Current Conditions
Temp5.0 C
RH8 %
WindE 33 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
10 AM HST (2000 UTC) Thursday 19 January 2017
Warning(s)
Moderate (tapering) winds
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, but there is a possibility for very thin, nearly transparent cirrus along the northern skies through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 6 C this afternoon and 2 C for the night. Winds will be from the ESE at 20-35 mph for today, decreasing to 15-30 mph by the end of the night. Seeing will be near 0.9-1 arcsecond, while precipitable water is expected to be in the 1.25-1.75 mm range for the first half of the night and 1.75-2.25 mm range for the second half.
Discussion
The tradewind inversion will continue to cap low-level moisture at or below 7 thousand feet and ensure the summit remains dry and stable through at least Friday night. Building instability, coupled with an influx of moisture and increasing low-level trades could weaken the inversion toward 10 thousand feet through Saturday night and perhaps erode the inversion all together for parts of the following 2 nights. This will raise the stakes on fog, ice, high humidity and flurries at the summit particularly for Sunday and Monday night. Daytime clouds will be minimal and short-lived through Saturday, but could pick up for Sunday and turn extensive for the early part of next week.

There is a possibility for very thin, nearly transparent cirrus along the northern skies for tonight and the opening half of tomorrow night. A narrow band of high clouds is expected to move in from the west and pass briefly over the summit area early Saturday morning, then linger along the eastern skies before departing eastward on Sunday. However, there is a possibility that patches of thicker clouds will develop in the area early Sunday morning and could deepen for later that night and for Monday night.

Precipitable water is expected to start out near 1.5 mm this evening, but increase toward 2 mm for the second half of the night and for tomorrow night. It may increase further to 2.5 mm for Saturday night and probably ~4 mm for the following 2 nights.

Boundary layer turbulence will contribute to poor seeing for tonight and perhaps parts of tomorrow night. Should winds slip toward 10-15 mph, there is a good chance that seeing will improve toward 0.55-0.6 arcseconds as relatively calm skies prevail in the free atmosphere during the latter night. However, an increase in upper-level turbulence may degrade seeing for Saturday night, while patches of mid-level turbulence further deteriorate seeing for Sunday and Monday night.

A deep ridge sitting over the state is expected to gradually break down as the upper portion shifts off toward the SW and the lower half splits eastward in response to a trough digging in from the NW over the next few days. Nonetheless, strong large-scale subsidence will prevail in the area, which will easily maintain a very well defined inversion near 6-7 thousand feet and ensure the summit-level air mass remains dry and stable through at least Saturday morning. Winds are also continue to steadily decline and veer off toward the south, though it will still stir up boundary layer turbulence and contribute to poor/bad seeing for tonight and probably the opening half of tomorrow night. There is a chance that winds will slip below 15 mph during the second half of the latter night, which should help to improve seeing as relatively light/calm winds prevail aloft. However, the aforementioned trough will likely bring upper-level turbulence to the area and send a dissipating cold front through over the weekend. Although the bulk of the low-level moisture associated with the front is not expected reach the Big Island until Sunday night, its upper portion will likely arrive and help weaken/lift the inversion toward 10-11 thousand feet during the previous night. The front is set to stall out over the Big Island on Sunday night, just as a short-wave trough passes through the area. This SWT could revitalize what's left of the front, and together with the building low-level trades, further erode the inversion for Sunday and Monday night. That could significantly raise the stakes on fog, high humidity, ice and light flurries at the summit during that time (short-lived fog is also possible for Saturday night).
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 Jan 19 - 2 PM0-209.75-100 / 06ESE/20-35NaN1-2
8 PM0-209.75-100 / 02ESE/20-350.7-1.31.25-1.75
Fri Jan 20 - 2 AM0-209.75-100 / 02SE/15-300.6-1.21.75-2.25
2 PM0-209.75-100 / 07SSE/15-30NaN2-3
8 PM0-209.5-100 / 02S/15-300.6-0.91.75-2.25
Sat Jan 21 - 2 AM10-309-100 / 01.5SSW/10-200.5-0.71.75-2.25
2 PM0-20Clear0 / 05WSW/5-15NaN2-3
8 PM0-20Clear10 / 0-1W/0-100.5-0.82-3
Sun Jan 22 - 2 AM0-208-925 / 5-2SSE/5-150.5-0.92-3
2 PM60-804-860 / 302SSE/5-15NaN3-6
Mon Jan 23 - 2 AM50-704-875 / 40-3SSE/10-200.7-1.33-6
2 PM70-904-990 / 750WSW/5-15NaN6-10
Tue Jan 24 - 2 AM40-604-675 / 25-2WNW/10-200.5-1.13-5
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 Jan 19 - Fri Jan 20 18:16 19:23 5:43 6:50 0:49 N/A 45 14 23.9 -9 25
Fri Jan 20 - Sat Jan 21 18:16 19:24 5:43 6:50 1:38 N/A 35 15 10.2 -12 33
Sat Jan 21 - Sun Jan 22 18:17 19:24 5:43 6:50 2:27 N/A 27 15 57.3 -15 10
Sun Jan 22 - Mon Jan 23 18:18 19:25 5:43 6:50 3:16 N/A 19 16 45.5 -17 10
Mon Jan 23 - Tue Jan 24 18:18 19:25 5:43 6:49 4:06 N/A 12 17 35.0 -18 27
Forecast Issued by: Ryan Lyman
Next update at 5 PM HST Thursday 19 January (0300 UTC Friday 20 January) 2017.
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