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February/March 2021 - Frigid or Flop? Pattern/Longterm Forecast Thread.

John1122

By John1122,
in Tennessee Valley

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Daniel Boone

Daniel Boone

Posted
Posted
1 hour ago, Carvers Gap said:

Looks like the 18z GFS and 12z Euro have indeed reversed rolls for next weekend.  Well, at least both now correlate their MJO looks.    

 

It would be our luck after virtually no MJO effects for it to affect us adversely now that it's active. Hopefully, not the case since , even if it does, we have an offsetting player . The -NAO.

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I’m still in Des Moines guys so I figured I would share a pic with y’all.  Light snow most of the day today.  Wind chill tonight is supposed to be around -30!!!  Next 5-7 days are going be brutally co

Math/Met
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Carver,  Just wanted to say that you do a great job with these pattern discussions. It always makes for a good read.

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Matthew70

Matthew70

Posted
Posted
34 minutes ago, PowellVolz said:


I absolutely agree with that and I understand your frustration living in the mid state where you all have hit a dry spell the last 10 years. We in Knoxville usually share that same frustration but this season has been a good one for us. My location is a good one for living in the valley but 4 to 5 times a year I can drive 20 minutes and be in a completely different climate while back at my house it’s 33 and rain. It sucks but it is what it is. I wouldn’t trade living in ETn for nothing even though I’m always on the outside looking in. Your time will come, just keep a positive outlook and enjoy the ride.


.

I loved living in East Tn growing up.  Miss my mountains.

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PowellVolz

PowellVolz

Posted
Posted
Winter weather isn't as difficult to forecast as it seems, starts with pattern recognition at 500. What is difficult, is living and dying by every model run. Remember models are just one small piece of the puzzle. Learn from Carvers/Jax/John/Holston (just to name a few), and figure out if what those mods are showing makes any sense.

I use to be that guy who would freak out on d7 when the euro took a detour. Tellico your name should be listed as one of the “ones to listen too”. You’re a great poster also.


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jaxjagman

jaxjagman

Posted
Posted

Euro is having a rough time,its been warm but now went back cold around Valentines day,well at least colder anyways

  

CMWF Deterministic FORECAST FOR: BNA    LAT=  36.12 LON=  -86.68 ELE=   591

                                            00Z FEB08
                 2 M     2 M     2 M     SFC     SFC    6 HR    FROZN   TOTAL
                 MXT     MNT     TMP     DEW     WIND    QPF     PCP    CLOUD
                 (F)     (F)     (F)     (F)    (KTS)   (IN)    (IN)    (PCT)
MON 00Z 08-FEB                  29.1    22.1    08003                     36    
MON 06Z 08-FEB  29.5    25.4    26.3    21.8    03002                      7    
MON 12Z 08-FEB  26.5    23.9    24.9    21.1    13003   0.00    0.00      16    
MON 18Z 08-FEB  44.0    24.6    44.4    30.2    19001   0.00    0.00      23    
TUE 00Z 09-FEB  50.0    38.0    37.8    33.6    05003   0.00    0.00      97    
TUE 06Z 09-FEB  38.8    34.4    37.6    35.2    18005   0.00    0.00      21    
TUE 12Z 09-FEB  39.6    36.7    37.8    35.5    34002   0.00    0.00      79    
TUE 18Z 09-FEB  46.3    36.9    46.1    37.6    35005   0.00    0.00      98    
WED 00Z 10-FEB  46.1    39.3    39.2    35.0    01006   0.03    0.00     100    
WED 06Z 10-FEB  39.2    37.7    37.6    36.0    03005   0.03    0.00     100    
WED 12Z 10-FEB  38.1    37.4    37.7    37.4    01003   0.03    0.00      93    
WED 18Z 10-FEB  45.4    37.6    45.7    43.4    02002   0.02    0.00     100    
THU 00Z 11-FEB  46.8    41.6    41.5    40.8    01005   0.02    0.00     100    
THU 06Z 11-FEB  41.5    38.0    38.1    37.5    03004   0.03    0.00     100    
THU 12Z 11-FEB  38.2    36.8    36.8    36.4    02006   0.05    0.00     100    
THU 18Z 11-FEB  39.3    36.4    39.1    38.9    02005   0.46    0.00     100    
FRI 00Z 12-FEB  40.8    38.5    38.4    37.7    35006   0.09    0.00     100    
FRI 06Z 12-FEB  38.4    33.4    33.3    31.1    34007   0.01    0.00     100    
FRI 12Z 12-FEB  33.3    27.5    27.3    24.6    36006   0.00    0.00      64    
FRI 18Z 12-FEB  39.5    26.6    39.8    27.8    01006   0.00    0.00      11    
SAT 00Z 13-FEB  43.7    36.4    36.2    25.0    36007   0.00    0.00       0    
SAT 06Z 13-FEB  36.2    27.1    26.9    19.0    01007   0.00    0.00       0    
SAT 12Z 13-FEB  26.9    21.5    21.4    14.1    00009   0.00    0.00      66    
SAT 18Z 13-FEB  30.9    20.9    31.1    14.3    36010   0.00    0.00      87    
SUN 00Z 14-FEB  32.5    21.8    21.4     7.5    35011   0.00    0.00      57    
SUN 06Z 14-FEB  21.4    11.9    11.7    -4.6    35011   0.00    0.00       0    
SUN 12Z 14-FEB  11.7     7.3     7.4    -4.8    36010   0.00    0.00       7    
SUN 18Z 14-FEB  24.0     7.3    24.4    -5.4    03010   0.00    0.00       0    
MON 00Z 15-FEB  28.3    23.3    23.1   -10.0    03008   0.00    0.00       0    
MON 06Z 15-FEB  23.1    17.5    17.4    -7.5    05008   0.00    0.00       0    
MON 12Z 15-FEB  17.4    15.9    16.0    -4.9    06007   0.00    0.00       0    
MON 18Z 15-FEB  38.9    16.0    39.4   -10.4    09005   0.00    0.00      61    
TUE 00Z 16-FEB  44.1    36.4    36.2    -6.1    09005   0.00    0.00      88    
TUE 06Z 16-FEB  36.6    33.2    33.9     7.4    14007   0.00    0.00      70    
TUE 12Z 16-FEB  35.0    33.4    34.0    11.9    14006   0.00    0.00      87    
TUE 18Z 16-FEB  38.6    32.2    37.8    37.4    13009   0.36    0.00     100    
WED 00Z 17-FEB  40.5    37.4    40.7    39.2    17007   0.66    0.00     100    
WED 06Z 17-FEB  43.3    39.2    43.2    42.4    20008   0.21    0.00     100    
WED 12Z 17-FEB  43.3    38.4    38.3    37.8    27005   0.01    0.00     100    
WED 18Z 17-FEB  40.1    37.3    40.2    34.9    27006   0.00    0.00     100    
THU 00Z 18-FEB  42.5    38.9    38.7    31.6    30005   0.00    0.00     100

 

 

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Carvers Gap

Carvers Gap

Posted
Posted

6z GEFS and 0z CMC are again showing a long term overrunning event.  The 0z Euro is not.  The temps on the 6z GFS for late next weekend for western TN are nearly 50 degrees BN(departures from normal) and around 10-17 below zero.    Honestly, we probably need to be pulling for the Euro to be right...just compared to latest the GFS and CMC runs.  The 6z GFS is brutally cold and the 0z CMC has an ice storm.  With this set-up(as long as the severe cold is near us), there should be a period of significant winter weather in the Ohio Valley and/or middle/west forum areas...and then that boundary likely pushing eastward.  I don't think that is set in stone, by IF the Euro comes on board....would make an already strong signal even stronger.

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Carvers Gap

Carvers Gap

Posted
Posted

Morning disco out of Memphis... 

With the front stationary the situation doesn`t change much for
Wednesday with the notable exception of the cold air behind the
front. Light overrunning across this front could bring a wintry mix
across mainly northern sections of the Mid-South Tuesday night
through Thursday night. By Wednesday night into Thursday the
stationary front becomes a cold front and starts pushing south
through the area.  The best chance for wintry precipitation appears
to be Wednesday night into Thursday when a more significant upper
level disturbance moves through the area. This could result in
advisory level icing to NE AR, the MO Bootheel and portions of
northern TN. There could be some freezing rain into the Memphis
metro area by early Thursday. The problem is there is still some
disagreement with the models. While the Euro is still warmer which
means rain for Memphis the GFS is still colder and means ice for
Memphis. The CMC is still siding with the GFS, just slightly warmer.
Stuck to the middle ground here with this forecast. Further south in
north MS we could see thunderstorms. There is elevated instability
but at this time nothing severe is expected.

Now by Thursday afternoon into the evening this front moves out of
the area. By Friday we are expecting dry weather which should
continue into Saturday. The bad news is because this was a cold
front temperatures will be very cold. High temperatures during this
timeframe will be into the 20s and 30s with low temperatures into
upper teens to mid 20`s. With winds elevated wind chills will come
into play with the possibility of single digit wind chills.

Now for Sunday and Monday the next disturbance approaches the area.
Cold temperatures will be in place and we could get another shot at
wintry precipitation. It is too far out to pinpoint any exact
details or impacts this might bring but it is worth the mention.
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CG2

CG2

Posted
Posted

Morning disco out of Nashville.... 

Upper pattern has shown
little consistency between the models over the past runs, even
between the models individually. Thursday trough associated with
the cold front and push of cold air southward behind is weaker
than previous runs, and precip amounts have dropped a little.
Instability wants to creep into the south during the day Thursday,
so a clap of thunder is not out of the question, but in northern
zones, temps will cool near or below freezing, bringing chances
not only for a rain/snow mix but even some freezing rain/sleet if
the GFS pans out. The GFS is trying to hold onto a sharper cold
front with better separation of the surface front/850 mb front,
bringing colder air in sooner at the surface and allowing for
potential sleet/freezing rain Thursday morning and again in the
evening. Still way too soon to call.

Friday looks to be dry, and models still disagree on the strength
of the CAA behind the front. Not as big of a spread as previous
runs, but at least are getting closer to lining up better. Still a
slight chance for some snow on the Plateau Saturday night, and
models do hint at a Midwest trough again Sunday, but not enough
agreement for any confidence on timing. Starting off next week,
the only thing that models can agree on is staying in an active
pattern, with chances for precip and shortwaves moving through
aloft. Based on the low level temperature profile, winter is not
ready to loosen its grip just yet.
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Holston_River_Rambler

Holston_River_Rambler

Posted
Posted

Looks like the Euro has now gone back to pushing the arctic front through after the first overunning event, however that turns out. I've never seen one while I've been participating on weather forums, so will reserve my judgment on how models deal with them until I've seen a few. I will say the RGEM and the NAM to a lesser extent, continue the overnight trend of pushing the front through more quickly and hitting parts of western TN with some ice.

 

What seems to have happened to the Euro (at least to my eyes) over the last few days is that it's higher resolution (or maybe an AI guess, lol) allowed it to see correctly that the TPV parked over southern Canada would end up mirroring the retrograding NAO and following west into Canada. The GFS and the Canadian caught on to this for a bit yesterday and thus a few "torchy" (as the weenies say) runs. Now, what the Euro also caught on to more quickly, was that the TPV gets so far west that it shears out a chunk which gets pulled west, allowing the main lobe to roll back east. So what looks like a cave, is really just a compromise. 

giphy.gif

Almost ran out of digital crayons on this one, lol. The orange indicates the sheared out piece, the blue the main lobe and a southern stream disturbance, the brown SSJ dist. #2, and the green ssj disturbance #3. 

3 opportunities for suppression or interaction, although interaction becomes less likely as we go out in time, but that could also allow for the last one to amplify (as indeed it does late on the Euro run). 

 

6z GFS shows what could happen if the energy circled in orange gets pulled back with the "brown" energy piece:

giphy.gif

 

CMC is kind fo a worst case scenario where all that energy travels just in sync enough to keep ice going over west TN for days and days. 

ICON only out to 120, but looks like the GFS, at least in terms of the "orange" piece getting pulled back in by the "brown" vort. 

 

 

 

 

 

 

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Holston_River_Rambler

Holston_River_Rambler

Posted
Posted

Ukie, FWIW (maybe not much this season) brings the energy out too:

giphy.gif

sorry for the "loading images" was trying to get the precip map on that one gif too:

giphy.gif

 

Other considerations:

The NAO has kept the SE ridge squished and models have had trouble with that, but, what happens now as it retrogrades to western Canada? Can the SE ridge flex a little more? Or is it still able to bully the TPV so much that it doesn't matter? 

We essentially have two cut off pieces of vorticity, one relatively positive and one relatively negative; a cut off high (NAO) and a cut off low (TPV), both vying to determine not just one storm track, but the pattern across a continent. Hi res models should be fun this week! 

 

 

 

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Carvers Gap

Carvers Gap

Posted
Posted

MJO looks like hot garbage this morning.   Euro has the best solution which moves to COD and back towards 6.  GFS stalls in 7.  I am very suspicious of cold air that can hold on for very long given that set-up.  It does look like the NAO is going to try to hold on despite a brief retrograde.  The CHI maps still say phase1-2 of the MJO may occur....so I almost feel like the plot and the actual modeled look are a bit out of sync.

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Carvers Gap

Carvers Gap

Posted
Posted

Basically, the NAO and Atlantic blocking as well as the AO will have to spend February fighting the MJO if this morning's plots are correct.  This is going to be a SE ridge fighting a block for the next three weeks or so...and that might get pretty wild as wavelengths change.  Getting a good look at that battle in modeling later this week.  It is almost like a standing wave SER is locked against very cold air moving east past the Apps.  Going to make it very difficult to find the boundary and then model the speed as the boundary gets pushed eastward once it hits the Plateau(if at all).  

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Daniel Boone

Daniel Boone

Posted
Posted
36 minutes ago, Carvers Gap said:

Basically, the NAO and Atlantic blocking as well as the AO will have to spend February fighting the MJO if this morning's plots are correct.  This is going to be a SE ridge fighting a block for the next three weeks or so...and that might get pretty wild as wavelengths change.  Getting a good look at that battle in modeling later this week.  It is almost like a standing wave SER is locked against very cold air moving east past the Apps.  Going to make it very difficult to find the boundary and then model the speed the boundary gets pushed eastward once it hits the Plateau(if at all).  

Perfectly put Carvers ! Exactly what the deal is. Hopefully that block does shift back east and remains formidable.  If so, we may not get that missing piece, "Arctic cold" this Winter but, still should get Snow/frozen precip at times. 

      My worries regarding the MJO in my post yesterday are legit now, however.

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Carvers Gap

Carvers Gap

Posted
Posted
3 minutes ago, Vol4Life said:

From a storm evolution standpoint, what needs to happen in order for this to be more of a snow event versus zr?  Clearly, there’s some warming aloft.  Do we need the HP to be stronger or positioned differently?  Or is this more of a storm track issue?

The threat for ice is growing unfortunately.   I guess we could hope the front presses through and a Miller A forms and ejects all of the energy at once in one really big storm.  Right now modeling seems quite content to stall the boundary at the Plateau or Apps and then send pieces of energy along that positively tilted broad trough.  The problem right now is this is fresh cold which has a SER fighting it.  The likelihood of the cold getting trapped at the surface as a wave rolls over the top is growing with each run.  Miller A though is my answer to your question...just get all of that energy out in one swoop.

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