Latest Forecast for Mauna Kea Observatories
5 PM HST Wednesday 28 October (0300 UTC Thursday 29 October) 2020

Warnings
Fog and ice
Chance for thunderstorms and flurries
Strong winds

Cloud Cover and Precipitation Forecast
There is a high risk for fog, ice and patches of thick clouds in the area, while a narrow band of cirrus develops overhead throughout the night. Isolated convection may also pop up in the area and deposit flurries at the summit, particularly this afternoon and into the evening hours.

Summary of Key Meteorological Variables
Summit temperatures will be near -2 C, with winds from the WSW at 30-45 mph. Seeing and precipitable water are expected to exceed 1 arcsecond and 4 mm, respectively, through the night.

Graphical Summary

Discussion
Although the upper half of the atmosphere is expected to dry out over the next 12 hours, persistent instability and low-level moisture will keep the inversion rather indistinct and elevated probably well into the weekend. As a result, there is a high risk for periods of fog, ice and even light flurries at the summit particularly over the next 3 nights; this risk will subside as the weekend progresses. There is also a high probability for isolated convection in the are area, mainly during the afternoon hours along the Big Island slopes. Extensive daytime clouds are expected probably throughout the forecast period.

There is a possibility for lingering patches of thick clouds in the area over the next 2 nights, and residual cirrus from any afternoon convection may persist over/near the summit over the next 5 evenings. In addition, a narrow band of cirrus flowing out of the SW is expected to set up over the summit for tonight and into tomorrow evening, then will sag subtly southward through the latter night and into Friday night. More widespread banding clouds will eventually pass along the eastern skies and could be visible from the summit for the following 2 nights.

Precipitable water is expected to exceed 4 mm over the next 2 nights, slip toward 2 mm for Friday night, then increase back to 3-4 mm for the following 2 nights.

A mixture of boundary layer turbulence, free atmospheric turbulence and persistent instability will contribute to bad seeing for at least the next 4 nights. There is a possibility that seeing will improve as the atmosphere begins to stabilize and mid-level flow tapers for Sunday night.

No change since the morning forecast...The low to the north will remain quasi-stationary/steady to the north, displacing the ridge well off to the south for at least another 48 hours. While the low is then set to take off toward the NE on Friday, it will leave a large trough in its wake, which will eventually be reinforced by a short-wave trough passing through over the weekend. This will prevent the ridge from rebounding northward and allowing mostly an unstable air mass to persist in the area throughout the forecast period. Fortunately, the bulk of the upper-level moisture will continue to slide off toward the east over the next 6 hours. However, this persistent instability, combined with residual low-level moisture in the area will keep the inversion rather indistinct/elevated, likely resulting in more fog, ice and high humidity at the summit throughout much of the next 5 nights. Flurries are also possible, but it will mostly be linked with afternoon convection that may pop up along the Big Island slopes and persist into the evening hours. There is a chance that isolated convection may flare up at night, should a pocket of upper-level diffluence along the south side of the low and on the eastern side of the incoming SWT pass through (mainly over the next 2 nights and again on Saturday night). In addition to this, a tight wind gradient along the southern flank of the low and on the large trough will keep winds near 35-40 mph, with stronger gusts, well into the weekend.

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 28 Oct
02 am HST
Thu 29 Oct
02 pm HST
Thu 29 Oct
08 pm HST
Thu 29 Oct
02 am HST
Fri 30 Oct
02 pm HST
Fri 30 Oct
08 pm HST
Fri 30 Oct
02 am HST
Sat 31 Oct
02 pm HST
Sat 31 Oct
02 am HST
Sun 01 Nov
02 pm HST
Sun 01 Nov
02 am HST
Mon 02 Nov
02 pm HST
Mon 02 Nov
06 UTC
Thu 29 Oct
12 UTC
Thu 29 Oct
00 UTC
Fri 30 Oct
06 UTC
Fri 30 Oct
12 UTC
Fri 30 Oct
00 UTC
Sat 31 Oct
06 UTC
Sat 31 Oct
12 UTC
Sat 31 Oct
00 UTC
Sun 01 Nov
12 UTC
Sun 01 Nov
00 UTC
Mon 02 Nov
12 UTC
Mon 02 Nov
00 UTC
Tue 03 Nov
Cloud Cover (%) 60 to 80 40 to 60 80 to 100 60 to 80 40 to 60 80 to 100 20 to 40 20 to 40 60 to 80 20 to 40 60 to 80 20 to 40 70 to 90
Cloud Height (km) above sea level 4-8 4.5-7 4-10 4.5-10 4.5-10 4-10 9-10 9-10 4-10 9-10 4-10 9-10 4-8
Chance for Fog/Precip (%) 90/60 90/40 95/65 90/40 90/35 90/60 75/25 65/20 75/40 75/30 80/40 60/10 90/40
PW (mm, summit upward) 8 to 12 4 to 8 6 to 10 4 to 6 3.5 to 4.5 4 to 8 2 to 4 2 to 3 4 to 8 3 to 4 4 to 8 3 to 4 4 to 8
Mean Seeing (arcsecs) 1.5 ± 0.5 1.5 ± 0.5 N/A 1.5 ± 0.5 1.5 ± 0.5 N/A 1.5 ± 0.5 1.5 ± 0.5 N/A 1.1 ± 0.3 N/A 0.8 ± 0.3 N/A
Summit Temp (°C) -2 -2 3 -1 -1 4 0 -0.5 3 -1 3 -3 -2
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)

WSW/30 to 45

WSW/30 to 45

WSW/30 to 45

WSW/30 to 45

WSW/30 to 45

WSW/30 to 45

WSW/30 to 45

WSW/30 to 45

WSW/30 to 45

WSW/25 to 40

SW/20 to 35

S/15 to 30

S/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.Oct.28/Thu.Oct.29
17:58
19:04
5:08
6:13
16:23
5:02
95
0 52.5
0 16
Thu.Oct.29/Fri.Oct.30
17:58
19:03
5:08
6:13
16:56
5:50
99
1 36.2
5 16
Fri.Oct.30/Sat.Oct.31
17:57
19:03
5:08
6:14
17:29
6:39
100
2 20.6
10 03
Sat.Oct.31/Sun.Nov.01
17:57
19:02
5:09
6:14
18:04
7:29
99
3 06.5
14 29
Sun.Nov.01/Mon.Nov.02
17:56
19:02
5:09
6:15
18:41
N/A
97
3 54.3
18 21


Forecast issued by: Ryan Lyman
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Next update at 10 AM HST (2000 UTC) Thursday 29 October 2020.
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