Current Conditions
Temp8.6 C
RH23 %
WindNE 17 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
10 AM HST (2000 UTC) Thursday 27 April 2017
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 6.5 C this afternoon, 1.5 C this evening and 1 C tomorrow morning. Winds will be from the east at 5-15 mph for today, but will weaken and switch to a more SE direction through the night. Seeing will be near 0.45-0.5 arcseconds, while precipitable water is expected to be in the 1.25-1.75 mm range for the night.
Discussion
The tradewind inversion will continue to cap low-level moisture near 8-9 thousand feet and ensure the summit remains dry and stable through tonight. Building moisture and instability are expected to gradually erode the inversion through Friday night, allowing the atmosphere to become quite saturated for the following 3 nights. This will raise the stakes on fog, high humidity, ice and snow/rain at the summit, especially for the latter 3 nights. There is a possibility for convection in the area as well as periods of heavy snow at the summit mainly between sunrise Sunday and midnight Monday. Daytime clouds will be minimal and short-lived for today, but could begin to pick up tomorrow and turn quite extensive over the following 3-4 days.

Skies will remain clear for tonight, but patches of mid/upper-level clouds are expected to spread in from the NW through tomorrow night. More organized thick clouds will drift in from the north on Saturday and merge over/near the summit area with banding high clouds drifting in from the south later that night. There is very good chance that the former set will push southward, while more thick clouds develop over the summit for much of Sunday and Monday. Regardless, these clouds will likely contribute to periods of extensive cloud cover or even overcast skies for Saturday, Sunday and Monday night.

Precipitable water is expected to linger near 1.5 mm for tonight, then jump to 4+ mm for the following 4 nights.

Diminishing turbulence in the free atmosphere and relatively calm summit skies should allow for seeing to settle in near 0.45-0.5 arcseconds for tonight and perhaps even for early tomorrow evening. However, building instability and upper-level turbulence could degrade seeing during that latter night. Eventually boundary layer turbulence will further degrade seeing toward 1+ arcseconds for Saturday night and especially the following 2 nights.

Although the mid-level ridge will continue to shift off toward the east in response to a late-season trough building to the northwest, the ridge will remain close to support large-scale subsidence in the area over the next 24-30 hours. This subsidence will help maintain the inversion near 8-9 thousand feet and ensure a dry/stable and relatively calm/clear summit-level air mass during this time. The forementioned trough is set dig southward and deposit a cut-off low to the north of the state through tomorrow night. This low is then set to gradually sag southward over the state, before rapidly weakening and shift off toward the east around the middle part of next week. Nonetheless, this low will bring widespread instability and moisture to the area, which will help erode the inversion between late Friday night and Saturday afternoon. This will eventually lead to a saturated and very unstable air mass, likely allowing extensive fog, high humidity, ice and/or light flurries to plague the summit for the remainder of the forecast period. Conditions could deteriorate further as more focused instability and and upper-level diffluence within the center of the low and its eastern flank shifts over/near the Big Island between sunset on Sunday and midnight Monday. This could support the development of organized convection over/near the Big Island, which could deposit heavy snow at the summit during that period. In addition, winds are still scheduled to strengthen significantly (to 50+ mph), which may contribute to large drifting (and certainly boundary layer turbulence) for Sunday and Monday. Conditions/skies are set to improve as this low weakens and shifts out the area, allowing the ridge to restrengthen to the north around Tuesday/Wednesday.
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 Apr 27 - 2 PM0-20Clear0 / 06.5E/5-15NaN1-2
8 PM0-5Clear0 / 01.5ESE/5-150.4-0.61.25-1.75
Fri Apr 28 - 2 AM0-5Clear0 / 00.5SE/5-150.35-0.551.25-1.75
2 PM20-404-520 / 55N/0-10NaN2-4
8 PM20-406-825 / 5-0.5NNW/0-100.4-0.64-6
Sat Apr 29 - 2 AM40-606-840 / 5-1WSW/5-150.55-0.854-6
2 PM60-804-880 / 403WSW/10-20NaN4-8
8 PM60-804-680 / 40-2WSW/15-300.7-1.14-8
Sun Apr 30 - 2 AM80-1004-890 / 80-3SW/25-400.9-1.56-10
2 PM80-1004-1095 / 90-1SW/40-60NaN8-12
Mon May 01 - 2 AM80-1004-1095 / 85-6SW/50-701-28-12
2 PM80-1004-1095 / 90-2SW/50-70NaN8-12
Tue May 02 - 2 AM70-904-990 / 60-7WNW/35-501-24-8
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
Thu Apr 27 - Fri Apr 28 18:53 20:01 4:37 5:45 N/A 20:36 5 4 14.9 15 41
Fri Apr 28 - Sat Apr 29 18:54 20:02 4:36 5:45 N/A 21:41 12 5 16.2 17 49
Sat Apr 29 - Sun Apr 30 18:54 20:02 4:36 5:44 N/A 22:43 21 6 17.6 18 43
Sun Apr 30 - Mon May 01 18:54 20:03 4:35 5:43 N/A 23:42 31 7 18.1 18 21
Mon May 01 - Tue May 02 18:55 20:03 4:34 5:43 N/A 0:36 42 8 16.5 16 50
Forecast Issued by: Ryan Lyman
Next update at 5 PM HST Thursday 27 April (0300 UTC Friday 28 April) 2017.
Additional Information
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