Current Conditions
Temp5.6 C
RH66 %
WindW 2 mph
RoadOpen (4x4)
Maunakea Observatories Forecast
5 PM HST Friday 15 October (0300 UTC Saturday 16 October) 2021
Chance for fog/ice
Cloud Cover and Fog/Precipitation Forecast
There is moderate/high risk for periods of fog, high humdity and ice through the night. Thin patches of high clouds will continue to pass over/near the summit, particularly along the northern skies through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near -0.5 C this evening and -1.5 C tomorrow morning. Winds will be from the west at 10-20 mph, with seeing near 0.8-0.9 arcseconds for the night. Precipitable water is expected to be in the 2.5-3.5 mm range for the night.
The tradewind inversion will remain weak/elevated near 12 thousand feet, which could allow for periods of fog, ice and high humidity at the summit mainly over the next 2 nights. While the inversion is set to recover near 6-7 thousand feet thereafter, mid-level moisture may move into the area, keeping humidity around 50-70% and may allow for short-lived fog/ice at the summit into the early part of next week. Precipitation is unlikely throughout the forecast period. Extensive daytime clouds and isolated convection are possible over the next 2 days, then will taper a bit for Sunday and early part of next week.

Thin patches of high clouds will continue to pass over/near the summit, particularly along the northern skies, but cloud cover is not expected to exceed 20% for tonight. More organized clouds will eventually fill the northern and southern skies through tomorrow and may begin to build overhead through that night, perhaps contributing to extensive cloud cover by sunrise Sunday. There is a chance that these clouds will gradually break up thereafter, but periods of extensive cloud cover may persist through Monday night, and clearer skies are not expected until the middle part of next week.

Precipitable water is expected to linger in the 2.5-3.5 mm range for the next 2 nights, then jump back to 4+ mm for Sunday night and early part of next week.

An elevated inversion and moderate boundary layer turbulence will likely contribute to poor/bad seeing over the next 2 nights. While the inversion is set to gradully restrengthen thereafter, an influx of mid-level moisture and occasionaly bouts of light/moderate boundary layer turbulence may prevent any significant improvement in seeing for Sunday, Monday and Tuesday night.

Little change since the morning forecast...A rather deep/sharp mid/upper-level trough building into the area is expected to destabilize the air mass, which will help enhance the incoming low-level cloud field and raise the inversion toward 12-13 thousand feet probably through Sunday morning. This will increase the stakes on fog, ice and high humidity at the summit over the next 2 nights, and perhaps isolated convection in the area. In addition, the trough is expected deepen enough to enhance mid-level flow in the area, likely enough to stir up boundary layer or low-level turbulence and contribute to poorer than average probably throughout most of the forecast period. The elevated inversion may further degrade seeing over the next 2 nights. The atmosphere is set to stabilize a bit as the trough shifts further westward late in the weekend, deep southerly flow associated with a mid/upper-level ridge to SE could begin to advect rather widespread mid-level moisture into the area around that time and into the early part of next week. This will result in an abrupt increase in PW and probably push mean summit-level humidity toward 50-70%, which may allow for more short-lived fog at the summit, mainly for Sunday night, but perhaps even the following 2 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 (%) (Celsius) (Dir/MPH) (Arcseconds) (mm)
Fri Oct 15 - 8 PM0-209-1075 / 25-0.5W/10-200.6-12.5-3.5
Sat Oct 16 - 2 AM0-209.5-1075 / 25-1.5W/10-200.6-12.5-3.5
2 PM60-804-1085 / 303WNW/15-30NaN4-8
8 PM30-509-1065 / 20-1WNW/15-300.6-12.5-3.5
Sun Oct 17 - 2 AM50-707-1060 / 15-1W/15-300.6-12.5-3.5
2 PM60-806-1075 / 254WSW/10-20NaN4-8
8 PM40-606-1035 / 100WSW/5-150.5-0.84-8
Mon Oct 18 - 2 AM40-606-1030 / 100WSW/10-200.5-0.84-8
2 PM50-705-965 / 205WSW/10-20NaN4-8
Tue Oct 19 - 2 AM30-505-920 / 01W/10-200.5-0.94-8
2 PM20-405-840 / 106WNW/10-20NaN4-8
Wed Oct 20 - 2 AM20-405-810 / 01.5WNW/10-200.5-0.84-8
2 PM0-20Clear25 / 57WNW/10-20NaN4-8
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 Oct 17 - Mon Oct 18 18:06 19:10 5:04 6:09 N/A 4:53 95 0 06.0 -4 36
Mon Oct 18 - Tue Oct 19 18:05 19:09 5:04 6:09 17:02 5:44 98 0 51.7 1 01
Tue Oct 19 - Wed Oct 20 18:04 19:09 5:05 6:09 17:35 6:34 100 1 37.0 6 31
Wed Oct 20 - Thu Oct 21 18:03 19:08 5:05 6:10 18:09 7:25 99 2 22.6 11 41
Thu Oct 21 - Fri Oct 22 18:03 19:08 5:05 6:10 18:45 N/A 97 3 09.3 16 19
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Monday 18 October 2021.
Additional Information
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