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Spring severe weather chatter


Ian

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     I should know better, but it seems like Tuesday does have some sleeper potential.   

 

     Shortwave trough crosses the area during the early to mid afternoon.    Flow is unidirectional, but the speed shear is impressive, with a 100+ kt jet at upper levels.    Looks like 60+ kt of 0-6 km layer shear during the early afternoon decreasing slightly after that.   Sfc-based cape may be in the 1000-1500 range, and soundings have the inverted-V look, suggesting some wind threat.

 

      Downside is that convergence is limited, and there is no well-defined front (although there may be a sfc trough) on which to focus, but lift associated with the shortwave may compensate.    One further complicating factor is that we could be in a zone of subsidence as Colin passes to our southeast.

 

      I'd say it's worth a 5% outlook at this point.     The really strong short wave and associated cold front with better convergence actually comes through Wednesday midday according to the 00z NAM.     It implies a gusty line of showers (or perhaps boomers if the 1000 cape forecast pans out) then, although moisture is very limited.

 

All joking aside, are we really watching Tuesday for anythinf?

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So, SPC actually put us into a 15% outlook for Day 6!   (Saturday).     I'm kind of surprised that they outlooked an area, given the healthy spread in model details.   That said, all guidance has a ridge axis to our west with extremely fast northwest flow in a corridor from the Great Lakes through the Mid-Atlantic.     A sfc low is going to pop somewhere to our northwest, and there will likely be a very well-defined warm front to our north.   Can't disagree that supercells will be favored along the warm front and that fast-moving bows would be possible in the warm sector.    It's just a question of where the highest threats set up (and obvious potential for clouds and rain to inhibit destabilization, etc...)

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The GFS soundings on the COD site for Saturday are ridiculous. Has some crazy sup composite numbers and a random location sounding I looked at for 21z on Saturday in Central Maryland is showing supercell comp of 39.0, STP of 4.1, STP fixed of 7.3. It's a downright crazy sounding. No way it holds. It's all downhill from here. Unless of course we get our traditional derecho ;)

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And just like that - 12z GFS isn't like 6z at all. Expected.

Yep, Saturday Afternoon instead of Upper 60s to Low 70s Dew Points, 1.8-2.1" PWAT. 12z has Lower 50s Dew Points and PWAT's around 0.8". Stick with Euro for severe weather threats. Meanwhile GGEM goes to a 6z GFS like solution. Wacky models... >>>well really it's "pushed back" on the GFS, but still rather lame this run. 12z GFS seems to like severe for the Eastern 2/3 Next Week
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Yep, Saturday Afternoon instead of Upper 60s to Low 70s Dew Points, 1.8-2.1" PWAT. 12z has Lower 50s Dew Points and PWAT's around 0.8". Stick with Euro for severe weather threats. Meanwhile GGEM goes to a 6z GFS like solution. Wacky models... >>>well really it's "pushed back" on the GFS, but still rather lame this run. 12z GFS seems to like severe for the Eastern 2/3 Next Week

 

Yeah 12z GFS sort of has an okay period of parameters but it's 15z Sunday now which would be too early for meaningful severe. I'll watch but not be invested until Thursday or Friday. 

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The 12z EC is much different than the GFS - strong trough approaching from the northwest much sooner than in the GFS with a deepening sfc low moving across northern New England.      Still not much cape here verbatim.    With lots of model uncertainty, seems tough to justify the day 5 outlook unless you're hugging the EC really tight and modifying some details.

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It's still there in the D5 SPC outlook, but seems a stretch based on the current modeling.

 

...DISCUSSION...
ALTHOUGH DIFFERENCES IN SHORTWAVE TIMING EXIST AMONG THE VARIOUS
MODEL OUTPUT...A GENERAL CORRIDOR OF SEVERE WIND AND HAIL THREAT IS
EXPECTED TO DEVELOP POSSIBLY AS EARLY AS D4/FRI FROM NRN MN ACROSS
MI...THEN FROM MI SEWD ACROSS PA AND INTO MD/VA ON SAT/D5. AT THIS
TIME...IT APPEARS THE PATTERN WILL BE MORE FAVORABLE ON SAT/D5 AS
THE SHORTWAVE TROUGH STRENGTHENS AND SURFACE LOW DEEPENS OVER THE
NERN STATES...IN TURN STRENGTHENING WIND FIELDS AND AIDING IN FASTER
STORM MOTIONS FAVORABLE FOR DAMAGING WIND. HAVE EXPANDED AREAL
COVERAGE OF THE RISK AREA A BIT TO ACCOUNT FOR MORE UNCERTAINTY
GIVEN THE CURRENT MODEL SUITE. CURRENT OUTPUT SUGGESTS STORMS
FORMING OVER LOWER MI OR NRN OH SATURDAY AFTERNOON...DEVELOPING SEWD
SATURDAY NIGHT. BY SUN/D6 MORNING...ACTIVITY IS EXPECTED TO BE
OFFSHORE.

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Lots of uncertainty in the details, but there is agreement that an extremely impressive trough crosses our region Saturday night with big height falls, impressive wind fields, and a strong cold front.    It's hard to get nocturnal severe here, but it can happen, and this would be a setup that at least makes it a possibility.

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