Current Conditions
Temp4.0 C
RH5 %
WindNE 16 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Tuesday 07 July (0300 UTC Wednesday 8 July) 2020
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 4 C this evening and 3.5 C tomorrow morning. Winds will be from the east at 10-20 mph, with seeing near 0.6-0.65 arcseconds. Precipitable water is expected to be in the 0.8-1 mm range for the night.
A fairly well-defined inversion will continue to cap low-level moisture at or below 9 thousand feet and ensure the summit steers free of fog and precipitation throughout the forecast period. However, there is a possibility that an influx of moisture will push humidity toward 40-60% for Wednesday, Thursday and Friday night. Daytime clouds will be minimal and short-lived through tomorrow, but could pick up for Thursday and Friday, then taper again for the weekend.

Skies will remain predominately clear of organized clouds throughout the forecast period, but there is a chance for light stray strands will pass near/through the area on Thursday night and again on Saturday night.

Precipitable water is expected to linger just below 1 mm for tonight, trend up toward to 4 mm through tomorrow night, linger near that value for the Thursday night, then slip back toward 2 mm for the following 2 nights.

Steady low-level and light boundary layer turbulence will likely contribute to more average-like seeing for the next 2 nights. While this turbulence is set to subside thereafter and increase in free atmospheric turbulence will only allow for a modest improvement in seeing for Thursday, Friday and Saturday night.

No change since the morning forecast...Although the mid-level ridge will remain somewhat weak/indistinct as the tropical upper tropospheric trough (TUTT) slowly strengthens overhead, the low-level ridge will continue to sit to the NE and promote steady subsidence in the area throughout the week. This subsidence will help maintain a fairly well-defined inversion primarily near 8-9 thousand feet and ensure the summit steers free of fog and precipitation throughout the forecast period. There is a possibility that a dissipated tropical wave will pass through, bringing widespread mid/low-level moisture to the area and increase summit-level humidity and PW toward 40-60% and 4 mm, respectively between late Wednesday night and Friday evening. Aside from that, the incoming tropical wave will continue to place a somewhat tighter mid-level wind gradient over the summit through the next 2 nights. This will contribute to minor low-level or even boundary layer turbulence, and thus probably more average-like seeing during that time. Winds are set to subside thereafter, but the sub-tropical jet is expected to strengthen overhead as the TUTT becomes more defined. This will likely increase free atmospheric turbulence and only allow for a modest improvement in seeing for the remainder of the forecast period.
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 Jul 07 - 8 PM0-5Clear0 / 04ENE/10-200.5-0.80.8-1
Wed Jul 08 - 2 AM0-5Clear0 / 03.5ENE/10-200.5-0.70.8-1
2 PM0-20Clear0 / 09.5ESE/10-20NaN1-2
8 PM0-5Clear0 / 03.5SE/10-200.5-0.82-3
Thu Jul 09 - 2 AM0-5Clear0 / 02SE/10-200.55-0.753-4
2 PM0-20Clear0 / 07SE/10-20NaN4-6
8 PM0-10Clear0 / 02E/5-150.5-0.73-5
Fri Jul 10 - 2 AM0-10Clear0 / 01ESE/5-150.45-0.653-5
2 PM0-20Clear0 / 06ESE/5-15NaN4-6
Sat Jul 11 - 2 AM0-10Clear0 / 00NE/0-100.45-0.652-4
2 PM0-20Clear0 / 05NNE/0-10NaN2-3
Sun Jul 12 - 2 AM0-109.5-100 / 01NNW/0-100.45-0.651.5-2.5
2 PM0-20Clear0 / 07.5SE/5-15NaN1-2
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 Jul 07 - Wed Jul 08 19:15 20:28 4:26 5:39 21:25 N/A 88 22 00.8 -17 33
Wed Jul 08 - Thu Jul 09 19:15 20:28 4:27 5:40 22:05 N/A 81 22 49.9 -13 27
Thu Jul 09 - Fri Jul 10 19:15 20:28 4:27 5:40 22:42 N/A 73 23 36.3 -8 55
Fri Jul 10 - Sat Jul 11 19:15 20:28 4:28 5:40 23:16 N/A 64 0 20.7 -4 09
Sat Jul 11 - Sun Jul 12 19:14 20:27 4:28 5:41 23:49 N/A 55 1 04.2 0 42
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Wednesday 8 July 2020.
Additional Information
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This message is also available at the MKWC road conditions page.
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