Current Conditions
Temp0.8 C
RH18 %
WindW 18 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Friday 22 September (0300 UTC Saturday 23 September) 2017
Warning(s)
None
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable through the night. Scattered to broken banding high clouds are expected to stream out of the SW and over the summit area, perhaps contributing to periods of extensive cloud cover during the second half of the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 2.5 C, with winds from the WNW at 10-20 mph and seeing near 0.6-0.65 arcseconds. Precipitable water is expected to be in the 2-3 mm range for the night.
Discussion
A relatively well-defined tradewind inversion will continue to cap low-level moisture near 7-8 thousand feet and ensure the summit remains dry and stable throughout the forecast period. There is a small possibility for minor daytime clouds for today, which will become minimal and short-lived thereafter.

A band of scattered to broken high clouds is expected to stream out of the SW and over the summit area, perhaps contributing to periods of extensive cloud cover mainly during the second half of the night. This band is set to breakdown and shift off toward the SW through tomorrow, leaving relatively clear skies for most of that night and especially for the following 3 nights.

Precipitable water is expected to linger in the 2-3 mm range for tonight, trend toward 1 mm over the course of tomorrow night and probably slip below that value for Sunday night, only to rebound and drift back to 2 mm for the early part of next week.

A mixture of moderate turbulence in the free atmosphere and light boundary layer turbulence will likely keep seeing near 0.6-0.65 arcseconds for the next 2 nights. Both sources of turbulence are set to subside through Sunday allowing seeing to improve a bit during that night. Seeing may eventually settle in near 0.4-0.5 arcseconds as relatively calm skies and deep subsidence/easterly winds prevail for Monday and Tuesday night.

No change since the morning forecast...A persistent and rather broad ridge to the north and stretch across most of the Pacific, combined with subsidence along the SW flank of a relatively and equally persistent deep upper-level low to the northeast will help maintain a well-defined tradewind inversion near 7-8 thousand feet and ensure a dry/stable summit-level air mass throughout the forecast period. Unfortunately, the sub-tropical jet along the southern flank of the low will linger overhead before shifting off toward the SE later in the weekend. This jet will shuttle scattered to broken high clouds through the area over the next 24 hours and also promote moderate turbulence in the free atmosphere over the next 2 nights. The latter, combined with minor boundary layer turbulence will likely contribute to more average-like seeing during that time. Seeing is set to improve and skies will open up as the low/STJ shift off toward the SE in response to an upper-level ridge building in from the northwest late in the weekend and for the early part of next week. This ridge will help switch flow at and above the summit toward a more uniform northerly and eventually easterly direction and promote clear/calm skies and deep subsidence in the free atmosphere, which should translate to a fairly drastic improvement in seeing 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 Sep 22 - 8 PM40-609-100 / 02.5WNW/10-200.5-0.72-3
Sat Sep 23 - 2 AM60-808.5-100 / 02.5WNW/10-200.55-0.752-3
2 PM40-609-100 / 07.5WNW/15-25NaN1.5-2.5
8 PM20-409.5-100 / 02NW/15-250.5-0.81.25-1.75
Sun Sep 24 - 2 AM0-20Clear0 / 01.5NW/10-200.5-0.81-1.5
2 PM0-20Clear0 / 07NNW/10-20NaN1-1.5
8 PM0-5Clear0 / 02.5N/10-200.45-0.650.8-1.1
Mon Sep 25 - 2 AM0-5Clear0 / 02.5NNW/10-200.45-0.650.8-1.1
2 PM0-20Clear0 / 08NW/15-25NaN1-2
Tue Sep 26 - 2 AM0-5Clear0 / 03NW/10-200.35-0.551.5-2.5
2 PM0-20Clear0 / 09N/5-15NaN2-3
Wed Sep 27 - 2 AM0-5Clear0 / 04.5NE/10-200.3-0.52-3
2 PM0-20Clear0 / 09ENE/20-35NaN2-4
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
Sun Sep 24 - Mon Sep 25 18:25 19:29 4:58 6:03 N/A 21:54 25 16 04.8 -15 56
Mon Sep 25 - Tue Sep 26 18:24 19:28 4:59 6:03 N/A 22:37 34 16 53.6 -18 01
Tue Sep 26 - Wed Sep 27 18:23 19:27 4:59 6:03 N/A 23:22 43 17 43.1 -19 21
Wed Sep 27 - Thu Sep 28 18:22 19:26 4:59 6:03 N/A 0:09 52 18 33.3 -19 50
Thu Sep 28 - Fri Sep 29 18:21 19:25 4:59 6:04 N/A 0:58 61 19 24.0 -19 28
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Monday 25 September 2017.
Additional Information
For public road conditions and snow report message please call (808) 935-6268.
This message is also available at the MKWC road conditions page.
NWS Hawaiian Islands Synoptic Discussion and Guidance
Honolulu National Weather Service Data and Products