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Feb 25-26 Discussion/pbp


Wow

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Honestly, hard to believe the 21z SREF...but I'll take it...just seems like a huge outlier for most....I mean everyone gets 5"+ it seems like...that would be incredible if it happened but when's the last time it did? If we cut these totals by 2-3" they seem believable.

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Upstate SC is definitely looking pretty good at this point. Also the one thing I would see as promising in terms of the members is that they are making a tighter cluster towards the mean...

 

Loving that cluster of models in the 8-10 range.

 

OOC, how do you create a postable image of the SREF?

 

Not sure if there is a better way, but I just used print screen and photoshopped the rest of the screen out.

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Gsp discussion

Tuesday night through Thursday/... as of 230 PM Monday...an active southern stream interacting with the quasi-stationary polar front to the south will make for interesting forecasting this week. However...the beginning of the short range will be begin on the quiet side as weak high pressure ridges into the area form the west as a frontal wave moves well off the East Coast. Therefore...expect generally dry conditions to persist Tuesday night through perhaps the bulk of Wednesday. During that time...a more potent southern stream wave will be ejecting out of the desert SW inducing cyclogenesis over the northern gom on Wednesday which is forecast to scoot east along the front through North Florida and then into the Atlantic by early Thursday. As the wave moves eastward...upper divergence and isentropic lift increase rapidly across NE Georgia and the western Carolinas with precipitation spreading quickly over the region from south late Wednesday into Wednesday night. There is certainly model consensus at this point that precipitation wil occur...so will be increasing probability of precipitation considerably into the categorical/likely range subject to collaboration with our neighboring offices. The most difficult part of the forecast is as usual trying to pin down the details most notably in regard to the amount of quantitative precipitation forecast and the thermal structure of the atmosphere particularly in our southhern Piedmont areas where there may be a tight gradient between frozen precipitation and rain. The operational GFS/NAM show some subtle details in the thermal profiles across the Piedmont with the GFS somewhat warmer. Also the 12z GFS continues to be on the lower end of the quantitative precipitation forecast envelop. Wpc's day3 forecast is favoring higher quantitative precipitation forecast based on ensembles which translates into warning level snow across much of the area. Looking at the sref plumes there is a large spread in the members. For instance at clt...there is a range from over 10 inches to essentially a dusting with the mean somewhere around 3 inches or so. The concern across the Piedmont is that the boundary layer will be slower to cool than what the models are indicating as maximum temperatures should be well into the 40s Wednesday afternoon. Also...all the cooling will be be mostly dynamically induced with no cold high situated directly to the north. In fact...a blend of the NAM/GFS surface wet bulbs outside the mountains show middle to upper 30s at 00z Thursday... slowly falling to the upper 20s across the northern NC Piedmont to the middle 30s southern Greenwood County during Wednesday night. In the absence of a warm nose...snow generally occurs when surface wet bulb temperatures are at or below 33 degrees. The bottom line is that there is a good chance that some of the quantitative precipitation forecast across portions of the piemdont will be used up as rain before transitioning to snow. Also...with the amount of quantitative precipitation forecast in question... do not plan on any Winter Storm Watch headlines yet. If the the lower GFS quantitative precipitation forecast were to verify... warning level snow would be marginal at best. Precipitation will quickly end east of the mountains early on Thursday except for some lingering snow showers in the mountains. Used a model consensus for most fields. On Tuesday night...the models generally latch onto a scenario where an old closed low over the SW gets kicked out across the Southern Plains and encounters a plume of deeper moisture. The fairly strong short wave induces cyclogenesis over the northwest Gulf late Tuesday night and Wednesday morning. Later in the day...as the upper wave approaches...a coupled jet brings strong upper divergence across the western Carolinas while strong middle level forcing also moves in... which helps to force the development of precipitation across the region from the SW as the day progresses. Precipitation continues overnight on Wednesday night as the surface low moves past to the south. The low track on the latest guidance... especially the somewhat favored European model (ecmwf)...is farther north on the 00z run. All the guidance brings the northern fringe of the precipitation shield associated with the low across the western Carolinas while cold air is in close proximity...which points toward a wintry precipitation type scenario...most likely a rain/snow situation based on partial thicknesses. There is much uncertainty in spite of the model guidance which seems to be in better agreement. The main problem for the bulk of the forecast area is timing. The models suggest the precipitation will be moving in mainly during the late afternoon or early evening as the cold air also arrives to keep much of it in the form of snow along/north of I-85. The latest sref/gefs plume diagrams are compelling. The sref plumes point to snow as the most likely precipitation type across the majority of the forecast area for Wednesday night...with amts perhaps approaching warning criteria. Most of the gefs members suggest the precipitation beginning as rain or sleet...then changing to snow during the evening. That being said...the experienced Reader understands that across the Carolinas...expecting a changeover of precipitation to snow based on the arrival of cold air as the precipitation is falling is usually a suckers bet. Fortunately...we do not have to entertain issuing any weather watches on this cycle...so our expectations should be managed accordingly. Will limit the precipitation probability to the chance range for now. Expect some adjustments to the forecast as we move forward

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That didn't seem encouraging at all. I read it as saying this is currently modeled to be a minor event with most of it rain....never really going below freezing...

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You got that from their discussion? They said highs would be in the mid 40s wed and slowly drop with no cold feed. Said we would lose QPF to rain in beginning! I feel worse after reading that! Bad trends!
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WRAL just said they want to see more consistency before they jump all over this because moisture seems "limited" and cold as well.

I mean they're right and we all know being a TV met is hard work, more than likely they'll start talking specifics tomorrow since they can say "it will start tomorrow night" gives plenty of time to work out specifics and give people a heads up. Not hating on them for not doing so yet.

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That didn't seem encouraging at all. I read it as saying this is currently modeled to be a minor event with most of it rain....never really going below freezing...

I think we have to pay close attention to how warm we're likely to get on Wednesday. In CAD situations, which this is not, models tend to overestimate temps and the power of evaporational cooling. In these situations, where cold air is arriving in concert with the storm, it is usually slower than the models indicate. How many times do we have to see this play out before we take it as a serious concern? The cold air not being in place already is bothersome and is likely going to be the primary reason that totals are less than we are currently expecting/hoping for. Not trying to be a negative nancy, but we need to be on alert for this.

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You got that from their discussion? They said highs would be in the mid 40s wed and slowly drop with no cold feed. Said we would lose QPF to rain in beginning! I feel worse after reading that! Bad trends!

 

I wouldn't worry yet, they are just being level headed and conservative.  There is no huge rush to put out watches so I think you will see them come around late tonight or sometime tomorrow.  Assuming the models don't change drastically.

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