Irving Nature Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Irving Nature Park clear sky chart from 2005-11-06 to 2025-11-03.

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	21% 10% 3 7% 4 4 4 3 5% 7% 32%	126789
	Night	21% 11% 3 7% 4 4 4 3 5% 6% 32%	123351
Transparency	Day	35% 37% 7% 13% 7% 1	130322
	Night	35% 36% 6% 14% 8% 1	127905
Seeing	Day	26% 14% 29% 22% 8% 1	17834
	Night	27% 13% 28% 23% 8% 1	25609

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	15% 13% 3 8% 6% 5% 5% 4 5% 5% 31%	3157
	11th to 20th	Day	14% 14% 5% 10% 4 3 4 3 3 5% 36%	3525
	21st to end	Day	12% 9% 3 7% 5% 5% 5% 4 6% 7% 37%	4466
February	1st to 10th	Day	17% 13% 3 6% 5% 5% 4 4 6% 6% 31%	1800
	11th to 20th	Day	15% 11% 3 8% 5% 4 4 4 6% 8% 32%	1753
	21st to end	Day	11% 12% 4 8% 5% 5% 4 4 5% 7% 37%	1595
March	1st to 10th	Day	25% 10% 3 10% 5% 4 4 3 4 5% 28%	4769
	11th to 20th	Day	21% 11% 3 6% 5% 4 5% 4 5% 7% 29%	4980
	21st to end	Day	28% 10% 4 7% 4 4 4 3 5% 5% 25%	5466
April	1st to 10th	Day	23% 11% 3 6% 5% 4 4 3 5% 6% 29%	2317
	11th to 20th	Day	21% 9% 3 6% 4 4 3 3 4 7% 36%	2572
	21st to end	Day	23% 7% 2 8% 4 4 3 3 5% 7% 33%	2600
May	1st to 10th	Day	26% 13% 3 8% 6% 5% 4 3 5% 5% 21%	5886
	11th to 20th	Day	22% 8% 3 7% 4 4 4 3 5% 6% 32%	6175
	21st to end	Day	22% 10% 4 8% 5% 4 4 4 5% 7% 27%	6984
June	1st to 10th	Day	23% 9% 2 7% 4 5% 5% 3 6% 7% 29%	3000
	11th to 20th	Day	23% 7% 3 7% 4 4 3 3 4 7% 35%	3000
	21st to end	Day	30% 7% 2 6% 4 4 4 3 5% 7% 28%	3000
July	1st to 10th	Day	20% 11% 4 9% 5% 5% 5% 4 6% 8% 25%	6820
	11th to 20th	Day	23% 11% 3 6% 4 4 4 3 5% 9% 28%	6782
	21st to end	Day	17% 9% 3 6% 4 4 4 4 7% 9% 33%	6435
August	1st to 10th	Day	24% 10% 3 7% 4 4 4 3 5% 7% 28%	4235
	11th to 20th	Day	18% 7% 2 6% 5% 4 5% 3 7% 9% 33%	4175
	21st to end	Day	13% 6% 2 6% 4 4 4 3 6% 8% 44%	4652
September	1st to 10th	Day	17% 6% 2 5% 4 3 4 4 5% 8% 43%	2383
	11th to 20th	Day	19% 6% 2 4 3 3 4 3 4 6% 47%	2200
	21st to end	Day	21% 5% 2 5% 4 3 4 2 5% 6% 44%	2200
October	1st to 10th	Day	18% 6% 2 6% 4 4 4 3 5% 6% 42%	2025
	11th to 20th	Day	19% 7% 2 7% 4 4 4 3 5% 6% 39%	2000
	21st to end	Day	21% 8% 2 7% 5% 4 5% 3 5% 6% 34%	2110
November	1st to 10th	Day	23% 8% 2 7% 4 4 3 3 4 6% 35%	1714
	11th to 20th	Day	21% 6% 2 6% 4 4 3 3 7% 6% 38%	1600
	21st to end	Day	23% 10% 2 6% 5% 3 4 3 5% 7% 31%	1600
December	1st to 10th	Day	23% 9% 2 6% 3 4 3 4 5% 6% 34%	2610
	11th to 20th	Day	25% 11% 3 7% 4 3 3 2 2 4 36%	2727
	21st to end	Day	22% 11% 3 4 3 3 4 3 6% 7% 36%	3476
January	1st to 10th	Night	13% 13% 4 8% 6% 5% 5% 4 5% 7% 31%	6808
	11th to 20th	Night	17% 10% 4 9% 4 5% 4 3 5% 6% 33%	6331
	21st to end	Night	13% 11% 3 7% 4 4 4 4 5% 7% 38%	6490
February	1st to 10th	Night	19% 11% 3 7% 4 4 4 4 6% 7% 31%	2600
	11th to 20th	Night	17% 12% 3 8% 4 5% 6% 4 5% 6% 30%	2533
	21st to end	Night	16% 11% 3 8% 4 4 5% 4 5% 5% 35%	2032
March	1st to 10th	Night	26% 11% 4 8% 4 5% 4 3 4 4 27%	5057
	11th to 20th	Night	21% 13% 4 7% 5% 4 4 3 5% 6% 28%	4979
	21st to end	Night	31% 10% 3 6% 3 4 4 3 3 5% 29%	5466
April	1st to 10th	Night	23% 11% 3 7% 5% 5% 4 3 5% 4 31%	2079
	11th to 20th	Night	25% 8% 3 5% 4 4 4 3 5% 7% 33%	1778
	21st to end	Night	26% 8% 2 7% 4 4 4 4 5% 5% 31%	1800
May	1st to 10th	Night	29% 11% 4 6% 4 4 4 3 5% 6% 24%	4054
	11th to 20th	Night	24% 9% 2 6% 4 4 5% 4 5% 6% 31%	3730
	21st to end	Night	22% 12% 4 7% 4 4 4 3 4 6% 30%	3948
June	1st to 10th	Night	28% 11% 2 5% 4 4 4 3 6% 8% 25%	1406
	11th to 20th	Night	23% 8% 3 7% 4 4 3 4 4 7% 33%	1400
	21st to end	Night	32% 10% 3 6% 5% 3 4 3 4 5% 25%	1400
July	1st to 10th	Night	25% 13% 5% 9% 5% 5% 4 4 5% 5% 19%	3160
	11th to 20th	Night	24% 19% 3 6% 4 3 4 4 4 6% 23%	3193
	21st to end	Night	19% 11% 3 7% 4 4 4 4 4 8% 33%	4369
August	1st to 10th	Night	27% 14% 3 6% 4 3 4 3 4 6% 26%	2915
	11th to 20th	Night	19% 12% 3 8% 4 4 5% 3 6% 7% 30%	2872
	21st to end	Night	13% 10% 3 7% 4 3 4 3 5% 7% 42%	3244
September	1st to 10th	Night	20% 7% 2 5% 4 3 3 3 5% 7% 41%	2014
	11th to 20th	Night	19% 7% 2 5% 3 2 3 3 4 7% 44%	2200
	21st to end	Night	21% 7% 2 5% 4 3 3 2 5% 6% 42%	2200
October	1st to 10th	Night	21% 6% 2 5% 3 4 4 3 4 7% 42%	2375
	11th to 20th	Night	19% 7% 2 6% 4 3 4 3 4 6% 40%	2400
	21st to end	Night	23% 9% 3 7% 5% 3 4 3 4 6% 34%	2730
November	1st to 10th	Night	22% 7% 2 6% 4 3 4 4 5% 5% 38%	2629
	11th to 20th	Night	21% 8% 2 6% 5% 4 4 4 5% 6% 35%	2800
	21st to end	Night	22% 9% 3 6% 4 4 3 4 5% 7% 34%	2800
December	1st to 10th	Night	19% 11% 4 7% 4 3 4 3 5% 6% 36%	4580
	11th to 20th	Night	26% 10% 2 5% 3 3 3 3 4 5% 36%	5477
	21st to end	Night	22% 12% 3 6% 4 4 3 3 4 6% 33%	7502

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	44% 25% 11% 15% 4	3158
	11th to 20th	Day	38% 25% 6% 21% 8% 1	3555
	21st to end	Day	37% 27% 6% 11% 15% 3	4466
February	1st to 10th	Day	22% 62% 3 7% 4 2	1800
	11th to 20th	Day	21% 61% 4 8% 6% 1	1761
	21st to end	Day	18% 61% 4 10% 5% 2	1595
March	1st to 10th	Day	46% 28% 5% 9% 9% 3	4773
	11th to 20th	Day	42% 28% 10% 13% 6% 1	4980
	21st to end	Day	50% 27% 3 11% 9% 1	5466
April	1st to 10th	Day	22% 61% 3 7% 5% 2	2317
	11th to 20th	Day	21% 62% 4 9% 4 1	2572
	21st to end	Day	20% 62% 4 8% 5% 1	2600
May	1st to 10th	Day	49% 28% 7% 14% 3	5897
	11th to 20th	Day	41% 28% 10% 15% 4 1	6179
	21st to end	Day	45% 28% 7% 11% 9%	6984
June	1st to 10th	Day	20% 62% 5% 9% 4	3000
	11th to 20th	Day	20% 61% 4 10% 5%	3000
	21st to end	Day	20% 60% 4 9% 7% 1	3000
July	1st to 10th	Day	49% 25% 7% 12% 7%	6745
	11th to 20th	Day	44% 25% 7% 18% 5% 1	6701
	21st to end	Day	37% 26% 10% 19% 8%	6251
August	1st to 10th	Day	39% 36% 5% 14% 5%	4222
	11th to 20th	Day	31% 37% 11% 14% 6%	4214
	21st to end	Day	25% 35% 8% 17% 13% 1	4652
September	1st to 10th	Day	17% 57% 5% 13% 7% 1	2383
	11th to 20th	Day	19% 58% 5% 11% 7% 1	2200
	21st to end	Day	14% 57% 4 14% 10% 1	2200
October	1st to 10th	Day	32% 34% 6% 22% 6%	3298
	11th to 20th	Day	28% 35% 5% 24% 8%	3240
	21st to end	Day	27% 35% 12% 14% 12% 1	3386
November	1st to 10th	Day	25% 56% 6% 10% 3	1714
	11th to 20th	Day	23% 56% 6% 7% 6% 2	1600
	21st to end	Day	25% 57% 6% 9% 4	1600
December	1st to 10th	Day	32% 35% 10% 17% 5%	2610
	11th to 20th	Day	39% 30% 7% 10% 10% 3	2727
	21st to end	Day	36% 25% 8% 16% 12% 2	3476
January	1st to 10th	Night	41% 25% 7% 22% 4 1	6808
	11th to 20th	Night	41% 25% 7% 19% 7% 1	6376
	21st to end	Night	35% 27% 4 18% 12% 3	6490
February	1st to 10th	Night	22% 62% 3 6% 7% 1	2600
	11th to 20th	Night	21% 61% 3 9% 6% 1	2536
	21st to end	Night	20% 62% 2 7% 7% 2	2032
March	1st to 10th	Night	48% 28% 2 8% 10% 3	5066
	11th to 20th	Night	43% 28% 11% 11% 6% 1	4980
	21st to end	Night	49% 27% 2 13% 8% 1	5466
April	1st to 10th	Night	22% 62% 2 6% 6% 2	2079
	11th to 20th	Night	22% 62% 4 8% 5%	1778
	21st to end	Night	22% 62% 4 6% 6% 1	1800
May	1st to 10th	Night	49% 28% 8% 10% 5%	4060
	11th to 20th	Night	42% 27% 9% 17% 4 2	3731
	21st to end	Night	43% 27% 10% 14% 5% 1	3949
June	1st to 10th	Night	21% 62% 4 9% 4	1406
	11th to 20th	Night	19% 61% 5% 10% 4 1	1400
	21st to end	Night	23% 59% 3 8% 6% 1	1400
July	1st to 10th	Night	55% 24% 5% 8% 6%	3125
	11th to 20th	Night	52% 24% 5% 12% 6%	3151
	21st to end	Night	39% 25% 9% 16% 10% 1	4239
August	1st to 10th	Night	44% 36% 4 12% 4	2903
	11th to 20th	Night	35% 36% 11% 13% 5%	2899
	21st to end	Night	29% 35% 5% 17% 13% 1	3243
September	1st to 10th	Night	18% 57% 4 13% 7% 1	2014
	11th to 20th	Night	20% 56% 6% 11% 7%	2200
	21st to end	Night	17% 56% 3 15% 7% 1	2200
October	1st to 10th	Night	31% 35% 8% 18% 8% 1	3882
	11th to 20th	Night	24% 35% 6% 21% 14%	3899
	21st to end	Night	30% 35% 8% 17% 11% 1	4404
November	1st to 10th	Night	24% 55% 6% 10% 5%	2629
	11th to 20th	Night	23% 56% 4 9% 7% 1	2800
	21st to end	Night	25% 57% 5% 6% 7% 1	2800
December	1st to 10th	Night	32% 35% 5% 21% 7%	4580
	11th to 20th	Night	37% 30% 5% 15% 11% 2	5478
	21st to end	Night	41% 25% 7% 15% 10% 3	7502

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	29% 22% 27% 21% 2	200
	11th to 20th	Day	30% 22% 31% 14% 3 1	200
	21st to end	Day	19% 20% 38% 20% 2 1	440
February	1st to 10th	Day	26% 22% 32% 15% 4 1	400
	11th to 20th	Day	23% 25% 34% 15% 3	396
	21st to end	Day	18% 24% 35% 20% 4	387
March	1st to 10th	Day	24% 21% 34% 19% 2	500
	11th to 20th	Day	23% 20% 34% 18% 5%	500
	21st to end	Day	29% 17% 33% 15% 6% 1	550
April	1st to 10th	Day	34% 20% 29% 13% 3 1	500
	11th to 20th	Day	26% 17% 33% 18% 5% 1	492
	21st to end	Day	26% 17% 30% 19% 7% 1	500
May	1st to 10th	Day	27% 15% 33% 20% 5% 1	503
	11th to 20th	Day	26% 10% 30% 23% 9% 2	659
	21st to end	Day	31% 11% 27% 22% 7% 2	790
June	1st to 10th	Day	29% 9% 28% 23% 10% 1	730
	11th to 20th	Day	27% 10% 27% 24% 11% 1	730
	21st to end	Day	34% 6% 26% 23% 9% 2	730
July	1st to 10th	Day	27% 7% 28% 27% 9% 1	720
	11th to 20th	Day	29% 7% 20% 29% 12% 2	706
	21st to end	Day	26% 8% 30% 27% 8% 1	576
August	1st to 10th	Day	21% 6% 26% 33% 13% 1	526
	11th to 20th	Day	26% 5% 22% 34% 12% 2	519
	21st to end	Day	21% 10% 26% 27% 14% 2	583
September	1st to 10th	Day	21% 6% 28% 32% 12% 1	530
	11th to 20th	Day	24% 8% 28% 26% 11% 3	530
	21st to end	Day	22% 8% 32% 27% 10% 2	530
October	1st to 10th	Day	23% 11% 25% 26% 13% 3	434
	11th to 20th	Day	23% 14% 27% 26% 9% 1	420
	21st to end	Day	26% 15% 33% 20% 5% 1	462
November	1st to 10th	Day	27% 16% 29% 20% 6% 1	401
	11th to 20th	Day	28% 18% 31% 18% 5%	400
	21st to end	Day	31% 20% 31% 16% 2 1	400
December	1st to 10th	Day	29% 18% 32% 18% 4	400
	11th to 20th	Day	29% 28% 30% 10% 4	270
	21st to end	Day	28% 25% 27% 15% 5%	220
January	1st to 10th	Night	26% 20% 32% 18% 4	900
	11th to 20th	Night	27% 19% 32% 17% 4	809
	21st to end	Night	20% 21% 37% 16% 5%	880
February	1st to 10th	Night	26% 21% 33% 17% 3	800
	11th to 20th	Night	25% 23% 33% 16% 2 1	783
	21st to end	Night	23% 17% 34% 22% 4	660
March	1st to 10th	Night	24% 17% 35% 21% 2	800
	11th to 20th	Night	23% 15% 33% 24% 5%	800
	21st to end	Night	25% 14% 32% 20% 7% 1	880
April	1st to 10th	Night	31% 13% 32% 20% 4	699
	11th to 20th	Night	28% 9% 33% 25% 5%	594
	21st to end	Night	30% 9% 30% 23% 7% 1	600
May	1st to 10th	Night	30% 6% 29% 27% 8% 1	600
	11th to 20th	Night	30% 7% 25% 28% 9% 1	592
	21st to end	Night	28% 9% 28% 27% 7% 1	649
June	1st to 10th	Night	35% 5% 19% 30% 10%	406
	11th to 20th	Night	26% 7% 24% 32% 12% 1	400
	21st to end	Night	40% 3 12% 34% 12% 1	400
July	1st to 10th	Night	32% 4 16% 35% 12% 1	390
	11th to 20th	Night	33% 5% 17% 28% 15% 1	388
	21st to end	Night	29% 7% 17% 32% 15%	623
August	1st to 10th	Night	23% 3 18% 39% 16% 1	598
	11th to 20th	Night	29% 6% 15% 34% 14% 2	592
	21st to end	Night	20% 5% 22% 33% 18% 2	660
September	1st to 10th	Night	25% 4 24% 32% 14% 2	614
	11th to 20th	Night	24% 7% 20% 28% 19% 2	800
	21st to end	Night	26% 6% 25% 27% 13% 2	800
October	1st to 10th	Night	24% 8% 26% 29% 13% 2	800
	11th to 20th	Night	24% 12% 29% 23% 12% 1	800
	21st to end	Night	28% 16% 30% 22% 4	880
November	1st to 10th	Night	26% 13% 30% 22% 8% 1	822
	11th to 20th	Night	25% 19% 27% 21% 7% 1	900
	21st to end	Night	28% 21% 28% 18% 5%	900
December	1st to 10th	Night	32% 17% 32% 16% 3	900
	11th to 20th	Night	30% 23% 31% 12% 2	900
	21st to end	Night	30% 20% 29% 17% 4	990

Page generated at 2025-10-31 03:02:38. Version ac07

Copyright © 2025 Attilla Danko.