Area Forecast Discussion
Issued by NWS Portland, ME-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KGYX 281946
Area Forecast Discussion...CORRECTED
National Weather Service Gray ME
346 PM EDT Tue Mar 28 2017
Low pressure will pass to our south tonight. Behind this system,
a northwesterly flow will introduce cooler and drier air into
the region for the second half of the work week. High pressure
will build into the region for Thursday. Low pressure will
approach the region for late Friday into Saturday with snow and
mixed precipitation likely for the region.
.NEAR TERM /THROUGH TONIGHT/...
A weak shortwave impulse on GOES water vapor imagery was
crossing the mid Atlantic region with a 1009 millibar surface
reflection over the DELMARVA region and a weak surface boundary
extending northward into western New England. Widespread low
clouds remained across the region at moment. NWS Doppler radar
mosaic showed an expanding area of precipitation across the mid
Atlantic to southwestern New England that will cross southern
New Hampshire and adjacent southwest coastal Maine during the
late afternoon and early evening hours. Elsewhere...only
scattered precipitation is likely as a cold front over Quebec
drops southward across the region overnight. The activity should
taper quickly after midnight as the surface low and shortwave
impulse race offshore.
.SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/...
On Wednesday...a freshening northerly breeze in the wake of the
departing coastal low with a few clouds and upslope snow or
rain showers across the higher terrain. Highs will range from
near 40 in the mountains to near 50 over southeast New
Hampshire. Some lingering upslope clouds and snow showers
Wednesday night in the mountains...otherwise mostly clear
elsewhere with a diminishing northerly breeze and the surface
high begins building into eastern New England. Lows will range
from the mid 20s to around 30.
.LONG TERM /THURSDAY THROUGH MONDAY/...
-- Changed Discussion --Confidence is gradually increasing for a fairly significant late
season snow and/or mixed precipitation event starting Friday and
lasting into Saturday. 12z deterministic guidance is in general
agreement today on track of short wave troughs and attendant SFC
low pressure along with subsequent heavy snowfall for at least
the southern half of the CWA. The ECMWF ensemble probabilities
for 6 or more inches of snow have steadily increased over the
last 24 hours, now offering a 50-70 percent chance of 6"+ to a
fairly good chunk of the CWA.
However, with that said, we are still at least 3 days out and
even tight ensemble consensus can still go awry at this time
range. There are also questions about boundary layer
temperatures and perhaps even some warm mid level temps creeping
into southernmost zones. The track of the overall system could
still push further south also. These issues can certainly be the
cause of a lighter snowfall. So being a bit conservative in the
forecast temperature/qpf/snow grids is prudent at this time.
However, we did lower SFC temps Friday afternoon and night as most
raw model guidance slams SFC temps down to 31-33 degrees as
strong UVVs move into the area and allow for cooling via lift,
evaporation, and melting.
At this time I would expect at least interior southern zones to
pick up a plowable snowfall starting Friday afternoon or evening
and ending Saturday. However, there is low confidence at this
time for a lot more over a wide area, although possible. Bears
watch for sure. A heavier snowfall this time of year would
probably cause power outage issues.
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.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
Short Term...IFR to LIFR conds persist into tonight. Look for
improvement to VFR during Wed morning, with NW winds gusting to
btw 20 and 25 kt in the afternoon. Sct MVFR conditions will be
psb in mtn -shra/-shsn.
Long Term...IFR conditions possible in snow and mixed
precipitation starting Friday and lasting into Saturday.
Conditions likely improve Saturday night and Sunday.
Short Term...Winds will remain below small craft through
Wednesday afternoon. We`ll likely see winds and seas reach
Small Craft Advisory threshold by Wednesday evening outside the
bays in strengthening northerly flow.
Long Term...SCA conditions will subside Thursday. They will once
again be possible over the weekend as low pressure passes to the
south of the waters.
We`re entering the period of high astronomical tides. The
Wednesday and thursday night high tides...at 105 AM Thursday and
152 AM Friday respectfully are 11.1 ft MLLW (referenced to
Portland Harbor with a 12.0 ft MLLW flood stage). Fortunately
the flow will be offshore so no problems are anticipated with
these particular tides. However, the Friday night high tide at
243 AM is an 11.0 ft MLLW. With potential for a strengthening
onshore flow prior to this particular high tide cycle...we will
need to monitor this time period for possible coastal flooding
and beach erosion.