Spring and Summer thread for the Mountains

[MikeGold]

Yesterday's balloon launch by UNC-Asheville Meteorology students.(Photo courtesy of NOAA)

 

 

[Met1985]

A TON of data was indeed gathered from yesterday's storm.  In addition to all the ground based instrumentation(including a very cool ACHIEVE program instrumentation center in Maggie Valley), they put in numerous racing track high altitude flight paths over the Haywood County area and points to the SE to near the location of the NPOL radar site.

 

Here is a snippet of a brief comment that had about yesterday' storm: "..The precipitation forecast did not verify as the frontal precipitation developed into a squall line that, combined with a progressive short wave, propagated east and caused the back side of the precipitation to deteriorate faster than forecast.  This will be a good case to study how the structure of this system differed from progged."

 

The NOXP was active almost the entire time-the crew is worn out and is taking today off.  Reading through the log book..very cool.

 

An example below..they appear to be discussing the echos over my mtn top which is located on the Jackson/Haywood county line.

 

 

0122

The edge of the precip shield had entered Jackson County.  Some higher reflectivity echoes (over 60 dBZ) are forming right ahead of the shield closer to the Jackson/Haywood county line.

0132

Echoes on the Jackson/Haywood line are pulsing but are being overrun by the main precip shield.  Over 60 dBZ now noted up to 5.1 degrees.

0144

A NW to SE oriented line of 60 dBZ echoes moving due north are entering into Jackson & Transylvania counties.

Very very cool Mike! Great info man. Still very cool to have these people in our back yard.

[Met1985]

Was quite the cold morning here at home this morning with a low or 34 degrees! Did not have any frost this morning but we had a slight breeze most of the night.

[MikeGold]

Was quite the cold morning here at home this morning with a low or 34 degrees! Did not have any frost this morning but we had a slight breeze most of the night.

 

30 this morning up top. It could be worse..for instance it is snowing in Northern Michigan this morning!

[Met1985]

30 this morning up top. It could be worse..for instance it is snowing in Northern Michigan this morning!

Lol I saw that. I think this weekend could be interesting with the convective showers moving in and cold air aloft. Maybe just an outside chance at seeing some frozen precip. Anyway crazy weather up in Michigan and Illinois.

[MikeGold]

Couple of charts I prepared this morning showing the rather dramatic differences in rainfall from the top of my mtn vs down below in Waynesville. Down sloping absolutely decimates the rain that falls in Waynesville. Note that the effects are probably more dramatic than depicted as I estimate that the Mt. Lyn Lowry location is at least 20% low to due poor rain catch during wind events.

 

 

[Hvward]

Thanks for putting that together Mike.  Nice info and a testament to the effects of down sloping.  It would be neat to see this type of analysis for each 6000' peak and following valley.  Then we could compare and contrast how the elevation departure coincides with down sloping and rainfall differences.  Obviously that would take a while to compile but nonetheless would be interesting.  On a side note, most of the Hi-res models want to break out convection across SW WNC and possibly buncombe co. again today.  Just another day in the mountains.

 

 

 

...OH VALLEY TO CENTRAL/SRN APPALACHIANS TODAY...
   ISOLATED LOW-TOPPED THUNDERSTORMS WILL BE POSSIBLE FROM LATE MORNING
   INTO THE AFTERNOON IN ASSOCIATION WITH THE MIDLEVEL THERMAL
   TROUGH/COLD POOL.  THOUGH LOW-LEVEL MOISTURE WILL REMAIN
   LIMITED...500 MB TEMPERATURES OF -26 TO -28 C WILL COMBINE WITH
   DAYTIME HEATING TO SUPPORT LOW-MIDLEVEL LAPSE RATES NEAR 7 C/KM AND
   WEAK SURFACE-BASED BUOYANCY.

[MikeGold]

As is normally the case..upslope areas along the Blue Ridge did very well along with some enhancement in the Balsams.

 

 

[MikeGold]

Heavy snow showers on the mtn top currently and 34 degrees!!!! Will try to get a pic from the top relayed to me if possible. 

 

Meantime, a webcam view of it:

 

 

[MikeGold]

SPECIAL WEATHER STATEMENT  
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC  
212 PM EDT FRI MAY 16 2014  
 
NCZ033-048>053-058-059-062>064-162200-  
AVERY-MADISON-YANCEY-MITCHELL-SWAIN-HAYWOOD-BUNCOMBE-GRAHAM-  
NORTHERN JACKSON-MACON-SOUTHERN JACKSON-TRANSYLVANIA-  
INCLUDING THE CITIES OF...NEWLAND...SPRUCE PINE...CHEROKEE...  
BRYSON CITY...WAYNESVILLE...ASHEVILLE...SYLVA...FRANKLIN...  
BREVARD  
212 PM EDT FRI MAY 16 2014  
   
..SLEET AND SNOW MAY BE SEEN ABOVE 5000 FEET THIS AFTERNOON  
 
SHOWERS WILL CONTINUE TO MOVE ACROSS THE NORTH CAROLINA MOUNTAINS  
THIS AFTERNOON. WHILE THE VAST MAJORITY OF THE AREA WILL SEE ONLY  
RAIN...SOME SLEET AND SNOW HAS BEEN REPORTED ABOVE 5000 FEET  
ACROSS THE SMOKY MOUNTAINS. WITH TEMPERATURES IN THE HIGHEST  
ELEVATIONS HOVERING IN THE 30S...ADDITIONAL BRIEF PERIODS OF SLEET  
AND SNOW WILL BE POSSIBLE ABOVE 5000 FEET ACROSS THE NORTHERN AND  
CENTRAL MOUNTAINS. LITTLE OR NO ACCUMULATION IS EXPECTED.  

[Met1985]

Booom Mike! Wow Mid May and we get this kind of weather! Just woke up and my wife told me we had a sleet/hail storm earlier and so far we have had .20 inches of new rainfall! Also current temp is 42 cold degrees! Man this is a great time for NASA to be here with this kind of weather unfolding. Awesome you are seeing snow on your mountains! 

[Met1985]

I saw it snowing on top of Balsam mountain this afternoon. We have some really dark storm clouds around right know. Very windy also and pretty chilly.

[MikeGold]

I saw it snowing on top of Balsam mountain this afternoon. We have some really dark storm clouds around right know. Very windy also and pretty chilly.

0.5 inches at LeConte. The latest snow since 1993.

http://www.highonleconte.com/daily-posts/may-16-2014

[Met1985]

0.5 inches at LeConte. The latest snow since 1993.

http://www.highonleconte.com/daily-posts/may-16-2014

Lol absolutely awesome! Man I love this weather! It could snow year round and I would be happy. This is a treat this late in the season.

[MikeGold]

Radar set up above Canton..NSSL's NO-XP. X Band radar (pic courtesy of NOAA HMT-SE)

[Met1985]

This morning is even colder than yesterday morning with a low of 30 degrees with frost on the cars and patchy frost on the grass. Been a long time since it ha been this cold this late. I think we set a record low.

[franklin NCwx]

This morning is even colder than yesterday morning with a low of 30 degrees with frost on the cars and patchy frost on the grass. Been a long time since it ha been this cold this late. I think we set a record low.

yeah we had low 30's with frost.

[MikeGold]

Snowed again today at LeConte for about an hour this afternoon...

[MikeGold]

Snowed again today at LeConte for about an hour this afternoon...

My neighbor was just in the observation tower and reported temps in the 30s with wind to 30 mph and bitter wind chill. The NASA rain gauge wind shield is making a loud clanking sound with the wind and the grass is starting to grow. Remind me..what season is it?

[Met1985]

My neighbor was just in the observation tower and reported temps in the 30s with wind to 30 mph and bitter wind chill. The NASA rain gauge wind shield is making a loud clanking sound with the wind and the grass is starting to grow. Remind me..what season is it?

Lol impressive again for this time of the year.

[jburns]

My neighbor was just in the observation tower and reported temps in the 30s with wind to 30 mph and bitter wind chill. The NASA rain gauge wind shield is making a loud clanking sound with the wind and the grass is starting to grow. Remind me..what season is it?

lol Those NASA(?) guys are getting a quick education in NC mountain weather.

[MikeGold]

Pic from Friday's surprise heavy snow shower on the mtn top. As you can..snowed about 1/2 ".

[Met1985]

Couple of snow pics from Friday's surprise heavy snow shower on the mtn top. As you can..snowed about 1/2 ".

Never gets old seeing snow pic! Beautiful Mike. We ended up getting about .25 inches of rain from last night through this morning. Was a nice week for rainfall after being so dry.

[Met1985]

Should be a beautiful week shaping up with a warm up above normal towards the middle of the week then another cool down below normal towards the end of the week. 

[MikeGold]

Here's a bit of a write up on the snow event last Friday that I posted on the NASA website:

 

May 16th Surprise High Elevation Snow

 

Description: 

On May 16th, a very moist cold air mass was overhead in Western NC characterized by exceptionally steep lapse rates(see model sounding), mostly unidirectional winds out of the WSW and deep moisture extending to 600 mb-moisture extending into the optimum dendritic snow growth region in the clouds. 

 

Some showers advected in from Tennessee and were aided by afternoon heating. Temperatures had climbed into the low 40s even in the highest elevations but quickly wet bulbed to around freezing a few minutes after precipitation started.  Rain showers quickly changed over to a period of heavy snow featuring very large snow flakes. Despite the warm ground, the intensity of the snow overcame it and accumulations of about 1/2" were recorded at Mt. LeConte Lodge (6500 feet) and Mt. Lyn Lowry (6100 feet). Snow was also recorded at Clingmans Dome (6600 feet) , Newfound Gap (5200 feet), and a trace at Mt. Mitchell (6600 feet) with the snow level dropping to about 5000 feet. (Webcam view of Mt. Lyn Lowry at 18z)

 

 

This snow event prompted the NWS in Greenville to issue a Special Weather Statement at 18:12 Z:

212 PM EDT FRI MAY 16 2014  
   
..SLEET AND SNOW MAY BE SEEN ABOVE 5000 FEET THIS AFTERNOON  
 
SHOWERS WILL CONTINUE TO MOVE ACROSS THE NORTH CAROLINA MOUNTAINS  
THIS AFTERNOON. WHILE THE VAST MAJORITY OF THE AREA WILL SEE ONLY  
RAIN...SOME SLEET AND SNOW HAS BEEN REPORTED ABOVE 5000 FEET  
ACROSS THE SMOKY MOUNTAINS. WITH TEMPERATURES IN THE HIGHEST  
ELEVATIONS HOVERING IN THE 30S...ADDITIONAL BRIEF PERIODS OF SLEET  
AND SNOW WILL BE POSSIBLE ABOVE 5000 FEET ACROSS THE NORTHERN AND  
CENTRAL MOUNTAINS. LITTLE OR NO ACCUMULATION IS EXPECTED.  

 

Per records kept at Mt. LeConte Lodge, http://www.highonleconte.com/daily-posts/may-16-2014, this was the latest in the season that there has been accumulating snowfall since 1993.

 

Looking at disdrometer data for both Clingmans Dome and Mt. Lyn Lowry-the snow shower shows up well with it moving in earlier at Clingmans Dome and evidently more intense as compared to the lower elevation and more sheltered Mt. Lyn Lowry location. (NO-XP radar was not operating on the 16th.)  Some very large diameter objects were recorded corresponding to the large snowflake size that was observed during the event.

 

Image Field: 

Image Gallery:

[Met1985]

Nice write up about the snow and very interesting about the steep lapse rates also. Another cold morning with a temp of 35 degrees. This weather has been a treat.

[MikeGold]

If there is any convection late afternoon tomorrow..it would have the potential to be supercellular looking at model soundings and indices. The atmosphere will be uncapped but don't see an obvious trigger in the time frame where the best parameters come together. (There might be a vorticity max going through in the morning suggesting perhaps some sinking motion in the afternoon.)

 

Model soundings definitely show adequate wind shear/turning of height. CAPE profile looks rather skinny and not particularly threatening. 

 

(NOTE: 12Z NAM does break out some weak convection on the ridges this afternoon. Quick look at the latest SAT image shows some rather vigorous cumulus cloud development already on the ridges-especially from Mt. Mitchell and points to the NE.)

[Hvward]

SPC has parts of WNC under a TSTM advisory.  The sun is already glaring here in downtown AVL.  Could see convection get going later today.

 

 

 

Perceptible water index is increasing over SW WNC and looks to surging east with the moisture transport today.  I think we are in for a few storms today and over the next couple of days, as most models have abundant cape for our area.  Lower level helicity also seems to increase over the next few days so we could see some decent cells pop up.

[MikeGold]

Another day..another write-up. Weather geeks-enjoy! 

 

How 850 Millibar Windflow Modulates Heavy Rain Events-Balsam Mountains

 

Recent observations at the 6100 foot level of Mt. Lyn Lowry (NASA site APU-04) indicated that nearly every single significant rain event (2” or more in 24 hours) is accompanied by gale force winds. (This is causing rain catch problems for the rain gauges currently there.)  In addition, most of the significant rain appears to fall at night and during the early morning hours.

 

During a typical significant rain event, a moist SW wind low-level jet develops West of the Appalachian Mountains during the evening, slowly translates to the East crossing the mountains during the night and then shifts East of the mountains and weakens after daybreak.

 

Because of this, I decided to look closer at the relationship between winds at 850 mbs and significant rainstorms in the Balsam mountains.  In particular, the Plott Balsam mountains which are located at the divide between the Pigeon river basin and the Tuckasegee River basin.

 

Looking at a terrain map of Western NC, it is evident that Balsams form a natural 4000 to 6000 foot high barrier running from the Tennessee state line SSE  to NW of Brevard.

 

It is evident that due to the orientation of the Balsam Mountains, significant orographic enhancement can be realized from cloud level wind flow out of the Southwest.

 

From this NOAA publication: http://www.crh.noaa.gov/crh/?n=ta00-02

"In the atmosphere, vertical velocity can be the result of numerous processes. Some vertical velocities are driven by thermal instabilities, such as surface heating or horizontal temperature advection. Other vertical velocities are driven by atmospheric dynamics, such as large-scale trough-ridge interactions or jet streaks. This study quantifies the vertical velocity which develops when the horizontal wind at the surface is forced to ascend as it encounters changing topography.

The vertical velocity produced when the horizontal surface wind impinges upon enhanced terrain is a function of two variables: 1) the wind speed at the surface, and 2) the slope of the terrain in the direction the wind is blowing. The vertical velocity will tend to be greatest when the wind speed is high, and/or when the terrain is steeply sloped. The vertical wind component near the surface w_o is given by the equation:"

So for example, if assume a 25 knot horizontal wind, a 1000 meter rise over a distance of 6000 meters can generate low-level upward vertical motions of 2 meters/sec which is similar to that of an updraft in a thunderstorm. Locally, the highest vertical velocities would be generated where the terrain is steepest which is a couple of miles WSW of the location of interest with a SW low-level wind.  Strong winds may carry the zone of maximum precipitation a short distance to the NE. (NOTE: During a typical WAA weather regime featuring strong SW winds, a temperature inversion is often present. As such wind speeds in valley areas are very low.  As such, the actual vertical rise of the strong SW low-level jet will be less than 1000 meters which would generate more modest vertical velocities.)

How orographic induced vertical velocities translates into increased precipitation maybe via production of graupel above mountain peaks. Orographic uplift creates a series of short-lived convective cells, "each producing temporary pockets of supercooled cloud water that promoted riming of ice particles that sped up the growth and fallout of precipitation in that location."  Furthermore, "local orographic precipitation was embedded in the general layer of precipitation encompassing the mountains as the baroclinic trough passed over the region". "Thus, the pre-existing precipitation particles carry the orographically generated liquid water rapidly to the ground". "..the cells to consist typically of updraughts  ~ 3-5 km in width and ~1-3 m/s in intensity. 

(Refer to http://onlinelibrary.wiley.com/doi/10.1002/qj.67/pdf  Lessons on orographic precipitation from the Mesoscale Alpine Programme) for good discussion of low level jets interacting with mountain barriers.)

"Riming appears to play an important role in orographic enhancement of baroclinic precipitation...".  "...strong slightly unstable air impinges on the steep slopes and rises over them, transporting low-level mositure at higher levels and efficiently producing cloud liquid water both above the 0 C level, promoting riming, and below this level, promoting coalescence. Furthermore the slight instability promotes convective cell formation that enhances the liquid water production."

http://www.atmos.washington.edu/MG/PDFs/prep02_houz_comparison.pdf

Looking at local annual rainfall maps, depending on which data set one uses, annual totals may be as high as 88” on Mt. Lyn Lowry.   During the exceptionally wet year of 2013, over 110” fell.  More than 20 inches was recorded in January 2013 triggering mudslides in nearby Maggie Valley.   

 

 

Examining previous local research, I came upon this paper:

A Precipitation and Flood Climatology with Synoptic Features of Heavy Rainfall across the Southern Appalachian Mountains 

 

http://www.srh.noaa.gov/mrx/research/climo/pcptxtnwd.php

 

The authors highlighted commonly seen parameters for heavy rain events in the Southern Appalachian regions.  They listed the following:

 

“K-indices > 30

negative Lifted Indices

surface dewpoints at or above 60 F

850-mb temperatures > 13 C

850-mb dewpoints > 10 C

700-mb temperatures > 5 C

700-mb dewpoints > 2 C

Southerly winds were typically observed in the low levels with uni-directional southwest winds above 850 mb during synoptic and frontal events, while meso-high events typically exhibited weak uni-directional southwest flow between the surface and 500-mb levels prior to the onset of heavy rainfall. CAPE values did not seem to show a direct relationship to the occurrence of heavy rain.”

 

The authors made mention of 850 mb wind direction but failed to mention any correlation between wind speed and heavy rain events.

 

Since a good multi-year precipitation data set is not available for Mt. Lyn Lowry, I decided to examine a nearby COCORAHS site that is located couple miles to the East of Mt. Lyn Lowry and 1000 feet lower in elevation.  Looking at available data, there appears to be a good correlation between rainfall events at Mt. Lyn Lowry vs NC-HW-11 with the COCORAHS station often recording more precipitation likely due to its much more sheltered location from the wind and improved rain catch in the rain gauge.

From January, 2008 to May of 2014, I counted 31 heavy rain events that exceeded 2” in one 24 hour period ending at 7 AM local time at NC-HW-11.  I then examined archived 850 mb wind data for each event.  (http://www.spc.noaa.gov/obswx/maps/ )  I generally extrapolated data taken at 0Z at surrounding sounding locations to come up with an estimate of the wind speed and direction for each of the 31 events.  I also looked at 12Z data if it wasn’t clear what the predominant wind speed/direction of a particular event was.

The chart shows the average wind speed at 850 mbs in knots for all 31 events.  The average wind speed was 38 knots.  It appears that a minimum of 25 knots is needed to induce significant orographic enhancement.  Once that minimum wind speed number is reached, it appears from all the data that there is no correlation between increased wind speed and increased precipitation amounts.  In fact, none of the heavy rain events had 850 mb wind speeds above 50 knots.  The sweet spot appears to be 40 knots. This is probably due to a compromise between increasing vertical velocities with higher wind speeds versus the increasing storm motion/duration of the event.  Very dynamic events 60 knots or greater would likely be associated with fast moving squall lines producing intense but brief periods of precipitation.  (Tropical systems were not examined.) Note that the Mt. Lyn Lowry location is at about 810 mbs and wind speeds at that height are often about 10 knots higher than the 850 mb standard charts.

 

The table below depicts wind direction for each of the rain events. (See attachment.)

 

20 of the events winds were out the SW, 7 out of the S, the rest out of the SE or E.   Note that there is often veering of the wind with height in the low levels so that many of the South wind events might have been out of the SW at the elevation of the mountain top.

 

There isn’t enough data available to look closer at the diurnal distribution of rainfall from these heavy rain events. However, due to the correlation between the low-level jet and heavy rainfall, a correlation can be assumed.  Winds at 850 mb are adversely affected by surface heating during the day. Vertical mixing quickly disrupts the wind flow especially during the warm season.  Note that nearly all the heavy rain events occurred during the cold season. This suggests that indeed most of the heavy rain would be expected at night and during the early morning hours corresponding to the peak maturity of the low level jet.

 

In conclusion-the vast majority of significant rain events during the last six years in the Balsam mountains have occurred with a 25 knots or greater wind speed at the 850 mb level out of the southwest.  (Note: The Southern Balsams near the Transylvania county line were not looked at but this area is subject to heavy rain during SE wind  850 mb events.  The orientation of the terrain blocks heavy rain from falling at points to the NNW of the Southern Balsams such as at the Plott Balsams/Mount Lyn Lowry location.) 

Image Field: 

[Met1985]

Mike very interesting on the wind speed and direction correlating to heavy rainfall. I was wondering about the correlation of snowfall though here in the mountains. I am sure same could be said for if we had a storm coming from the south with south winds but what about typical northern flow snow and the typical northwest flow snows in the winter. I am sure that could be another interesting case study especially with the microclimates we have here in the mountains. It would be very interesting to do a study from Haywood county south because of such high peaks similar to what is being studied know. Thanks for all the info anyway Mike. Very cool and interesting.