Scientific Forecaster Discussion
fxus61 kgyx 200752
Area forecast discussion
National Weather Service Gray ME
352 am EDT Thu Jun 20 2019
low pressure tracks east toward the area today with rain
developing. It will be cool with clouds and an onshore wind
keeping the temperature down especially along the coast. Low
pressure moves through the region tonight into Friday morning
with rain coming to an end through the day on Friday. A cool,
dry northwest wind brings nicer conditions for the weekend with
plenty of sunshine and temperatures gradually warming.
Near term /today/...
there are a couple of different ways to describe the forecast.
The simplest is to say it's going to be cool and rainy. The more
complicated version involves no less than two frontal boundaries
and three waves tracking through the region today and tonight,
each delivering another dose of rain with the focus perhaps on a
slightly different part of the area.
The first frontal boundary exists across the Saint Lawrence
valley and into northern Maine this morning. Some isolated
showers with a lightning strike or two continue to be observed
in the far northern part of the forecast area this morning
associated with energy moving eastward along this front. Another
more potent wave will move east out of the Great Lakes today and
will bring a more widespread area of showers and isolated
thunderstorms again today as this front sinks slowly southward.
Another front is developing along the southern New England
coastline and will lift northward this morning into New
Hampshire and Maine. Some models generate a fair amount of
rainfall along the coast as this front lifts north today.
However, this may be a bit overdone as current radar imagery in
southern New England shows more of a widely scattered showers
The northward moving southern front and southward moving northern
front will converge over our area today just as the first wave
of low pressure moves east through the area this afternoon and
evening. By evening expect just about everyone to be getting
wet. Some thunderstorms are possible as well as the abundant low
level moisture combines with the advancing upper trough to
generate some instability mainly along and south of the front.
Abundant cloud cover and an onshore southeast wind will keep
temperatures cool today. Many models indicate coastal areas of
western Maine may struggle to even reach 60 degrees, however
dewpoints in the area area already near 60 so expect a few
degrees above 60 to be the high for most of western Maine.
Further to the south and west the maritime influence will not be
as strong and temperatures could approach 70 degrees with plenty
of cloud cover.
Short term /tonight and Friday/...
while the first wave of low pressure moves east tonight, the
second will be tracking eastward across southern New York and
New England. So while we may see rain come to an end with the
first wave's departure, it will likely start up again by morning
as the second low moves by. The front will have been driven
southward behind the first low to a position across southern New
England and the Gulf of Maine, with the next low pressure
tracking east along it. Thus we will be entirely in the cool
sector of this cyclone with rain being most likely across
southern areas through Friday morning. Rain ends from west to
east as the day GOES on and the low moves out to sea. Behind it
a north to northwest flow develops with clouds breaking up and
departing. By afternoon the temperature will likely top 70
degrees for many areas especially along the coast where
offshore/downsloping winds aid in low level mixing.
Long term /Friday night through Wednesday/...
a narrow ridge of high pressure will start to build into the
area overnight Fri into Sat. A seasonably strong pressure
gradient will set up across the area between the surface high
center and the departing low pressure over the Maritimes.
Unsurprisingly ensemble forecast wind speeds in the low to mid
levels are higher than normal for this time of year. As we sit
around the solstice strong insolation will lead to deep mixing
over land. Forecast soundings indicate the potential to mix down
some gusts near 30 kt. I have bumped wind gust forecasts up to
between 25 and 30 kt at most locations Sat. The strong
insolation will also lead to some afternoon convection nearer to
the upper low center where cooler temps reside aloft and steepen
lapse rates. That should be enough for some scattered showers
Sat afternoon mainly across wrn ME.
That stronger than normal flow is expected to linger into
sun...so I have also increased wind gusts forecasts for that
period as well...albeit not as much as Sat. Otherwise ridging
continues to build into the area...with decreasing winds and pop
and increasing temps. 800 mb temps are forecast to approach
15c...which will mean 80s becoming more widespread across the
forecast area sun into Mon. As the ridging continues to progress
ewd the next widespread chance for rain will come Tue. A shortwave
trof ejecting from The Four Corners region will try and top the
ridge later Tue. As it pushes a front towards the area it should
serve as a focus for showers and thunderstorms Tue afternoon.
Timing locally will determine how widespread the chances for
thunder area...and given the uncertainty I will keep the wording
at isolated to chance thunder.
Aviation /07z Thursday through Monday/...
short term...expect IFR to LIFR ceilings in a maritime air mass
across coastal Maine and eastern New Hampshire this morning
without much improvement as the day GOES on. In fact, rain
chances will be increasing as low pressure moves in from the
west. Generally expect a 1-3sm rainfall but with LIFR ceilings
persisting in the onshore southeast flow along the coast. Some
thunderstorms are also possible especially across southern New
Hampshire this afternoon and evening. There could be a break in
the rain late tonight before rain begins again early Friday
morning. Low pressure moves away on Friday with conditions
improving to VFR on a northerly wind.
Long term...gusty northwest winds are expected Sat behind departing low
pressure. Surface gusts to 30 kt are possible at all terminals.
Some afternoon diurnal rain showers are also possible nearer the upper
low center across wrn ME. Local MVFR or lower conditions are
possible in any rain showers...but expect these conditions to remain
widely scattered. High pressure builds in sun and holds over the
area into Mon. VFR conditions will prevail.
short term...weak pressure gradient keeps winds fairly light
across the Gulf of Maine despite a warm front lifting in from
the south and waves of low pressure moving along it and the
front shifting south as a cold front again. The strongest of
these waves will move through Friday morning, emerging offshore
near Cape Cod. The northerly flow behind this low could approach
advisory levels on Friday, but confidence is not high enough to
issue a Small Craft Advisory yet.
Long term...offshore flow dominates the weekend. Tough call on
wind gusts...as deeper mixing over land makes higher wind gusts
more likely there than over the colder water. It would not take
much mixing to see Small Craft Advisory conditions...but for now the greater
likelihood is actually in the bays and near shore. Sustained
offshore flow may allow seas to reach 5 ft beyond 10 to 15 nm
regardless of wind speed/gusts. High pressure and flow becoming
onshore will allow winds and seas to gradually diminish Mon and
into the early part of the work week.
ME...dense fog advisory until 9 am EDT this morning for mez018>028.
New Hampshire...dense fog advisory until 9 am EDT this morning for nhz014.