Latest Forecast for Mauna Kea Observatories
715 AM HST (1715 UTC) Friday 11 January 2019

Warnings
None

Cloud Cover and Precipitation Forecast
The summit will remain clear, dry and stable through the night.

Summary of Key Meteorological Variables
Summit temperatures will be near 9 C this afternoon and 4 C for the night. Winds will be from the NE at 5-15 mph for today, switching to a more SE direction by the end of the night. Seeing will be near 0.35-0.4 arcseconds, while precipitable water is expected to be in the 0.9-1.1 mm range for the first half of the night and 0.8-1 mm range for the second half.

Graphical Summary

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

Skies will remain predominately clear through the next 5 nights.

Precipitable water will start out near 1 mm for this evening, but will slowly and steadily drop, eventually settling in near 0.6-0.7 mm for the early part of next week.

Very calm/stable skies with relatively laminar north to northwesterly flow will prevail in the free atmosphere, which should allow seeing to settle in near 0.4 arcseconds probably throughout most of the forecast period. However, there is a possibility for some variability should very light winds set in for prolong periods, mainly for tomorrow night and early Sunday evening.

A relatively deep mid-level ridge will continue to linger over the state, while the low-level ridge and a broad zonal upper-level westerly jet prevails to the NE and NW, respectively well into the middle/late part of next week. Nonetheless, this will allos strong/steady large-scale subsidence to persist in the area, which will help maintain a well-defined tradewind inversion near 7-8 thousand feet and ensure a dry/stable and warm summit-level air mass throughout the forecast period. Skies will also remain predominately clear as jet constantly shuttle high clouds west to east, well north of the summit region during this time. The location of the jet should also allow relatively weak/laminar northwesterly flow to prevail aloft, minimizing turbulence in the free atmosphere during this time. This, combined with a very dry/stable air mass, should help seeing to settle in near 0.4 arcseconds, perhaps occasionally dipping toward 0.3 arcseconds, throughout most of the forecast period. There is a possibility for some variability should very light winds set in for prolong periods, mainly as the ridge briefly drifts overhead between late tomorrow afternoon and early Sunday evening. While PW is expected to start out near 1 mm for this evening, it will also benefit from the location of the ridge and steadily decline, eventually settling in near 0.6-0.7 mm by Sunday night 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
02 pm HST
Fri 11 Jan
08 pm HST
Fri 11 Jan
02 am HST
Sat 12 Jan
02 pm HST
Sat 12 Jan
08 pm HST
Sat 12 Jan
02 am HST
Sun 13 Jan
02 pm HST
Sun 13 Jan
08 pm HST
Sun 13 Jan
02 am HST
Mon 14 Jan
02 pm HST
Mon 14 Jan
02 am HST
Tue 15 Jan
02 pm HST
Tue 15 Jan
02 am HST
Wed 16 Jan
00 UTC
Sat 12 Jan
06 UTC
Sat 12 Jan
12 UTC
Sat 12 Jan
00 UTC
Sun 13 Jan
06 UTC
Sun 13 Jan
12 UTC
Sun 13 Jan
00 UTC
Mon 14 Jan
06 UTC
Mon 14 Jan
12 UTC
Mon 14 Jan
00 UTC
Tue 15 Jan
12 UTC
Tue 15 Jan
00 UTC
Wed 16 Jan
12 UTC
Wed 16 Jan
Cloud Cover (%) 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 5 0 to 20 0 to 5 0 to 20 0 to 5
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 to 1.5 0.9 to 1.1 0.8 to 1 0.8 to 1.2 0.8 to 1 0.7 to 0.9 0.8 to 1.2 0.6 to 0.8 0.6 to 0.8 0.6 to 1 0.5 to 0.8 0.6 to 1 0.5 to 0.8
Mean Seeing (arcsecs) N/A 0.4 ± 0.1 0.35 ± 0.1 N/A 0.4 ± 0.15 0.45 ± 0.15 N/A 0.45 ± 0.15 0.35 ± 0.1 N/A 0.4 ± 0.1 N/A 0.35 ± 0.1
Summit Temp (°C) 9 4 4 9 4 3.5 8.5 3.5 3.5 9 3.5 8 3
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)

NE/5 to 15

NE/5 to 15

ESE/5 to 15

SSE/5 to 15

SE/0 to 10

ESE/0 to 10

N/0 to 10

NNE/5 to 15

N/5 to 15

N/5 to 15

NNW/10 to 20

WNW/5 to 15

WNW/5 to 15


 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.Jan.11/Sat.Jan.12
18:10
19:19
5:42
6:50
N/A
23:07
31
0 07.4
-4 19
Sat.Jan.12/Sun.Jan.13
18:11
19:19
5:42
6:50
N/A
23:56
41
0 52.6
0 06
Sun.Jan.13/Mon.Jan.14
18:12
19:20
5:42
6:50
N/A
0:47
51
1 38.8
4 37
Mon.Jan.14/Tue.Jan.15
18:12
19:20
5:42
6:50
N/A
1:40
61
2 27.1
9 05
Tue.Jan.15/Wed.Jan.16
18:13
19:21
5:42
6:50
N/A
2:36
71
3 18.3
13 16


Forecast issued by: Ryan Lyman
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Next update at 5 PM HST Friday 11 January (0300 UTC Saturday 12 January) 2019.
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