Current Conditions
Temp1.6 C
RH62 %
WindESE 22 mph
Mauna Kea Observatories Forecast
5 PM HST Friday 19 September (0300 UTC Saturday 20 September) 2014
High humidity
Chance for fog/rain
Cloud Cover and Fog/Precipitation Forecast
There is a risk for fog, high humidity and perhaps light rain through the night. Mid/upper-level clouds will also litter the southern skies throughout the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 2.5 C this evening and 2 C tomorrow morning. Winds will be light and from the WSW, with seeing around 0.65-0.7 arcseconds. Precipitable water is expected to exceed 4 mm for the night.
Mid-level moisture is expected to drift in from the south, scraping the summit area and lifting the inversion toward 13-14 thousand feet over the next 48 hours. This will significantly raise the stakes on fog, high humidity and light rain over the next 2 nights. The air mass is slated to dry out allowing the inversion to rebuild back in near 6-7 thousand feet late Sunday morning. This should ensure the summit steers free of fog and precipitation for the following 3 nights. Extensive daytime clouds are possible through Sunday, but will become minimal and short-lived for the early part of next week.

Mid/upper-level clouds will continue to litter the southern skies, occasionally drifting over the summit area for the next 2 nights. The mid-level clouds are slated to dissipate early Sunday morning, but there is a possibility that a patch of high clouds will drift over/near the summit area for that night. Clear skies will prevail as these clouds dissipate and shift off toward the east for Monday and Tuesday night.

Precipitable water is expected to linger near or exceed 4 mm for the next 2 nights, then drop back to the 2-3 mm range for Sunday, Monday and Tuesday night.

Increasing turbulence in the free atmosphere will contribute to poor seeing for tonight and perhaps early tomorrow evening. This turbulence is slated to subside during the latter night, which could help improve seeing toward 0.4 arcseconds for Sunday night. However, strengthening winds will likely stir up boundary layer turbulence and degrade seeing for the early part of next week.

Not much change since the morning forecast...The mid-level ridge is slated to briefly shift off toward the west as a trough passes to the far north over the next 24-36 hours. Although instability associated with the trough will be relatively insignificant, mid/low-level moisture is expected to draw up from the south and scrape the Big Island over the next 48 hours. This will likely push summit-level humidity toward 60-80%, and increase cloud cover as well as the risk for fog and light rain over the next 2 nights. The tropical upper-tropospheric trough is also expected to pass over the summit, which will likely increase turbulence in the free atmosphere and contribute to poor seeing for tonight and probably tomorrow evening. Conditions and seeing is slated to improve as the trough shifts eastward and a deep ridge fills in to the north of the state for Sunday night. However, winds are expected to strengthen once the ridge settles in further eastward for the early part of next week. This could increase boundary layer turbulence and result in poor/bad seeing for Monday and Tuesday night (in fact, probably for much of next week).
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)
Fri Sep 19 - 8 PM20-404-550 / 52.5WNW/5-150.5-0.84-6
Sat Sep 20 - 2 AM20-404-560 / 102WSW/5-150.5-0.94-6
2 PM70-904-890 / 607W/5-15NaN4-8
8 PM20-404-675 / 252S/0-100.5-0.74-6
Sun Sep 21 - 2 AM20-404-575 / 152SW/0-100.45-0.654-6
2 PM40-604-4.540 / 108NW/5-15NaN4-6
8 PM20-409-1010 / 03N/5-150.35-0.452-3
Mon Sep 22 - 2 AM20-409-100 / 03NNE/5-150.4-0.52-3
2 PM0-20Clear0 / 07.5ENE/10-20NaN2-3
Tue Sep 23 - 2 AM0-20Clear0 / 03ENE/15-300.6-0.91.5-2.5
2 PM0-20Clear0 / 08E/15-30NaN2-3
Wed Sep 24 - 2 AM0-20Clear0 / 03E/20-350.7-1.12-3
2 PM0-20Clear0 / 07.5ENE/25-40NaN2-4
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
Sun Sep 21 - Mon Sep 22 18:28 19:32 4:58 6:02 4:48 17:00 3 10 38.1 4 41
Mon Sep 22 - Tue Sep 23 18:27 19:31 4:58 6:02 5:37 17:37 1 11 23.2 0 58
Tue Sep 23 - Wed Sep 24 18:26 19:30 4:58 6:02 6:26 18:14 0 12 08.5 -2 49
Wed Sep 24 - Thu Sep 25 18:25 19:29 4:58 6:03 7:16 18:52 1 12 54.8 -6 34
Thu Sep 25 - Fri Sep 26 18:24 19:28 4:59 6:03 N/A 19:32 4 13 42.3 -10 05
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Monday 22 September 2014.
Additional Information
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