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 2024-02-10.

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	15% 11% 5% 8% 7% 4 5% 5% 5% 7% 30%	77948
	Night	14% 13% 5% 9% 7% 4 4 4 5% 6% 29%	81059
Transparency	Day	53% 7% 12% 17% 10% 1	77648
	Night	55% 7% 12% 17% 8% 1	80880
Seeing	Day	20% 17% 31% 20% 9% 3	14515
	Night	20% 14% 32% 25% 9% 1	24374

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% 20% 10% 15% 8% 3 4 4 3 5% 14%	2527
	11th to 20th	Day	14% 16% 8% 16% 13% 9% 7% 4 4 4 6%	2530
	21st to end	Day	18% 20% 12% 11% 7% 3 5% 4 4 5% 11%	2783
February	1st to 10th	Day	11% 15% 7% 13% 14% 4 6% 4 5% 4 17%	1682
	11th to 20th	Day	12% 14% 8% 14% 10% 5% 4 4 4 4 20%	1712
	21st to end	Day	12% 18% 9% 12% 8% 4 4 3 3 5% 21%	1480
March	1st to 10th	Day	14% 11% 5% 9% 9% 4 5% 5% 5% 5% 28%	1800
	11th to 20th	Day	12% 12% 5% 9% 7% 3 5% 4 5% 5% 31%	1961
	21st to end	Day	18% 12% 5% 8% 6% 3 5% 4 4 5% 30%	2204
April	1st to 10th	Day	19% 14% 5% 8% 6% 4 4 4 4 6% 27%	2160
	11th to 20th	Day	20% 12% 4 6% 4 2 4 4 5% 6% 34%	2255
	21st to end	Day	16% 12% 4 7% 7% 2 4 5% 5% 7% 31%	2340
May	1st to 10th	Day	16% 10% 4 6% 6% 4 5% 3 6% 7% 34%	2340
	11th to 20th	Day	17% 8% 3 7% 5% 3 5% 4 5% 6% 38%	2306
	21st to end	Day	12% 6% 2 6% 5% 3 6% 5% 6% 8% 42%	2725
June	1st to 10th	Day	14% 6% 2 5% 5% 3 5% 6% 6% 8% 40%	2668
	11th to 20th	Day	13% 6% 2 5% 5% 4 5% 6% 7% 9% 39%	2700
	21st to end	Day	13% 5% 3 6% 5% 3 6% 6% 6% 8% 38%	2657
July	1st to 10th	Day	8% 5% 2 5% 5% 4 5% 5% 6% 9% 47%	2520
	11th to 20th	Day	11% 5% 3 5% 5% 3 5% 6% 7% 9% 41%	2520
	21st to end	Day	9% 5% 3 5% 6% 4 6% 6% 7% 9% 41%	2743
August	1st to 10th	Day	9% 5% 2 6% 6% 4 6% 7% 6% 10% 38%	2350
	11th to 20th	Day	10% 7% 2 6% 5% 3 5% 5% 6% 8% 42%	2303
	21st to end	Day	13% 7% 2 6% 5% 3 4 5% 5% 8% 42%	2515
September	1st to 10th	Day	14% 6% 3 5% 6% 4 6% 5% 6% 9% 38%	2102
	11th to 20th	Day	13% 6% 2 5% 5% 3 4 5% 5% 7% 45%	1980
	21st to end	Day	16% 7% 3 6% 6% 3 6% 6% 6% 9% 33%	1980
October	1st to 10th	Day	18% 9% 4 6% 6% 3 4 4 5% 6% 36%	1962
	11th to 20th	Day	23% 14% 3 9% 7% 3 4 3 5% 6% 22%	1744
	21st to end	Day	23% 15% 4 8% 6% 4 5% 5% 5% 6% 19%	1782
November	1st to 10th	Day	15% 14% 4 7% 5% 3 4 5% 6% 8% 27%	1672
	11th to 20th	Day	15% 17% 8% 9% 7% 4 5% 5% 4 6% 21%	1710
	21st to end	Day	19% 20% 7% 11% 7% 3 3 3 3 5% 18%	1573
December	1st to 10th	Day	15% 19% 11% 13% 7% 4 4 4 4 5% 14%	1364
	11th to 20th	Day	17% 19% 8% 12% 7% 4 5% 4 4 5% 16%	1675
	21st to end	Day	24% 24% 10% 15% 7% 3 3 3 2 3 7%	2623
January	1st to 10th	Night	15% 16% 11% 16% 8% 4 4 3 3 4 16%	4428
	11th to 20th	Night	12% 16% 8% 14% 13% 8% 7% 4 4 4 9%	4440
	21st to end	Night	15% 20% 10% 15% 8% 4 5% 4 4 4 10%	4884
February	1st to 10th	Night	11% 15% 7% 12% 12% 6% 6% 5% 4 5% 17%	2482
	11th to 20th	Night	14% 13% 7% 12% 8% 5% 6% 4 6% 5% 21%	2133
	21st to end	Night	15% 15% 6% 13% 7% 4 5% 4 4 4 23%	1776
March	1st to 10th	Night	13% 10% 5% 9% 6% 4 5% 4 4 5% 36%	2160
	11th to 20th	Night	13% 12% 6% 7% 6% 2 4 4 5% 5% 37%	1999
	21st to end	Night	16% 11% 4 7% 5% 3 4 4 5% 5% 35%	2168
April	1st to 10th	Night	16% 13% 4 8% 4 2 5% 4 6% 7% 30%	1800
	11th to 20th	Night	19% 10% 4 6% 4 2 3 4 5% 7% 36%	1652
	21st to end	Night	15% 10% 3 7% 5% 4 5% 4 4 6% 37%	1620
May	1st to 10th	Night	14% 7% 3 7% 6% 5% 5% 5% 5% 9% 34%	1620
	11th to 20th	Night	14% 8% 3 7% 6% 4 5% 5% 6% 6% 37%	1584
	21st to end	Night	13% 5% 2 4 5% 3 5% 5% 6% 8% 45%	1551
June	1st to 10th	Night	13% 4 3 5% 5% 3 5% 4 5% 9% 44%	1287
	11th to 20th	Night	8% 6% 2 5% 5% 3 4 4 7% 8% 47%	1260
	21st to end	Night	10% 7% 3 5% 4 3 4 5% 6% 7% 45%	1297
July	1st to 10th	Night	6% 4 2 4 3 2 4 5% 7% 10% 53%	1440
	11th to 20th	Night	7% 4 3 5% 5% 3 4 5% 6% 9% 50%	1440
	21st to end	Night	8% 6% 2 5% 4 3 4 5% 6% 7% 49%	1575
August	1st to 10th	Night	7% 4 3 5% 5% 3 5% 5% 5% 9% 49%	1587
	11th to 20th	Night	9% 4 2 4 4 3 4 6% 5% 7% 52%	1598
	21st to end	Night	11% 6% 3 4 4 3 4 5% 5% 7% 47%	1839
September	1st to 10th	Night	11% 5% 2 5% 5% 3 4 4 6% 6% 50%	1840
	11th to 20th	Night	12% 6% 2 4 3 2 4 4 5% 7% 50%	1980
	21st to end	Night	16% 7% 2 5% 5% 3 4 4 5% 9% 39%	1980
October	1st to 10th	Night	18% 8% 2 5% 5% 3 3 3 5% 6% 42%	1997
	11th to 20th	Night	20% 12% 4 7% 5% 3 4 3 5% 7% 29%	2214
	21st to end	Night	25% 12% 4 7% 5% 3 3 4 5% 6% 26%	2574
November	1st to 10th	Night	12% 12% 4 7% 6% 3 4 5% 6% 8% 33%	2406
	11th to 20th	Night	13% 18% 5% 10% 7% 4 5% 5% 4 5% 23%	2470
	21st to end	Night	18% 17% 7% 11% 6% 3 4 5% 4 6% 19%	2603
December	1st to 10th	Night	14% 16% 9% 12% 8% 4 5% 5% 5% 5% 15%	2813
	11th to 20th	Night	14% 18% 7% 14% 9% 4 5% 5% 4 5% 15%	3522
	21st to end	Night	23% 25% 8% 11% 6% 3 3 3 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% 7% 13% 3 1	1682
	11th to 20th	Day	67% 6% 8% 11% 7% 1	1722
	21st to end	Day	66% 5% 10% 14% 4 1	1480
March	1st to 10th	Day	57% 6% 12% 16% 8% 1	1800
	11th to 20th	Day	54% 6% 11% 18% 8% 3	1961
	21st to end	Day	56% 5% 10% 18% 10% 1	2204
April	1st to 10th	Day	58% 5% 11% 15% 9% 1	2160
	11th to 20th	Day	51% 5% 11% 18% 14% 1	2255
	21st to end	Day	52% 6% 12% 13% 13% 3	2340
May	1st to 10th	Day	49% 7% 10% 21% 11% 2	2340
	11th to 20th	Day	46% 6% 11% 21% 13% 2	2310
	21st to end	Day	40% 8% 14% 23% 14% 1	2725
June	1st to 10th	Day	40% 7% 13% 24% 14% 1	2668
	11th to 20th	Day	40% 7% 13% 22% 16% 1	2700
	21st to end	Day	41% 8% 13% 23% 13% 1	2657
July	1st to 10th	Day	33% 8% 14% 25% 19% 2	2451
	11th to 20th	Day	36% 9% 14% 24% 16% 1	2445
	21st to end	Day	37% 8% 15% 22% 17% 2	2591
August	1st to 10th	Day	38% 11% 15% 24% 11% 1	2335
	11th to 20th	Day	38% 8% 15% 24% 13% 2	2303
	21st to end	Day	40% 7% 15% 22% 14% 2	2515
September	1st to 10th	Day	41% 8% 13% 22% 14% 2	2102
	11th to 20th	Day	37% 7% 16% 28% 12% 1	1980
	21st to end	Day	45% 9% 15% 23% 8%	1980
October	1st to 10th	Day	48% 7% 11% 22% 11% 1	1962
	11th to 20th	Day	63% 6% 11% 15% 4	1744
	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% 8% 11% 5% 1	2482
	11th to 20th	Night	64% 6% 9% 15% 5% 1	2134
	21st to end	Night	64% 6% 10% 14% 7%	1776
March	1st to 10th	Night	50% 5% 13% 21% 11% 1	2160
	11th to 20th	Night	48% 7% 10% 21% 12% 2	1999
	21st to end	Night	50% 6% 12% 20% 11% 1	2168
April	1st to 10th	Night	52% 6% 11% 18% 12% 1	1800
	11th to 20th	Night	47% 6% 10% 21% 15% 2	1652
	21st to end	Night	47% 7% 12% 18% 15% 3	1620
May	1st to 10th	Night	46% 7% 13% 19% 11% 3	1620
	11th to 20th	Night	46% 6% 9% 22% 14% 2	1585
	21st to end	Night	36% 7% 16% 24% 15% 3	1552
June	1st to 10th	Night	38% 7% 10% 25% 18% 2	1287
	11th to 20th	Night	34% 8% 15% 25% 16% 2	1260
	21st to end	Night	36% 8% 12% 27% 15% 2	1297
July	1st to 10th	Night	24% 8% 16% 32% 18% 3	1400
	11th to 20th	Night	29% 8% 15% 29% 18%	1392
	21st to end	Night	32% 8% 17% 27% 16% 1	1487
August	1st to 10th	Night	30% 8% 19% 28% 13% 1	1578
	11th to 20th	Night	29% 8% 17% 29% 16%	1598
	21st to end	Night	35% 7% 15% 25% 15% 2	1839
September	1st to 10th	Night	33% 9% 13% 27% 17% 2	1840
	11th to 20th	Night	34% 6% 15% 33% 12%	1980
	21st to end	Night	43% 7% 17% 26% 8%	1980
October	1st to 10th	Night	44% 6% 13% 24% 12% 1	1997
	11th to 20th	Night	55% 6% 12% 19% 6% 1	2214
	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% 31% 35% 8% 3 1	267
	11th to 20th	Day	25% 31% 36% 7%	240
	21st to end	Day	33% 27% 35% 4 1	198
March	1st to 10th	Day	28% 35% 29% 9%	240
	11th to 20th	Day	23% 19% 34% 17% 6%	401
	21st to end	Day	29% 17% 28% 19% 5% 1	462
April	1st to 10th	Day	27% 20% 32% 15% 5% 1	420
	11th to 20th	Day	31% 20% 26% 14% 6% 2	412
	21st to end	Day	23% 22% 26% 20% 7% 2	420
May	1st to 10th	Day	25% 20% 31% 14% 7% 3	423
	11th to 20th	Day	20% 16% 29% 24% 6% 4	452
	21st to end	Day	17% 14% 32% 26% 10% 3	679
June	1st to 10th	Day	14% 17% 33% 25% 8% 2	630
	11th to 20th	Day	16% 14% 32% 25% 10% 3	630
	21st to end	Day	15% 12% 36% 24% 10% 3	630
July	1st to 10th	Day	8% 10% 34% 28% 14% 6%	621
	11th to 20th	Day	10% 13% 30% 28% 14% 5%	618
	21st to end	Day	10% 9% 34% 29% 12% 5%	684
August	1st to 10th	Day	11% 6% 27% 28% 18% 10%	469
	11th to 20th	Day	12% 8% 23% 32% 15% 10%	439
	21st to end	Day	18% 10% 26% 25% 17% 4	495
September	1st to 10th	Day	17% 10% 28% 24% 14% 7%	450
	11th to 20th	Day	12% 12% 23% 28% 17% 8%	450
	21st to end	Day	22% 12% 22% 26% 12% 6%	450
October	1st to 10th	Day	24% 16% 26% 19% 12% 2	450
	11th to 20th	Day	31% 18% 31% 15% 4	394
	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% 20% 38% 18% 4	777
	11th to 20th	Night	23% 21% 33% 19% 4	703
	21st to end	Night	27% 20% 32% 18% 2	592
March	1st to 10th	Night	18% 19% 35% 21% 7% 1	720
	11th to 20th	Night	21% 20% 34% 20% 5%	720
	21st to end	Night	21% 14% 35% 23% 5% 1	782
April	1st to 10th	Night	22% 17% 34% 21% 5% 1	540
	11th to 20th	Night	24% 14% 32% 24% 6% 1	533
	21st to end	Night	19% 13% 34% 27% 6% 1	540
May	1st to 10th	Night	16% 11% 36% 28% 7% 1	540
	11th to 20th	Night	18% 11% 30% 31% 10%	531
	21st to end	Night	15% 7% 28% 34% 15% 1	584
June	1st to 10th	Night	15% 6% 35% 34% 10% 1	387
	11th to 20th	Night	11% 6% 34% 40% 9%	360
	21st to end	Night	11% 6% 31% 36% 15% 1	397
July	1st to 10th	Night	8% 3 22% 44% 22% 1	525
	11th to 20th	Night	8% 6% 26% 36% 22% 2	522
	21st to end	Night	11% 5% 27% 37% 19% 1	591
August	1st to 10th	Night	9% 3 25% 41% 22% 1	537
	11th to 20th	Night	10% 6% 19% 35% 28% 3	534
	21st to end	Night	14% 5% 24% 39% 17% 1	594
September	1st to 10th	Night	12% 5% 27% 32% 21% 4	580
	11th to 20th	Night	14% 7% 25% 31% 18% 4	720
	21st to end	Night	19% 10% 24% 29% 13% 4	720
October	1st to 10th	Night	22% 10% 26% 28% 13% 1	720
	11th to 20th	Night	26% 15% 31% 22% 6%	720
	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

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