textproduct: Caribou

WHAT HAS CHANGED

-8:28PM UPDATE...Adjusted POPs for the the next several hours to account for trends with KCBW/KGYX radar echos. An axis of showers extends from just north of Bangor into the Central Highlands northeastward to Northeast Aroostook County. Expecting no significant eastward progression of these showers since these are ahead of a slowly stalling cold front. This will become the axis for rainfall on Wednesday. Additionally this is a aviation update for the 00z TAF, see below.

KEY MESSAGES

1) Isolated thunderstorms this afternoon, mainly across northern areas, could be accompanied by strong wind gusts.

2) A widespread rainfall is expected late tonight through Wednesday night, which will continue to improve the long term drought. The ponding of water in known poor drainage areas is possible.

3) Another widespread beneficial rainfall is possible late Sunday into Monday.

DISCUSSION

KEY MESSAGE 1... Isolated thunderstorms this afternoon, mainly across northern areas, could be accompanied by strong wind gusts.

KEY MESSAGE 1 DESCRIPTION... Showers and isolated thunderstorms are expected to develop this afternoon, mainly to the north and west of the Katahdin region. Any thunderstorms may be accompanied by locally stronger wind gusts.

The Storm Prediction Center has placed northern and central Maine in a marginal risk for severe thunderstorms today. Ahead of an approaching cold front, thunderstorm are expected to develop over eastern Quebec province and move eastward into northern and central Maine. Daytime heating should contribute to steep low-level lapse rates which in combination with sufficient low-level moisture advection should favor some weak surface based instability of around 500 J/kg. The main concern from these storms is gusty winds as a result of several factors including dry low-levels as represented by an inverted v sounding and relatively strong winds at the top of the boundary layer that could easily be mixed down to the surface.

While the SPC has highlighted a 2 percent risk of tornado for portions of the area and hodographs/SRH are favorable, high LCLs and limited instability should significantly limit or completely eliminate any tornado threat. The marine layer and frontal positioning relative to the strongest daytime heating, will significantly limit the thunderstorm threat along the southeast of interstate 95.

KEY MESSAGE 2... A widespread rainfall is expected late tonight through Wednesday night, which will continue to improve the long term drought. The ponding of water in known poor drainage areas is possible.

KEY MESSAGE 2 DESCRIPTION... Low pressure will move northeast toward the region late tonight through Wednesday, and then move northeast through the Canadian Maritimes Wednesday night. A soaking rainfall can be expected across much of the area Wednesday into Wednesday night.

A mean northern stream trough continues to build into the northeastern U.S. Wednesday night and Thursday. A strong shortwave embedded in the flow is expected to move into the area Wednesday night, then exit into the southern Maritimes Thursday. At the surface, a broad area of low pressure crosses southern Maine Wednesday night, then exits into the eastern Maritimes on Thursday.

With the region still under a coupled jet structure, being in the right rear quadrant of a 120+ kt upper jet to the north/northwest and the left front quadrant of a 140+ kt upper jet to the southwest, will see enhanced lift. This will be re- enforced by a secondary maxima in the low level jet passing just offshore Wednesday night. The combined forcing form the upper and low level jet will enable moderate to possibly locally heavy rainfall across the region Wednesday night. The rain should taper off from NW to SE from late Wednesday night through Thursday morning. There is also a slight chance of elevated convection due to strong lift from the jet dynamics and some elevated instability along the coast and coastal waters Wednesday night.

Storm totals will generally be 1 to 2 inches north and west of interstate 95, with one half to one inch expected for southern areas. Most precipitation for southern areas will occur Wednesday night, while northern areas will be more spread out now through Wednesday night. Impactful flooding is not expected, but some impact to travel is possible in heavier rainfall rates later Wednesday into Wednesday night.

KEY MESSAGE 3... Another widespread beneficial rainfall is possible late Sunday into Monday.

KEY MESSAGE 3 DESCRIPTION... There is good agreement among deterministic and ensemble guidance for a broad upper level trough becoming more amplified over the Great Lakes Sunday night into Monday. This will help transport higher PWATs and Gulf moisture over the area in a similar setup to the system tonight through Wednesday night. Ensembles and particularly the AI models favor the heaviest rain over the southern half of the forecast area with a swath of 1 to 2 inches. There is some guidance that shifts the heaviest axis of QPF offshore and some that are farther north with less QPF, so some uncertainty remains. This rainfall will continue the short term rainfall surplus and help to alleviate the long term drought.

AVIATION /00Z WEDNESDAY THROUGH SUNDAY/

UPDATE 00z TAFs

Widespread aviation impacts expected due to significant LLWS, gusty surface winds, and deteriorating cats. Conditions will start VFR to low-end MVFR this evening before crashing to IFR/LIFR across all terminals on Wednesday as a frontal system brings lowering cigs and steady -RA.

KFVE, KCAR, KPQI, KHUL...S to SW winds gusting 15-20kt will slowly weaken this eve. However, a potent LLJ will maintain widespread LLWS 40-50kt through the overnight hours. -SHRA give way to steady -RA/BR between 13Z and 15Z. Accompanying this precip, cigs will rapidly lower from MVFR (020-025) down to IFR/LIFR (004-006) by mid-morning. By 20Z, a frontal boundary sagging south will cause winds to shift to the NNE at KPQI and KHUL, and become light/variable at KFVE and KCAR, but LIFR cigs and reduced vsbys will remain.

KBGR, KBHB...S winds 10-15kt with gusts to 20kt. VFR conditions this evening will lower to MVFR around 08Z, then fall to IFR by 11Z as marine stratus (CIGS 006-008) pushes inland. S/SW winds gusting 25-30kt will be persistent, especially at KBHB. This evening LLWS likely, a secondary, stronger surge of LLWS (50-55kt) will impact both KBGR and KBHB after 20Z as the next LLJ streak moves overhead. Tomorrow features -RA and BR, maintaining IFR to localized LIFR conditions through 00Z tomorrow night.

Previous Discussion... Wednesday night...MVFR/IFR. W to NW 10-15kt winds.

Thursday to Thursday night: VFR. Slight chance of MVFR cigs/vis with -SHRA at northern terminals. WNW winds 5 to 15 kts.

Friday to Friday night: VFR with a chance of afternoon -SHRA, mainly at northern airports. W winds 5 to 15 kts.

Saturday to Saturday night: Becoming MVFR with a chance of -RA. S winds around 10 kts with gusts to 20 kts.

Sunday: VFR favored (70 percent chance) with MVFR/IFR possible, especially late. SW winds 5 to 15 kts.

MARINE

Winds and seas increase this afternoon with gusts around 30 kts expected out to 25 NM offshore and wind gusts in excess of 35 kts over the offshore waters from 25 to 60 NM offshore. A Gale Warning remains in effect for 25 to 60 NM offshore waters until 3AM, otherwise Small Craft Advisories are in effect for the rest of the waters. Winds will decrease quickly late Wednesday night into Thursday morning, but seas will remain at advisory levels across the waters further into Thursday. Patchy fog and moderate to briefly heavy rain will reduce visibility over the waters Wednesday night into early Thursday morning. A thunderstorm is also possible.

Winds and seas below SCA levels are expected Thursday night through Friday. Small chance (20 percent) of an SCA Friday night into Saturday. SCA conditions are possible again Sunday into Monday (40 percent chance).

CAR WATCHES/WARNINGS/ADVISORIES

ME...None. MARINE...Small Craft Advisory until 6 AM EDT Thursday for ANZ050-051. Small Craft Advisory until 6 PM EDT Wednesday for ANZ052. Gale Warning until 3 AM EDT Wednesday for ANZ080-081.