Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Gray ME
609 PM EST Sat Jan 31 2015

Synopsis...
cold high pressure moves in through Sunday. Another low will
track south of New England on Monday...potentially bringing
significant snow to the region. High pressure will follow midweek.
Low pressure will pass by to our south on Thursday.

&&

Near term /until 6 am Sunday morning/...
6pm update... winds are beginning to decouple in isolated valleys
and have adjusted winds slightly downward overnight. Clear skies
will still result in very cold temperatures which will keep wind
chills low despite lower wind speeds.

The last radar echoes of this system are fading over Penobscot Bay
this afternoon. And skies have cleared across most of the rest of
the County Warning Area. The gusty northwest winds will start to diminish around
sunset...as will the blowing snow. Will see some gusty winds into
the evening...but should become light across the area by midnight.
A very weak wave tracks southeast through the area after midnight and
spreads some clouds and maybe a few flurries in the mountains of New Hampshire.
Otherwise cold air advection should bring mins well down into the single digits
on the coast...and single digits below zero in the mountains...this
combined with winds up to 10 miles per hour will produce windchills below zero
near near the coast...-10 to -20 in northern New Hampshire...and -20 to -30 in
the western ME mountains therefore./..have dropped the wind chill advection in
northern New Hampshire...but kept it going in the ME mountains...where it will be a
little colder...and winds will be a little stronger.

&&

Short term /6 am Sunday morning through Sunday night/...
surface high noses in from the west on Sunday...and it should be
generally sunny with highs mostly in the teens...maybe reaching 20
on the coast and southern New Hampshire...and probability stuck in the single digits in
the mountains cirrus should begin to thicken in southern and western zones
late in the day.

Sunday night will start off clear in the NE as clouds overspread
the County Warning Area from the SW in advance of the next system. Some rad
cooling early in the north will allow temperatures to sro[ here...and then NE
flow picks up up late which will advect colder air in as well.
Lows again will generally be below zero across the entire
County Warning Area...although maybe low single digits near the coast. Light snow
will move in after midnight into southern and western New Hampshire...reaching western ME
around daybreak. Not much in the way of accumulation in this
period...most of that will hold off until Monday.

&&

Long term /Monday through Saturday/...
focus in the extended was mainly on the beginning of the
period...and shortwave trough lifting out of the middle MS valley. Middle level
low centers initially fill on approach to the East Coast...but
begin to deepen once over the tight baroclinic zone just offshore.
700 mb closes off again in the Gulf of ME...which would be a favorable
location for enhanced forcing for ascent across most of the
forecast area.

Confluent flow at 500 mb across southern Quebec will help to reinforce surface
high pressure north of the region into Monday. This leads ME to believe this
storm has more risk of ticking S than much more north at this
time...and also that the northern edge of the quantitative precipitation forecast will feature a sharp
gradient. Model spread is pretty low at this range...with
NAM...GFS...and CMC all near 1 inch quantitative precipitation forecast for coastal ME and southern New Hampshire.
The European model (ecmwf) is the /minor/ outlier with quantitative precipitation forecast closer to 0.60 inches.
Opted to blend evenly between available guidance...including
wpc...with a 2 times weighting of the European model (ecmwf). Resultant quantitative precipitation forecast has
about 0.75 inches quantitative precipitation forecast from kcon through kpwm to krkd. This tapers to
only 0.10 to 0.25 inches across the international border.
However...I will admit that this quantitative precipitation forecast forecast may even be on the
light side...especially if 00z model suite continues trending
towards a little more robust amplification in the Gulf of ME.

Similar to the last Tuesday blizzard the cold air is quite deep in the
low levels. Column should be well mixed through 950 mb. However
unlike Tuesday the core of the low level jet is much weaker and
further S. Could see the potential for 3o to 35 knots gusts...but
mainly confined to the immediate coast.

The snowfall forecast was a little tricky...as the northern edge of the 6
inch contour will reside in the forecast area
somewhere...impacting headline decisions. Taking a look at the
cips analog guidance...the mean coop snowfall guidance favors a swath
of significant snow near the New Hampshire/Massachusetts border. The 25th percentile coop
guidance ranged from 2 to 4 inches across southern New Hampshire...with 75th
percentile guidance 12+. This highlights some of the uncertainty
regarding subtle changes in storm track...but trends suggest 25th
percentile snowfall based on cips analogs are less likely. Wpc winter
weather desk percentile graphics seem more in line with our
thinking...putting lower and upper bounds for the southern forecast
area between 6 and 15 inches. The issues arise for northern
zones...where totals could range from nothing to as much as 4 to
6 inches...all from minor shifts in track. One mitigating factor
for lower quantitative precipitation forecast amounts on the northern edge of the forecast are snow
ratios. Model forecast soundings indicate a deep dendritic growth
zone /dgz/ across the entire forecast area. In some cases during
peak saturation the dgz is as deep as 300 or 400 mb. Cases such as
this often exhibit extremely high snow ratios...greater than 20:1 at
times. As long as this layer remains saturated snowfall ratios will
more than make up for meager quantitative precipitation forecast. Locations closer to the low pressure
without quantitative precipitation forecast worries may see double digit snowfall from quantitative precipitation forecast 0.75
inches or less. In addition...strong isentropic lift is forecast
to occur during the day Monday. 40 to 45 kts of lift is likely to
occur...lifting parcels from 950 mb through 800 mb over a short
distance. Seeing this kind of signal suggests that snowfall comes in
quickly...and will likely be heavy for a time during the day. It
is difficult to pin down at this range...but rates on the order of
1 inch or more an hour are possible. Winter storm watches have
been issued for all zones S of the mountains...with areas along
the ME coast and southern New Hampshire most likely to see 6 or more inches of
snowfall.

Beyond Monday and Monday night used a multi-model consensus for the
forecast. There is another chance of snow midweek...as a fast moving
clipper system redevelops in the Gulf of ME. Cold high pressure
replaces that departing storm...with another possible coastal
storm late week along the Arctic front.

&&

Aviation /23z Saturday through Thursday/...
short term...
gusty northwest winds diminish around and after sunset with VFR holding
into Sunday evening. Kleb/kmht/kcon could see MVFR to IFR conds
late Sun night in snow.

Long term...high confidence in a period of IFR or lower conditions
for southern New Hampshire and coastal terminals Monday in snowfall. Some uncertainty
remains for kleb and khie for just how far north heavier snowfall makes
it. Coastal terminals will also see gusty NE winds around 25 kts
Monday and Monday night. Another possible snow event may impact the area
midweek...but confidence is low at this time.

&&

Marine...
short term...gales will continue through tonight. Should see winds
begin to diminish around and after midnight. Cold air continues
to move over the waters and the fz spray advection will also hold over
night...but will see a little bit of break sun into sun
evening...before winds start to pick up again Sun night.



Long term...low pressure passing near the Gulf of ME will bring a
period of gales to the waters Monday into Tuesday. With gales currently
in effect opted not to put a watch up to avoid confusion.
However...a watch/warning will likely be needed in future forecast
updates. In addition...bitterly cold temperatures...winds...and seas will
combine to produce a period of moderate freezing spray.

&&

Equipment...
krkd has a bad wind sensor.

&&

Gyx watches/warnings/advisories...
ME...Winter Storm Watch from late Sunday night through Monday
evening for mez012>014-018>028.
Wind Chill Advisory until 5 PM EST Sunday for mez007>009.
New Hampshire...Winter Storm Watch from late Sunday night through Monday
evening for nhz003>015.
Marine...freezing spray advisory until 5 PM EST Sunday for anz150>154.
Gale Warning until 5 am EST Sunday for anz150>154.

&&

$$
Synopsis...
near term...Curtis
short term...cempa
long term...legro
aviation...
marine...
equipment...

National Weather Service Glossary of Abbreviations