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Central PA - second half of March 2013


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So thats what happened earlier this month where the winds from east brought in warm air

Early this month we had a butt-kicking Low level jet (75-80kts) coming straight off of the Atlantic. Thermal profiles at 850 were close to isothermal close to freezing. It wouldve taken low level temps at freezing to support snow through the column. As soon as surface temps went above freezing, it changed to rain for many. This is not the case this time and this is definitely not the same storm.

LLJ this time will be far weaker (around here), and oriented more out of the NE, and not directly off the ocean. This is why CTP is not necessarily concerned with p-type issues. Also, some pretty cold air aloft (850's & 700's) with values between -4 & -9 for even southern locations. The below-freezing air reaches all the way down to 925ish.

It's a snow profile, with the chance of mixing with rain in the SE portions. I don't think we have to worry about anything. Focus on the current temps/dewps right now and the high-res models. Also look at placements versus truth. No worries yet, folks

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Early this month we had a butt-kicking Low level jet (75-80kts) coming straight off of the Atlantic. Thermal profiles at 850 were close to isothermal close to freezing. It wouldve taken low level temps at freezing to support snow through the column. As soon as surface temps went above freezing, it changed to rain for many. This is not the case this time and this is definitely not the same storm.

LLJ this time will be far weaker (around here), and oriented more out of the NE, and not directly off the ocean. This is why CTP is not necessarily concerned with p-type issues. Also, some pretty cold air aloft (850's & 700's) with values between -4 & -9 for even southern locations. The below-freezing air reaches all the way down to 925ish.

It's a snow profile, with the chance of mixing with rain in the SE portions. I don't think we have to worry about anything. Focus on the current temps/dewps right now and the high-res models. Also look at placements versus truth. No worries yet, folks

no worries here MM

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i assume the 2nd blob on radar out to the west is the main show(atleast for my area?)

the western edge of the first precip batch seem to be falling apart.

will they combine?

They will combine, yes. But the main show is the energy east of St Louis. The overrunning stuff south of us will act to erode some dry air for our region before the show starts overnight

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Early this month we had a butt-kicking Low level jet (75-80kts) coming straight off of the Atlantic. Thermal profiles at 850 were close to isothermal close to freezing. It wouldve taken low level temps at freezing to support snow through the column. As soon as surface temps went above freezing, it changed to rain for many. This is not the case this time and this is definitely not the same storm.

LLJ this time will be far weaker (around here), and oriented more out of the NE, and not directly off the ocean. This is why CTP is not necessarily concerned with p-type issues. Also, some pretty cold air aloft (850's & 700's) with values between -4 & -9 for even southern locations. The below-freezing air reaches all the way down to 925ish.

It's a snow profile, with the chance of mixing with rain in the SE portions. I don't think we have to worry about anything. Focus on the current temps/dewps right now and the high-res models. Also look at placements versus truth. No worries yet, folks

 

I'm not very concerned about a situation resembling the March 6th storm either. Temps aloft are much colder for this event and surface temps/dewpoints are such that the column will easily get cold enough for snow. I'm still kicking myself in the butt for not fully realizing how marginal the temps were for that event in the southeastern areas. But anyways, this storm just looks like it has a more favorable alignment between the midwest low and the developing coastal low that it should eventually hang a pretty nice snow shield over PA. This type of setup has been a theme this winter, except that the midwest low has always been much further north as to create ptype issues and/or QPF issues. Still keeping an eye on the initial slug of precip and the more dynamic stuff associated with the upper low being a bit separated, but I think that should end up not being an issue. The early stuff is getting eaten up pretty good by the dry air so far anyways. 

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Don't understand the bolder, what the heck? All rain?

Tonight

A slight chance of light snow this evening...then snow after midnight. Snow accumulation around an inch. Lows around 30. Northeast winds 5 to 10 mph. Chance of snow near 100 percent.

Monday

Snow. Rain in the afternoon. Total snow accumulation of 4 to 6 inches. Highs in the mid 30s. North winds 5 to 10 mph. Chance of precipitation near 100 percent.

Monday Night

Cloudy. Rain and snow in the evening...then a chance of snow showers after midnight. Additional snow accumulation up to 1 inch. Lows in the lower 30s. Northwest winds 5 to 10 mph. Chance of precipitation 90 percent.

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Don't understand the bolder, what the heck? All rain?

Tonight

A slight chance of light snow this evening...then snow after midnight. Snow accumulation around an inch. Lows around 30. Northeast winds 5 to 10 mph. Chance of snow near 100 percent.

Monday

Snow. Rain in the afternoon. Total snow accumulation of 4 to 6 inches. Highs in the mid 30s. North winds 5 to 10 mph. Chance of precipitation near 100 percent.

Monday Night

Cloudy. Rain and snow in the evening...then a chance of snow showers after midnight. Additional snow accumulation up to 1 inch. Lows in the lower 30s. Northwest winds 5 to 10 mph. Chance of precipitation 90 percent.

 

I think the bulk of the heavier accumulating snow will be occurring overnight into the first half of the day and perhaps maybe the thinking is some of the leftover lighter stuff might be rain in the afternoon, which is plausible. Still kind of confusing looking though.. definitely a point and click special. I'm still thinking a general 2-5 for the Lower Sus Valley region with better amounts west of the river towards Zack and more in the realm of  2" or so in the far SE. I think Harrisburg proper should manage about 3-4" without too much trouble. 

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Storm definitely looks dry. You can see copious amounts of virga overhead.

As expected. The overrunning will help eat that dry layer. Then the dynamics will produce the precip to the surface as the primary low approaches.

Actually, the RAP showed this this morning. Showed precip overhead by the afternoon, but if you went to the forecast sounding for that same time period, it showed a substantial dewpoint depression.

It'll be overcome as we go into the overnight and higher DBZ values move in

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As expected. The overrunning will help eat that dry layer. Then the dynamics will produce the precip to the surface as the primary low approaches.

Actually, the RAP showed this this morning. Showed precip overhead by the afternoon, but if you went to the forecast sounding for that same time period, it showed a substantial dewpoint depression.

It'll be overcome as we go into the overnight and higher DBZ values move in

Totally agree the storm isn't even here yet folks think this initial batch south is what were expecting.

Still will stay firm 6 plus for MDT.

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Good call.

But the problem is Matt the mainly rain is snow down in s VA. They are getting hit as we speak.

I agree 2-4 is a good range for us. Still think we see more near MDT.

 

I feel like forecasters for local stations don't necessarily worry about being spot on for areas outside of their market (which is understandable IMO). To be fair the S VA snow like around Richmond wasn't really expected by many.

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Good call.

But the problem is Matt the mainly rain is snow down in s VA. They are getting hit as we speak.

I agree 2-4 is a good range for us. Still think we see more near MDT.

 

Right-o, however, the locations reporting snow in VA right now are at high elevations. Significantly higher than the elevation MDT is at. Also, the stuff hitting VA is overrunning, separated from the primary low back in Kentucky. Keep in mind, that the precipitation will be heaviest for MDT likely after daybreak...high sun-angles can kill accumulations, especially on pavement. In addition, surface temps will likely be above freezing (just slightly), and unless we have crazy precip rates we won't see much in the way of high accumulations. 2-4 was a conservative call last night and this morning, but it appears as though the "wild children" models have calmed down and are way more realistic. 

 

8:1 ratios are likely as well.

 

Edit: My bad -- you meant that it's snowing in VA now where I have mainly rain...this is true. But notice the time frame...midnight - tomorrow evening. Thinking the warmer air gets involved when the primary gets here to our south. It may be snowing now in VA, but likely will see some rain later, especially tomorrow. High elevations of VA could stay snow, though as the GFS/Euro have been showing.

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I feel like forecasters for local stations don't necessarily worry about being spot on for areas outside of their market (which is understandable IMO). To be fair the S VA snow like around Richmond wasn't really expected by many.

Oh I am not dinging him at all. Just stating fact as what reality is.

He has a good call. But he put the graphic up that includes VA mainly rain tonight is not the case.

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Right-o, however, the locations reporting snow in VA right now are at high elevations. Significantly higher than the elevation MDT is at. Also, the stuff hitting VA is overrunning, separated from the primary low back in Kentucky. Keep in mind, that the precipitation will be heaviest for MDT likely after daybreak...high sun-angles can kill accumulations, especially on pavement. In addition, surface temps will likely be above freezing (just slightly), and unless we have crazy precip rates we won't see much in the way of high accumulations. 2-4 was a conservative call last night and this morning, but it appears as though the "wild children" models have calmed down and are way more realistic.

8:1 ratios are likely as well.

Thanks for clarifying! I didn't know that about where other than reading in the another forum Matt.

Good stuff.

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Thanks for clarifying! I didn't know that about where other than reading in the another forum Matt.

Good stuff.

 

Here's a good radar reflection of what's going on with this storm....http://synoptic.envsci.rutgers.edu/site/radimg/anim_nerc.gif

 

Notice the separation between the overrunning and the primary low precip. Should fill in as the dynamics & shortwave shoot eastward tonight. It's the precip developing south o fWest Virginia that will pivot and impact us, so keep an eye on it!

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Here's a good radar reflection of what's going on with this storm....http://synoptic.envsci.rutgers.edu/site/radimg/anim_nerc.gif

Notice the separation between the overrunning and the primary low precip. Should fill in as the dynamics & shortwave shoot eastward tonight. It's the precip developing south o fWest Virginia that will pivot and impact us, so keep an eye on it!

Thanks.
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