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Wednesday, December 24, 2014

Christmas to New Years +4

1-4 - results.  GFS had lakes cutter consistently first, Euro bopped back and forth.  Euro and GFS blew the temp forecast as it just got to 51 here on a forecast of 58.  NAM got the surface temps right.  Snowed four hours or so, accumulating 1.5 inches before freezing rain set in.  Temps hovered around 33 for the better part of the night, and snow remained on the ground until the stronger southerlies came in this afternoon. Not much rain during the daylight today, though thick fog in the morning, less than .1 mile vis. 

1-3  Make the start time early afternoon. Snow on radar approaching at 12:30 with reports of heavy snow in NJ. Temp at 33 with DP of 23 makes a period of snow and sleet likely. Not a lot of virga reported despite DPs.

1-2  Models still agree on the setup of warm air overrunning cold air.  Details as to how much  of the moisture arrives before or after the warm air are still up in the air.  All models show some snow, but is it a quick change or do we get an inch, or several inches?  One change since the last post is that the moisture seems more spread out, rather than front loaded.  Forecast remains a mostly rain event on Sunday, starting late Saturday afternoon or evening as snow, one or two inches to be safe.  But still need to watch.  Euro and snow map below.

Euro 0z

NAM 6z

12-31 - Models still agree on primary storm track up the St Lawrence, a little difference on when, where and if a secondary forms.  GFS and long range NAM are indicating a CAD (cold air damming) event where we could get thumped with snow.  Both 6z gfs and 12z nam are forecasting snow for the areas north of NYC.  Upton, Taunton and Albany offices of NWS are also onto this and have mentioned possibly heavy snow prior to changeover.  So this isn't dead just yet.  Text from GFS shows at least .27 qpf in Danbury before changeover.  What we don't know is how much of the .75 the following 6hr period is snow v. sleet v. freezing rain v rain.  GFS and Euro are notoriously quick in warming the surface during CAD events, so that 1.0 for 2m temp is likely a -1 or 0 and the 5.6 is possible by 12z, but more likely 1 or 2.  The temps aloft will warm though, and eventually the surface, but potentially not until most of the precip has fallen.edit - 12z gfs in much warmer now, but still keep an eye on.  

GFS 0.5 Degree FORECAST FOR:  LAT =  41.38  LON =  -73.46

                                            06Z DEC31   * - APPROXIMATED
                 2 M     850     SFC     SFC     700    6 HR     500    1000 
                 TMP     TMP     PRS     RHU     RHU     QPF     HGT     500 
                 (C)     (C)    (MB)    (PCT)   (PCT)   (IN)    (DM)     THK 
SUN 06Z 04-JAN   1.0    -2.9    1030      95      95    0.27     569     545    
SUN 12Z 04-JAN   5.6     6.9    1017      99     100    0.75     569     555    

12-30 Euro flips back to a storm heading to the Great Lakes, or at least north west of us, so now all models in agreement 5 days out.   With today not warming up (27 degrees at 1230) I'll be curious as to how the cold air holds.  Some hints (6z gfs) that cold air dammning may be in place for the interior.  Could be icy Sat night.

12-29   Euro shunts storm to south still.  GFS still brings it up to the lakes. JMA hits us with a quick weak storm, moves it just to our south.  CMC flipped from a wave to the south, to a storm to the lakes.  UKMET just coming into range...but looks like its going to our west.  The parallel GFS though is like the JMA in that it goes just to our south. 
12z euro snow
12z CMC snow

12z GFS snow

Parallel GFS

12-28  0z euro has nothing until the 3rd/4th as the storm goes to the lakes.  Cold air blasts in behind it, perhaps changing to snow, but not likely.  Northern stream wave crosses the country, sparks a weak LP off NJ for what looks like a minor snow event on the 6th.  12z run has completely different look once past 132hr.  At the 500mb level, an upper low now cuts off, so without the digging trough, the northern and southern streams keep separate, allowing the norther stream to suppress the surface storm as it brings it over KY, VA and off the coast ENE.  The cold air is marginally in place, with 6" of snow on the snow map for most of PA, N NJ, HV, CT, RI.  4 panel maps below make it easier to compare. The 12z run has several northern stream snow opps afterwards as well. Euro has a bias for holding energy over the SW though, so I am suspicious. 
12z euro
0z Euro

GFS on the other hand is sticking with the storm going to the lakes.  It also is waffling with the strong cold air coming in afterwards.

CMC splits the difference with the Low coming closer to our area or just west. 

12-27 Evening - 12z euro backs of the idea below. Storm remains in the apps and does not reform at the coast, bringing rain to the EC.

Nothing other than a dusting for the end of the year.  Euro does change on the 3-5th time frame. It has the storm from the 3-4th going to the lakes, weak.  But it also forms a storm  over LA, rides up the apps and transfers off the coast 0z the 5th. By that time some high pressure has tried to come in behind the first storm to the lakes, bringing cold enough air in to have it snow a little.  The ensemble control keeps the main storm over the lakes and doesn't form the one over the gulf.  The operational puts out a foot for areas just to our south.
Loading Maps... But no such luck on the GFS although it does sneak some light snow into the mid atlantic on the 30th.  GFS runs the storm to the lakes, keeps it strong, as does the CMC, though the GFS is ont he 3rd, CMC on the 5th.  Still don't buy any pattern change based on the last few days of runs.  There are runs with cold air, but its transient and not matched with precip. Any sustained cold on the runs is gone by the next model run.  Just keeps getting pushed back and back.  Was supposed to turn cold for good in mid Dec, per many mets.  But I don't even see it changing by mid Jan.  See the previous post as to why we need snow in December.

12-26  Euro has storm forming on front, but sliding to our south, with just a little precip on the 29th. Next shot a storm on the fourth heading to the lakes.0z GFS doesn't form storm to south, just a wave and slides it off.  The 4th storm is a bit warm, but does exit the CONUS to our SE so a rain to snow event. 6z GFS has the 4th storm going right over us.  CMC has first wave on the 29th brushing the area, with the 4th hitting NYC dead on. 

12-25 - Still no snow until maybe the 3rd, on GFS.  Nothing on Euro this morning.

12-24  Post Christmas, warm air will stay in the Northeast as a weaker low heads NNE through the Great Lakes.  It looks like a cold front will pass through around the 28th.  That front looks to stall somewhere along the MidAtlantic and a wave (or waves) of lp will ride along it.  The location of the front and the strength of the cold air will determine what, if anything, we get from the 28th to the 1st.  0z GFS shows an inch or two, Euro 2 or three inches.  But the 6z gfs keeps the front to our south.  CMC is showing a better chance as gulf moisture streams up the front and forms better lp.  DGEX as well.  But the boundary is really close.  All models show more seasonably cold, if not below normal, temps following New Years. 

update: afternoon Euro and GFS suppress all the waves to our south.  CMC is further south, but still brings some snow.  Colder than normal air does not  hit us on those runs as a low runs up the Appalachians during the Jan 2-4 time frame, bringing rain. 

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