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Severe Weather possible weekend of the 21st?


weatherwiz

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HAVE UPDATED GRIDS TO SLOW DOWN THE PRECIP ESPECIALLY OVER EASTERN

AREAS UNTIL AROUND 18Z AND BEYOND. DEWPTS ARE MUCH HIGHER THAN

FORECAST...MAINLY IN THE MID 70S NEAR AND S OF THE MASS PIKE WHERE

THEY APPEAR TO BE POOLING...SO MAY BE A FOCUS OF ANY CONVECTION

THAT MAY DEVELOP PROBABLY AFTER 18Z. USED A BLEND OF OUR PREVIOUS

FORECAST WITH THE HRRR MODEL...WHICH APPEARS TO HAVE THIS SAME

FOCUS. OTHER CONVECTIVE PARAMETERS ARE MARGINAL...WITH MID LEVEL

LAPSE RATES ON ORDER OF 6C/KM...FOR LOW LEVEL LAPSE RATES ARE MUCH

HIGHER OVER CENTRAL AND EASTERN AREAS AS SEEN ON SPC MESO

ANALYSIS. SPC DID UPDATE THEIR CONVECTIVE OUTLOOK TO SHIFT IT A

BIT FURTHER S.

 

 

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HAVE UPDATED GRIDS TO SLOW DOWN THE PRECIP ESPECIALLY OVER EASTERN

AREAS UNTIL AROUND 18Z AND BEYOND. DEWPTS ARE MUCH HIGHER THAN

FORECAST...MAINLY IN THE MID 70S NEAR AND S OF THE MASS PIKE WHERE

THEY APPEAR TO BE POOLING...SO MAY BE A FOCUS OF ANY CONVECTION

THAT MAY DEVELOP PROBABLY AFTER 18Z. USED A BLEND OF OUR PREVIOUS

FORECAST WITH THE HRRR MODEL...WHICH APPEARS TO HAVE THIS SAME

FOCUS. OTHER CONVECTIVE PARAMETERS ARE MARGINAL...WITH MID LEVEL

LAPSE RATES ON ORDER OF 6C/KM...FOR LOW LEVEL LAPSE RATES ARE MUCH

HIGHER OVER CENTRAL AND EASTERN AREAS AS SEEN ON SPC MESO

ANALYSIS. SPC DID UPDATE THEIR CONVECTIVE OUTLOOK TO SHIFT IT A

BIT FURTHER S.

 

 

 

I also don't quite get what they mean by "other convective parameters are marginal".  Which parameters?  mid-level lapse rates aren't all that bad and Ekster has said in the past to overcome marginal or weak mid-level lapse rates you want dews in the low to mid 70's and that's what we have.  I'm confused as to which other convective parameters are marginal.

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There really isn't an ideal "checklist"...you just want to see a combination of several ingredients come together. However, for Cape values (SBcape/MLcape/MUcape) you 'd like to see these values at least 1000 J/KG, LI values you'd like to see at least -2C, 0-6km shear values at least 30 knots, mid-level lapse rates at least 6 C/KM, weak height falls at 500mb, you'd like to have at least 20 knots of wind at 925/850mb, 25-30 knots at 700mb, at least 40 knots at 500mb, then you want to be in the right entrance region (or exit region) of an ULJ which is at least 80-90 knots. You want surface dewpoints to be at least into the lower 60's and have dewpoints at 925/850 be in excess of 12-16C.

What I mentioned here though are just like minimum requirements you would like to see when dealing with the possibility of one or a few strong to severe storms. Obviously if you are looking for widespread severe or an outbreak you would want to see much higher numbers. You also have to look at the synoptic setup as well and see if you have any sources of lift (cold front or pre-frontal trough is ideal), etc.

Id even say 6.5c i think lapse rates are muy importante... you can have all the instability you want but without steep rates... pfftph
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Id even say 6.5c i think lapse rates are muy importante... you can have all the instability you want but without steep rates... pfftph

 

Well it's quite difficult to obtain extreme amounts of instability without steep lapse rates or an EML present, but one way to do so is to have very high surface dewpoints and low-level moisture in place.  The 12z OKX sounding had lapse rates up near 7 C/KM.  Mesoanalysis shows them closer to 6 C/KM but I would like to see what they actually are...mesoanalysis only does .5 increments.  I wish OKX would do an 18z launch.

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Well it's quite difficult to obtain extreme amounts of instability without steep lapse rates or an EML present, but one way to do so is to have very high surface dewpoints and low-level moisture in place. The 12z OKX sounding had lapse rates up near 7 C/KM. Mesoanalysis shows them closer to 6 C/KM but I would like to see what they actually are...mesoanalysis only does .5 increments. I wish OKX would do an 18z launch.

I don't think I'll ever advertise widespread wording w/o an EML
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I don't think I'll ever advertise widespread wording w/o an EML

 

We don't need an EML to get widespread severe weather...if we want to get widespread significant severe weather (widespread wind gusts greater than 65 knots, several hail reports exceeding 2'', or several F2 or stronger tornadoes) though than an EML becomes a bit more important.  

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We don't need an EML to get widespread severe weather...if we want to get widespread significant severe weather (widespread wind gusts greater than 65 knots, several hail reports exceeding 2'', or several F2 or stronger tornadoes) though than an EML becomes a bit more important.

How often do we actually see an EML in SNE?

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My question is this damage swath long enough to meet derecho criteria? :weenie:

 

Anyway here are my pics taken just off Exit 18 on I-89 in near Milton, VT

 

Great photos.

 

Might be a "macroburst" ...  They are like microbursts, but at the mesoscale.  

 

Derecho's are usually associated with advancing cool pools from aggregated outflow clusters, and their signatures tend to be much larger.   But then again, there are all kinds of labels the science puts on events in the atmosphere when in reality, the boundaries that differentiate them are blurred.  

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