March 26-28 Severe Threat

[A-L-E-K]

high quality for sure

[nwohweather]

One thing to consider is the almighty lakes. Typically it holds up advancing warm fronts, and I see no reason this is going to be different especially with precip and clouds ahead of the low

[Indystorm]

[andyhb]

Synoptics here scream regional severe wx outbreak. One of the more synoptically evident events we’ve seen in recent years. Now it’s down to the mesoscale to decide on ceiling. Not every day you see a trough with a 110+ kt 500 mb max impinging on a warm sector with mid-upper 60s dewpoints regardless of season.

Wind fields seem to be gradually shifting towards more of the “these cells could be strongly tornadic” idea, but I’d also like to see what we wake up with tomorrow. I have little doubt the NAM 3 km is at least somewhat off in terms of eastward extent of the warm sector though.

[crossbowftw3]

I would guess the Warm Front stalls within a 10-20 mile radius (+-) of Chicago metro. Even if the front gets hung up everything south of that is primed and ready.

[CheeselandSkies]

24 minutes ago, nwohweather said:

One thing to consider is the almighty lakes. Typically it holds up advancing warm fronts, and I see no reason this is going to be different especially with precip and clouds ahead of the low

We had a relatively mild winter, so Lake Michigan temperatures are above normal. Still will undoubtedly have some influence but perhaps not as much as you'd normally expect in an early season setup.

The frigid February of 2015 was one of the things in the back of my mind that had me throw in the towel before T time on Rochelle day...

[RyanDe680]

yasssss.  bout time.  something to do while in lockdown

[andyhb]

Pretty ridiculous fixed layer STP ensemble mean from the 12z HREF.

[bdgwx]

15Z RAP is primed with a convective melee of activity in the warm sector there in IL.

[bdgwx]

Man...I'm getting up to 70 mph right movers on some of these soundings.

[Bob's Burgers]

[snowlover2]

Slight risk expanded east into IN on new day 1.

Quote

DAY 1 CONVECTIVE OUTLOOK  
NWS STORM PREDICTION CENTER NORMAN OK  
1122 AM CDT FRI MAR 27 2020  
 
VALID 271630Z - 281200Z  
 
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS MAINLY TONIGHT  
FROM EASTERN KS TO CENTRAL AND NORTHERN MO/IL/IN...  
   
..SUMMARY  
 
SEVERE THUNDERSTORMS ARE POSSIBLE MOSTLY TONIGHT, FROM EASTERN  
KANSAS ACROSS PARTS OF THE MIDWEST.  
   
..SOUTHERN/CENTRAL PLAINS TO THE MIDWEST THROUGH TONIGHT  
 
A LEE CYCLONE WILL DEEPEN THIS AFTERNOON IN THE VICINITY OF  
SOUTHEAST CO, AND THEN MOVE NORTHEASTWARD ACROSS KS TONIGHT ALONG A  
PRE-EXISTING BAROCLINIC ZONE AS A MIDLEVEL TROUGH PROGRESSES FROM  
THE FOUR CORNERS TO THE HIGH PLAINS. IN RESPONSE TO THE DEEPENING  
CYCLONE, THE LOW-LEVEL JET IS EXPECTED TO STRENGTHEN BY TONIGHT IN  
TWO CORRIDORS - ONE ACROSS OK/KS AND ANOTHER FROM MO/AR INTO THE OH  
VALLEY. LOW-LEVEL MOISTURE (BOUNDARY-LAYER DEWPOINTS AT LEAST IN  
THE MID 60S) WILL REACH THE PRIMARY BAROCLINIC ZONE FROM KS/OK INTO  
THE OH VALLEY THROUGH THE DAY, BENEATH AN ELEVATED MIXED LAYER. A  
ZONE OF MIDLEVEL MOISTURE AND SOME WEAK MIDLEVEL CONVECTION (ROOTED  
WITHIN THE ELEVATED MIXED LAYER) IS EXPECTED TODAY FROM NORTH TX  
ACROSS OK TO SOUTHERN KS AND SOUTHWESTERN MO.  
 
THE PROSPECTS FOR SURFACE-BASED CONVECTION IN THE WARM SECTOR ARE  
LIMITED THROUGH THE DAY, GIVEN THE RELATIVELY WARM ELEVATED MIXED  
LAYER AND WEAK FORCING FOR ASCENT. THERE MIGHT BE A NARROW WINDOW  
OF OPPORTUNITY FOR STORMS ROOTED NEAR THE SURFACE ALONG THE FRONT  
FROM SOUTHEAST KS INTO CENTRAL MO LATE THIS EVENING INTO EARLY  
TONIGHT, WHERE THE CAP WILL NOT BE PARTICULARLY STRONG AND AS THE  
LOW-LEVEL JET BEGINS TO STRENGTHEN. BY TONIGHT, THE STRENGTHENING  
LOW-LEVEL JET SEGMENTS AND ASSOCIATED WARM ADVECTION WILL CONTRIBUTE  
TO INCREASING POTENTIAL FOR ELEVATED THUNDERSTORM DEVELOPMENT ALONG  
AND NORTH OF THE PRIMARY FRONT (AND IN ADVANCE OF THE SURFACE  
CYCLONE), FROM EASTERN KS ACROSS MO INTO IL/IN. THE ELEVATED STORMS  
WILL POSE A PRIMARY THREAT OF LARGE HAIL. OTHERWISE, SOME  
CONVECTION WILL BE POSSIBLE LATER TONIGHT ACROSS THE EASTERN HALF OF  
OK IN ADVANCE OF THE APPROACHING MIDLEVEL TROUGH AND WITH COOLING IN  
THE 850-700 MB LAYER, WITH A CONDITIONAL THREAT FOR ISOLATED LARGE  
HAIL.  
 
..THOMPSON/MOORE.. 03/27/2020  

 

[It's Always Sunny]

15 hours ago, andyhb said:

Every other model has temps above 70 over most of the IL warm sector at 21z.

Yeah you're right I was looking at temps just south of Chicago not to the west where the warm sector was.  Looks like 3km NAM temps are slightly warmer in the IL warm sector today than yesterday for 21Z.

15 hours ago, sdantwx said:

With mid-to-high 90s verifying in Oklahoma and Texas in the last couple of days, you really don't need to wait around to figure that it's going to be warmer than typical.

If they're verifying in OK & TX then modeled temps could hold some truth for the warm sector.  I haven't been checking modeled surface temps in OK & TX to see how they've been verifying.

[Hoosier]

1 hour ago, nwohweather said:

One thing to consider is the almighty lakes. Typically it holds up advancing warm fronts, and I see no reason this is going to be different especially with precip and clouds ahead of the low

Surface low position and nuances with the occlusion also matters.  Eventually as the surface low approaches, the warm front will be forced north up to a certain point.  Well maybe I shouldn't say certain because we're not sure exactly where, lol

[CheeselandSkies]

15Z RAP appears to show the warm front getting into central WI, with southeasterly surface winds across the state not turning easterly until about the latitude of Green Bay. I have to imagine that's overdone. Although, it only has the 60 degree dewpoints nosing just north of the IL/WI state line so this might be one of those cases where there are multiple "warm fronts."

I think the trick tomorrow might be finding the sweet spot where the winds are more backed in the 850-700mb layer. Seeing decent surface backing across the board, but they veer to SW pretty quick by 850mb in most soundings and pretty much stay in the same direction at least up to 700mb. At least they don't back again, then veer again (V-B-V).

[joshwx2003]

Holy cow STP values are maxed out with the 12z HRRR 33 hours out

[StormySquares]

What should be expected in terms of structure tomorrow? Like would it be easy to see tornadoes from a distance?

[Sydney Claridge]

26 minutes ago, joshwx2003 said:

Holy cow STP values are maxed out with the 12z HRRR 33 hours out

I believe those maxed-out STP values are from convectively-contaminated model output, which is not reflective of the background environment.  Nevertheless the 12z HRRR still shows high STP values in the background environment.

EDIT: never mind, given the linked post from Vortex Crew below.  I was looking at the 12z HRRR output on Pivotal Weather.

[joshwx2003]

11 minutes ago, StormySquares said:

What should be expected in terms of structure tomorrow? Like would it be easy to see tornadoes from a distance?

From Vortex Crew https://www.facebook.com/688039631377431/posts/1504752026372850/?d=n

[StormySquares]

Ehh 1730z Day 2 outlook is late, by like 15 minutes.

 

[crossbowftw3]

Just now, StormySquares said:

Ehh 1730z Day 2 outlook is late, by like 15 minutes.

 

Likely tons of discussions happening now at SPC hence why it's late.

[snowlover2]

New day 2

Quote

DAY 2 CONVECTIVE OUTLOOK  
NWS STORM PREDICTION CENTER NORMAN OK  
1246 PM CDT FRI MAR 27 2020  
 
VALID 281200Z - 291200Z  
 
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS EXTREME  
SOUTHEASTERN IOWA INTO PARTS OF NORTHERN ILLINOIS...  
   
..SUMMARY  
 
A SIGNIFICANT SEVERE WEATHER OUTBREAK IS POSSIBLE FOR PORTIONS OF  
THE MIDDLE MISSISSIPPI VALLEY ON SATURDAY. THE THREATS WITH THE  
STRONGER STORMS INCLUDE TORNADOES, A FEW WHICH MAY BE SIGNIFICANT,  
LARGE TO VERY LARGE HAIL, AND SEVERE GUSTS.  
   
..SYNOPSIS  
 
THE MOST PROMINENT FEATURE WITHIN THE UPPER FLOW PATTERN OVER THE  
U.S. SATURDAY WILL BE A STRONG SHORT-WAVE TROUGH SHIFITNG  
NORTHEASTWARD ACROSS THE PLAINS, AND EVOLVING INTO A COMPACT CLOSED  
LOW. THIS LOW SHOULD RESIDE OVER THE MID MISSOURI VALLEY DURING THE  
AFTERNOON, AND THEN CONTINUE MOVING NORTHEASTWARD TO A POSITION OVER  
WISCONSIN BY THE END OF THE PERIOD.  
 
AT THE SURFACE, A LOW INITIALLY OVER KANSAS IS EXPECTED TO MOVE  
STEADILY NORTHEASTWARD IN CONJUNCTION WITH THE EVOLVING UPPER LOW --  
OCCLUDING AS IT DOES. THE LOW SHOULD RESIDE OVER IOWA BY LATE  
AFTERNOON/EARLY EVENING, AND NORTHEASTERN WISCONSIN BY THE END OF  
THE PERIOD. A WARM FRONT EXTENDING EAST FROM THE EVOLVING LOW  
SHOULD RESIDE OVER THE MIDWEST THROUGH THE DAYLIGHT HOURS BEFORE  
ADVANCING NORTHWARD INTO THE GREAT LAKES OVERNIGHT, WHILE A COLD  
FRONT SHIFTS OUT OF THE PLAINS AND ACROSS THE MID MISSISSIPPI VALLEY  
THROUGH LATE AFTERNOON/EARLY EVENING, AND THEN THE  
OHIO/TENNESSEE/LOWER MISSISSIPPI VALLEYS OVERNIGHT. A SIGNIFICANT  
SEVERE-WEATHER EVENT IS EXPECTED ACROSS THE NORTHERN ILLINOIS AREA  
AND PORTIONS OF ADJACENT STATES -- FOCUSING DURING THE AFTERNOON AND  
EARLY EVENING HOURS.  
   
..EASTERN IA AND NORTHEASTERN MO EASTWARD TO OH  
 
A RAPIDLY EVOLVING ENVIRONMENT WILL CHARACTERIZE THE ENH AND MDT  
RISK AREAS -- I.E. THE MIDDLE MISSISSIPPI VALLEY AREA -- DURING THE  
FIRST HALF OF THE PERIOD, AS THE UPPER SYSTEM CLOSES OFF AND THE  
SURFACE LOW DEEPENS, AND EVENTUALLY OCCLUDES. EARLY-PERIOD  
CONVECTION ACROSS THE RISK AREA IS FORECAST TO SHIFT NORTHEASTWARD  
AND DISSIPATE, ALLOWING HEATING -- IN CONJUNCTION WITH RAPID  
STEEPENING OF MID-LEVEL LAPSE RATES -- TO YIELD MODERATE  
DESTABILIZATION. NEW STORM DEVELOPMENT IS FORECAST TO OCCUR DURING  
THE MID AFTERNOON TIME FRAME IN THE FAR EASTERN IOWA/FAR  
NORTHEASTERN MISSOURI/NORTHWESTERN ILLINOIS AREA, AND CELLULAR MODE  
IS ANTICIPATED.  
 
PRONOUNCED LOW-LEVEL VEERING IN THE WIND FIELD -- PARTICULARLY IN  
THE VICINITY OF THE WARM FRONT OVER NORTHERN ILLINOIS -- IS  
EXPECTED, WITH FLOW INCREASING TO SOUTHWESTERLY AT NEAR 100KT AT MID  
LEVELS, AS THE UPPER SYSTEM APPROACHES. THE RESULTING SHEAR WILL BE  
STRONGLY SUPPORTIVE OF STRONG UPDRAFT ROTATION -- AND THUS ATTENDANT  
RISK FOR TORNADOES, A FEW OF WHICH COULD BE SIGNIFICANT. VERY LARGE  
HAIL WILL ALSO BE POSSIBLE GIVEN UPDRAFT INTENSITY -- AIDED BY THE  
VERY STEEP LAPSE RATES ALOFT AND STRENGTH OF THE SHEAR PROFILE.  
LOCALLY DAMAGING DOWNBURST WINDS WILL ALSO BE POSSIBLE LOCALLY, WITH  
THE STRONGER STORMS. PEAK TORNADO RISK THROUGH LATE AFTERNOON  
SHOULD BEGIN TO GRADUALLY DIMINISH INTO THE EVENING, AS DIURNAL  
COOLING BEGINS. STILL, SEVERE RISK -- INCLUDING POTENTIAL FOR LARGE  
HAIL WITH ELEVATED STORMS NORTH OF THE WARM FRONT -- WILL LIKELY  
CONTINUE THROUGH THE EVENING BEFORE DECREASING OVERNIGHT.  
   
..KY AND TN SOUTHWESTWARD TO THE LOWER MS VALLEY AREA  
 
A BAND OF SHOWERS AND THUNDERSTORMS IS PROGGED TO GRADUALLY EVOLVE  
AHEAD OF THE ADVANCING COLD FRONT -- FROM FAR EAST  
TEXAS/NORTHWESTERN LOUISIANA NORTHEASTWARD ACROSS THE MID  
MISSISSIPPI/LOWER OHIO VALLEYS DURING THE AFTERNOON. THE STORMS  
WILL EVOLVE AS DIURNAL HEATING OF THE MOIST PRE-FRONTAL BOUNDARY  
LAYER YIELDS INCREASING CAPE, AND INCREASING LARGE-SCALE ASCENT  
HELPS TO ERODE A RESIDUAL WARM LAYER ALOFT.  
 
DESPITE MODEST LOW-LEVEL VEERING, DEEP-LAYER SHEAR WILL SUPPORT  
ORGANIZED/ROTATING STORMS -- WITH INCREASING RISK WITH NORTHWARD  
EXTENT ACROSS THE TENNESSEE VALLEY AND INTO THE OHIO VALLEY REGION  
THROUGH THE AFTERNOON/EARLY EVENING. DAMAGING WINDS AND HAIL WILL  
LIKELY BE THE PRIMARY RISK, THOUGH A COUPLE OF TORNADOES WILL BE  
POSSIBLE -- PARTICULARLY NEARER THE OHIO VALLEY. RISK SHOULD  
GRADUALLY DIMINISH BEGINNING IN THE EVENING AND INTO THE OVERNIGHT  
HOURS.  
 
..GOSS.. 03/27/2020  

 

[WeatherMonger]

Expanded the 10 and 15% hatching SW

Old

 

New

 

[andyhb]

12z Euro was a bit of a downtick from earlier. Weaker wind fields/less instability.

[A-L-E-K]

2020'd

[Radtechwxman]

Lol. Built the hype. Now time for it to get crushed. Yea 12z euro definitely was weaker esp with sfc wind speeds. Killed the hodo in the low levels. But since that isn't a high resolution model probably would put more faith in shorter term hi res models

[Chicago Storm]

NAM>Euro at this range.


.

[jojo762]

18Z HRRR continues to show what would probably be a significant tornado outbreak across Iowa and Illinois. *IF* you want to go all in on the HRRR solutions, would seem that the moderate and high-risk tornado delineations are going to have to be expanded to include a larger portion of both Iowa and Illinois, possibly even a small part of eastern/southeastern Missouri and western Indiana. 

[Chicago Storm]

Gave the NAM credit too soon...

18z run came in much slower, but still has the best environment across SE IA and W IL during late afternoon into the evening.

3km is laughably slower, with initiation at the KS/MO border at 18z.

[geddyweather]

Cracks me up how models have that uncanny ability to diverge in close range after 2-3 consistent runs.