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 2024-10-24.

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% 10% 3 8% 5% 5% 4 4 5% 7% 33%	101475
	Night	18% 11% 4 8% 5% 4 4 3 5% 6% 31%	97298
Transparency	Day	49% 8% 13% 20% 9% 1	101233
	Night	52% 8% 12% 18% 9% 1	97160
Seeing	Day	20% 12% 28% 24% 12% 4	14467
	Night	21% 9% 29% 30% 11% 1	23486

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% 17% 5% 12% 6% 5% 5% 3 4 4 21%	2517
	11th to 20th	Day	14% 13% 5% 14% 7% 5% 5% 3 6% 5% 23%	2520
	21st to end	Day	15% 19% 6% 10% 6% 6% 5% 4 5% 5% 19%	2837
February	1st to 10th	Day	14% 15% 5% 12% 7% 5% 4 4 5% 5% 25%	1710
	11th to 20th	Day	14% 16% 5% 10% 6% 4 5% 3 5% 6% 27%	1692
	21st to end	Day	20% 13% 4 9% 5% 5% 5% 3 5% 6% 25%	1570
March	1st to 10th	Day	20% 13% 4 10% 5% 5% 5% 3 4 5% 26%	3116
	11th to 20th	Day	14% 16% 5% 10% 5% 5% 5% 3 4 6% 27%	3432
	21st to end	Day	15% 8% 2 7% 5% 5% 4 3 5% 6% 40%	4064
April	1st to 10th	Day	22% 12% 3 6% 5% 4 3 3 3 5% 33%	2280
	11th to 20th	Day	23% 9% 3 7% 5% 3 3 3 5% 5% 35%	2254
	21st to end	Day	23% 10% 3 9% 5% 4 5% 2 4 5% 31%	2410
May	1st to 10th	Day	21% 8% 3 7% 5% 5% 5% 4 5% 7% 30%	4426
	11th to 20th	Day	19% 9% 3 8% 5% 4 4 3 5% 7% 34%	4398
	21st to end	Day	16% 7% 2 7% 5% 4 5% 4 6% 7% 37%	4837
June	1st to 10th	Day	23% 8% 3 7% 5% 5% 5% 4 5% 6% 30%	2660
	11th to 20th	Day	14% 6% 2 6% 5% 5% 5% 4 7% 8% 37%	2660
	21st to end	Day	20% 7% 3 6% 5% 4 4 6% 6% 7% 31%	2660
July	1st to 10th	Day	12% 7% 3 7% 6% 6% 5% 5% 6% 9% 35%	4440
	11th to 20th	Day	13% 6% 2 6% 5% 5% 5% 5% 7% 8% 38%	4440
	21st to end	Day	11% 6% 2 5% 4 4 4 4 7% 8% 44%	4814
August	1st to 10th	Day	15% 7% 3 7% 5% 5% 5% 4 6% 9% 35%	4423
	11th to 20th	Day	16% 7% 2 6% 4 4 4 4 7% 8% 38%	3953
	21st to end	Day	16% 5% 2 6% 4 4 5% 4 6% 10% 39%	4180
September	1st to 10th	Day	13% 6% 3 5% 5% 4 4 4 6% 8% 43%	2280
	11th to 20th	Day	13% 5% 1 5% 4 4 4 3 6% 7% 48%	2259
	21st to end	Day	18% 7% 2 5% 4 4 4 3 5% 7% 41%	2062
October	1st to 10th	Day	21% 8% 4 6% 4 3 4 4 4 7% 35%	1900
	11th to 20th	Day	22% 10% 3 8% 5% 5% 4 4 5% 6% 30%	1900
	21st to end	Day	27% 10% 2 8% 5% 5% 4 2 5% 5% 28%	1838
November	1st to 10th	Day	17% 9% 3 6% 6% 5% 4 4 6% 7% 33%	1671
	11th to 20th	Day	18% 13% 4 9% 5% 5% 4 3 4 5% 29%	1554
	21st to end	Day	22% 14% 4 9% 6% 4 5% 4 6% 5% 22%	1520
December	1st to 10th	Day	23% 16% 5% 9% 5% 6% 5% 4 4 5% 18%	1520
	11th to 20th	Day	21% 16% 4 9% 5% 4 4 3 4 5% 24%	1906
	21st to end	Day	28% 19% 5% 10% 5% 3 3 2 3 3 19%	2772
January	1st to 10th	Night	18% 18% 6% 11% 5% 4 4 3 4 5% 22%	4429
	11th to 20th	Night	14% 14% 6% 13% 8% 6% 5% 4 5% 5% 22%	4440
	21st to end	Night	17% 20% 7% 10% 5% 5% 3 3 4 5% 21%	4816
February	1st to 10th	Night	14% 14% 5% 11% 7% 6% 5% 4 5% 5% 24%	2470
	11th to 20th	Night	14% 13% 5% 10% 7% 5% 5% 3 4 6% 28%	2373
	21st to end	Night	17% 14% 4 9% 6% 4 4 3 5% 5% 30%	1884
March	1st to 10th	Night	20% 12% 4 8% 6% 4 4 3 4 4 30%	3724
	11th to 20th	Night	18% 16% 4 10% 5% 5% 3 3 4 6% 26%	3525
	21st to end	Night	15% 11% 3 8% 4 4 4 3 5% 5% 39%	3567
April	1st to 10th	Night	22% 11% 2 6% 6% 4 4 3 4 5% 32%	1900
	11th to 20th	Night	20% 9% 3 7% 5% 3 4 3 5% 5% 36%	1875
	21st to end	Night	22% 9% 3 7% 4 4 4 3 4 6% 35%	1786
May	1st to 10th	Night	21% 8% 3 8% 5% 4 4 4 6% 7% 29%	2514
	11th to 20th	Night	21% 8% 3 7% 3 5% 4 3 5% 6% 36%	2495
	21st to end	Night	16% 6% 3 6% 5% 4 5% 5% 6% 7% 38%	2738
June	1st to 10th	Night	16% 7% 2 6% 6% 4 5% 4 8% 9% 32%	1520
	11th to 20th	Night	15% 6% 3 5% 4 4 4 3 6% 7% 40%	1520
	21st to end	Night	19% 8% 2 6% 4 4 5% 4 6% 7% 35%	1520
July	1st to 10th	Night	13% 8% 3 8% 5% 6% 6% 4 5% 7% 35%	2520
	11th to 20th	Night	13% 6% 2 6% 5% 4 4 4 6% 8% 42%	2520
	21st to end	Night	11% 6% 3 6% 4 5% 5% 4 6% 7% 43%	2739
August	1st to 10th	Night	12% 8% 3 7% 5% 4 4 4 6% 8% 38%	2506
	11th to 20th	Night	15% 7% 2 6% 5% 3 5% 3 5% 7% 41%	2839
	21st to end	Night	12% 6% 2 7% 5% 5% 5% 4 6% 8% 40%	3476
September	1st to 10th	Night	11% 5% 2 7% 5% 5% 5% 3 5% 7% 45%	1900
	11th to 20th	Night	14% 5% 1 5% 4 3 3 3 5% 7% 49%	1920
	21st to end	Night	17% 6% 2 5% 4 4 4 3 4 6% 44%	2116
October	1st to 10th	Night	19% 7% 2 6% 4 4 5% 3 5% 6% 38%	2280
	11th to 20th	Night	20% 9% 2 7% 6% 5% 4 3 5% 5% 33%	2280
	21st to end	Night	23% 9% 3 9% 6% 4 4 3 5% 6% 29%	2585
November	1st to 10th	Night	20% 10% 2 8% 5% 4 3 3 5% 6% 34%	2407
	11th to 20th	Night	19% 10% 3 8% 5% 5% 5% 4 5% 5% 31%	2622
	21st to end	Night	22% 13% 4 9% 5% 4 4 3 5% 6% 24%	2660
December	1st to 10th	Night	22% 16% 6% 9% 6% 5% 4 4 4 4 19%	2660
	11th to 20th	Night	23% 14% 4 8% 5% 3 4 3 4 4 26%	3288
	21st to end	Night	31% 17% 4 10% 4 3 4 2 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% 6% 13% 15% 8% 1	1701
	21st to end	Day	59% 6% 10% 14% 10% 1	1570
March	1st to 10th	Day	58% 7% 10% 15% 8% 1	3119
	11th to 20th	Day	54% 9% 12% 15% 8% 1	3432
	21st to end	Day	43% 7% 9% 23% 16% 3	4064
April	1st to 10th	Day	54% 5% 8% 19% 12% 3	2280
	11th to 20th	Day	50% 5% 8% 21% 14% 2	2254
	21st to end	Day	55% 6% 9% 14% 13% 4	2410
May	1st to 10th	Day	49% 9% 11% 20% 9% 2	4440
	11th to 20th	Day	47% 10% 14% 18% 9% 2	4402
	21st to end	Day	42% 9% 13% 21% 13% 1	4837
June	1st to 10th	Day	52% 7% 12% 17% 10% 1	2660
	11th to 20th	Day	42% 9% 13% 22% 12% 2	2660
	21st to end	Day	48% 10% 14% 18% 9% 1	2660
July	1st to 10th	Day	44% 7% 15% 23% 11%	4370
	11th to 20th	Day	40% 8% 16% 29% 8%	4365
	21st to end	Day	34% 9% 15% 31% 10%	4661
August	1st to 10th	Day	45% 7% 16% 22% 9%	4409
	11th to 20th	Day	41% 8% 17% 28% 7%	3992
	21st to end	Day	40% 6% 18% 23% 11% 1	4180
September	1st to 10th	Day	37% 8% 16% 26% 12%	2280
	11th to 20th	Day	34% 8% 14% 31% 13% 1	2259
	21st to end	Day	42% 8% 15% 26% 10%	2062
October	1st to 10th	Day	48% 6% 12% 23% 10% 1	1900
	11th to 20th	Day	54% 8% 13% 18% 6% 1	1900
	21st to end	Day	59% 5% 14% 16% 6% 1	1838
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% 11% 19% 8%	2375
	21st to end	Night	55% 7% 9% 18% 11%	1884
March	1st to 10th	Night	54% 7% 11% 17% 9% 2	3734
	11th to 20th	Night	57% 8% 12% 14% 7% 2	3526
	21st to end	Night	44% 6% 8% 23% 15% 3	3567
April	1st to 10th	Night	52% 6% 9% 17% 13% 2	1900
	11th to 20th	Night	48% 7% 8% 21% 14% 1	1875
	21st to end	Night	50% 5% 10% 17% 15% 3	1786
May	1st to 10th	Night	49% 11% 10% 17% 9% 3	2520
	11th to 20th	Night	44% 12% 11% 18% 12% 2	2496
	21st to end	Night	41% 11% 12% 18% 17% 2	2739
June	1st to 10th	Night	46% 9% 15% 20% 10% 1	1520
	11th to 20th	Night	40% 8% 11% 22% 17% 2	1520
	21st to end	Night	45% 9% 14% 18% 13% 1	1520
July	1st to 10th	Night	46% 7% 16% 18% 12% 1	2480
	11th to 20th	Night	39% 6% 16% 31% 8%	2472
	21st to end	Night	38% 8% 16% 23% 14%	2651
August	1st to 10th	Night	43% 7% 16% 25% 8%	2496
	11th to 20th	Night	42% 6% 16% 29% 6%	2866
	21st to end	Night	40% 8% 16% 23% 12% 2	3476
September	1st to 10th	Night	38% 8% 13% 26% 15% 1	1900
	11th to 20th	Night	34% 7% 13% 33% 11% 1	1920
	21st to end	Night	39% 8% 13% 29% 11%	2116
October	1st to 10th	Night	45% 8% 12% 23% 12% 1	2280
	11th to 20th	Night	51% 8% 12% 20% 8%	2280
	21st to end	Night	56% 7% 13% 16% 8% 1	2585
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% 17% 39% 18% 2	299
	21st to end	Day	27% 12% 34% 24% 3	382
March	1st to 10th	Day	23% 11% 33% 25% 7%	460
	11th to 20th	Day	19% 20% 32% 24% 5% 1	460
	21st to end	Day	27% 14% 30% 17% 9% 2	506
April	1st to 10th	Day	25% 17% 31% 19% 8% 1	460
	11th to 20th	Day	27% 19% 23% 17% 11% 3	452
	21st to end	Day	25% 16% 30% 17% 9% 2	460
May	1st to 10th	Day	22% 11% 31% 25% 8% 3	463
	11th to 20th	Day	17% 14% 31% 22% 13% 3	487
	21st to end	Day	17% 12% 32% 24% 13% 3	529
June	1st to 10th	Day	23% 9% 28% 27% 10% 3	490
	11th to 20th	Day	14% 12% 29% 26% 17% 3	490
	21st to end	Day	21% 13% 24% 25% 14% 3	490
July	1st to 10th	Day	13% 6% 25% 33% 17% 6%	485
	11th to 20th	Day	11% 7% 30% 29% 19% 4	484
	21st to end	Day	14% 5% 26% 32% 18% 5%	532
August	1st to 10th	Day	15% 6% 22% 32% 21% 5%	486
	11th to 20th	Day	14% 5% 19% 30% 23% 9%	479
	21st to end	Day	13% 7% 26% 27% 18% 9%	539
September	1st to 10th	Day	16% 8% 26% 22% 17% 11%	490
	11th to 20th	Day	12% 6% 21% 22% 24% 15%	490
	21st to end	Day	18% 10% 26% 23% 17% 7%	490
October	1st to 10th	Day	23% 11% 26% 19% 15% 5%	490
	11th to 20th	Day	24% 14% 31% 21% 9% 1	490
	21st to end	Day	31% 11% 24% 25% 8%	420
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% 25% 5%	743
	21st to end	Night	22% 11% 32% 31% 4	628
March	1st to 10th	Night	23% 9% 33% 28% 6%	760
	11th to 20th	Night	23% 13% 33% 26% 5%	760
	21st to end	Night	21% 11% 30% 29% 9%	836
April	1st to 10th	Night	26% 10% 31% 28% 5%	760
	11th to 20th	Night	22% 14% 30% 25% 8% 1	751
	21st to end	Night	25% 11% 27% 29% 8% 1	646
May	1st to 10th	Night	23% 7% 29% 29% 9% 2	380
	11th to 20th	Night	22% 8% 27% 34% 9% 1	374
	21st to end	Night	14% 6% 34% 32% 13%	411
June	1st to 10th	Night	16% 4 28% 42% 11%	380
	11th to 20th	Night	14% 6% 28% 38% 12% 1	380
	21st to end	Night	20% 4 27% 32% 16% 1	380
July	1st to 10th	Night	8% 4 26% 44% 18%	370
	11th to 20th	Night	10% 5% 23% 43% 18% 1	368
	21st to end	Night	13% 3 20% 45% 19% 1	416
August	1st to 10th	Night	13% 4 18% 45% 19% 1	378
	11th to 20th	Night	12% 4 18% 35% 28% 2	592
	21st to end	Night	13% 5% 23% 37% 19% 2	836
September	1st to 10th	Night	13% 4 25% 38% 19% 1	760
	11th to 20th	Night	16% 5% 17% 33% 25% 3	760
	21st to end	Night	19% 6% 24% 28% 21% 2	760
October	1st to 10th	Night	22% 6% 28% 28% 16% 1	760
	11th to 20th	Night	24% 7% 31% 27% 10% 1	760
	21st to end	Night	26% 9% 28% 30% 6%	805
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 2024-10-21 02:20:00. Version ac07

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