textproduct: Caribou

WHAT HAS CHANGED

-Added potential for small hail or graupel in showers and isolated thunderstorms over the Saint John Valley Thursday afternoon. -Increasing confidence in weak coastal system Saturday night, and a slow down of the late weekend system leading to later timing now starting Monday.

KEY MESSAGES

1) Beneficial rainfall continues and will gradually shift south through tonight.

2) A weak system may impact the coast Saturday evening, while another widespread beneficial rainfall is possible Monday into Tuesday.

DISCUSSION

KEY MESSAGE 1...Beneficial rainfall continues and will gradually shift south through tonight.

KEY MESSAGE 1 DESCRIPTION... A soaking rainfall continues through tonight as low pressure develops along a cold front, eventually moving east of the area and forcing the cold front southward into the Gulf of Maine after midnight. Additional rainfall around an inch is expected for central areas, with around a half to three quarters of an inch for southern areas. Elevated instability and strong upper level jet dynamics will lead to a chance of thunderstorms for coastal and Downeast areas this evening, as well as briefly heavier rainfall rates that will cause ponding on roadways. Patchy fog observed just off the coastline today will move onshore this evening as well, leading to localized visibility reductions. The combination will make for more difficult travel than usual.

Rain will taper off quickly by around sunrise. Cold air aloft and modest surface heating from breaks in cloud cover will lead to very steep low to mid level lapse rates across northern Maine, resulting in daytime pulse shower development in a very low shear environment with only up to a few hundred joules of mixed layer CAPE. Due to the low freezing levels and cold temperatures, some small hail or graupel is possible in the stronger cells, especially over the Saint John Valley. Where ice is present in the clouds an isolated thunderstorm is also possible over these areas. Light showers or sprinkles are possible farther south, but are less likely to contain measurable precipitation.

KEY MESSAGE 2...A weak system may impact the coast Saturday evening, while another widespread beneficial rainfall is possible Monday into Tuesday.

KEY MESSAGE 2 DESCRIPTION... A series of weak shortwaves will pass through the area between Friday and Sunday, leading to a series of rain chances. Mainly showers Friday with a weak coastal system Saturday night. A 500mb trof will deepen over the Great Lakes during the latter half of the weekend. This will allow significant moisture transport from the Gulf. There is still some uncertainty in timing and track which will determine what areas receive the highest rainfall totals. At this time it appears the southern half of the area will see the highest amounts, though some guidance continues to keep the heaviest qpf offshore, mainly in the EC solutions. These rounds of rainfall will continue to help alleviate the long term drought.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

Through Thursday: MVFR/IFR tonight, becoming VFR late Downeast. MVFR persists into the morning across the north before improving to VFR, except at KFVE where intermittent MVFR ceilings may persist into the afternoon with -SHRA and possibly a thunderstorm. A thunderstorm is also possible along the coast this evening. LLWS is expected at central and southern airports through about 6z tonight.

Winds at southern terminals from KBGR southward will be S 5 to 15 kts with gusts to 25 kts through this evening. Light north winds are expected at northern terminals. Winds shift NW/WNW at remaining terminals and remain around 5 kt through Thursday.

Thursday night: VFR, with a chance of MVFR ceilings (30 percent) at northern terminals. Light W winds.

Friday...Mainly VFR, though brief MVFR possible in cigs and showers. Light W through Fri morning, then W 5-10 kt with gusts to 20 kt in the afternoon.

Friday night...VFR. SW 5kts, gusts 10 kt.

Saturday-Saturday night...MVFR with rain moving in Saturday evening. SSW 5-10kts, gusts 20kts.

Sunday...VFR/MVFR with possible IFR in rain. S 5-15kt, gusts to 20 kt.

Sunday night...MVFR with possible IFR in heavier rain. SE winds 5-10 kt gusting 15 kt.

Monday...MVFR with IFR possible in heavy rain. Winds shifting from SE to NNW at 5-10 kt, gusts to 15.

MARINE

Winds and seas will remain at Small Craft Advisory levels through tonight. Winds quickly decrease late tonight, with seas taking longer to fall below SCA levels over the outer waters by early to mid afternoon. Winds and seas below advisory levels are then expected late Thursday afternoon and Friday. Visibility will be reduced at times this evening and tonight with patchy fog and rain developing. A thunderstorm is also possible.

Below SCA conditions expected Saturday. There is a very small chance for SCA level winds Friday evening. Seas increase above 5ft Saturday evening, remain elevated into Sunday morning before diminishing. May see a return to SCA Sunday night through Monday.

CAR WATCHES/WARNINGS/ADVISORIES

ME...None. MARINE...Small Craft Advisory until 2 PM EDT Thursday for ANZ050-051. Small Craft Advisory until 8 AM EDT Thursday for ANZ052.