Current Conditions
Temp1.4 C
RH7 %
WindENE 11 mph
RoadOpen
Mauna Kea Observatories Forecast
5 PM HST Tuesday 16 January (0300 UTC Wednesday 17 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 2 C this evening and 1 C tomorrow morning. Winds will be from the ENE at 10-20 mph, with seeing near 0.5 arcseconds. Precipitable water is expected to be in the 0.6-0.8 mm range for the night.
Discussion
The 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 the next 5 nights. Daytime clouds will be minimal and short-lived throughout the forecast period.

Skies overhead will remain predominately clear through Thursday night. A stream of high clouds is expected to quickly move in from the west and pass over the summit area for Friday night, then exit eastward on Saturday, leaving clear skies again for that night.

Precipitable water is expected to dip toward 0.7 mm over the next 2 nights, slowly increase to 1 mm through Thursday night, then settle in near 1.25 mm for the following 2 nights.

Relatively calm skies at and above the summit should allow seeing to settle in near 0.5 arcseconds over the next 3 nights. There is chance that an increase in upper-level shear/turbulence will degrade seeing a bit (though better than average seeinw will still prevail) for Friday and Saturday night.

No change since the morning forecast...A fairly flat/deep ridge will persist just north of the state before weakening a bit and lifting off toward the NE in response to the westerly jet spreading eastward over the weekend. Nonetheless, the ridge will continue to promote steady/strong large-scale subsidence in the area, which will easily maintain a well-defined inversion near 7-8 thousand feet and ensure a very dry/stable summit-level air mass through the next 5 nights. In fact, an upper-level ridge passing to the south will help augment subsidence in the area and drive PW toward 0.6-0.8 mm over the next 2-3 nights. It may also help promote relatively calm skies at and above the summit, allowing seeing to settle in near 0.5 arcseconds during this time. Both PW and seeing are expected to increase a tad as the westerly jet injects minor moisture into the area and strengthens shear in the free atmosphere over the weekend. There is also a possibility that the westerly jet will briefly redevelop the sub-tropical jet in the area, which could tap into the tropics and send high clouds over the summit for Friday night. The sub-tropical jet is set to quickly shift eastward, taking the high clouds with it and opening up skies for the remainder of the weekend.
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 16 - 8 PM0-5Clear0 / 01.5ENE/10-200.4-0.60.6-0.8
Wed Jan 17 - 2 AM0-5Clear0 / 01ENE/10-200.4-0.60.6-0.8
2 PM0-20Clear0 / 06.5E/10-20NaN0.6-1
8 PM0-5Clear0 / 01.5E/10-200.35-0.550.6-0.8
Thu Jan 18 - 2 AM0-5Clear0 / 01ESE/10-200.4-0.60.6-0.8
2 PM0-20Clear0 / 06ESE/10-20NaN0.8-1.2
8 PM0-5Clear0 / 01ESE/10-200.4-0.60.7-0.9
Fri Jan 19 - 2 AM0-5Clear0 / 00SSE/10-200.4-0.60.8-1
2 PM40-609-100 / 05SE/5-15NaN1-1.5
Sat Jan 20 - 2 AM60-808-100 / 0-1SSE/5-150.45-0.651-1.5
2 PM20-409-100 / 04SSE/5-15NaN1-2
Sun Jan 21 - 2 AM0-10Clear0 / 0-1.5S/5-150.5-0.71-1.5
2 PM0-20Clear0 / 03.5NNW/5-15NaN1.5-2.5
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
Tue Jan 16 - Wed Jan 17 18:14 19:21 5:42 6:50 7:18 18:15 0 20 09.9 -18 45
Wed Jan 17 - Thu Jan 18 18:14 19:22 5:42 6:50 N/A 19:05 2 20 58.9 -16 52
Thu Jan 18 - Fri Jan 19 18:15 19:23 5:42 6:50 N/A 19:56 5 21 47.3 -14 15
Fri Jan 19 - Sat Jan 20 18:16 19:23 5:43 6:50 N/A 20:47 10 22 35.1 -11 00
Sat Jan 20 - Sun Jan 21 18:16 19:24 5:43 6:50 N/A 21:38 16 23 22.4 -7 14
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Wednesday 17 January 2018.
Additional Information
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This message is also available at the MKWC road conditions page.
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