textproduct: Caribou

WHAT HAS CHANGED

-6 AM Update to the Aviation section below with the 12z TAFs

-Low confidence in thunderstorms on Sunday. Higher confidence for some rain showers.

KEY MESSAGES

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

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

DISCUSSION

KEY MESSAGE 1...Showers and thunderstorms today, some of which may be strong with gusty winds and small hail.

KEY MESSAGE 1 DESCRIPTION...

A strong jet streak will develop aloft over the Gulf of Maine today, with the forecast area sitting in the left exit region. A cold front will push through the forecast area this afternoon, bringing synoptic lift strong enough for scattered to numerous showers and the development of thunderstorms at the time of peak diurnal heating.

Recent runs of the HREF and REFS indicate moderate shear of 25 to 30 kts, along with generous PWATs of 1.2 to 1.6 inches, with higher moisture content being within the marine layer near the coast. Finally, SBCAPE values of 1000 to 1500 J/kg. Parameters appear to be most favorable for stronger thunderstorm development within the Interior Downeast region, which aligns with the timing of the front with respect to peak diurnal heating, with recent CAMs guidance bringing the boundary into the Downeast region through the mid afternoon hours. 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 2...System bringing rain showers and chance for thunder moves in Sunday afternoon.

KEY MESSAGE 2 DESCRIPTION... Low pressure system in Canada moves eastward this weekend, with trough axis moving through Sunday afternoon. Cold front moves through the state Sunday evening, 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 and regional model outputs. Global models are keeping precipitation chances pretty modest, around 14 of an inch, while regional models are hinting at some more convective storms developing Sunday evening, bumping up rain totals to one half to three quarters of an inch in isolated locations, predominantly in the north and southeast. Instability parameters include few hundred joules of CAPE, 40-50 kts of effective shear, and some decent low level lapse rates, indicating 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. Confidence is still low for any severe thunderstorms to develop, given the model disagreement, but regional models are hinting at better instability parameters than earlier indicated.

AVIATION /09Z FRIDAY THROUGH TUESDAY/

Today...VFR/MVFR, becoming MVFR/IFR in showers and storms that move from west to east this afternoon. S winds 5 to 10 kts shifting W to NW behind a cold front in the afternoon. Gusty winds possible with any stronger thunderstorms.

Tonight...Improving to VFR by midnight as skies clear. Light NW winds around 5 kts.

Saturday...VFR under SKC. W winds 5 to 10 kts.

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 KBGR. MVFR in showers possible at KBHB. W/SW winds 5 to 10 kts.

Sunday night...MVFR with a chance of rain showers. NW winds at 5 to 10 knots.

Monday...VFR. NW winds at 5 to 10 knots.

Monday night...VFR. Light and variable winds.

Tuesday...VFR. Winds E/SE at 5-10kt.

MARINE

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

CAR WATCHES/WARNINGS/ADVISORIES

ME...Dense Fog Advisory until 9 AM EDT this morning for MEZ017-029- 030. MARINE...None.