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Area Forecast Discussion (AFD)

Issued by Caribou, ME (CAR)

FXUS61 KCAR 200458

Area Forecast Discussion
National Weather Service Caribou ME
1258 AM EDT Sat Apr 20 2019

A cold front will move across northern Maine this evening and 
will stall out across central Maine late tonight. The front will
then lift back northward as a warm front Saturday into Saturday
night. The region will remain in a very moist air mass this 
weekend and into early next week. Low pressure will approach 
from the southwest on Monday.


1am Update...
Only minor touchups to the forecast. Steady rain through the
whole area tonight.

Previous Discussion...
A cold front currently crossing the Caribou area will sink
southward tonight, but stall before reaching a Bangor to Calais
line later tonight. The front will then slowly lift northward on
Saturday. There are sharp temperature and moisture gradients
with this frontal boundary that will mark 20F differences in
temp and dew point from one side of the boundary tonight and
tomorrow. The discontinuity extends up to H925 where a very
tight gradient of about 15C exists tonight and tomorrow. Focused
along this thermal boundary will be locally heavy precip as deep
moisture streams northward from the Gulf of Mexico and is
focused along this boundary. PWs will be approaching as much as
an inch and a half...very high for this time of year. These PWs
will be aided by a deep warm cloud layer for efficient precip
processes, a strong LLJ and elevated instability. Furthermore,
some training cells may be possible. When these factors are
combined with snow melt and flash flood guidance of about one 
inch in an hour or 1.25 inches for 3 hours, there is the 
potential for flash flooding later tonight into Saturday 
morning. The soil is saturated in much of the area with little
capability to absorb heavy rainfall rates. The snow melt will 
be enhanced by fog...which will also cause visibility issues for
motorists to see water hazards on roadways tonight. WPC has put
the area in a slight risk for excessive rainfall. The heaviest 
rainfall tonight is expected on the north side of the frontal 
boundary...north of the Moosehead and Katahdin regions. The 
heavier precip shifts slightly southward during Saturday but 
embedded convection will bring locally heavier rainfall. Have 
not added thunderstorms into the forecast yet, but should be a 
strong consideration for the next updates. These storms will
fire off a very pronounced H925-H850 thermal ridge. Dense fog 
headlines are also a possibility later tonight into early 
Saturday morning under the frontal inversion...with the coast 
being the highest probability.


A strong southerly flow along the East Coast combined with an
upper level trough is expected to move across the northeast over
the next several days is expected to bring period of rain from
Saturday Night into Monday and Tuesday. The strong southerly
flow will also result in high dew points which will produce fog
and enhance snow melt. High temperatures through the weekend are
expected to be in the 50s and 60s while nighttime lows stay 
well above freezing.


The upper level system is expected to move off the East Coast 
on Tuesday. At the same time low pressure will approach from the
Great Lakes and move across the region on Wednesday and early 
Thursday. Another system is expected to approach from the west 
on Friday.


NEAR TERM: IFR and LIFR into tonight will be the predominant
conditions with rain and low clouds. Low level wind shear also
an issue mainly for KBHB and KBGR.

SHORT TERM: Expect MVFR/IFR conditions Sunday into Wednesday.


NEAR TERM: A very moist air mass over the cold waters will
generate areas of fog...if not widespread dense fog. In spite of
the stability and lack of gusts, the winds will still be strong
enough to gusts to 25 kts until decreasing Saturday afternoon.
Have adjusted winds...and particularly gusts...downward from
model guidance due to stability.

SHORT TERM: Have used the Nam to initialize winds however will
lower all model winds by 10 percent due to cold sea surface
temperature and expected strong warm advection. For Waves: A
southerly fetch will persist from the Gulf of Maine
Southeastward into the Atlantic through the day Sunday. So
expect wave heights to remain around 8 feet/9-10 seconds until
Monday then slowly subside. Total Water Level: High tide levels
are close to highest levels of the month next few days due to
astronomical tide levels however storm surge is expected to
remain below 1 foot therefore expect total water level to remain
2 feet below minimum flood level along the coast. In Bangor
fresh water run-off continues to increase anomaly at low tide 
+5 to +6 feet and also produce 2 foot or greater anomaly at high
tide Sunday which could bring total water level near or above 
action level in Bangor.


This weekend marks one of the most potentially eventful hydro 
events in many years that covers much of the forecast area. The
combination of remaining deep snowpack in northern zones and 
the clash with a very warm and humid air mass on the backside of
a Bermuda High will put a lot of water in the rivers. A 
stationary front will mark the boundary of the clash across the 
state tonight into Saturday and bring three separate hydro 
concerns. First is remaining ice jams on the Aroostook and Saint
John Rivers. The second concern is urban and small stream 
flooding due the combination of heavy rain and snow melt later 
tonight into Saturday. The last concern will be the response of 
main stem rivers Sunday into Monday. 

In terms of the ice jams, a Flood Warning remains in effect 
today along a portion of the Aroostook River. The gauge at 
Washburn is reading nearly 17 feet as of this afternoon, which 
is moderate flood stage. The gauge will continue to show 
fluctuations tonight and Aroostook Emergency Management reported
that Gardner Creek Road near Washburn remain closed due to an 
ice jam that extends from upstream of the Washburn bridge 
towards Crouseville. Emergency Management is also watching the 
Parsons Road between Washburn and Presque Isle. We are watching 
ice jams on the Saint John near Saint Francis, Frenchville and 
Van Buren, but have no need to issue warnings at this time. Most
or all ice jam issues should be resolved by later this weekend 
as rivers continue to rise.

A point Flood Warning also remains in effect for the 
Mattawamkeag above Mattawamkeag until further notice. The river 
is near 14 feet this afternoon and is expected to slowly rise to
15.1 feet by Sunday afternoon, with additional rises into early
next week. At 14 feet, flooding begins along the Bancroft Road 
between Wytopitlock and Danforth.

Snow melt is already causing issues on Route 1A in Easton and
Route 2 in Island Falls. These types of issues will be
exacerbated by locally heavy rainfall tonight into Saturday 
morning for small streams. The Flood Watch is now in effect for 
tonight through Monday evening. The combination of rainfall of 
1.5 to 3 inches of rain along with significant snowmelt in areas
that still have snow on the ground will lead to significant 
rises on streams tonight and Saturday...and on main stem rivers 
Sunday into early next week. There is high confidence that 
smaller streams will flood. There is also high confidence that 
some areas will experience minor to moderate flooding. 
Confidence is not as high as to whether any areas will 
experience major flooding, but it is a possibility. There are 
uncertainties in terms of the exact remaining SWE that will 
empty into rivers. According to dam operators, storage capacity 
in the Penobscot watershed is favorable and that will help 
mitigate potential main stem issues. &&

ME...Flood Watch from 2 AM EDT Saturday through Monday evening for 
MARINE...Small Craft Advisory until 6 PM EDT Saturday for ANZ050>052.


ME...Flood Watch through Monday evening for MEZ001>006-010-011-015-
MARINE...Small Craft Advisory until 6 PM EDT this evening for 



Near Term...Foisy/Norton/MCW
Short Term...Mignone
Long Term...Mignone