Current Conditions
Temp4.3 C
RH81 %
WindWSW 8 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
10 AM HST (2000 UTC) Wednesday 28 September 2016
Warning(s)
None
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, but there is a possibility for dissipating high clouds along the western skies through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 7.5 C this afternoon, 2.5 C this evening and 2 C tomorrow morning. Winds will be light and from the NE, with seeing around 0.45 arcseconds. Precipitable water is expected to be in the 1.5-2 mm range during the first half of the night and 1.25-1.75 mm range for the second half.
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 late Friday morning. However, building instability combined with an influx of tropical moisture are expected to erode the inversion, perhaps allowing most of the atmosphere to turn quite saturated for the majority of the next 3 nights. This will significantly raise the stakes on fog, high humidity and rain at the summit during that time. There is also an outside chance for convection in the area particularly for Saturday. Daytime clouds will be minimal and short-lived thorugh Thursday, but could pick up on Friday and turn very extensive over the weekend and into the early part of next week.

There is a possibility for dissipating high clouds along the western skies for tonight. Patches of these clouds may begin to stray further eastward for tomorrow night and could litter the northern skies for Friday night. In addition, there is a good chance that thick clouds will develop over and/or move in from the east, blanketing a good portion of the sky over the weekend.

Precipitable water is expected to increase toward 1.5-1.75 mm for tonight, briefly slop to 1 mm for tomorrow night, then jump to 4+ mm over the weekend.

Predominately calm skies and steady/deep subsidence will prevail in the free atmosphere, which should allow seeing to remain near 0.45-0.5 arcseconds through tomorrow night. However, an influx of low-level turbulence and/or upper-level turbulence/instability are expected to contribute to poor/bad seeing for the next 3 nights.

A combination of the mid/low-level ridge to the north and an upper-level ridge to the south, will allow strong/steady large-scale subsidence to prevail in the area through at least late Friday morning. This subsidence will maintain the inversion primarily near 8-9 thousand feet and ensure the summit remains dry and stable during this time. The upper-level ridge to the south will help keep the sub-tropical jet (STJ) displaced further northward, which will minimize turbulence in the free atmosphere and should allow for good/excellent seeing over the next 2 nights. Unfortunately, conditions and skies are expected to take a turn for the worse thereafter. First, a weak short-wave upper-level trough that passed through the area yesterday is expected stall out just east of the Big Island as the tropical upper-tropospheric trough (TUTT) redevelops to the west of the state over the next 48-60 hours. On one hand, these two features will restrengthen the STJ, which will help kill further development of tropical storm Ulika far to the SE, particularly after the next 24 hours. However, the these features will also draw Ulika's surrounding deep tropical moisture northward, where it will get caught up in the low-level easterly trades and pushed toward the Big Island. The leading edge of this moisture is set to arrive around Friday afternoon/evening and continue to fill in from the east into the early part of next week. This combination of deep tropical moisture and instability from the strengthening TUTT are expected to erode the inversion, which could allow the atmosphere near the Big Island to turn quite saturated between late Friday evening and Monday/Tuesday. This will significantly raise the stakes on fog/high humidty and rain at the summit during that period. There is also a possibility for convection in the area, particularly as the TUTT picks up steam and a more organized patch of tropical moisture passes through on Saturday.
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 Sep 28 - 2 PM0-20Clear0 / 07.5NE/0-10NaN1.5-2.5
8 PM0-209.5-100 / 02.5NE/0-100.35-0.551.5-2
Thu Sep 29 - 2 AM0-209.5-100 / 02NE/0-100.35-0.551.25-1.75
2 PM10-309-100 / 07E/5-15NaN1-2
8 PM10-309.5-100 / 02.5E/5-150.45-0.551-1.2
Fri Sep 30 - 2 AM0-209.5-100 / 02E/5-150.4-0.61-1.2
2 PM20-404-1040 / 106NE/5-15NaN2-4
8 PM40-604-1060 / 152.5ENE/5-150.6-0.93-5
Sat Oct 01 - 2 AM60-804-1075 / 501.5E/10-200.7-1.34-8
2 PM80-1004-1095 / 754ESE/5-15NaN8-12
Sun Oct 02 - 2 AM70-904-1090 / 601ESE/5-150.8-1.68-12
2 PM80-1004-1095 / 704ENE/0-10NaN8-12
Mon Oct 03 - 2 AM70-904-1090 / 601NNE/0-100.7-1.58-12
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
Wed Sep 28 - Thu Sep 29 18:21 19:25 4:59 6:04 5:02 17:12 2 11 20.6 4 33
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
Forecast Issued by: Ryan Lyman
Next update at 5 PM HST Wednesday 28 September (0300 UTC Thursday 29 September) 2016.
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