Latest Forecast for Mauna Kea Observatories
5 PM HST Wednesday 09 January (0300 UTC Thursday 10 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 3.5 C, with winds from the WNW at 10-20 mph for this evening, switching to a more NNW direction through the night. Seeing will be near 0.6-0.7 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 9 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 is expected to start out near 1.5 mm for this evening, but will quickly slip below 1 mm as the night progresses. It may briefly increase toward 1.25 mm for tomorrow night, then slip back to toward 1 mm over the next 2 nights, and perhaps drop to 0.7-0.8 mm for Sunday night.

Although very calm skies will prevail in the free atmosphere probably well into next week, a slight increase in winds may contribute to minor boundary layer turbulence and perhaps more average-like seeing for tonight. Winds are set to settle in near 5-10 mph, which should help significantly reduce boundary layer turbulence and allow seeing to settle in near 0.4-0.5 arcseconds for the remainder of the week.

Subtle changes have been made to the PW forecast...A new strong relatively deep ridge is expected to build in from the NW over the next 24 hours, then will settle in over the state probably well into next week. Nonetheless, this ridge will continue to promote steady/strong large-scale subsidence in the area, which will help maintain a well-defined tradewind inversion primarily near 8 thousand feet and ensure a dry/stable summit-level air mass throughout the forecast period. Skies will also remain predominately clear as a zonal westerly jet well north of the state throughout the forecast period. While this should also allow relatively weak/laminar northwesterly flow to prevail aloft, minimizing turbulence in the free atmosphere during this time, slightly stronger northerly flow along the eastern fringe of the building ridge may contribute to minor boundary layer turbulence and more average-like seeing for tonight. Winds are set to settle back in near 5-10 mph thereafter, which should allow seeing to settle in near 0.4-0.5 arcseconds probably for the remainder of the week. PW, on the other hand, could vary a bit over the next 5 nights, but should remain below 1.5 mm throughout the forecast period, and could easily linger near or below 1 mm, with the exception of when a patch of minor mid-level moisture passes through around tomorrow night.

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
Wed 09 Jan
02 am HST
Thu 10 Jan
02 pm HST
Thu 10 Jan
08 pm HST
Thu 10 Jan
02 am HST
Fri 11 Jan
02 pm HST
Fri 11 Jan
08 pm HST
Fri 11 Jan
02 am HST
Sat 12 Jan
02 pm HST
Sat 12 Jan
02 am HST
Sun 13 Jan
02 pm HST
Sun 13 Jan
02 am HST
Mon 14 Jan
02 pm HST
Mon 14 Jan
06 UTC
Thu 10 Jan
12 UTC
Thu 10 Jan
00 UTC
Fri 11 Jan
06 UTC
Fri 11 Jan
12 UTC
Fri 11 Jan
00 UTC
Sat 12 Jan
06 UTC
Sat 12 Jan
12 UTC
Sat 12 Jan
00 UTC
Sun 13 Jan
12 UTC
Sun 13 Jan
00 UTC
Mon 14 Jan
12 UTC
Mon 14 Jan
00 UTC
Tue 15 Jan
Cloud Cover (%) 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 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 to 1.5 0.8 to 1 0.8 to 1.2 1 to 1.5 1 to 1.5 1 to 1.5 0.9 to 1.1 0.9 to 1.1 1 to 1.5 0.8 to 1.2 0.8 to 1.2 0.6 to 1 0.8 to 1.2
Mean Seeing (arcsecs) 0.6 ± 0.1 0.65 ± 0.15 N/A 0.45 ± 0.1 0.45 ± 0.1 N/A 0.45 ± 0.1 0.45 ± 0.1 N/A 0.45 ± 0.1 N/A 0.5 ± 0.1 N/A
Summit Temp (°C) 3.5 3.5 9 4 4 9.5 4 4 9 4 8.5 3 8.5
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)

WNW/10 to 20

NNW/10 to 20

NNW/5 to 15

N/5 to 15

NE/5 to 15

NE/0 to 10

ENE/5 to 15

SE/5 to 15

S/5 to 15

S/0 to 10

N/5 to 15

N/5 to 15

N/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
Wed.Jan.09/Thu.Jan.10
18:09
19:17
5:41
6:49
N/A
21:30
16
22 37.3
-12 19
Thu.Jan.10/Fri.Jan.11
18:10
19:18
5:41
6:49
N/A
22:18
23
23 22.6
-8 30
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


Forecast issued by: Ryan Lyman
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Next update at 10 AM HST (2000 UTC) Thursday 10 January 2019.
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