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February 8-12 model Discussion II


Isopycnic

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It varies depending on the storm...typically the stronger a surface low, the closer together the 700mb, 850mb, and surface lows are. During episodes of CAD, you can get a pretty large separation between the 850mb low and the Surface reflection because the upper level in unimpeded by the surface high to the northeast, but the surface cyclone gets stuck, since the colder air near the surface is more dense and prevents the surface low from moving overhead. This case looks more like a hybrid CAD, because the low and the 850mb low are pretty close together. In this case, anybody that is immediately north of the 850mb low will likely stay below freezing throughout the column.

However, the tricky thing to watch is deep layer moisture. In a lot of cases, you might be completely below freezing in a sounding, but the moisture aloft at 700mb and above completely dries out. Not only due you need the atmosphere to be below freezing at all levels, but you also need to have sufficient moisture in the snow growth region (typically above 700mb) in order to allow.snowfall production. Otherwise, you just end up with sleet (if you have moisture above 850mb), or even freezing rain (only strong low level moisture). This is what happened to a lot of folks in last years major winter storm on January 30th, 2009.

You explained that really well. Thanks for taking the time to write all that out; I've always wondered how that worked.

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Until we get closer to the event, I'm going to go by what the local mets are saying....rain/snow mix.

Do you know how hard it is to try and tell my brain not to get excited that it may be more? :arrowhead:

When will you guys start posting maps? Tuesday?

They aren't even right when there is not a storm. They will change forecast about wednesday. Follow the GFS and most of the time they will get forecast from it and the National Weather Service. The two forecasts always match

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It is setting up SW to NE..

Thanks, in RAH's afternoon discussion they stated the triangle would be "on the line" between snow and rain. looks like they are looking at the euro right now. also this is very typical of winter storms. I have told people, for a long time, if they like snow/ice to live north or west of Raleigh, other wise live south or east. In fact when I was looking for a lot to build my house I drew a map running SW to NE right through Raleigh and told our relator to only look to the left of the line (no kidding). But, I have been burned a few times by storms hittling to the right of the line.

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12z ECMWF Ens mean track is about perfect for an RDU snowsotrm. At 120 just south of Fl panhandle, at 126 50-100 miles east of CHS, at 132 100 miles east of HAT.

Thanks Allan for the update!

Here a quote from me yesterday morning about this storm:

"At this point I don't see the RDU area getting anything out of this one except some rain. The trends are in the wrong direction for us. It always seems that if the euro starts taking a western track it's a lock. Hopefully this won't go to far west and alteast get some of the good folks in the SE. One thing I am happy about is I can see the writing on the wall 6 days out instead of waiting 2 days before the storm then pulling the carpet out from under me."

This a couple of things about this:

1) You never can tell what's going to happen in future runs and...

2) Allan said this was still up in the air for the RDU area but I chose not to see the writing on the wall.

The moral of this is to listen what the mets are telling you and don't listen to me....:lmao: ...:P

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Apparently word about this system is already starting to make its way to the public, my dad (who lives in a semi-rural part of south Alabama) just had a friend's daughter tell him that it was going to be 8 degrees on Friday morning. Said friend's daughter is a nutritionist at a nursing home, so I wonder where she heard that. She didn't tell dad where she heard it.

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Thought this was pretty funny. They've done a pretty good job this winter in Morristown.

.LONG TERM (SUNDAY NIGHT THROUGH SATURDAY)...WHILE MODELS AND

ENSEMBLES ARE IN REASONABLY GOOD AGREEMENT WITH RESPECT TO THE WEAK

SYSTEM ON MONDAY...THE SYSTEM EXPECTED BY MID WEEK REMAINS LOW

CONFIDENCE. A GREAT DEAL OF UNCERTAINTY STILL SURROUNDS THE TRACK...

TIMING...INTENSITY...PRECIP TYPE AND EVEN QPF. LATEST MODEL RUNS

SEEM TO HAVE SETTLED A BIT BETTER ON TIMING...MAINLY IN THE LATE

WEDNESDAY TO EARLY THURSDAY TIME FRAME. BASED ON THE EXPECTED

TIMING...ANTICIPATE THAT MOST OF THE PRECIP WILL OCCUR AS SNOW

GENERALLY. THE MAIN UNCERTAINTY NOW APPEARS TO BE QPF AS MODELS HAVE

BEEN BACKING OFF ON THIS PARAMETER IN LATEST RUNS. ONLY A FEW OF THE

21 GEFS ENSEMBLE MEMBERS ARE NOW PROJECTING EVEN 0.15 INCH QPF FOR

THAT TIME FRAME...WITH THE MORE SIGNIFICANT AMOUNTS REMAINING SOUTH

AND EAST. AT THIS TIME...ANY ATTEMPT AT TRYING TO QUANTIFY

SIGNIFICANCE OF THIS SYSTEM WOULD BE WILD SPECULATION. WILL CONTINUE

TO HIGHLIGHT IN HWO PRODUCT...BUT REMAIN INTENTIONALLY VAGUE

REGARDING ITS POTENTIAL IMPACT.

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