Severe Thunderstorm Warning 9, NWS Caribou, ME

Area Forecast Discussion
National Weather Service Caribou ME
152 PM EDT Thu Jun 18 2026

.WHAT HAS CHANGED...
- Increased rainfall totals across the Central Highlands with
  increasing convection likely over next few hours.

- Increased wind gusts this afternoon ahead of the occluded
  front.

- Increased seas into Friday above SCA criteria over the Coastal
  Waters.

&&

.KEY MESSAGES...
1) Widespread moderate to heavy rain into tonight, with
localized flooding possible. Gusty winds are also expected,
especially within any strong showers and storms.

2) Showers Friday into the weekend along with a
slight chance of afternoon thunderstorms Sunday.

&&

.DISCUSSION...
KEY MESSAGE 1...Widespread moderate to heavy rain into tonight,
with localized flooding possible. Gusty winds are also
expected, especially within any strong showers and storms.

KEY MESSAGE 1 DESCRIPTION...
A compact strong low pressure system in Southern Quebec is
kicking off rain across much of the area this afternoon.
Elevated instability and higher PWATs are working into GYX CWA
heading for portions of CAR CWA this afternoon. The key message
remains on track for the potential of excessive rainfall. The
greatest concern for isolated localized flash flooding will be
across the Central Highlands.

The moisture for this system will be well supported,
with model agreement that PWATs will approach 1.1 to 1.2 inches
in the north and 1.3 to 1.4 inches Downeast through most of the
event. For the northern half of the CWA, 1.2 inches is around
the 90th percentile for KCAR PWAT climatology, which is 1.25
inches. For Downeast, 1.4 is around the 90th percentile for KGYX
PWAT climatology, which is 1.44 inches. Exceedance of the
climatological 90th percentile for PWATs is one factor to
consider for the potential for efficient, heavy rainfall, and
for this ingredient the forecast is considered marginal.

Long, skinny CAPE profiles are another ingredient that would
favor flooding rain potential. That said, across the Downeast
region, the marine layer presents a deep low level inversion
that inhibits CAPE development, and there is little instability
at all to work with. (There is, however, no shortage of shear,
with 0-6 km bulk shear approaching 60 kts)

The 50 kt LLJ will likely mix some momentum to the surface
within moderate to heavy rainfall, leading to gusty winds which
could occasionally reach 30 to 35 mph in strength, especially
across higher terrain.

KEY MESSAGE 2...Showers Friday into the weekend along with a
slight chance of afternoon thunderstorms Sunday.

KEY MESSAGE 2 DESCRIPTION...
An upper level low will slowly cross the region Friday into the
weekend while a series of disturbances move around the low. Cold
air aloft will help increase diurnal instability. Unsettled
conditions with a chance of showers will occur Friday through the
weekend, with a slight chance of afternoon thunderstorms on
Sunday. The better shower/thunderstorm chances should occur
across northern areas. Another system approaches Monday night.

&&

.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
Today - Tonight...VFR conditions will decrease towards MVFR/IFR
through as rain showers increase and cigs decrease. Gusty SE
winds 10 to 15 kts with gusts 25 to 35 kts through this
afternoon. Winds begin to decrease tonight, though 45 to 50 kts
LLWS may enter in late as an inversion develops.

Friday...KBGR/KBHB and Downeast terminals improve to VFR through
the day, while northern terminal cigs remain MVFR/IFR with
lingering rain showers. SW winds slowly shifting W at 10 to 15
kts with gusts 20 to 25 kts.

Friday night...VFR/MVFR. Showers likely north. Southwest/west
winds 10 to 15 knots.

Saturday...VFR/MVFR with a chance of showers. West/southwest winds
10 to 15 knots with gusts up to around 20 knots, becoming
west/northwest.

Saturday night...VFR/MVFR. A slight chance of showers,
mostly north. Some patchy fog is possible. Northwest winds 10
to 15 knots, becoming north/northwest 5 to 10 knots.

Sunday...VFR/MVFR with a chance of showers. Slight chance of an
afternoon thunderstorm. West/northwest winds 5 to 10 knots,
becoming variable.

Sunday night...VFR. Winds light and variable.

Monday...MVFR/IFR in heavier showers, with a chance of
thunderstorms. South winds 5-10 knots, becoming northeast 5-10
knots.

&&

.MARINE...
A Gale Warning is in effect until 10PM for all the Waters
25nm-60nm. SE winds 20-30kt with gusts up to 40kt and seas
6-9ft. A Gale Warning in effect for the Coastal Waters from
Schoodic Point to Stonington out 25nm. SE winds 15-25kt with
gusts up to 35kt and seas 6-9ft. A Small Craft Advisory for the
Intra-Coastal Waters and the Coastal Waters from Schoodic Point
to Eastport/Hague Line out 25nm. South winds 15-25kt with gusts
up to 30kt, seas 6-9ft for Coastal Waters and 3-5ft for Intra-
Coastal Waters. Winds relax to 25kt or less on the Coastal
Waters Friday AM and Friday Eve on the outer waters. Seas remain
in SCA criteria on Friday on the Coastal Waters with winds/waves
below SCA on Intra-Coastal Waters on Friday. 4-5ft seas on
Coastal Waters on Saturday and winds/seas below SCA on Sun-Mon.

&&

.CAR WATCHES/WARNINGS/ADVISORIES...
ME...None.
MARINE...Small Craft Advisory until 8 AM EDT Friday for ANZ050-052.
     Gale Warning until 10 PM EDT this evening for ANZ051-080-081.

&&

DISCUSSION...AES/JS/JMM
AVIATION...JS