Latest Forecast for Mauna Kea Observatories
5 PM HST Friday 16 October (0300 UTC Saturday 17 October) 2020

Warnings
Chance for fog and high humidity

Cloud Cover and Precipitation Forecast
There is a very small risk for periods of fog and high humidity, while broken clouds continue to pass overhead through the night.

Summary of Key Meteorological Variables
Summit temperatures will be near 2.5 C, with light and variable winds and seeing near 0.5-0.55 arcseconds. Precipitable water is expected to exceed 4 mm for the night.

Graphical Summary

Discussion
Although the tradewind inversion will remain intact into next week, moisture organizing in the area may allow for periods of fog and high humidity at the summit throughout the forecast period; the odds are small and precipitation is not expected. Extensive afternoon clouds are possible throughout the forecast period and there is a chance for convection along the Big Island slopes over the weekend and early part of next week.

Broken to overcast thick clouds will continue to stream in from the west, blanketing most, if not all of the sky through the next 5 nights.

Precipitable water is expected to exceed 4 mm through the next 5 nights.

Relatively light/laminar SW flow will prevail at and above the summit, but there is a possibility for minor horizontal shear which may keep seeing near 0.5-0.55 arcseconds over the next 2 nights. An increase in free atmospheric turbulence, combined with mid-level moisture may degrade seeing toward 0.8 arcseconds for Sunday night and early part of next week.

No change since the morning forecast...The low to the NW will remain quasi-stationary steady, while a fairly deep ridge persists over or just south of the Big Island into the middle part of next week. While subsidence associated with the ridge will help keep the inversion intact at or below 10 thousand feet during this time, the low will draw moisture in from the tropics and organize it into a somewhat stationary frontal band over the western half of the state. There is a possibility that patches of moisture will spill into the area and contribute to periods of fog and high humidity at the summit at virtually anytime over the next 5 nights. In addition, deep SW mid/upper-level flow will continuously draw thick broken/overcast clouds out of the SW and stream it over the summit, blanketing most if not all of the sky during that time. PW will also not benefit from this influx of moisture, but there is a chance that initially better than average seeing will prevail as relatively laminar SW flow persists in the free atmosphere. Seeing may deteriorate as more mid-level moisture flows into the area and stronger upper-level turbulence builds in late in the weekend and early part of next week.

Astronomical Observing Quality Guidance
Seeing/CN2 Images are not available today. Sorry for the inconvenience.
Latest WRF CN2 Profiles Animation | Collage


5-day Forecast
Summary

Graphical Trend
08 pm HST
Fri 16 Oct
02 am HST
Sat 17 Oct
02 pm HST
Sat 17 Oct
08 pm HST
Sat 17 Oct
02 am HST
Sun 18 Oct
02 pm HST
Sun 18 Oct
08 pm HST
Sun 18 Oct
02 am HST
Mon 19 Oct
02 pm HST
Mon 19 Oct
02 am HST
Tue 20 Oct
02 pm HST
Tue 20 Oct
02 am HST
Wed 21 Oct
02 pm HST
Wed 21 Oct
06 UTC
Sat 17 Oct
12 UTC
Sat 17 Oct
00 UTC
Sun 18 Oct
06 UTC
Sun 18 Oct
12 UTC
Sun 18 Oct
00 UTC
Mon 19 Oct
06 UTC
Mon 19 Oct
12 UTC
Mon 19 Oct
00 UTC
Tue 20 Oct
12 UTC
Tue 20 Oct
00 UTC
Wed 21 Oct
12 UTC
Wed 21 Oct
00 UTC
Thu 22 Oct
Cloud Cover (%) 60 to 80 60 to 80 80 to 100 80 to 100 80 to 100 80 to 100 80 to 100 80 to 100 80 to 100 70 to 90 60 to 80 60 to 80 0 to 20
Cloud Height (km) above sea level 9-10 7-10 7-8 7-8 7-9 7-10 6.5-10 4-10 6-10 4-10 6-10 4-10 4-10
Chance for Fog/Precip (%) 15/0 20/0 30/5 20/0 20/0 30/5 25/0 25/0 50/10 30/0 50/10 25/0 35/5
PW (mm, summit upward) 4 to 6 4 to 6 4 to 8 4 to 6 4 to 6 6 to 10 6 to 10 6 to 10 6 to 10 4 to 8 6 to 10 4 to 8 4 to 8
Mean Seeing (arcsecs) 0.55 ± 0.1 0.5 ± 0.1 N/A 0.5 ± 0.1 0.55 ± 0.1 N/A 0.7 ± 0.2 0.8 ± 0.2 N/A 0.9 ± 0.2 N/A 0.8 ± 0.2 N/A
Summit Temp (°C) 2.5 2.5 8.5 3.5 3.5 8.5 8.5 3.5 8.5 3.5 8 3 7
Wind Dir/Speed (mph)
    Summit (615 hPa)
    19,000 ft (500 hPa)
    24,500 ft (400 hPa)
    31,000 ft (300 hPa)
    35,000 ft (250 hPa)
    40,000 ft (200 hPa)
    46,000 ft (150 hPa)
    54,000 ft (100 hPa)

E/0 to 10

E/0 to 10

NNE/0 to 10

NE/5 to 15

N/5 to 15

N/5 to 15

NNE/5 to 15

NNE/5 to 15

NNE/0 to 10

NNW/0 to 10

NNE/5 to 15

NNE/5 to 15

N/0 to 10


 Rise and Set times for the Sun and Moon
Night (HST)
Sun Set
Twilight End
Twilight Beg
Sun Rise
Moon Rise
Moon Set
Illum (%)
RA
Dec
Fri.Oct.16/Sat.Oct.17
18:06
19:11
5:04
6:09
7:09
18:30
1
14 08.2
-9 10
Sat.Oct.17/Sun.Oct.18
18:05
19:10
5:04
6:09
N/A
19:17
4
15 05.1
-14 43
Sun.Oct.18/Mon.Oct.19
18:05
19:09
5:04
6:09
N/A
20:06
10
16 03.8
-19 19
Mon.Oct.19/Tue.Oct.20
18:04
19:09
5:05
6:10
N/A
21:00
18
17 03.9
-22 39
Tue.Oct.20/Wed.Oct.21
18:03
19:08
5:05
6:10
N/A
21:56
27
18 04.7
-24 31


Forecast issued by: Ryan Lyman
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Next update at 10 AM HST (2000 UTC) Monday 19 October 2020.
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