Area forecast discussion...updated 
National Weather Service Gray ME 
917 am EDT Tuesday Aug 4 2015 


Synopsis... 
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. 


Previous disc... 
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 
next week. 


&& 


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. 


&& 


Marine... 
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 
morning. 


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. 


Gyx watches/warnings/advisories... 
ME...none. 
New Hampshire...none. 
Marine...none. 


&& 


Gyx watches/warnings/advisories... 
ME...none. 
New Hampshire...none. 
Marine...none. 


&& 


$$ 


Near term...legro 



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