Area Forecast Discussion
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FXUS61 KCAR 220201
Area Forecast Discussion
National Weather Service Caribou ME
1001 PM EDT Fri Apr 21 2017
Decaying low pressure in Quebec will slowly drift towards
northern Maine while a new area of low pressure organizes south
of Cape Cod tonight and intensifies south of the state on
Saturday. The low will move south of Nova Scotia Saturday night
and high pressure will build on Sunday.
.NEAR TERM /THROUGH SATURDAY/...
935 PM Update: Precip has turned over to all sn a little faster
then prev fcst, so we time shifted our fcst grids 1 hour forward
and hand edited precip types slightly to shade to all sn a
little faster and further S resulting in a 2 hour faster
transition then the prev fcst. Fcst 6 hrly and stm total snfls
were then updated to show a little more snfl over Nrn Penobscot
and SE Aroostook counties. One concern that could reduce sn
totals a little across the N is the potential of dry slotting
which a few models indicate could sharply reduce sn rates aft
mdngt across the region, with more intermittent lgt sn for the
late ngt. To erly to make any decisions at this tm, but
something to watch.
Otherwise, fcst ovrngt hrly temps were updated to reflect a
faster drop in temps into mid eve based on latest obs, but no
chg in fcst ovrngt lows attm, thinking that temps will not fall
much more with evaporational/ dynamic cooling processes mostly
used up across areas that have transitioned to sn attm.
Orgnl Disc: The big concern for this evening is a vigorous
shortwave trough rotating around the closed upper low in Quebec.
It will affect areas north of the Katahdin region and Houlton
this evening into the overnight hours. There`s a lot of lift
with this feature as evidenced by omega fields. There is some
upper level instability and the LFQ of a strong upper jet will
enter northern Maine later this evening. Although temperatures
are currently in the upper 30s to lower 40s in northern zones,
evaporative and dynamic cooling of the column will generate a
fairly quick changeover from rain to snow as the warm boundary
layer is eliminated. There is good omega in a rather high
dendritic layer later this evening and snowfall rates over an
inch an hour are possible as the shortwave crosses. The fact
that the heavier snow will be falling at night with these
snowfall rates means roads may become slippery at times
overnight. Overall snowfall of 3-5 inches in northern Aroostook
County and the potential for slick roads led to the decision to
issue a winter weather advisory for zones one and two. Snow will
linger in northern zones Saturday morning as the remnants of
the Quebec low become an inverted trough connected to the
offshore low. Further accumulation after daybreak Saturday is
not likely with lower snowfall rates and snow will gradually
change to rain as the boundary layer warms again.
The snow will mostly be a factor for areas north of Greenville
to Millinocket and Hodgdon. South of this line, snow may mix
with the rain at times late tonight, but no accumulation is
expected as lows will be 34 to 37F. Rain will fall tonight into
Saturday morning and gradually taper off Saturday afternoon. It
will be a chilly day for the entire region with highs only
reaching the upper 30s to near 40F.
.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/...
As the short term starts at 00z Mon/8PM Sun, the last remnants
of the system should be departing, with most likely areas of
rain and/or snow along the eastern border and also in the
northern/western high terrain. As the system moves away, weak
high pressure bringing calming winds could allow for some fog
across the area through Sun AM. At least patchy sunshine is
expected across the entire CWA Sun PM, and it may become mostly
sunny or clear south of the Katahdin and Moosehead region. Temps
will be near seasonal norms on Sunday.
A weak cold front then looks to approach from the NW Sun
evening, and bring some showers to the Crown of Maine. Precip
appears likely to start as rain showers, then taper to a mix or
snow showers. But all models show the precip associated with
his front drying up before sunrise Mon, with the sfc boundary
making it to the Bangor metro by 15z Mon, and off the coast
shortly thereafter. Some clouds are likely to linger behind the
front on Mon. The earlier passage of the front will lead to a
cooler day Mon up north. But for Bangor metro and Downeast, it
appears likely to be just as warm if not warmer thanks to SW`ly
winds ahead of the front, but the timing of the front will be
key to highs on Mon.
.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
Medium range models are suggesting a moderating temperature
trend by mid to late week with temperatures possibly rising to
above normal levels late next week. But before that we will be
dealing with the potential for some rain Tuesday into Wednesday
as low pressure develops along the southeast coast of the United
States and then tracks northeast and weakens through Wednesday.
This would bring the potential for some rain to the region,
especially across downeast areas. There could be a few showers
around on Thursday as an upper trough swings across. Drier
weather will return on Friday.
.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
NEAR TERM: Prevailing MVFR cigs will give way to LIFR vis in
snow north of HUL and GNR later this evening. The snow will let
up to IFR vis later in the night through Saturday morning. MVFR
returns Saturday afternoon.
For southern sites such as BGR and BHB, the trend will be
towards IFR cigs later tonight in rain and drizzle. Once these
cigs arrive, they will be very slow to depart on Saturday.
SHORT TERM: MVFR to IFR conditions will be widespread Sat night
as some low clouds are expected to persist, and areas of fog may
develop in light winds. Clouds should break up and fog will
dissipate Sun AM, allowing a return to VFR conditions, and
remain clear thru Sun evening. Low to mid-level clouds and
showers with a cold front may cause some MVFR to patchy IFR
conditions for KHUL thru KFVE Sun night, while fog is possible
for KBHB and KBGR ahead of the front Sun night and Mon AM.
NEAR TERM: 630 PM Update...we optd to go with an SCA for
outer MZs050-051 for marginal wind gusts of 25 kt and wv hts
upwards to 7 ft for a relatively narrow window between 4 and 11
am Sat morn.
Orgnl Disc...There is a chance of SCA conditions ANZ051 from
Schoodic Point to Stonington on Saturday morning as low pressure
moves south of the waters. Confidence is higher in seas above 5
feet on Saturday than wind gusts over 25 kts. Will await 00Z
guidance to get a better look and revisit the decision.
SHORT TERM: Both winds and seas are forecast to remain below SCA
criteria levels Sat night thru Mon. The biggest risk to safe
navigation offshore may be some dense fog possible Sun night
into Mon AM ahead of a cold front.
ME...Winter Weather Advisory until 11 AM EDT Saturday for MEZ001-
MARINE...Small Craft Advisory from 4 AM to 11 AM EDT Saturday for