Montgomery
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Montgomery clear sky chart from 2005-11-06 to 2024-01-14.

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	16% 6% 3 5% 5% 3 5% 5% 6% 7% 39%	74767
	Night	17% 7% 3 5% 5% 3 4 4 5% 7% 41%	74976
Transparency	Day	44% 5% 12% 23% 15% 2	74472
	Night	43% 5% 12% 23% 15% 2	74805
Seeing	Day	22% 14% 28% 22% 10% 3	13786
	Night	20% 12% 28% 29% 10% 1	23037

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% 7% 3 5% 5% 2 6% 5% 6% 8% 40%	1517
	11th to 20th	Day	16% 7% 3 6% 7% 3 5% 6% 6% 6% 34%	1464
	21st to end	Day	12% 8% 3 6% 5% 3 5% 5% 6% 8% 40%	1706
February	1st to 10th	Day	16% 10% 3 7% 6% 3 7% 5% 5% 8% 32%	1620
	11th to 20th	Day	14% 7% 3 6% 5% 4 5% 4 5% 7% 40%	1729
	21st to end	Day	19% 9% 4 5% 5% 3 4 4 4 6% 37%	1480
March	1st to 10th	Day	14% 7% 3 6% 6% 3 4 5% 5% 7% 40%	1797
	11th to 20th	Day	15% 8% 3 6% 6% 4 5% 5% 5% 7% 37%	1903
	21st to end	Day	20% 7% 3 5% 5% 3 5% 5% 4 5% 38%	2348
April	1st to 10th	Day	18% 7% 3 6% 5% 3 5% 4 5% 6% 38%	2160
	11th to 20th	Day	17% 6% 3 6% 5% 3 4 4 4 6% 41%	2134
	21st to end	Day	20% 6% 3 6% 5% 3 5% 5% 5% 5% 38%	2189
May	1st to 10th	Day	22% 7% 3 6% 4 3 4 5% 5% 7% 34%	2362
	11th to 20th	Day	18% 6% 2 5% 5% 3 5% 5% 6% 7% 37%	2478
	21st to end	Day	14% 6% 2 5% 5% 3 4 5% 6% 8% 41%	2725
June	1st to 10th	Day	17% 5% 2 5% 5% 4 6% 5% 6% 10% 35%	2520
	11th to 20th	Day	15% 5% 2 6% 6% 4 6% 6% 7% 9% 35%	2520
	21st to end	Day	13% 5% 3 6% 6% 4 5% 5% 7% 8% 39%	2520
July	1st to 10th	Day	12% 5% 3 5% 6% 4 6% 6% 7% 9% 38%	2520
	11th to 20th	Day	11% 4 2 5% 6% 4 5% 6% 6% 10% 40%	2520
	21st to end	Day	11% 5% 3 6% 5% 4 6% 7% 6% 9% 38%	2744
August	1st to 10th	Day	11% 6% 2 5% 5% 4 6% 6% 8% 9% 38%	2415
	11th to 20th	Day	12% 6% 2 5% 5% 4 5% 6% 7% 8% 39%	2126
	21st to end	Day	14% 5% 2 6% 5% 3 5% 4 5% 8% 43%	2376
September	1st to 10th	Day	15% 6% 3 5% 5% 4 5% 5% 5% 7% 42%	2160
	11th to 20th	Day	14% 4 2 5% 4 3 4 4 5% 7% 49%	2093
	21st to end	Day	16% 5% 2 5% 5% 3 5% 4 6% 6% 43%	1980
October	1st to 10th	Day	21% 6% 2 5% 5% 2 4 4 5% 6% 40%	1863
	11th to 20th	Day	15% 6% 2 5% 4 4 5% 4 6% 8% 42%	1800
	21st to end	Day	23% 7% 2 5% 5% 3 5% 5% 5% 6% 35%	1832
November	1st to 10th	Day	14% 6% 3 4 4 3 3 3 3 6% 51%	1671
	11th to 20th	Day	17% 6% 3 4 4 3 4 4 5% 7% 43%	1710
	21st to end	Day	16% 7% 3 5% 5% 4 3 6% 5% 6% 40%	1587
December	1st to 10th	Day	19% 8% 3 6% 5% 5% 4 5% 5% 6% 34%	1520
	11th to 20th	Day	22% 6% 2 4 4 2 4 4 5% 6% 41%	1906
	21st to end	Day	19% 10% 4 8% 6% 5% 5% 5% 5% 7% 28%	2772
January	1st to 10th	Night	15% 6% 2 6% 5% 2 5% 4 5% 7% 43%	2649
	11th to 20th	Night	17% 8% 4 5% 6% 3 5% 6% 5% 6% 36%	2569
	21st to end	Night	12% 8% 2 5% 5% 3 5% 5% 6% 8% 41%	2648
February	1st to 10th	Night	16% 9% 3 6% 5% 3 5% 4 5% 6% 39%	2340
	11th to 20th	Night	15% 8% 3 6% 6% 3 5% 4 6% 6% 38%	2116
	21st to end	Night	17% 7% 3 6% 6% 3 4 4 4 5% 41%	1776
March	1st to 10th	Night	16% 7% 2 5% 4 3 3 5% 5% 7% 43%	2150
	11th to 20th	Night	16% 8% 3 5% 5% 2 4 4 6% 7% 40%	2051
	21st to end	Night	17% 7% 3 5% 5% 3 6% 4 5% 7% 39%	2007
April	1st to 10th	Night	19% 7% 3 6% 6% 3 5% 4 5% 7% 36%	1800
	11th to 20th	Night	19% 6% 3 6% 5% 3 4 4 5% 7% 40%	1775
	21st to end	Night	21% 6% 3 5% 4 3 3 3 5% 6% 40%	1769
May	1st to 10th	Night	23% 8% 3 5% 5% 3 4 5% 4 7% 35%	1612
	11th to 20th	Night	18% 6% 3 5% 4 2 5% 4 6% 6% 39%	1415
	21st to end	Night	13% 6% 3 5% 4 4 4 4 6% 8% 43%	1550
June	1st to 10th	Night	15% 5% 2 5% 5% 3 5% 5% 5% 7% 42%	1440
	11th to 20th	Night	14% 6% 2 4 5% 3 5% 5% 5% 9% 41%	1440
	21st to end	Night	11% 4 2 4 4 3 4 5% 7% 9% 46%	1440
July	1st to 10th	Night	13% 5% 3 5% 4 2 5% 5% 5% 10% 43%	1440
	11th to 20th	Night	13% 5% 2 5% 5% 3 6% 5% 5% 10% 42%	1440
	21st to end	Night	11% 4 2 5% 4 4 5% 6% 6% 9% 43%	1574
August	1st to 10th	Night	9% 5% 2 5% 5% 4 5% 5% 7% 8% 45%	1508
	11th to 20th	Night	12% 6% 3 6% 7% 3 7% 5% 6% 8% 38%	1766
	21st to end	Night	15% 6% 2 5% 5% 3 3 5% 5% 8% 44%	1980
September	1st to 10th	Night	15% 6% 2 5% 5% 2 4 4 5% 7% 45%	1800
	11th to 20th	Night	14% 5% 2 4 4 3 3 4 3 6% 53%	1867
	21st to end	Night	16% 5% 2 4 4 2 3 4 5% 6% 47%	1980
October	1st to 10th	Night	21% 6% 2 5% 5% 2 4 4 4 6% 41%	2095
	11th to 20th	Night	16% 6% 2 5% 4 3 4 4 4 6% 47%	2160
	21st to end	Night	23% 7% 2 5% 4 2 4 5% 4 5% 39%	2522
November	1st to 10th	Night	13% 6% 3 5% 5% 3 4 4 5% 6% 47%	2407
	11th to 20th	Night	19% 6% 2 4 4 2 4 4 4 6% 44%	2470
	21st to end	Night	16% 5% 2 5% 4 3 4 5% 5% 7% 44%	2588
December	1st to 10th	Night	20% 7% 3 5% 5% 2 4 4 5% 7% 38%	2660
	11th to 20th	Night	20% 8% 3 4 5% 3 4 5% 5% 7% 37%	3288
	21st to end	Night	22% 10% 3 6% 5% 2 4 4 5% 5% 35%	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% 5% 11% 27% 13% 3	1518
	11th to 20th	Day	48% 4 15% 19% 11% 2	1464
	21st to end	Day	42% 3 12% 26% 14% 2	1706
February	1st to 10th	Day	50% 4 12% 20% 14% 1	1620
	11th to 20th	Day	46% 4 9% 22% 16% 3	1738
	21st to end	Day	49% 4 10% 22% 13% 2	1480
March	1st to 10th	Day	44% 4 13% 22% 13% 3	1800
	11th to 20th	Day	47% 4 10% 24% 14% 2	1903
	21st to end	Day	50% 3 7% 18% 17% 5%	2348
April	1st to 10th	Day	47% 5% 9% 21% 14% 4	2160
	11th to 20th	Day	44% 4 10% 22% 17% 3	2134
	21st to end	Day	48% 5% 8% 21% 14% 4	2189
May	1st to 10th	Day	50% 4 9% 19% 16% 2	2362
	11th to 20th	Day	46% 4 10% 22% 16% 3	2482
	21st to end	Day	40% 5% 16% 22% 14% 2	2725
June	1st to 10th	Day	43% 6% 14% 21% 14% 1	2520
	11th to 20th	Day	44% 7% 13% 24% 11% 2	2520
	21st to end	Day	41% 7% 11% 26% 14% 1	2520
July	1st to 10th	Day	41% 6% 13% 21% 16% 2	2450
	11th to 20th	Day	38% 5% 14% 27% 15% 1	2445
	21st to end	Day	41% 6% 13% 21% 16% 3	2591
August	1st to 10th	Day	40% 5% 13% 27% 13% 1	2401
	11th to 20th	Day	41% 7% 15% 24% 12% 1	2126
	21st to end	Day	39% 5% 12% 25% 17% 2	2376
September	1st to 10th	Day	41% 5% 11% 24% 16% 2	2160
	11th to 20th	Day	35% 4 9% 26% 24% 2	2093
	21st to end	Day	41% 5% 11% 23% 18% 3	1980
October	1st to 10th	Day	45% 4 10% 23% 15% 3	1863
	11th to 20th	Day	40% 4 13% 27% 16% 1	1800
	21st to end	Day	50% 3 10% 22% 13% 2	1832
November	1st to 10th	Day	37% 3 12% 27% 18% 3	1671
	11th to 20th	Day	42% 3 11% 23% 18% 3	1710
	21st to end	Day	43% 4 14% 27% 10% 2	1587
December	1st to 10th	Day	50% 4 14% 19% 13%	1520
	11th to 20th	Day	45% 3 16% 23% 11% 2	1906
	21st to end	Day	55% 5% 11% 21% 7%	2772
January	1st to 10th	Night	41% 3 12% 24% 16% 3	2649
	11th to 20th	Night	49% 5% 14% 22% 9% 2	2569
	21st to end	Night	40% 5% 11% 24% 18% 2	2648
February	1st to 10th	Night	47% 5% 13% 21% 12% 1	2340
	11th to 20th	Night	46% 4 10% 19% 16% 4	2118
	21st to end	Night	47% 3 7% 24% 16% 3	1776
March	1st to 10th	Night	41% 4 13% 24% 15% 3	2160
	11th to 20th	Night	44% 4 10% 23% 16% 3	2052
	21st to end	Night	46% 5% 9% 18% 19% 4	2007
April	1st to 10th	Night	49% 4 9% 20% 15% 3	1800
	11th to 20th	Night	44% 5% 10% 21% 19% 1	1775
	21st to end	Night	46% 4 8% 22% 15% 4	1769
May	1st to 10th	Night	51% 4 8% 19% 15% 2	1612
	11th to 20th	Night	45% 4 10% 20% 19% 2	1416
	21st to end	Night	39% 6% 17% 24% 11% 2	1551
June	1st to 10th	Night	41% 5% 11% 23% 17% 1	1440
	11th to 20th	Night	40% 7% 14% 28% 10% 1	1440
	21st to end	Night	34% 7% 15% 28% 15% 1	1440
July	1st to 10th	Night	37% 6% 14% 25% 15% 3	1400
	11th to 20th	Night	39% 6% 13% 29% 12% 1	1392
	21st to end	Night	34% 7% 17% 23% 17% 3	1486
August	1st to 10th	Night	36% 7% 15% 26% 15% 1	1498
	11th to 20th	Night	43% 6% 15% 23% 11% 1	1766
	21st to end	Night	39% 5% 11% 23% 20% 1	1980
September	1st to 10th	Night	39% 6% 10% 28% 16% 1	1800
	11th to 20th	Night	34% 3 11% 26% 25% 2	1867
	21st to end	Night	38% 5% 9% 24% 23% 1	1980
October	1st to 10th	Night	45% 5% 11% 22% 16% 2	2095
	11th to 20th	Night	39% 4 12% 29% 14% 1	2160
	21st to end	Night	47% 4 11% 24% 13% 1	2522
November	1st to 10th	Night	39% 3 11% 23% 21% 3	2407
	11th to 20th	Night	43% 3 10% 24% 17% 4	2470
	21st to end	Night	40% 3 14% 30% 11% 1	2588
December	1st to 10th	Night	47% 4 12% 24% 13% 1	2660
	11th to 20th	Night	47% 5% 13% 19% 14% 3	3288
	21st to end	Night	52% 4 12% 22% 9%	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	27% 21% 29% 19% 4	180
	11th to 20th	Day	33% 21% 30% 11% 4 1	166
	21st to end	Day	22% 25% 32% 16% 3 2	230
February	1st to 10th	Day	37% 23% 29% 9% 3	240
	11th to 20th	Day	25% 24% 36% 13% 2	397
	21st to end	Day	31% 22% 31% 14% 2	346
March	1st to 10th	Day	24% 20% 33% 18% 5%	420
	11th to 20th	Day	25% 24% 29% 18% 4 1	420
	21st to end	Day	31% 17% 29% 16% 5% 2	462
April	1st to 10th	Day	30% 20% 25% 16% 8% 2	420
	11th to 20th	Day	25% 23% 28% 13% 8% 2	412
	21st to end	Day	31% 19% 26% 16% 6% 2	420
May	1st to 10th	Day	35% 14% 28% 16% 6% 1	423
	11th to 20th	Day	20% 15% 36% 19% 7% 2	447
	21st to end	Day	19% 10% 26% 26% 16% 3	485
June	1st to 10th	Day	19% 11% 29% 25% 13% 2	450
	11th to 20th	Day	17% 13% 28% 28% 13% 2	450
	21st to end	Day	16% 12% 26% 30% 13% 3	450
July	1st to 10th	Day	15% 8% 26% 30% 17% 5%	445
	11th to 20th	Day	13% 4 27% 32% 18% 6%	444
	21st to end	Day	12% 6% 30% 34% 14% 3	488
August	1st to 10th	Day	11% 7% 25% 31% 19% 7%	446
	11th to 20th	Day	15% 6% 24% 32% 17% 6%	439
	21st to end	Day	13% 9% 24% 28% 17% 8%	495
September	1st to 10th	Day	19% 10% 22% 24% 16% 9%	450
	11th to 20th	Day	15% 9% 27% 23% 15% 12%	450
	21st to end	Day	19% 10% 26% 26% 14% 6%	450
October	1st to 10th	Day	29% 10% 20% 22% 13% 6%	450
	11th to 20th	Day	17% 14% 28% 25% 14% 2	450
	21st to end	Day	27% 12% 31% 19% 10% 1	421
November	1st to 10th	Day	19% 14% 27% 27% 10% 3	365
	11th to 20th	Day	23% 20% 26% 22% 7% 1	370
	21st to end	Day	22% 17% 31% 23% 7% 1	247
December	1st to 10th	Day	24% 21% 34% 14% 7%	180
	11th to 20th	Day	32% 20% 29% 15% 4	180
	21st to end	Day	24% 24% 30% 18% 3 1	198
January	1st to 10th	Night	19% 17% 37% 23% 4	760
	11th to 20th	Night	24% 15% 32% 26% 3	735
	21st to end	Night	18% 17% 36% 25% 4	792
February	1st to 10th	Night	23% 16% 35% 23% 2	720
	11th to 20th	Night	22% 19% 40% 18% 1	703
	21st to end	Night	23% 19% 35% 20% 4	592
March	1st to 10th	Night	24% 17% 32% 24% 4	720
	11th to 20th	Night	23% 21% 31% 22% 4	720
	21st to end	Night	20% 17% 34% 23% 6%	792
April	1st to 10th	Night	25% 15% 34% 21% 5%	720
	11th to 20th	Night	22% 14% 32% 26% 6%	711
	21st to end	Night	25% 14% 27% 26% 7% 1	689
May	1st to 10th	Night	27% 11% 29% 26% 7%	532
	11th to 20th	Night	21% 11% 31% 31% 6% 1	354
	21st to end	Night	15% 8% 19% 42% 15% 1	389
June	1st to 10th	Night	16% 5% 28% 35% 16% 1	360
	11th to 20th	Night	16% 6% 24% 38% 16%	360
	21st to end	Night	13% 3 21% 48% 14% 1	360
July	1st to 10th	Night	15% 3 17% 41% 22% 1	350
	11th to 20th	Night	12% 3 19% 42% 23% 1	348
	21st to end	Night	11% 4 20% 45% 19% 1	394
August	1st to 10th	Night	12% 2 18% 44% 21% 2	434
	11th to 20th	Night	13% 3 18% 40% 24% 2	702
	21st to end	Night	16% 4 16% 38% 25% 2	792
September	1st to 10th	Night	17% 5% 20% 35% 20% 2	720
	11th to 20th	Night	17% 5% 22% 31% 20% 5%	720
	21st to end	Night	18% 6% 21% 35% 18% 2	720
October	1st to 10th	Night	25% 8% 24% 26% 16% 2	720
	11th to 20th	Night	20% 10% 27% 32% 10% 1	720
	21st to end	Night	27% 11% 31% 24% 7%	792
November	1st to 10th	Night	16% 12% 31% 29% 11% 1	740
	11th to 20th	Night	23% 16% 29% 24% 7% 1	760
	21st to end	Night	20% 14% 32% 27% 7% 1	760
December	1st to 10th	Night	26% 15% 30% 24% 5%	760
	11th to 20th	Night	23% 16% 30% 27% 4	760
	21st to end	Night	26% 14% 35% 22% 3	836

Page generated at 2024-01-11 04:22:41. Version ac07

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