textproduct: Caribou

WHAT HAS CHANGED

- 6 AM Update: River valley fog across the northern half of the CWA has been reported as dense in spots, with visibility occasionally dipping below one quarter mile. Patchy dense fog may last another few hours, dissipating by 9 AM.

- Increased confidence in the chance for isolated to scattered rain showers late this afternoon into this evening

- Increased confidence in the threat for gusty winds with any strong thunderstorms that develop Friday afternoon

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 this afternoon which, in addition to peak diurnal heating, could provide enough lift and instability to support isolated to scattered showers and storms.

Most CAMs guidance and subsequently the NBM suggest a start time for precip in the CWA to begin around 00z tonight within the Central Highlands. However, the NAMNEST is an outlier, bringing shower development as early as around 16z. With this forecast, the start time to PoPs was sped up by a few hours to account for this uncertainty, though it is possible if the NAMNEST solution is correct that precip could start even earlier.

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 30 kts, along with generous PWATs of 1.0 to 1.5 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 to 11 kft, 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.

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. Rain moves into the north, generally expanding southeastward during the day Sunday. PWATs generally around 1-1.50 inches based on global model outputs, 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 /09Z THURSDAY THROUGH MONDAY/

Today...VFR across all terminals, with S winds increasing to 10 to 15 kts with gusts 20 to 25 kts. Brief LLWS possible this evening.

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

Friday...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.

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.