% 5% 1	760
	21st to end	Night	21% 21% 36% 16% 5% 1	836
April	1st to 10th	Night	23% 24% 31% 18% 4	760
	11th to 20th	Night	17% 18% 32% 25% 7%	751
	21st to end	Night	21% 17% 30% 23% 8% 1	760
May	1st to 10th	Night	21% 13% 26% 27% 12% 1	571
	11th to 20th	Night	21% 9% 28% 31% 11%	433
	21st to end	Night	14% 7% 26% 31% 19% 2	411
June	1st to 10th	Night	12% 3 29% 32% 22% 1	380
	11th to 20th	Night	15% 7% 22% 40% 16% 1	380
	21st to end	Night	9% 5% 23% 46% 16% 1	380
July	1st to 10th	Night	13% 3 17% 38% 26% 3	370
	11th to 20th	Night	8% 4 17% 40% 28% 3	423
	21st to end	Night	10% 3 18% 40% 26% 3	624
August	1st to 10th	Night	12% 3 12% 43% 28% 2	567
	11th to 20th	Night	11% 6% 13% 40% 27% 3	606
	21st to end	Night	13% 4 15% 39% 25% 4	836
September	1st to 10th	Night	16% 4 22% 31% 23% 3	760
	11th to 20th	Night	12% 6% 18% 33% 27% 4	760
	21st to end	Night	23% 10% 19% 28% 19% 3	760
October	1st to 10th	Night	21% 10% 18% 28% 20% 3	760
	11th to 20th	Night	17% 15% 27% 29% 11% 1	760
	21st to end	Night	20% 15% 28% 28% 8% 1	836
November	1st to 10th	Night	14% 15% 30% 29% 11% 1	760
	11th to 20th	Night	18% 23% 29% 23% 7% 1	760
	21st to end	Night	18% 22% 31% 23% 6% 1	760
December	1st to 10th	Night	22% 23% 30% 18% 6%	760
	11th to 20th	Night	20% 23% 32% 23% 3	760
	21st to end	Night	20% 21% 33% 25% 2	836

Page generated at 2024-11-03 02:11:30. Version ac07

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