196 
fxus61 kgyx 211347 
afdgyx 


Area forecast discussion 
National Weather Service Gray ME 
947 am EDT sun Mar 21 2010 


Synopsis... 
frontal boundary remains quasi stationary south and east of the region 
through Monday night. Low pressure over the Middle Atlantic States on 
Tuesday then tracks along this boundary to a position over Nova Scotia 
on Wednesday afternoon. A moderate northwesterly gradient develops 
behind the low later Wednesday before relaxing early Thursday. A brief 
wedge of high pressure crosses the region Thursday afternoon... with 
low pressure over southeastern Canada moving north of the region 
Thursday evening. A trailing cold front crosses the region Thursday 
night. High pressure approaches the region on Friday and moves across 
the region over the weekend. 


&& 


Near term /until 7 PM this evening/... 
the gridded and text forecasts were updated to account for trends 
in sky cover...precipitation probabilities and temperatures. 


The surface cold front that passed last evening is coming to rest 
across the northern Middle Atlantic States this morning. Right behind 
the cold front...some downward motion allowed clearing to occur 
across central and southern zones. In fact...portions of southern 
New Hampshire and southwest Maine still have sizeable breaks in 
the clouds. 


Would expect this to be relatively short lived as upglide from the 
surface front to the south continues over the 850 mb warm front 
across the northern portion of the forecast area. Warm air advection 
precipitation is occurring across northern and central areas right 
now. Surface reports and the look on the kgyx radar returns suggest 
that the precipitation falling across the mountains is snow. 


Further south...the precipitation looks more convective in nature. 
The 1200 UTC gyx sounding showed a large isothermal layer just 
above the surface...with dry air in place. This is allowing the 
spottier precipitation to fall as rain with lighter intensity...and 
snow or sleet with heavier intensity. Would expect this trend to 
continue until the column is moistened and the evaporative cooling 
is exhausted. 


Not too much change in the pattern is expected today. Will continue 
with the highest chance of precipitation across the higher terrain... 
where the cross barrier flow will help. Since the column is just 
cold enough for snow here...and the ground is fairly warm (where 
there is no snow cover)...would expect light snow accumulations. 


Further south...where the warm air advection is not as impressive... 
will continue with lower chances of precipitation. After the dry 
air is exhausted...would expect mainly light rain this afternoon. 
The Breaks in the clouds may allow southern areas to warm a bit 
more than forecast...but elsewhere do not see much of a 
temperature rise from this morning. 


&& 


Short term /7 PM this evening through 6 am Monday/... 
overrunning scenario continues tonight so it looks like cloudy 
with a chance of showers over southern/coastal sections with 
snow/rain showers likely over northern/mountain sections. Again 
used a blend of mav/met/current forecast parameters. 


&& 


Long term /Monday through Saturday/... 
00z model suite in good agreement in regards to the overall track 
and movement of the surface and upper level low early this week. 
Probability of precipitation increase during the day on Monday as warm air advection 
begins over the northeast. Appears there may be a few periods of 
snow across the highest terrain on Monday/Monday night...however 
even with some evaporational cooling...this will be mainly a 
liquid precipitation event...at least at the onset. All models 
agree surface low slowly heads into New England and ends up near 
psm by Tuesday night. It is at this point that cold air begins to 
become an issue as system pulls east...allowing cooler air to pour 
in across the higher terrain...and for cool air to be dynamically 
produced with the passage of the upper low. Will forecast a 
changeover to snow in the mountains...and this will need to be 
monitored...as advisory type snows will be possible across the 
high terrain. 


Thereafter...some upslope snow showers will occur during the 
midweek period. Shot of significantly colder air will arrive on 
Friday with the passage of a strong cold/Arctic front. 


&& 


Aviation /14z Sunday through Thursday/... 
near term /rest of today/...for the most part...conditions are VFR 
across the area. Would expect a slow transition to MVFR with bands 
of precipitation...mainly north of the terminals sites. 


Short term /tonight/...VFR with area of MVFR in rain/snow showers 
over northern/mountain sections and any rain showers over 
southern/coastal sections. 


Long term...conditions will continue to deteriorate Monday through 
Tuesday with mainly IFR conditions (and areas of lifr). Slow 
improvement begins Wednesday and Wednesday night. 


&& 


Marine... 
near term /rest of today/...the surface front is coming to rest 
well south of waters this morning...as high pressure builds down 
from Quebec. The surface gradient is weak...and a general east 
flow is expected this afternoon. Sea breeze circulations are 
possible this afternoon...especially near the southwest coast. In 
general... winds and seas are expected to remain well below small 
craft levels. 


Short term /tonight/...no flags tonight. 


Long term...gales are possible Tuesday ahead of the system and 
possibly Wednesday behind the system. Gusty winds over the coastal 
waters in a strong cold air advection flow on Friday. 


&& 


Hydrology... quantitative precipitation forecast of 2-3" possible with this next event. This will 
continue to be monitored for possible flood watches in upcoming 
packages. Most vulnerable locations remain southernmost portions of 
the forecast area. 


&& 


Tides/coastal flooding... 
we are at a relatively low part of our tide cycle. Onshore winds 
do not look overly strong and nearshore waves should remain near 
10 feet no Tuesday. Therefore...The Tides/waves and resulting 
beach erosion do not appear to be a problem at this time. Ended up 
publishing with old 12z wave watch model...as 00z run seamed too 
low. 


&& 


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


&& 


$$ 

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