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Area Forecast Discussion (AFD)

Issued by Gray - Portland, ME (GYX)

                            
000
FXUS61 KGYX 231305
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
905 AM EDT Tue Apr 23 2019

.SYNOPSIS...
Low pressure off the New England coast will move east into the
maritimes today as another area of low pressure approaches from
the west. Low pressure will move east through southern Quebec 
tonight and will continue east through northern Maine and into
the maritimes on Wednesday. High pressure will build in from the
west Wednesday night and will shift offshore on Thursday. A cold
front will approach from the west Thursday night and will move
east through the region on Friday. Cyclonic flow will persist
over the region behind the front Friday night and Saturday.

&&

.NEAR TERM /TODAY/... 
9AM UPDATE...
Upper low is tracking across the center of the forecast area
this morning, with showers in onshore flow generally east of its
axis (east of Portland) as well as a wrap around band of showers
extending along the Canadian border and down the Connecticut
River Valley in New Hampshire. This band won't move much, but 
is expected to dissipate largely in place over the next few 
hours. Onshore flow showers east of the trough axis will 
continue a bit longer, possibly into the early afternoon. There 
could also be another wrap around band that keeps showers around
for central Maine. Satellite imagery shows the back edge to the
cloud cover is rather sharp, and expect clouds to break up over
western New Hampshire this afternoon allowing the temperature 
to warm into the 60s. But much of Maine will stay cloudy and 
cool... in the low 50s for highs. Have updated the forecast to 
reflect these thoughts and to try to refine precipitation 
chances across the area.

635 AM UPDATE...
Mid level forcing with low tracking to our S and E is 
weakening, and showers will continue to diminish over the N and
W sections during the next couple hours. Will likely see the 
forcing closer to the sfc, and aided by the onshore flow will
continue to push a few showers onshore, especially along the 
mid-coast thru the morning, but should see precip winding down 
everywhere by around midday. NE flow will keep temps from going 
up too much in most of ME, and highs here will likely be in the 
low 40s /far NE/ to low to mid 50s /in SW ME/. In NH, especially
the western part of the state highs will reach into the the 
low to mid 60s, and some sun is expected here as well. 

ORIGINAL DISCUSSION...
Models seem to be doing a good job handling bands associated 
with the low shifting to our S and E this morning, as well as 
some waves of showers moving around the low. The band that's 
lined up along the Connecticut River Valley at 07Z should 
weaken over the next few hours with another weaker band 
developing across the ME mtns between 9 and 12Z. None of the 
precip is performing as efficiently as it did in srn areas last 
evening, so overall will likely not add significantly to river 
flow, but it still needs to be watched this morning. The showers
should diminish over NH during the first part of the morning, 
with some breaks of sun possible this afternoon. In ME, the 
showers look to end late morning to midday, but will likely stay
cloudy thru the afternoon with N-NE flow persisting. Highs 
range from the mid to upper 40s in the eastern zones, thanks to 
that NE flow, to the low to mid 60s in southern NH and the 
Connecticut River valley.

&&

.SHORT TERM /TONIGHT THROUGH WEDNESDAY/... 
Just as we say goodbye to one system, another moves in tonight.
This one will be fast moving, with generally light QPF. Precip 
will arrive in NH this evening, and into SW ME toward midnight,
crossing into the rest of ME midnight or shortly thereafter. 
This will be more showery, but could see a few hours of steadier
light rain overnight. Lows will range from the upper 30s in the
ME mtns, to 40-45 across most of the rest of the CWA.

The weak fast moving sfc low should be exiting the Gulf of ME
Wed morning, and this will likely bring SHRA to an end across
the srn zones in the morning. The 500 MB low crossed srn Quebec
and moves into the crown of ME during the afternoon, and so the
nrn zones will see a chc of showers thru the afternoon. Highs 
range from the upper 40s in the N to 55-60 in the south. Should 
see some clearing in the south as wind shift to the west there 
in the afternoon, but winds stay lighter closer to the low 
aloft in the north, and it will be tough to clear until that 
moves out Wed night.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
Low pressure will shift east into the maritimes Wednesday night as
weak high pressure builds in from the west. Will see a fair amount 
of cloudiness through the evening along with a few stray showers.
Looking for at least partial clearing after midnight as the upper 
trough pushes east. Low temperatures will generally range through 
the 30s to near 40.

Weak high pressure will crest over the region on Thursday before 
shifting offshore. Should see a mix of sun and clouds during the 
day as warmer air makes its way back into the region on return 
flow. High temperatures will range through the 50s north and lower 
to mid 60s south.

Next shortwave in a fairly active pattern will be on the way into 
the region Thursday night. After a mostly clear evening...expect 
increasing clouds after midnight and a chance of showers in 
western zones by daybreak Friday. Low temperatures will range 
from the mid 30s north to the mid 40s south.

Cold front will approach from the west Friday and will push into 
the region in the afternoon. Looking for rain through the day but
models begin to diverge on amounts at this point. GFS keeps the 
frontal system more progressive and moves system east Friday night
while the ECMWF slows the front over the area as low pressure 
tracks north along it. This results in substantially more 
rainfall Friday night through Saturday which may result in more 
flooding on area rivers.

Model differences continue through the remainder of the weekend 
and into next week so will be sticking close to SB numbers for 
later periods of the forecast.

&&

.AVIATION /13Z TUESDAY THROUGH SATURDAY/...
Short Term...Fairly dry air has kept most terminals either VFR
or MVFR tonight, but persistent rain fall will moisten up some
places so that some fog and IFR cigs develop for a few hours
around sunrise. Should see a brief improvement this afternoon, 
to VFR in some spots, but at least MVFR, before the next system
moves in and brings things down to IFR this evening. That will 
linger into Wed morning, with improvement to VFR expected Wed 
afternoon. 

Long Term...
Becoming VFR Wednesday night. VFR Thursday and Thursday night.
MVFR/IFR ceilings developing Friday...improving to VFR Friday
night with areas of MVFR ceilings in the mountains. VFR
Saturday.

&&

.MARINE...
Short Term...Will hold SCA as is for today, but this afternoon
winds will start to diminish. Will likely to convert SCA to Haz
Seas for the overnight, as seas stay high.  

Long Term...
SCA's likely late Friday night into Saturday.

&&

.HYDROLOGY...
Rivers will remain high through the week with additional 
snowmelt and several chances for rain. We will have to monitor 
this situation closely, as it would not take too much rain to 
cause the rivers to rise again. It does look like heaviest rain
from the current system is over. Another weak system passes 
tonight, but that is fast moving and will have limited QPF. Will
also have to watch for the chance of more significant rainfall 
Fri-Sat as some deterministic guidance and ensemble members 
suggest.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...None.
NH...None.
MARINE...Small Craft Advisory until 6 PM EDT this evening for ANZ150-
     152-154.

&&

$$

NEAR TERM UPDATE...Kimble 
SHORT TERM...Cempa 
LONG TERM...Sinsabaugh