Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service Caribou ME
1009 am EDT Thursday Apr 24 2014

Synopsis...
low pressure south of Nova Scotia will drift slowly east away
from the region today. High pressure will build east later
tonight into Friday night...then move east on Saturday. Another
low from the Great Lakes will approach Saturday night.
&&

Near term /through tonight/...
10am update:
accumulating snow has mostly ended with daytime heating and lower
intensity snow. The exception is elevations over 1000 feet in
northeastern portions of the forecast area where temperatures
remain at or below freezing. Did lower temperatures through the
day and extended the duration of snow in northern zones into this
afternoon. The upper low is pulling away and the bulk of the
precipitation is over...but rain and snow will persist most of the day
with another few tenths of an inch of precipitation expected.

Previous discussion...
strongly negative-tilted upper trough west/ a closed upper low just southeast of
the area continues to support deep surface low pressure just S of Nova Scotia at this time. As
this system has been captured by the upper level low...it will
continue to be slow to pull ewrd away from the area today west/ moisture
continuing to be pulled nwwrd up into especially our eastern areas along an
inverted surface trough which extends nwwrd from the surface low across eastern
Maine/western New Brunswick at this time. Airmass is cold enough along the northern and northwestern
portions of the precipitation shield (nrn/northestern fa) that wet snow is
occurring and could see a few inches of wet snow across the northern
third of the forecast area into the Erly am hours. Overall...made no major
changes to the existing grids west/ hyst probability of precipitation/quantitative precipitation forecast expected across
eastern/northestern areas today west/ 1-3 inches of wet snow across northern and northwestern
areas. Precipitation will gradually wind down later today and pull mostly
out of the area this evening as drier air associated west/ a surface ridge
begins to spread into the area. Low-level moisture will be slow to
leave however so expect clouds to hang around through much of tonight all
but southern/southwestern areas of our forecast area where downsloping nwrly winds should
help to dry things out a bit quicker. Northwest winds will be quite brisk
especially southern/southwestern areas where a few gusts to near 40 miles per hour are possible.
Temperatures will remain below seasonal norms today and tonight... &&

Short term /Friday through Saturday/...
weak ridging will build across the region on Friday, so expect a
dry day. Although the day will start out partly to mostly cloudy,
especially across the north, there should be some improvement by
late in the day. Temperatures will be near seasonal normal for
highs, ranging from around 50 in the north to the middle 50s south.

Precipitation begins to approach from the west Friday night as
low pressure moves across the Great Lakes. Overnight lows are a
bit tricky as they will depend on how quickly the cloud cover
moves east. Model relative humidity indicates that far northern and eastern
Maine will see a brief period of clearing during the middle to late
evening. This should allow temperatures to drop off more quickly
in these areas than further south where cloud cover will be
thicker. Much of the guidance is also indicating that dewpoints
will be in the 20s, so some cooling is possible at the onset of
precipitation. As such, current thinking is that northern areas
could see some wet snow mix in with the rain at the start,
especially in the higher terrain. However, the bulk of the
precipitation will fall during the day Saturday, so expect little
to no snow accumulation.

For Saturday...the aforementioned low will slowly push east along
the Saint Lawrence. Meanwhile, a secondary low will develop off
of Long Island and move eastward to the south of Nova Scotia.
Rain showers will spread from west to east through the morning
hours, covering the entire forecast area by afternoon. Rainfall
amounts through Saturday will generally be a quarter inch or
less. Temperatures will maximum out in the middle 40s to lower 50s
area wide.
&&

Long term /Saturday night through Wednesday/...
expect much of the long term to be cool and damp as the region
remains under the influence of a couple of slow-moving upper
lows. Showery weather will continue Saturday night right into
Monday. A ridge of high pressure will build across New England
Tuesday and Wednesday, but models indicate that a cut-off low is
going to develop across the Central Plains as we head into the
latter half of next week. While the details are still uncertain
with this system, there will be at least the chances for rain
later Wednesday into Wednesday night. Temperatures will be at or
below normal through the period.
&&

Aviation /14z Thursday through Monday/...
near term: low MVFR to IFR conds across the northern taf sites current
into tonight west/ MVFR conds possibly improving to VFR late. Expect VFR
to high MVFR across the southern taf sites improving to VFR later this
am.

Short to long term: expect MVFR conditions to start at the
northern terminals Friday morning, while the southern sites will
be VFR. However, improving ceilings means the northern sites will
reach VFR by 18z Friday and remain so through Saturday morning.
Rain showers will begin to move into the region early Saturday
morning and continue into early next week, but best chances for
MVFR or even IFR conditions will be Saturday night through
Monday. Snow may briefly mix in with the rain at the northern
sites Friday, Saturday, and Sunday nights, but no accumulation is
expected.
&&

Marine...
near term: strong Small Craft Advisory conds expected west/ occasional marginal glws possible
at times...

Short term: the current Small Craft Advisory may need to be
extended a few hours into Friday morning as winds will be slow to
subside. However, there is still plenty of time for subsequent
shifts to get a better handle on this and make changes
accordingly. Otherwise, conditions will remain below small craft
levels through the weekend. The main concern will be restricted
visibility in rain showers Saturday through Sunday.
&&

Car watches/warnings/advisories...
ME...none.
Marine...Small Craft Advisory until 5 am EDT Friday for anz050>052.
&&

$$
Near term...khw/mcw
short term...Hastings
long term...Hastings
aviation...khw/mcw/Hastings
marine...khw/mcw/Hastings