Current Conditions
Temp0.9 C
RH10 %
WindS 0 mph
RoadOpen (4x4)
Maunakea Observatories Forecast
5 PM HST Friday 16 April (0300 UTC Saturday 17 April) 2021
Warning(s)
Moderate winds
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, but there is a chance for lingering cirrus mainly along the eastern skies for this evening.
Summary of Key Meteorological Variables
Summit temperatures will be near -0.5 C this evening and -1 C for tomorrow morning. Winds will be from the west at 15-30 mph, with seeing near 0.8 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.
Discussion
A strong well-defined inversion will continue to cap low-level moisture at or below 8 thousand feet and ensure a dry/stable summit-level air mass through at least Monday night. There is a chance that the inversion will begin to breakdown as mid/low-level moisture builds into the area, increasing the risk for periods of fog, ice and high humidity at the summit for Tuesday night. Daytime clouds will be minimal and short-lived through Monday, but could pick up on Tuesday and Wednesday.

There is a chance for lingering high clouds in the area mainly for this evening. More high clouds are expected to spread in from the west and pass along the southern skies particularly as tomorrow night progresses. The bulk of these clouds will sag southward and break up on Sunday, but there is still a chance for patches of thin high clouds passing overhead for that night. Additional high clouds are set to fill in from the NW and slip over or along the northern skies for Monday, while mid-level clouds may build along the western skies for Tuesday night.

Precipitable water is expected to linger near 1.25-1.5 mm through the weekend, then increase into the 2-3 mm range for Monday night and perhaps trend toward 4 mm for Tuesday night.

Boundary layer and low-level turbulence will contribute to poor seeing for tonight and perhaps into tomorrow night. Seeing is set to improve and settle in near 0.45-0.5 arcseconds as relatively calm/laminar westerly flow prevails at and above the summit for Sunday and Monday night. However, an influx of moisture could degrade and/or contribute to more variable seeing for Tuesday night.

A rather broad low will continue to develop to the far north, which will help squash the ridge over the Big Island for the early part of the weekend. The ridge and low are set to rebound northward late Saturday, while the latter restrengthens further to the west as a short-wave trough digs in from the NW as the weekend progresses. Nevertheless, the ridge will remain close enough to promote strong/steady large scale subsidence in the area, which will easily maintain a well-defined inversion at or below 8 thousand feet and ensure a dry/stable summit-level air mass during this time. Unfortunately, winds are set to increase toward 20-25 mph with the development of the low over the next 18-24 hours. This will be enough to stir up boundary layer turbulence and contribute to poor seeing for tonight and probably into tomorrow evening. Winds are expected to subside as the low lifts northward, which should help to improve seeing as relatively light/laminar westerly flow prevails at and above the summit for the remainder of the weekend and early part of next week. Models suggest that the restrengthening low to the NNW will begin to organize a frontal band over the western half of the state late Monday. There is a chance that this frontal band will progress eastward by Tuesday, but I suspect it will fall apart as it loses its upper-level support by the time it reaches the Big Island on Tuesday/Wednesday.
HST CC (%) CLD HGT (km) Fog Prob (%) Prcp Prob (%) Temp (C) Wind (dir/mph) Seeing (asec) PW (mm)
---------------------------------------------------------------------------------------------------------------------------------------
04/16/2021 2000 0-20 8-9 0 0 -0.5 270/15-30 0.6-1 1.25-1.75
04/17/2021 0200 0-10 Clear 0 0 -1 270/15-30 0.6-1 1-1.5
04/17/2021 1400 0-20 9-10 0 0 4 270/15-30 NaN 1-2
04/17/2021 2000 0-20 9-10 0 0 -0.5 270/10-20 0.5-0.9 1.25-1.75
04/18/2021 0200 20-40 9-10 0 0 -0.5 270/10-20 0.5-0.8 1-1.5
04/18/2021 1400 0-20 9-9.5 0 0 5 240/5-15 NaN 1-1.5
04/18/2021 2000 0-20 9-9.5 0 0 0 240/5-15 0.4-0.6 1-1.5
04/19/2021 0200 0-20 9-9.5 0 0 0 270/5-15 0.35-0.55 1-1.5
04/19/2021 1400 0-20 Clear 0 0 5 225/5-15 NaN 1.5-2.5
04/20/2021 0200 0-20 9-10 0 0 0.5 240/0-10 0.35-0.55 2-3
04/20/2021 1400 20-40 4-7 20 10 5 240/0-10 NaN 3-5
04/21/2021 0200 20-40 6-8 25 10 0 240/0-10 0.5-0.8 2-4
04/21/2021 1400 60-80 4-8 40 20 6 270/0-10 NaN 4-8
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 Apr 16 - 8 PM0-208-90 / 0-0.5W/15-300.6-11.25-1.75
Sat Apr 17 - 2 AM0-10Clear0 / 0-1W/15-300.6-11-1.5
2 PM0-209-100 / 04W/15-30NaN1-2
8 PM0-209-100 / 0-0.5W/10-200.5-0.91.25-1.75
Sun Apr 18 - 2 AM20-409-100 / 0-0.5W/10-200.5-0.81-1.5
2 PM0-209-9.50 / 05WSW/5-15NaN1-1.5
8 PM0-209-9.50 / 00WSW/5-150.4-0.61-1.5
Mon Apr 19 - 2 AM0-209-9.50 / 00W/5-150.35-0.551-1.5
2 PM0-20Clear0 / 05SW/5-15NaN1.5-2.5
Tue Apr 20 - 2 AM0-209-100 / 00.5WSW/0-100.35-0.552-3
2 PM20-404-720 / 105WSW/0-10NaN3-5
Wed Apr 21 - 2 AM20-406-825 / 100WSW/0-100.5-0.82-4
2 PM60-804-840 / 206W/0-10NaN4-8
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 Apr 18 - Mon Apr 19 18:50 19:57 4:45 5:52 N/A 0:48 41 7 22.7 24 54
Mon Apr 19 - Tue Apr 20 18:50 19:57 4:44 5:51 N/A 1:37 51 8 17.3 23 24
Tue Apr 20 - Wed Apr 21 18:51 19:58 4:43 5:50 N/A 2:23 61 9 11.8 20 37
Wed Apr 21 - Thu Apr 22 18:51 19:58 4:42 5:49 N/A 3:07 71 10 05.8 16 40
Thu Apr 22 - Fri Apr 23 18:51 19:59 4:41 5:49 N/A 3:49 81 10 59.3 11 39
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Monday 19 April 2021.
Additional Information
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