February 8-12 2016 Cold and Possibly Snowy

[tnweathernut]

From MRX - LONG TERM...(THURSDAY THROUGH TUESDAY)...

THE BEGINNING OF THE LONG-TERM FORECAST WILL FEATURE COLD AIR
ADVECTION MOVING IN BEHIND THE FRONT. MOSTLY SUNNY SKIES WILL RETURN
BUT TEMPERATURES WILL BE NEAR NORMAL VALUES WITH HIGHS IN THE 40S
ACROSS MOST OF THE AREA. ANOTHER UPPER LEVEL TROUGH MOVES IN LATE
THURSDAY INTO EARLY FRIDAY BUT THE PW VALUES WILL BE AROUND 0.1-0.2
INCHES...WHICH IS NEAR THE MINIMAL VALUE FOR EARLY FEBRUARY.
THEREFORE...NOT EXPECTING ANY PRECIPITATION FROM THIS UPPER LEVEL
SYSTEM. WITH THIS DRY AIR IN PLACE...THURSDAY NIGHT SHOULD BE MOSTLY
CLEAR WITH LIGHT WINDS AS SURFACE HIGH PRESSURE MOVES OVER THE AREA.
THIS WILL ALLOW FOR IDEAL RADIATIONAL COOLING CONDITIONS WITH
TEMPERATURES DROPPING DOWN INTO THE 20S AREAWIDE. HIGH PRESSURE AT
THE SURFACE AND ABNORMALLY LOW PW VALUES WILL KEEP THINGS DRY INTO
THE WEEKEND. MODELS INDICATE A DEEP CLOSED LOW PIVOTING ACROSS THE
SOUTHEASTERN U.S. SATURDAY INTO SUNDAY. A LOW PRESSURE DEVELOPS OFF
THE CAROLINA COAST AND THE PRECIPITATION FROM THIS SYSTEM WILL
REMAIN WELL OFF TO THE EAST.

BIG CHANGES ARE IN STORE FOR THE BEGINNING OF THE WORK WEEK AS A
TROUGH RACES QUICKLY OUT OF THE NORTHERN PLAINS INTO THE TENNESSEE
VALLEY. COLD AIR WILL SPILL DOWN FROM CANADA WITH THIS SYSTEM. UPPER
LEVEL HEIGHTS WILL DECREASE SIGNIFICANTLY AS THE LOW CLOSES OFF
ACROSS THE AREA WITH MULTIPLE SHORTWAVE TROUGHS ROTATING THROUGH THE
MAIN LOW EARLY NEXT WEEK. MODELS INDICATE A SURFACE LOW MOVING
THROUGH THE AREA ON MONDAY AS TEMPERATURES BEGIN TO COOL DOWN WITH
THE COLDER AIR ALOFT. MOISTURE WILL SPREAD FROM WEST TO EAST DURING
THE DAY WITH TEMPERATURES COOLING. FOR NOW...IT APPEARS IT WILL
MAINLY BE A MIX OF RAIN/SNOW IN THE VALLEY THROUGHOUT MUCH OF THE
DAY WITH SNOW IN THE HIGHER TERRAIN. THE FREEZING LEVEL WILL BE
AROUND 2-3 KFT AND THIS IS WHY THERE WILL BE A MIXTURE OF RAIN/SNOW
IN THE VALLEY. BASED ON CURRENT MODEL SOUNDINGS...NOT SEEING ANY
INDICATION OF ANY OTHER PRECIP. TYPE OTHER THAN RAIN OR SNOW. THE
ATMOSPHERE CONTINUES TO COOL MONDAY AFTERNOON AND BASED ON CURRENT
GUIDANCE EXPECT THIS IS WHEN ALL LOCATIONS WILL TRANSITIONS TO SNOW.
THE GFS IS SHOWING SOME RATHER IMPRESSIVE LAPSE RATES MONDAY
AFTERNOON INTO TUESDAY MORNING WITH 850-500 MB LAPSE RATES OF 6.5-
7.5 C/KM. IS THIS WHERE TO VERIFY...THERE WOULD BE SOME HEAVIER
BURST OF SNOW. MODELS INDICATE ANOTHER SHORTWAVE TROUGH MOVING
THROUGH TUESDAY THAT COULD BRING ANOTHER ROUND OF SNOW AS A SURFACE
LOW TRACKS UP THE EAST COAST. IT IS STILL TOO EARLY TO GET SPECIFIC
BUT BASED ON THE LATEST MODELS...IT APPEARS A GOOD 2-4 INCH SNOWFALL
ACROSS THE AREA WITH HIGHER AMOUNTS IN THE MOUNTAINS. SNOW BEGINS TO
TAPER OFF FROM SOUTHWEST TO NORTHEAST TUESDAY NIGHT INTO WEDNESDAY.
PLEASE STAY TUNED TO THE LATEST FORECAST AS THERE ARE STILL MANY
MODEL RUNS TO COME BETWEEN NOW AND MONDAY.

[jaxjagman]

NATIONAL WEATHER SERVICE NASHVILLE TN
618 AM CST WED FEB 3 2016

.UPDATE...
FOR 12Z AVIATION DISCUSSION.

&&

.DISCUSSION...

WIND SPEEDS HAVE DECREASED MARKEDLY OVER THE PAST FEW
HOURS. WILL GO AHEAD AND END THE WIND ADVISORY. OTW... SHOWER
ACTIVITY IS NOW CONFINED TO AREAS GENERALLY EAST OF I-65. THE WEST
TO EAST TERMINATION OF THE RAINFALL WILL CONTINUE SLOWLY THROUGH THE
MORNING HOURS. HOWEVER...WILL NEED TO INCLUDE AT LEAST LOW POPS FOR
SHOWERS FOR THIS MORNING ACROSS ROUGHLY THE EASTERN THIRD OF THE MID
STATE. PARTIAL CLEARING FROM WEST TO EAST SHOULD COMMENCE BY
AFTERNOON. COLDER TEMPS WILL WORK IN. IN FACT...STEADY TO SLOWLY
FALLING TEMPS ARE EXPECTED.

GOING FORWARD...A FEW ADDED CLOUDS MAY SKIRT THE EASTERN HALF OF THE
CWA LATE TONIGHT AS AN IMPULSE SLIDES SOUTHWARD. MOSTLY CLEAR SKIES
ARE EXPECTED THU NT WITH A SEASONABLY COLD NIGHT EXPECTED. SUNNY ON
FRIDAY AS TEMPS BEGIN TO MODERATE.

IN THE EXT FCST...UPPER PATTERN TO BECOME RATHER ACTIVE BUT TEMPS
WILL BE NEAR TO SLIGHTLY ABOVE NORMAL AS THE UPPER LEVEL FEATURES
WILL BE RATHER WEAK. HOWEVER...A STRONGER SHORTWAVE WILL TRAVERSE
THE AREA SUNDAY NIGHT AND MONDAY. THIS FEATURE WILL CARRY AN ARCTIC
FRONT WITH IT AND TEMPERATURES WILL TURN NOTICEABLY COLDER.
ADDITIONALLY...UPSTREAM CURVATURE AND SHEAR LOOKS POTENT ENOUGH TO
CARRY A CHANCE OF SNOW FOR A GOOD PORTION OF THE MON-WED PERIOD.
EURO MODEL NOT QUITE AS BULLISH WITH THE COLD AIR AS THE GFS.
THEREFORE...WILL LEAN TOWARD THE GIVEN BLEND TO REFLECT THE COLDER
AIR.

[Snowless in Carrollton]

I'm off Mon and Tues and thinking of going up to monteagle sun night. I wonder if they could do well in this setup ?

[Greyhound]

Watching the 12z GFS run and it's giving the East TN area higher totals than previous runs.  I'll be honest....I'm not too amped on this one just yet, despite everything that is being shown and discussed in this forum. 

[jaxjagman]

Like the wording from MEG being they are on the western edge and even seem to expect colder temps than the euro is showing

 

THIS SECOND TROF WILL MOVE EAST SATURDAY NIGHT AND UPPER RIDGING
WILL OCCUR OVER THE MIDSOUTH AGAIN ON SUNDAY. EXPECT HIGHS IN THE
MID 50S.

SUNDAY NIGHT INTO MONDAY IS WHEN THINGS WILL START TO GET
INTERESTING. BOTH THE ECMWF AND GFS BRING A THIRD UPPER TROF INTO
THE CWA. THIS ONE WILL BE MORE POTENT THAN THE OTHER TWO. BOTH
MODELS ARE INDICATING PRECIPITATION WITH THE TROF WITH MUCH COLDER
AIR FILTERING INTO THE CWA. BOTH MODELS SHOW PRECIPITATION FALLING AS
SNOW LATE SUNDAY NIGHT INTO MONDAY WITH THE GFS HAVING SLIGHTLY
MORE QPF. FOR NOW HAVE ADDED A RAIN/SNOW MIX WITH 20/30 POPS. WILL
HOLD OFF MENTIONING IN THE HWO AS THIS IS THE FIRST RUN WITH
MODELS IN DECENT AGREEMENT WITH THIS SYSTEM. HOWEVER...THE SYSTEM
DEFINITELY BEARS WATCHING.

THE UPPER TROF WILL SWING EAST MONDAY NIGHT BUT WILL BE FOLLOWED BY
AN ARCTIC COLD FRONT THAT WILL BRING POSSIBLY THE COLDEST AIR OF
THE SEASON INTO THE MIDSOUTH ON TUESDAY. BOTH THE ECMWF AND GFS
INDICATE SOME SNOW SHOWERS COULD OCCUR ALONG AND AHEAD OF THE
FRONT. WOULD NOT BE SURPRISED IF HIGHS DO NOT REACH FREEZING ON
TUESDAY ACROSS MUCH OF THE CWA.

 

http://forecast.weather.gov/product.php?site=MEG&issuedby=MEG&product=AFD&format=CI&version=1&glossary=1

[John1122]

Kinda reminds me of a cold week we had in December 1997, these little vorts kept rotating through from the NW and we ended up with 8 inches of snow over 4 days. This won't likely be that impressive outside the mountains, but I could easily see 3-5 inches of fluffy stuff falling if it plays out as shown on models.

[John1122]

I'm also still baffled by the Monday rain forecast unless they just don't believe the models. No way it rains with the 532/528 line south of us and the 850s at -4 to -6. GFS is also spitting out temps in the mid to upper 30s at the surface but MRX has my high into the 40s. So I guess they are going above the GFS at least.

[Runman292]

Kinda reminds me of a cold week we had in December 1997, these little vorts kept rotating through from the NW and we ended up with 8 inches of snow over 4 days. This won't likely be that impressive outside the mountains, but I could easily see 3-5 inches of fluffy stuff falling if it plays out as shown on models.

Idk, 3-5 inches is impressive in the valley.

[ShawnEastTN]

Moving from other winter topic over here...

 

These being advertised aren't just low level NW flow moisture with no lifting mechanism in which cases only the High elevations score and low elevations only flurries if anything.  Looking at 12Z GFS only out to 162 there are no less than 4 pieces of energy rotating through in rapid succession to provide plenty of lift for accumulating snows essentially across the state assuming the moisture is there, which so far is modeled to be there.   Interesting is this year the Lakes ice cover isn't very extensive as compared to the last 2 years.  These vorts rotating through will use some lake moisture as well.  Lake Michigan and Superior are both less than 10% ice covered.  With this extreme cold flow and lifting mechanisms moving through, this could be a very fun, interesting and even novel thing to watch as its been quite many years since seeing a similar scenario with the lakes at their current ice coverage being so low.  Last year and the year before the lakes were pushing around record ice cover essentially cutting that moisture supply off almost completely.

 

Image of current ice coverage from NOAA, note gray and black mainly bays on the lakes are frozen.  Open waters are ice free with water temps on the image showing 40's primarily.  Take single digit air across 40's water...  Boom, lots of moisture to be picked up by these vorts to enhance them.

[ShawnEastTN]

Again moving from winter topic...

 

GFS 12Z Clown assuming 10-1 ratio.  I think for most its safe to double this as John was mentioning earlier, and I think some triple.  As is this map at 10-1 basically Nashville and east 1-3" plateau and mountains 3"-6".  So probably safe to say 2"-6" and wouldn't be surprised to for up to a foot in the Mountains by the time all is said and done and some spots on the plateau could approach that with the ratios that would be with these.  We are talking 522 to down as low as 500mb swinging through the region during the the snow. 

[John1122]

Starting with 18z yesterday, these are the last 4 runs of the GFS using the pivotal weather maps with what should be a closer ratio. So I could see why MRX would say 2-4 widespread is possible. The key, is this right? JKL seems to think with the set up shown rather than sit and spin and keeping on rotating spikes of energy across us that the parent ULL  will either be further north or will transfer off the coast. So obviously  not much set in stone, even though there's currently very good model agreement with the current solution.

 

 

[John1122]

12z, had to make another post due to file size.

[ShawnEastTN]

Canadian seems pretty close in agreement with GFS, though slightly beefier on snow totals by an inch or 2.  It advertises a slightly different approach to the low in the northern Lakes and vorts by transferring its energy down to central Indiana and then pulling a large slug of moisture from Lake Superior across the length of Lake Michigan and down across KY and all but extreme SW TN Memphis area.

[ShawnEastTN]

Starting with 18z yesterday, these are the last 4 runs of the GFS using the pivotal weather maps with what should be a closer ratio. So I could see why MRX would say 2-4 widespread is possible. The key, is this right? JKL seems to think with the set up shown rather than sit and spin and keeping on rotating spikes of energy across us that the parent ULL  will either be further north or will transfer off the coast. So obviously  not much set in stone, even though there's currently very good model agreement with the current solution.

Yeah I agree with that definitely not set in stone still time for this to potentially disappear or not be a big deal.  Essentially about a week out.  I do like what I see however if we cant get a gulf storm well then this works in proxy being beefier then normal northern stream events, with very not your every year set up.  As modeled currently. 

[JayCee]

Who knows how next week will play out, but it does sound very interesting.  Especially since it's not a quick 1 day shot of snow and cold, but something that lingers around for days. 

 

From MRX:

 

SUNDAY THROUGH WEDNESDAY...A DEEP UPPER LEVEL LOW OVER THE GREAT
LAKES WILL STRENGTHEN AND MOVE SLOWLY EAST...WITH STRONG NW FLOW
INTO THE AREA. A FRONT ON THE LEADING EDGE WILL BRING A CHANCE FOR
RAIN THROUGH MONDAY. THERE IS NOT A LOT OF MOISTURE PRESENT...WITH
LOW ACCUMULATIONS EXPECTED. AS TEMPERATURES COOL MONDAY
EVENING...THE RAIN WILL QUICKLY TRANSITION TO SNOW. NOT SEEING MUCH
CHANCE FOR A BREAK IN SNOW SHOWERS THROUGH THE REST OF THE EXTENDED
WITH SEVERAL WAVES OF ENERGY MOVING AROUND THIS LOW WITH THE AMOUNT
OF LIFT PRESENT. MOISTURE INCREASES THROUGH THE DAY ON TUESDAY AND
IS ABUNDANT WITH STRONG LAPSE RATES TUESDAY EVENING AND TUESDAY
NIGHT. WITH THE AREA LOCATED IN THE POSITION AT THE BASE OF THE
TROUGH...TEMPERATURES WILL SLOWLY DESCEND...WITH EACH DAY AND EACH
NIGHT THROUGH THE WORK WEEK BEING COLDER THAN THE DAY AND NIGHT
BEFORE THAT. AS THE TROUGH SLOWLY MOVES EAST...THAT COLD AIR FROM
CANADA WILL HAVE MORE OF A DIRECT LINE TO THE AREA...SO EXPECT THE
COLDEST TEMPERATURES TO BE AT THE END OF THE EXTENDED...DAYS AFTER
THE TROUGH STARTS TO IMPACT THE AREA.
 

 

[Greyhound]

The afternoon AFD from MRX seems rather non-commital based on their previous one. Only thing they do agree on is the low temperatures. And honestly.... think that's a safe bet at this juncture in time.

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[Carvers Gap]

I'm off Mon and Tues and thinking of going up to monteagle sun night. I wonder if they could do well in this setup ?

 

Boone and the ski slope areas near Banner Elk.  If we get upslope...money in the bank.  Roan Mountain State Park as well.

[John1122]

GFS just keeps getting stronger with that low lover the lakes. It's sitting at 990 over the tip of lower Michigan which would pretty much give a pitch down almost all of lake Michigan to gather moisture and send this way. It'll also drive severe cold and NW winds into the area.

[John1122]

This is some valley down sloping off the Plateau. 

 

[Runman292]

This is some valley down sloping off the Plateau.

I forgot, is downsloping bad for the Valley?

[ShawnEastTN]

GFS not as robust in totals as last couple runs.  10-1 map of course, still would double this clown at least.

 

 

[ShawnEastTN]

I forgot, is downsloping bad for the Valley?

Downsloping winds are drying winds, essentially in the shadow of the plateau.  So hurts moisture for the valley.  Northwest facing slopes do better.  Though this run of the GFS shows a little less moisture at play than previous runs still shows waves of energy moving over for lift.  Maybe the 0Z tonight will be juicier with qpf.  

[ShawnEastTN]

I would like to see that low the GFS has over the Upper Peninsula of Michigan to be further south at least Central Lower Michigan.  Different runs have its placement in different areas a tad south helps a bit to get the wind blowing out of the north over Lake Michigan verses more westerly/northwesterly across the lake as it does when the low is in the Upper Peninsula/Lake Superior region.

[ShawnEastTN]

Latest WPC QPF forecast looks good.  This is out through Thursday Feb 11th.  Most all of that qpf would be snow.  with an average of .25" qpf over the majority of the area and some spots pushing .5".  Not bad at the higher ratios we would see.  Still would look like 2-4 area wide with much higher plateau and mountains.

[John1122]

On 18z the vort didn't close off at 500 like it had on prior runs so the precip field was less enhanced.

[Carvers Gap]

Downsloping. On a broader scale it is what causes rain shadows and deserts on the lee sides of tall mountain ranges such as the Andes and Himalayas. If you go to Google Earth you can see that one side of the mountain range is green and lush...the other is desolate. Tibet and the Atacama are dry to varying degrees. Air that has to rise to get over mountain ranges has to release moisture to get over the range kind of like getting rid of excess baggage. The baggage is precip. Once the air begins to sink it is already dry from going over the mountain range. Sinking air in weather is also related to a lack of precip. So, downsloping for my own personal definition are winds that lack precip due to climbing a previous mountain tange and winds that warm due to descending the slope and the air molecules being compressed.

[John1122]

If nothing else it looks like we're getting 5-7 days of very cold weather and potentially several days with flakes flying in waves as these vorts rotate across. After that is up in the air. The Gfs has been advertising a monster winter storm around the 14th-16th too. Maybe it'll be another patten shift storm event. I'm at 13.8 inches on the season. If I can manage 4 more next week I'll be close to average on the year. Then anything from then until the season ends in early April will be padding my stats. Hopefully the valley areas can cash in during this frigid period and close in on their average.

[Runman292]

If nothing else it looks like we're getting 5-7 days of very cold weather and potentially several days with flakes flying in waves as these vorts rotate across. After that is up in the air. The Gfs has been advertising a monster winter storm around the 14th-16th too. Maybe it'll be another patten shift storm event. I'm at 13.8 inches on the season. If I can manage 4 more next week I'll be close to average on the year. Then anything from then until the season ends in early April will be padding my stats. Hopefully the valley areas can cash in during this frigid period and close in on their average.

I think the average for Knoxville is around 6 inches. In North Knoxville, we're at a little over 3 inches right now. I do think we will surpass our average.

[John1122]

00z with ratios factored was pretty big for a lot of us.

 

[John1122]

Some of the models insist on showing rain with this system and I can't understand quite why. Look at this panel of the GGEM. Note the 528 dm line south of the area. I'm sure most of us know that 540 thickness is 50/50 for snow at 1000 feet in elevation with snow actually possible at 546 the higher up you go. I'd think at below 528 it's far more likely to be a snow precip type than a rain precip type. Especially with nw winds, surface temps in the mid 30s, which are shown here, and 850s at around -5 or lower over the area, the 700 mb are -15 to -20 which is excellent for snow growth. Even the 925 temps are around 0 or below. It literally seems to be spitting out rain with the entire column below freezing from 700 down to almost the surface and the surface about 3 degrees above freezing. The odder part to me is that it's showing snow further east, which is actually the warmest area on this panel from 700 all the way to the surface.