NWS Forecast Discussion

For Fremont, NH

FXUS61 KGYX 201941

Area Forecast Discussion
National Weather Service Gray ME
341 PM EDT Sat Oct 20 2018

A trough of low pressure will linger over the region tonight. A
strong northwesterly flow will set up over the region on Sunday
as high pressure builds in from the west. High pressure will
crest over the region early Monday before shifting offshore.
Low pressure will approach from the west Monday night and will
cross the region Tuesday and possibly redevelop along coastal
areas Tue night. Low pressure will shift into the maritimes
Wednesday. High pressure will gradually build in from the west
Thursday through Friday.


The cold air arrives on two boundaries that move through, the
first of which passes thru the CWA this afternoon, and shifted
winds more westerly, and have lowered Tds a bit. A second surge
of cooler air will move through coincident with the 500 MB
trough axis which moves through Sunday morning. A wave will move
along the sfc front to our south and will push some clouds back
to the N toward daybreak and into early Sunday morning. A few
light SHRA or spkls may be possible across the srn tier of NH
zones, with best timing for this 08-12Z. There`s some cold air
advection, but sfc flow weakens ahead of the next wave this
evening, so winds diminish tonight. Lows will fall into the low
30s N to around 40 in the south.


By mid morning Sunday, should see skies start to clear and winds
begin to pick up in the NW downslope winds outside of the mtns.
Winds will likely gusts to 25-30 mph at times on Sunday,
especially in the afternoon. CAA will battle with the downslope
on the coastal plain and highs there will be in the mid to
upper 40s, while the mtns, with more clouds, will see highs in
the lower 40s.

Winds diminish somewhat around sunset, and skies clear out
everywhere. But, NW flow will persist enough to prevent much rad
cooling. Still, cold enough aloft, to push lows into the 20s in
most spots.


Keeping a very close eye on the high amplitude progressive
upper ridge that becomes progressive to 110W with rapidly rising
heights. This will be the key in driving southeastward several
powerful s/waves that will move thru Saskatchewan and Manitoba
early in the week and then thru the Great Lakes by Tue. U.S.
models have always had a history of poor performance with these
short waves moving thru those data sparse areas of Canada where
EURO has performed well. Ole rule of thumb also dictates
potential significant downstream closed upper low development along
northeast corridor 72-96 hrs after movement into the 110W area
with rapid height rises. With that said, EURO preferred model
and shows an outcome scenario that one would expect as it
continues to hint at the scenario of coastal development late
Tue into Wed. It would be a fools errand to try and predict
outcome at this point, but will begin nudging and hedging
forecast to EURO solution by increasing POPs and avoid flip
flopping of forecast for Tue into Wed time frame. Will lower
guidance temps during the event as decent UVV and dynamic
cooling would cause decent dynamic cooling and overcome warmer
boundary layer temps.

Will increase POPs for Tue for initial light overrunning mixed
ptype as a baroclinic zone begins to set up to our south. The
pcpn may increase and turn to snow over much of the area Tue
night depending on strength of digging s/wv and redevelopment
along or just off the ME/NH coast. Confidence not high yet for
anything more than a broadbrush approach Tue night into Wed.

Behind the system, mid to late in the week models agree on
large upper low that gets carved out into the maritimes allowing
a strong and very cold northwest flow to develop. Expect
orographic snow showers in the mountains with some light
accumulations. Downsloping areas should remain dry. Expect temps
to be too high for late in the week due to the climo weighting
function (time of Year) vs the very cold h85 temps due to upper
closed cyclonic flow over the northeast, for now just tweaked
them to stay within collaboration ranges.


Short Term...Mainly VFR though Sunday night. Will see gusty NW
winds during the day Sunday reaching to 25 kts or so, but
diminishing around sunset.

Long Term...VFR Mon, but deteriorating conditions to MVFR/IFR
Tue and possibly into Wed depending on potential development and
track of coastal low. Cyclonic flow aloft will keep MVFR
conditions in snow showers in the mtns but downsloping areas on
the northwest flow will keep those areas VFR.


Short Term...SCA will hold for now as we still see some
borderline wind gusts and seas are still 4-7 feet. Will see a
break overnight, but winds pick up again Sunday morning and a
period of gales are expected in the open waters Sunday afternoon
and evening.

Long Term...Timing and location of development of potential
coastal low in the Gulf of Maine late Tuesday into Wed will
determine strength and timing of backing northwest winds in its
wake. A lot of uncertainty remains for Tue night into Wed but
Gales may be needed by Wed.


MARINE...Small Craft Advisory until 7 PM EDT this evening for


LONG TERM...Marine

NWS GYX Office Area Forecast Discussion