Ithaca
Clear Sky Chart
History

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

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	15% 11% 4 9% 5% 5% 5% 4 6% 7% 29%	101531
	Night	16% 13% 4 9% 6% 4 4 3 5% 6% 29%	97540
Transparency	Day	54% 3 11% 21% 10% 1	105092
	Night	56% 3 11% 20% 9% 1	102067
Seeing	Day	26% 14% 29% 18% 10% 3	14699
	Night	25% 13% 24% 26% 10% 1	23934

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% 22% 9% 14% 6% 4 4 2 4 3 17%	2517
	11th to 20th	Day	13% 18% 10% 18% 7% 6% 3 3 4 5% 14%	2552
	21st to end	Day	17% 18% 10% 12% 10% 5% 5% 3 4 4 12%	3124
February	1st to 10th	Day	17% 15% 5% 16% 8% 5% 5% 3 5% 4 18%	1710
	11th to 20th	Day	13% 16% 6% 16% 8% 6% 5% 3 3 5% 18%	1686
	21st to end	Day	17% 15% 5% 13% 9% 4 3 3 4 4 22%	1570
March	1st to 10th	Day	21% 16% 5% 11% 5% 3 3 2 3 5% 25%	3231
	11th to 20th	Day	10% 19% 7% 10% 5% 4 4 2 5% 6% 28%	3480
	21st to end	Day	16% 12% 5% 12% 5% 5% 4 3 5% 5% 28%	3963
April	1st to 10th	Day	16% 15% 4 9% 5% 4 4 3 6% 6% 29%	2280
	11th to 20th	Day	18% 11% 3 8% 4 5% 3 3 5% 6% 34%	2254
	21st to end	Day	19% 13% 3 7% 5% 4 4 3 4 7% 33%	2309
May	1st to 10th	Day	22% 10% 3 6% 4 4 4 3 5% 6% 32%	4317
	11th to 20th	Day	17% 9% 4 8% 6% 5% 6% 5% 6% 8% 28%	4398
	21st to end	Day	12% 6% 2 7% 4 5% 5% 4 6% 8% 41%	4837
June	1st to 10th	Day	17% 8% 2 7% 5% 4 5% 4 6% 8% 34%	2660
	11th to 20th	Day	14% 6% 2 6% 5% 4 6% 5% 7% 10% 35%	2660
	21st to end	Day	12% 7% 3 7% 6% 5% 6% 5% 7% 10% 34%	2660
July	1st to 10th	Day	10% 6% 2 6% 4 4 6% 5% 8% 12% 37%	4440
	11th to 20th	Day	8% 5% 2 6% 6% 5% 6% 5% 10% 12% 34%	4440
	21st to end	Day	10% 6% 3 7% 6% 6% 7% 5% 6% 8% 36%	4764
August	1st to 10th	Day	16% 6% 3 7% 6% 6% 6% 4 6% 9% 31%	4104
	11th to 20th	Day	15% 8% 3 8% 6% 6% 6% 5% 6% 9% 29%	3948
	21st to end	Day	13% 8% 3 7% 5% 4 5% 4 5% 7% 38%	4180
September	1st to 10th	Day	16% 7% 2 6% 4 4 4 4 6% 8% 39%	2280
	11th to 20th	Day	14% 7% 2 6% 5% 4 4 3 5% 8% 43%	2280
	21st to end	Day	18% 8% 2 7% 5% 5% 6% 4 6% 7% 32%	2019
October	1st to 10th	Day	18% 9% 2 8% 4 5% 4 4 6% 6% 33%	1900
	11th to 20th	Day	19% 10% 3 7% 5% 6% 5% 4 5% 7% 30%	1900
	21st to end	Day	22% 15% 3 8% 5% 4 4 4 4 5% 26%	2037
November	1st to 10th	Day	14% 13% 4 8% 4 3 4 4 6% 5% 33%	1717
	11th to 20th	Day	15% 15% 6% 11% 5% 3 4 4 5% 7% 25%	1596
	21st to end	Day	16% 19% 6% 11% 6% 5% 4 3 5% 7% 19%	1520
December	1st to 10th	Day	18% 20% 7% 13% 5% 5% 4 3 4 6% 16%	1520
	11th to 20th	Day	19% 17% 8% 12% 6% 4 3 3 4 4 19%	1906
	21st to end	Day	24% 22% 6% 11% 5% 4 3 3 4 4 13%	2772
January	1st to 10th	Night	15% 20% 6% 16% 6% 5% 4 3 5% 4 15%	4429
	11th to 20th	Night	12% 19% 7% 14% 9% 6% 5% 3 4 5% 16%	4405
	21st to end	Night	21% 18% 6% 16% 9% 5% 4 2 3 3 12%	4532
February	1st to 10th	Night	15% 16% 6% 13% 8% 5% 4 3 4 5% 20%	2470
	11th to 20th	Night	13% 15% 6% 15% 9% 5% 5% 4 4 5% 19%	2379
	21st to end	Night	16% 14% 5% 16% 6% 4 4 3 5% 5% 22%	1884
March	1st to 10th	Night	18% 14% 6% 10% 5% 5% 4 3 4 5% 27%	3606
	11th to 20th	Night	14% 22% 6% 9% 5% 4 4 3 4 5% 25%	3479
	21st to end	Night	17% 13% 5% 10% 5% 5% 4 3 4 4 29%	3668
April	1st to 10th	Night	17% 15% 4 7% 5% 4 4 4 6% 6% 29%	1900
	11th to 20th	Night	20% 11% 4 7% 5% 3 4 3 5% 5% 33%	1875
	21st to end	Night	18% 9% 3 6% 5% 3 4 4 4 6% 36%	1886
May	1st to 10th	Night	24% 9% 3 7% 5% 4 4 3 5% 6% 29%	2624
	11th to 20th	Night	16% 8% 3 8% 5% 4 4 3 6% 7% 34%	2495
	21st to end	Night	12% 6% 2 7% 5% 4 5% 5% 7% 8% 39%	2738
June	1st to 10th	Night	16% 8% 2 6% 5% 3 4 4 6% 7% 38%	1520
	11th to 20th	Night	13% 6% 3 7% 5% 4 5% 4 6% 9% 39%	1520
	21st to end	Night	12% 6% 2 5% 5% 5% 5% 4 6% 8% 41%	1520
July	1st to 10th	Night	10% 7% 2 7% 6% 5% 4 4 6% 9% 41%	2520
	11th to 20th	Night	11% 5% 2 6% 5% 4 4 3 7% 9% 45%	2520
	21st to end	Night	12% 6% 2 7% 4 5% 4 4 7% 8% 41%	2786
August	1st to 10th	Night	17% 8% 3 7% 5% 4 4 4 5% 8% 36%	2825
	11th to 20th	Night	13% 7% 3 8% 5% 5% 5% 3 4 7% 39%	2849
	21st to end	Night	11% 9% 3 7% 4 4 4 4 6% 7% 42%	3476
September	1st to 10th	Night	13% 6% 2 6% 4 5% 6% 3 6% 6% 42%	1900
	11th to 20th	Night	14% 6% 2 5% 4 4 4 4 4 6% 49%	1900
	21st to end	Night	16% 8% 3 6% 4 5% 5% 4 4 7% 37%	2159
October	1st to 10th	Night	18% 9% 3 9% 4 4 5% 3 6% 5% 34%	2280
	11th to 20th	Night	19% 9% 3 7% 5% 4 3 3 5% 7% 35%	2280
	21st to end	Night	25% 14% 3 8% 4 3 4 3 4 6% 26%	2560
November	1st to 10th	Night	13% 14% 3 7% 5% 4 4 3 5% 6% 35%	2483
	11th to 20th	Night	17% 14% 4 8% 5% 5% 5% 3 5% 6% 29%	2580
	21st to end	Night	14% 17% 5% 10% 6% 5% 3 4 6% 6% 23%	2660
December	1st to 10th	Night	18% 19% 6% 12% 6% 5% 4 3 5% 5% 17%	2660
	11th to 20th	Night	19% 16% 6% 13% 6% 5% 5% 3 4 4 19%	3288
	21st to end	Night	25% 19% 6% 10% 5% 4 4 4 4 5% 13%	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% 2 7% 14% 3	2518
	11th to 20th	Day	76% 2 7% 10% 4	2552
	21st to end	Day	78% 2 9% 9% 3	3124
February	1st to 10th	Day	72% 2 8% 14% 4 1	1710
	11th to 20th	Day	72% 3 4 16% 5%	1695
	21st to end	Day	68% 2 7% 16% 7% 1	1570
March	1st to 10th	Day	66% 1 8% 18% 6%	3234
	11th to 20th	Day	60% 2 13% 15% 9% 1	3480
	21st to end	Day	60% 1 6% 22% 10% 1	3963
April	1st to 10th	Day	57% 2 7% 21% 10% 2	2280
	11th to 20th	Day	52% 3 11% 20% 13% 1	2254
	21st to end	Day	54% 2 7% 21% 14% 2	2309
May	1st to 10th	Day	54% 2 10% 20% 12% 2	4330
	11th to 20th	Day	56% 2 11% 23% 7% 1	4402
	21st to end	Day	43% 2 12% 27% 15% 1	4837
June	1st to 10th	Day	49% 3 10% 22% 14% 1	2660
	11th to 20th	Day	44% 5% 14% 25% 11% 1	2660
	21st to end	Day	45% 5% 13% 23% 12% 1	2660
July	1st to 10th	Day	38% 6% 16% 28% 10% 1	4370
	11th to 20th	Day	38% 7% 16% 26% 11% 1	4365
	21st to end	Day	43% 6% 15% 24% 12% 1	4612
August	1st to 10th	Day	49% 5% 12% 22% 11% 1	4091
	11th to 20th	Day	49% 6% 14% 24% 6%	3987
	21st to end	Day	44% 4 9% 33% 9% 1	4180
September	1st to 10th	Day	44% 3 10% 28% 14% 1	2280
	11th to 20th	Day	41% 3 10% 27% 18% 1	2280
	21st to end	Day	51% 3 11% 22% 12% 2	2019
October	1st to 10th	Day	44% 6% 12% 26% 12% 1	3160
	11th to 20th	Day	48% 4 12% 21% 15%	3140
	21st to end	Day	46% 4 15% 26% 8% 1	3339
November	1st to 10th	Day	51% 3 12% 20% 11% 2	1717
	11th to 20th	Day	59% 2 12% 17% 8% 2	1596
	21st to end	Day	67% 2 12% 15% 4	1520
December	1st to 10th	Day	72% 2 10% 12% 3	1520
	11th to 20th	Day	70% 3 13% 10% 4	1906
	21st to end	Day	77% 2 7% 12% 2	2772
January	1st to 10th	Night	75% 2 11% 9% 4	4429
	11th to 20th	Night	73% 2 7% 13% 5%	4405
	21st to end	Night	79% 2 5% 10% 3	4532
February	1st to 10th	Night	67% 3 10% 13% 7%	2470
	11th to 20th	Night	70% 2 8% 13% 5% 1	2381
	21st to end	Night	66% 2 9% 14% 8% 1	1884
March	1st to 10th	Night	63% 1 9% 19% 7%	3616
	11th to 20th	Night	64% 1 10% 18% 6%	3480
	21st to end	Night	60% 1 5% 21% 11% 2	3668
April	1st to 10th	Night	56% 3 10% 20% 10% 1	1900
	11th to 20th	Night	54% 3 9% 19% 14% 1	1875
	21st to end	Night	51% 2 9% 21% 14% 3	1886
May	1st to 10th	Night	57% 2 10% 19% 9% 3	2630
	11th to 20th	Night	50% 3 16% 22% 9% 1	2496
	21st to end	Night	43% 3 14% 22% 17% 2	2739
June	1st to 10th	Night	45% 3 10% 27% 15% 1	1520
	11th to 20th	Night	42% 4 14% 26% 13% 2	1520
	21st to end	Night	41% 5% 11% 29% 14% 1	1520
July	1st to 10th	Night	41% 6% 14% 23% 15% 1	2480
	11th to 20th	Night	35% 6% 15% 29% 14%	2472
	21st to end	Night	41% 6% 12% 22% 17% 2	2697
August	1st to 10th	Night	47% 5% 14% 25% 8% 1	2814
	11th to 20th	Night	43% 5% 15% 27% 9%	2876
	21st to end	Night	41% 4 12% 32% 10% 1	3476
September	1st to 10th	Night	42% 4 13% 25% 15% 2	1900
	11th to 20th	Night	37% 3 12% 30% 17% 1	1900
	21st to end	Night	48% 4 11% 23% 13% 1	2159
October	1st to 10th	Night	51% 6% 9% 23% 10%	3800
	11th to 20th	Night	45% 4 13% 21% 14% 3	3779
	21st to end	Night	46% 4 14% 27% 9%	4208
November	1st to 10th	Night	51% 3 10% 21% 12% 2	2483
	11th to 20th	Night	58% 2 10% 20% 8% 2	2580
	21st to end	Night	61% 3 14% 18% 4	2660
December	1st to 10th	Night	70% 3 11% 13% 3	2660
	11th to 20th	Night	70% 2 9% 14% 4	3288
	21st to end	Night	75% 2 9% 12% 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% 18% 35% 11% 2 1	180
	11th to 20th	Day	39% 25% 26% 7% 2 1	189
	21st to end	Day	29% 24% 34% 10% 2	297
February	1st to 10th	Day	36% 26% 30% 7% 2	270
	11th to 20th	Day	35% 26% 32% 7%	293
	21st to end	Day	38% 21% 28% 10% 2	382
March	1st to 10th	Day	36% 19% 27% 13% 4 1	460
	11th to 20th	Day	35% 19% 28% 13% 4	460
	21st to end	Day	34% 21% 26% 12% 5% 1	506
April	1st to 10th	Day	34% 17% 28% 15% 5% 1	460
	11th to 20th	Day	34% 19% 25% 11% 8% 3	452
	21st to end	Day	33% 15% 29% 14% 7% 2	460
May	1st to 10th	Day	29% 16% 30% 16% 7% 3	463
	11th to 20th	Day	23% 12% 34% 19% 10% 2	487
	21st to end	Day	19% 11% 31% 22% 14% 3	529
June	1st to 10th	Day	23% 12% 31% 21% 11% 2	490
	11th to 20th	Day	20% 9% 30% 27% 12% 2	490
	21st to end	Day	20% 12% 33% 23% 11% 2	490
July	1st to 10th	Day	14% 8% 31% 28% 15% 4	485
	11th to 20th	Day	12% 6% 28% 31% 18% 4	484
	21st to end	Day	13% 6% 37% 28% 12% 4	532
August	1st to 10th	Day	15% 7% 27% 27% 19% 5%	486
	11th to 20th	Day	17% 9% 27% 27% 13% 8%	479
	21st to end	Day	17% 9% 26% 23% 17% 9%	539
September	1st to 10th	Day	20% 10% 23% 23% 15% 8%	490
	11th to 20th	Day	16% 6% 24% 23% 21% 9%	490
	21st to end	Day	23% 11% 29% 21% 12% 4	490
October	1st to 10th	Day	26% 9% 27% 19% 15% 4	490
	11th to 20th	Day	25% 16% 29% 19% 9% 2	490
	21st to end	Day	35% 15% 29% 16% 4	511
November	1st to 10th	Day	26% 19% 23% 21% 10% 1	381
	11th to 20th	Day	34% 21% 28% 13% 4	256
	21st to end	Day	39% 18% 33% 9% 1	180
December	1st to 10th	Day	35% 22% 32% 8% 2 1	180
	11th to 20th	Day	37% 26% 26% 9% 2	180
	21st to end	Day	41% 15% 37% 7% 1	198
January	1st to 10th	Night	29% 21% 30% 17% 2	760
	11th to 20th	Night	31% 17% 25% 23% 4	760
	21st to end	Night	26% 19% 30% 22% 3	836
February	1st to 10th	Night	26% 21% 29% 23% 2	760
	11th to 20th	Night	29% 23% 30% 16% 2	743
	21st to end	Night	34% 18% 26% 19% 3	628
March	1st to 10th	Night	28% 22% 25% 21% 4	760
	11th to 20th	Night	28% 17% 28% 22% 5%	760
	21st to end	Night	29% 19% 23% 20% 7%	836
April	1st to 10th	Night	30% 15% 28% 23% 4	760
	11th to 20th	Night	30% 15% 24% 22% 8% 1	751
	21st to end	Night	25% 13% 27% 26% 8%	746
May	1st to 10th	Night	28% 7% 19% 34% 11% 1	451
	11th to 20th	Night	15% 9% 29% 34% 12% 1	374
	21st to end	Night	14% 5% 27% 38% 16% 1	411
June	1st to 10th	Night	19% 6% 22% 39% 14% 1	380
	11th to 20th	Night	16% 7% 19% 42% 15% 1	380
	21st to end	Night	15% 4 22% 44% 15%	380
July	1st to 10th	Night	8% 2 19% 48% 20% 3	370
	11th to 20th	Night	13% 2 15% 47% 22% 1	368
	21st to end	Night	15% 3 16% 41% 23% 2	439
August	1st to 10th	Night	14% 2 17% 39% 26% 3	567
	11th to 20th	Night	13% 3 15% 36% 28% 4	602
	21st to end	Night	17% 3 17% 37% 24% 2	836
September	1st to 10th	Night	18% 6% 22% 31% 20% 3	760
	11th to 20th	Night	18% 5% 16% 30% 26% 5%	760
	21st to end	Night	20% 8% 24% 26% 19% 2	760
October	1st to 10th	Night	24% 9% 24% 25% 18% 1	760
	11th to 20th	Night	27% 11% 25% 28% 8% 1	760
	21st to end	Night	35% 13% 26% 21% 5%	836
November	1st to 10th	Night	25% 13% 27% 26% 9%	764
	11th to 20th	Night	30% 15% 28% 19% 7% 1	760
	21st to end	Night	28% 17% 27% 23% 4 1	760
December	1st to 10th	Night	35% 19% 25% 17% 4	760
	11th to 20th	Night	30% 20% 27% 19% 3	760
	21st to end	Night	34% 19% 27% 18% 2	836

Page generated at 2024-11-03 13:19:05. Version ac07

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