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Feb 19-20 Winter Storm Threat

Buddy1987

By Buddy1987,
in Southeastern States

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Buddy1987

Buddy1987

Posted
Posted

Creating a thread here for the northern guys of the Southeast forum in anticipation of model runs beginning with 0z suite. Think it will work out better to keep this threat separate from the long range discussion.

18z models continued with the CAD trending stronger closer to game time.

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FallsLake

FallsLake

Posted
Posted

Not a big event, but at least it's something. 

From RAH:

.SHORT TERM /TUESDAY THROUGH WEDNESDAY/...

As of 256 AM Monday...

 

...Some threat of light icing and even wintry mixture increasing

over the Piedmont (damming region) late Tuesday and Tuesday night...

 

A strong (1040 mb) and chilly high pressure is forecast to be

located over the Great Lakes early Tuesday. This high pressure is

forecast to progressively move east to a favorable position for CAD

into our damming region Tuesday night (PA/NY state extending

strongly south into NC/SC and northeast GA). This occurs as yet

another storm system develops over the NW Gulf of Mexico and begins

to track NE toward the TN Valley region Wednesday. Timing of the

precipitation will be critical as to the P-Type for Tuesday afternoon

into the early evening, before warming aloft overwhelms the region

from the south. This is a favorable pattern for a winter storm for

our region; however, it appears the significant precipitation will

arrive Tuesday night and Wednesday, after the warming aloft will be

well underway.

 

For now, we will forecast a cloudy and chilly day on Tuesday. There

will be a chance of light precipitation during the afternoon in the

west and north. Top down and Partial Thicknesses support a mixture

of sleet and rain to start Tuesday afternoon with highs in the mid

to upper 30s in the Piedmont. Since the precipitation is expected to

be light and temperatures above freezing, no impacts are expected.

 

As the precipitation becomes more widespread in the western and

northern Piedmont by nightfall or during the evening, the

temperatures are expected to fall to around or slightly below 32 in

much of the Piedmont (strong evaporative cooling), especially along

and NW of a line from Albemarle to Raleigh to Warrenton. A mixture

of freezing rain and sleet (through around midnight - before the

warm nose aloft arrives - give or take a few hours either side of

midnight) may lead to the need for a Winter Weather Advisory in the

Piedmont. Remember, roads and the ground has been warmer than normal

due to the warm February thus far, so winter storm criteria is not

expected. It appears that the main issues would most likely be with

bridges and overpasses etc... and during the nighttime hours on

Tuesday night. Lows around 30 or 31 NW and N Piedmont, 32 or so

along the line from Albemarle to Raleigh to Warrenton, and above

freezing (mid 30s) across much of the southern and eastern areas of

the Southern Piedmont, Sandhills, and Coastal Plain.

 

The model blended QPF is around 0.25 to 0.40 in the Piedmont Tuesday

night through 12z/Wed. Amounts are less to the east with 0.10 to

near 0.25 in the Fayetteville, Goldsboro, and Rocky Mount areas

through 12z, which would be rain in this case.

 

The amount of frozen/freezing precipitation from 00z/WED through

12z/WED (overnight Tuesday) is expected to be limited to the

Piedmont, and the farther NW the higher the PROB of some

accumulation. For now, we will carry the potential for a light

coating of snow/sleet (less than 1/8 inch of sleet or 1/2 inch

of snow) before the change to freezing rain/rain over the Triad and

into the Triangle, up to a tenth of an inch or freezing rain can be

expected through 12z/Wednesday.

 

On Wednesday, the CAD will linger but the warm nose aloft will

gradually eat away at the cold air at the surface. Progressively

warmer rain processes will allow warming safely above freezing by

late morning. Highs generally mid to upper 30s NW-N Piedmont ranging

into the upper 40s SE (These highs will take all day to reach at

near 00z/Thu). We will carry a mixture of rain/freezing rain between

12z and 15z, transitioning to rain in the Piedmont. Rain elsewhere.

Any freezing rain will be self limiting as the rain falls at a

higher rate and the rain falls through a progressively warmer

column.

 

&&

 

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Buddy1987

Buddy1987

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Ice threat for northern NC counties and into southern VA is downright scary on some of the projections. One would hope that pingers would save the day. I still think the models are somewhat playing catch up with CAA from this impending Canadian HP. Usually 1032-1034 are good for wedging events but you get to 1040+ and those are big dog HP’s that will overperform. 

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FlatLander48

FlatLander48

Posted
Posted
10 minutes ago, Buddy1987 said:

Ice threat for northern NC counties and into southern VA is downright scary on some of the projections. One would hope that pingers would save the day. I still think the models are somewhat playing catch up with CAA from this impending Canadian HP. Usually 1032-1034 are good for wedging events but you get to 1040+ and those are big dog HP’s that will overperform. 

Two of the WRF models, regardless if they're even remotely accurate or not, have the HP closer to the mid 1040's at onset. The possibility exists that the HP could actually come across a bit stronger over the next few runs.

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Buddy1987

Buddy1987

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4 minutes ago, AsheCounty48 said:

Two of the WRF models, regardless if they're even remotely accurate or not, have the HP closer to the mid 1040's at onset. The possibility exists that the HP could actually come across a bit stronger over the next few runs.

Wow that’s nuts! I did not even see that. If that’s the case I would think the prospects of more snow and sleet accumulations are definitely in line and at that point the oozing of the cold air would make some more people in the forum happier with at least something wintry. 

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FallsLake

FallsLake

Posted
Posted
20 minutes ago, PackGrad05 said:

Anyone have the maps for latest NAM models?  I saw amounts on BUFKIT for RDU, but would like to see map.

Funny thing about the 6z NAM, it was actually colder at the surface (..dew points) then 0z. There was just less precip to start the event. 

So we're starting to get the colder look, we need to also focus on the start time/amounts of precip. 

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PackGrad05

PackGrad05

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16 minutes ago, FallsLake said:

Funny thing about the 6z NAM, it was actually colder at the surface (..dew points) then 0z. There was just less precip to start the event. 

So we're starting to get the colder look, we need to also focus on the start time/amounts of precip. 

I Just took a closer look at the 3K NAM precip depiction.  As the precipitation moves in, you can see a "blank" spot in the shape of the wedge over central NC.  Could the model be picking up on the moisture not overcoming the initial dry air in place?  If so, how well is that normally forecasted in models?

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FallsLake

FallsLake

Posted
Posted
18 minutes ago, PackGrad05 said:

I Just took a closer look at the 3K NAM precip depiction.  As the precipitation moves in, you can see a "blank" spot in the shape of the wedge over central NC.  Could the model be picking up on the moisture not overcoming the initial dry air in place?  If so, how well is that normally forecasted in models?

Could be. With dew points in the teens it would take some time to moisten the column. I'll be interested to see what 12z shows; which is coming up soon.  

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Buddy1987

Buddy1987

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Just now, AsheCounty48 said:

Any clue as to what is leading the massive snow changes out west and to the north of us between the 6z and 12z runs of the 3k nam? That's a pretty big difference.

For one the NAM suite spits out some relatively meager qpf totals compared to the other models. I hope its wrong in that aspect.

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Blue_Ridge_Escarpment

Blue_Ridge_Escarpment

Posted
Posted
9 minutes ago, Buddy1987 said:

For one the NAM suite spits out some relatively meager qpf totals compared to the other models. I hope its wrong in that aspect.

As crazy as it sounds, that has been the NAMs bias since the “upgrade”. NAM is no longer the model where you cut the qpf by 50%. 

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Buddy1987

Buddy1987

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2 minutes ago, Blue_Ridge_Escarpment said:

As crazy as it sounds, that has been the NAMs bias since the “upgrade”. NAM is no longer the model where you cut the qpf by 50%. 

Oh yea 100% agree I just cant wrap my head around it haha compared to what im used to regarding it.

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FallsLake

FallsLake

Posted
Posted
3 minutes ago, Buddy1987 said:

12z RGEM looks colder for NC mountains at onset of precip. Depicting more snow.

A little bit colder for the Triangle as well. At hour 42 all of Wake County under some kind of freezing/frozen precip. At hour 45 mid to upper Wake still wintery. 

Edit: then at hour 48 all of wake back to freezing rain. Definitely a (slightly) colder run. 

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