Current Conditions
Temp2.6 C
RH7 %
WindSE 12 mph
RoadOpen
Mauna Kea Observatories Forecast
5 PM HST Monday 28 July (0300 UTC Tuesday 29 July) 2014
Warning(s)
None
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, but there is a chance that isolated patches of high clouds will quickly drift overhead throughout the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 2 C this evening and 2.5 C tomorrow morning. Winds will be light and from the NE, with seeing around 0.5 arcseconds. Precipitable water is expected to be in the 1.5-2 mm range for the first half of the night and 1.25-1.75 mm range for the second half.
Discussion
The tradewind inversion will continue to cap low-level moisture near 7 thousand feet and ensure a dry/stable summit-level air mass through at least Thursday night. There is a possibility that the inversion will weaken as moisture fills into the area on Friday. This will raise the stakes on fog, high humidity and perhaps light rain at the summit for that night. Daytime summit-level clouds will be minimal and short-lived through Thursday, but could pick up on Friday.

Banding high clouds will continue to slip along the southeastern skies, with stray isolated patches occasionally passing overhead mainly for tonight. There is a chance that this band will get reinforced by more high clouds filling in from the tropics and drift back closer to the area through tomorrow night and especially for the following 2 nights. In addition, thicker clouds may drift in from the southeast and combine with these clouds around Friday. This could result in periods of extensive cloud cover mainly for Wednesday, Thursday and especially Friday night.

Precipitable water will linger near 1.5 mm for the next 2 nights, but will likely increase toward 3 mm for Wednesday night and probably exceed 4 mm for Thursday and especially Friday night.

Despite light/moderate turbulence in the free atmosphere, better than average seeing will likely prevail for the next 2 nights. There is a possibility that short-lived mid-level turbulence will degrade seeing toward more average-like values for Wednesday night, but seeing should improve again as this turbulence tapers for the following night. However, an influx of moisture, turbulence and instability could significantly degrade seeing for Friday night.

Changes have been made to the CC forecast....Although the mid-level ridge will remain rather weak/indistinct into the weekend, the low-level ridge will continue to sit just north of the state and instill strong/steady large-scale subsidence in the area during that time. This subsidence will negate the affects of a persistent but weak upper-level trough to the west of the Islands, maintain a fairly solid tradewind inversion near 6-7 thousand feet and ensure a dry/stable summit-level air mass through at least Thursday night. However, the trough and its associated sub-tropical jet will continue to stream high clouds along the southeastern skies through tomorrow evening. There is a possibility that more widespread high clouds will fill in from the southwest, contributing to extensive cloud cover for Wednesday and Thursday night. For the most part, better than average seeing will likely prevail as light/moderate turbulence persists in the free atmosphere over the next 4 nights. There is a possibility fairly good chance that conditions (and skies) will take a turn for the worse as the remnants of tropical storm Genevieve scrapes by to the south starting late Friday afternoon. The deep tropical moisture associated with this remnant storm may interact with the persistent trough's instability and weaken/erode the inversion, perhaps leading to a fairly saturated air mass for much of the weekend. While I suspect that the moisture will slip by further southward, I did increase the risk for extensive fog, high humidity and rain at the summit for Friday night.
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)
Mon Jul 28 - 8 PM10-309-100 / 02NNE/0-100.45-0.551.25-1.75
Tue Jul 29 - 2 AM10-309-100 / 02.5ENE/0-100.45-0.551.25-1.75
2 PM0-209-100 / 07.5WSW/0-10NaN1.25-1.75
8 PM0-209-100 / 02.5W/5-150.45-0.551.25-1.75
Wed Jul 30 - 2 AM0-20Clear0 / 02.5W/5-150.4-0.51.25-1.75
2 PM20-409-100 / 08.5W/0-10NaN1.25-1.75
8 PM40-608.5-100 / 03W/0-100.45-0.652-3
Thu Jul 31 - 2 AM60-808-100 / 03SSW/0-100.45-0.653-4
2 PM70-908-100 / 08S/0-10NaN3-6
Fri Aug 01 - 2 AM70-907-1010 / 02.5SSE/5-150.35-0.553-6
2 PM80-1004-1075 / 255SE/10-20NaN6-10
Sat Aug 02 - 2 AM80-1004-1075 / 402.5SE/15-300.8-1.66-10
2 PM80-1004-1075 / 257ESE/15-30NaN6-10
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
Mon Jul 28 - Tue Jul 29 19:10 20:20 4:37 5:47 N/A 20:22 5 10 13.0 6 25
Tue Jul 29 - Wed Jul 30 19:09 20:20 4:37 5:48 N/A 20:59 10 10 57.8 2 46
Wed Jul 30 - Thu Jul 31 19:09 20:19 4:38 5:48 N/A 21:35 17 11 42.6 -1 03
Thu Jul 31 - Fri Aug 01 19:08 20:18 4:38 5:48 N/A 22:12 24 12 28.1 -4 53
Fri Aug 01 - Sat Aug 02 19:08 20:18 4:39 5:49 N/A 22:51 33 13 14.9 -8 36
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Tuesday 29 July 2014.
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