Current Conditions
Temp2.1 C
RH77 %
WindE 0 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Wednesday 18 July (0300 UTC Thursday 19 July) 2018
Warning(s)
None
Cloud Cover and Fog/Precipitation Forecast
There is a small chance for lingering evening fog; precipitation is not expected and dry/stable conditions will return to the summit by the second half of the night (if not sooner). Scattered thin high clouds will continue to pass along the northern skies throughout the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 2.5 C this evening and 2 C this evening. Winds will be from the east at 5-15 mph, while seeing will start out near 0.7 arcseconds, but should improve toward 0.5 arcseconds as the night progresses. Precipitable water is expected to exceed 4 mm through the night.
Discussion
After briefly weakening this morning, the inversion will continue to recover before becoming well-established near 6-7 thousand feet by late this evening and for the remainder of the week. While this will be enough to ensure a dry/stable air mass during the second of the night and for the following 4 nights, there is a small chance for lingering fog for this evening; precipitation is not expected. Daytime clouds will be minimal and short-lived throughout the forecast period.

Scattered high clouds will continue to fill out of the west and pass mainly along the northern skies for tonight. Thicker more widespread mid/upper-level clouds are expected to build in from the SW through Thursday night, then continuously stream overhead contributing to periods of extensive cloud cover or occasionally overcast skies for the following 3 nights.

Precipitable water is expected to linger near or exceed 4 mm through the next 5 nights.

Despite an increase in upper-level turbulence, a drier more stable air mass and calm skies just above the summit should allow seeing to settle in near 0.55-0.6 arcseconds probably for most of the next 5 nights. However, there is a possibility for some variability in seeing should winds die off completely for prolong periods, particularly over the weekend.

No change since the morning forecast...Although the mid/low-level ridge will continue to sit to the north of the state and promote relatively strong/steady large-scale subsidence in the area through the week, deep low-level moisture along the northern flank of a weak tropical system passing to the south elevated the inversion this morning. Fortunately, the bulk of this moisture will continue to slide westward with the low-level trades by this evening, allowing the ridge to regain control of the air mass and strengthen the inversion near 6-7 thousand feet by midnight, if not sooner. Still, there is a small risk for lingering fog mainly for the first few hours of the night; precipitation is not expected and dry/stable conditions will return to the summit for the remainder of the forecast period. Meanwhile the tropial upper-tropospheric trough (TUTT) to the NW will subtly shift southward as an upper-level low develops to the north over the next few days. While neither the TUTT or the low will affect the stability of the atmosphere, the southward progression of the former will help place the sub-tropical jet over or just north of the state for much of the forecast period. This progression of the TUTT will also help flare up convection in the tropics, where the STJ will gain access to its corresponding cirrus exhaust and transport it over/through the summit area, contributing to extensive cloud cover as early as tomorrow night and especially over the weekend. The presence of the STJ and TUTT will hardly have an impact on seeing as mostly laminar westerly flow prevails in the free atmosphere and calm/stable skies prevail at/near the summit. This should allow seeing to settle in near 0.5-0.6 arcseconds once the air mass dries out, but there is a possibility for some variability in seeing should winds cease for prolong periods, particularly over 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)
Wed Jul 18 - 8 PM20-408-1020 / 02.5ENE/5-150.5-0.84-6
Thu Jul 19 - 2 AM10-308-90 / 02ENE/5-150.45-0.654-6
2 PM20-408-100 / 07NE/5-15NaN4-6
8 PM20-407-100 / 03NNE/5-150.4-0.64-6
Fri Jul 20 - 2 AM40-607-100 / 03NNE/5-150.45-0.654-6
2 PM60-806-100 / 08.5NNE/5-15NaN4-6
8 PM60-807-100 / 04NNE/5-150.45-0.654-6
Sat Jul 21 - 2 AM50-707-100 / 03.5NE/5-150.45-0.654-6
2 PM60-807-100 / 09ESE/0-10NaN4-6
Sun Jul 22 - 2 AM70-907-100 / 03.5ESE/0-100.45-0.754-6
2 PM60-807-100 / 08ENE/0-10NaN4-6
Mon Jul 23 - 2 AM60-807-100 / 03ENE/0-100.45-0.754-6
2 PM60-807-100 / 08.5ENE/5-15NaN4-6
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
Wed Jul 18 - Thu Jul 19 19:13 20:25 4:31 5:43 N/A 0:04 45 13 24.2 -4 00
Thu Jul 19 - Fri Jul 20 19:13 20:25 4:32 5:44 N/A 0:44 56 14 13.5 -8 27
Fri Jul 20 - Sat Jul 21 19:13 20:24 4:32 5:44 N/A 1:25 66 15 02.6 -12 26
Sat Jul 21 - Sun Jul 22 19:12 20:24 4:33 5:45 N/A 2:06 75 15 52.1 -15 50
Sun Jul 22 - Mon Jul 23 19:12 20:24 4:33 5:45 N/A 2:49 83 16 42.3 -18 29
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Thursday 19 July 2018.
Additional Information
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