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#52070 - 09/06/17 11:54 AM Contradicting info between NOAA and mountain-forecast
sankar Offline


Registered: 08/20/17
Posts: 8
Loc: Redwood City, California
Hello
I am planning to camp at Outpost on this Saturday, Sep 9 and do the summit hike on Sunday Sep 10.

NOAA says sunny Saturday and slight chance of rain on sunday afternoon.

mountain-forecast says the complete opposite. Clear sunday, but snow showers on Saturday.

And NOAA reports keep changing every few hours.

To make it worse, once I reach outpost, I will not have any way to find the latest weather changes.

Just wanted to hear experts advice on how to follow this changing weather pattern.

Thanks,
sankar

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#52083 - 09/07/17 07:21 AM Re: Contradicting info between NOAA and mountain-forecast [Re: sankar]
Halfdomer Homer Offline


Registered: 04/07/16
Posts: 20
Loc: Los Angeles, CA
I am in the same situation except I am day hiking on Sat Sept.9. NOAA says it is much warmer on the summit than mountain-forecast does. Below freezing for summit reported on MF. NOAA says low 40's. I am planning for near freezing. And one says rain and the other says clear, go fig. Have a safe one! Maybe I'll see you on the way down.


-Dan

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#52084 - 09/07/17 07:36 AM Re: Contradicting info between NOAA and mountain-forecast [Re: sankar]
SierraNevada Offline


Registered: 09/05/11
Posts: 1098
Loc: NorCal
Be careful about mountain-forecast predictions. They are computer generated without much human review. They're trying really hard to make detailed adjustments for mountain terrain. I would consider them experimental, but useful if you combine with other forecasts.

I'm not an expert, but here's how I would interpret this weekend on Mt Whitney:

mountain-forecast predicts no precipt on Saturday and 0.4" of snow Sunday PM at 4418m with is AT THE SUMMIT. PM means sometime between noon and midnight. Converting 0.4" to rain is about 0.05". Either way, its just a trace of precip.

NWS also attempts pin-point forecasts adjusted for elevation. Default location is 12,000 ft (Trail Camp). They are forecasting a slight chance to 20% chance of rain or snow starting after 11am Saturday all through the weekend.

Accuweather for Whitney Portal forecasts a "shower in spots" 0.04" Saturday and Sunday afternoon.

1. Looks like a small storm system is moving into the area. 2 models predict it will arrive Saturday around noon. The other model predicts it will arrive Sunday afternoon.

2. Precip amounts are very small for all 3 models, a few hundreds of an inch. Could be some snow or sleet mixed in at upper elevations near the summit. Some afternoon thunder is mentioned and I would expect that even if it doesn't rain.

3. Wind forecast for all 3 models is light (5-15 mph). Always anticipate winds on the summit.

4. All temps are above freezing, but I'd be ready for 32F at night.

All in all, the 3 forecasts are not that far off, and taken together, they paint a clear picture of what to expect - a mildly stormy weekend, mostly cloudy, occasional light rain, perhaps sleet or snow on upper mountain but no large amounts expected, generally breezy, windy at summit, day temps 40s and 50s, near freezing over night. Not bad for climbing if you bring the right layers. Could be some nice partly cloudy skies for good pictures at times.

This wouldn't worry me at all. It should be within your expectations for September. Have a great trip.


Edited by SierraNevada (09/07/17 07:45 AM)

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#52088 - 09/07/17 09:17 AM Re: Contradicting info between NOAA and mountain-forecast [Re: SierraNevada]
Steve C Offline


Registered: 09/22/09
Posts: 7224
Loc: Fresno, CA
Excellent explanation, SN. Thanks!

NOAA default location shows elevation of 12,000. I've clicked-around on their map, and this location returns an elevation of 13,110'. It is the quadrant containing Tulainyo Lake, which is just north of Mt Russell.

NOAA link: http://forecast.weather.gov/MapClick.php?lat=36.6&lon=-118.28

It's the link for the NOAA "Whitney summit weather" link on the Mt Whitney Weather page, which is always available above on the left.

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#52089 - 09/07/17 09:32 AM Re: Contradicting info between NOAA and mountain-forecast [Re: Steve C]
sankar Offline


Registered: 08/20/17
Posts: 8
Loc: Redwood City, California
Thank you everyone for your comments.
SN, great explanation. It gives me a good idea of what to expect. Being a first timer, I am going to play safe. I am preparing myself to turn-around at any time based on the weather and my physical conditions.

One dumb question: I understand that even if there is a slight chance of T-storm at the summit, anywhere from trail camp and above will be unsafe. what about outpost area?

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#52090 - 09/07/17 10:26 AM Re: Contradicting info between NOAA and mountain-forecast [Re: sankar]
SierraDave Offline


Registered: 09/03/17
Posts: 12
Loc: Sacramento, California
Sankar,

Great question and good luck. A first timer myself for this weekend, I was thinking the same thing.

See you on the trail.

SD

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#52101 - 09/07/17 06:15 PM Re: Contradicting info between NOAA and mountain-forecast [Re: SierraDave]
SierraNevada Offline


Registered: 09/05/11
Posts: 1098
Loc: NorCal
Based on the forecast, I wouldn't expect lightening strikes to be a concern, especially not in the mornings. To maximize safety, get an alpine early start and try to get off the summit by noonish and you should be fine.

Most likely you'll just hear some rumbling thunder from cloud-cloud electrical activity in the distance. You probably won't even see a flash, but if you do, count the seconds and use that as a guide to decide. Sound travels at about 5 seconds per mile.

The most common dangerous lightning in the southern Sierra is during afternoon monsoonal thunderstorms driven by hot air from the southern desert in the summer heat. This is a cool fall storm, but don't let your guard down entirely just because I wrote that.

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#52102 - 09/07/17 07:12 PM Re: Contradicting info between NOAA and mountain-forecast [Re: SierraNevada]
sankar Offline


Registered: 08/20/17
Posts: 8
Loc: Redwood City, California
Thank you again SN for the reply.
I am planning to start around 2am from OutPost camp for the summit day. Can't wait.

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#52103 - 09/07/17 07:39 PM Re: Contradicting info between NOAA and mountain-forecast [Re: sankar]
Debster Offline


Registered: 07/02/17
Posts: 4
Loc: Ca, Seal Beach
My husband and I went on Wednesday, Sept.6, 17. We left to attempt a one day summit with clear weather, full moon and a forecast for little rain .01 inches. We turned around right before Trail Camp because of dark clouds rolling in. People were laughing and saying we don't need to turn around because their gps said only 10% chance of rain. When we passed Lone Pine Lake and the log bridges the rain started pouring down thick and there was thunder and lightning!!! The trail turned into a river. We were thankful that we turned around when we did.

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#52109 - 09/07/17 09:37 PM Re: Contradicting info between NOAA and mountain-forecast [Re: sankar]
Steve C Offline


Registered: 09/22/09
Posts: 7224
Loc: Fresno, CA
Just so everybody knows...

Lightening ain't the same as lightning. grin   Lightening can't hurt you. The other can. smirk

I normally wouldn't post, but I fixed the word twice above. laugh

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#52129 - 09/11/17 08:29 AM Re: Contradicting info between NOAA and mountain-forecast [Re: Steve C]
SierraNevada Offline


Registered: 09/05/11
Posts: 1098
Loc: NorCal
Got it, Steve. Lightning lightens up the sky.

Just for chuckles, how did the actual weather compare to the forecasts for last weekend? Anybody?

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#52135 - 09/11/17 10:59 PM Re: Contradicting info between NOAA and mountain-forecast [Re: SierraNevada]
SierraNevada Offline


Registered: 09/05/11
Posts: 1098
Loc: NorCal
So how did the forecast do this particular weekend? None predicted much of a storm, wind < 15 mph. Chance of rain, about 0.05" if it happened. Only Mountain-forecast mentioned snow - about 0.4" on the summit. Chance of thunder. See above for details.

Since nobody has replied yet here, I'm copying a couple Facebook posts. It seems that the storm was a little bigger than expected, but not unusual. No mention of lightning or lightening.

"...not the greatest weather, as it had snowed overnight at the peak and hail and rain at trail camp. It was cold but bearable."

"We had a weather event every day except Sunday. Rain, snow or hail. I lost count of how many people on the main trail were surprised it was raining, snowing, etc. Many replied they even "checked the weather report". It can rain, snow, sleet pretty much any day of the year in this area."

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#52136 - 09/11/17 11:15 PM Re: Contradicting info between NOAA and mountain-forecast [Re: SierraNevada]
DUG Offline


Registered: 09/22/09
Posts: 367
Loc: Wildomar
My weather event post on FB was Fri-Sun at Grass Lake/LPP and Monday on the main trail/Whitney Peak. Even though it was raining/snowing/hailing at Grass Lake, there might be totally different conditions on the Whitney rail or at the summit.

Doug and Doug Jr did mention that the portal near the store got rain Friday.................................DUG

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#52138 - 09/12/17 08:09 AM Re: Contradicting info between NOAA and mountain-forecast [Re: DUG]
SierraNevada Offline


Registered: 09/05/11
Posts: 1098
Loc: NorCal
Thanks for the clarification, DUG. Hoping to get more reports from the actual trail.

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#52141 - 09/12/17 11:14 AM Re: Contradicting info between NOAA and mountain-forecast [Re: SierraNevada]
sankar Offline


Registered: 08/20/17
Posts: 8
Loc: Redwood City, California
The weather predictions from NOAA is pretty close compared to mountain-forecast.

NOAA forecasted afternoon showers for Friday (9/9), Sat (9/10) and Sunday 9/11.

It was raining (not heavy) on Friday evening at portal campground, and again rained on Saturday evening at Outpost camp.

Sunday, we started the hike from outpost at 1.30am and reached the summit by 8.30am. Weather was excellent. But by the time we were at the bottom of switchbacks, the clouds were covering the summit (but people were going up hill). We reached the parking lot at 4.45 pm and didn't see any rain until that time.

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#52143 - 09/12/17 07:08 PM Re: Contradicting info between NOAA and mountain-forecast [Re: sankar]
SierraNevada Offline


Registered: 09/05/11
Posts: 1098
Loc: NorCal
Congrats, Sankar. Way to go. 1:30 is a really early start from Outpost, but that kept you ahead of the weather.

I read that it ended up snowing on the summit, so mountain-forecast got that somewhat right I guess. They all seemed to underpredict the storm, but not too far off.

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#52161 - 09/13/17 05:05 PM Re: Contradicting info between NOAA and mountain-forecast [Re: SierraNevada]
Harvey Lankford Offline


Registered: 11/10/09
Posts: 984
Loc: Richmond, Virginia
Monday at guitar started light rain at noon, hard rain sleet, hail, lightning, wind from 6pm to midnight,next day Tuesday sept 12 with headlamp start rewarded hikers with some icy rocks above 13,000. On way down we saw helo with litter basket up high, no story yet

Steve, sorry you could not join us through Miter through to Whitney , one ice area we had t detour an hour as microspikes we had were not enough at least in early am. Coming down Crabtree Pass itself dry

More later

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#52162 - 09/13/17 08:59 PM Re: Contradicting info between NOAA and mountain-forecast [Re: Harvey Lankford]
SierraNevada Offline


Registered: 09/05/11
Posts: 1098
Loc: NorCal
It just hit me that we didn't check the local professional forecasters Dennis Mattinson and Howard Sheckter. Major malfunction there. This was a worthwhile exercise to compare NWS, Mountain-forecast, and Accuweather predictions against reality, but it's grossly incomplete without these local experts. Let's do this again and include them next time.

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