Rannie Road
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rannie Road clear sky chart from 2005-11-06 to 2024-11-04.

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	30% 11% 3 6% 4 3 3 3 4 5% 29%	105483
	Night	32% 12% 2 5% 3 3 3 2 4 4 29%	102116
Transparency	Day	57% 7% 11% 17% 7% 1	105233
	Night	59% 6% 11% 15% 8% 2	102013
Seeing	Day	32% 11% 21% 23% 10% 2	15325
	Night	37% 7% 18% 24% 13% 1	23496

By Month

Percentage Cloud Cover NW (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	45% 18% 4 5% 4 3 3 2 2 3 10%	2219
	11th to 20th	Day	33% 14% 4 8% 3 3 2 1 2 3 27%	2200
	21st to end	Day	61% 12% 1 4 2 2 2 1 2 2 12%	2796
February	1st to 10th	Day	39% 15% 4 6% 4 3 3 3 4 4 16%	1710
	11th to 20th	Day	34% 16% 4 6% 3 3 3 3 3 4 21%	1665
	21st to end	Day	28% 22% 5% 7% 4 5% 3 2 3 2 19%	1441
March	1st to 10th	Day	29% 26% 5% 7% 4 4 3 3 3 4 13%	3218
	11th to 20th	Day	28% 16% 3 6% 3 2 2 1 3 4 32%	3490
	21st to end	Day	34% 18% 3 6% 4 3 3 3 3 4 18%	3943
April	1st to 10th	Day	36% 16% 3 7% 6% 4 3 3 5% 4 13%	2280
	11th to 20th	Day	30% 15% 3 8% 6% 4 4 3 4 5% 20%	2330
	21st to end	Day	34% 15% 3 6% 5% 3 4 3 4 4 19%	2543
May	1st to 10th	Day	22% 13% 2 6% 4 4 4 3 4 5% 33%	4420
	11th to 20th	Day	22% 8% 2 6% 4 5% 5% 5% 6% 7% 30%	4377
	21st to end	Day	38% 13% 3 7% 5% 4 4 3 4 4 17%	4877
June	1st to 10th	Day	35% 9% 2 6% 4 3 4 3 4 6% 23%	2850
	11th to 20th	Day	36% 11% 3 8% 5% 5% 3 3 3 4 18%	2850
	21st to end	Day	26% 8% 2 6% 5% 4 4 3 5% 5% 31%	2850
July	1st to 10th	Day	12% 4 2 5% 3 3 3 3 4 5% 57%	4740
	11th to 20th	Day	10% 4 1 3 2 2 2 2 3 4 66%	4740
	21st to end	Day	19% 5% 2 4 3 3 3 3 5% 6% 47%	4853
August	1st to 10th	Day	10% 4 1 4 2 2 2 2 4 6% 63%	4401
	11th to 20th	Day	22% 8% 3 6% 4 3 3 3 5% 6% 36%	4028
	21st to end	Day	25% 7% 2 5% 4 4 4 3 4 5% 35%	4402
September	1st to 10th	Day	21% 8% 3 5% 4 4 2 2 4 6% 42%	2280
	11th to 20th	Day	26% 9% 2 6% 4 3 3 3 4 5% 36%	2280
	21st to end	Day	33% 7% 2 5% 4 3 3 2 4 4 33%	2002
October	1st to 10th	Day	30% 11% 3 7% 4 4 4 4 5% 4 25%	3180
	11th to 20th	Day	43% 7% 2 7% 3 4 4 3 3 4 21%	3161
	21st to end	Day	39% 17% 3 8% 4 3 3 2 3 4 14%	3162
November	1st to 10th	Day	47% 13% 3 6% 4 3 3 3 2 3 15%	1512
	11th to 20th	Day	47% 12% 2 5% 2 2 2 2 2 4 20%	1520
	21st to end	Day	45% 12% 2 4 3 3 3 3 3 4 18%	1520
December	1st to 10th	Day	36% 16% 3 4 4 2 3 3 3 3 24%	1516
	11th to 20th	Day	45% 15% 4 6% 2 2 3 2 2 3 16%	1685
	21st to end	Day	47% 19% 3 7% 4 3 3 2 2 2 10%	2442
January	1st to 10th	Night	45% 18% 3 6% 3 3 3 2 2 2 13%	4726
	11th to 20th	Night	34% 11% 2 5% 3 3 4 3 4 6% 27%	4696
	21st to end	Night	59% 13% 2 4 2 2 1 1 2 3 12%	4858
February	1st to 10th	Night	38% 14% 3 6% 4 3 3 2 4 5% 17%	2470
	11th to 20th	Night	31% 19% 3 6% 3 3 2 2 4 3 23%	2402
	21st to end	Night	31% 15% 2 7% 4 3 3 3 5% 3 24%	2013
March	1st to 10th	Night	29% 23% 3 5% 4 3 3 2 3 4 22%	3653
	11th to 20th	Night	29% 12% 3 4 3 2 3 2 3 4 33%	3489
	21st to end	Night	38% 16% 3 6% 3 3 2 2 3 3 20%	3710
April	1st to 10th	Night	32% 14% 3 8% 4 4 3 4 5% 5% 19%	1900
	11th to 20th	Night	27% 13% 3 7% 5% 4 4 3 4 5% 26%	1797
	21st to end	Night	31% 13% 3 6% 5% 4 4 2 5% 5% 22%	1636
May	1st to 10th	Night	20% 11% 3 6% 3 3 2 2 3 4 43%	2540
	11th to 20th	Night	17% 7% 2 5% 3 4 4 4 6% 8% 41%	2516
	21st to end	Night	34% 10% 3 6% 4 3 3 4 4 4 24%	2681
June	1st to 10th	Night	28% 8% 2 8% 5% 4 3 3 5% 5% 28%	1330
	11th to 20th	Night	26% 13% 2 7% 5% 4 4 3 5% 6% 25%	1330
	21st to end	Night	21% 8% 2 5% 3 4 4 4 5% 5% 38%	1330
July	1st to 10th	Night	8% 5% 1 3 3 2 2 2 5% 5% 62%	2220
	11th to 20th	Night	7% 3 1 3 2 2 2 2 3 4 74%	2220
	21st to end	Night	13% 4 1 4 3 3 4 3 5% 6% 54%	2696
August	1st to 10th	Night	6% 2 1 2 2 2 2 3 5% 6% 69%	2529
	11th to 20th	Night	14% 7% 2 5% 3 2 4 3 5% 7% 47%	2807
	21st to end	Night	20% 8% 2 5% 4 3 4 3 5% 6% 39%	3269
September	1st to 10th	Night	14% 5% 2 5% 3 4 4 3 3 6% 51%	1900
	11th to 20th	Night	25% 7% 2 6% 3 3 3 3 3 4 40%	1900
	21st to end	Night	29% 8% 2 5% 3 4 3 2 4 5% 35%	2175
October	1st to 10th	Night	28% 14% 3 7% 4 4 4 3 4 4 26%	3800
	11th to 20th	Night	40% 10% 2 5% 3 3 3 3 4 4 24%	3777
	21st to end	Night	39% 16% 4 6% 3 2 2 2 2 4 20%	4394
November	1st to 10th	Night	46% 12% 2 6% 4 3 3 2 3 4 16%	2638
	11th to 20th	Night	44% 11% 2 5% 3 3 2 2 3 3 21%	2660
	21st to end	Night	41% 13% 3 5% 3 3 3 2 3 3 20%	2660
December	1st to 10th	Night	36% 13% 3 5% 3 3 3 2 3 4 25%	2660
	11th to 20th	Night	48% 16% 3 5% 3 3 2 2 3 2 13%	3520
	21st to end	Night	50% 15% 3 5% 3 2 2 2 3 3 13%	5214

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	78% 7% 6% 6% 2 1	2219
	11th to 20th	Day	65% 4 7% 12% 7% 5%	2221
	21st to end	Day	82% 3 4 7% 3	2796
February	1st to 10th	Day	72% 5% 7% 8% 5% 2	1710
	11th to 20th	Day	68% 6% 7% 11% 7% 2	1674
	21st to end	Day	71% 5% 7% 10% 4 2	1441
March	1st to 10th	Day	72% 10% 6% 9% 3	3218
	11th to 20th	Day	59% 7% 7% 22% 5% 1	3490
	21st to end	Day	70% 7% 10% 10% 3	3943
April	1st to 10th	Day	73% 7% 10% 8% 2	2280
	11th to 20th	Day	66% 7% 6% 11% 8% 2	2330
	21st to end	Day	68% 7% 8% 10% 6%	2543
May	1st to 10th	Day	50% 11% 11% 22% 6%	4420
	11th to 20th	Day	48% 14% 17% 17% 3	4380
	21st to end	Day	66% 12% 11% 10% 1	4878
June	1st to 10th	Day	62% 7% 14% 11% 5% 2	2850
	11th to 20th	Day	69% 8% 11% 9% 3	2850
	21st to end	Day	54% 7% 15% 16% 7% 1	2850
July	1st to 10th	Day	30% 6% 9% 26% 21% 8%	4666
	11th to 20th	Day	23% 4 12% 41% 19% 2	4659
	21st to end	Day	36% 6% 21% 25% 10% 2	4700
August	1st to 10th	Day	24% 5% 11% 42% 17% 1	4384
	11th to 20th	Day	46% 7% 19% 18% 8% 2	4067
	21st to end	Day	49% 8% 15% 19% 9% 1	4401
September	1st to 10th	Day	44% 6% 11% 23% 11% 4	2280
	11th to 20th	Day	51% 7% 9% 18% 13% 2	2280
	21st to end	Day	54% 8% 12% 15% 9% 2	2002
October	1st to 10th	Day	60% 5% 13% 16% 6%	3180
	11th to 20th	Day	66% 6% 9% 12% 6% 1	3161
	21st to end	Day	73% 6% 6% 10% 5% 1	3162
November	1st to 10th	Day	76% 5% 7% 8% 4 1	1512
	11th to 20th	Day	71% 4 7% 9% 6% 2	1520
	21st to end	Day	71% 5% 5% 11% 8% 1	1520
December	1st to 10th	Day	66% 6% 7% 10% 10% 1	1516
	11th to 20th	Day	77% 4 6% 9% 2 2	1688
	21st to end	Day	81% 7% 3 6% 2 1	2442
January	1st to 10th	Night	77% 6% 4 10% 2 1	4726
	11th to 20th	Night	59% 5% 8% 15% 10% 4	4737
	21st to end	Night	81% 3 4 8% 3 1	4858
February	1st to 10th	Night	70% 5% 9% 9% 4 2	2470
	11th to 20th	Night	67% 7% 6% 10% 8% 2	2404
	21st to end	Night	64% 6% 8% 13% 6% 2	2013
March	1st to 10th	Night	67% 5% 9% 12% 7%	3653
	11th to 20th	Night	55% 8% 10% 20% 7%	3490
	21st to end	Night	70% 6% 12% 9% 3	3710
April	1st to 10th	Night	67% 7% 13% 11% 2	1900
	11th to 20th	Night	61% 7% 9% 14% 7% 2	1797
	21st to end	Night	64% 8% 10% 12% 6% 1	1636
May	1st to 10th	Night	45% 7% 16% 23% 9% 1	2540
	11th to 20th	Night	39% 15% 21% 20% 5%	2516
	21st to end	Night	61% 10% 16% 11% 3	2681
June	1st to 10th	Night	58% 7% 16% 12% 4 3	1330
	11th to 20th	Night	59% 10% 14% 13% 4	1330
	21st to end	Night	45% 9% 18% 16% 8% 3	1330
July	1st to 10th	Night	23% 6% 11% 32% 20% 8%	2185
	11th to 20th	Night	18% 4 12% 43% 23% 1	2178
	21st to end	Night	29% 5% 17% 29% 17% 3	2611
August	1st to 10th	Night	17% 5% 16% 38% 23% 2	2521
	11th to 20th	Night	36% 7% 27% 18% 8% 3	2834
	21st to end	Night	45% 7% 18% 21% 9% 1	3269
September	1st to 10th	Night	35% 8% 15% 23% 14% 5%	1900
	11th to 20th	Night	48% 5% 11% 16% 15% 4	1900
	21st to end	Night	53% 6% 13% 18% 8% 2	2175
October	1st to 10th	Night	61% 5% 14% 13% 6%	3800
	11th to 20th	Night	63% 5% 8% 15% 8%	3777
	21st to end	Night	70% 4 6% 13% 6%	4394
November	1st to 10th	Night	74% 4 8% 8% 4 1	2638
	11th to 20th	Night	70% 5% 7% 10% 6% 2	2660
	21st to end	Night	70% 5% 7% 8% 9% 1	2660
December	1st to 10th	Night	64% 6% 8% 12% 8% 2	2660
	11th to 20th	Night	79% 4 5% 6% 4 2	3516
	21st to end	Night	79% 5% 4 7% 5% 1	5214

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	49% 10% 19% 10% 8% 3	180
	11th to 20th	Day	54% 8% 13% 17% 7%	180
	21st to end	Day	52% 7% 17% 17% 8%	200
February	1st to 10th	Day	48% 11% 19% 16% 5% 1	370
	11th to 20th	Day	43% 13% 18% 21% 4 1	365
	21st to end	Day	40% 15% 24% 15% 6%	321
March	1st to 10th	Day	41% 15% 19% 18% 6% 1	460
	11th to 20th	Day	41% 12% 17% 19% 9% 1	460
	21st to end	Day	45% 14% 18% 16% 6% 1	506
April	1st to 10th	Day	40% 15% 18% 18% 7% 1	460
	11th to 20th	Day	34% 14% 24% 17% 9% 1	452
	21st to end	Day	35% 16% 23% 17% 9% 1	460
May	1st to 10th	Day	27% 14% 24% 25% 10% 1	463
	11th to 20th	Day	29% 10% 21% 25% 11% 4	488
	21st to end	Day	28% 15% 24% 21% 9% 4	567
June	1st to 10th	Day	30% 12% 24% 24% 8% 1	680
	11th to 20th	Day	33% 15% 23% 21% 7% 2	680
	21st to end	Day	24% 12% 22% 28% 13% 2	680
July	1st to 10th	Day	21% 8% 26% 31% 11% 3	671
	11th to 20th	Day	15% 9% 26% 34% 12% 4	668
	21st to end	Day	13% 7% 25% 36% 12% 6%	568
August	1st to 10th	Day	17% 9% 19% 34% 14% 7%	487
	11th to 20th	Day	14% 5% 23% 35% 17% 5%	477
	21st to end	Day	20% 12% 24% 28% 12% 3	539
September	1st to 10th	Day	24% 10% 23% 29% 13% 2	490
	11th to 20th	Day	30% 9% 19% 26% 13% 2	490
	21st to end	Day	30% 13% 19% 26% 11% 3	490
October	1st to 10th	Day	33% 9% 21% 22% 13% 2	490
	11th to 20th	Day	43% 8% 14% 20% 12% 3	490
	21st to end	Day	43% 12% 19% 17% 8% 2	389
November	1st to 10th	Day	48% 10% 15% 22% 6%	186
	11th to 20th	Day	54% 6% 9% 13% 14% 3	180
	21st to end	Day	51% 9% 17% 9% 8% 7%	180
December	1st to 10th	Day	51% 11% 12% 6% 16% 4	180
	11th to 20th	Day	56% 8% 14% 17% 4 2	180
	21st to end	Day	51% 11% 18% 16% 4 1	198
January	1st to 10th	Night	55% 9% 18% 14% 4	850
	11th to 20th	Night	49% 5% 20% 23% 3	848
	21st to end	Night	47% 10% 18% 20% 4	836
February	1st to 10th	Night	45% 8% 25% 18% 4	760
	11th to 20th	Night	42% 10% 22% 21% 5%	744
	21st to end	Night	39% 11% 24% 19% 7%	628
March	1st to 10th	Night	41% 9% 20% 21% 8% 1	760
	11th to 20th	Night	45% 9% 19% 21% 6%	760
	21st to end	Night	45% 9% 17% 21% 8% 1	836
April	1st to 10th	Night	38% 8% 21% 23% 9% 1	760
	11th to 20th	Night	32% 10% 26% 23% 9% 1	669
	21st to end	Night	38% 7% 22% 24% 9%	496
May	1st to 10th	Night	23% 7% 21% 31% 18% 1	380
	11th to 20th	Night	23% 4 13% 35% 23% 2	374
	21st to end	Night	26% 5% 17% 31% 21%	411
June	1st to 10th	Night	30% 6% 15% 32% 16% 2	380
	11th to 20th	Night	26% 11% 17% 26% 19% 2	380
	21st to end	Night	22% 5% 16% 32% 23% 2	380
July	1st to 10th	Night	13% 5% 10% 36% 32% 3	370
	11th to 20th	Night	12% 4 10% 33% 37% 5%	368
	21st to end	Night	8% 3 7% 33% 45% 3	416
August	1st to 10th	Night	11% 2 6% 29% 46% 6%	378
	11th to 20th	Night	10% 2 8% 36% 40% 5%	559
	21st to end	Night	19% 3 12% 35% 29% 2	698
September	1st to 10th	Night	15% 3 16% 37% 27% 1	760
	11th to 20th	Night	26% 4 14% 26% 26% 3	760
	21st to end	Night	33% 6% 13% 32% 16% 1	760
October	1st to 10th	Night	32% 4 19% 28% 16% 1	760
	11th to 20th	Night	43% 5% 18% 22% 11% 1	760
	21st to end	Night	43% 8% 22% 20% 7% 1	836
November	1st to 10th	Night	51% 9% 21% 18% 2	754
	11th to 20th	Night	51% 7% 21% 15% 6% 1	760
	21st to end	Night	47% 10% 20% 16% 7% 1	760
December	1st to 10th	Night	40% 9% 23% 23% 6%	760
	11th to 20th	Night	55% 10% 19% 13% 2	850
	21st to end	Night	52% 10% 24% 12% 1	935

Page generated at 2024-11-01 19:47:52. Version ac07

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