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 2026-07-31.

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% 8% 40%	138044
	Night	12% 6% 2 6% 4 4 5% 4 6% 7% 43%	134954
Transparency	Day	40% 6% 11% 23% 16% 4	141648
	Night	38% 6% 12% 24% 17% 3	139420
Seeing	Day	21% 13% 27% 22% 13% 5%	17168
	Night	18% 11% 24% 31% 14% 2	26841

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% 3 7% 5% 4 5% 4 5% 6% 44%	5236
	11th to 20th	Day	9% 9% 3 7% 5% 4 4 3 4 5% 47%	5280
	21st to end	Day	11% 6% 2 7% 5% 6% 5% 4 6% 6% 42%	5780
February	1st to 10th	Day	11% 8% 4 7% 5% 5% 4 4 6% 6% 40%	1890
	11th to 20th	Day	15% 8% 4 7% 5% 5% 5% 3 5% 6% 39%	1843
	21st to end	Day	15% 8% 3 7% 4 4 4 3 5% 6% 40%	1772
March	1st to 10th	Day	15% 7% 3 7% 4 4 4 3 5% 6% 41%	5045
	11th to 20th	Day	10% 5% 2 6% 4 4 4 3 5% 7% 50%	5090
	21st to end	Day	13% 7% 3 7% 5% 5% 5% 4 6% 6% 39%	5586
April	1st to 10th	Day	11% 7% 3 6% 6% 5% 5% 4 6% 7% 40%	2476
	11th to 20th	Day	12% 7% 2 5% 4 4 5% 3 5% 7% 46%	2494
	21st to end	Day	17% 6% 2 6% 5% 4 5% 3 6% 6% 40%	2600
May	1st to 10th	Day	14% 6% 2 7% 5% 6% 6% 5% 7% 9% 32%	7616
	11th to 20th	Day	18% 6% 2 6% 4 5% 5% 4 6% 9% 34%	7626
	21st to end	Day	21% 5% 2 6% 5% 4 5% 4 6% 7% 36%	8928
June	1st to 10th	Day	12% 5% 2 5% 5% 5% 6% 5% 7% 9% 41%	2940
	11th to 20th	Day	11% 4 2 6% 5% 6% 6% 5% 7% 11% 37%	2940
	21st to end	Day	9% 5% 2 5% 5% 5% 6% 5% 7% 9% 41%	2940
July	1st to 10th	Day	6% 4 2 7% 5% 5% 6% 5% 7% 10% 43%	6318
	11th to 20th	Day	8% 6% 2 7% 6% 6% 7% 6% 9% 12% 31%	6030
	21st to end	Day	9% 5% 2 7% 6% 5% 5% 5% 8% 10% 37%	6554
August	1st to 10th	Day	13% 6% 2 7% 6% 6% 6% 6% 7% 8% 32%	4234
	11th to 20th	Day	9% 4 2 7% 6% 5% 6% 5% 8% 9% 39%	4143
	21st to end	Day	9% 5% 2 6% 4 4 5% 4 6% 9% 46%	4312
September	1st to 10th	Day	13% 6% 3 5% 4 5% 4 3 5% 7% 46%	2400
	11th to 20th	Day	12% 6% 2 5% 3 5% 5% 3 5% 7% 47%	2304
	21st to end	Day	20% 7% 2 7% 5% 4 5% 3 5% 6% 35%	2140
October	1st to 10th	Day	15% 6% 3 6% 3 3 4 3 6% 7% 45%	2000
	11th to 20th	Day	14% 6% 3 5% 4 4 3 3 5% 5% 48%	2000
	21st to end	Day	13% 6% 2 5% 4 4 4 4 5% 7% 47%	2200
November	1st to 10th	Day	9% 5% 2 4 4 4 3 3 5% 7% 53%	2057
	11th to 20th	Day	13% 6% 2 4 4 3 5% 4 6% 6% 46%	1792
	21st to end	Day	13% 6% 2 5% 5% 4 4 3 5% 6% 45%	1680
December	1st to 10th	Day	11% 6% 2 5% 3 5% 5% 4 5% 7% 48%	2680
	11th to 20th	Day	17% 7% 2 6% 4 5% 4 4 4 6% 40%	3070
	21st to end	Day	16% 7% 3 7% 5% 5% 5% 4 6% 7% 35%	4048
January	1st to 10th	Night	9% 7% 2 6% 4 5% 5% 5% 6% 7% 43%	7653
	11th to 20th	Night	9% 7% 3 7% 3 3 4 3 5% 6% 50%	7680
	21st to end	Night	12% 7% 2 5% 4 4 4 3 5% 6% 49%	8401
February	1st to 10th	Night	11% 8% 3 7% 5% 4 4 5% 6% 6% 42%	2730
	11th to 20th	Night	15% 8% 2 7% 4 4 5% 4 6% 5% 39%	2663
	21st to end	Night	13% 8% 2 7% 5% 5% 5% 4 6% 7% 39%	2027
March	1st to 10th	Night	16% 6% 2 5% 4 3 4 3 5% 5% 47%	5028
	11th to 20th	Night	9% 4 1 5% 3 4 5% 3 6% 9% 52%	5090
	21st to end	Night	10% 6% 2 6% 4 5% 5% 4 5% 7% 46%	5588
April	1st to 10th	Night	13% 8% 2 7% 5% 3 5% 5% 5% 7% 41%	2143
	11th to 20th	Night	11% 6% 2 6% 5% 4 4 4 6% 8% 44%	2075
	21st to end	Night	14% 6% 2 5% 4 4 4 3 4 7% 46%	2037
May	1st to 10th	Night	16% 7% 2 7% 5% 5% 5% 4 7% 8% 35%	5237
	11th to 20th	Night	18% 7% 2 6% 4 4 5% 4 6% 8% 37%	5234
	21st to end	Night	21% 7% 3 7% 4 4 4 4 5% 7% 34%	5208
June	1st to 10th	Night	10% 5% 2 5% 5% 5% 4 4 6% 8% 46%	1680
	11th to 20th	Night	11% 7% 1 7% 5% 4 4 5% 6% 9% 41%	1680
	21st to end	Night	9% 4 2 5% 4 4 5% 5% 8% 10% 43%	1680
July	1st to 10th	Night	6% 5% 3 7% 5% 5% 6% 5% 8% 10% 41%	3854
	11th to 20th	Night	8% 7% 4 10% 6% 7% 6% 5% 7% 9% 30%	4147
	21st to end	Night	7% 5% 2 8% 5% 5% 7% 5% 8% 10% 38%	4517
August	1st to 10th	Night	13% 6% 2 7% 5% 4 6% 4 7% 9% 36%	2915
	11th to 20th	Night	10% 6% 3 6% 5% 5% 5% 4 7% 9% 40%	2875
	21st to end	Night	10% 5% 2 5% 4 4 4 4 5% 8% 48%	3581
September	1st to 10th	Night	12% 6% 2 6% 4 4 4 3 5% 6% 47%	2000
	11th to 20th	Night	12% 5% 3 4 3 4 4 3 6% 7% 49%	2092
	21st to end	Night	21% 7% 2 5% 3 3 5% 3 5% 6% 40%	2260
October	1st to 10th	Night	17% 6% 2 5% 3 3 4 3 5% 6% 47%	2400
	11th to 20th	Night	12% 5% 2 5% 3 3 3 3 5% 6% 51%	2400
	21st to end	Night	13% 5% 1 4 4 3 4 3 5% 6% 50%	2640
November	1st to 10th	Night	9% 6% 2 6% 3 4 4 3 5% 6% 52%	2461
	11th to 20th	Night	12% 7% 2 4 4 3 4 4 6% 6% 47%	2823
	21st to end	Night	12% 5% 2 6% 4 5% 5% 3 6% 7% 45%	2940
December	1st to 10th	Night	9% 5% 2 5% 4 4 4 3 6% 8% 50%	4720
	11th to 20th	Night	15% 8% 3 6% 5% 4 5% 4 4 6% 40%	5345
	21st to end	Night	14% 7% 2 7% 5% 5% 5% 5% 7% 8% 35%	7150

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% 4 8% 22% 20% 6%	5237
	11th to 20th	Day	39% 4 7% 18% 22% 11%	5280
	21st to end	Day	41% 5% 7% 28% 15% 4	5780
February	1st to 10th	Day	44% 5% 11% 22% 16% 3	1890
	11th to 20th	Day	46% 4 8% 20% 18% 3	1852
	21st to end	Day	44% 4 11% 20% 16% 4	1772
March	1st to 10th	Day	43% 5% 8% 20% 16% 8%	5045
	11th to 20th	Day	33% 5% 8% 28% 20% 6%	5090
	21st to end	Day	44% 6% 9% 17% 18% 5%	5586
April	1st to 10th	Day	41% 6% 10% 19% 17% 6%	2476
	11th to 20th	Day	37% 4 11% 21% 21% 5%	2494
	21st to end	Day	44% 5% 10% 23% 15% 3	2600
May	1st to 10th	Day	45% 8% 12% 22% 12% 2	7651
	11th to 20th	Day	44% 8% 11% 26% 10% 1	7630
	21st to end	Day	46% 7% 10% 18% 15% 3	8943
June	1st to 10th	Day	38% 8% 12% 24% 18% 1	2940
	11th to 20th	Day	39% 9% 14% 22% 14% 2	2940
	21st to end	Day	36% 8% 14% 26% 14% 2	2940
July	1st to 10th	Day	35% 10% 15% 24% 13% 4	6251
	11th to 20th	Day	41% 12% 16% 24% 7% 1	5961
	21st to end	Day	39% 8% 11% 25% 17% 1	6370
August	1st to 10th	Day	46% 9% 15% 23% 7%	4221
	11th to 20th	Day	37% 9% 12% 29% 13% 1	4182
	21st to end	Day	34% 6% 14% 29% 15% 1	4312
September	1st to 10th	Day	39% 6% 13% 18% 21% 4	2400
	11th to 20th	Day	37% 5% 7% 28% 20% 3	2304
	21st to end	Day	49% 5% 8% 20% 16% 2	2140
October	1st to 10th	Day	32% 5% 8% 21% 27% 6%	3260
	11th to 20th	Day	27% 4 9% 28% 20% 12%	3240
	21st to end	Day	25% 4 8% 30% 25% 8%	3538
November	1st to 10th	Day	32% 3 11% 25% 25% 4	2057
	11th to 20th	Day	37% 4 10% 21% 23% 5%	1792
	21st to end	Day	39% 5% 11% 24% 19% 2	1680
December	1st to 10th	Day	35% 6% 12% 25% 19% 4	2680
	11th to 20th	Day	44% 5% 10% 24% 14% 3	3066
	21st to end	Day	45% 6% 14% 20% 15% 1	4048
January	1st to 10th	Night	37% 5% 9% 23% 23% 3	7654
	11th to 20th	Night	34% 4 8% 22% 23% 8%	7680
	21st to end	Night	35% 5% 8% 28% 19% 4	8401
February	1st to 10th	Night	41% 5% 12% 25% 15% 2	2730
	11th to 20th	Night	45% 4 8% 22% 16% 4	2665
	21st to end	Night	42% 6% 11% 21% 15% 5%	2027
March	1st to 10th	Night	38% 5% 8% 25% 15% 8%	5028
	11th to 20th	Night	29% 6% 9% 29% 21% 5%	5090
	21st to end	Night	37% 5% 13% 22% 19% 5%	5588
April	1st to 10th	Night	41% 6% 10% 21% 17% 3	2143
	11th to 20th	Night	37% 6% 12% 24% 17% 4	2075
	21st to end	Night	39% 5% 10% 28% 15% 3	2037
May	1st to 10th	Night	45% 8% 13% 20% 12% 3	5264
	11th to 20th	Night	42% 8% 14% 26% 10% 1	5235
	21st to end	Night	49% 7% 13% 19% 10% 3	5215
June	1st to 10th	Night	34% 7% 13% 28% 16% 1	1680
	11th to 20th	Night	39% 8% 16% 23% 13% 1	1680
	21st to end	Night	34% 7% 17% 23% 17% 1	1680
July	1st to 10th	Night	36% 12% 18% 20% 12% 2	3813
	11th to 20th	Night	47% 11% 16% 18% 7% 1	4096
	21st to end	Night	35% 10% 17% 24% 13%	4387
August	1st to 10th	Night	43% 8% 17% 25% 7%	2904
	11th to 20th	Night	36% 8% 16% 24% 16%	2902
	21st to end	Night	33% 6% 15% 30% 14% 1	3581
September	1st to 10th	Night	38% 6% 13% 21% 18% 4	2000
	11th to 20th	Night	34% 5% 10% 31% 19% 2	2092
	21st to end	Night	46% 5% 9% 22% 17% 2	2260
October	1st to 10th	Night	37% 4 10% 23% 24% 3	3920
	11th to 20th	Night	25% 4 11% 22% 29% 9%	3899
	21st to end	Night	22% 4 11% 30% 27% 5%	4252
November	1st to 10th	Night	32% 4 11% 24% 23% 6%	2461
	11th to 20th	Night	36% 4 8% 25% 22% 5%	2823
	21st to end	Night	38% 5% 11% 24% 19% 3	2940
December	1st to 10th	Night	32% 5% 12% 30% 19% 2	4720
	11th to 20th	Night	44% 4 12% 19% 17% 4	5348
	21st to end	Night	42% 8% 13% 20% 16% 1	7150

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	326
	11th to 20th	Day	36% 25% 28% 9% 3	330
	21st to end	Day	29% 28% 34% 7% 2	363
February	1st to 10th	Day	30% 28% 31% 9% 2	330
	11th to 20th	Day	42% 22% 30% 5% 1	330
	21st to end	Day	35% 19% 30% 14% 2	409
March	1st to 10th	Day	28% 22% 26% 20% 4	540
	11th to 20th	Day	29% 22% 26% 17% 4 2	540
	21st to end	Day	26% 19% 31% 17% 5% 1	594
April	1st to 10th	Day	25% 22% 27% 18% 6% 1	540
	11th to 20th	Day	24% 16% 30% 17% 10% 3	532
	21st to end	Day	26% 13% 32% 17% 9% 2	540
May	1st to 10th	Day	24% 16% 32% 15% 9% 4	543
	11th to 20th	Day	23% 13% 29% 23% 8% 3	567
	21st to end	Day	21% 9% 29% 20% 15% 6%	617
June	1st to 10th	Day	15% 11% 26% 29% 13% 6%	570
	11th to 20th	Day	17% 8% 26% 26% 16% 6%	570
	21st to end	Day	12% 7% 31% 26% 18% 5%	570
July	1st to 10th	Day	12% 4 18% 31% 26% 9%	565
	11th to 20th	Day	8% 3 21% 32% 25% 10%	564
	21st to end	Day	12% 3 23% 29% 24% 10%	616
August	1st to 10th	Day	15% 5% 20% 27% 21% 11%	526
	11th to 20th	Day	13% 3 19% 29% 26% 11%	519
	21st to end	Day	11% 5% 20% 28% 22% 15%	583
September	1st to 10th	Day	16% 7% 18% 26% 22% 11%	530
	11th to 20th	Day	15% 3 21% 29% 22% 10%	530
	21st to end	Day	29% 9% 21% 24% 13% 4	530
October	1st to 10th	Day	19% 5% 23% 29% 20% 4	530
	11th to 20th	Day	21% 15% 25% 25% 13% 2	530
	21st to end	Day	20% 16% 32% 20% 10% 2	583
November	1st to 10th	Day	18% 14% 32% 24% 10% 3	535
	11th to 20th	Day	24% 15% 34% 19% 7% 1	314
	21st to end	Day	31% 15% 36% 15% 3	220
December	1st to 10th	Day	26% 20% 41% 8% 3 1	220
	11th to 20th	Day	25% 21% 32% 17% 5%	220
	21st to end	Day	24% 17% 36% 17% 4	242
January	1st to 10th	Night	23% 19% 33% 23% 3	840
	11th to 20th	Night	23% 17% 29% 28% 3	840
	21st to end	Night	19% 18% 37% 25% 1	924
February	1st to 10th	Night	18% 19% 32% 29% 2	840
	11th to 20th	Night	27% 22% 30% 19% 1	823
	21st to end	Night	25% 15% 35% 23% 2	692
March	1st to 10th	Night	22% 17% 33% 24% 4	840
	11th to 20th	Night	25% 19% 26% 24% 6% 1	840
	21st to end	Night	22% 17% 34% 21% 5% 1	924
April	1st to 10th	Night	22% 18% 29% 25% 7%	840
	11th to 20th	Night	19% 15% 30% 27% 9% 1	831
	21st to end	Night	19% 12% 25% 34% 9%	777
May	1st to 10th	Night	21% 8% 26% 30% 14% 2	630
	11th to 20th	Night	20% 6% 24% 33% 16% 1	621
	21st to end	Night	17% 3 21% 34% 21% 4	491
June	1st to 10th	Night	13% 2 22% 40% 21% 1	420
	11th to 20th	Night	15% 4 14% 44% 21% 2	420
	21st to end	Night	9% 3 20% 45% 21% 2	420
July	1st to 10th	Night	11% 2 11% 38% 31% 7%	479
	11th to 20th	Night	8% 1 10% 40% 36% 5%	612
	21st to end	Night	9% 2 14% 40% 30% 5%	687
August	1st to 10th	Night	12% 2 10% 41% 32% 4	597
	11th to 20th	Night	12% 2 10% 40% 32% 4	594
	21st to end	Night	12% 3 11% 37% 33% 4	875
September	1st to 10th	Night	17% 2 14% 31% 31% 5%	800
	11th to 20th	Night	13% 3 15% 35% 30% 5%	800
	21st to end	Night	25% 4 18% 32% 19% 2	800
October	1st to 10th	Night	22% 6% 16% 31% 22% 3	800
	11th to 20th	Night	16% 12% 24% 33% 15% 1	800
	21st to end	Night	18% 12% 24% 34% 12% 1	880
November	1st to 10th	Night	14% 10% 27% 36% 11% 1	820
	11th to 20th	Night	19% 15% 26% 29% 9% 1	840
	21st to end	Night	19% 16% 28% 29% 7% 1	840
December	1st to 10th	Night	20% 16% 30% 27% 6% 1	840
	11th to 20th	Night	18% 14% 32% 32% 4	840
	21st to end	Night	20% 15% 28% 35% 3	924

Page generated at 2026-07-28 03:25:23. Version ac07

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