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December 8-10, 2018 Winter Storm


Orangeburgwx
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Looking at the real time movement of air masses, there is a big push south by the arctic air mass with accompanied upper level energy and you can see why this system is modeled to be suppressed. However the slp has yet to form in the gulf and we know it will want to press north with waa. Its unclear how this will resolve. Interesting to see how well the models do with it.

https://weather.cod.edu/satrad/exper/?parms=global-northernhemi-10-48-0-100-1&checked=map&colorbar=undefined

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Just now, Pilotwx said:

Thunderstorms on the Gulf coast , probably robing moisture as well as warming the Atmosphere

Oh, Almost forgot about that potential feature in storms like this.  Definitely have an effect up this way wrt available moisture

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Just now, eyewall said:

And here we go. That is not a good look at all. 

Agree. And you could see it coming overnight as all the models were less impressive with the CAD. Plenty of time to play catchup, but pretending like this NAM run is a significant change from its prior runs (and not just out at 84 hours, but in the 48-60 hour range) is not a winning play. 

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2 minutes ago, wncsnow said:

The nam is definitely on the drier side for the whole area, which seems odd considering it used to be the most amped up/heavy qpf.... It shows the front end thump being not much more than a nuisance 

snku_acc.us_ma (3).png

Geez, check out the time on the map!!  The NAM is slower and the bulk of the moisture is just really getting into the N parts of NC. What I'm saying is this is just the totals for the very beginning of the storm. Be patient!  Yes, it's warmer aloft but we'll have to see what other model runs tell us. 

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Just now, GreensboroWx said:

Geez, check out the time on the map!!  The NAM is slower and the bulk of the moisture is just really getting into the N parts of NC. What I'm saying is this is just the totals for the very beginning of the storm. Be patient!  Yes, it's warmer aloft but we'll have to see what other model runs tell us. 

Yes it isn't finished but.. the front end thump being advertised isn't looking as impressive on the NAM.

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WPC Discussion

https://www.wpc.ncep.noaa.gov/discussions/hpcdiscussions.php?disc=qpfhsd

...Southern Appalachians... Day 3... Developing low pressure along the Gulf Coast will strengthen and push eastward to be near the GA/SC coast at the end of day 3. This low will develop in response to a southern stream shortwave moving through the Arklatex and into the TN Valley, as well as diffluence within the right entrance region to an upper jet streaking across New England. Guidance is in reasonably good agreement in the evolution and placement of this surface low, with the NAM a strong and very cold outlier, while the CMC is too fast with the phasing of northern stream energy, and is pulling the surface low too far north too quickly. A blend of the GEFS and ECEns mean is preferred, which suggests precipitation spreading across the Southeast during Saturday. The guidance has overall slowed precip onset due to dry air within a strong wedge of high pressure which remains in place as a result of robust mid-level confluence. E/SE low and mid-level winds spread northward atop the surface wedge, isentropic lift will increase, and precipitation will gradually saturate the column. This will result in wet-bulb cooling of the thermal profile and snow/sleet/freezing rain is all likely to develop Saturday night, with snow in the higher terrain and freezing rain/sleet elsewhere. Despite model differences in timing and p-type, there is a strong multi-model signal for more than 4 inches of snow in the Southern Appalachians before 12Z/Sunday and this is where WPC probabilities are highest for accumulating snow. Some uncertainty exists into how far north precipitation will spread on Day 3 due to dry air inhibition, and there is likely to be a sharp north gradient to snowfall. Additionally, a period of freezing rain and sleet is likely in portions of the mountains and foothills, and WPC probabilities have increased to 20 percent for 0.25 inches of accretion across portions of the area.

 

wpc.jpg

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Nam has position of HP back over western Wisconsin and also slow with the LP. hence position of HP compared to 6z results in CAA being started latter. Also wake up guys, Raleigh want be getting dry slotted. The model only goes out to 84 and has been the slowest with start up time by 6 to 12 hours compared to other models.

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