Possible SVR 1/20-1/21

[Charles L.]

SPC has outlined areas of southern middle TN and north/central AL in a Slight risk category for storms later on today into tonight.

Surface dewpoints have a good chance of getting to and over 60F for these areas. All modes of severe weather will be possible, including isolated tornadoes.

Looks to be your, typical, low CAPE/high shear setups.

[@NashSevereWx]

NAM shoves 60F DPs up to I-40, allowing for 1.0 EHI scores. GFS holds them about 60 mi S.  Watching the WF closely...

[Charles L.]

NAM shoves 60F DPs up to I-40, allowing for 1.0 EHI scores. GFS holds them about 60 mi S.  Watching the WF closely...

Yeah, if NAM is right then I like the SPC's placement...if GFS is right worse ingredients will stay south of middle TN.

DP's are getting closer to 50F across north AL, already there across central AL.

[Eric]

Looks like the SREF (which has been "King of Numericals" the past few events) is a blend between the GFS and the NAM, keeping 60F Tds just to the south of TN.  Shear values are decent, and coupled with MuCAPE values of 500-750j/kg, there coud definitely be isolated tornadoes...with that being said, though, if the SREF's SLP placement verifies, all the exciting stuff will stay across the Tn Valley.

[Charles L.]

That warm front will have to do a lot of moving over the next 10-12 hours if we are to see 60F DP's...those numbers are still back across southern MS (Hattiesburg and Jackson).

It can be done, but I am, currently, leaning towards the SREF and GFS...but, of course, nothing is set in stone yet. It is far from that point.

[toastido]

Looks like the SREF (which has been "King of Numericals" the past few events) is a blend between the GFS and the NAM, keeping 60F Tds just to the south of TN.  Shear values are decent, and coupled with MuCAPE values of 500-750j/kg, there coud definitely be isolated tornadoes...with that being said, though, if the SREF's SLP placement verifies, all the exciting stuff will stay across the Tn Valley.

MORE FOR ME! 

[Eric]

From the 1030 SPC Day 1 update:

...LOWER MS VALLEY INTO TN VALLEY AND SRN APPALACHIANS...
   
   12Z SOUNDINGS AND CURRENT SURFACE OBSERVATIONS INDICATE LOW-LEVEL
   MOISTURE INCREASING ACROSS THE LOWER MS VALLEY AND CNTRL GULF STATES
   WHERE BOUNDARY LAYER DEWPOINTS ARE RISING THROUGH THE 50S INTO
   LOWER-MID 60S.  EXPECT THIS PROCESS TO CONTINUE THROUGH THE D1
   PERIOD AS A LLJ DEVELOPS OVER THE LOWER MS VALLEY AND SUBSEQUENTLY
   EXPANDS THROUGH THE CNTRL/SRN APPALACHIANS TO MID-ATLANTIC COAST.
   HOWEVER...THIS LOW-LEVEL MOISTENING WILL OCCUR BENEATH A RELATIVELY
   STRONG CAP SAMPLED BY THE 12Z SOUNDINGS...EFFECTIVELY LIMITING THE
   DEGREE OF DESTABILIZATION AND RESULTANT SEVERE POTENTIAL ACROSS THE
   REGION TODAY.
   
   LATEST MODEL GUIDANCE IS RELATIVELY CONSISTENT IN SUGGESTING THAT
   CONVECTION WILL CONTINUE TO DEEPEN TODAY ACROSS PORTIONS OF
   MS/AL...FORCED BY LOW-LEVEL WAA/MOISTENING ALONG DEVELOPING LLJ.  AS
   MENTIONED ABOVE...FORECAST SOUNDINGS INDICATE THAT RELATIVELY WARM
   MIDLEVEL TEMPERATURES AND RESULTING POOR LAPSE RATES WILL LIMIT
   PARCEL BUOYANCY.  WHILE AN ISOLATED SEVERE STORM IS POSSIBLE /GIVEN
   THE STRENGTHENING VERTICAL SHEAR/...IT APPEARS THAT ORGANIZED STORM
   POTENTIAL WILL BE DELAYED UNTIL TONIGHT.
   
   BY TONIGHT...LARGE-SCALE FORCING FOR ASCENT/HEIGHT FALLS ASSOCIATED
   WITH ABOVE-MENTIONED SHORT-WAVE TROUGH WILL BEGIN TO OVERSPREAD
   EXPANDING WARM SECTOR.  TSTMS ARE EXPECTED TO INCREASE INITIALLY INVOF MIGRATORY SURFACE LOW OVER PORTIONS OF TN/KY WITH ACTIVITY SUBSEQUENTLY DEVELOPING SWWD ALONG THE FRONT ACROSS NRN PARTS OF MS/AL.  INSTABILITY WILL REMAIN WEAK WITH MLCAPE LESS THAN 500-1000
 J/KG.  HOWEVER...THE PRESENCE OF DEEP...WLY SHEAR OF 45-55 KT AND 0-1 KM SRH APPROACHING 250-400 M2/S2 INDICATE A THREAT FOR EMBEDDED SUPERCELL AND BOWING STRUCTURES CAPABLE OF A COUPLE TORNADOES AND LOCALLY DAMAGING WINDS.

[Thundersnow]

Actually, the latest Day 1 outlook takes the northern extent of the Slight Risk up to the KY border, including more of TN from what I can tell by comparing it to the earlier outlook.

[Eric]

Actually, the latest Day 1 outlook takes the northern extent of the Slight Risk up to the KY border, including more of TN from what I can tell by comparing it to the earlier outlook.

Thanks for the correction.   

[@NashSevereWx]

12Z GFS draws 60 Tds tangent to I-40, way up from the 6Z run. NAM 12Z is already there, tempting/mocking " to keep going a bit further, GFS."

HRRR appears unwilling to squirt moisture that far N by 6z.

Still, I'm afraid to take a glass of water outside considering helicity values at/exceeding 300. Hoping that wet air stays stuck where it is.

[Eric]

Eeeeesh.....17z RUC puts 60-63F Tds basically from I-40 east to I-65 and points southward valid 05z tomorrow (1100p tonight).

FWIW...latest surface obs show 33F dew point at BNA, but just 2 hours south at HSV, it's 54F.  I'd say the warm front is marching northward....

[jmundie]

Its crazy how "wintry" (for this year at least) it feels outside currently, to be talking about some decent severe weather tonight.

I imagine once the warm front comes through, it won't feel so wintry.

[Eric]

Not much change in the 18z RUC's northward progression of moisture advection...

[Kevin]

Not a big fan of rapid moisture advection events in the cool season...they usually are tough to play out. However...if/when they do...the best threat generally ends up on the northern fringe of the advection zone near the boundary...and of course that's where shear will be locally enhanced as well.

I don't think there's much of a tornado threat...mainly wind and perhaps some hail...but if one or two were to happen I'd think it would be near wherever the boundary ends up...which will probably be in a zone from N MS into Middle TN just south of the 40 corridor.

Fortunately...looks like Memphis metro and most of W TN will stay outside the unstable air and attendant severe threat...though some thunder possible. Will be monitoring in case it tries to briefly sneak in...a very narrow window may exist around mid-evening.

[Kevin]

Looks like SPC expanded the SLGT NW some into Memphis metro and other parts of W TN...likely based on the aforementioned window...though narrow...of the warm sector airmass moving in on some guidance (mainly RUC/NAM). We'll see how it plays out. Still believe the best threat is more to the E/SE.