Clearing off Thompson Road
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Clearing off Thompson Road clear sky chart from 2005-11-06 to 2026-03-03.

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	16% 12% 4 9% 5% 4 4 3 5% 6% 30%	132052
	Night	15% 13% 5% 11% 5% 4 4 3 4 6% 28%	129075
Transparency	Day	54% 3 10% 21% 10% 1	135631
	Night	57% 3 10% 19% 10% 1	133585
Seeing	Day	25% 14% 31% 19% 8% 3	16384
	Night	24% 12% 29% 25% 10% 1	25357

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% 16% 6% 13% 6% 5% 4 3 5% 5% 23%	4661
	11th to 20th	Day	9% 24% 10% 17% 8% 8% 5% 3 3 3 10%	4812
	21st to end	Day	10% 17% 8% 19% 7% 6% 5% 4 4 4 16%	5780
February	1st to 10th	Day	12% 19% 6% 17% 9% 5% 3 3 3 4 19%	1890
	11th to 20th	Day	13% 15% 8% 14% 7% 5% 4 3 4 5% 22%	1843
	21st to end	Day	15% 19% 7% 13% 7% 4 4 2 4 5% 20%	1583
March	1st to 10th	Day	18% 16% 5% 11% 6% 5% 3 2 4 5% 25%	4944
	11th to 20th	Day	12% 15% 6% 10% 6% 5% 6% 4 6% 7% 24%	4980
	21st to end	Day	18% 16% 4 8% 5% 3 3 2 3 4 34%	5465
April	1st to 10th	Day	21% 13% 4 8% 4 4 4 3 4 6% 28%	2391
	11th to 20th	Day	23% 13% 2 5% 4 4 3 3 4 4 34%	2451
	21st to end	Day	21% 13% 3 7% 4 4 4 2 5% 5% 32%	2600
May	1st to 10th	Day	19% 9% 3 7% 5% 5% 5% 3 5% 7% 32%	6044
	11th to 20th	Day	17% 10% 3 7% 5% 4 4 3 5% 7% 36%	6318
	21st to end	Day	21% 10% 3 7% 5% 4 4 3 5% 7% 33%	6949
June	1st to 10th	Day	20% 9% 3 6% 5% 4 5% 3 5% 8% 32%	2800
	11th to 20th	Day	15% 7% 2 6% 5% 5% 5% 4 7% 8% 36%	2911
	21st to end	Day	18% 8% 3 7% 5% 4 4 4 6% 7% 34%	3000
July	1st to 10th	Day	14% 6% 2 7% 4 5% 5% 4 7% 10% 35%	6737
	11th to 20th	Day	12% 6% 2 6% 4 4 4 3 6% 7% 46%	6360
	21st to end	Day	8% 5% 2 6% 4 4 4 4 6% 9% 47%	6729
August	1st to 10th	Day	15% 8% 2 7% 5% 5% 5% 4 6% 8% 34%	4234
	11th to 20th	Day	16% 8% 3 7% 4 4 5% 4 7% 9% 34%	4174
	21st to end	Day	9% 5% 2 5% 5% 5% 5% 4 7% 9% 43%	4489
September	1st to 10th	Day	16% 6% 2 7% 5% 5% 4 4 5% 9% 37%	2400
	11th to 20th	Day	14% 5% 2 6% 4 4 4 4 5% 8% 45%	2322
	21st to end	Day	18% 10% 2 7% 4 5% 4 3 4 6% 36%	2135
October	1st to 10th	Day	21% 9% 3 8% 5% 3 4 3 5% 7% 33%	2000
	11th to 20th	Day	25% 12% 3 8% 5% 5% 5% 4 4 6% 24%	2000
	21st to end	Day	28% 13% 4 8% 5% 4 4 3 4 5% 22%	2200
November	1st to 10th	Day	19% 14% 5% 8% 4 3 4 3 5% 6% 28%	1696
	11th to 20th	Day	17% 17% 6% 10% 6% 4 4 4 5% 5% 23%	1680
	21st to end	Day	19% 23% 6% 9% 5% 5% 3 4 4 5% 15%	1680
December	1st to 10th	Day	16% 26% 7% 13% 5% 4 3 3 5% 5% 13%	2680
	11th to 20th	Day	17% 23% 8% 16% 4 3 2 2 3 3 18%	3066
	21st to end	Day	22% 22% 6% 13% 4 4 3 2 3 4 16%	4048
January	1st to 10th	Night	13% 18% 10% 17% 6% 4 4 3 4 5% 17%	8234
	11th to 20th	Night	10% 20% 9% 22% 8% 6% 4 2 3 4 12%	8055
	21st to end	Night	10% 17% 9% 16% 8% 7% 4 3 4 4 19%	8401
February	1st to 10th	Night	12% 17% 6% 14% 8% 5% 4 4 5% 5% 20%	2730
	11th to 20th	Night	13% 17% 7% 13% 6% 5% 4 4 4 4 24%	2663
	21st to end	Night	15% 17% 5% 11% 8% 5% 6% 3 4 4 22%	2223
March	1st to 10th	Night	16% 15% 5% 12% 5% 4 3 3 4 5% 28%	4936
	11th to 20th	Night	9% 14% 7% 10% 6% 5% 5% 4 6% 7% 27%	4979
	21st to end	Night	20% 11% 5% 8% 4 4 4 3 5% 5% 31%	5467
April	1st to 10th	Night	21% 14% 5% 7% 4 5% 4 3 4 5% 28%	2008
	11th to 20th	Night	19% 10% 3 7% 4 4 4 3 6% 6% 35%	1915
	21st to end	Night	20% 10% 3 8% 5% 5% 4 4 5% 6% 30%	1800
May	1st to 10th	Night	20% 7% 2 7% 4 5% 5% 3 5% 7% 33%	3897
	11th to 20th	Night	14% 9% 2 6% 3 4 4 3 6% 7% 42%	3575
	21st to end	Night	18% 8% 3 6% 4 4 5% 4 4 7% 36%	3926
June	1st to 10th	Night	15% 9% 2 6% 6% 5% 5% 4 5% 7% 35%	1600
	11th to 20th	Night	14% 7% 2 6% 4 4 4 3 6% 9% 41%	1481
	21st to end	Night	16% 7% 2 8% 4 5% 4 4 6% 7% 37%	1400
July	1st to 10th	Night	13% 6% 3 8% 5% 5% 5% 4 5% 8% 38%	3221
	11th to 20th	Night	14% 6% 2 5% 4 3 3 3 5% 6% 47%	3600
	21st to end	Night	10% 6% 2 6% 4 3 3 3 5% 7% 52%	4106
August	1st to 10th	Night	11% 5% 2 5% 4 4 4 4 6% 7% 47%	2915
	11th to 20th	Night	15% 7% 3 6% 4 4 4 3 5% 7% 42%	2875
	21st to end	Night	14% 5% 2 5% 3 4 4 4 5% 7% 48%	3374
September	1st to 10th	Night	12% 6% 1 7% 4 4 4 4 5% 8% 44%	2000
	11th to 20th	Night	13% 5% 2 5% 4 3 3 3 5% 6% 51%	2075
	21st to end	Night	19% 7% 3 7% 4 3 4 3 4 6% 41%	2265
October	1st to 10th	Night	18% 7% 3 6% 4 4 5% 3 5% 6% 39%	2400
	11th to 20th	Night	23% 12% 3 9% 4 4 4 3 5% 6% 28%	2400
	21st to end	Night	24% 14% 4 8% 5% 4 4 3 4 5% 25%	2640
November	1st to 10th	Night	20% 14% 4 8% 4 3 4 3 4 6% 31%	2816
	11th to 20th	Night	17% 16% 4 8% 6% 4 4 3 5% 6% 26%	2940
	21st to end	Night	21% 19% 6% 10% 6% 5% 4 4 4 4 17%	2940
December	1st to 10th	Night	19% 24% 7% 12% 5% 4 3 3 4 4 14%	4720
	11th to 20th	Night	16% 23% 7% 17% 7% 4 4 3 3 4 13%	5348
	21st to end	Night	22% 21% 7% 14% 5% 4 3 2 3 3 15%	7150

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	63% 2 9% 18% 7%	4662
	11th to 20th	Day	81% 2 4 7% 6%	4842
	21st to end	Day	72% 2 7% 10% 8% 1	5780
February	1st to 10th	Day	71% 2 7% 14% 5% 1	1890
	11th to 20th	Day	66% 3 8% 13% 9% 2	1852
	21st to end	Day	69% 2 6% 14% 8% 1	1583
March	1st to 10th	Day	62% 3 11% 10% 14% 1	4947
	11th to 20th	Day	59% 3 12% 17% 7% 2	4980
	21st to end	Day	56% 2 6% 20% 14% 2	5465
April	1st to 10th	Day	58% 2 8% 19% 11% 2	2391
	11th to 20th	Day	54% 2 7% 22% 14% 1	2451
	21st to end	Day	56% 2 7% 20% 12% 3	2600
May	1st to 10th	Day	52% 3 9% 21% 10% 5%	6053
	11th to 20th	Day	49% 2 9% 21% 17% 1	6322
	21st to end	Day	52% 3 10% 19% 12% 3	6949
June	1st to 10th	Day	52% 3 9% 23% 13%	2800
	11th to 20th	Day	45% 5% 11% 25% 13% 2	2911
	21st to end	Day	49% 4 13% 23% 11% 1	3000
July	1st to 10th	Day	42% 6% 15% 27% 11% 1	6665
	11th to 20th	Day	37% 4 12% 33% 13%	6285
	21st to end	Day	33% 5% 14% 35% 13%	6535
August	1st to 10th	Day	47% 4 13% 25% 9% 1	4221
	11th to 20th	Day	46% 4 15% 27% 8%	4213
	21st to end	Day	36% 5% 12% 37% 9% 1	4489
September	1st to 10th	Day	45% 4 12% 27% 11% 1	2400
	11th to 20th	Day	38% 4 14% 31% 13% 1	2322
	21st to end	Day	51% 4 11% 24% 10%	2135
October	1st to 10th	Day	47% 4 12% 26% 10% 1	3260
	11th to 20th	Day	54% 4 11% 21% 10% 1	3240
	21st to end	Day	61% 4 12% 18% 6%	3538
November	1st to 10th	Day	57% 3 13% 21% 6%	1696
	11th to 20th	Day	62% 4 11% 15% 7% 1	1680
	21st to end	Day	72% 3 10% 10% 4 1	1680
December	1st to 10th	Day	74% 4 9% 10% 2	2680
	11th to 20th	Day	74% 3 5% 12% 6%	3066
	21st to end	Day	74% 2 5% 11% 7%	4048
January	1st to 10th	Night	72% 2 7% 13% 6%	8234
	11th to 20th	Night	78% 2 6% 7% 7% 1	8100
	21st to end	Night	70% 3 7% 10% 10% 1	8401
February	1st to 10th	Night	67% 3 8% 15% 6% 1	2730
	11th to 20th	Night	64% 3 8% 17% 8%	2665
	21st to end	Night	65% 2 8% 18% 6% 1	2223
March	1st to 10th	Night	59% 2 9% 13% 12% 4	4946
	11th to 20th	Night	56% 4 14% 17% 8% 1	4980
	21st to end	Night	55% 2 6% 21% 14% 2	5467
April	1st to 10th	Night	59% 2 7% 19% 11% 2	2008
	11th to 20th	Night	50% 2 8% 24% 15% 1	1915
	21st to end	Night	54% 4 8% 17% 15% 2	1800
May	1st to 10th	Night	51% 3 9% 19% 14% 4	3904
	11th to 20th	Night	42% 3 12% 23% 18% 2	3576
	21st to end	Night	48% 3 10% 24% 14% 1	3927
June	1st to 10th	Night	47% 4 11% 22% 15% 2	1600
	11th to 20th	Night	40% 3 11% 27% 17% 1	1481
	21st to end	Night	45% 4 14% 25% 12% 1	1400
July	1st to 10th	Night	42% 6% 13% 25% 12% 1	3185
	11th to 20th	Night	38% 4 10% 34% 14%	3552
	21st to end	Night	33% 4 9% 39% 15% 1	3986
August	1st to 10th	Night	36% 4 16% 27% 16% 1	2904
	11th to 20th	Night	41% 5% 17% 25% 12% 1	2902
	21st to end	Night	35% 4 12% 36% 12% 1	3374
September	1st to 10th	Night	38% 4 16% 29% 12% 1	2000
	11th to 20th	Night	34% 3 14% 34% 14%	2075
	21st to end	Night	46% 3 11% 27% 12%	2265
October	1st to 10th	Night	38% 4 10% 29% 19%	3920
	11th to 20th	Night	49% 4 13% 24% 9%	3899
	21st to end	Night	55% 4 15% 18% 7%	4252
November	1st to 10th	Night	55% 3 12% 22% 8%	2816
	11th to 20th	Night	58% 4 12% 17% 8% 1	2940
	21st to end	Night	70% 3 10% 13% 4	2940
December	1st to 10th	Night	75% 3 10% 9% 3	4720
	11th to 20th	Night	76% 3 7% 10% 5%	5348
	21st to end	Night	76% 2 5% 10% 6%	7150

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	26% 22% 34% 13% 4 1	220
	11th to 20th	Day	30% 17% 38% 12% 3 1	250
	21st to end	Day	28% 18% 35% 14% 5%	363
February	1st to 10th	Day	31% 25% 31% 10% 3 1	330
	11th to 20th	Day	30% 25% 36% 8% 1	330
	21st to end	Day	38% 23% 31% 8%	299
March	1st to 10th	Day	27% 19% 37% 14% 2	508
	11th to 20th	Day	25% 20% 35% 15% 4 1	500
	21st to end	Day	35% 15% 30% 15% 4 1	550
April	1st to 10th	Day	30% 20% 29% 14% 6% 1	500
	11th to 20th	Day	37% 15% 25% 13% 8% 2	492
	21st to end	Day	33% 16% 32% 12% 5% 2	500
May	1st to 10th	Day	28% 12% 32% 18% 6% 3	503
	11th to 20th	Day	22% 14% 31% 18% 12% 2	527
	21st to end	Day	23% 14% 30% 21% 9% 3	573
June	1st to 10th	Day	25% 12% 32% 24% 6% 1	530
	11th to 20th	Day	17% 12% 33% 24% 10% 3	641
	21st to end	Day	23% 12% 34% 21% 8% 2	730
July	1st to 10th	Day	13% 8% 35% 31% 10% 3	692
	11th to 20th	Day	17% 10% 27% 29% 13% 5%	524
	21st to end	Day	14% 10% 31% 31% 11% 4	576
August	1st to 10th	Day	17% 5% 26% 32% 15% 6%	526
	11th to 20th	Day	16% 5% 25% 29% 17% 7%	519
	21st to end	Day	16% 8% 31% 26% 15% 5%	583
September	1st to 10th	Day	18% 10% 29% 22% 15% 7%	530
	11th to 20th	Day	14% 6% 24% 23% 22% 11%	530
	21st to end	Day	23% 9% 27% 26% 11% 4	530
October	1st to 10th	Day	26% 13% 24% 19% 15% 3	530
	11th to 20th	Day	30% 17% 34% 15% 4 1	530
	21st to end	Day	37% 15% 29% 16% 4	583
November	1st to 10th	Day	37% 16% 31% 12% 4	263
	11th to 20th	Day	30% 21% 35% 9% 5%	220
	21st to end	Day	35% 20% 35% 9% 2	220
December	1st to 10th	Day	34% 20% 29% 15% 4	220
	11th to 20th	Day	40% 19% 27% 11% 2	220
	21st to end	Day	39% 21% 26% 11% 3	242
January	1st to 10th	Night	29% 18% 31% 18% 4	840
	11th to 20th	Night	29% 16% 32% 18% 5% 1	840
	21st to end	Night	22% 13% 35% 22% 7% 1	924
February	1st to 10th	Night	22% 21% 33% 21% 3	840
	11th to 20th	Night	23% 19% 35% 18% 5%	823
	21st to end	Night	27% 19% 30% 20% 3	692
March	1st to 10th	Night	23% 19% 34% 19% 4	809
	11th to 20th	Night	23% 15% 36% 21% 4 1	800
	21st to end	Night	24% 12% 32% 25% 7%	880
April	1st to 10th	Night	29% 15% 32% 19% 5%	800
	11th to 20th	Night	27% 14% 30% 20% 9% 1	731
	21st to end	Night	25% 11% 30% 26% 8% 1	600
May	1st to 10th	Night	24% 7% 27% 30% 11% 1	535
	11th to 20th	Night	21% 8% 31% 29% 10% 1	394
	21st to end	Night	15% 8% 31% 32% 13%	433
June	1st to 10th	Night	20% 6% 29% 37% 9% 1	400
	11th to 20th	Night	17% 9% 25% 37% 12%	400
	21st to end	Night	20% 6% 20% 40% 13%	400
July	1st to 10th	Night	9% 5% 25% 41% 18% 1	390
	11th to 20th	Night	14% 5% 23% 38% 19% 1	388
	21st to end	Night	12% 3 24% 41% 19%	517
August	1st to 10th	Night	13% 3 19% 36% 28% 2	597
	11th to 20th	Night	13% 4 15% 40% 25% 3	594
	21st to end	Night	17% 4 25% 31% 21% 2	746
September	1st to 10th	Night	15% 8% 26% 30% 19% 2	800
	11th to 20th	Night	17% 4 23% 30% 23% 4	800
	21st to end	Night	23% 9% 19% 30% 17% 3	800
October	1st to 10th	Night	22% 8% 28% 27% 15% 1	800
	11th to 20th	Night	31% 11% 27% 22% 8% 1	800
	21st to end	Night	32% 14% 27% 22% 5%	880
November	1st to 10th	Night	30% 12% 28% 23% 8%	820
	11th to 20th	Night	27% 17% 31% 17% 7% 1	840
	21st to end	Night	33% 13% 29% 19% 5%	840
December	1st to 10th	Night	34% 17% 29% 16% 4	840
	11th to 20th	Night	28% 18% 34% 16% 3 1	840
	21st to end	Night	35% 15% 28% 19% 3	924

Page generated at 2026-02-28 01:40:19. Version ac07

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