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STORMcast Advisory 2017-04

Issued: 08Feb17

Time:  0645 EST  

The STORMcasts shown here are intended for the students of UDHS's AGS and AES geoscience programs and are for educational/informational purposes only.  They frequently combine scientific concepts along with a sense of humor that often pokes fun at our behavior during weather events.  While intended to be informative, the STORMcasts should never be used to make life and death decisions during severe weather events.  Follow the appropriate bulletins posted by the National Weather Service and local media outlets for appropriate actions during these events.

 

Current National Weather Service advisory map as of STORMcast issuance...

WINTER STORM WARNING
- 4 AM to 4 PM Thurs. for much of the region including Phila. metro. for 4" - 6" of snow after a brief period of rain and sleet.  Gusty winds and low visibilities in snow squalls possible.

WINTER STORM WATCH -
Tonight into tomorrow for interior MD for possible snowfall of ~5".

WINTER WEATHER ADVISORY
- 8 AM to 2 PM for coastal NJ and central DE.  1" - 4" of snow with a possible extended period of sleet to start. 

GALE/STORM WARNING -
Offshore waters for those who might have the urge to go fishing tomorrow.  Seas 6-9' with winds in the 25-25 kt range. 

(Map courtesy of NWS)

One Day, Two Seasons

Hi everybody.  We've been tracking this one for about 48 hours in the STORMcast center although all eyes were on the tornadoes in the South yesterday.  Now that that has calmed down, it's back to this developing system for the Northeast.  To be honest, I was a bit surprised last night when the Winter Storm Watch went up (and is now a warning) but looking at the morning's models, things DO look like they are coming together.  Just keep in mind the threshhold for a "Winter Storm Warning" vs a "Winter Weather Advisory" in Phila. and Delco is 3" while the rest of the suburbs is 4" so it's not like something major has changed from last night to this morning.  We just crossed the 4" line...

Here's the scoop.

Today

In essence, this is a two part story.  Today, a strong low pressure center will pass to our west along the Great Lakes and move into western New England this afternoon.  With that storm center comes two distinct streams of energy both of which will be created by the counterclockwise spin of the low.  First, a significant amount of warm air will be advected into the region and bring us within striking distance of the record set back int he 1920s.  I'm already at 59F at Upper Dublin so it won't take long.  The fact we won't get all that much energy from the sun today reinforces just how much warmth is riding on this SW flow.  However, where there's lots of warm air advection on the front side, there's cold air advection on the back and by lunch, the cold front that is getting dragged along with the low should cross the area and it'll be all downhill from there with regard to temperature.

Overnight into tomorrow

Overnight tonight as temperatures continue to fall, a second low pressure center should form over VA along the frontal boundary and track northeastward moving out over the ocean by daybreak and <viola>, a Nor'easter is born (or perhaps a medium-sized string instrument, take your pick).  Precip. should begin working into the area in the 2 AM timeframe and increase in intensity as we near daybreak and the storm intensifies off the NJ coast.  Temperatures should also drop below freezing around 3 - 4 AM which will start the transition over to snow from rain and/or some sleet.  There is some concern about an extended period of moderate to even heavy sleet along the I-95 corridor before this switches over to snow by 6 -8 AM.  This is still speculation and would require the perfect mix of cold and warm air to come together but the NWS is watching for the potential.  If this materializes, snow depth will be less but will have a thick layer of ice beneath which will make for a hazardous morning commute.  Snow should end by lunchtime as the storm rapidly moves off to teh noortheast.  Again, classic Nor'easter so don't expect this to hand around for long.

The approximate position of the current low as of 7 AM Wed.  As the attached cold front moves through the area, temps. will start to fall and a secondary coastal low will develop along the DelMarVA overnight.  Image: PSU
As the storm moves off but intensifies, winds will noticeably increase and sustained N or NW winds of 15-25 mph are expected int he metro area around midday.  Gusts along the shore are likely to be higher.  By evening, things will calm down but we will not see a rise above freezing again until Saturday.  It is to laugh...        

Snow day?

I don't get paid enough to make that call at 4 AM and we see this combination of meteorological components almost every year so I don't get all that excited over 5"-6" of snow.  If it wasn't for the fact we're going to be at 63F today and less than half that tomorrow with a shovel in our hands, it wouldn't even be all that funny to talk about but the timing is right and the current trajectory looks about right for an event that will cause problems tomorrow morning if everything stays on track.  Whether it's an ice/snow sandwich or just deeper snow, the morning commute will likely be a mess.  A six hour late opening is all we really need but again, that's not my call.

You all know that storm track is the key and the infamous 50 mile "jiggle" has happened before but as of right now, confidence is pretty high on the track.  Snow totals will be the variable depending on how fast the temperature crashes overnight.  We might even hear some thundersnow towards morning as one or two convective bands of heavy snow make their way through the metro area.  This morning's hi-res model is showing some short-lived explosive snow growth around 8 AM in the 'burbs.  Nothing says a day off like snow with lightning in it.

If conditions change drastically this afternoon (and I have time), there might be an update later today but for now, I think about 5"- 6" of snow is a decent estimate for much of the metro area with slightly less if the sleet pans out.  Any school impact on Friday will depend on effectiveness of snow removal, not meteorology.

School Day Effects for Thursday (as of 0800 Thurs.)

Normal Day....................20% (Only if the storm is a miss)
Day Off............................80% (It's all or nothing!)
2 Hr Opening..................0%  (this really won't help due to the need for snow removal)
Early Dismissal.............0%

rs

0754

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