Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Gray ME
539 am EST Tuesday Jan 27 2015
strong low pressure will move northeastward to just south of
Nantucket Massachusetts today. The low will linger around through
Wednesday bringing a significant snowfall to our region. Another
storm system will likely bring a general snowfall to the area on
Near term /today/...
update...intense mesoscale deformation band has rotated fully
onshore now. Snowfall rates of 2 to 4 inches per hour are occurring
beneath this band. Have updated snowfall amounts in the previous and
next 6 hour periods to get a more accurate up to date total
accumulation grid to this hour. Again more focus is on the coast
and immediate interior for higher snowfall amounts...while trimming
the northern edge back. Snow is only now beginning to fall in the
mountains...so at best could only have an inch or two accumulation through
12z for these areas.
Previous discussion...as mentioned in the previous update...00z
model guidance has latched onto the idea of slightly weaker shortwave
feature phasing with the initial storm system that exited the East
Coast yesterday. This has allowed the system to slip further
east...rather than a stronger capture and tug back to the west.
GFS...CMC- regional...ECMWF...and NAM all have similar ideas
regarding evolution for the rest of today.
At this hour a very intense band of snowfall is more or less
paralleling the coast...and slowly inching nwwd. Modeled quantitative precipitation forecast has
been keying on the coast or just inland for several runs now.
Tossing quantitative precipitation forecast aside and looking aloft...NAM...GFS...and European model (ecmwf)
feature strong frontogenesis at 700 mb. Within this band of
frontogenesis there is also a deformation maximum. The strongest
bands of snowfall are favored just on the cool side of the
deformation maximum...within the strongest frontogenesis. As of
the 06-09z period this is verifying nicely. By 12z models suggest
this signal pivots inland more...and becomes nearly stationary
through 18z. During this time BUFKIT soundings for coastal locations
briefly attempt to near moist absolutely unstable above 700 mb. Would
not be surprised to see reports of thunder snow...but at the very
least convective elements will help to increase snowfall rates to 2-4
inches per hour at times. Have adjusted the highest snowfall amounts
towards the coast some. The other factor to consider with snowfall
amounts is very dry air in place and just north of the forecast area.
Northerly winds will advect this air southward...eroding the northern edge of snowfall
as we/ve seen for much of the night. That in combination with the
eastward model shift will yield a much sharper snowfall gradient than
originally forecast. For now only sightly lowered amounts in the
north...but subsequent updates may Need More aggressive lowering of
27.00z ecwmf continued with the idea of rotating a potent low
level jet northward across the forecast area today. At 900 mb it
increased from its previous forecast to 80 kts. Given the deep
cold air in place...mixing heights are quite high for a noreaster
even with a large inversion in place. Even a fraction of this low
level jet mixing down...especially during the heaviest
snowfall...yields the potential for gusts above 50 kts near the
coast. Given that winds are already gusting above 30 kts...this
seems entirely reasonable. Increased wind forecast slightly from
previous package. Wind potential decreases fairly quickly the
further inland one GOES...but gusts around 25 to 30 kts will be
possible. Based on BUFKIT soundings...best wind potential will
occur from this morning through early afternoon.
Cold high pressure to the north and northerly winds will ensure that temperatures
remain fairly static through the day. Expect that much of the event
will see snowfall in the teens and single digits. Strong system to
our S and those northerly winds will also keep coastal front
off shore...and any additional quantitative precipitation forecast enhancement off shore too. Cold
temperatures and strong winds will also combine to produce bitterly cold
wind chills. If stranded out in the storm...these conditions could
produce a potentially life threatening situation.
Short term /6 am this morning through 6 PM Wednesday/...
low pressure occludes and upper low drifts across the area through Wednesday.
This will continue -sn for much of the period...though intensity
will be far less than that experienced today. An additional couple
of inches of accumulations is possible. Temperatures will be on the cool
side with gusty westerly winds.
Long term /Wednesday night through Monday/...
the models are in general agreement on the long wave pattern
through early next week. However...significant differences exist
with timing and strength of individual shortwaves leading to
decreased confidence in sensible weather. The overall theme is
western ridge and eastern trough for the Continental U.S....with an extended
period of below normal temperatures and a chance for synoptic
snows roughly every two days...with Friday - Friday night...Sunday
night-Monday...the most likely time frames for our forecast area
at moment. We begin the period on a quiet note under ridging
surface and aloft Thursday. The next system arrives by Friday
morning with a general snowfall ending Friday night. Behind this
system...weak ridging follows for Saturday into Sunday. More
uncertainty with the next system for Sunday night - Monday as the
bulk of the precipitation shield may remain offshore.
Aviation /12z Tuesday through Saturday/...
short term...widespread IFR and LIFR is developing from southern New Hampshire to
coastal ME at this hour. This trend will continue as heavy snowfall
band slowly rotates northeastward. This will continue through early afternoon.
Kleb and khie will be slower to see IFR conditions...possibly
holding off until middle morning or later. Coastal terminals will
see north-northeasterly wind gusts near 45 kts at times. Snowfall winds down by Tuesday
evening...though precipitation lingers into Wednesday. Could see scattered IFR
conditions will lingering shsn.
Friday...MVFR in snow with local IFR conds pssbl.
Northwest surface wind gusting to 25 knots.
short term...storm warnings remain in effect for all
waters...except for outer waters S of Cape Elizabeth. Here a
period of 65 knots gusts appears likely...so have issued a hurricane
force wind warning. Also moderate freezing spray is already
occurring on the water based on buoy observations. Have issued a
freezing spray advisory through Wednesday morning as a result.
Thursday night - Sat...gale force winds are possible.
large...battering waves are building this morning right around
high tide. This in combination with a two foot storm surge will
allow Portland and Hampton to reach their flood stage. Winds will
switch to the north this afternoon just prior to high
tide...which may reduce the storm surge.
Used the North Atlantic regional team wave runup matrices to
forecast and warn for the two high tides today. The output shows
wave action will allow for locally significant erosion as well as
overwash at Fortunes Rocks...jennis...Camp Ellis and Ferry beaches
in Maine and New Hampshire.
Neracoos splash-over nomograms also showing significant issues at
the time of high tide for the beaches south of Portland.
ME...Winter Storm Warning until 4 am EST Wednesday for mez007>009-
Blizzard Warning until 4 am EST Wednesday for mez018>028.
Coastal Flood Advisory until 6 PM EST this evening for
Coastal Flood Warning until 6 PM EST this evening for mez023-
New Hampshire...Winter Storm Warning until 4 am EST Wednesday for nhz002>009-
Blizzard Warning until 4 am EST Wednesday for nhz010-012>014.
Winter Weather Advisory until 4 am EST Wednesday for nhz001.
Coastal Flood Warning until 6 PM EST this evening for nhz014.
Marine...Storm Warning until 7 am EST Wednesday for anz150>153.
Freezing spray advisory until 7 am EST Wednesday for
Hurricane force wind warning until 3 PM EST this afternoon for