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 2025-03-12.

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% 30%	108115
	Night	13% 13% 5% 11% 6% 5% 4 3 5% 6% 29%	111048
Transparency	Day	52% 6% 11% 19% 11% 1	111672
	Night	54% 6% 11% 18% 9% 1	115619
Seeing	Day	21% 17% 31% 20% 8% 3	15963
	Night	20% 14% 32% 25% 9% 1	25832

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	10% 18% 7% 23% 7% 5% 4 3 4 5% 15%	3617
	11th to 20th	Day	11% 15% 8% 22% 12% 10% 6% 3 3 3 6%	3620
	21st to end	Day	14% 18% 10% 16% 6% 4 5% 3 4 5% 15%	3982
February	1st to 10th	Day	11% 17% 6% 14% 13% 6% 5% 3 4 4 17%	1780
	11th to 20th	Day	12% 15% 7% 16% 10% 6% 4 3 4 4 19%	1908
	21st to end	Day	11% 18% 8% 13% 8% 5% 4 3 3 5% 22%	1650
March	1st to 10th	Day	13% 14% 5% 9% 5% 5% 5% 4 5% 5% 31%	3220
	11th to 20th	Day	11% 12% 7% 15% 5% 4 4 4 6% 5% 27%	3457
	21st to end	Day	18% 12% 7% 12% 6% 5% 4 3 4 4 24%	3867
April	1st to 10th	Day	18% 16% 4 8% 5% 5% 3 3 4 5% 28%	2280
	11th to 20th	Day	19% 13% 4 7% 3 4 3 3 5% 5% 34%	2382
	21st to end	Day	16% 12% 3 8% 6% 3 4 3 5% 6% 32%	2470
May	1st to 10th	Day	14% 9% 3 8% 5% 5% 5% 4 6% 7% 35%	4082
	11th to 20th	Day	13% 7% 2 7% 4 4 4 3 6% 7% 42%	4100
	21st to end	Day	12% 7% 2 5% 4 4 4 3 5% 8% 45%	4824
June	1st to 10th	Day	14% 6% 2 6% 5% 4 5% 5% 6% 8% 39%	2817
	11th to 20th	Day	13% 6% 2 6% 5% 5% 5% 5% 7% 8% 39%	2850
	21st to end	Day	14% 6% 3 7% 5% 5% 5% 5% 6% 8% 38%	2804
July	1st to 10th	Day	15% 7% 3 8% 6% 6% 5% 3 6% 8% 35%	4440
	11th to 20th	Day	8% 5% 2 5% 4 4 5% 5% 7% 10% 44%	4440
	21st to end	Day	8% 6% 3 6% 5% 5% 5% 5% 7% 9% 41%	4813
August	1st to 10th	Day	9% 5% 2 7% 5% 6% 6% 6% 8% 9% 37%	4140
	11th to 20th	Day	14% 6% 2 6% 4 4 5% 4 5% 7% 43%	4044
	21st to end	Day	12% 7% 2 7% 5% 5% 5% 4 5% 7% 41%	4417
September	1st to 10th	Day	13% 7% 2 6% 5% 6% 5% 3 6% 9% 39%	2218
	11th to 20th	Day	12% 6% 2 6% 4 4 4 4 6% 7% 46%	2090
	21st to end	Day	15% 8% 3 7% 5% 5% 5% 5% 6% 9% 34%	2090
October	1st to 10th	Day	17% 9% 3 7% 5% 3 4 3 5% 6% 38%	2071
	11th to 20th	Day	22% 15% 3 10% 6% 5% 3 3 5% 6% 23%	1840
	21st to end	Day	22% 15% 3 10% 5% 6% 5% 4 5% 6% 19%	1881
November	1st to 10th	Day	15% 16% 4 8% 5% 5% 4 4 7% 7% 28%	1762
	11th to 20th	Day	15% 18% 7% 10% 5% 4 5% 4 4 6% 21%	1800
	21st to end	Day	18% 21% 8% 12% 6% 4 3 2 4 5% 18%	1655
December	1st to 10th	Day	13% 26% 10% 17% 6% 5% 3 3 3 3 9%	2327
	11th to 20th	Day	15% 22% 11% 14% 7% 5% 4 3 3 3 14%	2625
	21st to end	Day	23% 26% 8% 14% 5% 4 3 2 2 3 9%	3752
January	1st to 10th	Night	11% 14% 9% 26% 7% 5% 3 3 3 4 15%	6348
	11th to 20th	Night	12% 16% 8% 18% 12% 10% 5% 3 4 4 8%	6360
	21st to end	Night	11% 20% 9% 18% 7% 5% 5% 3 5% 5% 12%	6996
February	1st to 10th	Night	10% 16% 6% 14% 11% 7% 5% 4 5% 5% 17%	2618
	11th to 20th	Night	13% 14% 6% 13% 8% 6% 5% 4 6% 5% 20%	2376
	21st to end	Night	14% 15% 5% 14% 7% 4 5% 4 4 5% 24%	1980
March	1st to 10th	Night	15% 9% 4 8% 4 4 4 3 5% 6% 38%	3853
	11th to 20th	Night	9% 13% 6% 8% 5% 3 4 4 5% 6% 37%	3532
	21st to end	Night	14% 14% 6% 11% 6% 4 3 3 5% 5% 30%	3794
April	1st to 10th	Night	16% 14% 4 8% 4 3 4 3 5% 7% 31%	1900
	11th to 20th	Night	19% 11% 3 7% 4 3 3 3 5% 6% 36%	1745
	21st to end	Night	15% 11% 3 8% 4 5% 5% 3 5% 6% 37%	1710
May	1st to 10th	Night	13% 7% 3 6% 5% 5% 4 4 5% 8% 40%	2813
	11th to 20th	Night	12% 8% 2 7% 5% 5% 4 4 6% 7% 41%	2791
	21st to end	Night	16% 6% 2 5% 4 4 4 4 6% 7% 44%	2743
June	1st to 10th	Night	13% 5% 3 6% 4 4 4 3 5% 8% 43%	1358
	11th to 20th	Night	8% 6% 2 6% 5% 4 4 4 7% 8% 47%	1330
	21st to end	Night	10% 8% 2 5% 4 4 4 4 6% 7% 44%	1370
July	1st to 10th	Night	10% 8% 3 6% 4 4 5% 4 7% 9% 40%	2530
	11th to 20th	Night	7% 4 2 5% 4 4 4 4 5% 7% 54%	2530
	21st to end	Night	8% 6% 2 6% 4 3 4 4 6% 8% 49%	2750
August	1st to 10th	Night	10% 5% 2 6% 5% 4 5% 5% 6% 8% 45%	2789
	11th to 20th	Night	14% 6% 2 4 3 3 4 4 5% 7% 50%	2785
	21st to end	Night	11% 6% 2 5% 3 4 4 4 6% 6% 48%	3237
September	1st to 10th	Night	10% 6% 2 6% 4 3 3 3 6% 6% 51%	1943
	11th to 20th	Night	11% 6% 2 4 3 3 4 3 5% 6% 52%	2090
	21st to end	Night	16% 7% 2 6% 4 3 4 3 6% 8% 40%	2090
October	1st to 10th	Night	17% 8% 2 6% 4 3 3 3 5% 6% 43%	2108
	11th to 20th	Night	19% 13% 4 8% 4 4 3 3 5% 6% 30%	2337
	21st to end	Night	23% 13% 4 8% 5% 4 3 3 5% 6% 26%	2717
November	1st to 10th	Night	13% 12% 3 8% 5% 4 4 4 6% 8% 33%	2536
	11th to 20th	Night	13% 20% 5% 11% 6% 6% 4 4 4 5% 23%	2600
	21st to end	Night	17% 19% 6% 12% 5% 4 4 4 5% 6% 18%	2740
December	1st to 10th	Night	12% 17% 7% 15% 7% 6% 5% 4 6% 6% 15%	4859
	11th to 20th	Night	12% 25% 8% 14% 6% 4 4 3 4 4 15%	5582
	21st to end	Night	22% 26% 8% 12% 5% 4 3 2 3 3 12%	7208

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	72% 6% 9% 8% 4 1	3618
	11th to 20th	Day	83% 5% 4 6% 2	3620
	21st to end	Day	71% 5% 12% 7% 4	3982
February	1st to 10th	Day	70% 6% 8% 12% 3 1	1780
	11th to 20th	Day	67% 6% 9% 11% 6% 1	1918
	21st to end	Day	64% 5% 10% 15% 4	1650
March	1st to 10th	Day	53% 6% 13% 18% 9% 1	3220
	11th to 20th	Day	55% 7% 12% 18% 6% 2	3457
	21st to end	Day	60% 7% 8% 14% 9% 1	3867
April	1st to 10th	Day	58% 6% 11% 15% 10% 1	2280
	11th to 20th	Day	51% 5% 10% 19% 14% 1	2382
	21st to end	Day	52% 6% 12% 14% 13% 3	2470
May	1st to 10th	Day	44% 9% 11% 17% 17% 1	4120
	11th to 20th	Day	37% 9% 14% 25% 14% 2	4104
	21st to end	Day	36% 7% 12% 21% 20% 3	4837
June	1st to 10th	Day	40% 8% 13% 24% 14% 1	2817
	11th to 20th	Day	40% 7% 12% 22% 17% 1	2850
	21st to end	Day	42% 8% 13% 23% 13% 1	2804
July	1st to 10th	Day	46% 6% 13% 19% 14% 1	4371
	11th to 20th	Day	32% 7% 14% 30% 16% 1	4365
	21st to end	Day	36% 7% 14% 23% 18% 1	4662
August	1st to 10th	Day	39% 8% 13% 25% 14% 1	4125
	11th to 20th	Day	40% 6% 12% 28% 13% 1	4083
	21st to end	Day	42% 6% 13% 26% 12% 1	4416
September	1st to 10th	Day	40% 8% 13% 23% 14% 2	2218
	11th to 20th	Day	36% 7% 15% 28% 14%	2090
	21st to end	Day	44% 8% 14% 23% 10%	2090
October	1st to 10th	Day	34% 5% 9% 32% 18% 2	3448
	11th to 20th	Day	53% 4 9% 21% 13%	3030
	21st to end	Day	62% 5% 11% 17% 5%	3081
November	1st to 10th	Day	54% 7% 12% 19% 8%	1762
	11th to 20th	Day	63% 9% 13% 10% 5%	1800
	21st to end	Day	70% 6% 10% 10% 3	1655
December	1st to 10th	Day	81% 4 7% 6% 1	2327
	11th to 20th	Day	77% 4 7% 10% 2	2621
	21st to end	Day	82% 4 4 6% 4	3752
January	1st to 10th	Night	71% 6% 8% 10% 4 1	6348
	11th to 20th	Night	79% 6% 6% 6% 3	6360
	21st to end	Night	72% 7% 8% 9% 3	6996
February	1st to 10th	Night	67% 7% 9% 11% 5% 1	2618
	11th to 20th	Night	63% 8% 10% 14% 5% 1	2377
	21st to end	Night	62% 6% 11% 15% 7%	1980
March	1st to 10th	Night	47% 6% 16% 21% 10% 1	3853
	11th to 20th	Night	44% 8% 14% 23% 10% 1	3532
	21st to end	Night	54% 8% 12% 19% 7% 1	3794
April	1st to 10th	Night	52% 6% 10% 19% 11% 1	1900
	11th to 20th	Night	48% 6% 9% 21% 14% 2	1745
	21st to end	Night	47% 7% 11% 18% 15% 3	1710
May	1st to 10th	Night	42% 7% 13% 17% 18% 3	2840
	11th to 20th	Night	39% 8% 11% 26% 15% 1	2792
	21st to end	Night	38% 7% 15% 20% 16% 5%	2751
June	1st to 10th	Night	39% 7% 10% 25% 18% 1	1358
	11th to 20th	Night	34% 8% 14% 25% 17% 2	1330
	21st to end	Night	37% 8% 12% 27% 15% 2	1370
July	1st to 10th	Night	39% 6% 14% 24% 13% 4	2490
	11th to 20th	Night	28% 6% 13% 37% 15% 1	2482
	21st to end	Night	32% 6% 18% 25% 17% 1	2662
August	1st to 10th	Night	36% 7% 15% 28% 14% 1	2780
	11th to 20th	Night	33% 5% 16% 31% 13%	2812
	21st to end	Night	35% 6% 15% 26% 17% 1	3237
September	1st to 10th	Night	32% 8% 13% 28% 17% 2	1943
	11th to 20th	Night	32% 6% 15% 33% 14%	2090
	21st to end	Night	42% 7% 16% 26% 9% 1	2090
October	1st to 10th	Night	34% 5% 12% 32% 16% 1	3511
	11th to 20th	Night	46% 4 10% 24% 14%	3873
	21st to end	Night	52% 6% 12% 24% 6%	4467
November	1st to 10th	Night	49% 7% 15% 21% 9% 1	2536
	11th to 20th	Night	63% 6% 11% 13% 6% 1	2600
	21st to end	Night	66% 7% 13% 11% 2 1	2740
December	1st to 10th	Night	68% 7% 13% 9% 2	4859
	11th to 20th	Night	71% 6% 8% 10% 5%	5585
	21st to end	Night	78% 5% 6% 5% 6%	7208

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	25% 22% 39% 11% 4	300
	11th to 20th	Day	24% 23% 40% 10% 3	300
	21st to end	Day	28% 20% 35% 13% 3 1	330
February	1st to 10th	Day	24% 32% 33% 8% 3 1	300
	11th to 20th	Day	26% 30% 36% 7% 1	300
	21st to end	Day	33% 26% 37% 4 1	249
March	1st to 10th	Day	27% 33% 31% 8%	300
	11th to 20th	Day	24% 21% 33% 16% 5%	443
	21st to end	Day	29% 19% 29% 18% 4 1	506
April	1st to 10th	Day	28% 20% 32% 15% 4 1	460
	11th to 20th	Day	31% 21% 27% 13% 6% 2	452
	21st to end	Day	24% 22% 26% 19% 7% 2	460
May	1st to 10th	Day	24% 19% 32% 15% 6% 3	463
	11th to 20th	Day	19% 16% 29% 24% 7% 4	493
	21st to end	Day	17% 14% 32% 26% 9% 3	734
June	1st to 10th	Day	15% 17% 34% 25% 8% 2	680
	11th to 20th	Day	16% 15% 34% 24% 9% 3	680
	21st to end	Day	16% 13% 35% 23% 9% 2	680
July	1st to 10th	Day	9% 10% 34% 27% 14% 5%	671
	11th to 20th	Day	10% 12% 31% 28% 14% 5%	668
	21st to end	Day	10% 8% 33% 31% 13% 5%	739
August	1st to 10th	Day	10% 7% 28% 28% 17% 10%	510
	11th to 20th	Day	12% 8% 23% 32% 16% 10%	479
	21st to end	Day	18% 10% 26% 26% 16% 4	539
September	1st to 10th	Day	17% 10% 28% 23% 14% 7%	490
	11th to 20th	Day	11% 11% 22% 28% 19% 8%	490
	21st to end	Day	21% 11% 23% 27% 12% 6%	490
October	1st to 10th	Day	24% 17% 26% 19% 12% 2	490
	11th to 20th	Day	30% 18% 33% 16% 3	430
	21st to end	Day	32% 25% 30% 10% 2 1	330
November	1st to 10th	Day	27% 21% 33% 15% 3 1	300
	11th to 20th	Day	30% 21% 36% 10% 3	300
	21st to end	Day	25% 25% 37% 12%	227
December	1st to 10th	Day	29% 25% 31% 11% 4 2	200
	11th to 20th	Day	29% 29% 32% 10% 2	200
	21st to end	Day	34% 28% 27% 7% 3 1	280
January	1st to 10th	Night	21% 20% 36% 19% 4 1	1000
	11th to 20th	Night	24% 19% 34% 18% 4 1	1000
	21st to end	Night	20% 13% 40% 21% 5%	1100
February	1st to 10th	Night	20% 20% 38% 18% 3	818
	11th to 20th	Night	23% 22% 32% 19% 4	783
	21st to end	Night	26% 20% 34% 18% 2	660
March	1st to 10th	Night	19% 19% 35% 21% 6% 1	800
	11th to 20th	Night	20% 20% 35% 20% 5%	767
	21st to end	Night	21% 15% 35% 23% 5% 1	825
April	1st to 10th	Night	22% 17% 35% 21% 5% 1	570
	11th to 20th	Night	25% 15% 31% 23% 6% 1	563
	21st to end	Night	20% 13% 34% 27% 6% 1	570
May	1st to 10th	Night	16% 11% 36% 29% 8% 1	570
	11th to 20th	Night	17% 11% 30% 32% 10%	561
	21st to end	Night	16% 7% 28% 34% 14% 1	617
June	1st to 10th	Night	15% 7% 35% 33% 9%	408
	11th to 20th	Night	10% 7% 36% 39% 8%	380
	21st to end	Night	12% 6% 32% 34% 14% 1	420
July	1st to 10th	Night	9% 3 22% 44% 21% 1	555
	11th to 20th	Night	8% 6% 27% 36% 22% 2	552
	21st to end	Night	12% 5% 26% 37% 20% 1	624
August	1st to 10th	Night	9% 3 25% 40% 22% 1	567
	11th to 20th	Night	11% 6% 19% 35% 27% 3	564
	21st to end	Night	14% 5% 24% 39% 17% 1	627
September	1st to 10th	Night	12% 6% 27% 31% 21% 4	613
	11th to 20th	Night	14% 6% 24% 32% 19% 4	760
	21st to end	Night	19% 10% 24% 30% 13% 4	760
October	1st to 10th	Night	21% 10% 27% 28% 13% 1	760
	11th to 20th	Night	25% 15% 31% 23% 6%	760
	21st to end	Night	30% 15% 29% 20% 5%	836
November	1st to 10th	Night	22% 15% 34% 21% 7% 1	780
	11th to 20th	Night	24% 19% 35% 17% 4	800
	21st to end	Night	27% 17% 37% 16% 3	800
December	1st to 10th	Night	24% 19% 34% 19% 4	962
	11th to 20th	Night	25% 20% 37% 13% 4 1	1000
	21st to end	Night	29% 17% 35% 17% 2	1100

Page generated at 2025-03-09 08:08:42. Version ac07

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