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 2025-01-07.

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% 10% 6% 5% 5% 4 5% 6% 28%	105388
	Night	13% 13% 5% 12% 6% 5% 4 3 5% 6% 27%	103590
Transparency	Day	53% 8% 11% 17% 9% 1	108974
	Night	54% 9% 11% 16% 9% 1	108093
Seeing	Day	21% 20% 31% 18% 8% 3	15123
	Night	19% 20% 31% 20% 8% 1	24259

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% 19% 10% 19% 8% 5% 4 3 3 4 12%	2317
	11th to 20th	Day	10% 20% 10% 23% 10% 11% 3 2 3 2 6%	2817
	21st to end	Day	15% 22% 8% 19% 7% 5% 4 3 3 4 10%	3124
February	1st to 10th	Day	11% 18% 8% 18% 11% 8% 5% 3 3 3 12%	1710
	11th to 20th	Day	11% 13% 8% 18% 11% 6% 4 3 5% 5% 14%	1663
	21st to end	Day	14% 18% 7% 13% 8% 6% 5% 3 4 4 18%	1495
March	1st to 10th	Day	15% 16% 5% 13% 6% 5% 4 3 4 4 26%	3392
	11th to 20th	Day	9% 14% 12% 15% 6% 4 5% 3 4 5% 24%	3480
	21st to end	Day	14% 13% 6% 9% 6% 5% 5% 4 4 6% 29%	3815
April	1st to 10th	Day	16% 16% 4 10% 6% 5% 4 3 5% 5% 25%	2209
	11th to 20th	Day	18% 14% 3 6% 4 4 4 3 4 6% 34%	2394
	21st to end	Day	20% 12% 4 7% 4 4 3 3 5% 5% 31%	2470
May	1st to 10th	Day	17% 10% 3 8% 4 4 4 3 6% 7% 33%	4108
	11th to 20th	Day	16% 10% 3 7% 6% 5% 5% 4 6% 8% 31%	4298
	21st to end	Day	14% 6% 2 6% 4 3 4 3 5% 8% 45%	4837
June	1st to 10th	Day	15% 8% 3 7% 4 5% 4 5% 6% 8% 35%	2663
	11th to 20th	Day	12% 7% 2 6% 4 5% 4 5% 6% 9% 40%	2850
	21st to end	Day	16% 7% 2 6% 4 4 5% 4 6% 7% 37%	2850
July	1st to 10th	Day	12% 7% 3 7% 5% 6% 6% 5% 7% 9% 33%	4760
	11th to 20th	Day	12% 6% 2 6% 5% 5% 6% 5% 6% 8% 40%	4494
	21st to end	Day	9% 7% 3 7% 5% 5% 4 4 6% 9% 40%	4466
August	1st to 10th	Day	14% 7% 3 7% 5% 5% 5% 4 7% 8% 34%	4104
	11th to 20th	Day	14% 8% 3 8% 5% 6% 5% 5% 8% 10% 29%	4044
	21st to end	Day	10% 6% 2 7% 5% 5% 6% 4 7% 8% 39%	4438
September	1st to 10th	Day	15% 8% 3 7% 5% 4 5% 4 4 7% 37%	2280
	11th to 20th	Day	13% 7% 2 7% 4 4 4 4 6% 8% 41%	2109
	21st to end	Day	16% 8% 4 8% 5% 4 5% 4 6% 8% 31%	2087
October	1st to 10th	Day	18% 11% 3 8% 5% 5% 4 4 5% 6% 31%	1900
	11th to 20th	Day	20% 16% 3 9% 5% 5% 5% 5% 5% 5% 23%	1900
	21st to end	Day	24% 19% 5% 9% 5% 4 4 3 5% 5% 17%	2072
November	1st to 10th	Day	14% 19% 5% 9% 5% 5% 5% 2 5% 5% 25%	1689
	11th to 20th	Day	13% 20% 6% 10% 7% 6% 4 3 6% 6% 20%	1600
	21st to end	Day	15% 23% 7% 13% 6% 5% 5% 3 4 5% 13%	1600
December	1st to 10th	Day	14% 25% 12% 17% 5% 5% 4 3 4 4 8%	2600
	11th to 20th	Day	18% 22% 9% 14% 6% 4 3 3 3 4 13%	2986
	21st to end	Day	21% 20% 8% 17% 7% 5% 4 2 3 3 9%	3767
January	1st to 10th	Night	13% 18% 10% 20% 8% 5% 5% 3 3 5% 9%	4746
	11th to 20th	Night	12% 13% 9% 24% 11% 12% 4 2 2 3 7%	4141
	21st to end	Night	16% 16% 8% 19% 8% 6% 5% 3 5% 4 10%	4532
February	1st to 10th	Night	11% 18% 6% 13% 10% 8% 5% 4 5% 5% 14%	2470
	11th to 20th	Night	11% 14% 6% 18% 8% 6% 5% 4 5% 5% 18%	2403
	21st to end	Night	12% 15% 6% 14% 7% 5% 6% 4 6% 6% 20%	1956
March	1st to 10th	Night	13% 11% 6% 10% 5% 5% 5% 4 5% 6% 28%	3447
	11th to 20th	Night	9% 13% 8% 12% 6% 5% 4 3 5% 5% 30%	3479
	21st to end	Night	13% 9% 4 11% 5% 5% 5% 4 5% 5% 34%	3817
April	1st to 10th	Night	17% 14% 4 9% 5% 4 4 3 5% 6% 28%	1971
	11th to 20th	Night	16% 11% 3 7% 4 5% 4 4 4 6% 36%	1753
	21st to end	Night	14% 13% 4 9% 5% 5% 4 4 5% 6% 31%	1710
May	1st to 10th	Night	15% 9% 2 7% 4 3 4 4 6% 6% 41%	2833
	11th to 20th	Night	15% 8% 2 6% 5% 4 4 4 5% 7% 38%	2592
	21st to end	Night	9% 7% 2 5% 4 3 4 4 5% 7% 49%	2738
June	1st to 10th	Night	14% 7% 3 7% 5% 5% 4 3 5% 8% 40%	1512
	11th to 20th	Night	9% 7% 2 5% 5% 4 5% 5% 7% 9% 43%	1330
	21st to end	Night	13% 7% 3 5% 4 3 4 3 6% 8% 43%	1330
July	1st to 10th	Night	7% 7% 2 6% 4 4 3 4 5% 8% 49%	2210
	11th to 20th	Night	11% 7% 2 5% 4 3 3 3 5% 7% 51%	2447
	21st to end	Night	7% 7% 2 6% 4 4 5% 4 6% 8% 47%	3087
August	1st to 10th	Night	12% 6% 2 6% 5% 4 4 3 5% 7% 47%	2825
	11th to 20th	Night	14% 8% 2 6% 4 4 4 3 5% 7% 44%	2785
	21st to end	Night	12% 6% 2 6% 5% 4 4 3 5% 7% 46%	3184
September	1st to 10th	Night	10% 6% 2 7% 4 4 4 3 6% 8% 46%	1900
	11th to 20th	Night	11% 6% 2 5% 5% 3 3 3 5% 7% 51%	2066
	21st to end	Night	16% 9% 3 6% 5% 4 4 2 5% 7% 38%	2092
October	1st to 10th	Night	17% 9% 3 7% 5% 4 4 3 5% 6% 36%	2280
	11th to 20th	Night	19% 13% 4 8% 5% 5% 4 3 5% 6% 27%	2280
	21st to end	Night	19% 16% 4 8% 6% 5% 5% 4 5% 5% 22%	2522
November	1st to 10th	Night	16% 16% 4 9% 6% 5% 5% 3 5% 5% 27%	2607
	11th to 20th	Night	14% 17% 5% 10% 5% 5% 5% 4 6% 6% 22%	2800
	21st to end	Night	17% 18% 8% 12% 6% 5% 4 3 5% 7% 16%	2800
December	1st to 10th	Night	14% 22% 9% 18% 6% 5% 4 3 4 5% 9%	4580
	11th to 20th	Night	11% 23% 11% 18% 7% 5% 4 3 3 3 12%	5208
	21st to end	Night	19% 22% 8% 18% 7% 6% 4 3 4 3 7%	7157

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	70% 11% 10% 7% 1	2318
	11th to 20th	Day	82% 9% 3 3 2 1	2817
	21st to end	Day	75% 9% 7% 6% 3	3124
February	1st to 10th	Day	76% 6% 5% 9% 3 1	1710
	11th to 20th	Day	68% 8% 7% 10% 5% 1	1672
	21st to end	Day	68% 8% 8% 11% 6%	1495
March	1st to 10th	Day	60% 7% 11% 12% 9% 1	3395
	11th to 20th	Day	60% 7% 9% 17% 6% 1	3480
	21st to end	Day	50% 10% 12% 15% 10% 2	3815
April	1st to 10th	Day	59% 7% 9% 16% 8% 1	2209
	11th to 20th	Day	50% 6% 10% 19% 14% 1	2394
	21st to end	Day	53% 7% 10% 17% 11% 2	2470
May	1st to 10th	Day	45% 9% 12% 19% 13% 1	4120
	11th to 20th	Day	46% 11% 15% 19% 8% 1	4302
	21st to end	Day	37% 8% 13% 21% 18% 4	4837
June	1st to 10th	Day	45% 8% 12% 20% 14% 1	2663
	11th to 20th	Day	39% 8% 12% 24% 16% 1	2850
	21st to end	Day	43% 8% 13% 23% 12% 1	2850
July	1st to 10th	Day	46% 8% 14% 18% 14% 1	4686
	11th to 20th	Day	38% 8% 12% 31% 11% 1	4415
	21st to end	Day	39% 8% 12% 22% 17% 1	4324
August	1st to 10th	Day	45% 8% 13% 21% 12% 1	4091
	11th to 20th	Day	47% 9% 15% 21% 8%	4083
	21st to end	Day	39% 9% 14% 28% 10% 1	4438
September	1st to 10th	Day	45% 7% 13% 22% 10% 2	2280
	11th to 20th	Day	39% 7% 14% 26% 13%	2109
	21st to end	Day	48% 10% 12% 21% 8% 1	2087
October	1st to 10th	Day	47% 7% 12% 23% 11% 1	3160
	11th to 20th	Day	50% 7% 11% 19% 13%	3140
	21st to end	Day	62% 6% 11% 16% 5%	3398
November	1st to 10th	Day	59% 7% 11% 15% 7%	1689
	11th to 20th	Day	63% 9% 10% 11% 6% 1	1600
	21st to end	Day	71% 9% 10% 8% 2	1600
December	1st to 10th	Day	79% 7% 9% 4 1	2600
	11th to 20th	Day	75% 6% 8% 8% 4	2986
	21st to end	Day	80% 7% 4 4 5%	3767
January	1st to 10th	Night	71% 14% 8% 5% 2	4746
	11th to 20th	Night	81% 10% 4 3 2	4141
	21st to end	Night	72% 13% 9% 4 2 1	4532
February	1st to 10th	Night	69% 9% 8% 11% 3	2470
	11th to 20th	Night	64% 9% 11% 12% 5%	2405
	21st to end	Night	60% 11% 11% 11% 7% 1	1956
March	1st to 10th	Night	52% 9% 15% 16% 8% 1	3457
	11th to 20th	Night	48% 12% 13% 17% 9% 2	3480
	21st to end	Night	47% 9% 11% 20% 11% 1	3817
April	1st to 10th	Night	56% 6% 9% 17% 12% 1	1971
	11th to 20th	Night	47% 7% 8% 20% 15% 2	1753
	21st to end	Night	52% 7% 10% 14% 15% 2	1710
May	1st to 10th	Night	42% 7% 13% 19% 15% 5%	2840
	11th to 20th	Night	40% 10% 14% 23% 11% 2	2593
	21st to end	Night	31% 9% 13% 24% 21% 3	2739
June	1st to 10th	Night	40% 8% 11% 23% 17% 2	1512
	11th to 20th	Night	35% 8% 14% 24% 18% 1	1330
	21st to end	Night	37% 7% 14% 26% 14% 1	1330
July	1st to 10th	Night	33% 7% 14% 23% 18% 4	2175
	11th to 20th	Night	32% 6% 12% 34% 16% 1	2403
	21st to end	Night	33% 9% 14% 28% 15% 1	2988
August	1st to 10th	Night	36% 7% 12% 27% 17% 1	2814
	11th to 20th	Night	38% 6% 16% 25% 13% 1	2812
	21st to end	Night	36% 8% 13% 30% 13% 1	3184
September	1st to 10th	Night	35% 7% 15% 28% 13% 1	1900
	11th to 20th	Night	32% 7% 13% 28% 18% 1	2066
	21st to end	Night	46% 8% 12% 24% 10%	2092
October	1st to 10th	Night	38% 8% 10% 24% 19% 1	3800
	11th to 20th	Night	47% 7% 12% 19% 14% 1	3779
	21st to end	Night	51% 8% 14% 20% 6%	4146
November	1st to 10th	Night	55% 9% 11% 17% 7% 1	2607
	11th to 20th	Night	59% 10% 13% 12% 5% 2	2800
	21st to end	Night	66% 10% 13% 9% 2 1	2800
December	1st to 10th	Night	76% 8% 9% 6% 1	4580
	11th to 20th	Night	75% 7% 7% 8% 3	5208
	21st to end	Night	81% 7% 5% 6% 2	7157

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	22% 31% 31% 14% 2 1	192
	11th to 20th	Day	19% 38% 31% 8% 3	265
	21st to end	Day	24% 29% 34% 12% 2	297
February	1st to 10th	Day	27% 33% 32% 7% 1	270
	11th to 20th	Day	24% 35% 35% 5%	270
	21st to end	Day	32% 36% 27% 5%	225
March	1st to 10th	Day	25% 26% 34% 11% 4	431
	11th to 20th	Day	24% 26% 33% 14% 3	460
	21st to end	Day	28% 22% 32% 13% 5%	506
April	1st to 10th	Day	26% 24% 34% 12% 4	460
	11th to 20th	Day	31% 24% 23% 12% 7% 2	452
	21st to end	Day	27% 20% 34% 13% 4 2	460
May	1st to 10th	Day	23% 18% 33% 20% 5% 2	463
	11th to 20th	Day	19% 16% 32% 21% 8% 3	487
	21st to end	Day	17% 16% 30% 25% 9% 3	529
June	1st to 10th	Day	19% 18% 31% 24% 7% 1	493
	11th to 20th	Day	15% 16% 34% 27% 6% 2	680
	21st to end	Day	17% 16% 37% 21% 7% 2	680
July	1st to 10th	Day	13% 13% 31% 27% 13% 4	671
	11th to 20th	Day	15% 11% 31% 25% 12% 6%	542
	21st to end	Day	11% 10% 37% 26% 11% 5%	532
August	1st to 10th	Day	10% 12% 31% 27% 14% 6%	486
	11th to 20th	Day	13% 10% 25% 26% 17% 8%	479
	21st to end	Day	13% 11% 31% 26% 15% 4	539
September	1st to 10th	Day	17% 15% 27% 24% 11% 6%	490
	11th to 20th	Day	11% 12% 24% 26% 17% 10%	490
	21st to end	Day	18% 17% 29% 20% 13% 4	490
October	1st to 10th	Day	22% 21% 27% 16% 12% 2	490
	11th to 20th	Day	24% 25% 33% 13% 4	490
	21st to end	Day	32% 24% 28% 13% 3	521
November	1st to 10th	Day	27% 28% 30% 11% 3	263
	11th to 20th	Day	31% 24% 35% 6% 4 2	200
	21st to end	Day	22% 31% 39% 8% 1	200
December	1st to 10th	Day	28% 35% 27% 10% 1	200
	11th to 20th	Day	31% 32% 28% 8% 1 1	200
	21st to end	Day	30% 32% 27% 8% 2 1	220
January	1st to 10th	Night	20% 32% 32% 13% 2	927
	11th to 20th	Night	24% 27% 33% 14% 2 1	760
	21st to end	Night	17% 22% 39% 18% 4	836
February	1st to 10th	Night	21% 31% 33% 13% 1	760
	11th to 20th	Night	22% 27% 34% 14% 2	743
	21st to end	Night	22% 31% 32% 13% 3	628
March	1st to 10th	Night	19% 26% 36% 16% 3	760
	11th to 20th	Night	20% 28% 34% 15% 3	760
	21st to end	Night	20% 21% 33% 20% 5% 1	836
April	1st to 10th	Night	23% 22% 36% 17% 2	760
	11th to 20th	Night	22% 22% 29% 19% 7% 1	629
	21st to end	Night	22% 19% 31% 21% 8%	570
May	1st to 10th	Night	16% 15% 32% 28% 8% 1	570
	11th to 20th	Night	18% 12% 32% 29% 10%	432
	21st to end	Night	12% 12% 31% 33% 12%	411
June	1st to 10th	Night	15% 10% 38% 29% 8%	380
	11th to 20th	Night	12% 12% 30% 36% 10%	380
	21st to end	Night	13% 13% 31% 30% 13% 1	380
July	1st to 10th	Night	7% 7% 29% 40% 16% 1	370
	11th to 20th	Night	9% 8% 34% 30% 17% 1	385
	21st to end	Night	10% 6% 31% 36% 16% 1	624
August	1st to 10th	Night	11% 5% 28% 34% 21% 1	567
	11th to 20th	Night	9% 7% 23% 36% 22% 3	564
	21st to end	Night	13% 10% 28% 28% 20% 2	661
September	1st to 10th	Night	13% 11% 30% 26% 16% 4	760
	11th to 20th	Night	13% 9% 28% 29% 17% 5%	760
	21st to end	Night	20% 12% 24% 28% 13% 3	760
October	1st to 10th	Night	20% 16% 32% 19% 12% 1	760
	11th to 20th	Night	24% 21% 30% 17% 7% 1	760
	21st to end	Night	25% 25% 32% 14% 3	836
November	1st to 10th	Night	24% 22% 30% 19% 5%	780
	11th to 20th	Night	23% 28% 29% 15% 5% 1	800
	21st to end	Night	26% 25% 33% 14% 2	800
December	1st to 10th	Night	27% 27% 33% 10% 3 1	800
	11th to 20th	Night	21% 30% 36% 11% 3	800
	21st to end	Night	28% 30% 28% 12% 1	950

Page generated at 2025-01-04 03:23:59. Version ac07

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