Current Conditions
Temp2.3 C
RH24 %
WindNNW 21 mph
RoadOpen
Mauna Kea Observatories Forecast
3 PM HST Friday 24 April (0300 UTC Saturday 25 April) 2015
Warning(s)
None
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 4 C this evening and 1.5 C tomorrow morning. Winds will be light and from the ESE, with seeing around 0.6 arcseconds. Precipitable water is expected to linger close to 2mm for the night.
Discussion
The tradewind inversion will continue to cap low-level moisture near 7 thousand feet and ensure dry and stable air masses through at least Sunday morning. There is a possibility that the inversion will lift/weaken toward 10-12 thousand feet as a band of low-level moisture drifts into the area, raising the stakes on periodic fog at the summit for Sunday, Monday and perhaps Tuesday night; precipitation is unlikely. Daytime clouds will be minimal and short-lived through tomorrow, but could pick up over the next few days.

Mid-High clouds overhead are breaking down and will slowly sag southward through this evening, leaving mostly residual pockets of isolated clouds in the area into Sunday evening. However, more high clouds will start to stream in from the southwest later that night, growing more organized and widespread for the early part of next week.

Precipitable water will linger near 2 mm for tonight, increase toward 3 mm for tomorrow night and likely exceed the 4 mm for the following 3 nights.

Light/moderate turbulence will persist in the free atmosphere, likely contributing to slightly poorer than average seeing for the next 2 nights. An influx of mid/low-level turbulence may further degrade seeing particularly for Sunday and Monday night. There is a possibility that this turbulence will begin to subside on Tuesday, allowing seeing to start to improve for that night.

Not much is changed since this morning forecast... Although the low to the northwest of the Islands will slowly shift off toward the NE over the weekend, the mid/low-level ridge will continue to linger just north of the Big Island and promote relatively strong/steady large scale subsidence in the area through at least Sunday morning. This will help maintain the tradewind inversion near 7 thousand feet and ensure the summit remains dry and stable over the next 2 nights. Skies are also expected to open up as the stream of high clouds shift off toward the SE with the slow migration of the low over the next 12-18 hours. However, there is a possibility that the low will bring a decaying low-level front over the Big Island as it slips further eastward around Sunday morning. This band is slated to stall in the area as the low weakens significantly and rapidly drifts off toward the NE with a passing trough later that night. While the departure of the low will limit the instability in the area, the residual moisture associated with the front is expected to weaken/lift the inversion toward 11-12 thousand feet and raise the stakes on fog at the summit for Sunday night and perhaps the early part of next week. Models expect this moiture to persist in the area until the middle/later part of the week, despite the building of a new (albeit weak) mid-level ridge around Tuesday/Wednesday. I suspect this is a little overdone and the inversion should start to rebuild perhaps as early as Tuesday morning. However, weak winds at and above the summit may allow some mid-level moisture to persist, which could result in high PW and humidity near 40-60% 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 Apr 24 - 8 PM20-407.5-100 / 04E/5-150.45-0.752-2.5
Sat Apr 25 - 2 AM0-20Clear0 / 01.5ESE/5-150.45-0.751.75-2.25
2 PM0-20Clear0 / 08W/5-15NaN2-3
8 PM0-20Clear0 / 02.5WNW/5-150.4-0.73-5
Sun Apr 26 - 2 AM10-306-90 / 00.5NW/5-150.4-0.82-4
2 PM10-306-960 / 204W/5-15NaN4-6
8 PM20-405-750 / 101WNW/5-150.5-0.94-6
Mon Apr 27 - 2 AM30-504-740 / 100.5NW/5-150.6-14-6
2 PM60-804-760 / 204NW/5-15NaN4-8
Tue Apr 28 - 2 AM80-1004-740 / 100.5NNW/5-150.8-1.24-8
2 PM80-1004-750 / 204WSW/5-15NaN4-8
Wed Apr 29 - 2 AM50-706-730 / 100.5SW/5-150.6-14-6
2 PM40-606-720 / 103W/5-15NaN4-6
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 Apr 26 - Mon Apr 27 18:53 20:01 4:38 5:46 N/A 2:03 63 9 31.2 10 07
Mon Apr 27 - Tue Apr 28 18:53 20:01 4:38 5:46 N/A 2:41 72 10 17.7 6 49
Tue Apr 28 - Wed Apr 29 18:53 20:02 4:37 5:45 N/A 3:18 80 11 03.4 3 15
Wed Apr 29 - Thu Apr 30 18:54 20:02 4:36 5:44 N/A 3:55 87 11 49.0 -0 30
Thu Apr 30 - Fri May 01 18:54 20:03 4:35 5:44 N/A 4:32 93 12 35.0 -4 17
Forecast Issued by: Ryan Lyman / Tiziana Cherubini
Next update at 10 AM HST (2000 UTC) Monday 27 April 2015.
Additional Information
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