Lenore and Walter Hawley Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lenore and Walter Hawley Observatory clear sky chart from 2005-11-06 to 2024-04-10.

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% 7% 3 6% 5% 3 5% 5% 5% 7% 38%	82938
	Night	18% 7% 3 6% 5% 3 4 4 5% 6% 39%	85832
Transparency	Day	45% 6% 11% 21% 14% 2	82643
	Night	45% 6% 11% 22% 14% 2	85661
Seeing	Day	25% 17% 29% 19% 8% 2	14126
	Night	22% 14% 31% 25% 7% 1	23192

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	14% 7% 3 5% 6% 3 4 5% 5% 6% 41%	2517
	11th to 20th	Day	15% 7% 4 7% 6% 3 4 5% 5% 7% 37%	2520
	21st to end	Day	18% 11% 4 7% 6% 3 5% 4 5% 5% 33%	2772
February	1st to 10th	Day	17% 8% 2 6% 6% 4 6% 5% 5% 7% 34%	1716
	11th to 20th	Day	12% 8% 3 7% 6% 3 5% 5% 6% 8% 38%	1848
	21st to end	Day	17% 9% 4 7% 6% 3 4 3 5% 6% 36%	1570
March	1st to 10th	Day	23% 13% 4 7% 6% 3 5% 4 4 5% 28%	3116
	11th to 20th	Day	14% 8% 3 7% 6% 3 5% 6% 6% 7% 36%	3313
	21st to end	Day	20% 9% 3 7% 5% 3 4 4 5% 7% 33%	4060
April	1st to 10th	Day	19% 8% 4 6% 5% 3 4 5% 4 5% 38%	2270
	11th to 20th	Day	18% 6% 2 5% 6% 3 5% 5% 6% 7% 38%	2149
	21st to end	Day	22% 7% 3 6% 6% 3 5% 5% 4 5% 33%	2340
May	1st to 10th	Day	24% 8% 3 7% 5% 3 4 4 4 6% 33%	2340
	11th to 20th	Day	18% 6% 3 5% 5% 3 5% 5% 4 7% 39%	2392
	21st to end	Day	15% 6% 3 5% 5% 3 5% 4 6% 7% 41%	2725
June	1st to 10th	Day	20% 6% 3 7% 6% 4 5% 4 6% 8% 31%	2520
	11th to 20th	Day	17% 5% 3 6% 5% 3 5% 4 6% 9% 36%	2520
	21st to end	Day	19% 7% 3 6% 6% 4 5% 5% 5% 8% 33%	2520
July	1st to 10th	Day	15% 5% 3 4 6% 3 6% 5% 5% 9% 39%	2520
	11th to 20th	Day	12% 5% 3 6% 6% 3 6% 6% 6% 9% 37%	2520
	21st to end	Day	13% 4 3 6% 6% 4 5% 6% 6% 8% 37%	2744
August	1st to 10th	Day	11% 6% 3 5% 6% 4 6% 6% 7% 9% 39%	2399
	11th to 20th	Day	13% 6% 2 5% 6% 4 5% 6% 7% 9% 37%	2283
	21st to end	Day	12% 5% 2 4 5% 3 5% 5% 6% 8% 44%	2376
September	1st to 10th	Day	13% 5% 2 5% 5% 3 4 6% 6% 7% 45%	2160
	11th to 20th	Day	15% 5% 2 5% 3 2 2 3 5% 5% 53%	1991
	21st to end	Day	16% 5% 3 4 4 2 4 4 4 7% 47%	1980
October	1st to 10th	Day	23% 7% 2 5% 4 2 4 4 4 5% 38%	1980
	11th to 20th	Day	16% 6% 2 4 5% 3 5% 5% 4 7% 43%	1734
	21st to end	Day	25% 6% 3 5% 5% 3 4 4 4 6% 36%	1782
November	1st to 10th	Day	15% 6% 2 4 4 3 3 3 5% 6% 48%	1671
	11th to 20th	Day	19% 6% 2 5% 3 2 3 4 4 6% 46%	1710
	21st to end	Day	20% 7% 2 4 5% 3 4 5% 4 6% 40%	1682
December	1st to 10th	Day	18% 7% 4 7% 5% 3 4 4 5% 7% 34%	1520
	11th to 20th	Day	22% 7% 3 5% 4 3 4 4 4 4 40%	1906
	21st to end	Day	24% 11% 3 6% 6% 3 4 4 5% 5% 31%	2772
January	1st to 10th	Night	17% 8% 2 4 4 3 4 4 5% 5% 44%	4429
	11th to 20th	Night	14% 7% 3 8% 6% 4 5% 5% 6% 6% 36%	4440
	21st to end	Night	21% 13% 4 7% 6% 3 4 4 4 5% 30%	4884
February	1st to 10th	Night	15% 8% 3 6% 6% 3 5% 4 5% 7% 37%	2458
	11th to 20th	Night	12% 9% 3 6% 5% 3 5% 5% 7% 6% 39%	2218
	21st to end	Night	16% 8% 2 5% 5% 3 5% 5% 5% 7% 40%	1884
March	1st to 10th	Night	27% 9% 2 5% 4 3 4 4 5% 5% 32%	3724
	11th to 20th	Night	13% 9% 3 7% 7% 3 6% 5% 5% 6% 36%	3645
	21st to end	Night	24% 8% 3 5% 4 2 4 5% 6% 6% 33%	3567
April	1st to 10th	Night	20% 7% 3 6% 5% 3 5% 4 5% 6% 36%	1900
	11th to 20th	Night	20% 6% 3 5% 4 2 4 5% 4 5% 40%	1758
	21st to end	Night	21% 7% 2 5% 5% 3 4 5% 5% 6% 37%	1620
May	1st to 10th	Night	22% 8% 3 7% 7% 3 4 4 5% 6% 32%	1620
	11th to 20th	Night	18% 6% 3 7% 5% 4 5% 4 5% 6% 38%	1517
	21st to end	Night	16% 6% 4 6% 5% 2 4 6% 5% 7% 39%	1550
June	1st to 10th	Night	20% 7% 3 6% 6% 3 4 4 5% 6% 37%	1440
	11th to 20th	Night	20% 5% 3 5% 4 3 4 5% 6% 9% 36%	1440
	21st to end	Night	18% 5% 3 4 5% 3 5% 5% 5% 9% 38%	1440
July	1st to 10th	Night	15% 5% 2 4 5% 3 6% 5% 5% 8% 42%	1440
	11th to 20th	Night	13% 4 3 4 5% 2 6% 5% 7% 10% 40%	1440
	21st to end	Night	13% 5% 2 3 4 2 5% 5% 6% 9% 46%	1574
August	1st to 10th	Night	11% 5% 2 4 6% 3 5% 5% 6% 7% 46%	1522
	11th to 20th	Night	13% 6% 3 6% 5% 4 6% 5% 6% 8% 39%	1614
	21st to end	Night	14% 4 2 5% 4 2 4 3 5% 8% 48%	1980
September	1st to 10th	Night	12% 6% 3 5% 4 3 3 4 4 8% 50%	1800
	11th to 20th	Night	15% 6% 1 4 4 2 3 3 4 6% 53%	1968
	21st to end	Night	14% 5% 2 4 4 2 3 4 5% 7% 49%	1980
October	1st to 10th	Night	22% 6% 3 5% 4 4 3 4 4 5% 40%	1980
	11th to 20th	Night	16% 7% 2 4 4 3 5% 5% 5% 8% 41%	2224
	21st to end	Night	23% 7% 2 6% 5% 3 4 4 5% 6% 36%	2574
November	1st to 10th	Night	16% 6% 3 5% 6% 2 4 4 4 6% 45%	2407
	11th to 20th	Night	17% 5% 3 6% 4 2 4 3 5% 5% 45%	2470
	21st to end	Night	16% 6% 3 4 5% 3 4 4 5% 7% 41%	2493
December	1st to 10th	Night	20% 8% 4 6% 4 3 5% 4 4 6% 37%	2660
	11th to 20th	Night	20% 8% 3 5% 4 2 4 4 4 7% 39%	3288
	21st to end	Night	22% 10% 3 7% 5% 3 4 4 5% 5% 33%	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	42% 5% 11% 31% 10% 1	2518
	11th to 20th	Day	47% 6% 15% 21% 10% 1	2520
	21st to end	Day	51% 6% 10% 22% 9% 2	2772
February	1st to 10th	Day	49% 5% 12% 21% 10% 2	1716
	11th to 20th	Day	44% 6% 12% 21% 14% 3	1857
	21st to end	Day	49% 5% 9% 20% 14% 2	1570
March	1st to 10th	Day	59% 5% 9% 13% 11% 3	3119
	11th to 20th	Day	41% 10% 14% 19% 13% 3	3313
	21st to end	Day	49% 5% 7% 17% 17% 5%	4060
April	1st to 10th	Day	49% 5% 8% 19% 15% 4	2270
	11th to 20th	Day	45% 6% 11% 19% 17% 3	2149
	21st to end	Day	52% 6% 8% 15% 16% 3	2340
May	1st to 10th	Day	53% 5% 7% 20% 13% 2	2340
	11th to 20th	Day	45% 6% 9% 19% 18% 3	2396
	21st to end	Day	42% 7% 13% 22% 13% 3	2725
June	1st to 10th	Day	50% 7% 12% 19% 11%	2520
	11th to 20th	Day	44% 7% 10% 19% 16% 3	2520
	21st to end	Day	49% 8% 11% 19% 12% 1	2520
July	1st to 10th	Day	41% 7% 12% 22% 17% 2	2450
	11th to 20th	Day	42% 8% 14% 23% 12% 1	2445
	21st to end	Day	41% 8% 13% 22% 14% 2	2591
August	1st to 10th	Day	41% 9% 15% 22% 13% 1	2385
	11th to 20th	Day	41% 9% 14% 23% 12% 2	2283
	21st to end	Day	36% 8% 12% 23% 18% 2	2376
September	1st to 10th	Day	37% 6% 14% 24% 17% 2	2160
	11th to 20th	Day	35% 5% 8% 26% 24% 2	1991
	21st to end	Day	37% 6% 9% 25% 20% 3	1980
October	1st to 10th	Day	47% 6% 9% 21% 14% 3	1980
	11th to 20th	Day	39% 7% 12% 29% 11% 2	1734
	21st to end	Day	50% 4 10% 20% 12% 3	1782
November	1st to 10th	Day	39% 4 13% 25% 17% 2	1671
	11th to 20th	Day	41% 4 11% 22% 20% 3	1710
	21st to end	Day	46% 4 16% 20% 12% 1	1682
December	1st to 10th	Day	49% 6% 14% 17% 12% 1	1520
	11th to 20th	Day	47% 6% 11% 17% 16% 4	1906
	21st to end	Day	55% 6% 12% 17% 10% 1	2772
January	1st to 10th	Night	41% 6% 13% 27% 11% 3	4429
	11th to 20th	Night	44% 8% 13% 22% 10% 3	4440
	21st to end	Night	56% 5% 10% 17% 10% 1	4884
February	1st to 10th	Night	46% 7% 12% 20% 13% 2	2458
	11th to 20th	Night	44% 6% 10% 21% 16% 3	2220
	21st to end	Night	43% 6% 11% 24% 13% 4	1884
March	1st to 10th	Night	54% 5% 10% 19% 11% 3	3734
	11th to 20th	Night	45% 9% 11% 19% 15% 2	3646
	21st to end	Night	48% 6% 7% 14% 19% 6%	3567
April	1st to 10th	Night	48% 5% 10% 18% 16% 3	1900
	11th to 20th	Night	45% 5% 8% 23% 18% 1	1758
	21st to end	Night	47% 6% 11% 19% 14% 4	1620
May	1st to 10th	Night	53% 5% 8% 19% 12% 3	1620
	11th to 20th	Night	47% 7% 11% 18% 15% 3	1518
	21st to end	Night	45% 7% 13% 22% 10% 2	1551
June	1st to 10th	Night	49% 6% 11% 21% 12% 1	1440
	11th to 20th	Night	45% 8% 13% 19% 13% 2	1440
	21st to end	Night	42% 10% 13% 21% 13% 1	1440
July	1st to 10th	Night	39% 10% 14% 22% 13% 2	1400
	11th to 20th	Night	37% 10% 16% 25% 12%	1392
	21st to end	Night	33% 9% 16% 30% 12% 2	1486
August	1st to 10th	Night	36% 10% 13% 25% 15% 1	1512
	11th to 20th	Night	42% 10% 14% 21% 13% 1	1614
	21st to end	Night	35% 6% 12% 27% 18% 1	1980
September	1st to 10th	Night	35% 6% 13% 26% 19% 1	1800
	11th to 20th	Night	33% 5% 10% 28% 22% 2	1968
	21st to end	Night	35% 6% 10% 29% 18% 2	1980
October	1st to 10th	Night	47% 5% 10% 22% 12% 3	1980
	11th to 20th	Night	40% 7% 13% 27% 12% 1	2224
	21st to end	Night	49% 5% 12% 21% 11% 2	2574
November	1st to 10th	Night	41% 5% 10% 23% 18% 3	2407
	11th to 20th	Night	42% 4 10% 24% 18% 3	2470
	21st to end	Night	43% 5% 14% 25% 12% 1	2493
December	1st to 10th	Night	49% 6% 11% 22% 11% 1	2660
	11th to 20th	Night	45% 6% 13% 17% 17% 1	3288
	21st to end	Night	53% 5% 10% 23% 10% 1	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	28% 26% 25% 18% 3	180
	11th to 20th	Day	31% 23% 32% 11% 2 2	180
	21st to end	Day	22% 30% 30% 15% 4	198
February	1st to 10th	Day	32% 26% 27% 13% 2	321
	11th to 20th	Day	32% 28% 25% 14% 2	456
	21st to end	Day	31% 23% 29% 14% 3	382
March	1st to 10th	Day	31% 18% 33% 16% 2	460
	11th to 20th	Day	32% 26% 26% 11% 3 1	460
	21st to end	Day	32% 20% 28% 12% 5% 2	506
April	1st to 10th	Day	35% 18% 28% 11% 5% 2	457
	11th to 20th	Day	30% 22% 28% 13% 6% 2	412
	21st to end	Day	32% 18% 29% 13% 5% 2	420
May	1st to 10th	Day	33% 20% 26% 14% 5% 2	423
	11th to 20th	Day	20% 21% 36% 16% 4 2	447
	21st to end	Day	20% 15% 33% 22% 8% 1	485
June	1st to 10th	Day	22% 14% 36% 19% 8% 1	450
	11th to 20th	Day	19% 17% 32% 22% 8% 2	450
	21st to end	Day	18% 16% 32% 22% 7% 3	450
July	1st to 10th	Day	18% 9% 31% 27% 12% 3	445
	11th to 20th	Day	16% 8% 32% 29% 11% 4	444
	21st to end	Day	13% 10% 33% 30% 11% 3	488
August	1st to 10th	Day	13% 10% 30% 29% 15% 3	446
	11th to 20th	Day	16% 10% 29% 26% 13% 5%	439
	21st to end	Day	13% 10% 32% 26% 15% 5%	495
September	1st to 10th	Day	18% 10% 24% 24% 16% 7%	450
	11th to 20th	Day	18% 15% 28% 16% 14% 8%	450
	21st to end	Day	18% 12% 30% 22% 12% 5%	450
October	1st to 10th	Day	29% 12% 22% 22% 10% 4	450
	11th to 20th	Day	22% 14% 31% 20% 10% 2	401
	21st to end	Day	33% 13% 27% 21% 7%	396
November	1st to 10th	Day	24% 17% 26% 24% 9% 1	365
	11th to 20th	Day	33% 17% 25% 19% 5% 1	370
	21st to end	Day	31% 18% 28% 16% 5% 1	342
December	1st to 10th	Day	27% 26% 26% 17% 4	180
	11th to 20th	Day	34% 21% 32% 11% 3	180
	21st to end	Day	35% 18% 28% 13% 5% 1	198
January	1st to 10th	Night	23% 21% 34% 20% 3	760
	11th to 20th	Night	28% 19% 32% 18% 3	760
	21st to end	Night	22% 19% 36% 20% 3	836
February	1st to 10th	Night	22% 17% 37% 21% 3	760
	11th to 20th	Night	23% 21% 36% 19% 2	743
	21st to end	Night	25% 21% 29% 22% 3	628
March	1st to 10th	Night	27% 18% 34% 18% 3	760
	11th to 20th	Night	25% 20% 30% 20% 4	760
	21st to end	Night	27% 18% 32% 19% 4	836
April	1st to 10th	Night	27% 18% 31% 20% 4	760
	11th to 20th	Night	25% 18% 32% 19% 6%	694
	21st to end	Night	27% 15% 33% 21% 3	540
May	1st to 10th	Night	26% 12% 36% 20% 6% 1	540
	11th to 20th	Night	21% 15% 33% 27% 5%	456
	21st to end	Night	21% 8% 30% 33% 8%	389
June	1st to 10th	Night	19% 8% 34% 29% 9% 1	360
	11th to 20th	Night	18% 11% 26% 35% 9% 1	360
	21st to end	Night	18% 8% 28% 38% 8%	360
July	1st to 10th	Night	16% 4 28% 41% 11% 1	350
	11th to 20th	Night	13% 5% 23% 42% 15% 2	348
	21st to end	Night	14% 4 27% 40% 13% 1	394
August	1st to 10th	Night	16% 4 23% 43% 14%	448
	11th to 20th	Night	16% 9% 27% 33% 14% 2	550
	21st to end	Night	16% 6% 23% 36% 17% 2	792
September	1st to 10th	Night	14% 6% 30% 31% 17% 1	720
	11th to 20th	Night	17% 8% 29% 28% 17% 2	720
	21st to end	Night	17% 9% 30% 28% 14% 2	720
October	1st to 10th	Night	25% 12% 23% 28% 11% 1	720
	11th to 20th	Night	20% 11% 33% 25% 11% 1	720
	21st to end	Night	26% 15% 29% 24% 6%	792
November	1st to 10th	Night	20% 14% 31% 26% 8% 1	740
	11th to 20th	Night	23% 18% 30% 22% 7% 1	760
	21st to end	Night	24% 18% 29% 22% 6%	760
December	1st to 10th	Night	26% 18% 33% 19% 4	760
	11th to 20th	Night	27% 19% 32% 19% 3	760
	21st to end	Night	27% 19% 32% 20% 3	836

Page generated at 2024-04-07 09:28:13. Version ac07

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