Current Conditions
Temp5.3 C
RH9 %
WindNNE 2 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Friday 29 July (0300 UTC Saturday 30 July) 2016
Warning(s)
None
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, but high clouds will continue to pass along the southern skies through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 4 C this evening and 3.5 C tomorrow morning. Winds will light and from the NNW for today, switching to a more SW direction later in the night. Seeing will be near 0.6-0.65 arcseconds, while precipitable water is expected to be in the 0.7-0.9 mm range for the night.
Discussion
The tradewind inversion will continue to cap low-level moisture near 7-8 thousand feet and ensure the summit remains dry and stable through Sunday morning. However, there is a chance that the inversion will breifly weaken/lift toward 12 thousand feet, which will increase the risk for periods of fog and high humidity between Sunday afternoon and early Monday evening; precipitation is unlikely. The inversion is set to recover near 8 thousand feet by midnight Monday, ensuring the summit steers free of fog/high humidity for the remainder of the forecast period. Daytime clouds will be minimal and short-lived through tomorrow, but could pick up for Sunday and Monday, then taper again for Tuesday.

There is a possibility that high clouds passing just south of the Big Island will pass over/near the summit through the weekend, and especially for most of Sunday. These clouds are set to shift eastward and/or dissipate on Monday, leaving clear skies again for the remainder of the forecast period.

Precipitable water is expected to linger near 0.8 mm for tonight, increase toward 3 mm for Saturday night and probably to 4+ mm for the following 3 nights.

Despite relatively calm skies in the free atmosphere, pockets of low-level turbulence will likely contribute to slightly poorer than average seeing over the next 2 nights. There is a possibility that a patch of upper-level turbulence/instability will further degrade seeing for Sunday night, but seeing should return toward more normal values or better as this source of turbulence subsides for the early part of next week.

No change since the morning forecast...The mid/low-level ridge will continue to sit to the north of the state and promote relatively steady large-scale subsidence in the area well into next week. While this subsidence will help maintain the inversion near 7-8 thousand feet and ensure the summit remains dry and stable for the next 2 nights, moisture/instability associated with a weak mid/upper-level trough/low (moving in from the east and eventually) passing over/near the Big Island may briefly lift the inversion toward 12 thousand feet between Sunday afternoon and early Monday evening. This could raise the stakes on short-lived fog and high humidity at the summit mainly for Sunday night; precipitation is very unlikely. In addition, pockets of low-level turbulence out ahead of and within this low/trough may contribute to poorer than average seeing through the weekend. PW, on the other hand, may benefit from the extra subsidence on the western side of the low and linger near 0.8 mm for tonight. However, mid-level tropical moisture/clouds drawn toward the low is expected to increase PW and CC over the remainder of the weekend. Skies are set to open up as the bulk of the clouds shift eastward and the low dissipates early next week. While this decay of the low should allow the ridge to regain control of the atmosphere and ensure the summit steers free of further periods of fog/high humidity during that time, linger mid-level moisture will likely keep PW near 4 mm 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 Jul 29 - 8 PM0-209.5-100 / 04NNW/0-100.5-0.70.7-0.9
Sat Jul 30 - 2 AM10-309.5-100 / 03.5SW/0-100.5-0.80.7-0.9
2 PM20-409.5-100 / 08.5SW/5-15NaN1-2
8 PM20-409-100 / 03SSW/5-150.5-0.82-3
Sun Jul 31 - 2 AM40-608-100 / 03SSW/10-200.5-0.72.5-3.5
2 PM60-804-1060 / 156.5SW/10-20NaN3-6
8 PM40-608-1060 / 52.5WSW/5-150.6-0.94-6
Mon Aug 01 - 2 AM20-409-1050 / 52SW/10-200.6-0.84-6
2 PM20-404-4.540 / 57WSW/10-20NaN4-6
Tue Aug 02 - 2 AM0-5Clear0 / 02.5SW/5-150.45-0.654-6
2 PM0-20Clear0 / 08WSW/0-10NaN3-5
Wed Aug 03 - 2 AM0-5Clear0 / 03.5ENE/5-150.4-0.63-5
2 PM0-20Clear0 / 010ENE/10-20NaN4-6
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
Fri Jul 29 - Sat Jul 30 19:09 20:19 4:37 5:48 2:51 N/A 14 5 35.1 17 39
Sat Jul 30 - Sun Jul 31 19:09 20:19 4:38 5:48 3:48 N/A 7 6 33.2 17 56
Sun Jul 31 - Mon Aug 01 19:08 20:18 4:38 5:48 4:46 17:31 3 7 30.5 17 08
Mon Aug 01 - Tue Aug 02 19:08 20:18 4:39 5:49 5:43 18:23 0 8 26.0 15 22
Tue Aug 02 - Wed Aug 03 19:07 20:17 4:39 5:49 6:39 19:12 0 9 19.3 12 46
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Monday 1 August 2016.
Additional Information
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