Current Conditions
Temp6.9 C
RH11 %
WindENE 11 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
10 AM HST (2000 UTC) Wednesday 26 April 2017
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 7 C this afternoon and 2 C for the night. Winds will be from the ENE at 5-15 mph, with seeing near 0.7 arcseconds. Precipitable water is expected to be in the 1.5-2 mm range for the first half of the night and 1-1.5 mm range for the second half.
The tradewind inversion will continue to cap low-level moisture at or below 9 thousand feet and ensure a dry and stable summit-level air mass through at least late Friday morning. Building instability and deep moisture filling into the area are expected to erode the inversion and increase the risk for fog, high humidity, ice and light snow/rain at the summit for the next 3+ nights. There is also a possibility for convection in the area and periods of heavy snow at the summit mainly as the weekend progresses. Daytime clouds will be minimal and short-lived through Thursday, but could pick up on Friday and turn quite extensive over the weekend.

Skies will remain predominately clear for the next 2 nights. However, patches of thick clouds are set to approach from the north on Friday, then begin to develop in the area contributing to periods of extensive cloud cover for Saturday and especially Sunday night. There is also a possibility that more organized high clouds will fill out of the SW during the latter two nights.

Precipitable water is expected to start out near 2 mm for this evening, but could slip toward 1 mm by the end of the night, only to increase back to 2-3 mm for tomorrow night. It will likely exceed 4 mm for Friday, Saturday and Sunday night.

An increase in mid/upper-level turbulence could contribute to slightly poorer than average seeing over the next 2 nights. This source of turbulence is set to diminish through Friday, but an strengthening shear in the free atmosphere, combined with an unstable environment and possibily an increase in boundary layer turbulence will likely degrade seeing for that night and almost certainly for Saturday and Sunday night.

The mid/low-level ridge will continue to gradually shift eastward as a large trough brewing to the NW creeps toward the state over the next 48 hours. Still, the ridge will remain close enough to support strong large-scale subsidence in the area, which will help maintain the tradewind inversion at or below 9 thousand feet and ensure a dry/stable summit-level air mass for the next 2 nights. While skies will remain predominately clear during this time, mid/upper-level turbulence along the western side of a low to the east could disrupt seeing a bit during this time. This source of turbulence is set to subside as the low shifts further eastward in response to this building trough on Friday. However, this trough is expected to bring moisture and widespread in stability to the area during that time, and eventually deposit a rather deep late-season cut-off low to the north of the state by later that night. This low is slated to shift southward and drift over or just west of the state by late in the weekend, then wobble eastward and weaken for the early part of next week. Nonetheless, the moisture/instability associated with the trough and low will likely dismantle the inversion as early as Friday evening, perhaps allowing the atmosphere to become fairly saturated, particularly during the second half of the weekend. This increase the stakes on fog, high humidity, ice and precipitation at the summit during that time. There is also a possibility for periods of convection in the area and heavy snow at the summit, mainly after midnight on Saturday. Winds are also slated to increase as the weekend progresses, and could easily top 50 mph by Sunday night and especially the early part of next week. This could contribute to large drifting during that time. All in all, expect fairly benign weather/skies for the next 2 nights, with the potential for bad/wet conditions/skies over the following 3-5 nights.
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)
Wed Apr 26 - 2 PM0-20Clear0 / 07ENE/5-15NaN2-3
8 PM0-5Clear0 / 02ENE/5-150.6-0.81.5-2
Thu Apr 27 - 2 AM0-5Clear0 / 02ENE/5-150.6-0.81-1.5
2 PM0-20Clear0 / 06.5SSE/5-15NaN1-2
8 PM0-5Clear0 / 01SSE/0-100.6-0.82-2.5
Fri Apr 28 - 2 AM0-5Clear0 / 00S/5-150.55-0.752.5-3
2 PM40-604-550 / 204SSW/5-15NaN3-6
8 PM20-406-860 / 15-1.5W/5-150.7-1.14-8
Sat Apr 29 - 2 AM40-605-860 / 20-2WSW/10-200.8-1.24-8
2 PM60-804-880 / 402W/15-30NaN4-8
Sun Apr 30 - 2 AM60-804-1075 / 50-4WSW/25-400.8-1.64-8
2 PM80-1004-1095 / 90-1WSW/35-50NaN8-12
Mon May 01 - 2 AM80-1004-1095 / 90-6SW/50-701-26-10
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
Wed Apr 26 - Thu Apr 27 18:53 20:01 4:38 5:46 N/A 19:32 1 3 14.9 12 28
Thu Apr 27 - Fri Apr 28 18:53 20:01 4:37 5:45 N/A 20:36 5 4 14.9 15 41
Fri Apr 28 - Sat Apr 29 18:54 20:02 4:36 5:45 N/A 21:41 12 5 16.2 17 49
Sat Apr 29 - Sun Apr 30 18:54 20:02 4:36 5:44 N/A 22:43 21 6 17.6 18 43
Sun Apr 30 - Mon May 01 18:54 20:03 4:35 5:43 N/A 23:42 31 7 18.1 18 21
Forecast Issued by: Ryan Lyman
Next update at 5 PM HST Wednesday 26 April (0300 UTC Thursday 27 April) 2017.
Additional Information
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