Wheelock
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wheelock clear sky chart from 2005-11-06 to 2024-09-14.

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% 12% 4 10% 6% 5% 5% 4 5% 6% 27%	100915
	Night	16% 13% 5% 11% 6% 5% 4 3 5% 6% 26%	97004
Transparency	Day	55% 7% 11% 17% 8% 1	100673
	Night	57% 8% 11% 16% 8% 1	96866
Seeing	Day	26% 18% 27% 18% 8% 2	14574
	Night	24% 15% 25% 26% 10% 1	23430

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% 16% 8% 19% 8% 5% 4 3 4 4 16%	2517
	11th to 20th	Day	12% 14% 7% 20% 13% 6% 5% 3 4 3 15%	2520
	21st to end	Day	13% 20% 9% 14% 6% 6% 5% 3 3 4 17%	2772
February	1st to 10th	Day	13% 15% 7% 14% 10% 5% 5% 3 4 4 19%	1630
	11th to 20th	Day	12% 12% 9% 17% 9% 7% 5% 3 5% 3 19%	1848
	21st to end	Day	13% 16% 5% 14% 9% 5% 5% 3 5% 5% 21%	1570
March	1st to 10th	Day	19% 18% 5% 11% 7% 5% 4 3 3 4 20%	3116
	11th to 20th	Day	14% 18% 7% 12% 6% 4 5% 3 3 5% 23%	3276
	21st to end	Day	17% 13% 5% 13% 5% 3 4 2 4 4 30%	4124
April	1st to 10th	Day	20% 16% 4 9% 5% 4 4 2 3 5% 27%	2280
	11th to 20th	Day	19% 11% 4 8% 5% 5% 4 3 4 5% 32%	2273
	21st to end	Day	22% 12% 4 9% 5% 4 3 3 5% 6% 26%	2470
May	1st to 10th	Day	25% 13% 4 7% 5% 4 5% 4 4 5% 25%	4128
	11th to 20th	Day	17% 10% 3 9% 7% 7% 5% 4 6% 7% 25%	4398
	21st to end	Day	13% 8% 3 7% 5% 5% 6% 5% 7% 9% 33%	4837
June	1st to 10th	Day	25% 9% 2 7% 5% 4 6% 3 6% 6% 26%	2660
	11th to 20th	Day	16% 8% 3 6% 5% 5% 5% 4 6% 7% 34%	2660
	21st to end	Day	21% 10% 3 7% 6% 6% 6% 4 5% 7% 25%	2660
July	1st to 10th	Day	13% 7% 3 7% 5% 5% 6% 5% 8% 11% 30%	4440
	11th to 20th	Day	11% 7% 3 7% 6% 6% 6% 6% 9% 11% 29%	4440
	21st to end	Day	16% 8% 3 7% 5% 5% 5% 4 6% 8% 34%	4814
August	1st to 10th	Day	15% 8% 3 9% 7% 6% 6% 5% 7% 7% 27%	4361
	11th to 20th	Day	16% 9% 2 9% 6% 5% 6% 5% 8% 9% 25%	4018
	21st to end	Day	12% 8% 3 7% 5% 5% 6% 5% 6% 8% 36%	4180
September	1st to 10th	Day	14% 7% 3 6% 4 4 5% 4 6% 7% 41%	2280
	11th to 20th	Day	16% 8% 2 6% 4 2 4 3 4 8% 44%	2055
	21st to end	Day	17% 7% 3 6% 5% 4 6% 3 6% 8% 35%	1980
October	1st to 10th	Day	24% 11% 3 8% 5% 4 4 3 6% 6% 27%	1962
	11th to 20th	Day	15% 14% 3 8% 5% 4 5% 4 5% 7% 30%	1706
	21st to end	Day	23% 20% 5% 7% 6% 4 3 3 3 4 23%	1782
November	1st to 10th	Day	14% 16% 4 10% 5% 4 4 3 6% 6% 28%	1671
	11th to 20th	Day	16% 15% 7% 12% 5% 5% 6% 3 4 5% 22%	1710
	21st to end	Day	18% 15% 5% 12% 6% 4 4 4 5% 6% 21%	1579
December	1st to 10th	Day	19% 19% 7% 15% 6% 4 4 3 3 4 16%	1520
	11th to 20th	Day	20% 17% 8% 10% 5% 4 2 2 5% 4 23%	1906
	21st to end	Day	22% 18% 7% 16% 6% 4 4 3 3 3 15%	2772
January	1st to 10th	Night	11% 18% 7% 20% 9% 5% 5% 3 4 4 14%	4429
	11th to 20th	Night	11% 15% 6% 20% 12% 7% 5% 3 4 4 14%	4440
	21st to end	Night	15% 19% 7% 16% 6% 6% 4 3 4 4 16%	4884
February	1st to 10th	Night	12% 16% 6% 14% 10% 6% 6% 4 4 5% 18%	2546
	11th to 20th	Night	11% 13% 6% 14% 10% 7% 6% 5% 4 5% 20%	2218
	21st to end	Night	12% 13% 4 12% 8% 7% 4 3 5% 5% 26%	1884
March	1st to 10th	Night	20% 17% 5% 7% 6% 6% 4 3 4 5% 24%	3724
	11th to 20th	Night	14% 16% 7% 11% 6% 5% 4 3 4 4 26%	3682
	21st to end	Night	16% 17% 6% 12% 7% 3 3 2 3 3 28%	3506
April	1st to 10th	Night	20% 12% 3 9% 6% 5% 4 4 5% 5% 27%	1900
	11th to 20th	Night	19% 11% 4 8% 6% 4 3 3 5% 5% 32%	1856
	21st to end	Night	19% 12% 3 7% 5% 4 3 4 6% 6% 31%	1710
May	1st to 10th	Night	24% 12% 3 8% 5% 4 4 3 5% 6% 26%	2834
	11th to 20th	Night	20% 9% 3 9% 5% 4 5% 4 6% 6% 31%	2501
	21st to end	Night	15% 6% 2 7% 5% 5% 5% 4 6% 8% 38%	2738
June	1st to 10th	Night	22% 10% 3 7% 5% 4 4 3 5% 8% 29%	1520
	11th to 20th	Night	17% 6% 2 6% 5% 4 4 5% 7% 7% 36%	1520
	21st to end	Night	21% 8% 3 6% 5% 5% 5% 4 6% 6% 30%	1520
July	1st to 10th	Night	11% 8% 3 7% 6% 6% 6% 6% 7% 9% 32%	2520
	11th to 20th	Night	16% 7% 2 7% 4 4 5% 4 6% 8% 37%	2520
	21st to end	Night	14% 7% 2 7% 5% 5% 5% 4 6% 7% 37%	2739
August	1st to 10th	Night	18% 9% 3 7% 5% 5% 4 4 6% 7% 31%	2538
	11th to 20th	Night	14% 8% 4 8% 5% 5% 6% 4 6% 8% 33%	2806
	21st to end	Night	13% 7% 3 7% 5% 5% 5% 4 6% 8% 37%	3476
September	1st to 10th	Night	14% 6% 2 6% 4 4 4 4 4 8% 43%	1900
	11th to 20th	Night	15% 7% 2 5% 3 3 4 3 5% 6% 47%	1982
	21st to end	Night	18% 8% 3 4 3 3 4 3 5% 7% 42%	1980
October	1st to 10th	Night	21% 10% 3 8% 5% 4 4 3 5% 7% 32%	1996
	11th to 20th	Night	17% 12% 3 8% 6% 5% 4 4 5% 7% 30%	2254
	21st to end	Night	22% 15% 4 9% 5% 4 4 3 4 6% 23%	2574
November	1st to 10th	Night	16% 13% 4 10% 5% 5% 4 4 5% 4 30%	2407
	11th to 20th	Night	17% 12% 6% 13% 5% 4 4 3 4 6% 27%	2470
	21st to end	Night	17% 13% 6% 14% 7% 5% 4 3 5% 5% 21%	2598
December	1st to 10th	Night	19% 19% 7% 14% 8% 5% 5% 4 4 4 13%	2660
	11th to 20th	Night	20% 16% 7% 14% 8% 5% 4 2 4 4 16%	3288
	21st to end	Night	23% 16% 5% 17% 6% 5% 4 3 4 3 15%	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% 6% 10% 11% 2	2518
	11th to 20th	Day	70% 9% 8% 8% 4 1	2520
	21st to end	Day	69% 6% 10% 9% 5% 1	2772
February	1st to 10th	Day	68% 5% 8% 11% 6% 1	1630
	11th to 20th	Day	68% 5% 9% 12% 5% 1	1857
	21st to end	Day	65% 5% 8% 12% 8% 3	1570
March	1st to 10th	Day	68% 6% 7% 9% 9% 2	3119
	11th to 20th	Day	62% 7% 9% 11% 9% 3	3276
	21st to end	Day	58% 5% 6% 15% 15% 2	4124
April	1st to 10th	Day	61% 4 8% 16% 9% 2	2280
	11th to 20th	Day	53% 7% 9% 19% 12% 1	2273
	21st to end	Day	59% 6% 8% 16% 8% 3	2470
May	1st to 10th	Day	57% 9% 10% 17% 6% 1	4142
	11th to 20th	Day	52% 12% 14% 14% 7% 1	4402
	21st to end	Day	42% 11% 14% 23% 9% 1	4837
June	1st to 10th	Day	56% 8% 11% 17% 8%	2660
	11th to 20th	Day	47% 8% 11% 21% 12% 2	2660
	21st to end	Day	55% 10% 10% 18% 7% 1	2660
July	1st to 10th	Day	44% 7% 16% 23% 10%	4370
	11th to 20th	Day	44% 9% 16% 26% 5%	4365
	21st to end	Day	47% 8% 11% 25% 10%	4661
August	1st to 10th	Day	52% 8% 14% 19% 7%	4347
	11th to 20th	Day	52% 8% 15% 20% 5%	4057
	21st to end	Day	43% 8% 16% 19% 13% 2	4180
September	1st to 10th	Day	41% 8% 11% 28% 12% 1	2280
	11th to 20th	Day	39% 6% 12% 29% 14% 1	2055
	21st to end	Day	44% 8% 14% 21% 11% 1	1980
October	1st to 10th	Day	56% 6% 11% 17% 9% 1	1962
	11th to 20th	Day	50% 8% 17% 19% 6%	1706
	21st to end	Day	66% 5% 9% 12% 7% 2	1782
November	1st to 10th	Day	54% 7% 12% 17% 9% 1	1671
	11th to 20th	Day	62% 8% 9% 10% 9% 2	1710
	21st to end	Day	62% 7% 14% 13% 3	1579
December	1st to 10th	Day	73% 5% 9% 10% 3	1520
	11th to 20th	Day	64% 5% 8% 15% 8% 1	1906
	21st to end	Day	74% 6% 5% 9% 5%	2772
January	1st to 10th	Night	71% 8% 12% 8% 2	4429
	11th to 20th	Night	71% 9% 10% 7% 3 1	4440
	21st to end	Night	70% 6% 10% 9% 4 1	4884
February	1st to 10th	Night	66% 7% 9% 11% 6% 1	2546
	11th to 20th	Night	64% 7% 9% 13% 7% 1	2220
	21st to end	Night	59% 7% 10% 15% 8% 2	1884
March	1st to 10th	Night	62% 5% 10% 14% 7% 2	3734
	11th to 20th	Night	60% 8% 8% 14% 10% 1	3683
	21st to end	Night	61% 5% 6% 13% 14% 2	3506
April	1st to 10th	Night	57% 6% 10% 16% 11% 1	1900
	11th to 20th	Night	53% 6% 9% 21% 11%	1856
	21st to end	Night	51% 9% 10% 16% 12% 2	1710
May	1st to 10th	Night	57% 9% 9% 16% 7% 1	2840
	11th to 20th	Night	50% 11% 14% 16% 8% 1	2502
	21st to end	Night	40% 12% 16% 19% 13% 1	2739
June	1st to 10th	Night	53% 9% 9% 20% 9% 1	1520
	11th to 20th	Night	44% 9% 16% 19% 10% 3	1520
	21st to end	Night	50% 11% 13% 18% 8% 1	1520
July	1st to 10th	Night	46% 9% 14% 20% 9%	2480
	11th to 20th	Night	42% 8% 14% 28% 8%	2472
	21st to end	Night	44% 10% 12% 25% 9%	2651
August	1st to 10th	Night	51% 8% 14% 22% 5%	2528
	11th to 20th	Night	48% 8% 18% 17% 9%	2833
	21st to end	Night	43% 7% 16% 22% 12%	3476
September	1st to 10th	Night	38% 9% 15% 27% 10%	1900
	11th to 20th	Night	37% 7% 12% 31% 12% 1	1982
	21st to end	Night	40% 8% 14% 25% 11% 2	1980
October	1st to 10th	Night	52% 7% 12% 18% 10% 1	1996
	11th to 20th	Night	52% 9% 13% 20% 6%	2254
	21st to end	Night	61% 7% 11% 12% 7% 1	2574
November	1st to 10th	Night	54% 7% 12% 17% 8% 1	2407
	11th to 20th	Night	57% 7% 10% 16% 8% 2	2470
	21st to end	Night	64% 6% 13% 13% 5%	2598
December	1st to 10th	Night	74% 6% 8% 9% 2	2660
	11th to 20th	Night	71% 5% 8% 9% 6%	3288
	21st to end	Night	73% 6% 7% 11% 3	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	24% 19% 33% 18% 5%	180
	11th to 20th	Day	32% 24% 29% 11% 4 1	180
	21st to end	Day	24% 24% 30% 16% 6%	198
February	1st to 10th	Day	33% 30% 26% 7% 2 1	242
	11th to 20th	Day	27% 28% 29% 13% 3	456
	21st to end	Day	33% 19% 28% 16% 4	382
March	1st to 10th	Day	32% 19% 28% 18% 3	460
	11th to 20th	Day	34% 20% 27% 14% 4 1	460
	21st to end	Day	33% 20% 25% 13% 7% 2	506
April	1st to 10th	Day	36% 19% 23% 15% 5% 2	460
	11th to 20th	Day	32% 25% 21% 14% 7% 2	452
	21st to end	Day	35% 19% 26% 12% 7% 1	460
May	1st to 10th	Day	34% 21% 23% 14% 6% 2	463
	11th to 20th	Day	24% 17% 32% 19% 6% 3	487
	21st to end	Day	19% 19% 34% 18% 8% 2	529
June	1st to 10th	Day	30% 18% 27% 16% 8% 2	490
	11th to 20th	Day	21% 16% 31% 20% 9% 3	490
	21st to end	Day	26% 17% 31% 17% 7% 1	490
July	1st to 10th	Day	19% 12% 31% 26% 10% 2	485
	11th to 20th	Day	14% 14% 32% 25% 12% 2	484
	21st to end	Day	17% 12% 34% 25% 10% 2	532
August	1st to 10th	Day	17% 13% 26% 25% 16% 2	486
	11th to 20th	Day	21% 10% 28% 23% 14% 5%	479
	21st to end	Day	17% 16% 24% 24% 13% 6%	539
September	1st to 10th	Day	17% 14% 26% 22% 15% 6%	490
	11th to 20th	Day	19% 13% 23% 17% 19% 9%	463
	21st to end	Day	18% 13% 27% 22% 14% 6%	450
October	1st to 10th	Day	28% 14% 23% 19% 12% 5%	450
	11th to 20th	Day	24% 18% 26% 19% 9% 2	403
	21st to end	Day	37% 17% 23% 17% 7%	396
November	1st to 10th	Day	29% 18% 19% 25% 8%	365
	11th to 20th	Day	27% 22% 25% 19% 5% 1	370
	21st to end	Day	33% 16% 28% 19% 4	239
December	1st to 10th	Day	32% 21% 26% 13% 8%	180
	11th to 20th	Day	35% 22% 30% 12% 2	180
	21st to end	Day	35% 21% 26% 16% 3	198
January	1st to 10th	Night	23% 22% 31% 20% 4	760
	11th to 20th	Night	28% 19% 29% 20% 4	760
	21st to end	Night	20% 20% 29% 26% 5%	836
February	1st to 10th	Night	20% 20% 35% 21% 4	760
	11th to 20th	Night	22% 21% 33% 20% 3	743
	21st to end	Night	22% 19% 32% 22% 4	628
March	1st to 10th	Night	25% 19% 28% 24% 3 1	760
	11th to 20th	Night	28% 18% 26% 20% 7%	760
	21st to end	Night	27% 18% 26% 21% 8% 1	836
April	1st to 10th	Night	28% 17% 26% 23% 6%	760
	11th to 20th	Night	25% 20% 26% 22% 8%	732
	21st to end	Night	27% 15% 30% 23% 5%	570
May	1st to 10th	Night	28% 14% 28% 22% 7% 1	570
	11th to 20th	Night	22% 12% 27% 30% 8% 1	380
	21st to end	Night	19% 12% 22% 35% 12%	411
June	1st to 10th	Night	26% 9% 22% 32% 9% 1	380
	11th to 20th	Night	19% 8% 21% 35% 16%	380
	21st to end	Night	23% 6% 21% 37% 12% 1	380
July	1st to 10th	Night	16% 6% 18% 44% 15% 1	370
	11th to 20th	Night	15% 4 21% 40% 18% 2	368
	21st to end	Night	14% 5% 17% 45% 19%	416
August	1st to 10th	Night	17% 4 14% 41% 24%	397
	11th to 20th	Night	16% 6% 22% 33% 20% 2	573
	21st to end	Night	17% 6% 19% 32% 23% 3	836
September	1st to 10th	Night	16% 9% 21% 34% 18% 2	760
	11th to 20th	Night	18% 10% 18% 28% 23% 3	736
	21st to end	Night	21% 10% 23% 25% 19% 2	720
October	1st to 10th	Night	27% 13% 18% 25% 15% 1	720
	11th to 20th	Night	24% 13% 23% 26% 13% 2	720
	21st to end	Night	32% 13% 26% 23% 6%	792
November	1st to 10th	Night	24% 17% 24% 26% 8% 1	740
	11th to 20th	Night	24% 17% 28% 21% 8% 2	760
	21st to end	Night	27% 20% 25% 20% 7% 1	760
December	1st to 10th	Night	30% 20% 27% 19% 4	760
	11th to 20th	Night	29% 18% 27% 22% 4	760
	21st to end	Night	31% 18% 26% 23% 3	836

Page generated at 2024-09-11 10:00:01. Version ac07

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