Dundalk
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dundalk clear sky chart from 2005-11-06 to 2026-05-02.

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% 12% 5% 11% 6% 5% 5% 3 5% 6% 28%	132336
	Night	13% 13% 5% 12% 7% 5% 4 3 5% 6% 27%	130114
Transparency	Day	54% 7% 11% 17% 10% 1	135912
	Night	56% 8% 10% 16% 9% 1	134626
Seeing	Day	21% 20% 31% 18% 7% 2	16831
	Night	20% 20% 31% 20% 7% 1	25967

By Month

Percentage Cloud Cover NE (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% 15% 9% 20% 10% 5% 4 3 4 4 12%	4239
	11th to 20th	Day	7% 20% 12% 26% 11% 11% 3 2 2 1 4	5223
	21st to end	Day	10% 16% 7% 23% 11% 10% 7% 3 3 3 8%	5780
February	1st to 10th	Day	11% 17% 8% 18% 11% 7% 5% 3 3 3 13%	1890
	11th to 20th	Day	12% 13% 8% 18% 13% 6% 4 3 5% 5% 13%	1843
	21st to end	Day	13% 18% 7% 13% 9% 6% 5% 3 4 4 17%	1648
March	1st to 10th	Day	15% 13% 5% 14% 7% 6% 4 3 4 4 26%	4987
	11th to 20th	Day	10% 13% 9% 14% 6% 4 5% 3 5% 6% 25%	5090
	21st to end	Day	17% 15% 8% 10% 5% 4 4 3 4 5% 27%	5586
April	1st to 10th	Day	17% 16% 4 10% 6% 5% 4 2 5% 5% 26%	2441
	11th to 20th	Day	18% 14% 3 6% 4 4 4 3 4 5% 34%	2649
	21st to end	Day	20% 12% 4 7% 4 4 4 3 5% 5% 31%	2730
May	1st to 10th	Day	17% 10% 3 8% 5% 4 4 3 5% 7% 35%	5901
	11th to 20th	Day	16% 11% 3 8% 5% 4 4 3 5% 6% 34%	6176
	21st to end	Day	19% 8% 3 6% 4 4 4 3 5% 7% 37%	6949
June	1st to 10th	Day	15% 8% 3 7% 5% 5% 4 5% 6% 8% 35%	2803
	11th to 20th	Day	12% 7% 2 6% 4 5% 4 5% 6% 9% 40%	3000
	21st to end	Day	16% 7% 2 6% 4 4 5% 4 6% 8% 37%	3000
July	1st to 10th	Day	11% 7% 3 7% 5% 5% 5% 5% 6% 9% 36%	6819
	11th to 20th	Day	11% 6% 2 6% 4 4 5% 4 6% 8% 43%	6442
	21st to end	Day	8% 6% 2 6% 4 5% 4 4 6% 8% 46%	6424
August	1st to 10th	Day	14% 7% 3 7% 5% 5% 5% 4 7% 8% 35%	4234
	11th to 20th	Day	14% 8% 3 8% 5% 6% 5% 5% 7% 9% 29%	4174
	21st to end	Day	10% 6% 2 7% 5% 5% 6% 4 7% 8% 40%	4578
September	1st to 10th	Day	15% 8% 3 7% 5% 5% 6% 4 5% 7% 37%	2400
	11th to 20th	Day	12% 7% 2 7% 4 4 4 4 6% 8% 43%	2220
	21st to end	Day	17% 8% 4 8% 5% 4 5% 4 6% 8% 32%	2197
October	1st to 10th	Day	17% 11% 3 8% 4 5% 4 4 5% 6% 33%	2000
	11th to 20th	Day	20% 15% 3 9% 5% 5% 5% 5% 5% 5% 23%	2000
	21st to end	Day	23% 18% 5% 9% 5% 4 4 3 5% 5% 18%	2181
November	1st to 10th	Day	14% 19% 5% 9% 5% 5% 4 2 5% 5% 25%	1775
	11th to 20th	Day	13% 20% 6% 10% 6% 6% 4 3 6% 5% 20%	1680
	21st to end	Day	14% 24% 8% 13% 6% 5% 5% 3 4 5% 13%	1680
December	1st to 10th	Day	14% 24% 12% 17% 6% 5% 4 3 4 4 9%	2680
	11th to 20th	Day	17% 22% 9% 14% 6% 4 3 3 3 4 13%	3066
	21st to end	Day	21% 20% 8% 18% 7% 5% 4 2 3 3 9%	3851
January	1st to 10th	Night	12% 15% 8% 24% 11% 5% 4 3 3 5% 10%	8654
	11th to 20th	Night	8% 16% 10% 25% 13% 10% 4 2 2 3 6%	7660
	21st to end	Night	9% 12% 7% 19% 11% 9% 6% 4 5% 5% 11%	8401
February	1st to 10th	Night	11% 18% 6% 14% 10% 7% 5% 5% 5% 5% 15%	2730
	11th to 20th	Night	11% 14% 6% 18% 9% 6% 5% 4 5% 5% 18%	2663
	21st to end	Night	12% 15% 6% 15% 7% 6% 6% 4 5% 6% 19%	2155
March	1st to 10th	Night	12% 11% 6% 11% 6% 5% 6% 4 6% 7% 26%	5072
	11th to 20th	Night	7% 11% 7% 12% 6% 5% 5% 4 6% 7% 30%	5089
	21st to end	Night	17% 11% 4 11% 5% 4 4 4 5% 5% 30%	5588
April	1st to 10th	Night	17% 14% 5% 10% 5% 4 4 3 5% 6% 27%	2179
	11th to 20th	Night	15% 11% 3 8% 5% 5% 4 4 4 6% 36%	1939
	21st to end	Night	13% 13% 4 9% 5% 5% 4 4 4 6% 32%	1890
May	1st to 10th	Night	18% 9% 2 7% 4 4 4 3 5% 6% 38%	4062
	11th to 20th	Night	13% 8% 2 6% 5% 4 4 4 5% 7% 41%	3714
	21st to end	Night	17% 9% 2 5% 4 3 4 3 4 7% 44%	3926
June	1st to 10th	Night	13% 7% 3 7% 5% 5% 4 3 5% 9% 41%	1591
	11th to 20th	Night	10% 7% 2 5% 5% 4 5% 5% 7% 9% 43%	1400
	21st to end	Night	13% 7% 3 5% 4 4 5% 3 6% 8% 43%	1400
July	1st to 10th	Night	8% 9% 2 6% 4 4 4 4 5% 8% 45%	3160
	11th to 20th	Night	12% 7% 2 5% 4 3 3 3 5% 7% 49%	3502
	21st to end	Night	9% 7% 2 5% 4 3 4 3 6% 7% 49%	4428
August	1st to 10th	Night	11% 6% 2 6% 5% 4 4 3 5% 7% 47%	2915
	11th to 20th	Night	14% 7% 2 6% 4 4 4 3 5% 7% 44%	2875
	21st to end	Night	12% 6% 2 6% 5% 4 4 3 5% 7% 46%	3285
September	1st to 10th	Night	10% 6% 2 7% 4 4 4 3 6% 8% 46%	2000
	11th to 20th	Night	10% 6% 2 5% 5% 3 3 3 5% 6% 52%	2175
	21st to end	Night	16% 10% 3 6% 5% 4 4 2 4 7% 38%	2202
October	1st to 10th	Night	16% 8% 3 7% 5% 4 4 3 5% 7% 37%	2400
	11th to 20th	Night	19% 13% 4 9% 5% 5% 4 3 5% 6% 28%	2400
	21st to end	Night	19% 15% 4 8% 6% 5% 5% 4 5% 5% 23%	2655
November	1st to 10th	Night	16% 16% 4 9% 6% 4 5% 3 5% 5% 27%	2741
	11th to 20th	Night	14% 17% 6% 10% 5% 5% 5% 3 6% 6% 22%	2940
	21st to end	Night	16% 19% 8% 12% 6% 5% 4 3 5% 6% 15%	2940
December	1st to 10th	Night	13% 22% 9% 18% 6% 5% 4 3 5% 5% 9%	4720
	11th to 20th	Night	11% 23% 10% 18% 7% 5% 4 3 3 3 13%	5348
	21st to end	Night	19% 21% 8% 18% 7% 6% 4 3 4 3 7%	7315

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% 8% 8% 4	4240
	11th to 20th	Day	87% 6% 3 3 2	5257
	21st to end	Day	78% 7% 7% 5% 2	5780
February	1st to 10th	Day	76% 6% 5% 10% 3 1	1890
	11th to 20th	Day	70% 8% 7% 10% 4 1	1852
	21st to end	Day	69% 7% 7% 11% 5%	1648
March	1st to 10th	Day	60% 6% 13% 11% 10%	4990
	11th to 20th	Day	57% 6% 12% 18% 5% 3	5090
	21st to end	Day	57% 7% 10% 15% 9% 1	5586
April	1st to 10th	Day	59% 6% 8% 17% 9% 1	2441
	11th to 20th	Day	51% 6% 10% 20% 13% 1	2649
	21st to end	Day	52% 7% 10% 18% 11% 2	2730
May	1st to 10th	Day	46% 7% 12% 18% 10% 6%	5910
	11th to 20th	Day	48% 9% 11% 15% 16% 1	6180
	21st to end	Day	45% 7% 11% 19% 14% 4	6949
June	1st to 10th	Day	45% 8% 12% 20% 15% 1	2803
	11th to 20th	Day	40% 8% 12% 24% 15% 1	3000
	21st to end	Day	43% 8% 13% 23% 12% 1	3000
July	1st to 10th	Day	44% 7% 13% 21% 15% 1	6746
	11th to 20th	Day	37% 7% 11% 30% 15% 1	6363
	21st to end	Day	34% 7% 13% 28% 17% 1	6240
August	1st to 10th	Day	45% 8% 13% 22% 11% 1	4221
	11th to 20th	Day	47% 9% 15% 21% 7%	4213
	21st to end	Day	39% 9% 14% 29% 10% 1	4578
September	1st to 10th	Day	45% 7% 13% 23% 10% 2	2400
	11th to 20th	Day	38% 7% 14% 27% 14%	2220
	21st to end	Day	48% 9% 12% 21% 9% 1	2197
October	1st to 10th	Day	46% 7% 12% 24% 11% 1	3260
	11th to 20th	Day	49% 7% 11% 19% 13%	3240
	21st to end	Day	61% 6% 11% 16% 5%	3507
November	1st to 10th	Day	59% 7% 11% 15% 7%	1775
	11th to 20th	Day	63% 9% 10% 12% 6% 1	1680
	21st to end	Day	71% 9% 9% 8% 2	1680
December	1st to 10th	Day	79% 6% 9% 5% 1	2680
	11th to 20th	Day	75% 6% 8% 8% 4	3066
	21st to end	Day	80% 7% 4 5% 5%	3851
January	1st to 10th	Night	72% 10% 8% 7% 4	8654
	11th to 20th	Night	83% 7% 3 5% 2	7701
	21st to end	Night	70% 10% 8% 5% 6%	8401
February	1st to 10th	Night	68% 9% 8% 11% 4	2730
	11th to 20th	Night	64% 9% 10% 12% 5%	2665
	21st to end	Night	61% 10% 11% 11% 7%	2155
March	1st to 10th	Night	54% 7% 14% 14% 10% 1	5082
	11th to 20th	Night	48% 9% 16% 17% 8% 2	5090
	21st to end	Night	52% 7% 11% 16% 12% 2	5588
April	1st to 10th	Night	57% 6% 9% 17% 11% 1	2179
	11th to 20th	Night	48% 6% 8% 20% 15% 1	1939
	21st to end	Night	51% 7% 10% 15% 15% 2	1890
May	1st to 10th	Night	46% 6% 12% 15% 13% 8%	4069
	11th to 20th	Night	39% 10% 12% 21% 16% 2	3715
	21st to end	Night	39% 7% 12% 25% 15% 2	3927
June	1st to 10th	Night	39% 8% 11% 23% 17% 2	1591
	11th to 20th	Night	36% 8% 14% 24% 17% 1	1400
	21st to end	Night	38% 7% 14% 26% 14% 1	1400
July	1st to 10th	Night	36% 6% 14% 23% 17% 3	3125
	11th to 20th	Night	35% 5% 10% 30% 18% 1	3458
	21st to end	Night	33% 7% 11% 32% 16% 2	4297
August	1st to 10th	Night	36% 7% 13% 27% 17% 1	2904
	11th to 20th	Night	38% 6% 16% 26% 13% 1	2902
	21st to end	Night	36% 7% 13% 30% 12% 1	3285
September	1st to 10th	Night	34% 7% 15% 29% 13% 1	2000
	11th to 20th	Night	31% 7% 13% 30% 18% 1	2175
	21st to end	Night	46% 7% 12% 23% 11% 1	2202
October	1st to 10th	Night	37% 8% 10% 24% 20% 1	3920
	11th to 20th	Night	48% 7% 12% 19% 14% 1	3899
	21st to end	Night	51% 8% 14% 20% 7%	4279
November	1st to 10th	Night	56% 9% 11% 17% 7% 1	2741
	11th to 20th	Night	59% 9% 13% 12% 6% 1	2940
	21st to end	Night	67% 10% 12% 9% 2 1	2940
December	1st to 10th	Night	76% 7% 9% 6% 1	4720
	11th to 20th	Night	75% 7% 7% 8% 4	5348
	21st to end	Night	81% 7% 5% 6% 2	7315

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	23% 33% 30% 12% 2	220
	11th to 20th	Day	22% 38% 30% 7% 3	325
	21st to end	Day	25% 31% 32% 11% 2	363
February	1st to 10th	Day	28% 30% 32% 9% 1	330
	11th to 20th	Day	26% 34% 34% 5%	330
	21st to end	Day	31% 36% 29% 5%	273
March	1st to 10th	Day	27% 25% 34% 11% 3	509
	11th to 20th	Day	29% 24% 30% 13% 3	540
	21st to end	Day	30% 23% 30% 13% 4	594
April	1st to 10th	Day	29% 23% 33% 11% 4	540
	11th to 20th	Day	32% 23% 23% 13% 7% 2	532
	21st to end	Day	27% 20% 34% 14% 3 2	540
May	1st to 10th	Day	22% 18% 35% 19% 5% 1	507
	11th to 20th	Day	20% 16% 33% 20% 8% 3	527
	21st to end	Day	19% 16% 30% 24% 9% 3	573
June	1st to 10th	Day	19% 19% 31% 23% 7% 1	533
	11th to 20th	Day	15% 16% 34% 26% 6% 2	730
	21st to end	Day	17% 16% 37% 22% 7% 2	730
July	1st to 10th	Day	13% 13% 31% 27% 13% 4	721
	11th to 20th	Day	15% 11% 32% 25% 12% 5%	585
	21st to end	Day	10% 10% 38% 26% 11% 5%	576
August	1st to 10th	Day	10% 11% 29% 30% 14% 6%	526
	11th to 20th	Day	13% 9% 25% 28% 17% 7%	519
	21st to end	Day	14% 11% 31% 25% 15% 4	583
September	1st to 10th	Day	16% 15% 27% 24% 11% 6%	530
	11th to 20th	Day	11% 11% 23% 26% 19% 10%	530
	21st to end	Day	18% 16% 29% 20% 13% 3	530
October	1st to 10th	Day	22% 20% 26% 18% 12% 2	530
	11th to 20th	Day	24% 24% 34% 14% 4	530
	21st to end	Day	31% 24% 29% 14% 3	564
November	1st to 10th	Day	29% 27% 30% 10% 3	289
	11th to 20th	Day	31% 24% 34% 6% 4 1	220
	21st to end	Day	24% 30% 38% 8%	220
December	1st to 10th	Day	28% 35% 26% 10% 1	220
	11th to 20th	Day	33% 30% 28% 7% 1	220
	21st to end	Day	31% 33% 27% 7% 2 1	242
January	1st to 10th	Night	20% 33% 32% 13% 2	990
	11th to 20th	Night	25% 27% 33% 14% 1	840
	21st to end	Night	18% 22% 39% 18% 4	924
February	1st to 10th	Night	21% 31% 32% 14% 1	840
	11th to 20th	Night	22% 27% 34% 14% 2	823
	21st to end	Night	22% 31% 32% 12% 2	692
March	1st to 10th	Night	20% 26% 36% 16% 3	840
	11th to 20th	Night	21% 27% 34% 15% 3	840
	21st to end	Night	22% 22% 32% 19% 5% 1	924
April	1st to 10th	Night	23% 23% 36% 16% 2	840
	11th to 20th	Night	22% 21% 29% 19% 7% 1	695
	21st to end	Night	21% 18% 31% 21% 8%	630
May	1st to 10th	Night	17% 14% 32% 28% 8% 1	603
	11th to 20th	Night	18% 12% 32% 28% 10%	455
	21st to end	Night	13% 12% 30% 33% 11%	433
June	1st to 10th	Night	14% 11% 39% 29% 8%	400
	11th to 20th	Night	12% 12% 30% 36% 10%	400
	21st to end	Night	14% 12% 31% 30% 12% 1	400
July	1st to 10th	Night	7% 7% 28% 41% 16% 1	390
	11th to 20th	Night	9% 8% 34% 31% 17% 1	406
	21st to end	Night	10% 6% 31% 35% 16% 1	657
August	1st to 10th	Night	10% 5% 27% 36% 21% 1	597
	11th to 20th	Night	9% 7% 23% 36% 22% 3	594
	21st to end	Night	13% 10% 28% 28% 19% 1	696
September	1st to 10th	Night	13% 11% 30% 26% 17% 4	800
	11th to 20th	Night	13% 9% 26% 30% 18% 5%	800
	21st to end	Night	20% 12% 24% 28% 12% 4	800
October	1st to 10th	Night	19% 15% 32% 20% 13% 1	800
	11th to 20th	Night	24% 21% 31% 17% 7% 1	800
	21st to end	Night	24% 24% 32% 16% 3	880
November	1st to 10th	Night	25% 22% 29% 19% 5%	820
	11th to 20th	Night	23% 29% 28% 15% 5% 1	840
	21st to end	Night	26% 25% 33% 13% 2	840
December	1st to 10th	Night	26% 27% 33% 10% 3	840
	11th to 20th	Night	21% 31% 36% 10% 2	840
	21st to end	Night	29% 30% 28% 11% 1	998

Page generated at 2026-04-29 02:21:43. Version ac07

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