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December Discobs Thread 2018

George BM

By George BM,
in Mid Atlantic

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Ji

Ji

Posted
Posted
4 minutes ago, nj2va said:

NAM twins are super wet for this weekend 2"+ for a good portion of the area.  Even though northern SC has more snow than us, at least we'll break the record for annual rainfall at DCA this weekend!!  

no other models show this much precip.  Euro shows .5 or so

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yoda

yoda

Posted
Posted
2 hours ago, Ji said:

no other models show this much precip.  Euro shows .5 or so

LWX says 1-3" 

Flood Watch
National Weather Service Baltimore MD/Washington DC
204 PM EST Thu Dec 13 2018

DCZ001-MDZ004>006-011-013-014-016>018-503>508-VAZ036>040-050>057-
501-502-505-506-140315-
/O.NEW.KLWX.FA.A.0008.181214T2300Z-181215T2300Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
District of Columbia-Frederick MD-Carroll-Northern Baltimore-
Southern Baltimore-Prince Georges-Anne Arundel-Charles-St. Marys-
Calvert-Northwest Montgomery-Central and Southeast Montgomery-
Northwest Howard-Central and Southeast Howard-Northwest Harford-
Southeast Harford-Nelson-Albemarle-Greene-Madison-Rappahannock-
Orange-Culpeper-Prince William/Manassas/Manassas Park-Fairfax-
Arlington/Falls Church/Alexandria-Stafford-Spotsylvania-
King George-Northern Fauquier-Southern Fauquier-Western Loudoun-
Eastern Loudoun-
Including the cities of Washington, Frederick, Ballenger Creek,
Eldersburg, Westminster, Reisterstown, Cockeysville, Baltimore,
Bowie, Suitland-Silver Hill, Clinton, College Park, Greenbelt,
Laurel, Camp Springs, Glen Burnie, Annapolis, Severn, South Gate,
Severna Park, Arnold, Odenton, St. Charles, Waldorf,
Lexington Park, California, Chesapeake Beach, Huntingtown,
Dunkirk, North Beach, Lusby, Prince Frederick, Germantown,
Damascus, Bethesda, Rockville, Gaithersburg, Silver Spring,
Lisbon, Columbia, Ellicott City, Jarrettsville, Aberdeen,
Lovingston, Charlottesville, Stanardsville, Madison, Orange,
Gordonsville, Culpeper, Dale City, Manassas, Woodbridge,
Lake Ridge, Montclair, Reston, Herndon, Annandale, Centreville,
Chantilly, McLean, Franconia, Arlington, Alexandria,
Falls Church, Falmouth, Fredericksburg, Dahlgren, Warrenton,
Turnbull, Purcellville, Leesburg, Ashburn, and Sterling
204 PM EST Thu Dec 13 2018

...FLOOD WATCH IN EFFECT FROM FRIDAY EVENING THROUGH SATURDAY
AFTERNOON...

The National Weather Service in Sterling Virginia has issued a

* Flood Watch for portions of Maryland, The District of
  Columbia, and Virginia, including the following areas, in
  Maryland, Anne Arundel, Calvert, Carroll, Central and
  Southeast Howard, Central and Southeast Montgomery, Charles,
  Frederick MD, Northern Baltimore, Northwest Harford, Northwest
  Howard, Northwest Montgomery, Prince Georges, Southeast
  Harford, Southern Baltimore, and St. Marys. The District of
  Columbia. In Virginia, Albemarle, Arlington/Falls
  Church/Alexandria, Culpeper, Eastern Loudoun, Fairfax, Greene,
  King George, Madison, Nelson, Northern Fauquier, Orange,
  Prince William/Manassas/Manassas Park, Rappahannock, Southern
  Fauquier, Spotsylvania, Stafford, and Western Loudoun.

* From Friday evening through Saturday afternoon

* Moderate rainfall is expected with locally heavy rain possible.
  Rainfall amounts around 1 to 2 inches are most likely with
  locally higher amounts around 3 inches possible. Runoff from the
  rainfall may cause creeks and streams to rise out of their
  banks as well as the potential for flooding in urban areas.
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arlwx

arlwx

Posted
Posted

Updated flood watches from LWX 

Flood Watch
National Weather Service Baltimore MD/Washington DC
429 AM EST Fri Dec 14 2018

DCZ001-MDZ004>006-011-013-014-016>018-503>508-VAZ036>040-050>057-
501-502-505-506-142000-
/O.CON.KLWX.FA.A.0008.181214T2300Z-181215T2300Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
District of Columbia-Frederick MD-Carroll-Northern Baltimore-
Southern Baltimore-Prince Georges-Anne Arundel-Charles-St. Marys-
Calvert-Northwest Montgomery-Central and Southeast Montgomery-
Northwest Howard-Central and Southeast Howard-Northwest Harford-
Southeast Harford-Nelson-Albemarle-Greene-Madison-Rappahannock-
Orange-Culpeper-Prince William/Manassas/Manassas Park-Fairfax-
Arlington/Falls Church/Alexandria-Stafford-Spotsylvania-
King George-Northern Fauquier-Southern Fauquier-Western Loudoun-
Eastern Loudoun-
Including the cities of Washington, Frederick, Ballenger Creek,
Eldersburg, Westminster, Reisterstown, Cockeysville, Baltimore,
Bowie, Suitland-Silver Hill, Clinton, College Park, Greenbelt,
Laurel, Camp Springs, Glen Burnie, Annapolis, Severn, South Gate,
Severna Park, Arnold, Odenton, St. Charles, Waldorf,
Lexington Park, California, Chesapeake Beach, Huntingtown,
Dunkirk, North Beach, Lusby, Prince Frederick, Germantown,
Damascus, Bethesda, Rockville, Gaithersburg, Silver Spring,
Lisbon, Columbia, Ellicott City, Jarrettsville, Aberdeen,
Lovingston, Charlottesville, Stanardsville, Madison, Orange,
Gordonsville, Culpeper, Dale City, Manassas, Woodbridge,
Lake Ridge, Montclair, Reston, Herndon, Annandale, Centreville,
Chantilly, McLean, Franconia, Arlington, Alexandria,
Falls Church, Falmouth, Fredericksburg, Dahlgren, Warrenton,
Turnbull, Purcellville, Leesburg, Ashburn, and Sterling
429 AM EST Fri Dec 14 2018

...FLOOD WATCH REMAINS IN EFFECT FROM THIS EVENING THROUGH
SATURDAY AFTERNOON...

The Flood Watch continues for

* Portions of Maryland, The District of Columbia, and Virginia,
  including the following areas, in Maryland, Anne Arundel,
  Calvert, Carroll, Central and Southeast Howard, Central and
  Southeast Montgomery, Charles, Frederick MD, Northern
  Baltimore, Northwest Harford, Northwest Howard, Northwest
  Montgomery, Prince Georges, Southeast Harford, Southern
  Baltimore, and St. Marys. The District of Columbia. In
  Virginia, Albemarle, Arlington/Falls Church/Alexandria,
  Culpeper, Eastern Loudoun, Fairfax, Greene, King George,
  Madison, Nelson, Northern Fauquier, Orange, Prince
  William/Manassas/Manassas Park, Rappahannock, Southern
  Fauquier, Spotsylvania, Stafford, and Western Loudoun.

* From this evening through Saturday afternoon

* Moderate rainfall is expected with locally heavy rain
  possible. Rainfall amounts around 1 to 2 inches are most
  likely with locally higher amounts around 3 inches possible.
  Runoff from the rainfall may cause creeks and streams to rise
  out of their banks as well as the potential for flooding in
  urban areas.


Flood Watch
National Weather Service Baltimore MD/Washington DC
429 AM EST Fri Dec 14 2018

MDZ003-VAZ025>031-507-508-WVZ050>053-055-142000-
/O.CON.KLWX.FA.A.0008.181214T2300Z-181215T2300Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Washington-Augusta-Rockingham-Shenandoah-Frederick VA-Page-Warren-
Clarke-Northern Virginia Blue Ridge-Central Virginia Blue Ridge-
Hampshire-Morgan-Berkeley-Jefferson-Hardy-
Including the cities of Hagerstown, Staunton, Waynesboro,
Stuarts Draft, Harrisonburg, Strasburg, Woodstock, Mount Jackson,
New Market, Winchester, Luray, Shenandoah, Stanley, Front Royal,
Berryville, Big Meadows, Wintergreen, Romney, Paw Paw,
Martinsburg, Charles Town, Shepherdstown, and Moorefield
429 AM EST Fri Dec 14 2018

...FLOOD WATCH REMAINS IN EFFECT FROM THIS EVENING THROUGH
SATURDAY AFTERNOON...

The Flood Watch continues for

* Portions of north central Maryland, Virginia, and West
  Virginia, including the following areas, in north central
  Maryland, Washington. In Virginia, Augusta, Central Virginia
  Blue Ridge, Clarke, Frederick VA, Northern Virginia Blue
  Ridge, Page, Rockingham, Shenandoah, and Warren. In West
  Virginia, Berkeley, Hampshire, Hardy, Jefferson, and Morgan.

* From this evening through Saturday afternoon

* Moderate rainfall is expected with locally heavy rain possible.
  Rainfall amounts of 1 to 2 inches are most likely with locally
  higher amounts of 3 inches possible. Runoff from the rainfall
  combined with melted snow may cause creeks and streams to rise
  out of their banks as well as the potential for flooding in
  urban areas.

 

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arlwx

arlwx

Posted
Posted

From the latest LWX discussion:


.NEAR TERM /THROUGH TONIGHT/...
Latest surface analysis places surface low pressure near the
Louisiana/Arkansas border, with high pressure already pushing
into the western Atlantic. High clouds are slowly thickening
across the region, but precipitation is still several hours
away. Temperatures have therefore dropped to near or below
freezing, but believe they should generally rise back above
freezing before precipitation arrives later this morning, even
in the southern Shenandoah Valley. That said, have left a
chance of freezing rain in the forecast across that area, while
the rest of the region should be solidly rain. Latest guidance
has increased the speed of rain`s arrival, with rain likely to
affect the entire CWA by the evening rush. Highs will be in the
40s in most of the region thanks to the increased cloud cover
and the arrival of the rain.

First push of warm advection and extremely moist air ahead of
the main low occurs tonight, so flood watch remains in effect.
PW`s get quite high for December and the low level jet is pretty
strong, so potential for some heavier rain is certainly present,
but guidance is not exactly in great agreement regarding how
heavy the rain will be tonight. However, enough models show the
heavy rain signal such that there is no reason to take it out,
especially considering the extremely wet weather we`ve had all
year. Now that it is the cold season, the soil is even less
capable of absorbing significant rainfall, and without active
vegetation, runoff is significantly higher, so it will not take
as much rain to get flooding. Temps will likely be steady or
slowly rise overnight.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
Rain likely tapers to showers on Saturday as the initial wave
moves east, but with the high PW air mass still in place,
heavier rain can still occur with showers through the day, so
the flood watch continues through the day. Some guidance is
hinting at a secondary burst of heavier rain Saturday night as
the upper low approaches and coastal low redevelopment occurs
just to our southeast, so its possible the flood watch may end
up getting extended into Sunday. With the surface system passing
east and winds becoming northerly by Sunday, Saturday will
likely be the warmest day just behind the initial push of
southerly winds, with a cooling trend Saturday night and temps
probably not changing much on Sunday. With the upper low finally
pulling east of us Sunday night, the chance of precip will
finally decline dramatically, so quickly taper pops by then.
Temps will also cool more, and whatever shower activity remains
could change to snow, most likely over the higher elevations,
but this doesn`t look like it will amount to much. Lows Sunday
night will drop back into the 30s.
(snip)

From here, global model solutions differ in the amplitude of an
upper trough crossing the Great Lakes Thursday and Thursday
night. GFS is much less amplified, and brings a cold front
through the area Thursday night with limited moisture. The ECMWF
on the other hand is significantly more amplified, stretching
the base of the upper trough all the way to the northern Gulf.
This allows for a surface low to develop along the Gulf Coast
states and tap into the Gulf moisture. This would bring much
more precipitation to the region as low pressure tracks up the
east coast Thursday night, with rain being the favored ptype.
Will carry middle of the road chance POPs Thursday and Thursday
night for now with near normal temperatures prevailing.

 

 

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nj2va

nj2va

Posted
Posted
25 minutes ago, WxUSAF said:

Forgive me for getting this info from tony Pann, but 12z NAM changes precip over to snow Sunday evening for folks near Baltimore. Both 3k and 12k. Euro showed this several days ago but haven’t seen it since.

I was just coming on to say this after I looked at the 3k NAM.  GFS does the same thing but its further north into the Poconos/etc.  3k NAM even gets changeover super close to DC.  

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WxUSAF

WxUSAF

Posted
Posted
5 minutes ago, nj2va said:

I was just coming on to say this after I looked at the 3k NAM.  GFS does the same thing but its further north into the Poconos/etc.  3k NAM even gets changeover super close to DC.  

Gfs isn’t far off if you account for the NAM getting the thermals better. Not sure how close euro has been to this the last few runs.

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Herb@MAWS

Herb@MAWS

Posted
Posted
9 minutes ago, nj2va said:

Euro 6z was similar to the Euro IRT to changeover placement...Poconos/NW Jersey and NE from there.

Wouldn't be the least bit surprising.  My friends in Middletown, NY (just above-and-northeast of the northern tip of NJ, with an elevation approx 1000-1200 feet in general) had a little snow yesterday and always seem to be in a sweet spot for snow during changeovers.  I have to live vicariouly thru them sometimes.  While we're at 42 and partly cloudy, they can be 32 with snow.  I get too many snow pix from them!  :-)

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