Current Conditions
Temp6.3 C
RH36 %
WindNNE 33 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
10 AM HST (2000 UTC) Monday 20 August 2018
Warning(s)
None
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 8 C this afternoon, 3 C this evening and 2 C tomorrow morning. Winds will be from the ENE at 10-20 mph, with seeing near 0.55-0.6 arcseconds. Precipitable water is expected to be in the 3-4 mm range for the night.
Discussion
A well-defined tradewind inversion will continue to cap low-level moisture near 7 thousand feet and ensure the summit remains dry and stable likely through early Tuesday evening. Building deep moisture and instability could begin to erode the inversion as that night progresses and eventually saturate the atmosphere for the following 3 nights. This will raise the stakes on fog and light rain at the summit through Tuesday night and likely result in inoperable conditions, as extensive fog, high humidity, ice and potentially heavy rain plagues the summit for the following 3 nights. Daytime clouds will be limited and short-lived through tomorrow, then will turn very extensive for the remainder of the week.

Skies will continue to clear up for tonight and likely into the early part of tomorrow evening. However, there is a good chance that patches of upper-level clouds will begin to spread in from the south early Wednesday morning, with thicker more widespread clouds following suit later that day. The latter set will likely blanket summit skies for the remainder of the forecast period.

Precipitable water is expected to linger in the 3-4 mm range for tonight, slip toward 2-3 mm for tomorrow night, then jump to 10+ mm probably for the remainder of the week.

Calmer skies and drier summit-level conditions should allow for better than average seeing for tonight and perhaps into tomorrow evening. However, patches of instability, turbulence and moisture spreading into the area will begin to degrade seeing during the latter night and contribute to bad seeing for Wednesday, Thursday and Friday night.

A relatively deep ridge spreading in from the east will promote strong steady large-scale subsidence in the area for the next 36-42 hours. This subsidence will help maintain a well-defined inversion near 6-7 thousand feet and ensure a dry/stable air mass, as well as fairly clear/calm skies through early tomorrow evening. However, moisture/clouds and instability surrounding TC Lane to the SE is set to move just Tuesday night, which could help erode the inversion and increase the risk for fog and light rain at the summit as that night progresses. The GFS has been fairly consistent with the expected track/intensity of the TC Lane, by maintaining its intensity as it continues to slowly slip eastward over the next 48-60 hours. It will then begin a gradual weakening trend as it tracks northward before it dissipates over/near the state through the weekend. While its still too early to anticipate any impacts TC Lane will have on low-lying areas, it will almost certainly result in inoperable conditions/skies at the summit for at least Wednesday, Thursday and Friday night. There is a high probability for heavy rains at the summit and widespread convection in the area, which may contribute to wash outs at any time during this period, though models suggest that the highest potential appears to favor as the center of the storm pass over/near the Big Island around the Thursday afternoon to Friday evening timeframe. Winds may also be an issue during that period, perhaps peaking near 80 mph around sunrise Friday, then quickly tapering through that day. While Lane is set to rapidly fall apart as it encounters increasing shear associated with the sub-tropical jet to north of the state thereafter, residual moisture and instability will likely linger in the area and could allow for more convection and brief periods of heavy rain well into the weekend.
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)
Mon Aug 20 - 2 PM0-20Clear0 / 08ENE/10-20NaN3-5
8 PM0-5Clear0 / 03ENE/10-200.5-0.73-4
Tue Aug 21 - 2 AM0-5Clear0 / 02ENE/10-200.45-0.653-4
2 PM0-20Clear0 / 08ENE/10-20NaN2-4
8 PM0-20Clear10 / 03ENE/10-200.5-0.72-3
Wed Aug 22 - 2 AM20-407-965 / 302.5E/15-250.7-1.12-3
2 PM80-1004-1095 / 904ESE/15-25NaN10-15
8 PM80-1004-10100 / 851E/20-351-210-15
Thu Aug 23 - 2 AM80-1004-10100 / 901SE/30-451-210-15
2 PM80-1004-10100 / 951SSE/40-60NaN10-15
Fri Aug 24 - 2 AM80-1004-10100 / 95-1S/50-701-310-15
2 PM80-1004-1095 / 902SW/40-60NaN10-15
Sat Aug 25 - 2 AM80-1004-1095 / 850WSW/25-401-210-15
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
Mon Aug 20 - Tue Aug 21 18:56 20:03 4:48 5:55 N/A 2:18 78 18 09.8 -21 01
Tue Aug 21 - Wed Aug 22 18:55 20:02 4:48 5:55 N/A 3:07 85 19 01.1 -21 15
Wed Aug 22 - Thu Aug 23 18:54 20:01 4:48 5:55 N/A 3:56 91 19 52.1 -20 33
Thu Aug 23 - Fri Aug 24 18:53 20:00 4:49 5:56 17:01 4:46 96 20 42.5 -18 56
Fri Aug 24 - Sat Aug 25 18:52 19:59 4:49 5:56 17:44 5:36 99 21 32.1 -16 30
Forecast Issued by: Ryan Lyman
Next update at 5 PM HST Monday 20 August (0300 UTC Tuesday 21 August) 2018.
Additional Information
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