Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Gray ME
346 PM EDT sun Apr 19 2015
high pressure will move offshore tonight. An increasing easterly
onshore flow will provide cool and damp weather Monday with rain
chances increasing ahead of an approaching low pressure system.
Significant rainfall and flooding... along with coastal flooding
from astronomical high tides... are possible with this system
Monday night and Tuesday. Unsettled weather then looks to dominate
middle to late week.
Near term /until 6 am Monday morning/...
it has been a beautiful day across the region as high pressure
moved over head. A few high cirrus clouds are beginning to move
into southwest New Hampshire... heralding the approach of a storm
system for Monday into Tuesday. Overnight look for high clouds to
begin moving in. Temperatures will fall to just below freezing in
the north as the cirrus wont' limit radiational cooling very much.
Short term /6 am Monday morning through Tuesday/...
low pressure currently in southern Illinois will track north
northeast into the Great Lakes sending a large slug of moisture
ahead of in and into northern New England. Precipitation will move
into our western regions by noon and cover the entire area by
around 5pm. Most models are in good agreement on the timing of
this system this close to onset and have gone with a blend. While
rain will continue from Monday afternoon through Tuesday
afternoon, the heaviest rain will be in the overnight period when
a low level jet of around 50kts helps to transport the moisture
into the region. Expect two precipitation maxima. One due to
orography in the Maine and New Hampshire foothills where upslope
flow will result in as much as 2.5" of total water. A secondary
maxima will be along the coast. As the high recedes towards New
Brunswick tonight a coastal front may set up. This would create a
secondary precipitation maxima along the coast from about York
County through to Penobscot Bay. Have tried to reflect both of
these maxima in the precipitation forecasts. In addition to the
heavy rain... elevations above 1500 to 2000 feet will see a period
of wet snow overnight Monday into Tuesday.
Long term /Tuesday night through Sunday/...
persistent upper level low pressure spins over southern Canada
and eventually drifts closer to be centered near the Saint Lawrence
River valley towards the end of the week. This keeps regular
waves of short wave energy moving our way out of central Canada
and the Great Lakes region.
We will have only a short break after the heavy rain event Monday/
Tuesday before the next precipitation event barrels our way.
Tuesday late evening into Wednesday morning there will only be
isolated showers. Wednesday will be relatively warm with
substantial cloud cover as southerly winds return again and
precipitable water increases to near an 1" for the second time
this week. This will not be a huge achievement as we will not have
had northwest winds to scour any remaining moisture out from the early
Steadier rain spreads from west to east Wednesday afternoon and
ends Thursday morning. Rain moves out quickly Thursday morning
after a mesolow forms and sweeps NE. Some instability is noted
Wednesday so have included isolated thunderstorms in the afternoon.
Quantitative precipitation forecast will be lighter with this event... on the order of a third to
a half inch... but it may exacerbate any ongoing flooding issues.
As colder air arrives... snow showers will be possible early
Thursday morning in the higher peaks.
Daily shower activity is likely through the weekend as ample low
level moisture and instability provided by the upper level low
Aviation /20z Sunday through Friday/...
short term...VFR conditions will prevail until the early morning
hours. Will see a MVFR ceiling move in from west to east after
10z with precipitation following soon afterwards. Expect IFR in
rain for all sites except hie through Tuesday. Hie will see a rain
shadow and stay MVFR. Along the coast wind gusts to 30kts are
possible through Monday afternoon.
Long term...IFR to MVFR conditions may continue for khie and kleb
into Wednesday morning in light -shsn.
MVFR conditions return areawide for Wednesday afternoon through
Thursday morning in -ra. Additional lighter showers are likely in
the higher terrain through Thursday and into Friday.
short term...easterly winds and seas will build Monday ahead of
the approaching system. A Gale Warning has been issued for the
outer waters where wind gusts will exceed 35kts and seas as high
as 15ft. The winds and waves will diminish on Tuesday.
Long term...wind gusts will drop to Small Craft Advisory or lower Tuesday night but
seas will take longer to subside...possibly until Thursday night.
onshore flow on Monday brings more moisture and eventually rain
to the area. A soaking rain is expected late Monday and Tuesday.
a widespread 1 to 2 inches of rain is expected from Monday
afternoon through Tuesday. However...given strong moisture
inflow...localized amounts of up to 3 inches could occur. This
would lead to flooding problems...especially in areas where snow
melt is still occurring. A Flood Watch remains in effect.
tonight's 12:32am high tide of 11.6ft MLLW in Portland should
pass without incident as almost no wind and waves will keep water
levels slightly below flood. As easterly winds pick up during the
day on Monday seas will build to 10 to 15 feet. High tide on April
21 is at 1:21am with a predicted height of 11.4ft MLLW. Onshore
winds are expected to result in a 1-2ft storm surge. The
combination of wind, waves and high tide will result in overwash
and possible inundation for the beaches of the South Coast of
Maine and New Hampshire. Further north the easterly wind direction
is less favorable to onshore inundation. Even so the significant
waves may result in some coastal flooding. Due to the uncertainty
the Flood Watch remains in effect for the midcoast.
ME...Flood Watch from Monday evening through Wednesday morning for
Coastal Flood Watch from Monday evening through late Monday
night for mez025>028.
Coastal Flood Warning from 11 PM Monday to 3 am EDT Tuesday
New Hampshire...Flood Watch from Monday evening through Wednesday morning for
Coastal Flood Warning from 11 PM Monday to 3 am EDT Tuesday
Marine...Small Craft Advisory from 5 PM Monday to 2 PM EDT Tuesday for
Gale Warning from 5 PM Monday to 2 PM EDT Tuesday for anz150-