Latest Forecast for Mauna Kea Observatories
10 AM HST (2000 UTC) Friday 13 October 2017

Warnings
Fog, high humidity and ice
Chance for convection and snow/rain

Cloud Cover and Precipitation Forecast
Fog, high humidity, clouds and ice will continue to plague the summit through the night. There is a good chance for convection in the area and periods light snow/rain over the next 24 hours.

Summary of Key Meteorological Variables
Summit temperatures will be near 3 C this afternoon, 0.5 C this evening and -0.5 C tomorrow morning. Winds will be light and from the SSW, while seeing and precipitable water are expected to exceed 1 arcsecond and 4 mm, respectively.

Graphical Summary

Discussion
The atmosphere near the Big Island will remain saturated and unstable, likely allowing extensive fog, high humidity and periods of ice to plague the summit through Sunday evening. There is also a chance for convection in the area and light rain/snow at the summit mainly over the next 36 hours and perhaps again on Sunday afternoon. The inversion is set to quickly recover near 7-8 thousand feet through Monday, ensuring the summit remains dry and stable for that night as well as Tuesday night. Extensive daytime clouds and perhaps even afternoon convection are expected through Sunday, then will become minimal and short-lived for the early part of next week.

Thick clouds surrounding the Big Island will contribute to extensive cloud cover or even periods of overcast skies for the next 2 nights. These clouds will shift off toward the west, opening up skies through Sunday night. However, there is a chance that scattered high clouds passing along the southern skies will move northward and scrape the western tip of the Big Island for the early part of next week.

Precipitable water is expected to exceed 4 mm through Sunday night, then will plummet toward and settle in near 1 mm for Monday and Tuesday night.

Instability, turbuence and moisture will contribute to inoperable conditions and likely poor/bad seeing through at least Sunday evening. There is a chance for a moderate improvement in seeing through Monday, but persistent shear/turbulence in the free atmosphere will likely keep seeing near 0.6-0.7 arcseconds for the early part of next week.

A strengthening mid/upper-level trough to the north will continue to destabilize the air mass for the next 48 hours, then will shift off toward the SE as a rather deep ridge fills in from the west late in the weekend and for the early part of next week. Unfortunately, widespread moisture filling in from the NE via the low-level trades will take advantage of this instability, contributing to mostly inoperable (foggy, high humidity and ice) summit conditions through at least Sunday evening. Although the blob of convetion to the east will likely dissipate a bit over the next 6 hours, there is a good chance that these clouds will move in over the summit and flare up again late this afternoon/evening. This could bring extensive cloud cover, convection to the area (particularly along the eastern slopes) and a mixture of light snow/rain at the summit for tonight. More patches of (mostly less organized) moisture will continue to flare up and drift in from the NE as long as the mid/upper-level trough persists to the north. This cloud allow for more rounds of mostly afternoon/evening convection and snow/rain at the summit into Sunday afternoon. The return of the aforementioned ridge to the north will help bring subsidence to the area and rapidly rebuild a well-defined inversion neare 8-9 thousand feet on Monday, ensuring dry/stable conditions at the summit for the early part of next week. However, there is a good chance that subt-tropical jet entrance region will linger overhead, shuttling high clouds through the area and allowing moderate turbulence to prevail in the free atmosphere during that time.

Astronomical Observing Quality Guidance
05 pm HST Friday 13 October (03 UTC Saturday 14 October)CN2
08 pm HST Friday 13 October (06 UTC Saturday 14 October)CN2
11 pm HST Friday 13 October (09 UTC Saturday 14 October)CN2
02 am HST Saturday 14 October (12 UTC Saturday 14 October)CN2
05 am HST Saturday 14 October (15 UTC Saturday 14 October)CN2
08 am HST Saturday 14 October (18 UTC Saturday 14 October)CN2
Latest WRF CN2 Profiles Animation | Collage


5-day Forecast
Summary

Graphical Trend
02 pm HST
Fri 13 Oct
08 pm HST
Fri 13 Oct
02 am HST
Sat 14 Oct
02 pm HST
Sat 14 Oct
08 pm HST
Sat 14 Oct
02 am HST
Sun 15 Oct
02 pm HST
Sun 15 Oct
08 pm HST
Sun 15 Oct
02 am HST
Mon 16 Oct
02 pm HST
Mon 16 Oct
02 am HST
Tue 17 Oct
02 pm HST
Tue 17 Oct
02 am HST
Wed 18 Oct
00 UTC
Sat 14 Oct
06 UTC
Sat 14 Oct
12 UTC
Sat 14 Oct
00 UTC
Sun 15 Oct
06 UTC
Sun 15 Oct
12 UTC
Sun 15 Oct
00 UTC
Mon 16 Oct
06 UTC
Mon 16 Oct
12 UTC
Mon 16 Oct
00 UTC
Tue 17 Oct
12 UTC
Tue 17 Oct
00 UTC
Wed 18 Oct
12 UTC
Wed 18 Oct
Cloud Cover (%) 80 to 100 80 to 100 70 to 90 80 to 100 70 to 90 70 to 90 80 to 100 60 to 80 40 to 60 20 to 40 10 to 30 20 to 40 40 to 60
Cloud Height (km) above sea level 4-10 4-10 4-10 4-10 4-10 4-10 4-10 4-10 6-10 9-10 9-10 9-10 9-10
Chance for Fog/Precip (%) 100/90 100/90 100/75 100/80 95/60 90/60 90/75 75/25 25/5 5/0 0/0 0/0 0/0
PW (mm, summit upward) 8 to 12 8 to 12 8 to 12 8 to 12 8 to 12 8 to 12 8 to 12 8 to 12 4 to 8 1 to 2 0.8 to 1.2 1 to 1.5 0.8 to 1.2
Mean Seeing (arcsecs) N/A 1.5 ± 0.5 1.5 ± 0.5 N/A 1.5 ± 0.5 1.2 ± 0.4 N/A 0.9 ± 0.2 0.65 ± 0.15 N/A 0.6 ± 0.1 N/A 0.6 ± 0.1
Summit Temp (°C) 3 0.5 -0.5 2 0 -0.5 2 -0.5 -0.5 6 1.5 7 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)

SSW/0 to 10

S/0 to 10

SSW/0 to 10

WNW/0 to 10

NW/5 to 15

NW/5 to 15

NW/0 to 10

N/0 to 10

NNE/0 to 10

NNE/5 to 15

ENE/10 to 20

ENE/10 to 20

E/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
Fri.Oct.13/Sat.Oct.14
18:09
19:13
5:03
6:07
1:33
N/A
29
9 15.1
15 06
Sat.Oct.14/Sun.Oct.15
18:08
19:12
5:03
6:08
2:31
N/A
19
10 09.1
11 50
Sun.Oct.15/Mon.Oct.16
18:07
19:11
5:04
6:08
3:27
N/A
12
11 00.8
8 00
Mon.Oct.16/Tue.Oct.17
18:06
19:11
5:04
6:08
4:22
N/A
6
11 50.7
3 50
Tue.Oct.17/Wed.Oct.18
18:06
19:10
5:04
6:09
5:15
17:09
2
12 39.2
-0 27


Forecast issued by: Ryan Lyman
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Next update at 5 PM HST Friday 13 October (0300 UTC Saturday 14 October) 2017.
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