Warnings Winds will increase towards 40 mph. Cloud Cover and Precipitation Forecast The summit will remain free of fog and precipitation through the night. A narrow band of high clouds will move in from the northwest through the next 24 hours, and cover roughly 10 to 20% of the sky by tomorrow morning. Summary of Key Meteorological Variables Summit temperatures will be near 1 C tonight and 0 C tomorrow morning. Precipitable water is expected to be in the 0.75 to 1.25 mm range tonight and 1 to 1.5 mm range tomorrow morning. Summit winds will be from the NNW at 20 to 35 mph for tonight and 25 to 40 mph tomorrow morning. Shear is expected to be near 50 to 60 mph for tonight and 40 to 50 mph tomorrow morning. Discussion The inversion will remain very strong and well-established at 6-7 thousand feet over the next 36 hours. It is then slated to weaken slightly and increase to 10-11 thousand feet as bands of low-level moisture move in from the northeast beginning Friday and through most of the weekend. While the mid-level air mass will remain quite dry probably through Sunday night, the odds on fog will increase as more and more low-level moisture begins to move in after Friday night. By the beginning of next week, the atmosphere is expected to head toward saturation, in which case there is a good chance for fog and maybe even precipitation. Daytime clouds will be very minimal over the next two days, but will become more extensive over the weekend and into next week. Precipitation is possible on Monday and Tuesday. Narrow fingers of scattered high clouds are expected to occasionally move in from the northwest over the next 3-4 days. The first set is slated to drift in later tonight, and pass over or just to the north of the summit. This band will eventually dissipate, before another finger floats in on Saturday morning. This band will follow the previous band by dissipating before the final one moves in on Sunday afternoon. Overall, mostly clear skies with just a few scattered cirrus are expected for the next 3-4 nights. After that mostly isolated residual cirrus is expected to move in from time to time, while more organized high clouds begin to develop to the northeast. By Tuesday night, cloud cover could begin to increase toward 30%. Precipitable water is expected to bottom out at just less than 1 mm through most of today. After that it will begin a gradual incline; it will be near 1.2 mm tomorrow morning, 1.5 mm tomorrow night, 2 mm on Sunday night, and near 3 mm on Monday night. By Tuesday night it could be > 4 mm. WARNING: Summit winds will continue to increase over the next 24 hours. It is expected to peak at 50 mph, with gusts near 60 mph, Friday afternoon/evening, then slowly subside over the following 2-3 days. A Kona low has developed to the northeast of the state as expected. This low will bring very dry air and relatively clear skies to the summit as the Big Island will be situated on far enough and along the stable southwestern side of the low for the next 24 to 36 hours. As a result, precipitable water is expected to be < 1 mm for at least the first half of the night. However, I suspect the highly variable/bad seeing will continue as the low sends pockets of mid/upper-level mesoscale eddies toward the summit. Moreover, summit level winds are slated to increase towards 50 mph, which will likely produce more locally induced turbulence. After tomorrow evening, the low is expected to move close enough to the islands which may allow conditions at the summit to gradually downhill. Initially, the low will send bands of low-level moisture toward the Islands. This will act to weaken and increase the height of the inversion to 10-12 thousand feet. Thus, the odds on fog will increase as the weekend moves on. Precipitable water will also slowly increase as pockets of mid-level moisture begins to move through. Fortunately, summit level winds are expected to decrease as the low moves too close to the islands and begins to weaken. However, starting Sunday, the low will gain additional upper-level support to allow it to make a final push through the islands. If this works out, it will likely result in a saturated environment for at least the first half of next week. Astronomical Observing Quality Guidance Seeing/Cn2 Images are not available today. Sorry for the inconvenience.

5-day Forecast Summary Graphical Trend

02 pm HST Thu 20 Nov

08 pm HST Thu 20 Nov

02 am HST Fri 21 Nov

02 pm HST Fri 21 Nov

08 pm HST Fri 21 Nov

02 am HST Sat 22 Nov

02 pm HST Sat 22 Nov

02 am HST Sun 23 Nov

02 pm HST Sun 23 Nov

02 am HST Mon 24 Nov

02 pm HST Mon 24 Nov

02 am HST Tue 25 Nov

00 UTC Fri 21 Nov

06 UTC Fri 21 Nov

12 UTC Fri 21 Nov

00 UTC Sat 22 Nov

06 UTC Sat 22 Nov

12 UTC Sat 22 Nov

00 UTC Sun 23 Nov

12 UTC Sun 23 Nov

00 UTC Mon 24 Nov

12 UTC Mon 24 Nov

00 UTC Tue 25 Nov

12 UTC Tue 25 Nov

Cloud Cover (%)

0 to 10

5 to 15

10 to 20

0 to 10

0 to 10

5 to 15

10 to 20

5 to 15

10 to 30

5 to 15

10 to 30

10 to 30

Chance for Fog/Precip (%)

0/0

0/0

0/0

0/0

5/0

10/0

20/0

20/0

30/5

40/0

50/10

50/10

PW (mm, summit upward)

0.5 to 1

0.75 to 1.25

1 to 1.5

1.5 to 2

1.25 to 1.75

1.25 to 1.75

1.5 to 2

2 to 3

2 to 3

2.5 to 3.5

4 to 6

4 to 8

Summit Temp (oC)

4

1

0

4

0

-1

4

0.5

5.5

0.5

5

0

Wind Dir/Speed (mph)     Summit (615 hPa)     19,000 ft (500 hPa)     24,500 ft (400 hPa)     31,000 ft (300 hPa)     35,000 ft (250 hPa)     40,000 ft (200 hPa)     46,000 ft (150 hPa)     54,000 ft (100 hPa)

NNW/20 to 35 NW/23 NNW/29 NNW/61 NNW/78 NNW/81 NW/59 NW/47

NNW/25 to 40 NNW/29 NW/35 NW/59 NW/70 NW/68 WNW/61 NW/41

NNW/25 to 40 NW/29 NW/39 WNW/54 NW/58 NW/61 WNW/61 NW/39

NW/35 to 50 WNW/35 WNW/49 NW/71 NW/87 NW/87 NW/59 WNW/48

NW/35 to 50 NW/42 NW/52 NW/83 NW/90 NW/80 WNW/64 NW/52

WNW/30 to 45 WNW/43 NW/60 NW/80 NW/90 NW/86 WNW/65 NW/45

NW/25 to 40 NW/48 NW/60 NW/69 NW/71 NW/67 WNW/69 NW/44

NNW/20 to 35 NW/34 NW/44 NW/53 NW/62 NNW/77 NW/70 NW/42

WNW/15 to 30 WNW/23 WNW/36 WNW/48 WNW/53 NW/52 WNW/53 WNW/46

W/15 to 30 W/27 WNW/34 WNW/44 WNW/47 WNW/51 WNW/63 WNW/49

W/25 to 40 W/33 W/40 W/52 W/57 WNW/61 WNW/68 WNW/50

W/25 to 40 N/A N/A N/A N/A N/A N/A N/A

 Rise and Set times for the Sun and Moon

Night (HST)	Sun Set	Twilight End	Twilight Beg	Sun Rise	Moon Rise	Moon Set	Illum (%)	RA	Dec
Thu.Nov.20/Fri.Nov.21	17:51	18:58	5:17	6:25	4:02	N/A	9	13 30.7	-6 54
Fri.Nov.21/Sat.Nov.22	17:51	18:58	5:18	6:25	5:05	16:17	3	14 24.8	-13 10
Sat.Nov.22/Sun.Nov.23	17:51	18:58	5:18	6:26	6:13	17:03	0	15 22.6	-18 46
Sun.Nov.23/Mon.Nov.24	17:51	18:58	5:19	6:26	7:22	17:54	0	16 24.2	-23 13
Mon.Nov.24/Tue.Nov.25	17:51	18:58	5:19	6:27	N/A	18:52	3	17 28.9	-26 04

Forecast issued by: Ryan Lyman
rlyman@hawaii.edu
(808) 932-2323

Next update at 5 PM HST Thursday 20 November (0300 UTC Friday 21 November) 2003.
Please call or email to be placed on the Mauna Kea Weather Bulletin email list.

This page was last modified on: Wed, Apr 22 2009 - 2058 UTC
Send comments to: Ryan Lyman