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Area Forecast Discussion (AFD)

Issued by Caribou, ME (CAR)

                            
000
FXUS61 KCAR 251344
AFDCAR

Area Forecast Discussion
National Weather Service Caribou ME
944 AM EDT Thu Apr 25 2019

.SYNOPSIS...
Weak high pressure will build over the area today. Low pressure
will approach from the southwest tonight and Friday and track
across the region Friday night into Saturday.

&&

.NEAR TERM /THROUGH TONIGHT/...
940am Update...
Cool and mostly cloudy today into the north, and partly cloudy
Downeast. No precipitation. Increased cloudcover a bit today,
otherwise no changes.

Previous Discussion... 
The small low which brought some rain and snow showers last 
night will continue tracking away to the east through the 
Maritimes today as weak upper level ridging and surface high 
pressure build over the area. Moisture lingers in the boundary 
layer, especially across the north, and soundings are showing an
unstable layer up to around 4.5K ft today. This will result in 
a mostly cloudy sky over the north although some breaks of 
sunshine will be possible through midday. Downeast will turn out
partly cloudy. Tonight will then remain partly to mostly cloudy
as high pressure slides to our east. Our focus on Friday will 
then be on a large storm system approaching from the Midwest. 
Clouds will thicken during the day and rain will move in from 
southwest to northeast through the midday hours. By Friday 
evening the low center will be to our west as rain, 
southeasterly winds and fog push in across the area. The rain 
and warmer southeast wind melting remaining snow across the 
north may result in some minor flooding of small streams and low
lying areas.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY/...
Another dose of significant rainfall to move across the region
w/rainfall totals of 1 to possibly 1.5 inches by Saturday
evening. A 40-45 kt jet at the 925-850mb layer will aid in some
heavier rainfall on Saturday as low pres lifts up across the
region bringing an occluded front w/it. As it looks right now, 
the heaviest rainfall could occur between 12-18Z timeframe 
w/amounts of 0/50-.075 inches. Rainfall winds down early 
Saturday evening w/totals expected to be on the order of 1 to 
1.5 inches. This will allow more rises on streams and rivers in
the CWA as well as rises on the lakes w/the ice possibly
breaking up. More on this in the Hydrology section below. Colder
air moving in behind the departing system has the potential for
some snow on the backside. The 00Z ECMWF matches its 12Z run and
has been consistent w/this scenario showing 925mb temps dropping
to -1C or so. The 00z GFS is warmer and shows the closed low 
lifting up across the region similar to the ECMWF. The Canadian 
Global appears to be in the middle and not as cool as it has the
closed low further w. Decided on a blend of the guidance and 
leaned w/leftover rain mixing w/some snow before ending. Areas 
across the St. John Valley and the Allagash could be looking at 
a change over to snow w/a white coating before it ends. 

Drier but still cool on Sunday with a good deal of clouds as the
associated cold front is forecast to slide across the region.
Temps on Sunday will average below normal for late April. The
long range guidance was showing a low pres system to move in on
the heels of the last rain event by later Sunday into Sunday
night. There is good agreement that this low will pass by to our
south giving the Downeast coast as glancing blow, as it looks
right now. This trend has been showing up over the last 2 runs,
but given that a shift back to the north is still possible,
decided to use a blend showing 30-40% pops for the Downeast 
region and slight chance pops(20%) for the north. Some cold air
to move in behind this system from James Bay later Sunday night
into Monday morning. We are talking 925mb temps of -6 to 
-8 C across the region translating to temps in the 20s and lower
30s. If this trend holds, there could be some temps dropping to
near 20F across the far n and w.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
The trend in the long range guidance is for some well needed
drying Monday into Tuesday as high pres builds across the
region. There is some uncertainty in regards to Tuesday as the 
ECMWF showed low pres passing across southern New England 
bringing, believe it or not, snow to the region. The GFS is 
somewhat similar w/the placement of the low, but warmer and 
keeps the bulk of the precip further s. Given this is day 6, and
there is plenty of time for a change in the track and intensity,
decided to go w/20% pops. At any rate, the colder airmass looks
like it holds in place w/a continuation of below normal temps.

&&

.AVIATION /14Z THURSDAY THROUGH MONDAY/...
NEAR TERM: IFR to MVFR conditions early this morning will
likely become MVFR by late morning then VFR through midday and 
this afternoon across the area as ceilings rise. Ceilings may
lower to MVFR late tonight, then drop to IFR from south to north
midday Friday as lower clouds and rain move in. 

SHORT TERM: IFR/LIFR w/rain on Saturday for all terminals.
Conditions to gradually improve Saturday night w/IFR-MVFR
especially for KBGR and KBHB. The improvement looks to continue
into Sunday w/KBGR and KBHB seeing VFR, while the northern
terminals will hang to some MVFR cigs into early afternoon, and
then an improvement to VFR.

&&

.MARINE...
NEAR TERM: Winds should remain light through Friday as high
pressure slides across then east of the area. Winds will then
increase from the southeast to SCA Friday night, and possibly
approach gale by early Saturday morning. 

SHORT TERM: SCA conditions Saturday into Sunday. SW winds of
20-25 krs will swing around to the WNW behind the departing low.
Gust potential is there for 30 kts. Seas will average 7-9 ft and
gradually subside, but slower due to a swell component.
Conditions are forecast to improve by Monday as high pres builds
toward the region. Winds of 15 kts are expected and seas
dropping back to 3-4 ft.

&&

.HYDROLOGY...
River Flood Warning remains in effect for the Mattawamkeag 
River near Mattawamkeag. The Mattawamkeag River is holding 
steady.

Flood warning issued for Portage Lake, with water levels
becoming very high. Water levels also high on Fish River Chain
of Lakes, but no products have been issued yet due to limited
known impacts.

There is potential for 1 to 1.5 inches of rain is possible 
Friday night into Saturday. This would be enough to show some 
rises on rivers and streams, including the major rivers such as 
the St. John, Aroostook and Penobscot. If the system turns out 
to be wetter than expected, flooding problems could result 
especially on the smaller rivers and streams.

&&

.CAR WATCHES/WARNINGS/ADVISORIES...
ME...None.
MARINE...None.

&&

$$

Near Term...Bloomer/Foisy
Short Term...Hewitt
Long Term...Hewitt
Aviation...Bloomer/Foisy/Hewitt
Marine...Bloomer/Foisy/Hewitt
Hydrology...Foisy/Hewitt