Latest Forecast for Mauna Kea Observatories
5 PM HST Friday 12 October (0300 UTC Saturday 13 October) 2018

Warnings
Extensive fog high humidity
Chance for flurries, ice and convection

Cloud Cover and Precipitation Forecast
Extensive fog, high humidity, thick clouds and light ice/flurries are expected to plague the summit through the night.

Summary of Key Meteorological Variables
Summit temperatures will be near 0 C this evening and -1 C tomorrow morning. Winds will be from the WNW at 15-30 mph, while seeing and precipitable water are expected to exceed 1 arcsecond and 4 mm, through the night.

Graphical Summary

Discussion
The atmosphere near the Big Island is expected to turn saturated and unstable, allowing extensive fog, high humidity, ice and flurries to plague the summit for tonight and likely the opening half of tomorrow night, at least; there is a possibility for convection in the area and brief periods of moderate snow during this time. While there is a chance that the upper air mass will dry out, reducing the risk for precipitation, the inversion may remain rather indistinct/elevated, which could still allow for periods of fog and high humidity well into next week. Extensive daytime clouds are expected throughout the forecast period, and there is a possibility for afternoon convection along the slopes particularly for tomorrow days.

Broken thick clouds are expected to spread in from the west, likely blanketing summit skies for tonight. There is a good chance that the bulk of the clouds will slip off toward the SE through Saturday night, but patches of mid-level clouds may persist in the area, while a band of cirrus sets up over or just SE of the Big Island, contributing to extensive cloud cover probably through Sunday night. Bot sets of clouds will likely shift subtly to the east, which could help open up skies for the early part of next week.

Precipitable water is expected to linger near or exceed 4 mm throughout the forecast period.

An influx of moisture/instability and boundary layer turbulence will contribute to bad seeing for tonight. While there is a good chance that seeing will improve with conditions, an elevated inversion, the possibility for low-level moisture and an increase in horizontal shear in the free will limit this improvement, likely prohibiting seeing to average-like values or worse probably for the remainder of the forecast period.

No change since the morning forecast...A sharp mid/upper-level trough digging in from the NNW will continue to destabilize the air mass and organize a patch of deep moisture to the west of the state and push it through the area over the next 24-36 hours. This will help erode the inversion, saturate the air mass and allow extensive fog, high humidity, thick clouds and periods of ice and/or flurries/rain to plague the summit for tonight. There is also a possibility that isolated convection will develop along the western and interior slopes and/or even pass through/over the Big Island area through tomorrow evening. The bulk of this moisture will develop into a weak frontal-like band and push just east of the Big Island late tomorrow evening then stall and slowly detrain into the surrounding atmosphere thereafter. While this has been consistently projected by the model during past runs, the last few runs shift this frontal band further westward as the trough lifts northward a bit earlier than expected and leaves a large-scale trough in the area well into next week. The global model also keeps the mid-level ridge from rebuilding, allowing weak instability to persist in the area during this time. Consequently, there is a possibility that the inversion will remain weak/indistinct easily through the weekend and perhaps well into next week. This, combined with residual moisture in the area may allow for more periods of fog and high humidity especially for Saturday night and perhaps for the following 3 nights. In addition to this, the last few model runs now place a rather strong sub-tropical jet move over the Big Island, which could stream lots of high clouds out of the tropics and over the summit area for Saturday and Sunday night. The jet is expected to shift eastward a tad, opening up skies overhead and to the NW, but high clouds could still be visible along the eastern skies for Monday and Tuesday 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
Fri 12 Oct
02 am HST
Sat 13 Oct
02 pm HST
Sat 13 Oct
08 pm HST
Sat 13 Oct
02 am HST
Sun 14 Oct
02 pm HST
Sun 14 Oct
08 pm HST
Sun 14 Oct
02 am HST
Mon 15 Oct
02 pm HST
Mon 15 Oct
02 am HST
Tue 16 Oct
02 pm HST
Tue 16 Oct
02 am HST
Wed 17 Oct
02 pm HST
Wed 17 Oct
06 UTC
Sat 13 Oct
12 UTC
Sat 13 Oct
00 UTC
Sun 14 Oct
06 UTC
Sun 14 Oct
12 UTC
Sun 14 Oct
00 UTC
Mon 15 Oct
06 UTC
Mon 15 Oct
12 UTC
Mon 15 Oct
00 UTC
Tue 16 Oct
12 UTC
Tue 16 Oct
00 UTC
Wed 17 Oct
12 UTC
Wed 17 Oct
00 UTC
Thu 18 Oct
Cloud Cover (%) 80 to 100 80 to 100 80 to 100 60 to 80 60 to 80 70 to 90 60 to 80 50 to 70 60 to 80 20 to 40 60 to 80 20 to 40 70 to 90
Cloud Height (km) above sea level 4-10 4-10 4-10 6-10 6-9 4-10 7-10 8-10 4-8 9-10 4-10 9-10 4-10
Chance for Fog/Precip (%) 100/95 100/95 95/85 75/30 65/20 75/25 60/15 60/15 65/25 50/10 60/20 50/10 50/15
PW (mm, summit upward) 10 to 15 10 to 15 10 to 15 8 to 12 6 to 10 6 to 10 6 to 10 4 to 8 4 to 8 4 to 6 4 to 8 4 to 6 4 to 8
Mean Seeing (arcsecs) 1.5 ± 0.5 1.5 ± 0.5 N/A 0.9 ± 0.2 0.8 ± 0.2 N/A 0.75 ± 0.15 0.7 ± 0.15 N/A 0.65 ± 0.15 N/A 0.7 ± 0.2 N/A
Summit Temp (°C) -0.5 -1 4 1 1.5 5 1.5 1.5 5 1 4.5 0.5 4.5
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)

SW/15 to 30

WNW/15 to 30

W/15 to 30

W/10 to 20

W/5 to 15

WSW/5 to 15

W/5 to 15

W/5 to 15

SW/5 to 15

SW/5 to 15

NNW/0 to 10

ESE/0 to 10

W/0 to 10


 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.Oct.12/Sat.Oct.13
18:09
19:14
5:03
6:07
N/A
21:18
19
16 44.7
-18 40
Sat.Oct.13/Sun.Oct.14
18:09
19:13
5:03
6:07
N/A
22:05
28
17 36.5
-20 29
Sun.Oct.14/Mon.Oct.15
18:08
19:12
5:03
6:08
N/A
22:53
37
18 28.2
-21 20
Mon.Oct.15/Tue.Oct.16
18:07
19:12
5:03
6:08
N/A
23:42
46
19 19.5
-21 13
Tue.Oct.16/Wed.Oct.17
18:06
19:11
5:04
6:08
N/A
0:32
56
20 10.0
-20 09


Forecast issued by: Ryan Lyman
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Next update at 10 AM HST (2000 UTC) Monday 15 October 2018.
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