Jerome
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Jerome clear sky chart from 2005-11-06 to 2025-03-27.

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	13% 6% 2 6% 5% 5% 5% 4 6% 7% 41%	108978
	Night	13% 6% 2 6% 4 4 4 4 6% 7% 44%	110348
Transparency	Day	40% 6% 11% 23% 16% 4	112626
	Night	37% 6% 12% 24% 18% 3	114839
Seeing	Day	22% 13% 27% 22% 13% 5%	15355
	Night	19% 11% 24% 31% 14% 2	25180

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	12% 6% 2 6% 5% 5% 5% 4 5% 5% 45%	4034
	11th to 20th	Day	10% 9% 3 8% 6% 5% 4 2 4 5% 45%	4060
	21st to end	Day	12% 8% 3 7% 5% 5% 4 3 5% 6% 43%	4466
February	1st to 10th	Day	11% 8% 4 8% 5% 5% 4 4 6% 6% 38%	1800
	11th to 20th	Day	15% 8% 4 7% 5% 5% 5% 3 5% 6% 39%	1753
	21st to end	Day	15% 8% 3 7% 4 4 4 3 5% 6% 41%	1690
March	1st to 10th	Day	17% 9% 3 8% 4 5% 4 3 4 6% 36%	3545
	11th to 20th	Day	9% 6% 2 6% 4 4 4 3 5% 7% 51%	3590
	21st to end	Day	16% 8% 3 7% 5% 4 5% 4 5% 6% 38%	3881
April	1st to 10th	Day	10% 7% 3 6% 6% 5% 6% 4 7% 7% 40%	2240
	11th to 20th	Day	13% 7% 2 6% 4 4 5% 3 5% 6% 46%	2254
	21st to end	Day	17% 6% 2 6% 6% 4 5% 3 6% 6% 39%	2352
May	1st to 10th	Day	19% 7% 2 8% 5% 6% 5% 5% 6% 8% 29%	4082
	11th to 20th	Day	23% 7% 2 6% 5% 5% 4 4 5% 8% 32%	4081
	21st to end	Day	10% 5% 2 6% 5% 5% 6% 5% 7% 10% 40%	4761
June	1st to 10th	Day	12% 5% 2 5% 5% 5% 6% 5% 7% 9% 40%	2660
	11th to 20th	Day	10% 4 2 6% 6% 6% 6% 5% 7% 11% 37%	2660
	21st to end	Day	9% 4 2 6% 5% 5% 6% 5% 7% 9% 41%	2660
July	1st to 10th	Day	6% 4 2 7% 5% 6% 6% 5% 8% 9% 43%	4318
	11th to 20th	Day	9% 5% 2 6% 5% 6% 7% 4 8% 11% 37%	4120
	21st to end	Day	11% 7% 3 8% 6% 6% 5% 5% 6% 9% 34%	4466
August	1st to 10th	Day	13% 6% 2 7% 6% 6% 6% 6% 7% 8% 31%	4104
	11th to 20th	Day	9% 4 2 7% 5% 5% 6% 5% 8% 9% 40%	4014
	21st to end	Day	9% 5% 2 6% 4 4 5% 4 6% 9% 46%	4180
September	1st to 10th	Day	14% 6% 3 5% 4 5% 4 3 5% 7% 44%	2280
	11th to 20th	Day	12% 6% 2 5% 4 5% 5% 3 5% 7% 47%	2189
	21st to end	Day	20% 7% 2 6% 5% 4 5% 3 5% 7% 37%	2033
October	1st to 10th	Day	15% 6% 3 6% 3 3 4 3 6% 7% 44%	1900
	11th to 20th	Day	15% 6% 3 5% 4 4 3 3 5% 5% 47%	1900
	21st to end	Day	14% 6% 2 4 4 4 4 4 5% 6% 48%	2090
November	1st to 10th	Day	10% 5% 2 4 4 4 3 3 5% 7% 53%	1957
	11th to 20th	Day	13% 6% 2 4 4 3 5% 4 7% 6% 46%	1708
	21st to end	Day	13% 6% 2 5% 5% 4 4 3 5% 6% 46%	1600
December	1st to 10th	Day	11% 5% 2 5% 3 5% 4 4 5% 7% 49%	2600
	11th to 20th	Day	17% 7% 2 6% 4 4 4 4 4 6% 40%	2990
	21st to end	Day	16% 7% 3 7% 4 5% 5% 4 6% 7% 35%	3960
January	1st to 10th	Night	9% 7% 2 5% 4 4 4 4 5% 7% 48%	5907
	11th to 20th	Night	10% 8% 3 7% 3 3 4 4 5% 6% 48%	5900
	21st to end	Night	14% 7% 2 5% 3 3 4 3 5% 5% 48%	6490
February	1st to 10th	Night	11% 8% 3 7% 5% 4 4 5% 6% 6% 41%	2600
	11th to 20th	Night	15% 8% 2 7% 4 4 5% 4 6% 5% 39%	2533
	21st to end	Night	13% 8% 2 7% 5% 4 5% 5% 6% 7% 38%	1934
March	1st to 10th	Night	18% 8% 2 6% 4 4 4 4 5% 5% 38%	3528
	11th to 20th	Night	9% 4 2 5% 3 4 5% 4 6% 7% 50%	3590
	21st to end	Night	12% 6% 2 5% 4 4 4 3 5% 7% 47%	3890
April	1st to 10th	Night	13% 8% 2 7% 4 3 5% 5% 5% 7% 41%	1939
	11th to 20th	Night	11% 6% 2 6% 5% 4 4 4 6% 8% 44%	1875
	21st to end	Night	15% 5% 2 5% 4 4 4 4 4 7% 45%	1843
May	1st to 10th	Night	21% 9% 2 7% 5% 4 4 4 6% 8% 31%	2813
	11th to 20th	Night	22% 9% 2 7% 4 4 4 3 4 5% 36%	2812
	21st to end	Night	10% 5% 2 6% 4 4 5% 5% 6% 9% 44%	2776
June	1st to 10th	Night	10% 5% 1 5% 5% 5% 4 4 7% 9% 46%	1520
	11th to 20th	Night	10% 7% 1 7% 5% 4 4 5% 7% 9% 41%	1520
	21st to end	Night	9% 4 2 5% 4 4 5% 5% 8% 10% 44%	1520
July	1st to 10th	Night	6% 4 2 6% 5% 5% 6% 5% 8% 10% 42%	2637
	11th to 20th	Night	8% 6% 3 7% 5% 5% 5% 5% 7% 10% 39%	2840
	21st to end	Night	9% 6% 2 9% 6% 5% 6% 5% 7% 9% 37%	3087
August	1st to 10th	Night	13% 6% 2 7% 5% 4 6% 4 7% 9% 36%	2825
	11th to 20th	Night	10% 6% 3 6% 5% 5% 5% 4 7% 9% 41%	2785
	21st to end	Night	11% 5% 2 5% 4 4 4 4 5% 9% 48%	3471
September	1st to 10th	Night	13% 6% 2 6% 4 4 5% 4 5% 6% 46%	1900
	11th to 20th	Night	12% 5% 3 4 3 4 4 3 6% 7% 50%	1987
	21st to end	Night	20% 7% 2 5% 3 3 4 3 5% 6% 41%	2147
October	1st to 10th	Night	18% 6% 2 5% 3 3 4 3 5% 6% 45%	2280
	11th to 20th	Night	12% 5% 2 5% 3 3 3 3 5% 6% 51%	2280
	21st to end	Night	14% 5% 2 4 4 3 4 3 5% 6% 51%	2508
November	1st to 10th	Night	10% 6% 2 6% 3 4 4 3 5% 6% 52%	2341
	11th to 20th	Night	12% 7% 2 4 4 3 4 4 6% 6% 47%	2689
	21st to end	Night	12% 5% 2 6% 4 5% 5% 3 5% 7% 45%	2800
December	1st to 10th	Night	9% 5% 2 5% 4 4 4 3 5% 8% 51%	4580
	11th to 20th	Night	15% 8% 3 7% 5% 4 5% 4 4 6% 40%	5205
	21st to end	Night	14% 7% 2 7% 5% 5% 5% 5% 7% 8% 35%	6996

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	40% 4 5% 22% 22% 7%	4035
	11th to 20th	Day	42% 4 7% 17% 20% 10%	4060
	21st to end	Day	41% 5% 8% 25% 17% 4	4466
February	1st to 10th	Day	45% 5% 10% 22% 14% 3	1800
	11th to 20th	Day	47% 4 9% 20% 18% 3	1762
	21st to end	Day	43% 4 12% 19% 17% 5%	1690
March	1st to 10th	Day	49% 5% 9% 20% 13% 4	3545
	11th to 20th	Day	32% 5% 7% 29% 23% 4	3590
	21st to end	Day	46% 6% 10% 20% 15% 3	3881
April	1st to 10th	Day	41% 7% 10% 19% 17% 6%	2240
	11th to 20th	Day	38% 4 10% 21% 21% 5%	2254
	21st to end	Day	45% 5% 10% 21% 15% 4	2352
May	1st to 10th	Day	50% 8% 10% 21% 9% 1	4120
	11th to 20th	Day	49% 7% 10% 24% 8% 1	4085
	21st to end	Day	37% 9% 14% 21% 16% 3	4775
June	1st to 10th	Day	39% 8% 12% 25% 16% 1	2660
	11th to 20th	Day	40% 9% 14% 22% 13% 2	2660
	21st to end	Day	35% 8% 14% 26% 14% 2	2660
July	1st to 10th	Day	35% 9% 17% 24% 9% 5%	4251
	11th to 20th	Day	37% 8% 16% 28% 9% 1	4051
	21st to end	Day	46% 6% 9% 23% 15% 1	4324
August	1st to 10th	Day	46% 9% 15% 23% 7%	4091
	11th to 20th	Day	37% 9% 12% 29% 13% 1	4053
	21st to end	Day	35% 6% 15% 28% 15% 1	4180
September	1st to 10th	Day	40% 5% 13% 18% 21% 4	2280
	11th to 20th	Day	37% 5% 7% 28% 19% 4	2189
	21st to end	Day	47% 5% 8% 20% 17% 2	2033
October	1st to 10th	Day	33% 5% 8% 21% 26% 6%	3160
	11th to 20th	Day	27% 4 9% 28% 20% 12%	3140
	21st to end	Day	25% 4 8% 31% 25% 8%	3428
November	1st to 10th	Day	32% 3 10% 26% 24% 4	1957
	11th to 20th	Day	38% 4 10% 20% 23% 5%	1708
	21st to end	Day	39% 5% 11% 24% 20% 2	1600
December	1st to 10th	Day	35% 5% 11% 25% 19% 5%	2600
	11th to 20th	Day	44% 5% 11% 23% 14% 3	2986
	21st to end	Day	45% 6% 14% 19% 15% 1	3960
January	1st to 10th	Night	34% 5% 8% 22% 27% 4	5907
	11th to 20th	Night	36% 5% 8% 23% 20% 8%	5900
	21st to end	Night	37% 4 8% 27% 19% 4	6490
February	1st to 10th	Night	42% 5% 12% 25% 14% 2	2600
	11th to 20th	Night	45% 4 9% 21% 16% 4	2535
	21st to end	Night	43% 6% 11% 21% 15% 5%	1934
March	1st to 10th	Night	46% 6% 8% 25% 12% 3	3528
	11th to 20th	Night	31% 7% 8% 27% 23% 3	3590
	21st to end	Night	37% 5% 11% 25% 19% 4	3890
April	1st to 10th	Night	41% 7% 10% 21% 18% 4	1939
	11th to 20th	Night	37% 5% 12% 23% 18% 5%	1875
	21st to end	Night	40% 5% 11% 27% 15% 3	1843
May	1st to 10th	Night	50% 7% 12% 18% 10% 2	2840
	11th to 20th	Night	49% 7% 10% 25% 8% 1	2813
	21st to end	Night	34% 9% 17% 27% 9% 4	2783
June	1st to 10th	Night	34% 8% 14% 29% 15% 1	1520
	11th to 20th	Night	37% 9% 16% 24% 13% 1	1520
	21st to end	Night	33% 7% 17% 23% 17% 2	1520
July	1st to 10th	Night	33% 11% 21% 18% 13% 3	2594
	11th to 20th	Night	38% 9% 18% 24% 10% 1	2786
	21st to end	Night	40% 9% 16% 23% 12%	2988
August	1st to 10th	Night	42% 8% 17% 25% 7%	2814
	11th to 20th	Night	36% 8% 16% 24% 16%	2812
	21st to end	Night	33% 6% 15% 31% 13% 1	3471
September	1st to 10th	Night	39% 6% 13% 20% 18% 5%	1900
	11th to 20th	Night	34% 4 10% 31% 19% 2	1987
	21st to end	Night	44% 4 9% 23% 18% 2	2147
October	1st to 10th	Night	38% 4 10% 22% 23% 3	3800
	11th to 20th	Night	25% 4 11% 22% 29% 9%	3779
	21st to end	Night	22% 3 11% 31% 27% 6%	4120
November	1st to 10th	Night	33% 4 11% 24% 22% 6%	2341
	11th to 20th	Night	37% 4 8% 25% 21% 5%	2689
	21st to end	Night	38% 5% 11% 24% 19% 3	2800
December	1st to 10th	Night	31% 5% 12% 30% 20% 2	4580
	11th to 20th	Night	44% 4 12% 19% 17% 4	5208
	21st to end	Night	43% 8% 13% 20% 16% 1	6996

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	35% 23% 29% 9% 3 1	296
	11th to 20th	Day	35% 22% 30% 10% 3	300
	21st to end	Day	29% 26% 35% 8% 2	330
February	1st to 10th	Day	31% 28% 31% 8% 1	300
	11th to 20th	Day	43% 21% 30% 4 1	300
	21st to end	Day	36% 19% 28% 15% 2	379
March	1st to 10th	Day	30% 22% 25% 20% 4	500
	11th to 20th	Day	27% 23% 26% 17% 5% 2	500
	21st to end	Day	27% 20% 30% 16% 6% 1	530
April	1st to 10th	Day	24% 23% 27% 18% 6% 1	460
	11th to 20th	Day	23% 17% 28% 17% 10% 4	452
	21st to end	Day	27% 13% 32% 17% 9% 3	460
May	1st to 10th	Day	25% 14% 31% 15% 10% 4	463
	11th to 20th	Day	24% 12% 29% 23% 8% 4	487
	21st to end	Day	18% 7% 29% 22% 17% 7%	529
June	1st to 10th	Day	16% 11% 26% 28% 13% 6%	490
	11th to 20th	Day	16% 8% 25% 27% 17% 7%	490
	21st to end	Day	12% 7% 33% 27% 17% 4	490
July	1st to 10th	Day	12% 4 19% 31% 26% 8%	485
	11th to 20th	Day	9% 2 21% 32% 25% 10%	484
	21st to end	Day	13% 3 22% 29% 23% 10%	532
August	1st to 10th	Day	14% 5% 21% 27% 21% 12%	486
	11th to 20th	Day	13% 3 20% 28% 26% 11%	479
	21st to end	Day	11% 4 19% 28% 22% 15%	539
September	1st to 10th	Day	17% 7% 17% 25% 22% 12%	490
	11th to 20th	Day	15% 3 22% 28% 22% 10%	490
	21st to end	Day	29% 9% 21% 24% 13% 4	490
October	1st to 10th	Day	20% 5% 24% 28% 19% 3	490
	11th to 20th	Day	20% 14% 24% 26% 13% 2	490
	21st to end	Day	19% 15% 32% 21% 11% 2	539
November	1st to 10th	Day	18% 13% 31% 25% 10% 3	495
	11th to 20th	Day	22% 15% 34% 20% 7% 1	290
	21st to end	Day	31% 15% 38% 14% 3 1	200
December	1st to 10th	Day	27% 20% 41% 9% 4 1	200
	11th to 20th	Day	25% 22% 31% 17% 6%	200
	21st to end	Day	23% 16% 37% 18% 5%	220
January	1st to 10th	Night	23% 19% 32% 22% 3	800
	11th to 20th	Night	23% 16% 28% 30% 3	800
	21st to end	Night	19% 18% 36% 26% 1	880
February	1st to 10th	Night	18% 19% 32% 29% 2	800
	11th to 20th	Night	27% 23% 29% 19% 1	783
	21st to end	Night	25% 15% 35% 23% 2	660
March	1st to 10th	Night	22% 17% 33% 25% 4	800
	11th to 20th	Night	24% 19% 26% 23% 6% 1	800
	21st to end	Night	22% 17% 33% 22% 6% 1	863
April	1st to 10th	Night	22% 18% 28% 26% 6%	760
	11th to 20th	Night	19% 15% 29% 27% 10% 1	751
	21st to end	Night	20% 12% 26% 33% 9%	703
May	1st to 10th	Night	21% 7% 24% 30% 16% 2	570
	11th to 20th	Night	21% 5% 24% 32% 16% 1	561
	21st to end	Night	15% 2 20% 35% 23% 4	443
June	1st to 10th	Night	13% 2 23% 38% 22% 2	380
	11th to 20th	Night	14% 4 13% 44% 23% 2	380
	21st to end	Night	9% 2 20% 47% 21% 1	380
July	1st to 10th	Night	12% 2 11% 40% 29% 7%	432
	11th to 20th	Night	8% 1 11% 39% 37% 4	552
	21st to end	Night	9% 2 13% 41% 29% 6%	624
August	1st to 10th	Night	13% 1 10% 40% 33% 4	567
	11th to 20th	Night	12% 2 10% 40% 31% 4	564
	21st to end	Night	13% 3 11% 36% 34% 4	831
September	1st to 10th	Night	17% 2 14% 30% 32% 5%	760
	11th to 20th	Night	13% 3 15% 34% 31% 5%	760
	21st to end	Night	25% 4 18% 31% 20% 2	760
October	1st to 10th	Night	23% 6% 16% 31% 21% 3	760
	11th to 20th	Night	16% 11% 24% 33% 15% 1	760
	21st to end	Night	18% 12% 23% 34% 12% 1	836
November	1st to 10th	Night	13% 10% 27% 37% 12% 2	780
	11th to 20th	Night	20% 14% 25% 30% 10% 1	800
	21st to end	Night	19% 15% 27% 30% 8% 1	800
December	1st to 10th	Night	21% 16% 29% 27% 6% 1	800
	11th to 20th	Night	18% 13% 32% 32% 5%	800
	21st to end	Night	19% 15% 27% 36% 3	880

Page generated at 2025-03-24 09:04:31. Version ac07

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