Current Conditions
Temp2.4 C
RH16 %
WindNE 25 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Wednesday 26 July (0300 UTC Thursday 27 July) 2017
Warning(s)
None
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, but banding high clouds are set to quickly move in from the south toward the end of the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 3 C, with winds from the ENE at 15-25 mph and seeing near 0.7-0.75 arcseconds. Precipitable water is expected to be in the 1-1.5 mm range for the night.
Discussion
The tradewind inversion will continue to cap low-level moisture primarily near 8 thousand feet and ensure a dry/stable air mass through at least midnight Thursday. There is a chance that the inversion will begin to weaken/lift near sunrise Friday and may allow the atmosphere below 18 thousand feet to become fairly saturated for Friday and Saturday night. This could raise the stakes on periodic fog, high humidity and light rain at the summit during that time. Convection is also possible in the area, mainly for Friday. The inversion is set to quickly rebuild near 7-8 thousand feet through Sunday, allowing dry/stable conditions to return to the summit by that night. Daytime clouds will be minimal and short-lived through Thursday, but could turn extensive for Friday and Saturday, then taper again thereafter.

Skies will start out quite clear for this evening, but banding high clouds are set to quickly move in from the south during the second half of the night and could contribute to extensive cloud cover for tomorrow night. These clouds will break up a bit and shift northward on Friday, but there is a chance that patches of summit/mid-level clouds and possibly convection will move in from the east and/or develop in the area for Friday and perhaps Saturday night. The bulk of the clouds will move out of the area on Sunday, leaving residual high clouds along the western skies for that night.

Precipitable water is expected to linger near 1.25 mm for tonight, increase toward 1.5-2 mm for tomorrow night, then will likely exceed 4 mm for at least Friday and Saturday night. There is a chance that it will slip back toward 2 mm over the course of Sunday night.

Boundary layer turbulence combined with increasing turbulence in the free atmosphere will contribute to poor seeing for tonight. There is a chance that seeing will improve as the boundary layer turbulence subsides for tomorrow night. However, an increase in mid-level turbulence may degrade seeing again mainly for Friday night. Deep subsidence slowly building into the area, combined with relatively uniform/light easterly flow aloft should allow seeing to improve drastically through Saturday and especially Sunday night.

No change since the morning forecast...The persistent mid/low-level ridge to the NE will continue to supply strong/steady large-scale subsidence in the area well into next week. While this subsidence will help maintain a well-defined inversion near 7-8 thousand feet and ensure a dry/stable air mass through at least midnight Thursday, the last three model runs now suggest that the remnants low-level cloud field of Greg to the east will begin to move in early Friday morning. This cloud field is then set to flare up as it encounters a short-wave upper-level trough to the west, which could erode the inversion and saturate most of the air mass below 18 thousand feet between sunrise Friday and late Saturday night. That could result in periods of fog, high humidity and light precipitation at the summit during that time. Convection may also pop up in the area at virtually anytime (especially on Friday), and could be flare up along the slopes during the afternoon hours. An upper-level ridge building in from the SE is expected to flatten out the trough, while the mid/low-level ridge pushes the moisture westward as the weekend progresses. This should help rebuild the inversion and allow clear/calm skies to build in over the summit by Sunday 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)
Wed Jul 26 - 8 PM0-20Clear0 / 03ENE/15-250.6-0.91-1.5
Thu Jul 27 - 2 AM20-409-100 / 03ENE/15-250.55-0.851-1.5
2 PM60-809-100 / 08.5E/10-20NaN1-2
8 PM80-1008-100 / 03E/10-200.45-0.651.5-2
Fri Jul 28 - 2 AM80-1008-1025 / 52.5SE/10-200.45-0.651.75-2.25
2 PM80-1004-1090 / 755ESE/10-20NaN6-10
8 PM60-804-1075 / 402E/10-200.7-1.14-8
Sat Jul 29 - 2 AM60-804-1075 / 252SE/10-200.6-14-8
2 PM60-804-1080 / 505SSE/5-15NaN6-10
Sun Jul 30 - 2 AM40-605-760 / 152ESE/5-150.4-0.74-8
2 PM20-404-4.520 / 57.5E/0-10NaN4-8
Mon Jul 31 - 2 AM0-20Clear0 / 04NE/5-150.35-0.552-4
2 PM0-20Clear0 / 011ENE/10-20NaN2-4
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
Wed Jul 26 - Thu Jul 27 19:10 20:21 4:36 5:47 N/A 22:05 19 11 50.2 3 29
Thu Jul 27 - Fri Jul 28 19:10 20:21 4:36 5:47 N/A 22:45 28 12 39.1 -0 47
Fri Jul 28 - Sat Jul 29 19:10 20:20 4:37 5:47 N/A 23:24 37 13 26.7 -4 55
Sat Jul 29 - Sun Jul 30 19:09 20:20 4:37 5:48 N/A 0:03 47 14 13.8 -8 47
Sun Jul 30 - Mon Jul 31 19:09 20:19 4:38 5:48 N/A 0:42 57 15 00.9 -12 15
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Thursday 27 July 2017.
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