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Area Forecast Discussion (AFD)

Issued by Gray - Portland, ME (GYX)

FXUS61 KGYX 161659

Area Forecast Discussion
National Weather Service Gray ME
1159 AM EST Thu Nov 16 2017

Low pressure will develop over southern New England then track 
through the Gulf of Maine this evening. Coastal rain and some 
accumulating interior snows are expected. Gusty northwest winds
follow this system late tonight and Friday. High pressure builds
in again for Friday before the next storm system arrives late 
Saturday and Sunday with another mixed bag of precipitation. 
High pressure then returns for early next week.



1158 AM...For this ESTF update I made minor adjustments to near
term grids to reflect radar trends for precipitation timing as 
well as the current mesonet. 

Prev disc...
900 AM...The current forecast is largely on track. For this 
ESTF update...I adjusted the near term grids to reflect radar 
trends as well as the latest mesonet. 

Prev disc...
645 AM Update...Little change to the going forecast
early this morning as light precipitation is arriving on time 
across western zones. The precip is taking the form of light 
snow and rain depending on location. The same is expected as the
leading edge moves into ME later this morning. A few locations,
especially those with decent elevation, may see a coating of 
snow this morning before going over to rain. The higher 
elevations of the Whites and western ME mountains are still 
expected to be the only ones with several inches of snowfall 
through this evening.


A short wave trough approaching from the west will allow light 
precipitation to overspread the forecast area from west to east 
this morning. Much of this precipitation will be in the form of 
rain, but higher elevations will likely see light snow. Lower 
elevations may start as snow or a mix of snow, sleet, and rain. 
However, SFC temperatures are already rising so little if any 
accumulations are expected at lower elevations. Elevations above
2,000 ft may pick up 2 to 5 inches of snow today. 

Secondary low pressure develops and deepens in the Gulf of 
Maine later this afternoon and continues to make the forecast 
for late this afternoon and evening a bit tricky. As the 
secondary low develops, mid level frontogenetical forcing will 
become quite strong on the coastal plain up through central 
Maine. This will likely result in a relatively short period of 
moderate to heavy precipitation moving from south to north. Much
of this will be in the form of rain despite the strong upward 
vertical motion as the column below 850 mb will be just a bit 
too warm. 

However, there will be a window of opportunity centered a few 
hours either side of 00z where the dynamics may be strong 
enough to cool the column sufficiently for a period of heavy 
snow in a potential comma head. This would mainly be along/near 
the I-95 corridor north of Lewiston. Have forecasted a 
relatively small area of 1-3" centered around Kennebec County to
account for this possibility. However, if the forcing for 
ascent is weaker or mainly offshore, then the precipitation will
fall in the form of rain outside of the higher elevations. In 
any event, it will be interesting to see how things unfold late 
this afternoon and early evening. But for now, winter weather 
advisories are not necessary as any areas of >4" snowfall 
should be confined to the higher elevations.

Other than that, there could be some minor urban/poor drainage
flooding This afternoon on the coastal plain in the period of
locally heavy rainfall. In addition, areas of fog are expected 
to develop by early afternoon.


The low pressure system quickly moves away this evening, ending
the precipitation from south to north. In fact southern and
western zones will likely see an end to the precip late this
afternoon. Northwesterly winds will kick in behind the
strengthening low later tonight and become gusty. These winds
will continue through Friday with gusts up to 40 MPH not out of
the question. Upslope snow showers in the mountains will add to
the snow totals in the higher elevations.


The weekend starts off with a brief ridge of high pressure 
before a potent storm system dives southwards and crosses the 
region Saturday night into Sunday. The cold air lingers for the 
start of next week. 

Friday night will see temperatures fall to the low teens north 
to low 20s south as weak high pressure moves over the region. 

The next system will move out of the Great Lakes and up the St.
Lawrence Valley on Saturday. As it does a warm front will lift 
north through our area on Saturday afternoon. With the later in 
the day onset for precipitation expect all but the far northern 
portions of the forecast area to rise above freezing before 
precipitation begins resulting in a mostly rain event. In the 
north, and above 1500ft rain will mix with and change over to 

Overnight Saturday into Sunday the warm sector pushes well into
the region, at least aloft, as the 850hPa passes to our 
northwest. There will likely be a few areas in the north which change
over to freezing rain, especially any sheltered valleys where 
the warm air is unable to mix out. The freezing rain will 
rapidly change back over to snow as a strong cold front pushes 
through early Sunday morning. This front has a lot of upper 
level support with tropopause falling to around 500mb behind the
front. This will create a burst of strong winds on Sunday 
morning as the front passes. Additionally the strong front may 
touch off some snow squalls as it moves through northern New 
Hampshire and western Maine. 

Soundings show a well mixed lower layer which will result in 
wind gusts to 40 mph possible across the area. The warm 
temperatures, reaching as high as almost 50F in the south will 
go hand in hand with the stronger wind gusts as both are the 
result of a well mixed atmosphere. Again in the northern 
mountain valley a few areas may struggle to rise above freezing 
at all with the result being calmer winds and a changeover from 
freezing rain directly to snow on the backside of the front. 

Looking at the system as a whole, a mix of snow, sleet, and 
freezing rain will likely require Winter Weather Advisories for
Saturday night into Sunday for the northern portion of the 
area. Winds will approach wind advisory criteria on land, and 
gust in excess of Gale force over the ocean water. 

The cold are advection and breezy conditions will continue 
through the day on Sunday and into Sunday night. Upslope snow 
showers will persist through Sunday night along with the 
northwesterly winds. 

As we head into the busy travel week of Thanksgiving the 
pattern remains fairly progressive with a chance for more snow 
by mid week.


Short Term /through Thursday Night/...Conditions will become IFR
today as rain and snow overspreads the region along with fog. 
The snow will be confined mainly to the mountains. However, a 
period of snow will be possible around KAUG early this evening. 
Conditions improve tonight with VFR returning which will last
through Friday except in the mountains. Westerly winds gust
around 30 kt Friday.

Long Term...Expect IFR in fog and then drizzle to develop along
the coast as a warm front lifts northwards on Saturday. The
conditions will then improve to MVFR until the cold front comes
through on Sunday. Wind gusts to 40mph possible as the front
moves through. Conditions will improve to VFR by Sunday
afternoon for all but the northern mountains where MVFR snow
showers will persist.


Short Term /Through Friday/...Gale warnings continue for Friday
as wind gusts of 35-40 kt are expected.

Long Term...
Warm front will lift north of the waters on Saturday before a 
strong cold front passes on Sunday morning. During Fropa and 
behind the front will see wind gusts to gale force expected 
across the waters. Winds will remain strong through the 
afternoon Sunday before the pressure gradient finally relaxes.


MARINE...Gale Warning from 4 AM to 8 PM EST Friday for ANZ150>154.