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Coastal cyclogenesis and minor to moderate impact Feb 8/ 8.5, primarily SE areas ...for now.


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And the GFS now looks the best at H5 after being the last model to catch on. Model chaos, with too many small disturbances in the same region, difficulty resolving which one will amplify. We know—based on our climo—that baroclincity strongly favors shortwaves that amplify along the SE coast. My read is the GFS could use a “climo correction” or “parameterization” in the eastern CONUS. 

Anyway, significant positive changes on the GFS, albeit coming from a very disorganized state. The latest depiction is clearly worth tracking for SE NH.

gfs_z500_vort_eus_fh60_trend.gif

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Not sure what to think on this one. Safe bet is to just say almost nothing except N ORH county for SNE and then a narrow stripe into interior NH and W Maine but there’s still some major differences on guidance. 
 

If 06z GFS is catching onto a legit trend, then it could get more interesting. Would still need to trend a little more. 
 

My guess is the 12z suite will clarify things more…and I’m not expecting much of anything interesting for most of SNE. 

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6 minutes ago, ORH_wxman said:

Not sure what to think on this one. Safe bet is to just say almost nothing except N ORH county for SNE and then a narrow stripe into interior NH and W Maine but there’s still some major differences on guidance. 
 

If 06z GFS is catching onto a legit trend, then it could get more interesting. Would still need to trend a little more. 
 

My guess is the 12z suite will clarify things more…and I’m not expecting much of anything interesting for most of SNE. 

6Z Euro 

index (23).png

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BOX AFD isn’t overly impressed which makes sense

Monday night into Tuesday... Model guidance in reasonable agreement on southern stream low tracking a bit south and east of the benchmark late Mon night into Tue. Much of the precip shield directly linked to this storm will be offshore. However, separate northern stream trough upstream will induce an inverted trough at the surface which extends into New Eng. This will be a focus for a period of precip Mon night within deepening moisture plume. There is uncertainty with the westward extent of precip and QPF amounts. GFS and much of its ensembles are furthest east and confine precip to eastern New Eng while Canadian ensembles are wettest and furthest west. We leaned toward ECMWF solution which is a compromise with ensembles supporting a light QPF event with somewhat heavier precip possible in the east. Regarding ptype, southerly flow preceding this event will warm boundary layer enough for mainly rain in the coastal plain including Boston to Providence, with best chance of snow further in the interior, especially north and west of I-495. Due to uncertainty with how far back the steadier precip gets this is looking like a minor snow event for the interior. We discounted the NAM solution which is a strong outlier. In fact, ensemble probs for greater than 3 inches from GEFS and ECMWF ensembles are near zero and only a few Canadian ensemble members have a more significant snowfall. Best chance for a few inches will be in the Worcester hills.

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2 hours ago, jbenedet said:

And the GFS now looks the best at H5 after being the last model to catch on. Model chaos, with too many small disturbances in the same region, difficulty resolving which one will amplify. We know—based on our climo—that baroclincity strongly favors shortwaves that amplify along the SE coast. My read is the GFS could use a “climo correction” or “parameterization” in the eastern CONUS. 

Anyway, significant positive changes on the GFS, albeit coming from a very disorganized state. The latest depiction is clearly worth tracking for SE NH.

gfs_z500_vort_eus_fh60_trend.gif

Glad someone else noted the 500 mb moves ...  I noticed the 00z run ( actually...) had rotated the trough more neutral as opposed to previous - which at that time the model's surface evolution was fine relative to itself. But what made that peculiar is that despite more neutral tilt, and somewhat more coherent local DPVA contained, the surface reflection on that run actually trend more SE than the 18z (ugh), a motif it continue in the 06z solution. But, this latter runs seems to be introducing a second aspect:  it's blossoming a new QPF swath over SNE/CNE [apparently] driven almost entirely by emerging frontogenics.  The 06z was also continuing along the improvement trend at 500 mb that began at 00z as described above - even slightly more so... It may be, that is how we get anything out of this.  The 'mid level magic' as it were. There may be some sensitivity there...where the more the 500 mb leads to more of this latter production sequencing..

For the record, this did not congeal in the guidance as I first visualized it could - but again again again..this was advertised as low confidence, for minor to moderate.  At the time there was nothing better to do, for one.  But, there was also decent ens support; in fact, spread was west with some members even down as far as the 990 range.  Not terrible, considering the footprint flow. There isn't as much L/W --> S/W interference ( manifested as gradient/ velocity saturation..).

It is interesting that despite that, en masse, the cluster moved away from amplitude, when @ < 108 hours.  I suppose if that sort of correction needs to be made, you want it out there instead of on the morning of the event.. huh.  These S/W's being delivered from the Pac are kinda "short-bus" material. 

It also occurs to me that some of the extension west of these NAM QPF layouts have also likely been related to mid level forcing - weak, however doing so with a PWAT loaded S origin..etc.  Lot of detail migraines.  Including also that the NAM hasna NW bias for EC frontal positions and storm tracks > 48 hrs.  I've not seen much in recent seasons to suggest that is not true any longer. I just saw this behavior this season several times - though subtle. That said, the 06z was also a 500 mb rotation of trough mechanics, too, and smears QPF back to ALB.  

The Euro has cyclogenesis, but limits any mid level aspect to not occurring at all.  It'll be interesting to see which..

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2 minutes ago, dendrite said:

Yeah even back here that’s pretty much near isothermal 0C 850-down.

This is a spring blue bonnet special - assuming anything comes of it.  Even a minoring snow accumulation is going to be dependent upon falling through that type of sounding you describe, and magnitude/fall rates ...etc overcoming. It's moving metric.  Some locals may flip between light rain and moderate 'chutes ... May as well be late March

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