Current Conditions
Temp2.6 C
RH58 %
WindSSE 19 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Thursday 30 June (0300 UTC Friday 1 July) 2016
Warning(s)
Increasing winds
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, but more broken widespread mid/upper-level clouds are set to build from the south, contributing to mostly overcast skies for tonight.
Summary of Key Meteorological Variables
Summit temperatures will be near 2 C this evening and 1 C tomorrow morning. Winds will be from the east at 10-20 mph for today, increasing to 15-30 mph for the morning hours. Seeing will be near 0.75-0.85 arcseconds, while precipitable water is expected to exceed 4 mm for the night.
Discussion
A strengthening inversion near 6 thousand feet, coupled with a drier air mass between 6-18 thousand feet will ensure the summit steers free of fog and precipitation through at least Sunday morning. However, there is a possibility that the inversion will lift toward 10-12 thousand feet, which could increase the risk for short-lived fog at the summit for Sunday and Monday night. Some afternoon clouds are possible through Saturday, and could turn extensive for Sunday and early part of next week.

Broken to widespread mid/upper-level clouds are expected to build in from the south, contributing to mostly overcast skies for the next 2 nights. The bulk of these clouds will shift toward the NW and thin out on Saturday, which could help open up skies for that night. However, there is a possibility that more high clouds will fill out of the tropics and litter the northern skies and perhaps drift over the summit for Sunday and especially Monday night.

Precipitable water will continue to linger near or exceed 4 mm for the next 3 nights, then slip toward 3 mm for Sunday and Monday night.

A mixture of moderate upper-level turbulence, mid/upper-level moisture/instability and/or boundary layer turbulence will likely contribute to poor/bad seeing over the next 3 nights. There is a chance that seeing will improve toward 0.6-0.65 arcseconds as the atmosphere stabilizes and becomes more calm for Sunday and Monday night.

Very little change since the morning forecast...An upper-level low to the NW and embedded in the persistent tropical upper-tropospheric trough extending (TUTT) from the west coast out to Guam will continue to stream mid/upper-level moisture/clouds through the area, contributing to extensive cloud cover and high PW for the next 2 nights. Fortunately, an upper-level ridge is expected to strengthen to the SE, which will augment the subsidence provided by the mid/low-level ridge to the north and help dry out the air mass between 6-18 thousand feet through the next 3 nights. While this will ensure the summit steers free of fog/precipitation during this time, summit-level winds is set to increase as upper-level momentum is redistributed into the mid-levels especially for tomorrow night. Winds will subside as the upper-level ridge shifts westward and broadens zonally a bit late over the weekend. This could also help to push the TUTT and its associated subtropical jet off toward the NW, which will open up skies a bit for Saturday night. However, the upper-level ridge is expected to sag southward, allowing the STJ to return to the area and transport more high clouds out of the tropics and over/near the summit area (particularly the northern skies) for the following 2 nights. Global models still expect a tropical wave to pass just south of the Big Island, bringing mostly low-level moisture/instability to the area between Sunday and Tuesday. While this moisture/instability could lift the inversion toward 10-12 thousand feet and thus increase the risk for short-lived fog at the summit for Sunday and Monday night, each model run backs off how much as well as the depth of the moisture that moves through the area (as was the case with the latest afternoon run). I suspect this trend will continue, hopefully, reducing the odds on fog over the next several days.
WRF Astronomical Observing Quality Guidance
Cloud Cover and Precipitable Water Analyses
MK CN² Profiles
5 Day Forecast Summary (Graphical Trend)
HST Cloud Fog/Precip Temp Wind Seeing PW
Cover (%) Height (km) Probability (%) (Celcius) (Dir/MPH) (Arcseconds) (mm)
Thu Jun 30 - 8 PM80-1006-90 / 02E/10-200.6-0.94-6
Fri Jul 01 - 2 AM80-1006-100 / 01E/15-300.6-1.14-6
2 PM80-1004-100 / 07E/20-35NaN4-8
8 PM80-1006.5-100 / 02ENE/25-401-1.64-6
Sat Jul 02 - 2 AM80-1006.5-90 / 02.5ENE/25-401-1.64-6
2 PM60-806-80 / 010ENE/20-35NaN4-8
8 PM40-607-80 / 05ENE/15-300.6-1.24-6
Sun Jul 03 - 2 AM20-407-910 / 04.5ENE/15-300.6-14-6
2 PM40-608-1030 / 010E/10-20NaN4-8
Mon Jul 04 - 2 AM40-609-1020 / 05E/5-150.4-0.83-4
2 PM60-808-1030 / 010S/0-10NaN4-8
Tue Jul 05 - 2 AM60-808-1020 / 04N/0-100.4-0.93-4
2 PM0-208-1025 / 09NNE/0-10NaN4-8
Rise and Set times for the Sun and Moon
Night (HST) Sun Set Twilight End Twilight Beg Sun Rise Moon Rise Moon Set Illumination (%) RA DEC
Thu Jun 30 - Fri Jul 01 19:15 20:29 4:23 5:37 3:09 N/A 12 3 53.6 14 39
Fri Jul 01 - Sat Jul 02 19:15 20:29 4:24 5:37 4:04 N/A 6 4 52.6 16 50
Sat Jul 02 - Sun Jul 03 19:15 20:29 4:24 5:38 5:01 17:48 2 5 52.2 17 54
Sun Jul 03 - Mon Jul 04 19:15 20:29 4:24 5:38 6:00 18:47 0 6 51.3 17 48
Mon Jul 04 - Tue Jul 05 19:15 20:28 4:25 5:38 N/A 19:42 1 7 49.0 16 37
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Friday 1 July 2016.
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