textproduct: Caribou

WHAT HAS CHANGED

Refined timing/coverage for convection through Sunday.

Updated aviation section for 06z TAFs.

KEY MESSAGES

1) Hit or miss showers and thunderstorms through the weekend. Some may be severe, with the best chance of this on Sunday. Any stronger storm could produce locally heavy rainfall, which could cause localized flooding.

2) Scattered rain showers and isolated thunderstorms early next week.

DISCUSSION

KEY MESSAGE 1... Hit or miss showers and thunderstorms through the weekend. Some may be severe, with the best chance of this on Sunday. Any stronger storm could produce locally heavy rainfall, which could cause localized flooding.

KEY MESSAGE 1 DESCRIPTION... A series of weak low-mid level shortwaves pass over the top of an northeast extension of the Bermuda High, and gradually weaken it through tonight. This allows for a stronger northern stream shortwave trough to approach later tonight, then cross the area on Sunday. At the surface, a series of weak troughs of low pressure cross the region through tonight. A cold front approaches Sunday morning then moves through western Maine Sunday afternoon.

There will be two main focusing mechanisms for convection today, the passing troughs of low pressure and the sea breeze front. When those two intersect, you will see the highest likelihood for precipitation and most likely the strongest localized storms. This places the best threat for more widespread showers and storms over Downeast Maine and the Bangor Region.

In general you should see around 750-1500 J/kg of CAPE along with with 10-20kt of bulk shear. The low values of shear should keep the vast majority, if not all storms today below severe limits. With storm motion of 5-15Kt and precipitable waters mainly around 1.5-1.75 inches - there is the risk for locally heavy rainfall over a concentrated area. This could result in localized flooding and is the main threat for today.

On Sunday, storm motion increases to around 20 kt, so flooding should be a more limited threat. However, CAPE increases to 1000-2000 J/kg and shear increases to 20-30kt. This increases the risk of strong to possibly severe thunderstorms. Accordingly, SPC has most of Northern and Eastern Maine in a Marginal (level 1 of 5) risk for severe thunderstorms, with the main threat localized damaging wind gusts.

KEY MESSAGE 2...Scattered rain showers and isolated thunderstorms early next week.

KEY MESSAGE 2 DESCRIPTION... Rounds of shortwaves move through the north early next week, bringing a chance for rain showers and some thunderstorms. Thunder possible, mainly in areas north of Bangor, Monday night into Tuesday. Environment does not look too impressive for strong thunderstorms with limited instability, so could just be some brief isolated storms below severe criteria.

AVIATION /06Z SATURDAY THROUGH WEDNESDAY/

Other than possibly some MVFR/IFR conditions in river fog early this morning, northern terminals should see VFR conditions through the TAF period with one possible exception. That is if an isolated thunderstorm goes directly over a terminal, then a period of MVFR to IFR conditions (if prolonged heavy rainfall) is possible. At this time, the chance of a thunderstorm at any given northern terminal is too low to reflect in the TAFs.

Baring the same issue with isolated to scattered thunderstorms at northern terminals at KBGR from late this morning to early evening, it should be VFR through then. Then MVFR then IFR conditions should develop through the evening.

At KBHB, a period of MVFR to IFR conditions is possible early this morning. A steady period of MVFR conditions should develop by this afternoon, with any stronger convection once again bringing with it the chance for IFR conditions as it passes. There is a better chance for persistent IFR conditions at KBHB this evening. At this time, the confidence in thunder at both KBGR and KBHB is too low to reflect explicitly in the TAFs.

Outside of stronger convection, and maybe a brief period with the sea breeze this afternoon at KBGR, winds should be light and variable through the TAF period.

Late tonight: VFR, except for MVFR or lower possible in any patchy fog/low stratus.

Sunday: VFR, except MVFR or lower possible in any stronger shower or thunderstorm if it passes over a terminal. W winds G15 KT possible Sunday afternoon.

Sunday night: VFR. Winds from the W at 5 kt.

Monday: MVFR possible in any afternoon storms, otherwise VFR. SW/W winds, gusting to 15-20 kt possible.

Monday night-Tuesday: MVFR possible in any showers Monday night and any storms Tuesday afternoon, otherwise VFR. Light winds overnight, becoming W 5-10 kt Tuesday afternoon.

Tuesday night-Wednesday: VFR overnight. MVFR possible in any showers Wednesday afternoon. Winds W at 5-10 kt.

MARINE

Winds on the waters out to 60 nm should be 15 kt or less and seas 3 ft or less through Wednesday.

Patchy fog reducing visibility to 1nm or less is possible through this morning.

Isolated showers and thunderstorms are possible Sunday afternoon and evening. There is also the potential for some showers on Monday into Tuesday.

CAR WATCHES/WARNINGS/ADVISORIES

ME...None. MARINE...None.