Area forecast discussion 
National Weather Service Gray ME 
645 PM EST Friday Feb 12 2016 


Synopsis... 
an Arctic cold front will cross the region tonight through Saturday 
ushering in the coldest airmass of the season thus far. As this 
cold air interacts with a trough of low pressure over the Gulf of 
Maine...a period of moderate to heavy snow will be possible along 
the midcoast region of Maine. Beyond this...the combination of cold 
temperatures and strong northwest winds will cause dangerously cold 
wind chills Saturday night and Sunday. Temperatures will rapidly 
moderate next week with a wintry mix of precipitation potentially 
transitioning to rain on Monday night and Tuesday along with strong 
southerly winds. 


&& 


Near term /until 6 am Saturday morning/... 
635 PM update...have continued to pour over latest obervational 
and mesoscale model data early this evening to try and pin down 
the formation and movement of an inverted trough that may bring 
heavy snowfall to a portion of the middle coast. Unfortunately at 
this time it is a little to early to see anything significant in 
the latest observational data such as buoys and radar. As far as 
the mesoscale models go...there is still a lot of spread in where 
this band will /or will not/ develop over land. The latest runs of 
the NAM and rgem as well as the 2.5 km Canadian hit Knox and 
Waldo counties pretty hard. However...the latest runs of the hrrr 
and rap keep much of the accumulating snowfall offshore except 
perhaps the peninsulas and islands of the middle coast. With so much 
uncertainty remaining and no sign of development yet in 
observational data...can/T really justify a Winter Storm Warning. 
Will hold onto the watch for a few more hours. Will likely make a 
decision by 10 PM...and if there is still a lot of uncerainty by 
then we may just go with an advisory and let the next shift 
upgrade to a warning if need be. 


Previously... 


High impact weather potential: snow develops along the midcoast 
overnight. Current pattern: early afternoon water vapor imagery 
reveals ridge- trough pattern across the Continental U.S....with impressive 
portion of the polar vortex currently centered over James Bay. 
South of this feature...water vapor imagery defines a digging 
shortwave /darkening of the imagery/ over the Northern Ohio 
valley. This will help force cyclogenesis off the middle Atlantic 
coast that will race northeast well south and east of New England 
through Saturday. A weaker surface low is currently depicted over 
the eastern Great Lakes associated with forcing ahead of the 500 mb 
low over James Bay. As this latter feature dives south and east 
towards New England this weekend...the associated surface low will 
be absorbed into the developing system offshore. Our primary 
weather impacts will be 1- what happens between these systems as 
impressive middle and upper level forcing combines with very 
substantial instability over the relatively warm Gulf of Maine 
waters and 2- the ramifications of arriving Arctic air. Temperatures at 
800 mb this morning were -35c over James Bay with temperatures close 
to this reaching New England on Saturday...presenting wind chill 
concerns as impressive cold advection drives this air into the 
region. 


Tonight: expect a general increase in middle and upper level 
cloudiness per a look at afternoon visible satellite imagery as 
weak warm advection continues ahead of approaching surface low now 
north of Lake Ontario. Forcing for ascent will be on the increase 
with top down saturation likely bringing snow shower activity into 
the mountains overnight. We/ll talk more about the norlun event in 
the short term section below...but experimental hrrr is on board 
with the 12z guidance suite in developing llevel convergence in the 
vicinity of Penobscot Bay by midnight tonight...with snow developing 
in this region and continuing through the morning. With a good 
fluff factor helping accumulations...could see 1-3 inches over 
Knox/Waldo counties by daybreak. 


Temperatures: with southwest flow ongoing and clouds on the 
increase...temperatures will be a good bit warmer than the previous 
night but given the chilly highs of today...will certainly not be 
warm. Expect lows in the single digits in the mountains through the 
lower teens along the coast. 


&& 


Short term /6 am Saturday morning through Saturday night/... 
significant snow along the middle coast becoming increasingly 
likely Saturday... 


Dangerously cold wind chills Saturday night throughout the 
region... 


High impact weather potential: heavy snow totals possible in the 
vicinity of Penobscot Bay Saturday with attention then turning to 
advisory-warning level wind chills Saturday night. 


Saturday: core of 500 mb low aloft sinks from James Bay at daybreak 
south and east into northern New England towards evening with t8s 
nearing -30c over my western zones by 00z/sun. Col region between 
low level reflection of this 500 mb low and the developing system well 
south and east of the benchmark appears to be allowing all the 
ingredients for a Bona-fide norlun event to be present as the 800 mb 
flow GOES slack along with a developing llevel convergence zone. 
There will be ample instability in the llevels with water surface to 
800 mb Delta ts near -15 and Delta ts to 700 mb nearing -30c. This allows 
for a tremendous amount of llevel instability...with ocean-induced 
cape values of 500-1000 j/kg portrayed on the 12z NAM and GFS. 
This could very well promote thunder with any snow band that does 
develop. 


Snow ratios: the dendritic growth zone will be below the primary 
area of lift during the height of the event...but it will still get 
clipped and see no reason why we can/T force 15-20:1 ratios out of 
this setup. 


There is uncanny agreement in the 12z suite /NAM-GFS-ECMWF-Gem/ on 
the placement of the mesoscale band over Penobscot Bay. While this 
would tend to suggest above normal confidence...the fact that this 
is a norlun event begs caution. A look a the 00z ncar ensemble 
shows about 40% of the members directly impacting our area. Would 
really like to see this event come into the near term-high 
resolution guidance window and as such...with the word out right now 
with the watch...will let the evening shift take a final look at 
things before making a final decision on winter storm warnings vs. 
Winter weather advisories. That being said...certainly cannot rule 
out some 1 foot+ snowfall amounts somewhere in the middle coast region 
given the setup above. 


Temperatures: may rise slightly in the early morning...but will 
then reverse course and fall through the afternoon with all 
locations in the single digits above and below zero by evening. Wind 
chills will reach advisory levels in the mountains in the 
afternoon...with the most dangerous values holding off until 
Saturday night. Nonetheless...wind chills will become 
increasingly dangerous by late afternoon/evening. 


Winds: very impressive cold air advection will yield steep llevel 
lapse rates...which should be able to mix anything the atmosphere 
has to offer wind-wise in the lowest 5kft. Highest winds in the 
column are around 30kts /a bit higher offshore/ so will paint gusts 
around 30mph inland /higher on the hilltops/ and 30-40mph along the 
coast. Note: winds will not be this strong in the vicinity of the 
norlun trough and thus significant blowing/drifting will not 
initially be a problem. However...by Saturday evening...there 
will likely be significant blowing/drifting...and will have to 
watch for this if the snow does materialize. 


Saturday night: 500 mb low opens up and shifts east with the core of the 
coldest air aloft overhead under continued strong northwest winds as 
gradient between 1035 mb high over the Great Lakes combines with 
offshore-moving norlun to continue winds of 15g25kts. Concerns will 
turn to dangerously cold wind chills...which should have no problem 
hitting warning criteria in the mountains and foothills...but likely 
remain at advisory levels along the coast. Am honestly a bit 
surprised in the met/mav low temperature spread as we should 
remain well-mixed through the night. Did give some nod to the 
colder met...with lows below zero in all locations...and perhaps 
as low as -20 in the mountains. 


&& 


Long term /Sunday through Friday/... 
high impact weather: dangerously cold wind chills linger into at 
least Sunday morning. A storm could bring snow/freezing rain/rain 
to the region Monday night into Tuesday night. Strong winds are 
possible with this system as well. 


Deep persistent 500 trough over the eastern Continental U.S. On Sunday will shift 
NE and weaken by early next week...and this allows the hemispheric 
wave pattern to become less amplified with a higher wave number. 
The overall +pna pattern weakens early to mid-week...and tries to 
break down by the end of the week. Of note though...is southern stream 
wave that digs over S central Continental U.S. Monday and lifts northward Tuesday and Wednesday 
as northern stream dives into it and this could produce the high impact 
storm over New England around Tuesday. 


Sunday start in the throes of the the very cold air mass in the 
region with strong pressure gradient in place and gusty northwest winds. The 
dangerous wind chills linger through the morning but as temperatures warm 
from lows below zero everywhere...and with pressure gradient 
slackening as surface high builds in should see wind chills rise to 
more bearable levels by afternoon. Still...the tail of the cold air advection will 
hold through most of the day and highs will struggle to reach zero in 
the north...and to reach 10f in the south. As the surface high moves over 
the region look for decoupling in most places and very given good rad 
cooling given cold air in place and a starting point near or below 
zero. Went below superblend for mins in most places...and 
significantly below in the more sheltered spots. This should bringus 
lows 10 below to zero in the coastal plain...with lows dropping 
to -20 or lower in the sheltered mountain valleys. 


On Monday look for warmer air to start working in...and highs 
rebound into the teens to middle 20s...with increasing clouds in the 
afternoon. 


The next system moves in on Monday night and Tuesday. Some differences in 
the model as to have far west the surface low tracks...with the GFS and 
ggem passing it S-north through the middle of ME...and the Euro and gefs 
mean bringing it northward along the New York/Vermont border...which would be the 
warmer solution...and likely lead to snow to freezing rain/pl to rain solution in 
many spots. The more easterly track would see snow last longer 
into the storm away from the coast. P-type will be one of the big 
issues with this system and confidence is low as to how it will 
all unfold. One thing to note is that we are coming out of very 
cold airmass...and despite the best winds above the inversion it 
will be slow to break out of that low level cold air...which will 
probably hold on longer than the models suggest. Another issue 
could be strong winds...although with the inversion may be tough 
for those winds to mix to the surface...at least for any significant 
length of time. 


The whole system will move out late Tuesday night and Wednesday. Could bust 
out into warmer air on Wednesday behind the system with highs climbing 
into the upper 30s to low 40s. Cold front swings through Wednesday night 
with upper level trough on Thursday and temperatures drop back again...below 
normal...but not too far...with highs in the 20s to around 30. 


&& 


Aviation /00z Saturday through Wednesday/... 
short term...VFR under mostly clear conditions at this time. Expect 
deteriorating conditions through the coming taf period with snow 
developing overnight at rkd and likely Aug with IFR/LIFR 
restrictions. For a period Saturday...inch per hour snowfall rates 
are possible...most likely at rkd. Further west...Arctic front 
will bring a round of snow showers...most likely to bring 
restrictions to leb/hie...but brief restrictions are possible 
south and east of this as well. Conditions improve Saturday night 
with VFR conditions returning for Sunday. 


After light winds overnight...strong northwest winds /15g25kts/ 
will develop by late morning Saturday and continue through 
Saturday night. 


Long term...mainly VFR sun through Monday with gusty northwest winds 
diminishing during Sun afternoon. Could see extended period of 
IFR or lower in snow/fzra/ra Monday night into Tuesday night. 


&& 


Marine... 
short term...winds/waves below small craft levels into tomorrow 
morning before intense cold advection behind an Arctic cold front 
brings a period of gales to the outer waters by late Saturday 
afternoon through Sunday morning with winds likely remaining below 
gale force in the bays. In addition...heavy freezing spray 
warnings have been hoisted Saturday evening through Sunday morning 
given the combination of the aforementioned winds and the coldest 
airmass of the season thus far. 


Long term...northwest wind diminish slowly through Sunday...as does 
intensity of freezing spray...but will likely hold to Small Craft Advisory winds 
through sun evening. After a brief break in the winds on Monday and Monday 
night...look for S winds to reach Small Craft Advisory levels early Tuesday and could 
reach gales by Tuesday afternoon and evening...before diminishing Wednesday. 


&& 


Gyx watches/warnings/advisories... 
ME...wind chill warning from midnight Saturday night to 10 am EST 
Sunday for mez012>014-018>022. 
Wind chill warning from 7 PM Saturday to 10 am EST Sunday for 
mez007>009. 
Wind Chill Advisory from midnight Saturday night to 10 am EST 
Sunday for mez023>028. 
Winter Storm Watch from midnight EST tonight through Saturday 
evening for mez022-027-028. 
New Hampshire...wind chill warning from midnight Saturday night to 10 am EST 
Sunday for nhz004>013-015. 
Wind chill warning from 7 PM Saturday to 10 am EST Sunday for 
nhz001>003. 
Wind Chill Advisory from midnight Saturday night to 10 am EST 
Sunday for nhz014. 
Marine...heavy freezing spray warning from 7 PM Saturday to noon EST 
Sunday for anz150>154. 
Small Craft Advisory from noon Saturday to noon EST Sunday for 
anz151-153. 
Gale Warning from 4 PM Saturday to noon EST Sunday for anz150- 
152-154. 


&& 


$$ 


Near term update...ekster 
short term...Arnott 
long term...cempa 
aviation...Arnott/cempa 
marine...Arnott/cempa 






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