Latest Forecast for Mauna Kea Observatories
5 PM HST Wednesday 07 November (0300 UTC Thursday 8 November) 2018

Warnings
Chance for fog/high humidity
Possibility for afternoon convection

Cloud Cover and Precipitation Forecast
There is a moderate risk for periods of fog and high humidity mainly during the first half of the night; precipitation is unlikely. Scattered thin high clouds will continue to pass along the southern skies through the night.

Summary of Key Meteorological Variables
Summit temperatures will be near 1 C this evening and 1.5 C tomorrow morning. Winds will be from the WSW at 5-15 mph, with seeing near 0.75-0.8 arcseconds. Precipitable water is expected to exceed 4 mm for the night.

Graphical Summary

Discussion
The tradewind inversion will remain rather weak/indistinct near 10-12 thousand feet which may allow for periods of fog and high humidity at the summit for tonight. While the inversion is set to strengthening near 6-7 thousand feet around tomorrow evening, an influx of moisture may saturate the mid-level air mass and increase the risk for fog, high humidity, ice and light flurries at the summit for that night. There is a very good chance that the inversion will breakdown, allowing the entire air mass to become saturated, further increasing this risk for Friday and Saturday night. Dry and stable conditions are expected to quickly return to the summit as this moisture moves out of the area and the inversion becomes well-defined near 6-7 thousand feet for Sunday night. Some afternoon clouds and convection are possible for the next 2 days, then may become more widespread and extensive for Friday and Saturday, only to taper again for Sunday.

Scattered thin high clouds will continue to pass along the southern skies for tonight, then shift off toward the east just after sunrise tomorrow. However, there is a chance that more light high clouds will pass along the southern skies, while thicker mid-level clouds also move in from the SE for tomorrow night. Thicker more widespread clouds are set to move into and/or develop in the area, likely blanketing summit skies for Friday and Saturday night. These clouds are set to rapidly shift off toward the east around sunrise Sunday, leaving clear skies for that night.

Precipitable water is expected to exceed 4 mm for the next 4 nights, then plummet toward 0.7-0.8 mm for Sunday night.

Mid/upper-level turbulence, an elevated inversion and/or influx of mid-level moisture will contribute to poor seeing over the next 2 nights. Seeing is expected to degrade further as the atmosphere turns saturated for Friday and Saturday night. While there is very good chance that the air mass will dry out on Sunday, lingering mid-level/boundary layer turbulence and/or gravity waves may still contribute to poor seeing for that night.

No change since the morning forecast...The mid-level ridge will remain rather weak and indistinct as a large trough persists to the NW of the state over the next 24 hours. This may prevent the inversion from strengthening, which could allow for the development of afternoon convection along the slopes and perhaps fog/high humidity at the summit for tonight. There is a chance that a mid-level ridge will briefly develop to the SE in response to the strengthening of the large-scale trough as an embedded short-wave trough digs in from the NW around tomorrow afternoon/evening. While this could help build the inversion, deep southerly flow between the ridge and the strengthening trough will likely bring widespread mid-level moisture, which could further increase the risk for fog/high humidity and light flurries at the summit for that night. The trough is actually expected to deposit a slow moving low to the north of the state, which will gather the moisture in the area and develop a cold front to the NW of the state around Thursday night. Instability associated with the low combined with the widespread moisture in the area will eventually erode the inversion and saturate the entire air mass, likely contributing to extended periods inoperable conditions and overcast skies for Friday and most of Saturday night. The low's cold front will eventually shift through the state, taking the bulk of the moisture off toward the east near sunrise on Sunday. This could allow very dry/stable conditions to return to the summit by that night, though there is a possibility that mid-level turbulence and/or gravity waves will follow in the wake of the front, which may continue to disrupt seeing during that time.

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 07 Nov
02 am HST
Thu 08 Nov
02 pm HST
Thu 08 Nov
08 pm HST
Thu 08 Nov
02 am HST
Fri 09 Nov
02 pm HST
Fri 09 Nov
08 pm HST
Fri 09 Nov
02 am HST
Sat 10 Nov
02 pm HST
Sat 10 Nov
02 am HST
Sun 11 Nov
02 pm HST
Sun 11 Nov
02 am HST
Mon 12 Nov
02 pm HST
Mon 12 Nov
06 UTC
Thu 08 Nov
12 UTC
Thu 08 Nov
00 UTC
Fri 09 Nov
06 UTC
Fri 09 Nov
12 UTC
Fri 09 Nov
00 UTC
Sat 10 Nov
06 UTC
Sat 10 Nov
12 UTC
Sat 10 Nov
00 UTC
Sun 11 Nov
12 UTC
Sun 11 Nov
00 UTC
Mon 12 Nov
12 UTC
Mon 12 Nov
00 UTC
Tue 13 Nov
Cloud Cover (%) 20 to 40 10 to 30 60 to 80 40 to 60 60 to 80 80 to 100 80 to 100 80 to 100 80 to 100 80 to 100 0 to 20 0 to 5 0 to 20
Cloud Height (km) above sea level 9-10 9.5-10 4-6 4.5-7 4-8 4-9 4-10 4-10 4-10 4-10 5-6 N/A N/A
Chance for Fog/Precip (%) 50/10 40/10 60/15 65/30 75/40 95/80 95/90 95/75 95/90 90/75 25/5 0/0 0/0
PW (mm, summit upward) 4 to 6 4 to 6 4 to 8 4 to 8 6 to 10 10 to 15 10 to 15 10 to 15 10 to 15 6 to 10 1 to 2 0.6 to 1 0.6 to 1
Mean Seeing (arcsecs) 0.8 ± 0.2 0.75 ± 0.15 N/A 0.9 ± 0.2 1.0 ± 0.2 N/A 1.5 ± 0.5 1.5 ± 0.5 N/A 1.5 ± 0.5 N/A 0.8 ± 0.2 N/A
Summit Temp (°C) 1 1.5 5 1 0.5 3 0 -0.5 1 -2 3 0 7
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/5 to 15

WSW/5 to 15

SSW/10 to 20

SW/15 to 30

SSW/15 to 30

SW/10 to 20

WSW/10 to 20

WSW/15 to 30

WSW/15 to 30

W/15 to 30

W/15 to 30

NNE/15 to 30

NE/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.Nov.07/Thu.Nov.08
17:54
19:00
5:11
6:17
7:16
18:24
1
15 34.8
-14 43
Thu.Nov.08/Fri.Nov.09
17:54
19:00
5:12
6:18
N/A
19:09
3
16 26.5
-17 49
Fri.Nov.09/Sat.Nov.10
17:53
19:00
5:12
6:19
N/A
19:56
8
17 18.5
-20 01
Sat.Nov.10/Sun.Nov.11
17:53
18:59
5:13
6:19
N/A
20:44
14
18 10.6
-21 15
Sun.Nov.11/Mon.Nov.12
17:53
18:59
5:13
6:20
N/A
21:33
21
19 02.4
-21 29


Forecast issued by: Ryan Lyman
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Next update at 10 AM HST (2000 UTC) Thursday 8 November 2018.
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