Hammond
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hammond clear sky chart from 2005-11-06 to 2024-02-20.

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	18% 9% 4 7% 6% 3 5% 5% 5% 6% 32%	78192
	Night	18% 11% 4 7% 6% 3 4 4 5% 6% 31%	80991
Transparency	Day	51% 8% 12% 19% 10% 1	77897
	Night	53% 7% 12% 18% 9% 1	80820
Seeing	Day	21% 12% 28% 24% 12% 4	13481
	Night	22% 9% 29% 30% 10% 1	22719

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	18% 16% 5% 11% 8% 4 5% 4 5% 4 21%	2517
	11th to 20th	Day	15% 13% 6% 12% 8% 4 5% 4 5% 5% 23%	2520
	21st to end	Day	15% 18% 6% 9% 7% 5% 6% 5% 5% 5% 19%	2837
February	1st to 10th	Day	15% 14% 5% 11% 8% 3 5% 4 5% 5% 25%	1710
	11th to 20th	Day	14% 15% 6% 9% 7% 3 5% 4 4 6% 28%	1682
	21st to end	Day	21% 13% 5% 8% 6% 4 5% 4 4 6% 24%	1480
March	1st to 10th	Day	16% 11% 5% 11% 6% 4 6% 4 4 5% 29%	1797
	11th to 20th	Day	18% 11% 4 7% 6% 3 5% 4 4 6% 31%	1946
	21st to end	Day	21% 9% 3 6% 5% 3 4 4 4 6% 36%	2316
April	1st to 10th	Day	22% 11% 4 6% 5% 3 3 4 3 5% 33%	2160
	11th to 20th	Day	22% 7% 3 6% 6% 3 3 4 4 6% 36%	2134
	21st to end	Day	23% 9% 3 7% 6% 3 5% 3 4 6% 30%	2282
May	1st to 10th	Day	21% 7% 3 6% 6% 3 5% 5% 5% 6% 34%	2520
	11th to 20th	Day	17% 7% 3 5% 5% 3 4 4 5% 6% 40%	2478
	21st to end	Day	17% 6% 3 5% 6% 4 5% 5% 6% 7% 37%	2725
June	1st to 10th	Day	23% 7% 3 6% 5% 4 5% 5% 5% 7% 30%	2520
	11th to 20th	Day	15% 6% 2 5% 5% 4 6% 5% 6% 8% 38%	2520
	21st to end	Day	20% 7% 3 5% 6% 3 5% 6% 6% 8% 31%	2520
July	1st to 10th	Day	12% 6% 2 4 6% 4 5% 5% 6% 8% 41%	2520
	11th to 20th	Day	12% 6% 3 6% 5% 3 6% 6% 7% 9% 38%	2520
	21st to end	Day	12% 5% 2 5% 6% 3 5% 5% 8% 9% 39%	2744
August	1st to 10th	Day	12% 6% 3 5% 6% 4 5% 5% 5% 8% 40%	2506
	11th to 20th	Day	13% 5% 2 5% 5% 4 6% 5% 7% 8% 40%	2254
	21st to end	Day	13% 5% 2 5% 4 3 5% 5% 6% 9% 42%	2376
September	1st to 10th	Day	14% 5% 3 4 5% 3 4 5% 6% 8% 42%	2160
	11th to 20th	Day	14% 4 1 4 4 3 4 4 6% 7% 47%	2141
	21st to end	Day	18% 6% 3 4 5% 3 5% 5% 5% 7% 41%	1954
October	1st to 10th	Day	21% 8% 4 5% 5% 3 4 5% 5% 6% 35%	1800
	11th to 20th	Day	23% 9% 3 7% 6% 4 4 5% 5% 6% 28%	1800
	21st to end	Day	27% 9% 3 6% 7% 4 4 4 5% 5% 27%	1810
November	1st to 10th	Day	17% 8% 3 5% 6% 3 5% 5% 6% 7% 33%	1671
	11th to 20th	Day	19% 11% 4 8% 6% 4 5% 4 4 6% 29%	1554
	21st to end	Day	22% 13% 4 8% 7% 3 5% 4 6% 5% 22%	1520
December	1st to 10th	Day	23% 14% 6% 9% 6% 4 6% 5% 4 5% 19%	1520
	11th to 20th	Day	21% 15% 4 8% 6% 3 4 4 4 5% 25%	1906
	21st to end	Day	28% 18% 5% 9% 5% 3 3 3 3 3 19%	2772
January	1st to 10th	Night	18% 17% 7% 10% 7% 3 4 4 4 5% 22%	4429
	11th to 20th	Night	14% 13% 6% 11% 9% 4 5% 5% 5% 5% 22%	4440
	21st to end	Night	17% 20% 7% 9% 6% 3 4 3 4 5% 22%	4816
February	1st to 10th	Night	15% 13% 6% 10% 7% 5% 7% 4 5% 5% 24%	2470
	11th to 20th	Night	14% 12% 6% 9% 8% 4 5% 4 4 6% 28%	2368
	21st to end	Night	17% 13% 4 8% 6% 4 5% 4 5% 5% 30%	1776
March	1st to 10th	Night	16% 13% 5% 8% 8% 3 5% 4 5% 5% 28%	2150
	11th to 20th	Night	17% 12% 4 8% 7% 3 4 3 4 5% 33%	2011
	21st to end	Night	18% 9% 3 7% 5% 3 3 3 4 4 39%	2039
April	1st to 10th	Night	23% 10% 3 5% 6% 2 5% 4 4 5% 33%	1800
	11th to 20th	Night	20% 8% 3 6% 6% 2 4 4 4 6% 36%	1775
	21st to end	Night	22% 9% 3 6% 5% 3 4 3 4 6% 34%	1693
May	1st to 10th	Night	22% 7% 3 5% 5% 2 4 4 5% 7% 36%	1440
	11th to 20th	Night	19% 7% 3 5% 4 2 3 3 5% 6% 42%	1415
	21st to end	Night	15% 5% 3 5% 5% 3 4 6% 5% 7% 43%	1550
June	1st to 10th	Night	17% 7% 3 5% 6% 3 5% 5% 7% 9% 33%	1440
	11th to 20th	Night	15% 6% 3 5% 5% 3 4 4 6% 7% 41%	1440
	21st to end	Night	18% 7% 3 5% 5% 3 5% 6% 6% 8% 36%	1440
July	1st to 10th	Night	11% 5% 2 4 5% 4 6% 5% 5% 7% 45%	1440
	11th to 20th	Night	11% 6% 2 5% 5% 3 4 5% 6% 9% 43%	1440
	21st to end	Night	10% 5% 3 6% 6% 3 5% 6% 6% 8% 42%	1574
August	1st to 10th	Night	9% 6% 3 6% 5% 3 4 5% 6% 10% 42%	1432
	11th to 20th	Night	12% 6% 2 4 6% 3 5% 4 6% 7% 45%	1624
	21st to end	Night	11% 6% 2 6% 5% 3 5% 5% 5% 8% 44%	1980
September	1st to 10th	Night	11% 5% 2 6% 7% 3 6% 4 5% 7% 44%	1800
	11th to 20th	Night	15% 5% 2 4 4 2 3 4 5% 7% 48%	1818
	21st to end	Night	17% 6% 2 5% 5% 3 4 4 4 6% 44%	2004
October	1st to 10th	Night	20% 7% 3 6% 5% 3 5% 5% 5% 6% 37%	2160
	11th to 20th	Night	21% 9% 2 6% 6% 4 4 4 5% 5% 33%	2160
	21st to end	Night	24% 8% 3 8% 7% 3 4 4 5% 6% 29%	2546
November	1st to 10th	Night	20% 10% 3 7% 5% 3 4 4 5% 6% 34%	2407
	11th to 20th	Night	20% 10% 4 7% 6% 3 5% 5% 4 5% 31%	2622
	21st to end	Night	22% 12% 5% 8% 5% 3 4 5% 5% 6% 24%	2660
December	1st to 10th	Night	22% 14% 7% 8% 7% 4 5% 5% 4 5% 19%	2660
	11th to 20th	Night	24% 13% 5% 7% 6% 2 4 4 4 4 27%	3288
	21st to end	Night	31% 17% 4 9% 5% 2 4 3 4 3 19%	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	62% 11% 11% 10% 5% 1	2518
	11th to 20th	Day	60% 7% 13% 14% 6% 1	2520
	21st to end	Day	65% 9% 12% 9% 5%	2837
February	1st to 10th	Day	60% 5% 10% 18% 5% 2	1710
	11th to 20th	Day	58% 5% 13% 15% 8% 1	1691
	21st to end	Day	61% 5% 9% 14% 9% 1	1480
March	1st to 10th	Day	57% 6% 10% 15% 10% 1	1800
	11th to 20th	Day	54% 6% 12% 15% 11% 2	1946
	21st to end	Day	50% 6% 8% 17% 14% 4	2316
April	1st to 10th	Day	54% 4 8% 19% 12% 3	2160
	11th to 20th	Day	49% 5% 8% 21% 15% 2	2134
	21st to end	Day	55% 6% 9% 13% 13% 4	2282
May	1st to 10th	Day	50% 6% 8% 19% 14% 3	2520
	11th to 20th	Day	45% 6% 10% 20% 15% 3	2482
	21st to end	Day	45% 8% 13% 19% 13% 2	2725
June	1st to 10th	Day	52% 7% 12% 17% 11% 1	2520
	11th to 20th	Day	42% 9% 12% 22% 12% 2	2520
	21st to end	Day	48% 10% 14% 17% 10% 1	2520
July	1st to 10th	Day	39% 9% 14% 24% 14% 1	2450
	11th to 20th	Day	39% 10% 16% 25% 10%	2445
	21st to end	Day	38% 12% 16% 23% 10%	2591
August	1st to 10th	Day	41% 10% 17% 23% 9%	2492
	11th to 20th	Day	38% 11% 17% 24% 9% 1	2254
	21st to end	Day	38% 9% 16% 26% 12% 1	2376
September	1st to 10th	Day	38% 9% 16% 26% 12%	2160
	11th to 20th	Day	35% 8% 13% 30% 13% 1	2141
	21st to end	Day	42% 8% 15% 27% 9%	1954
October	1st to 10th	Day	48% 7% 12% 22% 10% 1	1800
	11th to 20th	Day	56% 9% 13% 16% 6% 1	1800
	21st to end	Day	59% 5% 13% 16% 7% 1	1810
November	1st to 10th	Day	48% 9% 15% 20% 7% 1	1671
	11th to 20th	Day	57% 6% 13% 15% 8% 1	1554
	21st to end	Day	61% 9% 12% 12% 5%	1520
December	1st to 10th	Day	67% 8% 12% 10% 2	1520
	11th to 20th	Day	61% 8% 13% 13% 4	1906
	21st to end	Day	70% 5% 7% 14% 4	2772
January	1st to 10th	Night	64% 8% 15% 10% 4	4429
	11th to 20th	Night	59% 11% 15% 11% 5%	4440
	21st to end	Night	65% 7% 12% 10% 6% 1	4816
February	1st to 10th	Night	60% 6% 11% 15% 6% 1	2470
	11th to 20th	Night	57% 6% 10% 19% 8%	2370
	21st to end	Night	55% 7% 8% 18% 11%	1776
March	1st to 10th	Night	57% 7% 10% 15% 10% 2	2160
	11th to 20th	Night	54% 4 11% 17% 10% 3	2012
	21st to end	Night	48% 5% 8% 19% 15% 4	2039
April	1st to 10th	Night	52% 6% 9% 17% 13% 2	1800
	11th to 20th	Night	48% 6% 8% 21% 15% 1	1775
	21st to end	Night	51% 5% 10% 16% 14% 4	1693
May	1st to 10th	Night	46% 8% 8% 18% 15% 5%	1440
	11th to 20th	Night	43% 6% 10% 19% 19% 4	1416
	21st to end	Night	40% 8% 14% 19% 17% 3	1551
June	1st to 10th	Night	45% 9% 15% 20% 10% 1	1440
	11th to 20th	Night	41% 9% 11% 21% 17% 2	1440
	21st to end	Night	44% 10% 14% 18% 13%	1440
July	1st to 10th	Night	35% 9% 14% 25% 16% 2	1400
	11th to 20th	Night	36% 8% 15% 29% 12%	1392
	21st to end	Night	37% 10% 16% 23% 14%	1486
August	1st to 10th	Night	37% 9% 19% 23% 12% 1	1422
	11th to 20th	Night	36% 8% 18% 27% 10%	1624
	21st to end	Night	35% 11% 16% 27% 11%	1980
September	1st to 10th	Night	38% 8% 13% 26% 14% 1	1800
	11th to 20th	Night	35% 7% 13% 33% 10% 1	1818
	21st to end	Night	40% 8% 12% 30% 10%	2004
October	1st to 10th	Night	46% 8% 12% 22% 12% 1	2160
	11th to 20th	Night	51% 8% 12% 20% 8%	2160
	21st to end	Night	56% 7% 13% 16% 8% 1	2546
November	1st to 10th	Night	50% 6% 15% 20% 8%	2407
	11th to 20th	Night	54% 7% 13% 17% 9% 1	2622
	21st to end	Night	60% 8% 13% 15% 5%	2660
December	1st to 10th	Night	67% 7% 10% 12% 3	2660
	11th to 20th	Night	61% 6% 10% 16% 7% 1	3288
	21st to end	Night	70% 6% 7% 13% 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	27% 16% 23% 28% 4 1	180
	11th to 20th	Day	22% 17% 32% 23% 5% 2	180
	21st to end	Day	18% 11% 36% 26% 8%	217
February	1st to 10th	Day	29% 15% 38% 14% 4	270
	11th to 20th	Day	23% 18% 39% 18% 2	295
	21st to end	Day	28% 11% 34% 24% 3	346
March	1st to 10th	Day	23% 11% 33% 25% 8%	420
	11th to 20th	Day	20% 19% 32% 24% 5% 1	420
	21st to end	Day	29% 13% 27% 19% 10% 3	462
April	1st to 10th	Day	25% 16% 30% 19% 9% 1	420
	11th to 20th	Day	26% 18% 22% 19% 12% 3	412
	21st to end	Day	26% 15% 29% 19% 9% 2	420
May	1st to 10th	Day	22% 11% 31% 24% 8% 3	423
	11th to 20th	Day	17% 14% 31% 23% 11% 4	447
	21st to end	Day	17% 11% 33% 24% 12% 3	485
June	1st to 10th	Day	23% 9% 28% 26% 10% 4	450
	11th to 20th	Day	14% 11% 28% 26% 16% 4	450
	21st to end	Day	19% 12% 24% 27% 15% 3	450
July	1st to 10th	Day	13% 6% 23% 34% 18% 7%	445
	11th to 20th	Day	11% 6% 30% 30% 20% 4	444
	21st to end	Day	15% 5% 26% 31% 18% 5%	488
August	1st to 10th	Day	14% 6% 22% 31% 22% 5%	446
	11th to 20th	Day	13% 5% 18% 31% 23% 9%	439
	21st to end	Day	13% 8% 25% 27% 18% 10%	495
September	1st to 10th	Day	16% 7% 25% 22% 18% 12%	450
	11th to 20th	Day	13% 7% 23% 23% 22% 13%	450
	21st to end	Day	18% 10% 25% 24% 16% 7%	450
October	1st to 10th	Day	24% 10% 25% 19% 15% 6%	450
	11th to 20th	Day	24% 14% 31% 20% 10% 1	450
	21st to end	Day	31% 11% 24% 26% 8%	410
November	1st to 10th	Day	23% 16% 24% 24% 11% 1	365
	11th to 20th	Day	27% 13% 35% 19% 6% 1	214
	21st to end	Day	23% 21% 28% 19% 7% 2	180
December	1st to 10th	Day	27% 12% 32% 22% 7%	180
	11th to 20th	Day	26% 17% 35% 19% 2 1	180
	21st to end	Day	31% 16% 35% 13% 4 1	198
January	1st to 10th	Night	27% 10% 31% 27% 5%	760
	11th to 20th	Night	28% 10% 30% 26% 5% 1	760
	21st to end	Night	19% 8% 33% 32% 7% 1	836
February	1st to 10th	Night	21% 9% 38% 28% 5%	760
	11th to 20th	Night	20% 11% 38% 26% 5%	742
	21st to end	Night	23% 10% 31% 31% 4	592
March	1st to 10th	Night	23% 9% 33% 28% 6%	720
	11th to 20th	Night	23% 13% 33% 26% 6%	720
	21st to end	Night	22% 10% 29% 30% 9%	792
April	1st to 10th	Night	26% 9% 31% 28% 5%	720
	11th to 20th	Night	22% 12% 31% 26% 8% 1	711
	21st to end	Night	25% 11% 27% 29% 8% 1	613
May	1st to 10th	Night	23% 7% 29% 29% 9% 2	360
	11th to 20th	Night	22% 7% 28% 33% 9% 1	354
	21st to end	Night	15% 5% 34% 32% 13% 1	389
June	1st to 10th	Night	17% 4 28% 42% 10%	360
	11th to 20th	Night	14% 6% 28% 38% 13% 1	360
	21st to end	Night	18% 4 27% 33% 17% 1	360
July	1st to 10th	Night	8% 4 27% 43% 18%	350
	11th to 20th	Night	10% 5% 23% 43% 19% 1	348
	21st to end	Night	12% 3 21% 45% 18% 1	394
August	1st to 10th	Night	13% 4 19% 44% 19% 1	358
	11th to 20th	Night	12% 4 17% 37% 28% 2	560
	21st to end	Night	13% 5% 23% 37% 20% 2	792
September	1st to 10th	Night	13% 4 25% 38% 20% 1	720
	11th to 20th	Night	17% 6% 18% 34% 23% 2	720
	21st to end	Night	18% 6% 24% 28% 21% 2	720
October	1st to 10th	Night	23% 6% 28% 27% 15% 1	720
	11th to 20th	Night	24% 7% 31% 28% 10% 1	720
	21st to end	Night	27% 9% 28% 30% 6%	792
November	1st to 10th	Night	25% 10% 26% 29% 10% 1	740
	11th to 20th	Night	23% 12% 34% 21% 10%	760
	21st to end	Night	27% 11% 29% 25% 8%	760
December	1st to 10th	Night	28% 12% 31% 23% 5%	760
	11th to 20th	Night	28% 12% 31% 23% 5% 1	760
	21st to end	Night	33% 11% 30% 22% 4	836

Page generated at 2024-02-17 06:28:39. Version ac07

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