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December 11 Week Event(s)


mitchnick

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Even though the snowfall maps are not high on this period after looking over the runs I think we are just a small step or two from seeing a minor to possible somewhat moderate event for Saturday. We have been seeing an adjustment on the models with the trough in the east which is becoming more favorable for our region with the development of the low off the coast at that time. Changes on the models in regards to the trough are indicative that the models may be over playing the strength and progressiveness of the NS which we saw both models do with our previous system. If we see just a couple/few more small adjustments in weakening the NS I believe our region comes into play for possibly more then just a trace/inch type deal. And with this being 90 some hours there is plenty of time to see these adjustments. Especially considering we saw both the GFS and Euro making these adjustments (weakening of the NS) on the previous system into the 24-48 period of time.

eta: Also keep an eye on our Thursday clipper. If the models are too strong with the NS as well with that feature then we may see a slowing down and better intensification. All of which would mean a stronger, slower low closer to the 50/50 region with the ability to back the flow somewhat for the low forming off the coast.

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RGEM gives us some light snowfall with a band of WAA in front of the clipper. Unfortunately guidance is converging on a track just a little too far north right now. Will need to see some sort of shift south today to feel better about prospects but the last 2-3 runs of everything have looked pretty much the same. 

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LWX has a decent disco from this morning in their AFD:

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
An Alberta clipper system will pass through the Ohio Valley
Wednesday evening before passing through our area overnight
Wednesday into Thursday morning. This system will bring a period
of snow with it...but there is still some uncertainty as to
exactly where with the gradient between accumulating snow vs.
little or no snow setting up over our CWA. Typically with these
systems...most of the snow falls north of the track of the
surface low where the frontogenetical forcing and warm advection
line up best. Latest guidance has the low tracking just south
of the Mason-Dixon Line. This means that the best chance for
snow will be near the Mason-Dixon line into Pennsylvania...and
this has been reflected in the latest forecast. However...a
slight shift southward and the accumulating snow will make it
into the Metro areas and possibly points south. Therefore...this
will have to be monitored closely over the next couple days.
One other thing to note is that an upslope flow and cold
advection behind the clipper system will cause snow showers for
locations along/west of the Allegheny Front and accumulating
snow is likely across these areas as well.

The clipper system will pull away from the area later Thursday
and high pressure will briefly build into the area Thursday
night...bringing dry and chilly conditions.

The high will move offshore Friday and an upper-level trough
will swing through the area later Friday into Friday night.
Latest guidance keeps the northern stream energy and southern
stream energy separate. This means that a coastal low with the
southern stream energy would move out to sea. However...some
southern stream moisture may still get drawn into the area ahead
of the trough axis...and this would result in a period of snow
or rain/snow mix. Will continue to monitor...because it may
affect the evening rush across most areas. Also...should these
systems phase a bit sooner than expected that would have a
significant impact on the forecast with more significant snow.

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Yoda, nam was showing stream interaction and that's why precip was breaking out. It's not a phase but the streams are working together instead of being completely separate. GFS is supportive of something similar. It's really close to a light/mod event and this is something that can shift quick at shorter leads. We'll see where we stand once the timing differences between the models tightens up

namconus_z500_vort_us_53.png

 

gfs_z500_vort_us_16.png

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1 minute ago, wdavis5784 said:

I would be excited if it wasn’t the JMA....

Yea, I'll admit that it isn't looking good across the main globals but too early to call it one way or the other. We usually need wiggle room to the south at this point so previous events favor a track too far north. 

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37 minutes ago, Bob Chill said:

RGEM gives us some light snowfall with a band of WAA in front of the clipper. Unfortunately guidance is converging on a track just a little too far north right now. Will need to see some sort of shift south today to feel better about prospects but the last 2-3 runs of everything have looked pretty much the same. 

12z RGEM gives us basically nothing through 48

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Yoda, nam was showing stream interaction and that's why precip was breaking out. It's not a phase but the streams are working together instead of being completely separate. GFS is supportive of something similar. It's really close to a light/mod event and this is something that can shift quick at shorter leads. We'll see where we stand once the timing differences between the models tightens up

namconus_z500_vort_us_53.png&key=d35fca887b0ef0eeab1619f45a5bf9bbe80320cae8fc1043b2a6e09cfc4abf30

 

gfs_z500_vort_us_16.png&key=f54ee12c78087c44f4a284acd73c2254a424994fca30952b4e7b20d0328bf961



That’s a pretty nice shot Bob. Not going to take much more interaction to get an advisory type event in these parts. Something tells me we may not have a better idea until later tomorrow as the focus will be what happens with the first disturbance. A little more amplification of the northern stream and bingo.


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Just now, MillvilleWx said:

 


That’s a pretty nice shot Bob. Not going to take much more interaction to get an advisory type event in these parts. Something tells me we may not have a better idea until later tomorrow as the focus will be what happens with the first disturbance. A little more amplification of the northern stream and bingo.


.

 

It's a shame that the SS isn't all juiced up. All it does is enhance the northern stream enough to potentially give us some precip. The good thing is just yesterday and the day before the 2 streams looked completely separate on most guidance. Now they are trying to work together. If there's one thing the last event taught us, complicated setups can move around a lot at short leads. 

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It's a shame that the SS isn't all juiced up. All it does is enhance the northern stream enough to potentially give us some precip. The good thing is just yesterday and the day before the 2 streams looked completely separate on most guidance. Now they are trying to work together. If there's one thing the last event taught us, complicated setups can move around a lot at short leads. 



That’s why I’m think it’s not going to be until later tomorrow into Thursday we’ll have a better handle on what’s to come. It’s right on that cusp of being something good. This is literally all you could ask for this early in season. Last few December’s were just terrible. Good to track things this go around.


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4 minutes ago, yoda said:

Doesn't look like 12z GFS is going to do anything for us on Friday/Sat

It's really anemic and has the wave way offshore, does give us a dusting....no real snow.  Sadly, we have to hang our hats on the GGEM.  That the Euro and GFS and the Euro ensembles look meh or worse and we're hoping for the NAM and GGEM to lead the way is sad.  Possible but is bucking the odds. 

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