Current Conditions
Temp4.3 C
RH18 %
WindWNW 0 mph
RoadOpen
Mauna Kea Observatories Forecast
5 PM HST Wednesday 30 July (0300 UTC Thursday 31 July) 2014
Warning(s)
None
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, but patches of mid/upper-level clouds are slated to fill in from the southwest throughout the night.
Summary of Key Meteorological Variables
Summit temperatures will be 3 C, with light southerly winds and seeing around 0.4-0.5 arcseconds. Precipitable water is expected to be in the 1-1.5 mm range for the night.
Discussion
The tradewind inversion will continue to cap low-level moisture near 7 thousand feet and keep the mid/summit-level air mass dry and stable through at least midnight Thursday. However, an influx of moisture and instability is expected to dismantle the inversion early Friday morning, which could lead to a saturated atmosphere for that night. This will significantly raise the stakes on extensive fog, high humidity and rain at the summit between early Friday morning and late Saturday afternoon. The odds on moisture at the summit will subside as the atmosphere dries out and the inversion rebuilds through Saturday night (and reaches full strength by Sunday morning). Daytime clouds will be minimal and short-lived through tomorrow, but could turn extensive for Friday and Saturday, only to taper again on Sunday.

A narrow band of patchy mid/upper-level clouds is slated to fill in from the southwest and pass over the summit area during the next 36 hours. There is a strong possibility that thicker clouds will drift in from the southeast and merge with this band, contributing to overcast skies between Friday morning and Saturday morning. These clouds are slated to breakdown and shift out of the area through Saturday, leaving relatively clear skies for that night and especially Sunday night.

Precipitable water is expected to linger near 1.25 mm for tonight, but will abruptly increase to 4+ mm for Thursday, Friday and probably most of Saturday night. It should return toward 2 mm again for Sunday night.

Relatively calm skies should allow seeing to linger neaer 0.45-0.5 arcseconds through tomorrow evening. However, an influx of moisture, instability and mid/low-level turbulence will likely degrade seeing through tomorrow night and probably contribute to poor/bad seeing for at least tomorrow night. Seeing will likely improve with conditions through Saturday night, but increasing low-level/boundary layer turbulence may still contribute to poor seeing through the remainder of the weekend.

No change since the morning forecast...The low-level ridge will continue to sit to the north of the state and promote steady/strong large-scale subsidence in the area through at least midnight Thursday. This will help maintain a fairly well-defined tradewind inversion, negate the affects of a persistent upper-level trough to the west of the state, and ensure a dry/stable summit-level air mass, despite the absence of a prominent mid-level ridge, during this time. The trough will send patches of mid/upper-level clouds over the summit area during this time, and there is a chance that these clouds will thicken a become more widespread as the remnants of TS Genevieve begin to fill in from the southeast late tomorrow night. The deep tropical moisture associated with Genevieve will likely interact with the minor instability produced by the trough and dismantle the inversion near sunrise Friday. This could lead to a saturated atmosphere, which will significantly raise the stakes on extensive fog, high humidity and rain at the summit between sunrise Friday and late Saturday morning. There is also a possibility for convection in the area mainly around Friday afternoon/evening. Conditions are set to improve as the bulk of the moisture slides off toward the west, the mid/low-level ridge strengthens to the north of the state, an upper-level ridge develops over or just south of the Big Island, and the upper-level trough rebuilds further westward near the Dateline starting early Saturday afternoon. Although this will likely help to dry out and warm up the summit-level air mass for the second half of the weekend, there is a possibility that summit-level winds will pick up in response to the deep subsidence in the area during that time.
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 30 - 8 PM20-408-90 / 03S/0-100.4-0.51-1.5
Thu Jul 31 - 2 AM20-408-90 / 03S/0-100.4-0.51-1.5
2 PM40-607-100 / 08SSE/0-10NaN2-4
8 PM60-806-100 / 03SE/0-100.4-0.54-6
Fri Aug 01 - 2 AM80-1005-1050 / 102.5SSE/5-150.5-0.74-8
2 PM80-1004-1090 / 605S/5-15NaN8-12
8 PM80-1004-1095 / 752.5SE/5-151-28-12
Sat Aug 02 - 2 AM80-1004-1090 / 502.5SE/5-150.8-1.68-12
2 PM60-804-860 / 306ESE/5-15NaN4-8
Sun Aug 03 - 2 AM20-406-820 / 53.5ESE/10-200.6-1.24-6
2 PM10-306-70 / 010ESE/10-20NaN3-5
Mon Aug 04 - 2 AM0-20Clear0 / 04ENE/15-300.5-1.12-4
2 PM0-20Clear0 / 011NE/15-30NaN2-4
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 30 - Thu Jul 31 19:09 20:19 4:38 5:48 N/A 21:35 17 11 42.6 -1 03
Thu Jul 31 - Fri Aug 01 19:08 20:18 4:38 5:48 N/A 22:12 24 12 28.1 -4 53
Fri Aug 01 - Sat Aug 02 19:08 20:18 4:39 5:49 N/A 22:51 33 13 14.9 -8 36
Sat Aug 02 - Sun Aug 03 19:07 20:17 4:39 5:49 N/A 23:32 43 14 03.7 -12 04
Sun Aug 03 - Mon Aug 04 19:07 20:16 4:40 5:49 N/A 0:17 53 14 55.2 -15 06
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Thursday 31 July 2014.
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