Iron Mountain
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Iron Mountain clear sky chart from 2005-11-06 to 2024-12-09.

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% 10% 3 8% 5% 5% 5% 4 5% 7% 35%	101872
	Night	14% 10% 4 8% 5% 4 4 4 5% 7% 35%	98049
Transparency	Day	27% 46% 6% 13% 7%	105345
	Night	28% 46% 6% 13% 6% 1	102663
Seeing	Day	22% 13% 32% 20% 9% 3	16151
	Night	21% 10% 31% 27% 10% 1	26071

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	12% 14% 6% 14% 6% 5% 4 4 6% 7% 22%	2527
	11th to 20th	Day	11% 16% 4 12% 6% 6% 6% 5% 7% 7% 22%	2530
	21st to end	Day	12% 17% 8% 15% 6% 5% 5% 4 4 5% 19%	2783
February	1st to 10th	Day	9% 12% 5% 11% 5% 6% 5% 4 6% 6% 31%	1625
	11th to 20th	Day	9% 13% 4 11% 6% 4 5% 4 5% 6% 32%	1786
	21st to end	Day	12% 14% 5% 10% 5% 5% 5% 5% 5% 8% 27%	1570
March	1st to 10th	Day	11% 12% 3 7% 4 4 4 3 5% 6% 40%	3118
	11th to 20th	Day	7% 13% 4 11% 9% 5% 5% 4 5% 6% 31%	3265
	21st to end	Day	19% 12% 5% 14% 5% 6% 4 3 3 5% 24%	4165
April	1st to 10th	Day	16% 16% 4 9% 5% 5% 3 3 5% 6% 28%	2280
	11th to 20th	Day	19% 11% 4 8% 5% 5% 5% 3 5% 5% 31%	2254
	21st to end	Day	18% 11% 2 8% 4 4 5% 4 6% 7% 32%	2470
May	1st to 10th	Day	15% 7% 3 7% 5% 4 4 3 5% 6% 39%	4290
	11th to 20th	Day	14% 7% 2 6% 4 4 4 4 6% 7% 41%	4399
	21st to end	Day	14% 7% 2 8% 5% 5% 5% 4 5% 8% 36%	4837
June	1st to 10th	Day	13% 6% 2 6% 6% 4 4 4 6% 8% 41%	2660
	11th to 20th	Day	15% 7% 2 7% 5% 5% 5% 4 6% 8% 36%	2660
	21st to end	Day	13% 7% 2 7% 5% 5% 6% 5% 6% 9% 35%	2660
July	1st to 10th	Day	15% 4 2 5% 6% 5% 5% 4 7% 8% 39%	4440
	11th to 20th	Day	6% 3 1 5% 4 5% 5% 5% 6% 8% 50%	4440
	21st to end	Day	9% 5% 2 5% 4 4 4 4 7% 8% 47%	4814
August	1st to 10th	Day	10% 6% 2 7% 5% 6% 5% 4 7% 8% 39%	4423
	11th to 20th	Day	13% 6% 2 5% 3 4 4 3 6% 7% 47%	4062
	21st to end	Day	16% 6% 2 6% 4 4 4 3 4 6% 43%	4180
September	1st to 10th	Day	12% 6% 3 7% 5% 5% 4 3 5% 7% 43%	2280
	11th to 20th	Day	13% 6% 2 7% 4 5% 5% 4 6% 8% 41%	2175
	21st to end	Day	14% 9% 3 8% 5% 5% 6% 4 5% 9% 35%	2090
October	1st to 10th	Day	16% 8% 3 7% 5% 4 4 3 6% 8% 36%	1996
	11th to 20th	Day	21% 13% 3 8% 5% 5% 5% 3 5% 7% 25%	1824
	21st to end	Day	22% 14% 4 7% 5% 5% 5% 3 5% 6% 26%	1881
November	1st to 10th	Day	15% 11% 5% 6% 5% 5% 5% 4 6% 7% 31%	1762
	11th to 20th	Day	15% 14% 6% 10% 5% 5% 5% 4 5% 6% 24%	1745
	21st to end	Day	16% 13% 6% 11% 6% 5% 5% 5% 5% 6% 23%	1600
December	1st to 10th	Day	11% 13% 4 13% 8% 6% 6% 4 6% 6% 25%	1584
	11th to 20th	Day	15% 15% 6% 11% 7% 6% 6% 4 4 6% 21%	1914
	21st to end	Day	23% 23% 6% 9% 5% 3 3 3 4 4 17%	2783
January	1st to 10th	Night	14% 15% 6% 12% 4 4 4 3 5% 6% 28%	4428
	11th to 20th	Night	10% 15% 6% 11% 8% 7% 5% 4 5% 7% 21%	4440
	21st to end	Night	12% 16% 8% 13% 7% 6% 4 4 5% 6% 21%	4884
February	1st to 10th	Night	10% 13% 5% 11% 6% 5% 5% 4 6% 7% 30%	2551
	11th to 20th	Night	9% 12% 3 10% 7% 6% 4 4 6% 6% 33%	2279
	21st to end	Night	13% 15% 5% 8% 6% 5% 4 4 6% 6% 29%	1884
March	1st to 10th	Night	11% 10% 3 7% 4 4 4 3 5% 8% 40%	3722
	11th to 20th	Night	9% 10% 5% 10% 5% 5% 5% 4 5% 7% 35%	3722
	21st to end	Night	17% 11% 5% 10% 8% 4 4 3 5% 6% 27%	3466
April	1st to 10th	Night	19% 12% 3 7% 6% 4 4 4 5% 7% 30%	1900
	11th to 20th	Night	21% 9% 3 7% 5% 4 3 3 5% 5% 36%	1875
	21st to end	Night	16% 9% 4 7% 5% 5% 5% 4 5% 7% 34%	1710
May	1st to 10th	Night	16% 8% 3 6% 5% 4 4 4 4 6% 40%	2654
	11th to 20th	Night	14% 7% 3 7% 4 4 4 4 6% 6% 41%	2506
	21st to end	Night	18% 6% 2 6% 5% 5% 4 3 6% 7% 37%	2750
June	1st to 10th	Night	11% 6% 3 6% 4 4 4 3 5% 8% 46%	1520
	11th to 20th	Night	14% 7% 3 7% 4 6% 5% 3 6% 7% 39%	1520
	21st to end	Night	14% 7% 2 5% 4 4 5% 3 6% 9% 41%	1520
July	1st to 10th	Night	15% 4 2 5% 3 4 4 4 5% 9% 44%	2530
	11th to 20th	Night	6% 3 1 4 3 4 3 3 6% 7% 58%	2530
	21st to end	Night	10% 5% 2 6% 3 3 3 3 5% 7% 54%	2750
August	1st to 10th	Night	12% 6% 2 7% 4 4 4 4 5% 7% 45%	2517
	11th to 20th	Night	13% 5% 1 5% 3 3 4 3 5% 6% 50%	2753
	21st to end	Night	15% 5% 2 7% 4 4 4 3 4 5% 47%	3476
September	1st to 10th	Night	10% 6% 2 5% 4 3 4 4 5% 7% 51%	1900
	11th to 20th	Night	12% 6% 2 5% 4 4 4 3 5% 7% 49%	1985
	21st to end	Night	15% 7% 2 6% 4 4 4 4 5% 6% 42%	2090
October	1st to 10th	Night	15% 7% 2 5% 4 3 5% 4 5% 6% 43%	2180
	11th to 20th	Night	17% 12% 3 7% 5% 4 4 3 4 6% 34%	2356
	21st to end	Night	20% 12% 3 7% 5% 4 4 4 5% 8% 27%	2717
November	1st to 10th	Night	15% 10% 3 7% 5% 4 4 4 6% 7% 35%	2536
	11th to 20th	Night	16% 12% 4 9% 6% 5% 5% 4 5% 6% 28%	2652
	21st to end	Night	15% 13% 5% 10% 5% 5% 4 5% 5% 6% 27%	2800
December	1st to 10th	Night	12% 14% 5% 10% 6% 4 4 4 7% 7% 27%	2779
	11th to 20th	Night	13% 13% 6% 12% 7% 5% 4 4 5% 5% 27%	3283
	21st to end	Night	24% 20% 7% 9% 5% 4 3 2 3 4 19%	4884

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	41% 37% 8% 10% 4	2528
	11th to 20th	Day	38% 36% 9% 13% 3	2530
	21st to end	Day	45% 39% 7% 8% 1	2783
February	1st to 10th	Day	18% 65% 5% 7% 5%	1625
	11th to 20th	Day	21% 64% 3 8% 4	1795
	21st to end	Day	19% 64% 4 8% 5% 1	1570
March	1st to 10th	Day	24% 40% 7% 14% 13% 1	3120
	11th to 20th	Day	34% 40% 6% 13% 5% 1	3265
	21st to end	Day	41% 39% 4 10% 6%	4165
April	1st to 10th	Day	22% 65% 3 6% 4	2280
	11th to 20th	Day	20% 65% 2 8% 4 1	2254
	21st to end	Day	18% 65% 2 9% 5% 1	2470
May	1st to 10th	Day	27% 39% 4 17% 12% 1	4302
	11th to 20th	Day	26% 38% 7% 21% 8%	4403
	21st to end	Day	31% 39% 5% 11% 13% 1	4837
June	1st to 10th	Day	14% 65% 3 11% 5% 1	2660
	11th to 20th	Day	17% 65% 4 7% 6% 1	2660
	21st to end	Day	16% 64% 5% 9% 5%	2660
July	1st to 10th	Day	31% 36% 9% 15% 7% 1	4371
	11th to 20th	Day	18% 36% 8% 27% 9% 2	4365
	21st to end	Day	21% 36% 8% 23% 13%	4662
August	1st to 10th	Day	27% 38% 10% 17% 8%	4408
	11th to 20th	Day	25% 38% 11% 21% 6%	4103
	21st to end	Day	31% 37% 10% 13% 9%	4179
September	1st to 10th	Day	19% 60% 5% 11% 4	2280
	11th to 20th	Day	16% 60% 7% 11% 5%	2175
	21st to end	Day	19% 60% 5% 12% 4	2090
October	1st to 10th	Day	19% 37% 7% 21% 17%	3321
	11th to 20th	Day	32% 37% 5% 15% 11%	3014
	21st to end	Day	36% 37% 10% 13% 4	3081
November	1st to 10th	Day	25% 57% 4 9% 5%	1762
	11th to 20th	Day	27% 57% 6% 6% 4	1745
	21st to end	Day	28% 58% 5% 6% 3 1	1600
December	1st to 10th	Day	25% 58% 5% 8% 3	1584
	11th to 20th	Day	35% 48% 4 7% 4 1	1915
	21st to end	Day	48% 37% 2 10% 4	2783
January	1st to 10th	Night	39% 36% 6% 13% 6%	4428
	11th to 20th	Night	42% 36% 8% 12% 3	4440
	21st to end	Night	43% 39% 8% 9% 2	4884
February	1st to 10th	Night	20% 64% 4 7% 5% 1	2551
	11th to 20th	Night	18% 64% 3 10% 4 1	2280
	21st to end	Night	18% 64% 4 7% 6% 1	1884
March	1st to 10th	Night	23% 41% 15% 14% 7% 1	3733
	11th to 20th	Night	31% 41% 5% 17% 6%	3723
	21st to end	Night	40% 39% 5% 9% 7% 1	3466
April	1st to 10th	Night	21% 65% 3 5% 6% 1	1900
	11th to 20th	Night	19% 66% 3 6% 5% 1	1875
	21st to end	Night	19% 65% 2 7% 6% 1	1710
May	1st to 10th	Night	26% 39% 6% 18% 10%	2661
	11th to 20th	Night	25% 39% 6% 20% 9% 1	2507
	21st to end	Night	31% 39% 9% 10% 7% 4	2751
June	1st to 10th	Night	14% 65% 4 10% 7%	1520
	11th to 20th	Night	18% 65% 4 7% 5% 1	1520
	21st to end	Night	16% 63% 4 12% 5% 1	1520
July	1st to 10th	Night	29% 36% 13% 13% 6% 3	2490
	11th to 20th	Night	15% 37% 10% 29% 10% 1	2482
	21st to end	Night	22% 36% 7% 17% 17% 1	2662
August	1st to 10th	Night	26% 38% 9% 13% 13% 1	2508
	11th to 20th	Night	25% 38% 11% 19% 7% 1	2778
	21st to end	Night	28% 38% 7% 17% 9%	3476
September	1st to 10th	Night	16% 60% 6% 13% 4	1900
	11th to 20th	Night	16% 60% 6% 13% 5%	1985
	21st to end	Night	18% 60% 6% 11% 4 1	2090
October	1st to 10th	Night	20% 37% 5% 25% 12% 1	3635
	11th to 20th	Night	23% 37% 8% 19% 12%	3905
	21st to end	Night	34% 37% 6% 16% 6%	4467
November	1st to 10th	Night	24% 56% 5% 11% 4	2536
	11th to 20th	Night	24% 57% 6% 9% 4	2652
	21st to end	Night	28% 57% 5% 8% 3 1	2800
December	1st to 10th	Night	25% 57% 6% 9% 3	2779
	11th to 20th	Night	31% 50% 4 11% 4	3281
	21st to end	Night	47% 36% 2 10% 4	4884

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% 13% 33% 22% 8% 1	270
	11th to 20th	Day	30% 15% 30% 20% 4 1	270
	21st to end	Day	25% 12% 39% 20% 4	297
February	1st to 10th	Day	22% 22% 37% 14% 4 1	270
	11th to 20th	Day	24% 27% 34% 11% 3	270
	21st to end	Day	26% 22% 42% 8% 1	225
March	1st to 10th	Day	21% 21% 42% 13% 2	270
	11th to 20th	Day	27% 15% 38% 15% 5%	294
	21st to end	Day	28% 19% 29% 16% 7% 1	506
April	1st to 10th	Day	31% 15% 30% 18% 5%	460
	11th to 20th	Day	32% 16% 26% 19% 6% 1	452
	21st to end	Day	34% 13% 26% 18% 8% 2	460
May	1st to 10th	Day	27% 16% 31% 14% 9% 2	567
	11th to 20th	Day	25% 15% 34% 17% 7% 3	675
	21st to end	Day	21% 13% 33% 21% 8% 5%	734
June	1st to 10th	Day	19% 15% 32% 22% 9% 4	680
	11th to 20th	Day	21% 11% 36% 19% 10% 3	680
	21st to end	Day	18% 12% 31% 25% 9% 4	680
July	1st to 10th	Day	10% 9% 33% 29% 15% 5%	671
	11th to 20th	Day	11% 9% 35% 23% 16% 6%	668
	21st to end	Day	10% 8% 34% 27% 13% 8%	739
August	1st to 10th	Day	12% 9% 29% 30% 15% 5%	676
	11th to 20th	Day	15% 5% 24% 29% 18% 9%	541
	21st to end	Day	22% 8% 24% 23% 18% 5%	539
September	1st to 10th	Day	19% 8% 26% 28% 13% 6%	490
	11th to 20th	Day	13% 7% 32% 32% 13% 4	490
	21st to end	Day	22% 13% 24% 26% 12% 4	490
October	1st to 10th	Day	27% 13% 29% 19% 11% 2	396
	11th to 20th	Day	30% 19% 33% 13% 4	300
	21st to end	Day	33% 18% 36% 11% 2	330
November	1st to 10th	Day	26% 16% 36% 16% 6% 1	300
	11th to 20th	Day	27% 23% 32% 12% 4 1	300
	21st to end	Day	28% 18% 37% 10% 6% 1	300
December	1st to 10th	Day	21% 17% 39% 14% 7%	294
	11th to 20th	Day	31% 16% 34% 16% 3	270
	21st to end	Day	37% 16% 31% 11% 3 1	297
January	1st to 10th	Night	19% 15% 38% 22% 5%	950
	11th to 20th	Night	23% 14% 35% 20% 7% 1	950
	21st to end	Night	19% 10% 39% 23% 8% 1	1045
February	1st to 10th	Night	19% 14% 39% 21% 7% 1	950
	11th to 20th	Night	22% 16% 34% 21% 7%	804
	21st to end	Night	24% 15% 37% 21% 4	628
March	1st to 10th	Night	19% 13% 33% 26% 8% 1	760
	11th to 20th	Night	20% 16% 36% 22% 6% 1	746
	21st to end	Night	20% 10% 31% 29% 8% 1	627
April	1st to 10th	Night	26% 12% 31% 24% 7% 1	570
	11th to 20th	Night	28% 10% 29% 26% 7% 1	563
	21st to end	Night	23% 10% 31% 27% 7% 1	570
May	1st to 10th	Night	23% 10% 30% 29% 8% 1	570
	11th to 20th	Night	22% 8% 33% 29% 7% 1	561
	21st to end	Night	16% 6% 29% 36% 12%	617
June	1st to 10th	Night	16% 8% 28% 37% 12%	570
	11th to 20th	Night	20% 6% 25% 39% 9% 1	570
	21st to end	Night	17% 4 27% 36% 14% 1	570
July	1st to 10th	Night	11% 4 26% 41% 17% 1	555
	11th to 20th	Night	12% 3 28% 37% 20%	552
	21st to end	Night	11% 2 28% 39% 17% 2	624
August	1st to 10th	Night	12% 3 26% 40% 18% 2	567
	11th to 20th	Night	13% 3 22% 35% 25% 3	564
	21st to end	Night	15% 4 23% 37% 20% 1	627
September	1st to 10th	Night	13% 6% 25% 31% 21% 4	570
	11th to 20th	Night	14% 6% 29% 33% 16% 2	655
	21st to end	Night	19% 9% 27% 31% 13% 1	760
October	1st to 10th	Night	22% 10% 29% 26% 13% 1	760
	11th to 20th	Night	25% 13% 31% 24% 7%	760
	21st to end	Night	29% 10% 29% 24% 7%	836
November	1st to 10th	Night	22% 12% 35% 23% 7% 1	780
	11th to 20th	Night	26% 15% 32% 20% 7%	852
	21st to end	Night	24% 16% 30% 24% 5%	1000
December	1st to 10th	Night	23% 15% 36% 20% 5% 1	993
	11th to 20th	Night	22% 13% 32% 24% 7% 2	950
	21st to end	Night	31% 13% 31% 19% 5%	1045

Page generated at 2024-12-06 02:54:48. Version ac07

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