Area Forecast Discussion
Issued by NWS Portland, ME-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KGYX 160351
Area Forecast Discussion
National Weather Service Gray ME
1051 PM EST Wed Feb 15 2017
-- Changed Discussion --Low pressure will rapidly develop in the Gulf of Maine tonight
and pulls away Thursday leaving behind upslope snow showers in
the mountains. High pressure will build into the region on
Friday as the storm departs to the maritimes. A few upslope snow
showers will linger in the mountains through Saturday but
elsewhere skies will be mainly sunny. Temperatures will warm
through the weekend reaching the mid 40s by Sunday.
-- End Changed Discussion --
.NEAR TERM /THROUGH THURSDAY/...
-- Changed Discussion --1045 pm...Second band of moderate to heavy snow extends from
from around KLEW southward through the Portland area, and then
offshore of York and Rockingham counties. This band should
shift W through around 06Z or so before dissipating. Rates of an
inch an hour are likely in this band, and could see them as
high as 2" per hours. HRRR has been excellent with these bands
today and tonight. Will hold the WSW for now as we will see some
synoptic snow developing over the ern zones, but may be a
struggle to reach warning criteria here.
8 PM...Intense sfc convergence, along with mid lvl frontogenesis
have combines to produce a persistent band of heavy precip from
around Casco bay NW through Cumberland and southern Oxford
counties. We`ve had reports of 2-3" an hour for a couple hours
in this band. Just got reports in the last hour of a changeover
along the coast and in Portland, which will limit total snow
accums there. Forecasts for this evening lean heavily on meso
models, including HRRR, and meso model ensembles. This rotates
this band of heaviest precip SSE through York county/ including
NH border towns in Carroll county/ and then into Strafford and
Rockingham toward midnight. The band will weaken a bit later
this evening, so amounts to the south will probably not reach
the totals we`ll see in interior SW ME, but should still reach
warning criteria. This will also limit the snow to some degree
over ern zones, and may not see warning criteria here, but will
hold the warning to see how synoptic precip develops this
Previously...A dynamic storm is in store for this evening and
overnight. Temps have pushed into the mid and upper 30s over
parts of Srn NH and coastal Wrn ME. This has allowed precip to
start as rain. Farther inland snow has continued in the higher
terrain much of the day...with accumulations already around 6
Now things really start to get interesting. As mid level low
centers rapidly develop this evening...colder air will be
dragged back S thru the forecast area. This will turn any rain
back to snow. KGYX 88D dual-pol data is already showing low ZDR
and high CC values collapsing back towards the coast as heavier
areas of lift and precip move thru. At GYX we flipped from light
rain to heavy snow in a matter of minutes as stronger lift moved
overhead. I expect this to be the trend thru the evening...with
mixed precip transition quickly to heavy snow with rapid
accumulations. The coast will be the last place to flip back to
snow...but when it does it will be a significant hazard for
those on the road. Roads will become slippery in a hurry.
The surface trof remains wedged at the NH/ME border back towards
the White Mtns. I expect it to hold more or less stationary thru
the early evening. For that reason I have focused the higher QPF
across extreme SWrn ME into the White Mtns. Later this evening
strong low pressure developing in the Gulf of ME will drag
this trof Swd. This should be when the heaviest snow occurs for
Srn NH. It may not last more than an hour or two...but snow
could be very heavy for that short duration. For the rest of the
night intensity of snow will taper off but continue into
Headlines remain as they were earlier today. Highest snowfall
amounts should be near the NH/ME border...especially where SE
facing upslope assisted in lift. The lowest confidence in
snowfall amounts are just W of the current trof axis...where
shorter duration of snowfall may limit totals some. Also to the
E over central ME...lower snowfall totals are possible due to
mixing and lack of precip. Their best snowfall may come later
tonight when low pressure begins to throw moisture back NWrd.
The very mesoscale nature of this event will lead to some wildly
varying snowfall amounts over short distances.
-- End Changed Discussion --
.SHORT TERM /THURSDAY NIGHT/...
Low pressure will gradually pull away from the area Thu.
Lingering low level moisture and NW flow will lead to plenty of
upslope snow showers in the mtns thru the day. An additional
several inches of accumulation is possible. We stay in cyclonic
flow Thu night...and that should keep the boundary layer fairly
mixed. I stayed close to 2 m temp guidance for lows.
.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
High impact weather potential: None
A rather quiet period of weather as we move into the end of the
week and the weekend. The forecast begins with a relatively
progressive high amplitude pattern over North American. As of
Wednesday morning a large ridge was build up through western
North American with above freezing surface temperatures all the
way to the Northwest Territories in in Western Canada, and a
trough moving through New England and southern Quebec. This
ridge will move east over the weekend keeping high pressure in
control through the start of next week.
Friday the departing low will bring upslope snow showers to the
mountains of northern New Hampshire. Have increased QPF and snow
amounts slightly compared to guidance as those areas are often
able to squeeze quite a bit of snow out of this pattern.
Saturday a high builds into the region and temperatures will
warm above freezing across most of the area.
A weak system passing to the north on Sunday may bring a few
scattered flurries to the mountains and increasing clouds
however temperatures will again remain warm reaching the mid 40s
south to upper 30s north. Those flurries and clouds will stick
around into Monday.
By Tuesday there is the potential for another storm to bring
more widespread precipitation. Confidence is very low at this
time and have gone with a consensus blend of guidance.
.AVIATION /04Z THURSDAY THROUGH MONDAY/...
Short Term...Widespread IFR or lower is expected tonight in deep
onshore flow. -RA along the coast will change to SN...heavy at
times. Eventually this may even clip CON and MHT...as snowfall
drops Swd tonight. Conditions improve to MVFR and VFR early
Thu...except in the mtns where SHSN will keep occasional IFR.
Surface gusts around 20 to 25 kts possible at all terminals Thu.
Long Term... VFR will prevail from Friday right through the
weekend except in the mountains where HIE will see periods of
MVFR in SHSN.
Short Term...Winds and seas will build especially behind rapid
strengthening low pressure in the Gulf of ME. Gale warnings for
the outer waters and SCAs for the bays remain in effect into
Thu. Winds and seas will gradually diminish as low pressure
Long Term... Very quiet period on the waters with high pressure
built overhead. Expect conditions to remain below SCA right
through the start of next week.
ME...Winter Storm Warning until 10 AM EST Thursday for MEZ012>014-
Winter Storm Warning until 7 PM EST Thursday for MEZ007>009.
NH...Winter Storm Warning until 10 AM EST Thursday for NHZ004>006-
Winter Storm Warning until 7 PM EST Thursday for NHZ001>003.
Winter Weather Advisory until 7 AM EST Thursday for NHZ007-011-
MARINE...Small Craft Advisory until 10 AM EST Thursday for ANZ151-153.
Gale Warning until 6 PM EST Thursday for ANZ150-152-154.