Current Conditions
Temp7.6 C
RH14 %
WindNNW 12 mph
RoadClosed
Mauna Kea Observatories Forecast
5 PM HST Thursday 15 August (0300 UTC Friday 16 August) 2019
Warning(s)
Increasing winds
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, while broken high clouds currently filling in from the SSW are set to stream along the northern skies after passing over the summit area early this evening.
Summary of Key Meteorological Variables
Summit temperatures will be near 4.5 C, with winds from the east 15-30 mph for the night. Seeing will likely be near 0.9-1 arcseconds, while precipitable water is expected to be in the 0.9-1.1 mm range for the night.
Discussion
A strong well-defined inversion will continue to cap low-level moisture near primarily near 8 thousand feet and ensure the summit remains dry and stable through at least early Monday evening. There is a small chance that a patch of fairly deep tropical moisture will fill in from the east, lift the inversion and increase the risk for fog, high humidity and light rain at the summit mainly toward the end of Monday night. Daytime clouds will be relatively minimal and short-lived through Monday, but could pick up on Tuesday.

The high clouds currently filling in from the SSW are set to stream along the northern skies after passing over the summit area early this evening. It will eventually help form a band of steady high clouds which will sag southward, pass directly over the summit and contribute to a brief period of extensive cloud cover if not overcast skies for tomorrow evening. This band will slip southward early Saturday morning, leaving only residual patches of high clouds mainly to the east of the Big Island for the remainder of the weekend. More high clouds may band up along the southern skies for the early part of next week.

Precipitable water is expected to linger near 1 mm for tonight, then increase to and probably settle in near 2-2.25 mm for the remainder of the forecast period.

Another round of boundary layer turbulence will likely contribute to poor seeing over the next 2 nights. Boundary layer turbulence is set to subside with winds through Saturday, allowing seeing to return toward more average-like values for that night and probably slip toward 0.5 arcseconds for Sunday night and early Monday evening, at least. A possible influx of moisture could degrade seeing toward sunrise on Tuesday.

No change since the morning forecast...The mid/low-level ridge will continue to sit to the north of the state well into next week, and will actually expand westward as the tropical upper-tropospheric trough to the NW lifts northward and weakens, allowing an upper-level ridge to fill in from the west over the next 48 hours. Nevertheless, the ridge will promote steady/strong large-scale subsidence in the area, which will help maintain a well-defined inversion near 7-8 thousand feet and ensure a dry/stable summit-level air mass into at least the early part of next week. Unfortunately, winds are set to pick up again as the mid-level portion of the ridge expands westward over the next 48 hours. This will stir up boundary layer turbulence and contribute to poor seeing over the next 2 nights. High clouds will also continue to fill in from the south (toward the TUTT), via the sub-tropical jet to the NW of the state during this time. There is a good chance that the bulk of the high clouds will pass along the northern skies for tonight, but will sag southward and over the summit area, contributing to extensive cloud cover mainly around tomorrow evening. The bulk of these clouds will slip to the southern and eastern skies, opening up most of the sky probably for the remainder of the weekend. Winds are also set to diminish as the ridge retracts further northward through Saturday, allowing seeing to improve through that night and probably settle in near 0.5 arcseconds for Sunday and most of Monday night. Longer-term projects suggest that a tight upper-level low will form to the south of the Big Island as a remnant tropical storm/wave fills in from the east around Tuesday. This combination could erode the inversion (despite the presence of the persitent ridge to the north) and increase the risk for moisture at the summit around sunrise on Tuesday.

Please Note: There will be no forecasts on Friday, August 16, in observance of Statehood Day. The normal forecast schedule will resume on Monday, August 19.
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 Aug 15 - 8 PM50-709-100 / 04.5E/15-300.6-1.20.9-1.1
Fri Aug 16 - 2 AM30-509-100 / 04E/15-300.7-1.30.9-1.1
2 PM50-708-100 / 010ESE/20-35NaN1-2
8 PM70-908-90 / 05E/20-350.9-1.51.75-2.25
Sat Aug 17 - 2 AM50-708-8.50 / 04ESE/15-300.7-1.32-2.5
2 PM10-309.5-100 / 010ENE/10-20NaN2-3
8 PM0-20Clear0 / 05NE/10-200.5-0.92-2.5
Sun Aug 18 - 2 AM0-20Clear0 / 04NE/10-200.5-0.81.75-2.25
2 PM0-20Clear0 / 09.5NE/5-15NaN2-4
Mon Aug 19 - 2 AM0-10Clear0 / 04.5NNE/5-150.4-0.62-3
2 PM0-20Clear0 / 010NNE/5-15NaN2-4
Tue Aug 20 - 2 AM0-20Clear30 / 104.5ENE/5-150.4-0.82-3
2 PM60-804-1060 / 208ESE/10-20NaN3-6
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
Sun Aug 18 - Mon Aug 19 18:57 20:05 4:47 5:54 21:01 N/A 86 0 42.4 -1 35
Mon Aug 19 - Tue Aug 20 18:57 20:04 4:47 5:54 21:35 N/A 79 1 26.9 3 00
Tue Aug 20 - Wed Aug 21 18:56 20:03 4:47 5:55 22:11 N/A 71 2 12.2 7 29
Wed Aug 21 - Thu Aug 22 18:55 20:02 4:48 5:55 22:48 N/A 61 2 59.2 11 43
Thu Aug 22 - Fri Aug 23 18:54 20:01 4:48 5:55 23:28 N/A 51 3 48.6 15 30
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Monday 19 August 2019.
Additional Information
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