Whiteway
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Whiteway clear sky chart from 2005-11-06 to 2026-01-02.

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	22% 17% 6% 10% 5% 4 4 3 4 5% 21%	127349
	Night	22% 18% 6% 11% 5% 4 4 3 4 5% 19%	124260
Transparency	Day	65% 5% 11% 13% 5%	130830
	Night	68% 6% 10% 12% 4	128893
Seeing	Day	34% 20% 27% 14% 4 1	19725
	Night	33% 19% 28% 16% 4	26382

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% 25% 11% 15% 4 3 2 2 3 4 13%	3183
	11th to 20th	Day	17% 24% 10% 16% 5% 3 3 2 3 3 14%	3562
	21st to end	Day	12% 17% 10% 21% 6% 4 4 2 3 5% 16%	3982
February	1st to 10th	Day	21% 15% 8% 13% 8% 5% 5% 3 4 4 14%	1723
	11th to 20th	Day	20% 21% 7% 12% 6% 4 4 3 4 4 13%	1773
	21st to end	Day	14% 18% 8% 18% 7% 5% 3 3 4 5% 15%	1650
March	1st to 10th	Day	22% 17% 7% 13% 7% 4 4 3 3 4 16%	4508
	11th to 20th	Day	21% 19% 9% 13% 5% 4 3 2 3 4 18%	4980
	21st to end	Day	22% 19% 9% 14% 5% 4 3 2 3 4 14%	5467
April	1st to 10th	Day	19% 19% 6% 12% 7% 4 4 3 4 4 17%	2420
	11th to 20th	Day	23% 19% 4 9% 5% 4 3 2 4 4 23%	2571
	21st to end	Day	22% 20% 5% 8% 5% 4 4 3 4 5% 20%	2600
May	1st to 10th	Day	25% 23% 6% 8% 4 3 3 2 4 5% 18%	5885
	11th to 20th	Day	23% 18% 4 9% 4 4 3 3 4 5% 22%	6399
	21st to end	Day	21% 20% 5% 9% 5% 4 3 3 5% 5% 20%	7428
June	1st to 10th	Day	28% 17% 4 10% 6% 4 3 3 4 4 18%	3000
	11th to 20th	Day	25% 13% 4 7% 5% 5% 4 3 5% 6% 24%	3000
	21st to end	Day	25% 14% 4 7% 5% 4 4 3 5% 6% 23%	3000
July	1st to 10th	Day	31% 13% 3 7% 4 3 4 3 5% 6% 21%	6800
	11th to 20th	Day	20% 11% 4 8% 5% 5% 4 4 5% 5% 29%	6741
	21st to end	Day	20% 9% 3 7% 5% 4 5% 4 5% 7% 31%	6927
August	1st to 10th	Day	26% 12% 4 7% 4 4 4 3 5% 7% 23%	4345
	11th to 20th	Day	18% 12% 4 9% 5% 5% 4 3 6% 6% 28%	4176
	21st to end	Day	21% 10% 3 7% 4 4 4 3 5% 8% 30%	4675
September	1st to 10th	Day	18% 11% 4 7% 4 4 5% 3 6% 6% 32%	2389
	11th to 20th	Day	23% 9% 3 7% 4 5% 5% 3 5% 6% 30%	2200
	21st to end	Day	19% 11% 3 6% 5% 5% 4 4 5% 7% 32%	2200
October	1st to 10th	Day	21% 14% 4 7% 5% 4 4 3 4 6% 30%	2105
	11th to 20th	Day	22% 17% 4 9% 5% 4 5% 3 4 5% 22%	1940
	21st to end	Day	23% 18% 3 9% 5% 5% 4 2 5% 6% 19%	1980
November	1st to 10th	Day	21% 19% 4 9% 5% 5% 3 3 4 5% 23%	1826
	11th to 20th	Day	23% 20% 5% 9% 6% 4 3 3 4 6% 17%	1680
	21st to end	Day	24% 23% 6% 8% 6% 3 3 2 4 4 17%	1601
December	1st to 10th	Day	18% 18% 5% 10% 5% 5% 5% 4 5% 7% 19%	2360
	11th to 20th	Day	16% 23% 8% 10% 4 4 3 2 3 4 22%	2698
	21st to end	Day	21% 23% 9% 14% 5% 4 3 2 3 4 12%	3575
January	1st to 10th	Night	17% 26% 11% 12% 6% 5% 4 2 3 3 12%	6805
	11th to 20th	Night	15% 22% 10% 17% 6% 5% 4 3 3 4 12%	6341
	21st to end	Night	11% 14% 10% 21% 8% 5% 5% 3 4 4 17%	6996
February	1st to 10th	Night	21% 17% 8% 16% 7% 5% 3 2 4 4 13%	2675
	11th to 20th	Night	22% 20% 7% 13% 7% 4 3 3 3 5% 13%	2512
	21st to end	Night	14% 19% 7% 14% 6% 6% 5% 3 4 5% 17%	1980
March	1st to 10th	Night	22% 16% 8% 15% 5% 4 4 3 4 4 16%	5332
	11th to 20th	Night	20% 17% 10% 15% 7% 4 4 3 4 4 14%	4979
	21st to end	Night	27% 20% 8% 12% 4 3 3 3 3 3 13%	5465
April	1st to 10th	Night	23% 21% 8% 10% 4 3 3 2 3 4 19%	1975
	11th to 20th	Night	24% 18% 6% 9% 3 4 3 3 3 4 23%	1778
	21st to end	Night	23% 23% 6% 8% 4 3 4 2 3 3 20%	1800
May	1st to 10th	Night	33% 21% 7% 7% 3 3 3 2 3 4 16%	4075
	11th to 20th	Night	26% 17% 4 10% 5% 4 4 3 4 4 19%	3511
	21st to end	Night	26% 21% 5% 7% 4 4 4 3 4 5% 18%	3468
June	1st to 10th	Night	28% 18% 4 8% 4 4 3 3 3 5% 18%	1400
	11th to 20th	Night	26% 14% 4 8% 5% 5% 4 3 6% 6% 21%	1400
	21st to end	Night	28% 14% 4 8% 4 4 4 3 4 7% 21%	1400
July	1st to 10th	Night	38% 15% 4 6% 4 3 3 2 3 6% 16%	3179
	11th to 20th	Night	29% 15% 3 7% 4 4 4 3 5% 6% 21%	3224
	21st to end	Night	24% 13% 3 7% 4 4 3 3 4 5% 29%	3948
August	1st to 10th	Night	25% 13% 3 7% 4 3 4 4 6% 7% 23%	2813
	11th to 20th	Night	25% 12% 4 6% 3 4 3 2 5% 6% 29%	2881
	21st to end	Night	28% 9% 3 7% 4 4 4 3 4 6% 27%	3234
September	1st to 10th	Night	22% 11% 3 7% 4 4 4 3 5% 7% 30%	2007
	11th to 20th	Night	24% 13% 3 8% 4 4 4 3 4 6% 27%	2200
	21st to end	Night	20% 12% 4 8% 5% 4 4 3 4 6% 31%	2200
October	1st to 10th	Night	24% 14% 3 8% 4 4 3 3 4 6% 28%	2295
	11th to 20th	Night	25% 15% 3 8% 4 4 3 4 5% 6% 23%	2455
	21st to end	Night	26% 18% 4 8% 4 5% 4 3 3 4 21%	2860
November	1st to 10th	Night	24% 21% 4 7% 5% 3 3 3 4 5% 22%	2689
	11th to 20th	Night	23% 21% 6% 8% 5% 4 4 3 4 5% 18%	2940
	21st to end	Night	19% 23% 5% 9% 5% 5% 4 3 4 5% 18%	3017
December	1st to 10th	Night	17% 21% 6% 11% 5% 5% 4 3 3 4 20%	5050
	11th to 20th	Night	19% 23% 7% 12% 6% 4 3 2 3 3 17%	5731
	21st to end	Night	19% 21% 8% 12% 6% 4 4 3 3 4 15%	7645

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	76% 4 4 9% 5% 1	3184
	11th to 20th	Day	74% 7% 6% 8% 4	3591
	21st to end	Day	70% 5% 8% 10% 6%	3982
February	1st to 10th	Day	74% 5% 9% 7% 5% 1	1723
	11th to 20th	Day	74% 5% 8% 8% 3 1	1780
	21st to end	Day	70% 7% 9% 7% 6% 1	1650
March	1st to 10th	Day	73% 5% 8% 9% 4 1	4512
	11th to 20th	Day	71% 6% 8% 9% 4 2	4980
	21st to end	Day	76% 4 6% 9% 4 1	5467
April	1st to 10th	Day	72% 5% 7% 11% 5%	2420
	11th to 20th	Day	67% 4 8% 12% 9% 1	2571
	21st to end	Day	68% 5% 8% 11% 7% 1	2600
May	1st to 10th	Day	70% 5% 9% 10% 5% 1	5897
	11th to 20th	Day	65% 5% 11% 14% 5%	6403
	21st to end	Day	67% 6% 9% 15% 4	7428
June	1st to 10th	Day	72% 5% 7% 11% 4 1	3000
	11th to 20th	Day	62% 6% 12% 14% 6%	3000
	21st to end	Day	63% 7% 10% 15% 6%	3000
July	1st to 10th	Day	64% 6% 12% 15% 3	6725
	11th to 20th	Day	57% 6% 15% 15% 6%	6659
	21st to end	Day	53% 6% 19% 19% 4	6730
August	1st to 10th	Day	61% 6% 13% 16% 4	4331
	11th to 20th	Day	56% 6% 14% 21% 3	4215
	21st to end	Day	53% 6% 16% 22% 3	4675
September	1st to 10th	Day	52% 7% 11% 21% 8%	2389
	11th to 20th	Day	55% 6% 12% 18% 9%	2200
	21st to end	Day	50% 8% 15% 20% 7% 1	2200
October	1st to 10th	Day	63% 6% 10% 15% 5%	3435
	11th to 20th	Day	61% 4 14% 14% 6%	3153
	21st to end	Day	67% 5% 8% 15% 5%	3191
November	1st to 10th	Day	65% 6% 13% 12% 4	1826
	11th to 20th	Day	69% 7% 8% 11% 4	1680
	21st to end	Day	71% 5% 10% 9% 4	1601
December	1st to 10th	Day	64% 5% 12% 14% 5%	2360
	11th to 20th	Day	68% 5% 11% 9% 7%	2697
	21st to end	Day	76% 5% 8% 9% 2	3575
January	1st to 10th	Night	76% 5% 6% 7% 4 1	6805
	11th to 20th	Night	73% 9% 8% 7% 3	6387
	21st to end	Night	67% 7% 10% 11% 4 1	6996
February	1st to 10th	Night	75% 4 8% 8% 4 1	2675
	11th to 20th	Night	73% 6% 8% 9% 3	2516
	21st to end	Night	66% 8% 9% 11% 6%	1980
March	1st to 10th	Night	71% 5% 8% 10% 5% 1	5341
	11th to 20th	Night	74% 5% 8% 7% 4 1	4980
	21st to end	Night	76% 5% 6% 10% 3	5465
April	1st to 10th	Night	70% 4 7% 11% 6% 1	1975
	11th to 20th	Night	66% 4 8% 13% 7% 1	1778
	21st to end	Night	70% 5% 7% 11% 7%	1800
May	1st to 10th	Night	74% 5% 7% 12% 2	4080
	11th to 20th	Night	68% 6% 8% 12% 6%	3512
	21st to end	Night	68% 7% 9% 12% 4	3469
June	1st to 10th	Night	69% 5% 10% 12% 4	1400
	11th to 20th	Night	62% 8% 12% 14% 4	1400
	21st to end	Night	63% 6% 13% 15% 4	1400
July	1st to 10th	Night	71% 5% 10% 12% 3	3146
	11th to 20th	Night	64% 5% 10% 18% 2	3182
	21st to end	Night	57% 5% 14% 21% 3	3831
August	1st to 10th	Night	59% 6% 16% 15% 4	2802
	11th to 20th	Night	57% 5% 15% 19% 4	2908
	21st to end	Night	57% 6% 13% 21% 3	3233
September	1st to 10th	Night	53% 7% 11% 20% 7% 1	2007
	11th to 20th	Night	58% 6% 14% 14% 8% 1	2200
	21st to end	Night	53% 6% 14% 19% 8%	2200
October	1st to 10th	Night	61% 6% 14% 15% 4	3750
	11th to 20th	Night	59% 5% 15% 13% 7%	3991
	21st to end	Night	62% 5% 11% 16% 6%	4610
November	1st to 10th	Night	65% 6% 13% 12% 5%	2689
	11th to 20th	Night	68% 7% 10% 10% 3	2940
	21st to end	Night	67% 7% 11% 10% 4	3017
December	1st to 10th	Night	67% 5% 8% 14% 6%	5050
	11th to 20th	Night	73% 4 11% 8% 3	5733
	21st to end	Night	72% 6% 8% 10% 3	7645

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	33% 26% 27% 10% 3	403
	11th to 20th	Day	33% 24% 28% 12% 3 1	400
	21st to end	Day	33% 27% 27% 10% 3	440
February	1st to 10th	Day	32% 24% 29% 12% 2	400
	11th to 20th	Day	36% 32% 22% 9% 2	396
	21st to end	Day	31% 28% 30% 9% 2	331
March	1st to 10th	Day	37% 27% 27% 7% 2	400
	11th to 20th	Day	32% 25% 26% 13% 3 2	400
	21st to end	Day	37% 24% 27% 8% 4 1	440
April	1st to 10th	Day	40% 24% 24% 9% 3	526
	11th to 20th	Day	38% 22% 24% 12% 3	689
	21st to end	Day	36% 23% 24% 13% 3 1	700
May	1st to 10th	Day	38% 20% 23% 12% 4 1	703
	11th to 20th	Day	29% 19% 30% 16% 5% 1	724
	21st to end	Day	35% 16% 30% 14% 3 1	790
June	1st to 10th	Day	42% 15% 25% 13% 4 1	730
	11th to 20th	Day	34% 17% 28% 15% 5% 1	730
	21st to end	Day	34% 15% 30% 15% 5% 1	730
July	1st to 10th	Day	31% 16% 31% 15% 6% 1	720
	11th to 20th	Day	28% 15% 32% 20% 5% 1	718
	21st to end	Day	31% 17% 27% 19% 7%	795
August	1st to 10th	Day	30% 13% 29% 19% 7% 2	725
	11th to 20th	Day	27% 15% 28% 21% 7% 1	717
	21st to end	Day	30% 15% 27% 21% 7% 1	803
September	1st to 10th	Day	27% 13% 28% 24% 7% 1	555
	11th to 20th	Day	34% 20% 25% 17% 4	420
	21st to end	Day	27% 20% 33% 15% 5%	420
October	1st to 10th	Day	28% 19% 32% 16% 5%	420
	11th to 20th	Day	33% 22% 25% 14% 5% 1	420
	21st to end	Day	36% 23% 23% 13% 3 2	462
November	1st to 10th	Day	39% 21% 26% 11% 3	425
	11th to 20th	Day	40% 22% 20% 14% 3 1	430
	21st to end	Day	43% 23% 23% 9% 2	430
December	1st to 10th	Day	35% 22% 28% 11% 4	430
	11th to 20th	Day	38% 27% 25% 8% 2	430
	21st to end	Day	31% 23% 29% 12% 4 1	473
January	1st to 10th	Night	32% 24% 29% 11% 3	906
	11th to 20th	Night	34% 22% 28% 12% 4 1	900
	21st to end	Night	31% 24% 29% 15% 2	990
February	1st to 10th	Night	32% 26% 30% 10% 2	900
	11th to 20th	Night	36% 25% 26% 11% 1	872
	21st to end	Night	26% 24% 30% 16% 4	660
March	1st to 10th	Night	27% 29% 29% 12% 3	792
	11th to 20th	Night	26% 20% 27% 21% 6%	600
	21st to end	Night	34% 22% 27% 14% 2	660
April	1st to 10th	Night	34% 22% 26% 14% 4	600
	11th to 20th	Night	32% 19% 31% 14% 3	594
	21st to end	Night	36% 17% 27% 16% 3 1	600
May	1st to 10th	Night	34% 14% 30% 18% 4	600
	11th to 20th	Night	31% 15% 28% 20% 6%	592
	21st to end	Night	34% 17% 27% 19% 4	649
June	1st to 10th	Night	37% 15% 26% 18% 4	600
	11th to 20th	Night	33% 14% 28% 20% 5%	600
	21st to end	Night	34% 11% 32% 17% 5% 1	600
July	1st to 10th	Night	31% 12% 31% 22% 3 1	586
	11th to 20th	Night	31% 12% 36% 19% 3	582
	21st to end	Night	30% 12% 33% 19% 5%	656
August	1st to 10th	Night	29% 9% 31% 24% 7%	598
	11th to 20th	Night	28% 11% 30% 24% 7%	592
	21st to end	Night	30% 9% 32% 23% 6%	660
September	1st to 10th	Night	27% 9% 32% 26% 6%	600
	11th to 20th	Night	34% 12% 29% 20% 5% 1	600
	21st to end	Night	29% 15% 28% 23% 5%	600
October	1st to 10th	Night	30% 14% 30% 21% 5%	652
	11th to 20th	Night	35% 16% 27% 16% 6%	765
	21st to end	Night	36% 17% 25% 17% 4	1001
November	1st to 10th	Night	35% 22% 25% 15% 3	930
	11th to 20th	Night	37% 18% 24% 16% 4	950
	21st to end	Night	35% 24% 27% 11% 3	950
December	1st to 10th	Night	34% 22% 26% 15% 4	950
	11th to 20th	Night	39% 26% 23% 9% 2	950
	21st to end	Night	31% 22% 28% 14% 3 1	1045

Page generated at 2025-12-30 02:14:08. Version ac07

Copyright © 2025 Attilla Danko.