Current Conditions
Temp5.2 C
RH24 %
WindNNE 13 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Friday 27 May (0300 UTC Saturday 28 May) 2016
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, with thin high clouds passing over and especially to the south through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 1 C this evening and 0.5 C tomorrow morning. Winds will be from the WNW at 15-30 mph, with seeing near 0.65-0.7 arcseconds. Precipitable water is expected to be in the 2.5-3.5 mm range for the night.
The tradewind inversion will continue to cap the fairly limited supply of low-level moisture at or below 9 thousand feet and ensure the summit remains dry and stable through the next 5 nights. Some afternoon clouds are possible for today, but will become minimal and short-lived for the remainder of the forecast period.

Thin high clouds will continue to pass along the southern skies through Monday afternoon/evening, and may occasionally pass over the Big Island mainly for this evening and again around Sunday. These clouds are set to pass eastward through Monday night, leaving clear skies Tuesday night.

Precipitable water is expected to linger near 3-3.5 mm for the next 3 nights, briefly slip toward 2 mm for early Monday evening, then climb back toward 4 mm for Tuesday.

Persistent light/moderate boundary layer turbulence, coupled with bouts of upper-level turbulence and/or low-level turbulence will likely contribute to poorer than average seeing throughout most of the forecast period.

Changes have been made to the CC forecast to account for the very high clouds spreading further nortward than previously anticipated...Although the mid-level ridge will remain rather weak/indistinct and/or off toward the south, the sub-tropical jet (STJ) will maintain a relatively zonal orientation over or just south of the Big Island, minimizing upper-level instability in the area throughout the forecast period. This will allow the low-level ridge to govern the air mass near the state, which will ensure large-scale subsidence prevails in the area during this time. This will help maintain the tradewind inversion at or below 9 thousand feet and ensure the summit remains dry and stable over the next 5 nights. Unfortunately, the mid-level ridge to the south will continue to transfer minor mid-level moisture out the tropics and over the Big Island, which will likely keep PW near 3-4 mm throughout most of the forecast period. In addition, a relatively tight wind gradient along northern fringe of this ridge will maintain westerly summit-level winds near 20-25 mph, which will stir up light/moderate boundary layer turbulence during this time. This combined with bouts of upper-level turbulence (via the STJ) over the next 2 nights and low-level turbulence from a weak/decayed cold front/shearline for the early part of next week, will likely contribute to poorer than average seeing over the next 5 nights. Finally, it looks like the STJ has gained access to very high clouds filing out of the tropics and will continue to stream it along the southern skies probably through Monday afternoon/evening. There is a very good chance that these clouds will occasionally cover the Big Island area mainly for this evening and again when a slightly thicker batch moves through on Sunday. All in all, while dry/stable conditions are expected, less than stellar skies will likely prevail thorughout the forecast period.
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)
Fri May 27 - 8 PM60-809.75-100 / 01W/15-250.5-0.92.5-3.5
Sat May 28 - 2 AM40-609.75-100 / 00.5W/15-250.5-0.82.5-3.5
2 PM30-509.75-100 / 06WNW/15-25NaN3-5
8 PM20-409.75-100 / 01WNW/15-250.5-0.83-4
Sun May 29 - 2 AM20-409.5-100 / 01W/10-200.5-0.73-4
2 PM60-808.5-100 / 06.5W/15-25NaN3-5
8 PM50-709-100 / 02WNW/10-200.5-0.83-4
Mon May 30 - 2 AM30-509-100 / 01.5WNW/10-200.5-0.82.5-3.5
2 PM10-309.5-100 / 08WNW/10-20NaN1-2
Tue May 31 - 2 AM0-209.5-100 / 03NW/10-200.5-0.92-4
2 PM0-20Clear0 / 010NW/5-15NaN3-5
Wed Jun 01 - 2 AM0-20Clear0 / 05NNE/5-150.5-0.83-5
2 PM0-20Clear0 / 010NE/5-15NaN2-4
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
Mon May 30 - Tue May 31 19:07 20:20 4:20 5:33 2:01 N/A 29 0 24.8 0 23
Tue May 31 - Wed Jun 01 19:07 20:20 4:19 5:32 2:47 N/A 19 1 19.5 4 52
Wed Jun 01 - Thu Jun 02 19:07 20:21 4:19 5:32 3:35 N/A 10 2 15.8 9 06
Thu Jun 02 - Fri Jun 03 19:08 20:21 4:19 5:32 4:27 N/A 4 3 13.9 12 47
Fri Jun 03 - Sat Jun 04 19:08 20:22 4:19 5:32 5:21 17:59 1 4 13.5 15 38
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Monday 30 May 2016.
Additional Information
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