Roscommon
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Roscommon clear sky chart from 2005-11-06 to 2026-07-16.

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	14% 11% 4 10% 6% 5% 5% 4 5% 6% 31%	137114
	Night	13% 13% 5% 11% 6% 5% 4 3 5% 6% 30%	135799
Transparency	Day	51% 6% 11% 19% 12% 1	140626
	Night	54% 6% 11% 18% 10% 1	140351
Seeing	Day	21% 17% 31% 20% 8% 3	17881
	Night	20% 14% 32% 25% 9% 1	27531

By Month

Percentage Cloud Cover SE (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% 18% 8% 22% 8% 5% 3 3 3 4 12%	4691
	11th to 20th	Day	10% 17% 9% 21% 12% 9% 6% 2 3 3 8%	4710
	21st to end	Day	11% 15% 9% 15% 8% 7% 7% 3 4 5% 16%	5156
February	1st to 10th	Day	10% 17% 6% 14% 13% 6% 5% 3 4 4 17%	1869
	11th to 20th	Day	12% 14% 6% 16% 9% 6% 4 3 4 4 19%	2006
	21st to end	Day	11% 18% 8% 13% 8% 5% 4 3 3 5% 22%	1730
March	1st to 10th	Day	12% 11% 4 11% 5% 5% 5% 4 5% 6% 32%	4580
	11th to 20th	Day	13% 12% 6% 12% 5% 4 4 4 7% 7% 26%	5042
	21st to end	Day	22% 11% 8% 12% 5% 4 4 3 4 4 24%	5665
April	1st to 10th	Day	18% 17% 5% 8% 5% 5% 3 3 4 5% 27%	2520
	11th to 20th	Day	19% 13% 4 7% 3 4 3 3 5% 6% 34%	2636
	21st to end	Day	16% 12% 3 9% 6% 4 4 3 5% 7% 31%	2730
May	1st to 10th	Day	15% 9% 3 8% 5% 5% 5% 4 6% 7% 34%	7616
	11th to 20th	Day	14% 10% 2 7% 4 4 5% 3 6% 6% 39%	7659
	21st to end	Day	14% 8% 2 6% 4 4 4 3 4 6% 44%	9047
June	1st to 10th	Day	13% 6% 2 6% 5% 4 5% 5% 6% 8% 40%	3113
	11th to 20th	Day	13% 7% 2 6% 5% 5% 5% 5% 7% 8% 37%	3150
	21st to end	Day	13% 6% 3 7% 5% 5% 5% 5% 6% 8% 37%	3098
July	1st to 10th	Day	13% 6% 2 6% 5% 5% 4 3 6% 9% 40%	6500
	11th to 20th	Day	9% 5% 2 5% 4 4 5% 4 6% 9% 45%	6431
	21st to end	Day	7% 5% 2 6% 4 5% 5% 4 7% 10% 44%	6924
August	1st to 10th	Day	9% 5% 2 7% 5% 5% 6% 6% 8% 9% 38%	4271
	11th to 20th	Day	14% 6% 2 6% 4 4 5% 4 5% 7% 43%	4174
	21st to end	Day	12% 6% 2 7% 5% 5% 5% 4 5% 7% 41%	4556
September	1st to 10th	Day	13% 6% 2 6% 5% 6% 5% 3 6% 9% 39%	2334
	11th to 20th	Day	12% 6% 2 6% 4 4 4 4 5% 7% 46%	2200
	21st to end	Day	15% 8% 3 7% 5% 4 5% 4 6% 9% 35%	2200
October	1st to 10th	Day	17% 8% 3 6% 5% 3 4 3 5% 6% 39%	2180
	11th to 20th	Day	21% 14% 3 10% 6% 5% 4 3 5% 6% 24%	1937
	21st to end	Day	21% 15% 3 10% 5% 6% 5% 4 5% 6% 20%	1980
November	1st to 10th	Day	15% 15% 4 7% 5% 4 4 4 7% 7% 28%	1852
	11th to 20th	Day	15% 18% 7% 10% 5% 4 5% 4 4 6% 21%	1890
	21st to end	Day	18% 21% 7% 12% 6% 4 3 2 4 5% 17%	1738
December	1st to 10th	Day	12% 26% 10% 18% 6% 5% 3 3 3 3 9%	2399
	11th to 20th	Day	15% 21% 11% 14% 7% 5% 4 3 3 3 13%	2695
	21st to end	Day	23% 26% 8% 15% 5% 4 3 2 2 3 9%	3835
January	1st to 10th	Night	13% 15% 8% 25% 9% 5% 3 3 3 3 14%	8232
	11th to 20th	Night	10% 19% 10% 18% 11% 10% 5% 3 4 4 7%	8280
	21st to end	Night	8% 16% 8% 18% 9% 7% 6% 4 5% 5% 12%	9058
February	1st to 10th	Night	10% 16% 6% 14% 11% 7% 5% 4 4 5% 17%	2749
	11th to 20th	Night	13% 14% 6% 14% 8% 6% 4 3 6% 5% 21%	2498
	21st to end	Night	14% 15% 5% 14% 7% 4 4 3 5% 5% 23%	2076
March	1st to 10th	Night	15% 9% 5% 8% 7% 4 4 3 4 6% 35%	5493
	11th to 20th	Night	11% 12% 5% 9% 5% 4 4 4 5% 7% 34%	5138
	21st to end	Night	19% 13% 6% 10% 5% 3 3 3 4 5% 31%	5550
April	1st to 10th	Night	16% 14% 4 9% 4 3 4 4 5% 6% 30%	2100
	11th to 20th	Night	18% 12% 4 7% 4 3 3 3 5% 6% 36%	1931
	21st to end	Night	15% 11% 3 8% 4 4 4 3 5% 6% 37%	1890
May	1st to 10th	Night	12% 7% 3 6% 5% 5% 4 4 6% 8% 40%	5237
	11th to 20th	Night	14% 10% 2 6% 4 4 4 3 5% 6% 41%	5187
	21st to end	Night	16% 5% 2 5% 4 4 4 3 5% 6% 47%	5139
June	1st to 10th	Night	13% 6% 3 6% 4 4 5% 3 5% 8% 44%	1500
	11th to 20th	Night	9% 6% 2 6% 5% 4 4 4 7% 8% 45%	1470
	21st to end	Night	11% 9% 2 5% 4 4 4 4 6% 7% 43%	1514
July	1st to 10th	Night	10% 8% 3 6% 4 4 5% 4 7% 8% 41%	3698
	11th to 20th	Night	8% 6% 2 5% 3 4 4 4 5% 8% 52%	3657
	21st to end	Night	8% 6% 2 6% 4 3 4 3 6% 7% 51%	3947
August	1st to 10th	Night	10% 5% 2 6% 5% 4 5% 5% 6% 8% 46%	2878
	11th to 20th	Night	14% 6% 2 4 3 3 4 4 4 7% 50%	2875
	21st to end	Night	10% 6% 2 5% 3 4 4 4 6% 6% 48%	3339
September	1st to 10th	Night	10% 6% 2 6% 4 3 4 3 6% 6% 50%	2045
	11th to 20th	Night	11% 6% 2 4 3 3 4 3 5% 6% 52%	2200
	21st to end	Night	16% 8% 2 6% 5% 3 4 3 5% 8% 40%	2200
October	1st to 10th	Night	16% 8% 2 6% 4 3 3 3 5% 6% 44%	2219
	11th to 20th	Night	19% 13% 4 8% 4 4 3 3 5% 6% 31%	2460
	21st to end	Night	23% 12% 4 8% 5% 4 3 3 5% 6% 28%	2860
November	1st to 10th	Night	13% 13% 4 8% 5% 4 4 4 6% 8% 32%	2666
	11th to 20th	Night	12% 20% 5% 11% 6% 6% 4 3 5% 5% 24%	2730
	21st to end	Night	17% 20% 6% 12% 5% 4 4 4 5% 6% 18%	2877
December	1st to 10th	Night	12% 17% 7% 15% 7% 6% 5% 4 6% 6% 15%	5007
	11th to 20th	Night	11% 25% 8% 15% 6% 4 4 3 4 4 15%	5732
	21st to end	Night	22% 25% 7% 12% 5% 4 3 2 3 3 12%	7367

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% 5% 9% 7% 3 1	4692
	11th to 20th	Day	82% 4 3 7% 3	4710
	21st to end	Day	70% 4 11% 10% 5%	5156
February	1st to 10th	Day	70% 6% 8% 13% 3 1	1869
	11th to 20th	Day	67% 6% 8% 12% 6%	2016
	21st to end	Day	65% 5% 10% 15% 4	1730
March	1st to 10th	Day	51% 5% 15% 16% 10% 3	4580
	11th to 20th	Day	55% 6% 15% 16% 8% 1	5042
	21st to end	Day	63% 5% 8% 14% 9%	5667
April	1st to 10th	Day	58% 5% 10% 15% 10% 1	2520
	11th to 20th	Day	51% 5% 10% 19% 14% 1	2636
	21st to end	Day	52% 6% 13% 15% 13% 3	2730
May	1st to 10th	Day	46% 6% 9% 21% 15% 2	7651
	11th to 20th	Day	44% 6% 9% 23% 16% 2	7663
	21st to end	Day	41% 5% 8% 21% 22% 4	9061
June	1st to 10th	Day	40% 7% 12% 24% 15% 1	3113
	11th to 20th	Day	41% 7% 13% 22% 16% 1	3150
	21st to end	Day	42% 8% 13% 23% 13% 1	3098
July	1st to 10th	Day	40% 5% 13% 24% 17% 1	6431
	11th to 20th	Day	34% 5% 12% 32% 16% 1	6356
	21st to end	Day	34% 5% 15% 29% 16% 1	6728
August	1st to 10th	Day	38% 8% 13% 26% 14% 1	4256
	11th to 20th	Day	40% 6% 13% 28% 13% 1	4213
	21st to end	Day	42% 6% 14% 27% 12% 1	4555
September	1st to 10th	Day	40% 8% 14% 24% 14% 2	2334
	11th to 20th	Day	36% 7% 15% 28% 14%	2200
	21st to end	Day	44% 8% 14% 23% 11%	2200
October	1st to 10th	Day	34% 5% 9% 33% 18% 2	3557
	11th to 20th	Day	52% 4 9% 21% 13%	3127
	21st to end	Day	61% 5% 11% 17% 6%	3180
November	1st to 10th	Day	53% 7% 12% 20% 8%	1852
	11th to 20th	Day	63% 8% 13% 11% 5%	1890
	21st to end	Day	70% 6% 10% 10% 3	1738
December	1st to 10th	Day	81% 4 7% 7% 1	2399
	11th to 20th	Day	77% 4 7% 10% 2	2691
	21st to end	Day	82% 4 4 6% 4	3835
January	1st to 10th	Night	74% 5% 8% 8% 4 1	8233
	11th to 20th	Night	80% 5% 5% 6% 3	8280
	21st to end	Night	71% 6% 8% 10% 5%	9058
February	1st to 10th	Night	67% 7% 8% 12% 5% 1	2749
	11th to 20th	Night	62% 7% 10% 15% 5% 1	2499
	21st to end	Night	62% 6% 11% 15% 6%	2076
March	1st to 10th	Night	51% 4 16% 18% 10%	5493
	11th to 20th	Night	47% 6% 19% 19% 8% 1	5138
	21st to end	Night	55% 6% 11% 18% 10% 1	5550
April	1st to 10th	Night	53% 6% 10% 19% 11% 1	2100
	11th to 20th	Night	49% 5% 9% 20% 15% 2	1931
	21st to end	Night	47% 6% 12% 18% 14% 2	1890
May	1st to 10th	Night	41% 5% 11% 21% 18% 3	5264
	11th to 20th	Night	43% 5% 9% 26% 16% 1	5188
	21st to end	Night	37% 5% 10% 23% 21% 4	5149
June	1st to 10th	Night	38% 6% 10% 24% 19% 2	1500
	11th to 20th	Night	36% 7% 14% 25% 16% 2	1470
	21st to end	Night	38% 7% 12% 26% 15% 2	1514
July	1st to 10th	Night	38% 5% 14% 25% 14% 4	3660
	11th to 20th	Night	30% 5% 12% 35% 17% 1	3612
	21st to end	Night	32% 5% 18% 29% 16% 1	3832
August	1st to 10th	Night	35% 7% 15% 28% 14% 1	2869
	11th to 20th	Night	34% 5% 17% 31% 13%	2902
	21st to end	Night	35% 6% 15% 26% 17% 1	3339
September	1st to 10th	Night	32% 8% 14% 28% 16% 2	2045
	11th to 20th	Night	32% 6% 15% 33% 14%	2200
	21st to end	Night	42% 7% 16% 25% 10% 1	2200
October	1st to 10th	Night	33% 5% 12% 33% 16% 1	3622
	11th to 20th	Night	46% 4 10% 24% 15%	3996
	21st to end	Night	51% 5% 12% 25% 6%	4610
November	1st to 10th	Night	50% 7% 14% 20% 9% 1	2666
	11th to 20th	Night	62% 6% 11% 14% 6% 1	2730
	21st to end	Night	67% 7% 13% 10% 2 1	2877
December	1st to 10th	Night	69% 7% 13% 10% 2	5007
	11th to 20th	Night	71% 6% 8% 10% 5%	5735
	21st to end	Night	78% 5% 6% 6% 6%	7367

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	27% 22% 38% 10% 4	330
	11th to 20th	Day	26% 25% 38% 9% 2	330
	21st to end	Day	28% 20% 36% 13% 2 1	363
February	1st to 10th	Day	24% 32% 32% 8% 3 1	330
	11th to 20th	Day	27% 28% 36% 8% 1	330
	21st to end	Day	33% 27% 35% 4 1	273
March	1st to 10th	Day	28% 32% 31% 8%	330
	11th to 20th	Day	27% 22% 31% 15% 5%	518
	21st to end	Day	32% 19% 28% 16% 4 1	594
April	1st to 10th	Day	30% 19% 32% 14% 4 1	540
	11th to 20th	Day	32% 20% 27% 13% 5% 2	532
	21st to end	Day	24% 20% 28% 19% 6% 2	540
May	1st to 10th	Day	23% 21% 33% 15% 6% 3	543
	11th to 20th	Day	20% 17% 31% 22% 7% 3	574
	21st to end	Day	18% 15% 32% 24% 9% 2	844
June	1st to 10th	Day	15% 17% 36% 23% 7% 2	780
	11th to 20th	Day	18% 15% 34% 22% 8% 2	780
	21st to end	Day	16% 13% 38% 23% 9% 2	780
July	1st to 10th	Day	9% 11% 36% 26% 13% 5%	771
	11th to 20th	Day	10% 12% 33% 27% 13% 5%	744
	21st to end	Day	10% 8% 34% 31% 12% 5%	794
August	1st to 10th	Day	10% 6% 28% 29% 18% 10%	551
	11th to 20th	Day	12% 8% 24% 32% 15% 9%	519
	21st to end	Day	17% 10% 26% 27% 16% 4	583
September	1st to 10th	Day	16% 11% 28% 23% 14% 8%	530
	11th to 20th	Day	11% 11% 21% 28% 19% 10%	530
	21st to end	Day	21% 11% 23% 28% 12% 5%	530
October	1st to 10th	Day	23% 17% 27% 20% 12% 2	530
	11th to 20th	Day	29% 17% 34% 16% 3	467
	21st to end	Day	30% 25% 30% 11% 3 1	363
November	1st to 10th	Day	28% 21% 33% 14% 4 1	330
	11th to 20th	Day	30% 22% 34% 11% 3	330
	21st to end	Day	27% 25% 36% 12%	250
December	1st to 10th	Day	28% 25% 30% 11% 4 1	220
	11th to 20th	Day	31% 28% 30% 9% 2	220
	21st to end	Day	36% 28% 26% 7% 3 1	308
January	1st to 10th	Night	22% 20% 35% 18% 4	1050
	11th to 20th	Night	25% 19% 34% 18% 4 1	1050
	21st to end	Night	19% 14% 41% 21% 5%	1155
February	1st to 10th	Night	20% 19% 38% 18% 4	859
	11th to 20th	Night	24% 22% 32% 20% 4	823
	21st to end	Night	27% 19% 34% 18% 2	692
March	1st to 10th	Night	19% 19% 35% 21% 6%	840
	11th to 20th	Night	23% 19% 34% 19% 4	840
	21st to end	Night	22% 15% 35% 22% 4 1	911
April	1st to 10th	Night	23% 17% 35% 20% 4	630
	11th to 20th	Night	26% 15% 30% 22% 7%	623
	21st to end	Night	20% 12% 34% 27% 6% 1	630
May	1st to 10th	Night	15% 12% 36% 30% 7%	630
	11th to 20th	Night	18% 11% 30% 31% 10%	621
	21st to end	Night	16% 8% 29% 32% 14% 1	683
June	1st to 10th	Night	15% 7% 35% 34% 9%	450
	11th to 20th	Night	12% 7% 36% 37% 8%	420
	21st to end	Night	13% 7% 33% 33% 14% 1	464
July	1st to 10th	Night	9% 3 22% 44% 20% 1	615
	11th to 20th	Night	9% 6% 26% 36% 21% 2	597
	21st to end	Night	11% 5% 27% 38% 19% 1	657
August	1st to 10th	Night	9% 3 25% 40% 23% 1	597
	11th to 20th	Night	11% 6% 19% 36% 26% 3	594
	21st to end	Night	13% 5% 24% 38% 18% 1	660
September	1st to 10th	Night	12% 6% 26% 31% 22% 4	645
	11th to 20th	Night	13% 6% 23% 32% 21% 4	800
	21st to end	Night	19% 9% 24% 30% 14% 4	800
October	1st to 10th	Night	21% 10% 27% 29% 13% 1	800
	11th to 20th	Night	25% 15% 31% 23% 6%	800
	21st to end	Night	29% 14% 30% 21% 6%	880
November	1st to 10th	Night	23% 15% 34% 21% 7% 1	820
	11th to 20th	Night	24% 20% 35% 17% 4	840
	21st to end	Night	27% 18% 37% 16% 3	840
December	1st to 10th	Night	24% 19% 35% 19% 3	1010
	11th to 20th	Night	25% 21% 37% 13% 4 1	1050
	21st to end	Night	30% 18% 35% 16% 2	1155

Page generated at 2026-07-13 03:14:48. Version ac07

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