Latest Forecast for Mauna Kea Observatories
10 AM HST (2000 UTC) Friday 21 February 2020

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 C this afternoon and -2 C for the night. Winds will be from the NE at 5-15 mph for today, switching to a more easterly direction and increasing to 10-20 mph for the morning hours. Seeing will be near 0.55-0.6 arcseconds, while precipitable water is expected to be in the 0.6-0.8 mm range for the night.

Graphical Summary

Discussion
A well-defined tradewind inversion will continue to cap low-level moisture near 6-7 thousand feet and ensure a dry/stable summit-level air mass through the next 5 nights. Daytime clouds will be minimal and short-lived throughout the forecast period.

Skies will remain predominately clear throughout the forecast period.

Precipitable water is expected to settle in near 0.6-0.7 mm through the next 5 nights.

Lighter winds and calm skies with deep northerly flow in the free atmosphere should allow for better than average seeing for most of the night. There is a chance for a slight increase in boundary layer turbulence as well as mid-level turbulence, which may contribute to poor seeing for Saturday night. A modest improvement in seeing is possible as both sources of turbulence subsides for Sunday night, but another round of slightly stronger boundary layer turbulence may degrade seeing for the early part of next week.

The mid/low-level ridge will continue to sit to the state, before sagging southward late in the weekend, then will rebound northward as a new ridge fills in from the west during the early part of next week. Nevertheless, it will remain close enough to promote steady/strong large-scale subsidence in the area to maintain a well-defined inversion near 6-7 thousand feet and ensure a dry/stable summit-level air mass throughout the forecast period. Flow aloft will also maintain a fairly zonal orientation as the sub-tropical jet moves off to the east and the westerly jet prevails to the north during this time. As a result, skies will remain clear and very dry, allowing PW to settle in near 0.6-0.7 mm through the next 5 nights. Which calm skies will also prevail in the upper atmosphere, there is a chance for minor low-level turbulence which could affect seeing for Saturday night. In addition, boundary layer turbulence may also be an issue as the ridge expands a bit on Saturday night and a new ridge fills into the area for the early part of next week. Average or slightly better seeing will likely prevail as winds drop toward 10 mph for tonight and again as the ridge sags southward on Sunday 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
02 pm HST
Fri 21 Feb
08 pm HST
Fri 21 Feb
02 am HST
Sat 22 Feb
02 pm HST
Sat 22 Feb
08 pm HST
Sat 22 Feb
02 am HST
Sun 23 Feb
02 pm HST
Sun 23 Feb
08 pm HST
Sun 23 Feb
02 am HST
Mon 24 Feb
02 pm HST
Mon 24 Feb
02 am HST
Tue 25 Feb
02 pm HST
Tue 25 Feb
02 am HST
Wed 26 Feb
00 UTC
Sat 22 Feb
06 UTC
Sat 22 Feb
12 UTC
Sat 22 Feb
00 UTC
Sun 23 Feb
06 UTC
Sun 23 Feb
12 UTC
Sun 23 Feb
00 UTC
Mon 24 Feb
06 UTC
Mon 24 Feb
12 UTC
Mon 24 Feb
00 UTC
Tue 25 Feb
12 UTC
Tue 25 Feb
00 UTC
Wed 26 Feb
12 UTC
Wed 26 Feb
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) 0.8 to 1.2 0.6 to 0.8 0.6 to 0.8 0.8 to 1.2 0.5 to 0.7 0.5 to 0.7 0.7 to 1.1 0.5 to 0.7 0.55 to 0.75 0.75 to 1.25 0.55 to 0.8 0.75 to 1.25 0.55 to 0.8
Mean Seeing (arcsecs) N/A 0.55 ± 0.1 0.6 ± 0.1 N/A 0.8 ± 0.2 0.8 ± 0.2 N/A 0.65 ± 0.1 0.6 ± 0.1 N/A 0.8 ± 0.2 N/A 0.8 ± 0.2
Summit Temp (°C) 3 -2 -2 4.5 -1 -1.5 5 0 0 5.5 0.5 6 0.5
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)

NE/5 to 15

NE/5 to 15

E/10 to 20

ESE/15 to 25

SE/15 to 25

SSE/15 to 25

S/15 to 25

SSW/10 to 20

SW/10 to 20

NW/5 to 15

NNW/15 to 30

N/15 to 30

N/15 to 30


 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.Feb.21/Sat.Feb.22
18:33
19:38
5:33
6:38
6:16
17:15
1
21 32.8
-18 14
Sat.Feb.22/Sun.Feb.23
18:33
19:38
5:32
6:37
6:55
18:07
0
22 20.5
-14 49
Sun.Feb.23/Mon.Feb.24
18:34
19:38
5:32
6:36
N/A
18:57
1
23 06.2
-10 51
Mon.Feb.24/Tue.Feb.25
18:34
19:39
5:31
6:36
N/A
19:46
3
23 50.3
-6 30
Tue.Feb.25/Wed.Feb.26
18:34
19:39
5:31
6:35
N/A
20:34
7
0 33.5
-1 56


Forecast issued by: Ryan Lyman
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Next update at 5 PM HST Friday 21 February (0300 UTC Saturday 22 February) 2020.
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