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Thursday, January 21, 2016

1-23 update

Afternoon  NAM giveth, NAM taketh away.  This is why you discount the nam, especially on northern edges of the precip.  However, I do think its coming to its solution - GFS went from .26 at 6z to .45.  Euro is at .46.  Nam is at 1.5 -sounds too high still although the three images below show a sharp dropoff.  I still like 3-5, but we may get my original 6-8.  The NWS is at 3-5 for Fairfield county now, and their min is 0, max is 20.  So.....

0z >2 feet

6z top edge getting less
12 whole state getting less.

Morning  Still holding 3-5 for CT until either the NAM or GFS caves.  This is really a blend and if the GFS wins, we could be seeing 1", and if the NAM wins, 10"+

Low confidence forecast for CT, South of CT should get 6-12-18" North to south.
SREF ensembles, NAM and short range models continue to show copious amounts of moisture penetrating CT, with 1" qpf making it far north as Worcester.  GFS at 0z on the other hand is still bouncing around at DXR, with .09 at 12z, .3 at 18z (yesterday), down to .08 at 0z and back to .26.  Its having a problem both with the precip field, but also continues to reform a low 200 miles to the east (see below).  The cause of this is speculative - some have said convective feedback (model chasing tstorms to reform the low), others divergence, with my theories being another baroclinic boundary as the cold air comes around the low and into the gulf stream.  My theory is a bit off, as the gulf stream is further south, but the water temps are much higher.  Thus, cold air forcing warmer air up causing thunderstorms and a new low to form.  On the other hand, the GFS routinely sends precip/tstorms out of the low pressure resulting in convective feedback, which usually corrects by now.  So which is it - the low chasing the tstorms on the model, or thunderstorms forming due to a new low formed by the entrance of colder air over warmer water.

SREF plumes have been consistently increasing over the past 4 runs - 1.24, 1.25, 1.52 and 1.56.  NAM 12k is also consistently increasing from 1.2 12z yesterday to 2.19 6z today.   Euro has gone from .13 yesterday 12z, to .4 today 0z.  RGEM has also slowly crept north going from 1" at 0z to 3" at 6z.  If the global models (euro/cmc/ukmet/gfs) continue to increase the precip for DXR, we know the problem was convective feedback.  If they retreat, again, or if the NAM starts to drop drastically, then we know the NAM was in typical over blown precip mode.  The check for that is lp position, which is further north for the srefs, than the gefs, and the Nam holds the low under the UL while the GFS ejects the low east.  So I don't think the NAM is overdoing precip, considering how much is from the Gulf and an Atlantic which is 2-4 degrees above normal temps.  It may just be the NAM captures the low, the GFS doesn't.


After the gfs roller coaster yesterday, plus the increase in Euro, then decrease, the global operational models are indicating.... flurries.


But... the higher resolution short term models are still going to town. Two versions of the NAM exist  -both have the same QPF, but calculate snow differently.  Plus the SREF ensembles showing Oxford ct with over 1" of precip both on the 3z and 9z.  And the Euro control has 3-6 in most of CT.  CMC/GEM has 1-5.  Canadian Ensembles have .5" qpf for most of CT
accuweather version nam
instantweather version

So...  6-8 still looks unlikely, unless you weigh equally the sref with the gfs.  Typically the SREF is overstated, as is the NAM, when it comes to precip (QPF).  So I usually take 50-60% of that figure which still gives us 6".  This usually matches the GFS, but since it doesn't, blend in the GFS/Euro models and you get 3".  Have to lower to 3-5", but keep an eye on the still sharp cutoff.  One thing the NAM picture on instantweather is that the cutoff from 12" to 0"is about 30 miles wide, if not smaller.

And then there is the incredability that this set up on the UKMET is not going to bring us more than flurries.

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