Roscommon
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Roscommon clear sky chart from 2005-11-05 to 2024-10-14.

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 9% 5% 5% 5% 4 5% 7% 32%	100890
	Night	14% 13% 5% 10% 5% 5% 4 3 5% 6% 31%	97716
Transparency	Day	51% 7% 12% 19% 11% 1	100681
	Night	53% 7% 12% 18% 9% 1	97602
Seeing	Day	20% 17% 31% 20% 9% 3	15546
	Night	20% 14% 32% 25% 9% 1	25175

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	13% 21% 9% 16% 7% 4 4 3 3 5% 14%	2527
	11th to 20th	Day	14% 17% 7% 17% 11% 11% 6% 3 3 3 6%	2530
	21st to end	Day	18% 21% 12% 13% 5% 4 4 3 4 5% 11%	2783
February	1st to 10th	Day	10% 18% 6% 14% 13% 6% 5% 3 4 4 17%	1691
	11th to 20th	Day	11% 15% 7% 15% 9% 6% 4 3 4 4 20%	1810
	21st to end	Day	11% 18% 8% 13% 8% 5% 4 3 3 5% 22%	1570
March	1st to 10th	Day	13% 14% 5% 9% 5% 5% 5% 4 5% 5% 31%	3120
	11th to 20th	Day	11% 12% 7% 15% 5% 4 4 4 6% 5% 27%	3447
	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	23% 15% 3 10% 6% 5% 3 3 5% 6% 21%	1774
	21st to end	Day	22% 16% 3 10% 5% 5% 5% 4 5% 6% 19%	1782
November	1st to 10th	Day	14% 15% 4 8% 5% 5% 4 4 7% 7% 27%	1672
	11th to 20th	Day	15% 18% 7% 10% 5% 4 6% 4 4 6% 21%	1710
	21st to end	Day	19% 21% 7% 12% 6% 4 3 2 4 5% 18%	1573
December	1st to 10th	Day	15% 20% 10% 14% 6% 5% 3 4 4 4 14%	1364
	11th to 20th	Day	16% 20% 7% 13% 7% 5% 4 3 4 4 16%	1675
	21st to end	Day	23% 25% 9% 16% 6% 4 3 2 2 3 7%	2623
January	1st to 10th	Night	14% 17% 10% 18% 6% 5% 3 3 3 4 16%	4428
	11th to 20th	Night	12% 17% 8% 17% 11% 11% 5% 3 4 4 9%	4440
	21st to end	Night	15% 21% 10% 17% 7% 5% 5% 3 4 4 10%	4884
February	1st to 10th	Night	10% 16% 6% 14% 11% 7% 5% 4 5% 4 17%	2488
	11th to 20th	Night	13% 14% 6% 14% 8% 6% 5% 4 6% 5% 20%	2255
	21st to end	Night	15% 15% 5% 13% 7% 4 4 4 4 5% 24%	1884
March	1st to 10th	Night	15% 9% 4 8% 4 4 4 3 5% 6% 38%	3733
	11th to 20th	Night	9% 13% 6% 8% 5% 3 4 4 5% 6% 37%	3513
	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	20% 13% 4 8% 4 4 3 3 5% 6% 29%	2257
	21st to end	Night	24% 13% 4 8% 5% 4 3 3 5% 6% 25%	2574
November	1st to 10th	Night	12% 12% 4 8% 5% 4 5% 4 6% 8% 33%	2406
	11th to 20th	Night	13% 19% 4 11% 6% 6% 4 4 4 5% 23%	2470
	21st to end	Night	18% 19% 6% 12% 5% 4 4 4 5% 6% 19%	2603
December	1st to 10th	Night	14% 19% 7% 13% 7% 5% 5% 4 6% 5% 15%	2813
	11th to 20th	Night	14% 20% 6% 16% 7% 5% 5% 3 4 5% 15%	3522
	21st to end	Night	23% 26% 7% 13% 4 4 3 2 3 3 11%	5040

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% 8% 11% 6% 3	2528
	11th to 20th	Day	82% 7% 5% 5% 1	2530
	21st to end	Day	76% 6% 12% 4 2	2783
February	1st to 10th	Day	70% 6% 8% 12% 3 1	1691
	11th to 20th	Day	66% 6% 9% 12% 7% 1	1820
	21st to end	Day	64% 5% 10% 15% 4 1	1570
March	1st to 10th	Day	54% 6% 13% 18% 8% 1	3120
	11th to 20th	Day	55% 8% 12% 17% 6% 2	3447
	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	46% 7% 11% 24% 11% 1	2071
	11th to 20th	Day	64% 6% 11% 15% 4	1775
	21st to end	Day	65% 7% 12% 11% 5%	1782
November	1st to 10th	Day	54% 7% 13% 19% 8%	1672
	11th to 20th	Day	62% 9% 14% 10% 5%	1710
	21st to end	Day	69% 6% 11% 10% 3	1573
December	1st to 10th	Day	73% 6% 9% 9% 1 1	1364
	11th to 20th	Day	72% 6% 10% 10% 2	1671
	21st to end	Day	84% 4 5% 4 2	2623
January	1st to 10th	Night	70% 7% 9% 11% 3	4428
	11th to 20th	Night	77% 8% 7% 6% 2	4440
	21st to end	Night	75% 8% 10% 5% 1	4884
February	1st to 10th	Night	67% 7% 9% 11% 5% 1	2488
	11th to 20th	Night	63% 8% 10% 15% 5% 1	2256
	21st to end	Night	62% 6% 11% 14% 7%	1884
March	1st to 10th	Night	46% 6% 16% 22% 10% 1	3733
	11th to 20th	Night	44% 8% 14% 23% 10% 1	3513
	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	42% 6% 12% 26% 12% 1	2108
	11th to 20th	Night	55% 6% 12% 20% 6% 1	2261
	21st to end	Night	59% 7% 12% 16% 7%	2574
November	1st to 10th	Night	48% 7% 15% 21% 9% 1	2406
	11th to 20th	Night	63% 7% 11% 14% 6%	2470
	21st to end	Night	65% 7% 14% 11% 2 1	2603
December	1st to 10th	Night	69% 9% 9% 11% 2	2813
	11th to 20th	Night	70% 8% 11% 8% 3	3525
	21st to end	Night	79% 6% 7% 5% 3	5040

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% 21% 38% 11% 4	270
	11th to 20th	Day	24% 23% 40% 11% 3	270
	21st to end	Day	28% 19% 36% 14% 3 1	297
February	1st to 10th	Day	22% 32% 35% 7% 3 1	270
	11th to 20th	Day	24% 31% 36% 7% 1	270
	21st to end	Day	32% 27% 36% 4 1	225
March	1st to 10th	Day	26% 34% 31% 9%	270
	11th to 20th	Day	24% 21% 33% 17% 5%	440
	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	32% 18% 32% 15% 3	406
	21st to end	Day	32% 25% 30% 9% 3 1	297
November	1st to 10th	Day	25% 20% 34% 16% 4 1	270
	11th to 20th	Day	27% 22% 38% 10% 3	270
	21st to end	Day	23% 27% 36% 13%	205
December	1st to 10th	Day	29% 23% 32% 11% 4 2	180
	11th to 20th	Day	31% 28% 30% 9% 2	180
	21st to end	Day	32% 30% 28% 7% 2	252
January	1st to 10th	Night	21% 20% 36% 19% 4 1	950
	11th to 20th	Night	24% 19% 33% 19% 4 1	950
	21st to end	Night	20% 13% 40% 22% 5%	1045
February	1st to 10th	Night	20% 19% 38% 18% 4	778
	11th to 20th	Night	23% 21% 33% 20% 4	743
	21st to end	Night	26% 20% 33% 18% 2	628
March	1st to 10th	Night	18% 19% 35% 21% 7% 1	760
	11th to 20th	Night	20% 20% 35% 20% 5%	760
	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	26% 15% 31% 22% 6%	735
	21st to end	Night	31% 14% 29% 19% 6% 1	792
November	1st to 10th	Night	21% 15% 34% 21% 7% 1	740
	11th to 20th	Night	23% 20% 36% 17% 4	760
	21st to end	Night	26% 16% 37% 17% 3	760
December	1st to 10th	Night	25% 19% 35% 18% 4	913
	11th to 20th	Night	24% 20% 38% 13% 4 1	950
	21st to end	Night	29% 18% 36% 16% 2	1045

Page generated at 2024-10-11 10:49:59. Version ac07

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