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April 2019 Discussion II


powderfreak
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What I find interesting about this quasi-closed low's slow evolution through the east is how much that reminds of a lesser amplified version of that meridian coastal flow you sometimes set up in late summers... 

I've quipped in the past, " ...Bermuda blue pattern.." when describing those larger scaled circulation constructs.  ~ August 20 to September 20 regimes, a weakness in the geopotential medium sets up stationary for a week or so ... roughly over Appalachia ... On the eastern limb a deep layer, deep tropical conveyor runs from Nassau  clear to Maine...  Within that stream, it doesn't get torridly hot, but you  often end up with 82 /76 type air., with remarkably clear quality.  It's really like Bahama tropical sky and ambiance visits the area.  You even get those tropical puff CU's with an over active turret ... under which a dark bottom features a single rain shaft that's blinding heavy for two pixels on a radar scan.

I've often mused ... if a hurricane were ever approaching the Bahamas in that ilk of larger circulation mien ... but man!  Never seems to time that way. ... In the 30 years I've been more sentient of said matters, I've only ever seen the irrepressible excitement junkies .. seemingly have to will hurricanes in between early frost air masses of all things.

Picture it: It's a crispy early morning chill. A low dew point air mass swashed in as a 'shot across the bow' warning how the changing season looms.  It's 37 F degrees, ...early September, and the cold dew laden over the lawn's greenery and car tops looks like frost but just managed to say liquid ...  Meanwhile same category 4 circular saw is cutting it's way WNW some 60 nautical miles NE of San Juan PR ... Two days later... we're condensation conduction dew onto pantry windows because the air mass outside with rising DPs turned around too quickly. There's an18 hour window when the steering winds veered S along and off the Eastern Seaboard and up she comes...  Only to curve smartly ENE near the Del Marva and sparing us actually succeeding in timing, being the most common result ...but you get my drift.  

Obviously, neither is prevalent over this weekend's run through with this trough over Appalachia.  However, we do have a deep layer southerly trajectory that set up and the system is moving slowly enough to allow a DP positive anomaly to persists. 

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5 minutes ago, weatherwiz said:

Don't think it's all day sun with this

image.png.ecddc079bd3970af1237fcc71507a082.png

That's not that impressive ...to me.  It's not that appreciably deep...though it's certainly unstable should any day time heating manage to warm the lower troposphere under the rim of it... 

That could be a pancake cu with a couple over achieving shower bands but ... it's hard to know.  Have to see the soundings -

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7 minutes ago, Typhoon Tip said:

 

I've quipped in the past, " ...Bermuda blue pattern.." when describing those larger scaled circulation constructs.  ~ August 20 to September 20 regimes, a weakness in the geopotential medium sets up stationary for a week or so ... roughly over Appalachia ... On the eastern limb a deep layer, deep tropical conveyor runs from Nassau  clear to Maine...  Within that stream, it doesn't get torridly hot, but you  often end up with 82 /76 type air., with remarkably clear quality.  It's really like Bahama tropical sky and ambiance visits the area.  You even get those tropical puff CU's with an over active turret ... under which a dark bottom features a single rain shaft that's blinding heavy for two pixels on a radar scan.

I've often mused ... if a hurricane were ever approaching the Bahamas in that ilk of larger circulation mien ... but man!  Never seems to time that way. ... In the 30 years I've been more sentient of said matters, I've only ever seen the irrepressible excitement junkies .. seemingly have to will hurricanes in between early frost air masses of all things.

 

So September 1938 pattern, right?

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9 minutes ago, Typhoon Tip said:

That's not that impressive ...to me.  It's not that appreciably deep...though it's certainly unstable should any day time heating manage to warm the lower troposphere under the rim of it... 

That could be a pancake cu with a couple over achieving shower bands but ... it's hard to know.  Have to see the soundings -

Shear is garbage but lapse rates are quite steep. Freezing levels pretty low too. Certainly maybe nothing widespread, but these set ups often always produce at least something. 

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7 minutes ago, Hoth said:

So September 1938 pattern, right?

Heh ...maybe  I dunno.  

I thought I read somewhere that '38 even was preceded by a humid pattern but don't quote me.  

I definitely read that both Hazel and Carol in the 1950s had cool snaps the week prior ...and would seem consistent with that description of turning said air mass around and then having a 'temporal window' synoptically 

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10 minutes ago, weatherwiz said:

Shear is garbage but lapse rates are quite steep. Freezing levels pretty low too. Certainly maybe nothing widespread, but these set ups often always produce at least something. 

well... You had mentioned 'no sun' or something of that conceptual nature ... I was speaking to that, specifically .. 'quality of the day' ... 

As far as instability and all that other stuff, ... same - not sure.  That could all be mostly above the 650 mb level...in which case it's sunny for a while and then unstable through 200 mb depth...  so you get crispy CU that slam shut under an stable sounding above... Or, if that cold pool extends deeper, ...again, soundings -

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what does one expect I suppose ...but geesh!    Look at the 300 hour GFS from the 00z run and compare it to this one - 

Talkin' about as precisely exact 180 degrees opposite as is physically plausible in any fluid medium with that pattern handling ...  

The funny thing is ...even in the prior ridgy look, the model was finding a way to keep that lower troposphere wedged in with some kind of belated wfrontal suppression.   Separate matter altogether but ...I've noticed that about the GFS ...it simply cannot see "warm season" beyond D10 ... it always always always... regardless of all, defaults back to late February in that time range.  interesting... when the pattern looks like it would flip hot...it finds a way to be cool using whatever means necessary at least excuse imagined... Otherwise, February.  

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2 hours ago, Damage In Tolland said:

Summer is basically here 

Hasn't reached our garden, which still had 10" snow this morning.  Hope that's all gone by sometime Sunday.

This afternoon's map from GYX bumped up total RA by 1/2-1", and the heaviest pretty much coincides with the Kennebec watershed.

 

Overview

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