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Central PA - Winter 2020/2021 Part 2


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1 minute ago, Cashtown_Coop said:

IMO, .50” is when you start getting into trouble.  Sure .25” can take down limbs and a dead ash tree but .50” is the threshold for widespread tree and power line damage and impactful power outages.  

80554815-4A0D-4D5C-85B6-75786ACD3A59.jpeg

Agreed. .5-.75 is the danger zone. Anything over .75 is catastrophic. 

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Depending on how far below freezing the rain falls dictates how fast the accrual process is.  Currently, with MDT forecast to get 0.87" of freezing rain, it is highly unlikely that all of that rain ends up accruing.  If the temp is 30 you won't get anywhere near 0.87" of accrual.  I have no idea how cold it would have to be to even reach 0.50" of accretion.  25 degrees?  20 degrees?  Actually, another factor affecting accretion would be the intensity of the rain.  Light rain has a much higher chance to accrue versus moderate or heavy rain.

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I’m riding in the CTP point & click train. This is the current forecast for Harrisburg International Airport (MDT) for this week.

Monday Night
A chance of snow, freezing rain, and sleet before 1am, then snow and sleet. Low around 26. Chance of precipitation is 80%. New snow and sleet accumulation of less than one inch possible. 
Tuesday
Snow and sleet likely, possibly mixed with freezing rain, mainly before 1pm. Mostly cloudy, with a high near 33. Chance of precipitation is 70%.
Tuesday Night
Partly cloudy, with a low around 15.
Wednesday
Partly sunny, with a high near 31.
Wednesday Night
A chance of snow after 1am. Mostly cloudy, with a low around 21. Chance of precipitation is 40%.
Thursday
Snow. High near 36. Chance of precipitation is 80%.

 

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Just now, Blizzard of 93 said:

I’m riding in the CTP point & click train. This is the current forecast for Harrisburg International Airport (MDT) for this week.

Monday Night
A chance of snow, freezing rain, and sleet before 1am, then snow and sleet. Low around 26. Chance of precipitation is 80%. New snow and sleet accumulation of less than one inch possible. 
Tuesday
Snow and sleet likely, possibly mixed with freezing rain, mainly before 1pm. Mostly cloudy, with a high near 33. Chance of precipitation is 70%.
Tuesday Night
Partly cloudy, with a low around 15.
Wednesday
Partly sunny, with a high near 31.
Wednesday Night
A chance of snow after 1am. Mostly cloudy, with a low around 21. Chance of precipitation is 40%.
Thursday
Snow. High near 36. Chance of precipitation is 80%.

 

Sounds like the GFS came in really warm for Tuesday and Thursday.

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I’ll also ride this HWO train from CTP.

Hazardous Weather Outlook

Hazardous Weather Outlook
National Weather Service State College PA
449 AM EST Sat Feb 13 2021

PAZ024>028-033>036-050>053-056>059-063>066-141000-
Cambria-Blair-Huntingdon-Mifflin-Juniata-Somerset-Bedford-Fulton-
Franklin-Snyder-Montour-Northumberland-Columbia-Perry-Dauphin-
Schuylkill-Lebanon-Cumberland-Adams-York-Lancaster-
449 AM EST Sat Feb 13 2021

This Hazardous Weather Outlook is for central Pennsylvania.

.DAY ONE...Today and tonight.

Patchy light snow and sleet accumulation and possible spotty ice
glaze is possible Saturday afternoon or evening.

.DAYS TWO THROUGH SEVEN...Sunday through Friday.
A pair of winter storms could bring significant snow and ice Monday
into Tuesday and Thursday into Friday.
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40 minutes ago, CarlislePaWx said:

Depending on how far below freezing the rain falls dictates how fast the accrual process is.  Currently, with MDT forecast to get 0.87" of freezing rain, it is highly unlikely that all of that rain ends up accruing.  If the temp is 30 you won't get anywhere near 0.87" of accrual.  I have no idea how cold it would have to be to even reach 0.50" of accretion.  25 degrees?  20 degrees?  Actually, another factor affecting accretion would be the intensity of the rain.  Light rain has a much higher chance to accrue versus moderate or heavy rain.

Correct, the heavier the rate the less accretion. 

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More from CTP this morning 

SYNOPSIS... Quiet conditions expected into Saturday morning spotty light mixed precipitation is possible late Saturday through Saturday night. A pair of winter storms could bring significant snow and ice Monday- Tuesday and Thursday- Friday. Temperatures are forecast to remain below average into the second half of February.

 

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One final thing from CTP for now...

LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... An active weather pattern will continue into the long-term, as Pennsylvania remains in the vicinity of baroclinic zone between an anomalous upper-level trough over the Plains states and a ridge off of the East Coast. Latest model guidance suggests that another period of light snow (possibly a light mix across the southeast) is in store for Monday, associated with jet streak over the St Lawrence Valley and associated fgen forcing over PA.


The bigger concern comes Monday night into early Tuesday, however, with a wave of low pressure lifting out of the Gulf of Mexico. This moisture-laden system will ride northward along the spine of the Appalachians before transferring energy to the Mid-Atlantic Coast on Tues, and it should bring a swath of significant snow to some portion of central PA, with a wintry mix once again possible across the south. This system will exit the area later Tues, followed by a brief period of fair and seasonable weather for Wednesday as upper level ridging builds into the region.

By late week, medium range guidance is indicating another significant area of low pressure will track northward from the Gulf Coast towards PA. Given that this storm is still 7 days away, it`s still a little early to pin down the exact track of the low and resulting ptypes.

 

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Sounds like the GFS came in really warm for Tuesday and Thursday.

I trust the HRRR and 3k-NAM inside 18 hours.
Seems like the rest are having an epically horrible time separating the signal from the noise.

I’ve been telling people that unless it’s within 24 hours to ignore any and all forecasts


.
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The 12z Euro did tick slightly southeast with the snow line compared to the 6z run for Tuesday.

For example, at 6z Harrisburg had 1.4 inches of snow by the end of Tuesday and now at 12z, it had 2.2 of snow.

It seems subtle, but still time to pull the 6 inches of snow from State College & Selinsgrove down to the Harrisburg area with the track depicted.

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What’s the temp showing on the euro the night before storm? During storm? What time is it suppose to start? Most important is how long is duration? Is this 1” going to come in a 6 hr period or 24 hours? If it’s the latter and you have generators I’d advise to test them and fuel up.


.

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8 minutes ago, Jns2183 said:

What’s the temp showing on the euro the night before storm? During storm? What time is it suppose to start? Most important is how long is duration? Is this 1” going to come in a 6 hr period or 24 hours? If it’s the latter and you have generators I’d advise to test them and fuel up.


.

Here is a snapshot of 4am Tuesday with surface, 925, 850 & 700mb temps for 4am as well.

This is very close to a better front end thump of snow for the Harrisburg and I-81 areas and north west from there. A small shift will make all of the difference.

Here is the surface precip type map for 4am and the surface temps.

 

53230B52-FE16-4E5A-888D-2A1DD35AF168.png

13662567-FA39-4D79-A43F-F453E24DD3E9.png

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