Weather Discusion , Learning and Questions

Over the last year many people have asked about weather resources including during last nights meeting about having weather discussions and a place to discuss weather and ask questions, Im not a weather guru like others but I just wanted to start the discussion.

here is a link to steves weather resourceshttp://rmhpa.org/messageboard/viewtopic.php?f=9&t=6010

rmhpa has weather links also http://rmhpa.org/weather/

Which i like to read the NWS aviation forecast discussion , NWS soaring forecast in boulder,
and the winds aloft from usairnet http://www.usairnet.com/cgi-bin/Winds/Aloft.cgi?location=DEN&Submit=Get+Forecast&hour=06&course=azimuth

From talking to Steve some things to be weary about in the NWS weather discussion during winter are subsiding air mass, down sloping winds and shortwaves

In the winter in the front range and summer i always look behind the hill and make sure its not west more then 5mph at such as stations like Genesee behind lookout and sugarloaf for boulder.

Hey Gary,

Thanks for the conversation yesterday. The little slide show that I did during 2010 rmhpa.org/downloads/ForecastTools_SF.pdf might be helpful as well when using the resource list that I posted in October.

All of the resources that Jan has added to the Weather links are quite useful as well.

Here are a few things to remember about flying the Front Range over the next few months: 1) The unseasonable warm day is usually due to the heating produced by downslope winds… so look for seasonable to slightly cooler temps with sunshine. 2) A front coming from the pacific NW is rarely good and may be called a shortwave in the discussion - gusty N and NW winds are what generally follow these systems and they are often proceeded by gusty SW winds (both conditions are generally downslope in nature). 3) a low pressure surface trough (yellow dashed line on weather map) to our east can create a pressure gradient that draws the downslope across the isobar lines to feed the trough line in a direction perpendicular to the orientation of the trough line… a significant downslope event can be driven by this kind of feature when it is not to far east of the foothills, particularly if it is high pressure west of the Divide. 4) watch for surface cold fronts diving south out Canada along the east slopes of the Rockies - these can produce good flying because the cold air wedges under the warm air and lifts it, but beware the initial front arriving if it is a strong front (you may need to wait until after initial passage for winds to die a bit)… soaring forecast will often show “poor” because this feature is not captured in that forecast. 5) Nov and Dec are often the transition time for the northern Jetstream to transition to a more southerly track across the US. As a consequence, we will often see the jet right over head. 6) a mention of subsiding airmass in the DEN forecast discussion will generally point to downslope conditions.

Solstice will be here in 30 days or so… everyday gets longer after that and Front Range flying will improve within 30 days or so after Solstice.

SF

WX, weekend of 21/22 May 2016:

A strong low has moved on shore and will be over the Great Basin area. Circulation and compression around this low will bring strong SSW winds to the state on Saturday, stronger on Sunday. Moisture will fetch in on the flow as well with a bit of a dry slot east of the Divide on Saturday. Current winds aloft forecast for 0-12 Zulu (5pm Fri to 5am Sat) indicate mid 20 knots at 9&12K at Den and ALS; 12K at GJT in 30-35 knot range… As the low moves further east, we can anticipate these winds increasing throughout the day on Saturday and well into Sunday. In ortherwords, high winds this weekend; strong potential for squalls and OD west of the Divide on Saturday; squalls and OD more widespread over the mountains and state on Sunday. There is potential for shear issues (velocity rather than directional) aloft too so eastern plains may see a few cells approach severe levels over Friday through Sunday.

Midday gust differential in the mountains on Saturday will be on the order of 20+ when heating really influences things… With base surface winds in the 15 plus range, that means winds will vary between zero (thermal block) and 35+ (thermal downwind) and that means midday is not suitable for our wings. Since winds are forecast to increase throughout the day, evening flights are not likely either (if winds were forecast to ramp down, I would go for the evening in a heartbeat, but that ain’t happening this weekend).

To bad we don’t have a nice south facing ridge well east of Denver Metro area… And to bad we don’t have big old lake out there too 'cause kite boarding and sailing could be great!

It’s the Spring transition time. We would like to see the northern Jet transition to a track north of us and have the lows track further north rather than into the Great Basin track. As El Niño wanes and the tendency for a standing ridge (hot water pool = high pressure) in the Pacific diminishes, we should see things moving in that direction. Hopefully we will have a few weeks in late spring during this time before the monsoon begins to affect us… Sea surface temps off the coast of Baja and SoCal continue to be above average and this will likely contribute to the available moisture fetch when monsoon fires up. NAM Relative Humidity/Lifted Index data coupled with winds aloft data will be very useful when judging if it is prudent to mountain fly over the next 3 plus months. Forecasts will be difficult more than a couple days out from a flying day so watch trends in the forecast updates as the flying day approaches because the trends will clue you in on how fast/slow systems are moving and how they might affect where you would like to fly.

'hope this is of use.

SF

'might see monsoon-like flow starting up by Friday, 24 June. So we had a short window this Spring.

I suspect that Fall should be great in 2016 since we should be in the beginning of a La Niña cycle. Spring 2017 should be much better tha 2015 and 2016 again due to La Niña

Rich might have more details, including a description of a dirty ridge which I suspect that we will see several times over the next 6-8 weeks.

SF