Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Gray ME
917 am EDT Tuesday Aug 4 2015
persistent low pressure aloft...situated over Quebec...will bring
the threat of showers and thunderstorms both today and Wednesday.
A few storms could be severe later today with strong winds and
large hail...with another round of strong storms possible
Wednesday afternoon. Cooler air moves in for the middle to late week
period...and it will be mainly dry...although scattered showers
will be possible in the mountains Thursday. Friday looks mostly
dry for now. There is chance for some rain over the weekend as low
pressure just off the coast.
Near term /until 6 PM this evening/...
mesoscale update...have adjusted grids to reflect large wind
producing mesoscale convective system sliding just S of much of the forecast areas. Thunderstorms
this morning mainly confined to the waters.
As for this afternoon...based on latest available guidance...the
threat for severe thunderstorms continues for much of the forecast area
S of the mountains drier air is advecting in from the north...though middle
60s dewpoints reside along the coastal plain. In the wake of
morning mesoscale convective system abundant sunshine will warm those areas into the 80s.
Residual middle level lapse rates on the order of 6.5 c/km will
support cape values increasing to at least 1500 j/kg near the
coast. Stronger forcing arrives this afternoon in the form of the
left exit region of a near 90 knots upper jet.
The end result is at least scattered thunderstorms are expected to develop
across central portions of the forecast area...and move towards
the coast...as individual cells propagate northeastward. Shear is forecast
to be stronger than yesterday...so storms will be organized with
all modes possible...including discrete cells and clusters. Strong
flow aloft will support a damaging wind threat...and lowered
freezing levels will aid in discrete cells possessing a hail
threat as well. Residual boundaries from previous night/S
convection and any marine/sea breeze front will also carry a non-
zero tornado threat...but wind and hail appear to be the main
concern. The moist environment and strong forcing will also result
in efficient rainfall in stronger storms.
Forecast will be updated as necessary with any changes to the
expected evolution this afternoon.
at 06z...a prefrontal trough was draped across the forecast area
with a cold front over the eastern Great Lakes. For today...the
front will inch eastward with convection increasing in coverage
with daytime heating and approach of upper impulse and associated
surface cold front. Modified BUFKIT forecast soundings from
NAM/GFS yield convective available potential energy near 2000 j/kg and moderate shear. Expect
organized storms and line segments once again today with damaging
winds and large hail the primary threats. Highs will range from
70s in the mountains to the 80s elsewhere.
Short term /6 PM this evening through 6 PM Wednesday/...
the cold front will clear the area overnight...bringing cooler
and drier air back to the region. With lows in the 50s and lower
60s. Wednesday will prove to be another interesting day as cool
cyclonic flow..daytime heating and passing impulse produce another
round of convection with potential for small hail and gusty winds.
Long term /Wednesday night through Monday/...
high impact weather: none.
500 mb pattern starts with strengthening ridges over the southern Continental U.S.
And mean toughing in the northestern US. While there is some flattening
of the trough toward the end of the week...the general trend is
for the trough to hold to some degree through early next week. This
pattern would keep the hot air to out west but surprisingly the
air in the trough is not all cool. This would keep temperatures near
normal with unsettled conditions.
Specifically...Wednesday night should feature a secondary push of the
cooler and drier surface air in northwest flow...with perhaps a few rain showers in
the mountains Thursday and Friday look mainly dry as weak surface high builds in
beneath nearly zonal flow aloft. The forecast becomes much more
muddled for the weekend as the 00z medium range models show quite
divergent solutions...which range from the gems complete miss of a
coastal low well to the south...to the euros winter-like coastal
bomb. Not much confidence in the forecast beyond Friday at this
point. Given that all models look to be dealing with convective scaling
issues and at times do not make meteorological sense...have opted
to go with just chance probability of precipitation Sat-sun...with the best chance Sat
night...as this is closest to what might called model
consensus...and agrees with superblend. See wpc extended forecast
discussion /pmdepd/ for a good explanation of the model issues
with this system. Still...one thing to take home about the models
in the medium to long range is that they are probably picking up
on something...but how that pans out and what its impacts will be
need to been from a shorter timeframe than days 5 and 6.
Temperatures Thursday and Friday will see highs in the low 70s north to
around 80 in interior SW ME and southern New Hampshire...with overnight mostly in
the 50s. Depending on how the system over the weekend
plays...and assuming it amounts more to showers and some cooler
north-NE flow...daytime highs will be in the 70s and overnight lows in
the middle 50s to low 60s. Should see at least slight warm up early
Aviation /13z Tuesday through Saturday/...
short term /through Wednesday/ ... areas of MVFR in rain showers/thunderstorms and rain with local
IFR possible in +tsra along with strong wind gusts and large hail
through 02z. Areas of stratus and fog with local IFR tonight. Areas
of MVFR Wednesday in shra/tsra.
Long term...mainly VFR Thursday through Saturday...although high
probability of valley fog at khie/kleb Wednesday and Thursday night.
short term...persistent south-southwest flow ahead of slowly approaching cold
front will keep winds and seas just below Small Craft Advisory thresholds through
this evening. Small Craft Advisory was dropped with new marine package this
Long term...Thursday and Friday will see conds comfortably below Small Craft Advisory
levels. Depending on track of low pressure this weekend could see
a period of Small Craft Advisory winds seas over the weekend.