Latest Forecast for Mauna Kea Observatories
10 AM HST (2000 UTC) Monday 11 February 2019

Warnings
Strong winds
Chance for fog/ice and flurries.

Cloud Cover and Precipitation Forecast
There is a small risk for periods of fog, ice and flurries at the summit through the night; skies will remain predominately clear.

Summary of Key Meteorological Variables
Summit temperatures will be near -5 C this afternoon and -8 C for the night. Winds will be from the west at 60-80 mph for today, easing to 50-70 mph for the night. Seeing will exceed 1 arcsecond, while precipitable water is expected to be in the 0.7-1 mm range for the night.

Graphical Summary

Discussion
Although the tradewind inversion is expected to rebuild through the next 24 hours, strong winds may still usher moisture up to the summit and contribute to period of fog/ice and perhaps light flurries at the summit, mainly over the next 3 nights. This risk may briefly increase as a band of deep moisture passes through, which could weaken/lift the inversion on Wednesday. Extensive daytime clouds are possible over the next 3 days, particularly on Wednesday, then will taper a bit for Thursday and Friday.

Skies will remain predominately clear of organized clouds throughout the forecast period, but there is a possibility that patches of low-level clouds will move in from the north and pass over summit area on Wednesday evening.

Precipitable water is expected to linger just below 1 mm for tonight, increase subtly toward 1-1.5 mm for much of tomorrow night and into the early part of Wednesday night, then slip to 0.6-0.7 mm (possibily less) for Thursday and Friday.

A mixture of strong boundary layer/free atmospheric turbulence and perhaps instability/moisture will contribute to bad seeing through the next 5 nights.

The strong low to the NE will continue to depart eastward, allowing the air mass to stabilize and winds to taper a bit over the next 12-24 hours. While this should help diminish the risk for moisture at the summit for tonight and into tomorrow night, winds will still linger or even exceed 50 mph as a very large/strong mid/upper-level low lingers in the area probably throughout most of the forecast period (the parent trough is expected to settle in the area well into next week). In addition, a band of mid/low-level moisture wrapping around the northern portion of the low is set to spread southward over the next 36-48 hours, which could help briefly destabilize the air mass and increase the risk for fog/ice and flurries at the summit mainly for Wednesday. The air mass should stabilize again as this moisture passes southward and the mid/upper-level low shifts eastward a bit on Thursday. This may also allow very dry/mid-level air to settle in over the summit, which could drive PW toward 0.5-0.6 mm for that night and into Friday night. Still, there is a very good chance that moderate/strong winds will persist, stirring up boundary layer turbulence and contributing to poor/bad seeing throughout the forecast period. Long term projections suggest that this mid/upper-level low will retrograde westward and weaken a bit over the weekend. Although this may help to finally reduce summit-level winds to more managable levels, unstable air along the eastern flank of the low could settle in overhead, which could increase the risk for moisture at the summit during that time and into the 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
Mon 11 Feb
08 pm HST
Mon 11 Feb
02 am HST
Tue 12 Feb
02 pm HST
Tue 12 Feb
08 pm HST
Tue 12 Feb
02 am HST
Wed 13 Feb
02 pm HST
Wed 13 Feb
08 pm HST
Wed 13 Feb
02 am HST
Thu 14 Feb
02 pm HST
Thu 14 Feb
02 am HST
Fri 15 Feb
02 pm HST
Fri 15 Feb
02 am HST
Sat 16 Feb
00 UTC
Tue 12 Feb
06 UTC
Tue 12 Feb
12 UTC
Tue 12 Feb
00 UTC
Wed 13 Feb
06 UTC
Wed 13 Feb
12 UTC
Wed 13 Feb
00 UTC
Thu 14 Feb
06 UTC
Thu 14 Feb
12 UTC
Thu 14 Feb
00 UTC
Fri 15 Feb
12 UTC
Fri 15 Feb
00 UTC
Sat 16 Feb
12 UTC
Sat 16 Feb
Cloud Cover (%) 40 to 60 0 to 20 0 to 20 40 to 60 0 to 20 0 to 20 60 to 80 20 to 40 0 to 20 20 to 40 0 to 20 20 to 40 0 to 20
Cloud Height (km) above sea level 4-6 N/A N/A 4-5 N/A 4-4.5 4-8 4-5 4-4.5 N/A N/A N/A N/A
Chance for Fog/Precip (%) 60/20 40/10 20/5 60/15 30/15 65/30 90/75 65/40 40/10 20/5 10/0 25/5 10/0
PW (mm, summit upward) 2 to 4 0.7 to 1 0.7 to 1 2 to 4 1 to 1.5 1 to 1.5 3 to 6 0.8 to 1.2 0.6 to 0.8 1 to 2 0.5 to 0.8 1 to 2 0.5 to 0.8
Mean Seeing (arcsecs) N/A 2.0 ± 1.0 2.0 ± 1.0 N/A 2.0 ± 1.0 2.0 ± 1.0 N/A 2.0 ± 1.0 1.5 ± 0.5 N/A 1.2 ± 0.4 N/A 1.0 ± 0.3
Summit Temp (°C) -5 -8 -8 -5 -9 -10 -5 -9 -9 -1 -6 -2 -6
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)

W/60 to 80

W/50 to 70

W/50 to 70

W/50 to 70

W/40 to 60

W/40 to 60

WNW/25 to 40

NW/25 to 40

NW/25 to 40

WNW/25 to 40

NW/25 to 40

NW/20 to 35

NW/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
Mon.Feb.11/Tue.Feb.12
18:29
19:34
5:38
6:43
N/A
0:25
44
3 01.0
11 57
Tue.Feb.12/Wed.Feb.13
18:29
19:34
5:38
6:43
N/A
1:21
54
3 52.5
15 41
Wed.Feb.13/Thu.Feb.14
18:30
19:35
5:37
6:42
N/A
2:19
65
4 47.7
18 43
Thu.Feb.14/Fri.Feb.15
18:30
19:35
5:37
6:42
N/A
3:20
75
5 46.6
20 46
Fri.Feb.15/Sat.Feb.16
18:30
19:36
5:36
6:41
N/A
4:21
85
6 48.9
21 33


Forecast issued by: Ryan Lyman
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Next update at 5 PM HST Monday 11 February (0300 UTC Tuesday 12 February) 2019.
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