Current Conditions
Temp-0.1 C
RH56 %
WindSSE 0 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Friday 19 January (0300 UTC Saturday 20 January) 2018
Warning(s)
None
Cloud Cover and Fog/Precipitation Forecast
The summit will remain clear, dry and stable 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 SE at 5-15 mph, with seeing near 0.6 arcseconds. Precipitable water is expected to be in the 0.8-1 mm range for the night.
Discussion
A well-defined tradewind inversion will continue to cap low-level moisture at or below 8 thousand feet and ensure a dry/stable summit-level air mass through at least early Saturday evening. There is a chance that building instability combined with persistent low-level moisture will erode the inversion and increase the risk for fog, ice, high humidity and even light flurries at the summit between midnight Saturday and late Wednesday morning. There is also a possibility for isolated convection along the eastern skies during that time. Daytime clouds will be minimal and short-lived through Saturday, but could turn extensive for Sunday and early part of next week.

There is a possibility that patches of high clouds will pass along the southern and northern skies through early Saturday evening. These clouds will shift eastward thereafter, but there is a chance that patches of summit/low-level clouds will begin to develop over the eastern end of the Big Island on Sunday and could persist through Tuesday night.

Precipitable water is expected to linger near 1 mm for tonight, and perhaps early tomorrow evening, trend toward 2 mm through the latter night, and likely exceed 4 mm for Sunday night and early part of next week.

Slightly better than average seeing is expected through tomorrow evening, despite building/moderate turbulence in the free atmosphere. An increase in upper-level instability and eventually low-level moisture will likely degrade seeing through Saturday night and probably contribute to poor/bad seeing for the following 3 nights.

No change since the morning forecast...The mid/low-level ridge will continue to slowly slide off toward the NE and weaken as a rather large trough builds in from the west over the next 48 hours. Fortunately, the ridge will still promote fairly strong large-scale subsidence, which will help maintain a well-defined inversion near 8 thousand feet and ensure a dry/stable summit-level air mass through at least early tomorrow evening. However, a residual low-level frontal band currently lingering over/near the Big Island is expected to become enhanced by the building instability associated with the trough after midnight Saturday. This combination will help erode the inversion through Sunday and significantly increase the risk for fog, ice, high humidity and even light flurries at the summit particularly for that night. There is also a possibility for isolated convection along the eastern skies between sunrise Sunday and Monday afternoon. There is a chance that the trough will help push the bulk of this moisture eastward through Monday night, but persistent instability will prohibit the inversion from restrengthening thereafter. In fact, there is also a possibility that this moisture will eventually return westward with the developing trades around the middle/later part of next week. Regardless, an elevated/indistinct inversion will likely allow for more periods of fog, ice and high humidity at the summit for the early part of next week.
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 Jan 19 - 8 PM20-409-100 / 0-1SE/5-150.5-0.70.9-1.1
Sat Jan 20 - 2 AM20-408-100 / 0-1.5SE/5-150.5-0.70.9-1.1
2 PM20-408-90 / 03.5SE/5-15NaN1-2
8 PM0-208-90 / 0-1.5ESE/5-150.5-0.71-1.5
Sun Jan 21 - 2 AM0-20Clear25 / 5-2SE/10-200.55-0.851.5-2.5
2 PM60-804-875 / 301SSE/5-15NaN4-8
8 PM20-404-675 / 25-2.5SSE/5-150.7-1.14-6
Mon Jan 22 - 2 AM20-404-675 / 25-3S/0-100.7-1.14-6
2 PM60-804-875 / 251SSW/0-10NaN4-8
Tue Jan 23 - 2 AM10-304-550 / 10-2W/0-100.6-14-6
2 PM60-804-875 / 252N/0-10NaN4-8
Wed Jan 24 - 2 AM20-404-660 / 15-1.5E/0-100.65-1.054-6
2 PM60-804-650 / 203SSW/5-15NaN4-8
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
Sun Jan 21 - Mon Jan 22 18:17 19:24 5:43 6:50 N/A 22:29 24 0 09.8 -3 06
Mon Jan 22 - Tue Jan 23 18:18 19:25 5:43 6:50 N/A 23:22 33 0 58.0 1 16
Tue Jan 23 - Wed Jan 24 18:18 19:25 5:43 6:50 N/A 0:16 44 1 47.5 5 42
Wed Jan 24 - Thu Jan 25 18:19 19:26 5:42 6:49 N/A 1:12 55 2 39.3 9 58
Thu Jan 25 - Fri Jan 26 18:19 19:26 5:42 6:49 N/A 2:11 66 3 34.1 13 50
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Monday 22 January 2018.
Additional Information
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