Current Conditions
Temp1.0 C
RH10 %
WindESE 1 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Thursday 29 September (0300 UTC Friday 30 September) 2016
Warning(s)
None
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, but there is a possibility for patches of scattered cirrus, particularly along the northern and southern skies through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 2 C this evening and 1.5 C tomorrow morning. Winds will be light and from the east, with seeing around 0.5-0.55 arcseconds. Precipitable water is expected to be in the 1-1.2 mm range for the night.
Discussion
The tradewind inversion will continue to cap low-level moisture near 7-8 thousand feet and ensure the summit remains dry and stable for at least tonight. However, building instability and deep tropical moisture filling into the area, will help to erode the inversion through Friday night and into Saturday evening, allowing the atmosphere to turn fairly saturated for the remainder of the weekend and into the early part of next week. Consequently, there is a moderate/high risk for fog/high humidity and precipitation after tonight. Flurries, ice and convection are also a possibility mainly for Sunday. Minor daytime clouds are possible for tomorrow and will likely turn extenisve for the remainder of the forecast period.

While the high clouds rapidly approaching from the south is expected to shift eastward before moving over the Big Island, there is still a possibility it could be visible from the summit, particularly for this evening. There is also a chance for passing high clouds along the northern skies for much of tonight. More scattered high clouds will begin to spread in from the west through Friday night and rapidly thicken and become more widespread through the weekend. There is a very good possibility that mid-level clouds will start to develop in the area and/or drift in from the east as the weekend progresses. This will likely contribute to extensive cloud cover or even overcast skies for Saturday, Sunday and Monday night.

Precipitable water is expected to slip toward 1-1.2 mm for tonight and probably the start of tomorrow evening, but will rapidly trend toward 4 mm by sunrise Saturday and likely exceed that value for the remainder of the forecast period.

Weak turbulence in the free atmosphere should allow for better than average seeing for tonight. However, building upper-level turbulence and instability, coupled with an influx of low-level turbulence will likely degrade seeing through Friday night and contribute to poor/bad seeing for the following 3 nights.

No change since the morning forecast...Although the mid and especially low-level ridge will continue to sit to the north of the state probably well into next week, large-scale subsidence will only prevail in the area while an upper-level ridge persists to the SW for another 36 hours. Nonetheless, this subsidence will maintain a fairly well-defined inversion near 7-8 thousand feet and ensure a dry/stable air mass for tonight and perhaps into early tomorrow evening. The upper-level ridge will also keep the sub-tropical displaced further northward, which should help minimize turbulence in the free atmosphere and likely allow for better than average seeing during this period. Unfortunately, conditions and skies are expected to go downhill after that. First the sub-tropical jet is expected to strengthen as the tropical upper-tropospheric trough (TUTT) intensifies and produces weak but fairly widespread instability over the state over the weekend and into next week. The TUTT will also deposit a rather deep mid/upper-level low just west of the state , which will provide more focused/localized instability in the area particularly for Sunday and Monday. In addition, deep tropical moisture associated with the remnants of TS Ulika is set arrive late Friday and will continue to pour in from the east into the early part of next week. There is also a possibility that the upper-level low will either draw more deep moisture in from the SW and/or shift the remnant moisture in the area back over the state as it slips off toward the NE and dissipates around the middle part of next week. Nonetheless, this influx of deep tropical moisture and building instability is expected to erode the inversion through Friday night and allow the atmosphere to turn very saturated probably for the following 3 nights. This will likely contribute to extensive fog/cloud cover, high humidity and possibly rain at the summit between midnight on Friday and at least Monday night (likely into Wednesday/Thursday). The more localized instability from the low, combined with the widespread tropical moisture may result in ice and flurries at the summit and convection in the area, particularly between midnight Saturday and early Monday morning.
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)
Thu Sep 29 - 8 PM10-309-100 / 02E/0-100.45-0.551-1.2
Fri Sep 30 - 2 AM0-209-100 / 01.5ENE/5-150.45-0.651-1.2
2 PM20-404-4.520 / 07ENE/5-15NaN2-4
8 PM20-409-1025 / 52NE/5-150.45-0.651-2
Sat Oct 01 - 2 AM40-608-1075 / 301.5E/0-100.5-12-4
2 PM70-904-1080 / 404.5SSE/5-15NaN4-8
8 PM60-804-1090 / 600.5ESE/0-100.8-1.68-12
Sun Oct 02 - 2 AM80-1004-1095 / 750SSE/0-101-28-12
2 PM80-1004-10100 / 902.5N/5-15NaN8-12
Mon Oct 03 - 2 AM80-1004-1095 / 750ENE/0-101-28-12
2 PM80-1004-1095 / 753.5N/0-10NaN8-12
Tue Oct 04 - 2 AM80-1004-1090 / 601.5NNW/0-100.8-1.68-12
2 PM80-1004-1090 / 653NNW/0-10NaN8-12
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
Thu Sep 29 - Fri Sep 30 18:20 19:24 5:00 6:04 5:52 17:51 0 12 06.7 0 46
Fri Sep 30 - Sat Oct 01 18:19 19:23 5:00 6:04 6:41 18:28 0 12 52.2 -3 01
Sat Oct 01 - Sun Oct 02 18:18 19:22 5:00 6:04 N/A 19:06 2 13 37.4 -6 39
Sun Oct 02 - Mon Oct 03 18:17 19:21 5:00 6:05 N/A 19:44 5 14 22.9 -10 01
Mon Oct 03 - Tue Oct 04 18:16 19:21 5:01 6:05 N/A 20:23 10 15 09.1 -13 00
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Friday 30 September 2016.
Additional Information
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