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December Discobs Thread

George BM

By George BM,
in Mid Atlantic

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WxUSAF

WxUSAF

Posted
Posted

Whoa LWX issued a WWA

http://forecast.weather.gov/wwamap/wwatxtget.php?cwa=lwx&wwa=winter weather advisory

Quote

 

URGENT - WINTER WEATHER MESSAGE National Weather Service Baltimore MD/Washington DC 930 PM EST Tue Dec 26 2017 MDZ004>006-011-503>508-VAZ505-506-271030- /O.NEW.KLWX.WW.Y.0026.171227T0700Z-171227T1600Z/ Frederick MD-Carroll-Northern Baltimore-Southern Baltimore- Northwest Montgomery-Central and Southeast Montgomery- Northwest Howard-Central and Southeast Howard-Northwest Harford- Southeast Harford-Western Loudoun-Eastern Loudoun- 930 PM EST Tue Dec 26 2017 ...WINTER WEATHER ADVISORY IN EFFECT FROM 2 AM TO 11 AM EST WEDNESDAY... * WHAT...Light snow likely. Plan on slippery road conditions, including during the morning commute on Wednesday. Total snow accumulation of a coating to 1 inch is likely. * WHERE...The Baltimore Metropolitan area...north-central and central Maryland...portions of northern Virginia...and the northern suburbs of Washington DC. * WHEN...From 2 AM to 11 AM EST Wednesday. * ADDITIONAL DETAILS...Any light snow that does fall can cause many roads to quickly turn icy due to the recently cold conditions. This could lead to dangerous traveling conditions, multiple accidents, and extensive delays during the morning commute for Wednesday. PRECAUTIONARY/PREPAREDNESS ACTIONS... A Winter Weather Advisory for snow means periods of snow will cause primarily travel difficulties. Be prepared for snow covered roads and limited visibilities, and use caution while driving. The latest road conditions for the state you are calling from can be obtained by calling 5 1 1. $$

 

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Eskimo Joe

Eskimo Joe

Posted
Posted
Quote 

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
948 PM EST Tue Dec 26 2017

.SYNOPSIS...
A reinforcing arctic cold front and weak upper level disturbance
will cross the region early Wednesday, with arctic high pressure
over the region Thursday. Low pressure will develop offshore 
late Thursday through Friday before arctic high pressure returns
during the weekend.

&&

.NEAR TERM /TONIGHT AND WEDNESDAY/... 
Shortwave energy is approaching the region this evening in 
culmination with a jet streak to our west southwest. This has 
allowed for mid to high level clouds to increase over the area. 
Light snowfall is being observed over western PA and north 
central WV this evening with some decreased visiblities. This 
disturbance will overspread our area overnight bringing an 
increase in very light snow, starting between 1 to 3 am, 
primarily along and northward of the District. Some factors 
supporting light snow fall across these areas are the favored 
location of the left exit region of the aforementioned jet, 
increased moisture in the dendritic snow growth zone, and some 
light vertical velocities owing to frontogentical forcing. 

QPF trends from model guidance have been light, generally less 
than a tenth of an inch, but with the cold antecedent 
conditions and higher snow to liquid ratios, a coating to an 
inch will be possible through mid morning Wednesday. This will 
result in a potential commuting hazard Wednesday morning for the
metro areas, so allow plenty of time to reach your destination.

As a result, we have issued a Winter Weather Advisory for the 
Baltimore-Metropolitan area, north central and central Maryland,
portions of northern Virginia, and the northern suburbs of the 
District from 2am to 11am Wednesday. High res guidances 
indicates a focused band of light snow, will reside just north 
and west of the D.C. area. The light snow is expected to taper 
off around mid morning Wednesday as the shortwave and upper 
level jet begins to exit to our east. Clearing skies can be 
expected by the afternoon hours. Winds will be picking up the 
the wake of this system, with gusts in excess of 20 mph likely. 
High temperatures will remain below the freezing mark during the
day on Wednesday.

 

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Bob Chill

Bob Chill

Posted
Posted
10 minutes ago, WxWatcher007 said:

Meanwhile, the NAMs still aren't biting. Would be fun to wake up to some cold and snow tomorrow. All I want is a coating. I think that's possible..

That's the part I don't understand. This type of event is exactly why the nams exist in the first place. 

Euro, cmc, and rgem show it but the gfs and nams have zippo. If the snow verifies then the US team really sucks right now. Especially with the gfs/gefs manufacturing a significant storm next week run after run with zero support. Very bad not good. 

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RDM

RDM

Posted
Posted

   If the intensity and duration of forecast upcoming cold stretch holds there could be a wide-spread mess for first responders.  In addition to the burst water pipes and lines in buildings not properly protected, the frost heave could wreck havoc with building foundations.  Around here, the building code for the depth of footers is typically only 2 feet below grade.  Back in Ohio where I grew up building code is 4 feet deep, to keep below the frost line for even a "harsh" winter.

   Back when I was in HS in Ohio we had one period when it only got above freezing a couple of days on month (think it was 78, was a long time ago).  Had several stretches well below zero for nearly a week or longer.  The prolonged duration and intensity of the cold pushed the frost line down to over 5 feet.  The impact on foundations, bridges, roads, water mains and water service lines to residential and commercial facilities was enormous.

  Remember our municiple water tower froze over.  The main water main leading from the tower to the town froze solid.  So the system thought the tower was empty and kept trying to fill it.  The relatively warm water from the city wells ran out the overflow at the top of the tower and generated the nicest 300 + foot ice fall you've ever seen.  What looked nice at first became a problem when they couldn't turn it off and everything froze up on the ground and on the houses and church located in the immediate vicinity.

   Haven't heard of any special preparations for around here.  We're on well and septic at our home and I have no idea how deep our supply line is from the well head to the house.  Guess we'll find out if it's deep enough or not. 

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Eskimo Joe

Eskimo Joe

Posted
Posted
Just now, RDM said:

   If the intensity and duration of forecast upcoming cold stretch holds there could be a wide-spread mess for first responders.  In addition to the burst water pipes and lines in buildings not properly protected, the frost heave could wreck havoc with building foundations.  Around here, the building code for the depth of footers is typically only 2 feet below grade.  Back in Ohio where I grew up building code is 4 feet deep, to keep below the frost line for even a "harsh" winter.

   Back when I was in HS in Ohio we had one period when it only got above freezing a couple of days on month (think it was 78, was a long time ago).  Had several stretches well below zero for nearly a week or longer.  The prolonged duration and intensity of the cold pushed the frost line down to over 5 feet.  The impact on foundations, bridges, roads, water mains and water service lines to residential and commercial facilities was enormous.

  Remember our municiple water tower froze over.  The main water main leading from the tower to the town froze solid.  So the system thought the tower was empty and kept trying to fill it.  The relatively warm water from the city wells ran out the overflow at the top of the tower and generated the nicest 300 + foot ice fall you've ever seen.  What looked nice at first became a problem when they couldn't turn it off and everything froze up on the ground and on the houses and church located in the immediate vicinity.

   Haven't heard of any special preparations for around here.  We're on well and septic at our home and I have no idea how deep our supply line is from the well head to the house.  Guess we'll find out if it's deep enough or not. 

Water line breaks are on about a 36 - 48 hours delay from onset of cold.  It takes about that long for the cold to really penetrate down...WSSC will be busy again.

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high risk

high risk

Posted
Posted
42 minutes ago, Bob Chill said:

That's the part I don't understand. This type of event is exactly why the nams exist in the first place. 

Euro, cmc, and rgem show it but the gfs and nams have zippo. If the snow verifies then the US team really sucks right now. Especially with the gfs/gefs manufacturing a significant storm next week run after run with zero support. Very bad not good. 

        Besides, the NAMs, it's worth noting that the Hi-res Windows don't have it either, and they're designed for this type of event too.    The NSSL-WRF, a very good model, also doesn't have it.     I'm not sure what to think....      

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Eskimo Joe

Eskimo Joe

Posted
Posted
2 minutes ago, high risk said:

        Besides, the NAMs, it's worth noting that the Hi-res Windows don't have it either, and they're designed for this type of event too.    The NSSL-WRF, a very good model, also doesn't have it.     I'm not sure what to think....      

Think about waking up to nada tomorrow.

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RDM

RDM

Posted
Posted
19 minutes ago, Eskimo Joe said:

Water line breaks are on about a 36 - 48 hours delay from onset of cold.  It takes about that long for the cold to really penetrate down...WSSC will be busy again.

Depends on a lot of variables like how cold it gets, how deep the water lines are, the type of soil strata and moisture content.  A dry soil like we have now won't propagate freezing as quickly as a moist soil will.  Frozen water mains and lines are self evident when it happens.  The impact of a deeply frozen ground may not be apparent until spring or even longer.  Forgive the banter, but below is a perfect example of just how delayed the impact may be... 

The example that comes to mind is a chimney at my parent's home in Ohio.  In circa 72 my parent's had a fireplace with a large 2 story chimney with two flues installed in our old Victorian era home.  The masons (who were very experienced) excavated down 4 feet below grade for the footers for the cinder block foundation (per code).  Unfortunately, when the deep freeze hit the mid-west a few years later, the ground froze so deep, it undermined the integrity of the footer for the chimney.  The next year a gap appeared between the house and the chimney up near the roof line that gradually grew to about an inch over several years.  Not good...

Not wanting our chimney to end up in our next door neighbor's living room, which was well within reach of the top of the chimney if it fell, my dad contacted the masons to see if they could do anything.  Their solution was to tear down the chimney and build a new one, to the tune of big bucks $$$. 

Being the creative guy he is, my dad got a post hole digger and dug down about 6 feet.  Got some thick steel plate and cut two L shaped brackets long enough to reach down and under the chimney footers.  Used two thick I-beams stacked on top of each other, two house jacks, some thick chain and a lot of "persuasion".  He was able to jack up the foundation of the chimney from below and tilt the entire chimney back against the house.  Of course, he did this very slowly and carefully over several days.

With the chimney under load from the lifting setup of beams and jacks, he excavated more down and under the chimney foundation.  Then he poured everything full of concrete up to about a foot below grade.  This essentially created a concrete grade beam below and adjacent to the foundation for the chimney.  He let everything setup for a few weeks, removed the I-beams and torched off the steel plate just above the concrete, but well below grade.  Back-filled the holes with soil and you can't tell anything was done.  Mind you my dad only went to school through the 8th grade and didn't get his GED until he was nearly 70.  (but he was one of the first paramedics in the state of Ohio).  He just has the "knack" for figuring things out... 

Am hoping I don't have to apply any of that gene pool to this upcoming cold spell... 

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Eskimo Joe

Eskimo Joe

Posted
Posted
1 minute ago, high risk said:

 

    well-played.     My hesitance is that the HRRR usually underdoes these light events, not overdoes them.    So I am slow to dismiss when it shows one, and the parallel HRRRX shows it happening too.

Well, I'll say this.  Jet dynamics are interesting and places in WV are reporting SN- with a 15 degree dewpoint depression.  Radar doesn't look terrible:  http://weather.cod.edu/satrad/

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RDM

RDM

Posted
Posted

Down to 27 with a dp of 17.  Anything that comes will have a high ratio with it.  So even if we can eek out .10, that could be enough to make it interesting in the morning (I know, .1 is likely wishful thinking).  Of course, even if the roads are dry with the pixie dust blown to the shoulders, even the mere sight of a few flakes will put commuters into convulsive fits of incoherence...

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Bob Chill

Bob Chill

Posted
Posted
13 minutes ago, high risk said:

        Besides, the NAMs, it's worth noting that the Hi-res Windows don't have it either, and they're designed for this type of event too.    The NSSL-WRF, a very good model, also doesn't have it.     I'm not sure what to think....      

0z gfs finally got it. At least it picked it up before onset. :lol:

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