textproduct: Caribou

WHAT HAS CHANGED

- Added gusty winds enhanced wording to thunderstorms across the southern 1/2 of the CWA tomorrow.

- Adjusted QPF on Friday to match latest hi-res CAMs to account for convection.

KEY MESSAGES

1) Isolated thunderstorms possible late this afternoon. Scattered showers regionwide tonight, with isolated thunderstorms possible.

2) Showers and thunderstorms on Friday, some of which may be strong with gusty winds and small hail.

3) System bringing rain showers and chance for thunder moves in Sunday afternoon.

DISCUSSION

KEY MESSAGE 1...Isolated thunderstorms possible late this afternoon. Scattered showers regionwide tonight, with isolated thunderstorms possible.

KEY MESSAGE 1 DESCRIPTION... A small, weak jet streak will develop aloft over the Gulf of Maine, with our forecast area sitting in the left exit region. These dynamics will support the development of some brief vort max late this afternoon which, in addition to peak diurnal heating, could provide enough lift and instability to support isolated to scattered showers and storms. Latest satellite and webcams confirm the development of a cu field across the CWA away from the coast (seabreeze and stable). A few of these cu have been getting high enough to produce some sprinkles or light showers. So far nothing is high enough to produce lightning but will give an isolated thunder threat the rest of the afternoon across the central and northeast portions of the CWA. Showers and thunderstorms across Quebec will push towards the Maine/Quebec border around or after sunset tonight. This will lead to lessening thunder chances but scattered showers are expected tonight.

KEY MESSAGE 2...Showers and thunderstorms on Friday, some of which may be strong with gusty winds and small hail.

KEY MESSAGE 2 DESCRIPTION... A stronger, more robust jet streak will develop aloft over the Gulf of Maine on Friday, with our forecast area once again sitting in the left exit region. A cold front will push through the forecast area on Friday, bringing synoptic lift strong enough for scattered to numerous showers and the development of thunderstorms by the afternoon.

Recent runs of the HREF and REFS indicate moderate shear of 25 to 35 kts, along with generous PWATs of 1.2 to 1.7 inches, with higher moisture content being within the marine layer near the coast. What seems more up in the air is the amount of CAPE, with the HREF mean indicating 1000 to 1500 J/kg of SBCAPE, while the REFS has less with around 500 to 1000 J/kg of SBCAPE. The amount of CAPE may come down to how much high cloud cover is in the area through the day on Friday, with more cloud cover potentially limiting how much the atmosphere is able to charge before storms fire. With higher CAPE values, in combination with the shear available, there could be the threat for some stronger thunderstorms that may produce gusty winds or even some small hail, though freezing levels may lift to 10-12kft, allowing for ample melting of any hail to push threats more in the direction of gusty winds. Additionally, forecast profiles indicate most of the CAPE profile could be above the saturated layer, which is another indicator that any strong to severe threat will be in the form of wind. Have added enhanced wording of gusty winds in storms along a line from Dover-Foxcroft to Baxter to Houlton and points southward to the Airline (Route 9). This area has the best chance of seeing high enough instability and best bulk shear environment.

Key Message 3...System bringing rain showers and chance for thunder moves in Sunday afternoon.

Low pressure system in Canada moves eastward this weekend, with trough axis moving through Sunday afternoon. Associated cold front moves through the state Sunday, funneling in some cooler air behind it. Expecting some showers to move into the north, generally expanding southeastward during the day Sunday. Confidence on how far south these showers get during the day is low but the highest probabilities across the north. PWATs generally around 1-1.50 inches, so currently not anticipating any rain totals over one quarter inch. There will be a few hundred joules of CAPE, 40-50 kts of effective shear, and some decent low level lapse rates. Combined, there is enough instability that a thunderstorm is not out of the question. Heating ahead of the cold front in eastern Maine could aid in initiating some convection along the boundary, but not anticipating severe storms at this time.

AVIATION /18Z THURSDAY THROUGH TUESDAY/

Tonight...Gradual lowering of cigs to IFR, with scattered showers and thunderstorms possible overnight. S winds 5 to 10 kts.

Friday...AM low cigs/vsby from BR/FG will becoming VFR. Brief MVFR/IFR in scattered showers and storms. S winds 5 to 10 kts shifting W to NW behind a cold front in the afternoon. Gusty winds possible with strong thunderstorms.

Friday night...Improving to VFR after midnight, as rain showers move eastward. Light NW winds.

Saturday...VFR. W/NW winds 5-10kt.

Saturday night...VFR. Chance for valley fog, which would reduce visibility. Light SW winds.

Sunday... MVFR/IFR in afternoon showers and thunderstorms at northern terminals, and potential MVFR at southern terminals. SW winds 5 to 10 kts.

Sunday night...MVFR with a chance of rain showers. Northwest/west winds 5 to 10 knots.

Monday...VFR. Variable winds 5 to 10 knots.

Tuesday...VFR/MVFR with PM VCSH/-SHRA possible. Winds E-SE 5-10kt.

MARINE

Winds/seas below SCA levels this weekend through early next week. Seas 2 to 4 ft. Fog possible Friday night and Saturday night. Slight chance for rain showers Sunday night. Winds become NW Friday night, shifting SW Saturday night into Sunday.

CAR WATCHES/WARNINGS/ADVISORIES

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