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 2024-04-03.

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	33% 11% 3 5% 4 2 3 3 3 4 27%	78398
	Night	35% 11% 3 5% 4 2 3 3 4 4 26%	81680
Transparency	Day	61% 6% 10% 15% 6% 1	78109
	Night	62% 6% 10% 14% 7% 2	81550
Seeing	Day	33% 11% 21% 23% 10% 2	14428
	Night	37% 7% 18% 23% 13% 1	22874

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	46% 18% 4 5% 4 2 3 2 2 3 10%	2219
	11th to 20th	Day	33% 13% 4 7% 3 3 2 2 2 3 27%	2200
	21st to end	Day	61% 11% 2 3 2 1 2 2 2 2 12%	2796
February	1st to 10th	Day	39% 14% 4 6% 4 2 3 3 4 4 16%	1710
	11th to 20th	Day	34% 15% 4 5% 4 2 3 3 3 4 21%	1665
	21st to end	Day	29% 20% 5% 7% 4 4 4 2 3 3 19%	1441
March	1st to 10th	Day	33% 20% 4 6% 5% 3 3 3 2 4 17%	1944
	11th to 20th	Day	40% 16% 4 6% 4 2 3 2 2 3 19%	2090
	21st to end	Day	37% 17% 4 6% 5% 3 3 3 3 4 16%	2370
April	1st to 10th	Day	36% 15% 4 6% 7% 3 4 3 5% 4 14%	2185
	11th to 20th	Day	32% 13% 4 7% 7% 3 4 4 4 4 18%	2205
	21st to end	Day	34% 14% 4 6% 6% 2 4 4 4 4 19%	2409
May	1st to 10th	Day	27% 10% 4 6% 5% 3 5% 4 4 5% 27%	2520
	11th to 20th	Day	26% 10% 3 5% 5% 3 5% 5% 5% 7% 26%	2477
	21st to end	Day	30% 9% 4 7% 7% 3 4 4 3 5% 26%	2759
June	1st to 10th	Day	35% 9% 3 6% 4 2 4 3 4 6% 23%	2700
	11th to 20th	Day	38% 9% 4 7% 5% 4 4 4 3 5% 17%	2700
	21st to end	Day	26% 7% 3 5% 6% 3 4 3 4 6% 32%	2700
July	1st to 10th	Day	20% 5% 2 5% 5% 2 4 3 4 5% 44%	2700
	11th to 20th	Day	18% 6% 3 4 4 2 4 4 4 5% 46%	2700
	21st to end	Day	14% 4 2 3 4 2 3 3 4 6% 56%	2776
August	1st to 10th	Day	18% 6% 2 4 4 2 3 3 4 5% 50%	2507
	11th to 20th	Day	13% 5% 2 4 4 2 3 4 5% 6% 51%	2300
	21st to end	Day	21% 6% 2 5% 5% 3 4 4 5% 6% 39%	2507
September	1st to 10th	Day	21% 7% 3 5% 4 3 3 3 4 5% 42%	2160
	11th to 20th	Day	26% 8% 3 5% 5% 2 3 3 4 4 37%	2160
	21st to end	Day	33% 6% 2 4 5% 2 3 3 4 4 34%	1898
October	1st to 10th	Day	30% 9% 3 4 4 2 3 4 4 5% 33%	1800
	11th to 20th	Day	40% 8% 2 6% 3 3 4 4 3 5% 24%	1800
	21st to end	Day	44% 10% 1 4 3 1 2 3 4 5% 22%	1829
November	1st to 10th	Day	47% 11% 3 5% 4 3 3 3 2 3 15%	1488
	11th to 20th	Day	47% 11% 3 5% 3 1 2 2 2 4 20%	1520
	21st to end	Day	45% 11% 3 4 3 2 3 3 3 4 18%	1520
December	1st to 10th	Day	37% 14% 4 4 4 2 2 4 3 3 24%	1516
	11th to 20th	Day	45% 15% 4 5% 3 2 2 3 2 3 16%	1685
	21st to end	Day	47% 18% 3 6% 4 3 3 3 2 2 10%	2442
January	1st to 10th	Night	45% 18% 3 5% 4 2 3 3 2 2 13%	4726
	11th to 20th	Night	34% 10% 2 4 4 2 3 4 4 6% 27%	4696
	21st to end	Night	59% 13% 2 3 2 1 1 2 2 3 12%	4858
February	1st to 10th	Night	38% 13% 3 5% 4 3 4 3 4 5% 17%	2470
	11th to 20th	Night	31% 18% 4 6% 4 2 3 3 4 3 23%	2402
	21st to end	Night	32% 13% 3 6% 5% 2 3 4 5% 4 24%	2013
March	1st to 10th	Night	34% 16% 3 5% 5% 2 3 4 3 4 21%	2233
	11th to 20th	Night	38% 13% 4 4 4 2 3 3 3 4 20%	2089
	21st to end	Night	38% 14% 3 5% 4 3 3 3 3 4 18%	2228
April	1st to 10th	Night	32% 12% 4 7% 5% 3 3 4 5% 6% 20%	1820
	11th to 20th	Night	29% 12% 4 6% 6% 3 4 4 4 5% 25%	1702
	21st to end	Night	31% 12% 2 5% 5% 3 5% 3 5% 5% 23%	1550
May	1st to 10th	Night	22% 8% 3 6% 5% 3 4 4 4 7% 36%	1440
	11th to 20th	Night	22% 7% 2 5% 4 4 6% 5% 6% 8% 30%	1416
	21st to end	Night	25% 6% 4 6% 5% 2 4 4 5% 6% 33%	1513
June	1st to 10th	Night	28% 8% 3 7% 5% 3 3 4 5% 6% 28%	1260
	11th to 20th	Night	26% 11% 3 6% 6% 3 5% 4 5% 7% 25%	1260
	21st to end	Night	21% 7% 2 4 3 3 4 5% 6% 6% 39%	1260
July	1st to 10th	Night	14% 6% 2 4 5% 3 3 3 5% 6% 49%	1260
	11th to 20th	Night	12% 4 2 4 3 2 3 3 4 6% 56%	1260
	21st to end	Night	7% 3 1 3 3 2 4 3 4 5% 63%	1538
August	1st to 10th	Night	11% 4 1 3 3 2 3 3 4 4 61%	1432
	11th to 20th	Night	9% 3 2 2 3 2 3 4 5% 7% 62%	1597
	21st to end	Night	14% 6% 3 5% 4 3 4 5% 6% 8% 43%	1849
September	1st to 10th	Night	15% 5% 2 5% 4 3 4 4 3 6% 51%	1800
	11th to 20th	Night	26% 6% 3 5% 3 2 4 3 4 4 41%	1800
	21st to end	Night	29% 8% 2 5% 3 3 3 3 3 6% 35%	2060
October	1st to 10th	Night	28% 7% 2 5% 4 3 4 3 3 3 37%	2160
	11th to 20th	Night	38% 8% 3 4 4 3 3 3 4 4 26%	2160
	21st to end	Night	41% 8% 2 5% 4 2 3 3 3 5% 24%	2524
November	1st to 10th	Night	46% 11% 2 5% 5% 2 3 2 3 4 17%	2590
	11th to 20th	Night	44% 11% 3 5% 3 2 3 3 3 4 21%	2660
	21st to end	Night	42% 11% 3 4 4 2 3 3 3 4 21%	2660
December	1st to 10th	Night	36% 12% 3 4 4 2 3 3 3 4 25%	2660
	11th to 20th	Night	48% 15% 3 4 3 2 2 3 3 2 13%	3520
	21st to end	Night	50% 15% 3 5% 4 2 2 2 2 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% 6% 7% 10% 4	1944
	11th to 20th	Day	73% 5% 6% 11% 5% 1	2090
	21st to end	Day	74% 6% 8% 10% 2	2370
April	1st to 10th	Day	73% 7% 10% 8% 3	2185
	11th to 20th	Day	69% 7% 6% 10% 7% 1	2205
	21st to end	Day	68% 7% 9% 9% 6%	2409
May	1st to 10th	Day	58% 9% 12% 16% 5% 1	2520
	11th to 20th	Day	57% 8% 13% 17% 5%	2480
	21st to end	Day	61% 7% 13% 16% 2	2760
June	1st to 10th	Day	62% 7% 14% 11% 4 2	2700
	11th to 20th	Day	70% 7% 11% 8% 3	2700
	21st to end	Day	54% 7% 15% 16% 7% 1	2700
July	1st to 10th	Day	43% 7% 13% 23% 11% 2	2626
	11th to 20th	Day	40% 6% 17% 27% 9% 1	2619
	21st to end	Day	30% 5% 16% 31% 14% 3	2622
August	1st to 10th	Day	37% 7% 15% 28% 11% 2	2490
	11th to 20th	Day	32% 8% 18% 25% 14% 3	2300
	21st to end	Day	44% 8% 15% 25% 6% 1	2507
September	1st to 10th	Day	45% 6% 11% 23% 10% 4	2160
	11th to 20th	Day	51% 6% 9% 18% 14% 3	2160
	21st to end	Day	54% 7% 12% 15% 9% 2	1898
October	1st to 10th	Day	55% 5% 12% 17% 11%	1800
	11th to 20th	Day	63% 6% 11% 15% 5% 1	1800
	21st to end	Day	66% 5% 9% 11% 7% 1	1829
November	1st to 10th	Day	76% 5% 7% 8% 4 1	1488
	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	66% 5% 11% 12% 5%	2233
	11th to 20th	Night	70% 5% 8% 11% 6% 1	2090
	21st to end	Night	71% 6% 13% 9% 2	2228
April	1st to 10th	Night	67% 7% 13% 11% 3	1820
	11th to 20th	Night	62% 7% 9% 14% 6% 1	1702
	21st to end	Night	63% 7% 10% 12% 6% 1	1550
May	1st to 10th	Night	50% 8% 17% 17% 6% 1	1440
	11th to 20th	Night	50% 9% 18% 16% 6%	1416
	21st to end	Night	51% 9% 18% 17% 4	1513
June	1st to 10th	Night	58% 7% 16% 12% 4 3	1260
	11th to 20th	Night	59% 11% 14% 13% 3	1260
	21st to end	Night	44% 10% 19% 17% 8% 3	1260
July	1st to 10th	Night	37% 7% 14% 24% 14% 3	1225
	11th to 20th	Night	31% 7% 20% 29% 12% 1	1218
	21st to end	Night	21% 7% 15% 35% 17% 5%	1453
August	1st to 10th	Night	27% 7% 18% 28% 18% 3	1424
	11th to 20th	Night	22% 7% 25% 27% 14% 6%	1597
	21st to end	Night	38% 7% 19% 26% 9% 2	1849
September	1st to 10th	Night	35% 8% 15% 23% 15% 4	1800
	11th to 20th	Night	48% 5% 11% 16% 16% 5%	1800
	21st to end	Night	52% 6% 13% 18% 9% 2	2060
October	1st to 10th	Night	53% 5% 13% 18% 11% 1	2160
	11th to 20th	Night	62% 6% 10% 15% 7% 1	2160
	21st to end	Night	65% 5% 8% 13% 9%	2524
November	1st to 10th	Night	74% 4 8% 9% 4 1	2590
	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	41% 14% 17% 20% 6% 1	429
	11th to 20th	Day	35% 14% 22% 18% 10% 1	412
	21st to end	Day	34% 15% 24% 17% 9% 1	420
May	1st to 10th	Day	27% 13% 25% 25% 9% 1	423
	11th to 20th	Day	30% 8% 20% 26% 12% 4	448
	21st to end	Day	26% 14% 25% 22% 10% 4	521
June	1st to 10th	Day	30% 12% 24% 24% 8% 2	630
	11th to 20th	Day	33% 15% 23% 22% 7% 1	630
	21st to end	Day	23% 11% 22% 28% 13% 2	630
July	1st to 10th	Day	22% 8% 26% 31% 11% 3	621
	11th to 20th	Day	17% 10% 26% 32% 12% 3	618
	21st to end	Day	11% 7% 25% 37% 13% 6%	522
August	1st to 10th	Day	18% 10% 18% 34% 14% 7%	447
	11th to 20th	Day	13% 5% 24% 35% 17% 5%	437
	21st to end	Day	19% 13% 24% 28% 13% 3	495
September	1st to 10th	Day	25% 10% 24% 28% 11% 1	450
	11th to 20th	Day	29% 8% 19% 27% 14% 2	450
	21st to end	Day	29% 12% 18% 26% 12% 3	450
October	1st to 10th	Day	33% 7% 22% 21% 14% 2	450
	11th to 20th	Day	42% 8% 14% 20% 13% 3	450
	21st to end	Day	43% 10% 20% 17% 8% 2	355
November	1st to 10th	Day	47% 10% 15% 22% 6%	180
	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% 20% 8% 1	836
April	1st to 10th	Night	39% 7% 21% 23% 9% 1	728
	11th to 20th	Night	33% 10% 24% 23% 9% 1	634
	21st to end	Night	38% 6% 23% 24% 9%	470
May	1st to 10th	Night	24% 6% 21% 30% 18% 1	360
	11th to 20th	Night	23% 5% 12% 34% 23% 3	354
	21st to end	Night	25% 4 17% 32% 22%	389
June	1st to 10th	Night	29% 5% 15% 32% 17% 2	360
	11th to 20th	Night	25% 11% 17% 26% 19% 2	360
	21st to end	Night	21% 5% 16% 33% 23% 2	360
July	1st to 10th	Night	14% 6% 9% 35% 33% 3	350
	11th to 20th	Night	12% 4 10% 33% 36% 5%	348
	21st to end	Night	8% 3 7% 34% 45% 4	394
August	1st to 10th	Night	12% 2 6% 27% 46% 6%	358
	11th to 20th	Night	9% 2 8% 36% 40% 5%	529
	21st to end	Night	18% 3 12% 35% 30% 2	661
September	1st to 10th	Night	15% 3 17% 37% 27% 1	720
	11th to 20th	Night	26% 4 14% 26% 26% 3	720
	21st to end	Night	32% 6% 12% 33% 17% 1	720
October	1st to 10th	Night	31% 4 18% 28% 16% 1	720
	11th to 20th	Night	43% 5% 17% 22% 12% 1	720
	21st to end	Night	42% 7% 21% 21% 7% 1	792
November	1st to 10th	Night	51% 9% 21% 18% 2	740
	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 2024-03-31 03:08:51. Version ac07

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