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 2024-01-16.

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	16% 10% 4 8% 7% 3 5% 5% 5% 7% 29%	74742
	Night	16% 12% 5% 8% 7% 3 5% 4 5% 6% 29%	75047
Transparency	Day	55% 3 11% 20% 10% 1	74449
	Night	57% 3 11% 19% 9% 1	74874
Seeing	Day	26% 14% 29% 18% 10% 3	13565
	Night	25% 13% 24% 26% 10% 1	22949

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	12% 16% 8% 13% 10% 3 7% 4 5% 5% 16%	1517
	11th to 20th	Day	14% 17% 8% 16% 10% 4 5% 4 4 5% 12%	1498
	21st to end	Day	11% 13% 10% 14% 13% 4 6% 5% 5% 4 15%	1782
February	1st to 10th	Day	18% 14% 6% 15% 9% 4 5% 4 5% 4 16%	1620
	11th to 20th	Day	14% 15% 7% 14% 9% 4 6% 4 3 5% 17%	1595
	21st to end	Day	18% 14% 5% 13% 10% 3 4 3 4 4 21%	1480
March	1st to 10th	Day	15% 13% 8% 14% 7% 3 5% 4 4 5% 23%	1856
	11th to 20th	Day	15% 15% 8% 8% 6% 3 4 4 5% 6% 26%	1980
	21st to end	Day	19% 12% 6% 9% 7% 3 4 4 4 5% 27%	2257
April	1st to 10th	Day	15% 13% 5% 8% 6% 4 4 4 6% 6% 29%	2160
	11th to 20th	Day	18% 10% 3 6% 5% 4 4 4 5% 6% 35%	2134
	21st to end	Day	19% 12% 4 6% 6% 3 4 3 4 7% 32%	2187
May	1st to 10th	Day	16% 11% 3 6% 6% 3 5% 5% 5% 6% 33%	2452
	11th to 20th	Day	17% 8% 3 6% 6% 3 6% 5% 5% 8% 34%	2478
	21st to end	Day	14% 6% 2 6% 6% 3 5% 5% 6% 8% 39%	2725
June	1st to 10th	Day	18% 8% 3 5% 6% 3 4 5% 5% 8% 35%	2520
	11th to 20th	Day	15% 6% 2 5% 5% 4 5% 6% 7% 10% 35%	2520
	21st to end	Day	12% 6% 4 6% 6% 3 6% 6% 6% 9% 35%	2520
July	1st to 10th	Day	12% 5% 3 6% 6% 3 5% 6% 6% 9% 39%	2520
	11th to 20th	Day	12% 5% 3 5% 7% 3 6% 6% 8% 10% 37%	2520
	21st to end	Day	11% 5% 3 6% 7% 4 7% 7% 6% 9% 36%	2720
August	1st to 10th	Day	13% 4 2 5% 6% 4 6% 6% 7% 11% 35%	2327
	11th to 20th	Day	14% 7% 2 6% 7% 4 5% 6% 7% 10% 31%	2249
	21st to end	Day	15% 6% 3 6% 6% 4 5% 6% 6% 9% 34%	2376
September	1st to 10th	Day	16% 6% 3 6% 5% 3 5% 5% 5% 8% 38%	2160
	11th to 20th	Day	14% 6% 2 6% 5% 3 4 4 5% 8% 42%	2160
	21st to end	Day	17% 7% 2 5% 6% 4 6% 6% 5% 8% 34%	1914
October	1st to 10th	Day	18% 9% 2 7% 5% 4 5% 5% 6% 6% 32%	1800
	11th to 20th	Day	19% 9% 3 6% 6% 5% 5% 5% 5% 7% 29%	1800
	21st to end	Day	24% 15% 3 7% 6% 3 4 4 4 5% 24%	1930
November	1st to 10th	Day	15% 13% 4 7% 6% 2 4 5% 6% 6% 33%	1671
	11th to 20th	Day	15% 14% 6% 9% 6% 3 4 5% 5% 8% 25%	1596
	21st to end	Day	16% 18% 6% 10% 7% 3 5% 4 5% 6% 19%	1520
December	1st to 10th	Day	18% 19% 7% 12% 6% 4 4 4 4 6% 16%	1520
	11th to 20th	Day	19% 17% 8% 11% 7% 2 4 4 4 5% 19%	1906
	21st to end	Day	24% 21% 7% 10% 7% 3 3 4 4 4 14%	2772
January	1st to 10th	Night	15% 17% 7% 14% 9% 5% 6% 5% 5% 4 15%	2649
	11th to 20th	Night	16% 16% 7% 11% 10% 4 6% 5% 4 6% 16%	2570
	21st to end	Night	11% 15% 7% 13% 12% 5% 7% 5% 5% 6% 15%	2574
February	1st to 10th	Night	16% 14% 8% 12% 9% 3 5% 4 4 5% 20%	2340
	11th to 20th	Night	14% 14% 7% 13% 10% 4 6% 4 4 5% 19%	2250
	21st to end	Night	17% 12% 6% 15% 7% 3 5% 3 5% 6% 21%	1776
March	1st to 10th	Night	12% 15% 8% 12% 7% 4 5% 3 4 6% 24%	2088
	11th to 20th	Night	15% 15% 6% 9% 7% 3 4 4 4 5% 29%	1979
	21st to end	Night	17% 14% 4 8% 6% 3 4 4 4 5% 30%	2098
April	1st to 10th	Night	17% 13% 5% 6% 6% 3 5% 5% 6% 6% 30%	1800
	11th to 20th	Night	19% 10% 5% 6% 5% 3 4 4 5% 5% 34%	1775
	21st to end	Night	19% 9% 4 5% 6% 3 4 4 4 6% 36%	1787
May	1st to 10th	Night	20% 11% 3 6% 6% 3 4 5% 5% 6% 31%	1508
	11th to 20th	Night	12% 6% 2 6% 6% 3 5% 5% 7% 9% 38%	1415
	21st to end	Night	12% 6% 2 6% 5% 3 5% 5% 7% 7% 42%	1550
June	1st to 10th	Night	16% 7% 3 5% 6% 2 4 5% 7% 8% 38%	1440
	11th to 20th	Night	13% 6% 3 6% 6% 3 4 4 6% 9% 40%	1440
	21st to end	Night	12% 5% 3 5% 5% 4 5% 6% 5% 8% 42%	1440
July	1st to 10th	Night	8% 6% 2 4 6% 3 5% 4 6% 10% 45%	1440
	11th to 20th	Night	10% 4 2 5% 5% 3 5% 5% 7% 9% 46%	1440
	21st to end	Night	12% 6% 2 5% 5% 4 5% 4 7% 10% 40%	1595
August	1st to 10th	Night	10% 5% 2 5% 6% 3 5% 5% 6% 9% 44%	1611
	11th to 20th	Night	11% 6% 3 7% 6% 4 6% 5% 5% 9% 38%	1634
	21st to end	Night	13% 5% 2 5% 5% 3 4 5% 7% 9% 42%	1980
September	1st to 10th	Night	14% 6% 3 6% 5% 3 6% 4 6% 7% 41%	1800
	11th to 20th	Night	15% 6% 2 4 4 3 4 4 4 7% 48%	1800
	21st to end	Night	15% 7% 3 5% 5% 4 5% 6% 4 7% 39%	2044
October	1st to 10th	Night	18% 9% 3 8% 5% 3 5% 4 6% 5% 34%	2160
	11th to 20th	Night	20% 9% 3 5% 6% 4 4 4 4 7% 34%	2160
	21st to end	Night	27% 13% 4 6% 5% 3 4 4 4 6% 24%	2425
November	1st to 10th	Night	13% 13% 4 6% 6% 3 4 4 5% 6% 35%	2407
	11th to 20th	Night	17% 13% 5% 7% 6% 3 6% 4 5% 6% 29%	2580
	21st to end	Night	14% 16% 6% 9% 7% 3 4 4 6% 7% 23%	2660
December	1st to 10th	Night	18% 18% 7% 11% 7% 4 4 4 5% 5% 17%	2660
	11th to 20th	Night	19% 15% 6% 11% 8% 4 5% 4 4 5% 19%	3288
	21st to end	Night	26% 18% 7% 9% 6% 3 5% 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	71% 3 8% 13% 4	1518
	11th to 20th	Day	75% 3 8% 9% 4	1498
	21st to end	Day	73% 3 9% 10% 5%	1782
February	1st to 10th	Day	73% 2 8% 12% 4 1	1620
	11th to 20th	Day	72% 3 4 16% 4	1604
	21st to end	Day	69% 2 7% 15% 7% 1	1480
March	1st to 10th	Day	65% 3 11% 15% 6%	1859
	11th to 20th	Day	61% 3 8% 17% 11% 1	1980
	21st to end	Day	61% 2 7% 17% 11% 2	2257
April	1st to 10th	Day	56% 3 8% 22% 10% 2	2160
	11th to 20th	Day	51% 3 11% 20% 14% 1	2134
	21st to end	Day	54% 2 8% 21% 13% 2	2187
May	1st to 10th	Day	53% 3 10% 21% 11% 2	2452
	11th to 20th	Day	49% 3 10% 23% 13% 2	2482
	21st to end	Day	44% 4 16% 23% 12% 1	2725
June	1st to 10th	Day	49% 3 10% 22% 14% 1	2520
	11th to 20th	Day	45% 4 14% 25% 11% 1	2520
	21st to end	Day	45% 5% 13% 24% 12% 1	2520
July	1st to 10th	Day	42% 5% 12% 28% 12% 2	2450
	11th to 20th	Day	42% 3 16% 27% 12% 1	2445
	21st to end	Day	45% 4 13% 24% 14% 1	2568
August	1st to 10th	Day	43% 4 14% 27% 12% 1	2314
	11th to 20th	Day	48% 4 13% 26% 9%	2249
	21st to end	Day	47% 4 10% 26% 13% 1	2376
September	1st to 10th	Day	46% 3 10% 27% 13% 1	2160
	11th to 20th	Day	42% 3 10% 26% 18% 1	2160
	21st to end	Day	49% 3 11% 24% 12% 2	1914
October	1st to 10th	Day	52% 3 10% 21% 12% 1	1800
	11th to 20th	Day	55% 3 11% 22% 9%	1800
	21st to end	Day	64% 2 10% 15% 7% 1	1930
November	1st to 10th	Day	52% 3 12% 19% 12% 2	1671
	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	73% 3 8% 10% 6%	2649
	11th to 20th	Night	71% 3 10% 11% 4	2570
	21st to end	Night	70% 4 7% 13% 5% 1	2574
February	1st to 10th	Night	68% 3 10% 12% 7%	2340
	11th to 20th	Night	70% 2 8% 13% 5% 1	2252
	21st to end	Night	66% 2 9% 14% 8% 1	1776
March	1st to 10th	Night	65% 2 9% 17% 6%	2098
	11th to 20th	Night	60% 2 8% 20% 9% 1	1980
	21st to end	Night	58% 2 7% 17% 13% 2	2098
April	1st to 10th	Night	55% 3 10% 20% 10% 2	1800
	11th to 20th	Night	54% 3 10% 19% 14% 1	1775
	21st to end	Night	52% 2 10% 20% 13% 3	1787
May	1st to 10th	Night	54% 3 9% 18% 13% 3	1508
	11th to 20th	Night	43% 4 11% 25% 15% 2	1416
	21st to end	Night	41% 4 15% 24% 13% 2	1551
June	1st to 10th	Night	45% 3 10% 27% 15% 1	1440
	11th to 20th	Night	43% 3 14% 25% 13% 2	1440
	21st to end	Night	40% 5% 11% 29% 14% 1	1440
July	1st to 10th	Night	36% 5% 15% 26% 16% 2	1400
	11th to 20th	Night	35% 4 15% 30% 16% 1	1392
	21st to end	Night	40% 4 14% 24% 15% 2	1506
August	1st to 10th	Night	37% 4 16% 31% 12% 1	1600
	11th to 20th	Night	43% 4 15% 29% 9%	1634
	21st to end	Night	39% 4 15% 27% 14% 2	1980
September	1st to 10th	Night	43% 4 13% 25% 14% 2	1800
	11th to 20th	Night	38% 2 12% 30% 17% 1	1800
	21st to end	Night	46% 4 11% 25% 13% 1	2044
October	1st to 10th	Night	52% 4 10% 21% 12%	2160
	11th to 20th	Night	52% 3 14% 21% 10% 1	2160
	21st to end	Night	64% 2 10% 15% 8% 1	2425
November	1st to 10th	Night	52% 3 10% 21% 13% 2	2407
	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	40% 25% 25% 7% 2 1	178
	21st to end	Day	28% 26% 33% 10% 3	264
February	1st to 10th	Day	39% 27% 28% 5% 2	240
	11th to 20th	Day	36% 24% 34% 6%	262
	21st to end	Day	39% 21% 27% 11% 2	346
March	1st to 10th	Day	35% 20% 27% 13% 3	420
	11th to 20th	Day	35% 19% 28% 14% 4	420
	21st to end	Day	34% 20% 26% 12% 6% 1	462
April	1st to 10th	Day	32% 17% 29% 15% 5% 1	420
	11th to 20th	Day	32% 18% 26% 11% 9% 3	412
	21st to end	Day	34% 14% 29% 13% 7% 2	420
May	1st to 10th	Day	28% 16% 30% 15% 7% 3	423
	11th to 20th	Day	23% 12% 34% 19% 10% 2	447
	21st to end	Day	20% 10% 31% 21% 14% 4	485
June	1st to 10th	Day	23% 12% 31% 21% 11% 2	450
	11th to 20th	Day	21% 9% 30% 26% 12% 2	450
	21st to end	Day	18% 11% 33% 24% 11% 2	450
July	1st to 10th	Day	15% 7% 28% 28% 16% 5%	445
	11th to 20th	Day	13% 5% 28% 32% 19% 4	444
	21st to end	Day	13% 6% 37% 27% 13% 4	488
August	1st to 10th	Day	14% 5% 27% 28% 20% 6%	446
	11th to 20th	Day	17% 8% 26% 27% 14% 9%	439
	21st to end	Day	16% 9% 27% 23% 16% 9%	495
September	1st to 10th	Day	20% 10% 23% 23% 15% 9%	450
	11th to 20th	Day	17% 6% 27% 22% 19% 9%	450
	21st to end	Day	21% 11% 29% 22% 13% 5%	450
October	1st to 10th	Day	26% 8% 27% 19% 15% 5%	450
	11th to 20th	Day	26% 16% 29% 20% 8% 1	450
	21st to end	Day	38% 15% 28% 16% 4	470
November	1st to 10th	Day	26% 18% 23% 21% 11% 1	365
	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	32% 16% 25% 22% 4	741
	21st to end	Night	26% 19% 30% 22% 2	792
February	1st to 10th	Night	27% 21% 29% 22% 2	720
	11th to 20th	Night	29% 24% 30% 16% 2	703
	21st to end	Night	34% 18% 26% 20% 3	592
March	1st to 10th	Night	28% 23% 25% 21% 4	720
	11th to 20th	Night	28% 17% 28% 22% 5%	720
	21st to end	Night	29% 18% 23% 21% 8%	792
April	1st to 10th	Night	30% 16% 28% 23% 4	720
	11th to 20th	Night	29% 15% 24% 22% 8% 1	711
	21st to end	Night	26% 13% 27% 26% 8%	707
May	1st to 10th	Night	28% 7% 18% 34% 12% 1	428
	11th to 20th	Night	14% 10% 29% 35% 11% 1	354
	21st to end	Night	14% 5% 26% 38% 16% 1	389
June	1st to 10th	Night	19% 6% 21% 40% 14% 1	360
	11th to 20th	Night	17% 8% 18% 41% 16% 1	360
	21st to end	Night	14% 3 22% 45% 15%	360
July	1st to 10th	Night	8% 2 19% 47% 21% 3	350
	11th to 20th	Night	14% 2 15% 46% 22% 1	348
	21st to end	Night	16% 3 16% 41% 23% 2	415
August	1st to 10th	Night	13% 2 17% 39% 26% 3	537
	11th to 20th	Night	13% 3 15% 37% 28% 4	570
	21st to end	Night	16% 3 17% 37% 24% 2	792
September	1st to 10th	Night	18% 5% 22% 32% 21% 3	720
	11th to 20th	Night	19% 5% 17% 29% 24% 6%	720
	21st to end	Night	19% 8% 24% 27% 20% 2	720
October	1st to 10th	Night	24% 8% 24% 25% 18% 1	720
	11th to 20th	Night	28% 11% 25% 28% 8% 1	720
	21st to end	Night	36% 13% 25% 21% 5%	792
November	1st to 10th	Night	25% 13% 27% 26% 9%	740
	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 2024-01-13 01:38:09. Version ac07

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