Latest Forecast for Mauna Kea Observatories
5 PM HST Friday 11 August (0300 UTC Saturday 12 August) 2017

Warnings
None

Cloud Cover and Precipitation Forecast
The summit will remain dry and stable, but there is a chance for scattered high clouds along the far northern skies through the night.

Summary of Key Meteorological Variables
Summit temperatures will be near 4.5 C this evening and 4 C tomorrow morning. Winds will be from the ENE at 10-20 mph, with seeing near 0.4-0.45 arcseconds. Precipitable water is expected to be in the 1.5-2 mm range for the first half of the night and 1.25-1.75 mm range for the second half.

Graphical Summary

Discussion
A strong well-defined tradewind inversion will continue to cap low-level moisture primarily near 8 thousand feet and ensure the summit remains dry and stable through the next 5 nights. Daytime clouds will be minimal and short-lived through the forecast period.

Skies overhead will remain predominately clear through the next 5 nights, but there is a possibility for isolated to scattered high clouds along the western and northern skies for tonight.

Precipitable water is expected to slip toward 1.5 mm for tonight, then settle in near 1 mm for the remainder of the forecast period.

Deep subsidence in the area, combined with light winds aloft should allow seeing to linger near 0.4-0.45 arcseconds through at Sunday evening. There is a possibility for a minor increase in shear and decrease in upper-level subsidence, which may result in a very slight degradation in seeing for the remainder of the forecast period (still better than average seeing should prevail).

No change since the morning forecast...The mid/low-level ridge will continue to sit to the north of the state and promote steady/strong large-scale subsidence in the area well into next week. This subsidence will easily maintain a well-defined tradewind inversion near 7-8 thousand feet and ensure the summit remains dry and stable throughout the forecast period. An upper-level ridge is also expected to linger just south of the Big Island, which will not only augment the subsidence in the area, but allow clear/calm skies to prevail through the weekend. This should help seeing to settle in near 0.4-0.45 arcseconds during this period and also drive PW back down toward 1 mm, especially after tonight. The upper-level ridge will eventually breakdown and shift off toward the SE as the tropical upper-tropospheric trough (TUTT) and an embedded upper-level low barges in from the NE toward the end of the weekend. While neither are expected to affect the stability of the atmosphere enough to impact summit-level conditions, it could help strengthen the sub-tropical jet a bit overhead for the early part of next week. This could contribute to minor shear/turbulence in the free atmosphere and degrade seeing toward 0.5-0.6 arceconds during that time. Fortunately, the STJ will likely maintain a relatively zonal orientation, thus limiting its access to high cloud flowing out of the tropics.

Astronomical Observing Quality Guidance
05 pm HST Friday 11 August (03 UTC Saturday 12 August)CN2
08 pm HST Friday 11 August (06 UTC Saturday 12 August)CN2
11 pm HST Friday 11 August (09 UTC Saturday 12 August)CN2
02 am HST Saturday 12 August (12 UTC Saturday 12 August)CN2
05 am HST Saturday 12 August (15 UTC Saturday 12 August)CN2
08 am HST Saturday 12 August (18 UTC Saturday 12 August)CN2
Latest WRF CN2 Profiles Animation | Collage


5-day Forecast
Summary

Graphical Trend
08 pm HST
Fri 11 Aug
02 am HST
Sat 12 Aug
02 pm HST
Sat 12 Aug
08 pm HST
Sat 12 Aug
02 am HST
Sun 13 Aug
02 pm HST
Sun 13 Aug
08 pm HST
Sun 13 Aug
02 am HST
Mon 14 Aug
02 pm HST
Mon 14 Aug
02 am HST
Tue 15 Aug
02 pm HST
Tue 15 Aug
02 am HST
Wed 16 Aug
02 pm HST
Wed 16 Aug
06 UTC
Sat 12 Aug
12 UTC
Sat 12 Aug
00 UTC
Sun 13 Aug
06 UTC
Sun 13 Aug
12 UTC
Sun 13 Aug
00 UTC
Mon 14 Aug
06 UTC
Mon 14 Aug
12 UTC
Mon 14 Aug
00 UTC
Tue 15 Aug
12 UTC
Tue 15 Aug
00 UTC
Wed 16 Aug
12 UTC
Wed 16 Aug
00 UTC
Thu 17 Aug
Cloud Cover (%) 0 to 10 0 to 10 0 to 20 0 to 5 0 to 5 0 to 20 0 to 5 0 to 5 0 to 20 0 to 5 0 to 20 0 to 5 0 to 20
Cloud Height (km) above sea level N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A
Chance for Fog/Precip (%) 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0
PW (mm, summit upward) 1.5 to 2 1.25 to 1.75 1 to 2 0.9 to 1.1 0.9 to 1.1 1 to 1.5 1 to 1.2 1 to 1.2 1 to 1.5 0.9 to 1.3 1 to 1.5 0.8 to 1.2 1 to 1.5
Mean Seeing (arcsecs) 0.4 ± 0.1 0.45 ± 0.1 N/A 0.45 ± 0.1 0.45 ± 0.1 N/A 0.45 ± 0.1 0.5 ± 0.1 N/A 0.55 ± 0.15 N/A 0.55 ± 0.15 N/A
Summit Temp (°C) 4.5 4 9.5 4.5 4 9.5 4 3.5 9 3.5 8.5 3 9
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)

ENE/10 to 20

E/10 to 20

E/5 to 15

E/5 to 15

E/5 to 15

SE/0 to 10

NE/0 to 10

NE/0 to 10

ESE/0 to 10

E/5 to 15

ESE/5 to 15

ENE/5 to 15

ENE/10 to 20


 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.Aug.11/Sat.Aug.12
19:02
20:10
4:44
5:52
21:47
N/A
77
1 08.5
2 08
Sat.Aug.12/Sun.Aug.13
19:01
20:09
4:44
5:52
22:30
N/A
67
2 00.6
6 32
Sun.Aug.13/Mon.Aug.14
19:01
20:09
4:45
5:53
23:15
N/A
57
2 54.3
10 37
Mon.Aug.14/Tue.Aug.15
19:00
20:08
4:45
5:53
0:02
N/A
45
3 49.9
14 07
Tue.Aug.15/Wed.Aug.16
18:59
20:07
4:46
5:53
0:54
N/A
34
4 47.8
16 47


Forecast issued by: Ryan Lyman
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Next update at 10 AM HST (2000 UTC) Monday 14 August 2017.
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