textproduct: Caribou

WHAT HAS CHANGED

- 10:13PM UPDATE...Adjusted POPs across Northern Maine with isolated to scattered showers developing. Monitoring a line of Thunderstorms crossing the St. Lawrence River in Quebec that will track ESE into Western New Brunswick and just north of the St. John Valley potentially skimming past the valley. Canadian Doppler Radar (CASVD) has a good look at this activity and there is a tail developing which may bring showers and perhaps a strike or two of lightning so made adjustments for the Thunderstorm activity in the grids. Potential arrival time for the Fort Kent to Madawaska region is between 11PM and Midnight. No other major changes.

KEY MESSAGES

1) Warm to very warm with a chance for thunderstorms Tuesday and Wednesday afternoon. A few stronger storms are possible.

2) Below average temperatures are expected Thursday and Thursday Night. Near freezing temperatures are possible early Friday morning across the north, which may require actions to protect vulnerable plants.

DISCUSSION

KEY MESSAGE 1... Warm to very warm with a chance for thunderstorms Tuesday and Wednesday afternoon. A few stronger storms are possible.

KEY MESSAGE 1 DESCRIPTION... A little shortwave ahead of a larger trough will drape a warm front over the area that moves north through the day Tuesday. This warm front will bring warm temperatures and instability. Some cloud cover could prevent increased daytime heating which could limit convection. Thunderstorm chances are highest in central and south Maine. Storms may contain gusty winds and potentially small hail and lightning. The risk of a tornado cannot be ruled out.

The models have significantly slowed down the progression of the cold front through the region, with it now progged to move through mainly on Wednesday night. This is due to the front being almost parallel to the winds aloft as well as subsidence under the ridging exiting to the east on Wednesday. As a result, Wednesday likely will be the warmest day of the week across most of eastern and south central Maine. Because of this, models are now keying on convection firing mainly along/just north of the sea breeze front over Downeast Maine and into the Bangor region. With around 1000 J/kg of CAPE, 40-50kt of Bulk Shear, could see strong to locally severe storms across this region, with the main threat being strong gusty winds and hail. The tornado threat remains non- zero, with Energy Helicity Index of 0.5 to 1, 0-3km SRH 100-175 m2/s2 and 0-1km SRH 50-100 m2/s2. However the threat is much lower than on Tuesday.

Also of note on Wednesday is that the winds should be rather gusty with gusts of 30-35 mph, with some peak gusts to around 40 mph across the Saint John Valley.

Highs on Wednesday should run 15-20 degrees above normal. With Dewpoints peaking out around 60, and falling off in the afternoon, this should limit apparent temperatures to the upper 70s to lower 80s across most of eastern and central Maine, with low-mid 70s across the North Woods.

KEY MESSAGE 2... Below average temperatures are expected Thursday and Thursday Night. Near freezing temperatures are possible early Friday morning across the north, which may require actions to protect vulnerable plants.

KEY MESSAGE 2 DESCRIPTION... NW flow in the low levels advects in a much cooler air mass into the region Thursday into Thursday night, as Canadian High pressure builds in from the northwest and west. This high then builds over the area through Friday night. The result will be lows running 5-10 degrees below normal both nights. This should result in frost mainly across Northern Maine. Zones 2, 5, 6, 10, 11, 31 and 32 get added to the frost freeze program on May 21, so a frost advisory could be needed for at least part of that area on both nights if current forecast trends hold.

AVIATION /02Z TUESDAY THROUGH SATURDAY/

00z TAF UPDATE...

Tonight, conditions are starting off predominantly VFR across all terms this eve. The primary concern tonight will be widespread LLWS developing at all TAF sites between 03z to 05z and persisting through roughly 10z-12z before easing.

Overnight... KBGR/KBHB: KBHB will see a rapid deterioration to IFR/LIFR due to FG and low stratus after 06z, with visibilities dropping to 1/4SM in FG. KBGR is also expected to see a brief window of IFR conditions in patchy fog and low stratus between 08z and 11z.

KFVE/KCAR/KPQI/KHUL: MVFR cigs will begin working into KFVE by 03z and VCSH, low confidence isolated TStorm threat (PROB30 03z-07z). KCAR, KPQI, and KHUL should hold onto VFR cigs.

Tuesday AM, marine fog Downeast will lift between 11z-13z, returning KBGR and KBHB to VFR. Conversely, northern terminals will see cigs steadily lower to MVFR, with KFVE deteriorating further to IFR cigs through the late morning and afternoon.

By Tuesday afternoon (after 18z), an approaching boundary will trigger scattered to numerous showers and thunderstorms across the region. PROB30 groups have been included for -TSRA at KFVE, KCAR, KPQI, KHUL, and KBGR. Brief IFR vsby (2SM) and erratic, gusty winds can be expected in and near any heavier convective elements. KBHB is expected to remain south of the main convective threat, carrying only VCSH.

Surface winds will generally remain light (under 10 kts) out of the S/SW overnight and into Tuesday AM. Winds will become somewhat variable by Tuesday afternoon, eventually shifting to the W/NW late in the TAF period (around 23z).

Previous Discussion... Tuesday night...MVFR possible at northern terminals, IFR possible at KFVE. VFR elsewhere. Some rain showers at northern terminals possible. WSW winds 5 to 10 kt, ramping up through the night, with gusts to 20 kt.

Wednesday: Low chance of MVFR early at northern terminals, otherwise VFR. Tempo MVFR/IFR is possible at southern terminals in any strong convection. W-WNW winds G25-30KT likely with a chance of gusts to 35KT at far northern terminals.

Wednesday night-Saturday: VFR. NW winds G20-30KT possible during the day Thursday and Friday.

MARINE

Winds stay below SCA criteria Monday night, with some gusts of 25 kt on outer waters Tuesday out of the southwest. Some fog is possible Monday night. Rain showers and some thunderstorms are possible on Tuesday.

Marginal Small Craft Advisory seas around 4 to 6 feet are possible over the coastal ocean waters Tuesday night. Wave heights to around 5 to 7 feet along with gusts up to 25 kt are possible across the outer waters.

Small Craft conditions are likely across the coastal waters Wednesday through Thursday, with gusts of 25-30kt and seas of 4-6 ft over the outer waters during this time frame as well. From Thursday night through Saturday, sub-SCA conditions are predicted for the coastal waters and winds less than 25 kt and seas of 5 ft or less are forecast for the outer waters.

There is a small chance for some strong thunderstorms over the coastal waters Wednesday afternoon and early Wednesday evening.

Sea surface temperatures remain very cold, but are beginning to moderate into the mid 40s.

CAR WATCHES/WARNINGS/ADVISORIES

ME...Air Quality Alert from 10 AM to 10 PM EDT Tuesday for MEZ029- 030. MARINE...None.