Current Conditions
Temp4.5 C
RH9 %
WindENE 0 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
10 AM HST (2000 UTC) Tuesday 21 January 2020
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 6.5 C this afternoon, 2 C this evening and 1.5 C tomorrow morning. Winds will be from the NNE at 5-15 mph for today, easing and switching to a more WNW direction through the night. Seeing will be near 0.45-0.5 arcseconds, while precipitable water is expected to be in the 0.7-0.9 mm range for the night.
Discussion
A strong well-defined inversion will continue to cap low-level moisture near 5-6 thousand feet and ensure a dry/stable summit-level air mass through the next 5 nights. Daytime clouds will be minimal and short-lived throughout the forecast period.

Skies will remain predominately clear through the next 5 nights.

Precipitable water is expected to briefly increase toward 0.8 mm for tonight, then settle in near 0.65-0.7 mm for the remainder of the forecast period.

Relatively calm skies with laminar NW to westerly flow will prevail in the free atmosphere, allowing seeing to linger primarily near 0.4-0.5 arcseconds throughout most of the forecast period, particularly after this evening. There is a possibility that seeing will dip below 0.4 arcseconds as winds aloft taper mainly for Wednesday night. There is also a chance for some variability due to upper-level horizontal shear for Friday night.

A deep ridge will continue to sit to the almost directly over the Big Island and promote strong/steady subsidence in the area through the week. This subsidence will help maintain a well-defined inversion near 5-6 thousand feet and ensure a dry/stable summit-level air mass throughout the forecast period. The westerly jet will maintain a zonal orientation off to the north, allowing clear/calm skies and very dry air to prevail above the summit during this time. This should allow seeing and PW to settle in near 0.4-0.5 arcseconds and 0.6-0.7 mm throughout the forecast period, particularly after a small pocket of moisture and winds aloft taper after tonight. There is a possibility that seeing could dip below 0.4 arcseconds due to a slight northward retraction of the westerly jet for Wednesday night. However, an expansion of the jet may briefly increase horizontal shear in the free atmosphere, perhaps resulting in minor degradation/variability in seeing for Friday 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)
Tue Jan 21 - 2 PM0-20Clear0 / 06.5NNE/5-15NaN0.8-1.2
8 PM0-5Clear0 / 02NNE/0-100.4-0.60.7-0.9
Wed Jan 22 - 2 AM0-5Clear0 / 01.5WNW/0-100.35-0.550.7-0.9
2 PM0-20Clear0 / 08W/5-15NaN0.8-1.2
8 PM0-5Clear0 / 03NW/5-150.35-0.550.6-0.8
Thu Jan 23 - 2 AM0-5Clear0 / 03NW/5-150.3-0.50.55-0.7
2 PM0-20Clear0 / 08NNW/5-15NaN0.8-1.2
8 PM0-5Clear0 / 03.5NW/0-100.25-0.450.55-0.7
Fri Jan 24 - 2 AM0-5Clear0 / 03NW/0-100.3-0.50.55-0.7
2 PM0-20Clear0 / 07WSW/5-15NaN0.7-1.1
Sat Jan 25 - 2 AM0-5Clear0 / 02WNW/5-150.3-0.50.55-0.75
2 PM0-20Clear0 / 07WNW/5-15NaN0.7-1.1
Sun Jan 26 - 2 AM0-5Clear0 / 01.5W/5-150.35-0.650.55-0.75
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
Tue Jan 21 - Wed Jan 22 18:17 19:24 5:43 6:50 5:06 N/A 6 18 13.3 -22 52
Wed Jan 22 - Thu Jan 23 18:17 19:24 5:43 6:50 6:00 16:39 2 19 08.6 -23 08
Thu Jan 23 - Fri Jan 24 18:18 19:25 5:43 6:50 6:50 17:33 0 20 02.8 -22 13
Fri Jan 24 - Sat Jan 25 18:18 19:26 5:42 6:49 7:36 18:28 0 20 55.1 -20 14
Sat Jan 25 - Sun Jan 26 18:19 19:26 5:42 6:49 N/A 19:21 2 21 45.0 -17 22
Forecast Issued by: Ryan Lyman
Next update at 5 PM HST Tuesday 21 January (0300 UTC Wednesday 22 January) 2020.
Additional Information
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This message is also available at the MKWC road conditions page.
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