Current Conditions
Temp1.4 C
RH64 %
WindESE 5 mph
RoadOpen
Mauna Kea Observatories Forecast
5 PM HST Wednesday 22 October (0300 UTC Thursday 23 October) 2014
Warning(s)
Evening fog/high humidity
Cloud Cover and Fog/Precipitation Forecast
There is a chance for fog, high humidity and summit-level clouds, mainly for this evening; precipitation is unlikely.
Summary of Key Meteorological Variables
Summit temperatures will be near 2 C with winds from the NE at 5-15 mph. Seeing will start out near 0.75 arcseconds, but improve toward 0.55 arcseconds through the night. Precipitable water is expected to be in the 2-4 mm range for the first half of the night and 1-2 mm range for the second half.
Discussion
The atmosphere will remain a bit moist and unstable, which may allow for fog and high humidity mainly through this evening. The inversion is set to rebuild near 7-8 thousand feet during the second half of the night and will ensure a dry/stable air mass by sunrise and especially tomorrow night. However, another patch of moisture/instability is expected to breakdown the inversion and increase the risk for fog, high humidity and light rain at the summit between late Friday morning and early Saturday evening. The inversion will strengthen through the latter night, which will allow conditions to return to normal later that night and for Sunday night. Daytime clouds will taper for tomorrow, pick up again on Friday and Saturday, then become minimal and short-lived for Sunday and early part of next week.

There is a possibility for summit-level clouds for this evening, but these clouds are expected to dissipate and/or shift off toward the southwest, opening up skies as the night progresses and especially for tomorrow night. However, a patch of mid/summit-level clouds may slip through the area again, perhaps contributing to periods of extensive cloud cover for Friday night. This patch is also expected to drift off toward the southwest, leaving predominately clear skies for Saturday and Sunday night.

Precipitable water may start out near 4 mm early this evening, but will quickly drop toward 1 mm by the end of the night and settle in near 0.9 mm for tomorrow night. There is a good chance that it will increase back to 4+ mm for Friday night, then slip to 1 mm again for most of Saturday night and Sunday night.

Lingering low-level turbulence may contribute to poor seeing for this evening, but seeing is expected to improve toward more average-like values as this turbulence subsides through the night. While seeing will likely settle in near 0.45-0.5 arcseconds as minimal turbulence persists in the atmosphere for tomorrow night, another patch of turbulence may disrupt seeing again for Friday night and perhaps Saturday evening. Seeing should drop back toward 0.5-0.55 arcseconds as this turbulence moves out of the area during the latter night and for Sunday night.

No change since the morning forecast...A patch of moisture/instability sliding in from the northeast is expected to breakdown the inversion for much of today, which may allow for summit-level clouds, fog, high humidity and perhaps light rain through this evening. Fortunately, the patch is slated to shift off toward the southwest late this evening, allowing the ridge to north to regain control of the atmosphere, rebuild the inversion near 6-7 thousand feet and practically ensure the summit remains dry and stable for the second half of the night and especially tomorrow night. It will also help to improve summit skies and allow seeing and PW to settle in near 0.45-0.5 arcseconds and 0.8-1 mm, respectively mainly for tomorrow night. However, another patch of moisture is expected to slide in from the NE around the same time that an upper-level trough drifts in from the east between late Friday morning and early Saturday evening. These features may help erode the inversion and likely bring another round of moisture and turbulence to the summit during that time. Conditions and skies are expected to improve as this patch slides off toward the southwest, the trough shifts back to the east and a deep ridge tries to fill in to the northwest through the remainder of the weekend.
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 Oct 22 - 8 PM20-404-4.575 / 152NE/5-150.6-0.92-4
Thu Oct 23 - 2 AM0-20Clear15 / 02NNE/5-150.5-0.61-2
2 PM0-20Clear0 / 08NNE/5-15NaN1-2
8 PM0-10Clear0 / 03NE/5-150.45-0.550.8-1
Fri Oct 24 - 2 AM0-10Clear0 / 02.5NNE/5-150.4-0.50.8-1
2 PM40-604-560 / 156NE/5-15NaN2-4
8 PM50-704-675 / 251ENE/10-200.6-14-6
Sat Oct 25 - 2 AM50-704.5-675 / 250.5ENE/10-200.7-1.14-8
2 PM40-604-675 / 306ENE/5-15NaN4-8
Sun Oct 26 - 2 AM0-20Clear0 / 02ENE/5-150.5-0.71-2
2 PM0-20Clear0 / 07ENE/10-20NaN1-2
Mon Oct 27 - 2 AM0-20Clear0 / 02.5NE/5-150.45-0.651-2
2 PM0-20Clear0 / 08.5E/10-20NaN2-4
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 Oct 22 - Thu Oct 23 18:02 19:07 5:06 6:10 6:02 17:30 0 13 30.2 -9 07
Thu Oct 23 - Fri Oct 24 18:02 19:07 5:06 6:11 6:55 18:11 0 14 19.6 -12 24
Fri Oct 24 - Sat Oct 25 18:01 19:06 5:06 6:11 N/A 18:56 2 15 11.0 -15 11
Sat Oct 25 - Sun Oct 26 18:00 19:05 5:06 6:12 N/A 19:44 7 16 04.6 -17 15
Sun Oct 26 - Mon Oct 27 18:00 19:05 5:07 6:12 N/A 20:36 13 16 59.9 -18 26
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Thursday 23 October 2014.
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