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Jan 31 - Feb 1 Ice Possibilities


Holston_River_Rambler
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Pretty good model consensus for a light icing event.  On some modeling it is worse.  Both Nashville and Memphis have good write-ups this morning about it.  Trend overnight, as Holston mentioned, is south.  Models are feeling that cold air parked over the top.  My guess is that at some point it begins trending back north at the last minute - that is normal.  Memphis mentioned that ice storm criteria have not been met.  However, I would suspect WWAs might be posted if models continue to lock in.

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1 hour ago, Carvers Gap said:

Pretty good model consensus for a light icing event.  On some modeling it is worse.  Both Nashville and Memphis have good write-ups this morning about it.  Trend overnight, as Holston mentioned, is south.  Models are feeling that cold air parked over the top.  My guess is that at some point it begins trending back north at the last minute - that is normal.  Memphis mentioned that ice storm criteria have not been met.  However, I would suspect WWAs might be posted if models continue to lock in.

Good point; however, I think even with the northern last-minute adjustment, the southern net will allow WWA's to be posted along and north of 40 at least for middle TN. I hate saying that b/c it's so cliche but I could see that scenario unfolding. 

Side note: One of these days, OHX's over-conservative approach is going to bite them. Not saying their latest write-up is wrong at all though I am saying I look forward to their next serving of crow. To the public they take any forecast and make it sound so blah. It's irritating to me. Flash vent over. Carry on. :D

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10 minutes ago, Carvers Gap said:

18z short range modeling is now very consistent (and still going a tic southward) with several waves of sleet, ice, snow and ZR for middle and west TN.  

Edit:  slight tic northward for the RGEM and NAM

You said a last minute jog North would happen. I bet when it gets even closer there will be hardly any frozen in TN. Maybe very far NW corner.  

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4 minutes ago, Matthew70 said:

You said a last minute jog North would happen. I bet when it gets even closer there will be hardly any frozen in TN. Maybe very far NW corner.  

I don't think it will jog that far, but I never say never regarding trends.  The 18z GFS is now bullseye for Memphis.  Time of day is really important.  I think that is why E TN is not involved right now.  Even SW VA and NE TN are not out of the woods with later waves.   I will be surprised if WWAs, at the very least, are not issued for west TN by tomorrow morning.  I don't see an afternoon disco yet for Memphis.  So, they may be coordinating w/ other NWS offices right now.  The numbers for 18z modeling are fairly stout.  It may be there isn't a northward jog at all, but just the northward expanse of the precip shield filling in.

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They are flirting with a very fine line....

Area Forecast Discussion
National Weather Service Memphis TN
424 PM CST Sun Jan 29 2023

...New SYNOPSIS, DISCUSSION, AVIATION...

.SYNOPSIS...
Issued at 307 PM CST Sun Jan 29 2023

Cloudy conditions will prevail through the evening hours as light
rain moves across north Mississippi. Rain should increase
overnight ahead of a slow moving cold front. Precipitation will
return to the Midsouth Monday night in the form of freezing rain
along and north of Interstate 40. Icing potential will continue,
reaching as far south as northwest Mississippi Tuesday night.

&&

.DISCUSSION...
(This evening through next Saturday)
Issued at 307 PM CST Sun Jan 29 2023

Rain will move through the region this evening into early Monday.
The area will catch a small break Monday before the first chance
of icing for the Mid South Monday night into Tuesday. Latest
guidance continues to trend slightly cooler for Monday night
through Wednesday timeframe. With that being said, the most likely
scenario is that there will be two distinct chances for icing over
the Mid South through Wednesday.

The first of which will be Monday night into Tuesday morning as a
subtle wave moves across the region. The best chances for that
icing will be along and north of I-40. Ice accumulations less
than a tenth of an inch will be possible. Now, with that we will
catch a break in the precipitation on Tuesday during the day...and
depending on ow far south the initial cold air surges will be
important on how far north and how much melting occurs for the
first shot of ice. Temperatures will be in the low to mid 30s
area wide and the freezing line will dictate impacts to roads and
other infrastructure for the next shot of ice Tuesday night into
Wednesday. This chance has the potential to be the bigger threat
as heavier precip will move through overnight when temps are at
their coldest. Models have trended south some on this possible
band of ice in the forecast and would include Memphis metro and
possibly into northwest Mississippi. Accumulations Tuesday night
into Wednesday could reach up to 0.20 inches of ice. As far as
winter weather advisories and warnings are concerned, we will
continue to evaluate the situation as the duration and the two
distinct shots of ice make this difficult as to not have a watch
out for several hours before any impacts. Winter weather
advisories will be needed, and there is a non zero chance of a
winter storm warning being issued. Stat tuned to the forecast for
any changes.

The good news is that we should be above freezing on Wednesday
and that will allow for melting of any ice to occur. The southern
branch upper low will weaken and pass through the Arklamiss region
by late Thursday evening, pushing the downstream warm conveyor
belt and associated heavier rainfall into Alabama late Thursday
night. Milder temperatures should return to the Midsouth by next
Saturday, ahead of progressive open upper level trough.
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40 minutes ago, Carvers Gap said:

I don't think it will jog that far, but I never say never regarding trends.  The 18z GFS is now bullseye for Memphis.  Time of day is really important.  I think that is why E TN is not involved right now.  Even SW VA and NE TN are not out of the woods with later waves.   I will be surprised if WWAs, at the very least, are not issued for west TN by tomorrow morning.  I don't see an afternoon disco yet for Memphis.  So, they may be coordinating w/ other NWS offices right now.  The numbers for 18z modeling are fairly stout.  It may be there isn't a northward jog at all, but just the northward expanse of the precip shield filling in.

I agree with you, Carver. I don't such a dramatic last-second trend that takes all of middle TN out of the game. Maybe southern middle gets taken out but that's all I can imagine. 

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Yep I will be watching how big the precip waves are correlated with the amount of cold. Sometimes these precip shields can be less or more than advertised. We definitely have a potential winter weather system to track across middle and west Tennessee and other areas in upper east tenn may not be out it on the waves of precip on the back side of this but that is more in doubt right now.

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1 hour ago, Carvers Gap said:

Here is the 18z RGEM compared to 12z.  Newest run is on the left...

Screen_Shot_2023-01-29_at_5.10.41_PM.png

 

This puts me in mind of a similar setup in January 1990( similar winter). An Arctic air mass was moving southward pretty much as this one and waves rode the boundary that stalled in our area. freezing rain made it to Lee and Scott County at southern extent. 

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6 minutes ago, Carvers Gap said:

The 0z 3k/12k NAM depictions push the ice line southward with each run.   

Yeah, I noticed that. Pretty substantial difference in places that were already below freezing as well. 3 to 4 degrees colder. Unfortunately, it makes the risk for ice much worse in places like west and middle TN. If it stays at 31-32, it probably won't be too bad. But if creeps into the upper 20s...

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Ice storm warnings have been posted for much of west TN, NW MS, NE Arkansas.  WWAs all the way to Nashville.

URGENT - WINTER WEATHER MESSAGE
National Weather Service Memphis TN
321 AM CST Mon Jan 30 2023

ARZ026>028-035-036-048-049-058-MSZ001>003-007-008-TNZ003-004-
019>022-048>055-088>090-301800-
/O.NEW.KMEG.IS.W.0001.230131T0000Z-230201T1800Z/
Craighead-Poinsett-Mississippi-Cross-Crittenden-St. Francis-
Lee AR-Phillips-DeSoto-Marshall-Benton MS-Tunica-Tate-Weakley-
Henry-Dyer-Gibson-Carroll-Benton TN-Lauderdale-Tipton-Haywood-
Crockett-Madison-Chester-Henderson-Decatur-Shelby-Fayette-
Hardeman-
Including the cities of Jonesboro, Harrisburg, Blytheville,
Wynne, West Memphis, Forrest City, Marianna, Helena, West Helena,
Southaven, Olive Branch, Holly Springs, Ashland, Tunica,
Senatobia, Martin, Dresden, Paris, Dyersburg, Humboldt, Milan,
Huntingdon, Camden, Ripley TN, Covington, Brownsville, Alamo,
Jackson, Henderson, Lexington, Parsons, Decaturville, Bartlett,
Germantown, Collierville, Memphis, Millington, Somerville,
Oakland, and Bolivar
321 AM CST Mon Jan 30 2023

...ICE STORM WARNING IN EFFECT FROM 6 PM THIS EVENING TO NOON CST
WEDNESDAY...

* WHAT...Significant icing expected. Ice accumulations of a
  quarter to one half an inch.

* WHERE...Portions of East Arkansas, North Mississippi and West
  Tennessee.

* WHEN...From 6 PM this evening to noon CST Wednesday.

* IMPACTS...Power outages and tree damage are likely due to the
  ice. Travel could be nearly impossible. The hazardous
  conditions could impact the morning or evening commute.

* ADDITIONAL DETAILS...Partial ice melting may occur Tuesday
  afternoon before freezing rain returns Tuesday evening.

 

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.DISCUSSION...
(Today through Sunday)
Issued at 530 AM CST Mon Jan 30 2023

00Z model guidance consensus trended significantly higher with
respect to ice accumulation, following days of relative stability
of depicting 0.1 to 0.2 inches of maximum ice accumulations.
Model spread remained less than ideal 24 hours out from event
onset, with the Canadian ensemble members on the high end, and GFS
members on the low side. Overall, the 00z consensus signal is
clear for greater than 0.25 inches of ice accumulation. The WPC
Super Ensemble mean showed 0.30 inches for Memphis through
Wednesday - among the highest amounts depicted for the Midsouth.
For reference, Ice Storm Warning criteria is 0.25 inches.

The primary reason for the bump in ice accumulations are the
downward trend in temperature guidance through Tuesday night.
2 to 3 degrees makes a big difference when temperatures are near
freezing.

Higher sleet ratios are expected over far northeast AR, the MO
bootheel and far northwest TN through Wednesday. This would reduce
forecast ice accumulations below Ice Storm Warning criteria.
However, if more than 0.5 inches of sleet becomes likely, areas
north of the Ice Storm Warning may be upgraded to a Winter Storm
Warning.

As mentioned in previous discussions and in the recently issued
Ice Storm Warning, partial melting will be possible Tuesday
afternoon, which may relieve trees and powerlines from the ice
load that accumulated Monday night. Based on forecast surface
temperatures, this partial melting would be most likely to occur
southeast of a line from West Helena to West Memphis AR, to
Covington and Camden, TN. This includes Shelby County, TN. As
always, forecasting shallow Arctic air is a challenge. The
official forecasted temperatures for Tuesday morning and afternoon
follow the NBM, which was colder by 1-2 degrees than the mean of
the NBM ensemble members. In other words, the NBM and the official
forecast are on the conservative (cold) side of the model
guidance envelope for temperatures Monday night and Tuesday.

A second round of ice is expected Tuesday evening, as midlevel
subtropical moisture continues to stream into our region from
Texas. Low level moisture transport will increase above the
shallow Arctic air, under the right entrance of a strengthening
upper jet core over the Ohio River Valley. Total precipitable
water values will reach 1 inch as far north as the TN/MS border
Tuesday night. At the surface, Tuesday night temperatures will
cool into the upper 20s along the I-40 corridor, and the mid 20s
over northeast AR, the MO bootheel and northwest TN.

By Wednesday morning, the center of the Arctic surface pressure
ridge will move to the upper Ohio River Valley, with near neutral
surface pressure and temperature advection over the Midsouth by
daybreak. Under building heights aloft, temperatures should slowly
warm above freezing Wednesday afternoon over all the Midsouth. As
with Tuesday, official temperature forecasts for Wednesday
followed the NBM, which remained a 1-2 degrees cooler than NBM
ensemble mean.

Rain will continue Wednesday night, with some threat of a changeover
to light freezing rain over far northeast AR and the MO bootheel.
At this time, QPF and temperature trends suggest less than 0.10
inches of ice, before temps warm well above freezing on Thursday.
This may need to be addressed in a future Winter Weather advisory.

A welcome change will arrive Friday and Saturday, as shortwave
ridging aloft brings sunshine, and mild temperatures.

 

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4 minutes ago, Carvers Gap said:

If this comes to fruition, this is a coup for the Canadian RGEM and CMC.  They had this from the word "go," and never budged.

Yep. 

RGEM has been pretty darn good this year. If not always perfect at least consistent. 

It's at range but it favors the ice to continue with the next wave Thursday. Not much else does right now, so it will be interesting to see how that evolves.

rgem_mslp_pcpn_frzn_us_81.png

 

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1 minute ago, Holston_River_Rambler said:

Yep. 

RGEM has been pretty darn good this year. If not always perfect at least consistent. 

It's at range but it favors the ice to continue with the next wave Thursday. Not much else does right now, so it will be interesting to see how that evolves.

rgem_mslp_pcpn_frzn_us_81.png

 

Very definition of an over-running event if it lasts that long.  

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It is fairly amazing to see the GFS bend completely to the CMC on this ice storm.  I think most assumed(me included) that the CMC had overdone the boundary, and maybe will once it verifies.  But that is pretty solid and tight cone for the ice even this week.  This should be a 48-72 hour overrunning event.  Modeling has done a really good job up to this point with that.

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