Area forecast discussion 
National Weather Service Gray ME 
525 PM EST sun Dec 21 2014 


Synopsis... 
an onshore flow may trigger some flurries or light snow mainly over 
southern regions right through Tuesday. A significant low 
pressure system system will gradually organize Wednesday...before 
moving over the Great Lakes. This could bring windy conditions and 
the potential for heavy rain around Christmas evening into early 
Christmas morning. Another low pressure system will pass by to our 
northwest late in the week and early next weekend. 


&& 


Near term /until 6 am Monday morning/... 
areas of light snow will continue into this evening hours 
associated with "ocean effect" onshore flow...and also due to the 
proximity of a weak middle level low. In general...will be lowering 
probability of precipitation as we head into the late evening hours...with the greatest 
chance of a snow showers along and near the coastline. The beach 
areas will need to be monitored however...as there is some 
indication of a weak norlun trough over the region. 


&& 


Short term /6 am Monday morning through 6 PM Monday/... 
scattered snow showers and flurries will continue right through 
Monday night over southern areas due to a persistent northeast 
flow over the moist Gulf of Maine. Mesoscale models within the 12z 
model suite continue to have a difficult time picking up on this 
low level moisture and precipitation. Have therefore raised probability of precipitation Above 
All available guidance. 


A cold air damming signature will be forming by Monday night. 
Therefore...the ptype should be all snow through the short term 
portion of the forecast...before the warm air pours into the 
region. 


&& 


Long term /Monday night through Sunday/... 
the weak onshore flow continues into Tuesday with low level 
moisture deepest along the coast. On Tuesday the warmer onshore 
flow deepens as the high moves further offshore allowing a 
southeast flow to increase...so scattered light intermittent 
precipitation expected...mostly in the form of rain except some 
in the form of light snow in the mountains before changing over to 
rain even in those areas. The main event will be the onset of the 
heavier precipitation late Tuesday night and especially Christmas 
evening where the rain will become heavy at times as a strong warm 
advection pattern develops being accompanied by a strong low/middle 
level jet. The main upper low passes well to our west as it moves 
through the Great Lakes. Quantitative precipitation forecast totals for late Tuesday into Thursday 
could be in the 2-4 inch range. Due to very warm air this will be 
in the form of rain even in the mountains. Some flooding problems 
may arise in the headwaters by Wednesday night or Thursday due to 
the combination of some snowmelt and the heavy rains. All models 
agree on mild temperatures...used a blend of the models. 


System finally exits to the northeast by Thursday afternoon as a 
dry slot moves across the area followed by a cold front with a 
return to seasonal temperatures for Friday. 


Another system which will be weaker will approach for the weekend. 
Models differ in run to run continuity and also variances in 
timing, strength, and position of this system. For now will broad 
brush due to all the uncertainty as well as ptype. 


&& 


Aviation /00z Monday through Friday/... 
short term...mainly VFR through Monday night...however there may 
be briefly MVFR conditions in scattered snow showers southern 
locations. 


Long term...MVFR conds expected Tuesday and then lowering to IFR Tuesday 
night and LIFR conditions Wednesday into Thursday. Conditions improve by late 
Thursday to VFR. 


&& 


Marine... 
short term...winds and seas will remain mostly out of the 
northeast through Monday night. Winds and seas will remain below 
Small Craft Advisory conditions. 


Long term...strong low pressure will move well to the west and 
will cause winds to increase to gales Tuesday night through 
Wednesday with borderline storm force wind gusts possible 
Wednesday night. Seas could build in excess of 15 feet over the 
outer waters by Wednesday night or early Thursday. Guidance looks 
low on both winds and seas which is typical for these type of 
events. 


&& 


Hydrology... 
models continue to back off on rainfall totals for 
the Christmas evening/early Christmas morning event...but area still 
in the 1 to 3 inch range. Hoping the snowpack in the mountains and 
foothills will take in some of the 1 to 2 inch rainfall amounts in 
that area...but still expected rapid rises in the headwaters. Over 
southern locations...2 to 3 inches of rain expected. In any 
case...flooding is a distinct possibly Christmas evening and Christmas 
morning associated with the heavy rain and snowmelt. 


&& 


Tides/coastal flooding... 
astronomical tides are at their peak for the month. This...in 
combination with strong southerly developing gales (with possible 
storm force gusts) will likely allow for about a 1 foot storm 
surge. With building waves in the 15 foot range...expect a few 
areas to have coastal flooding...splash-over and beach erosion. 


Nart wave run-up matrices are already predicting the potential for 
coastal flooding...overwash and erosion across most locations in 
Maine and New Hampshire based on our current storm surge and wave 
predictions. 


The question is however...when will the peak winds and seas 
arrive? Right now it is too early to tell if this period of 
inclement weather/ocean conditions will arrive near the time of 
high tide. The midday tides on Christmas evening and Christmas day are 
the highest at 11 feet...while the 1 am Christmas morning high 
tide is lower at 10 feet. 


&& 


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


&& 


$$ 



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