textproduct: Caribou

WHAT HAS CHANGED

Risk for severe weather on Tuesday increased to Enhanced (level 3 of 5) across Northern Somerset, most of Piscataquis and Northern Penobscot, and mainly Northern Aroostook counties. Threat level remains the same elsewhere.

Very Warm to Hot Conditions now look limited to Tuesday

KEY MESSAGES

1) Severe thunderstorms are possible over north/central areas Tuesday, continuing into Tuesday evening areawide.

2) Very warm to hot temperatures Tuesday. The highest heat indices of the period should be Tuesday and over southern Piscatiquis County and the Bangor region, with heat indices in the mid 90s possible.

DISCUSSION

KEY MESSAGE 1...Severe thunderstorms are possible over north/central areas Tuesday, continuing into Tuesday evening areawide.

KEY MESSAGE 1 DESCRIPTION... Threat level for severe thunderstorms has increased to Enhanced (level 3 of 5) across Northern Somerset, most of Piscataquis and Northern Penobscot, and mainly Northern Aroostook counties for Tuesday. The remainder of the area remains in a Slight Risk (level 2 of 5) except for coastal Downeast which remains in a Marginal Risk (level 1 of 5).

Multiple northern stream shortwaves will cross the region, bringing multiple waves of convection with them. The first push should be Tuesday morning, most likely across the north. The second wave comes Tuesday afternoon/early Tuesday evening, at this time it appears it should be focused from Southern portions of the Northwoods, into the Central Highlands and possibly the Bangor Region into Downeast Maine. Models disagree on how quickly this second wave of convection pushes to the southeast.

Unfortunately, the timing/placement of individual shortwaves is not a model strength, so the timing/location of any convection is subject to change this far out.

At the surface this allows for the pooling of heat and moisture ahead of a strong cold front which should cross the region Tuesday night.

CAPE should rapidly build on Tuesday reaching 1500-2500 J/kg by early Tuesday afternoon, then gradually diminish in the evening, remaining highest across Downeast Maine. As the CAPE diminishes, a 110+ upper level jet builds in by Tuesday evening.

Shear during the day should be around 40-50 kt, which is around 10 kt lower than previously predicted. Given the high values of CAPE, this is more than sufficient to produce strong to severe thunderstorms across the region.

The main threat is for strong damaging wind gusts up to around 70 mph. There is some potential for a long lived complex of thunderstorms to roll through the at least portions of the area with the second wave of storms. If this happens, then there is the potential for wind gusts to hurricane force. In addition to the wind threat, there is also a chance for large hail up to around 2 inches in diameter, and an isolated tornado cannot be ruled out. The chance for the latter is increased if any discrete cells form out ahead of main areas of convection.

If the environment has not been worked over with the daytime storms, then strong to severe storms could last through Tuesday night.

KEY MESSAGE 2... Very warm to hot temperatures Tuesday. The highest heat indices of the period should be Tuesday and over southern Piscatiquis County and the Bangor region, with heat indices in the mid 90s possible.

KEY MESSAGE 2 DESCRIPTION... Northern stream ridging builds in from the Plains on Tuesday, allowing for very warm to hot air to build into the region, with 850mb temperatures increasing to 16-20C and 925mb temperatures to 22-26C this supports highs from the mid 80s to lower 90s away from the coast. Coupled with dewpoints in the mid to upper 60s, this should yield heat indices from the upper 80s to the middle 90s. At this time the highest heat indices should be in southern portions of both Piscataquis and Penobscot counties.

Given the uncertainty in the timing and placement of any convection, its impacts on the temperature and the dewpoint at any location is uncertain. Given the potential for a round of convection over the exact area the highest temperatures/heat indices are expected late in the day, it gives sufficient uncertainty not to issue any heat headlines for Tuesday at this time.

For Wednesday, temperatures should be much cooler than the previous days. The exiting cold front will switch winds to a NW flow, thus ushering in a cooler airmass. Expected temps in the upper 70s for the north and low 80s for the south. Dewpoints should be slightly less, making for a less muggy day.

AVIATION /12Z MONDAY THROUGH FRIDAY/

High confidence in VFR through the TAF period at southern terminals. For northern terminals, there is a chance for MVFR to develop tonight, with also a chance for IFR ceilings at KFVE.

Light and variable winds, become SW-WSW at around/just under 10KT by mid morning at inland terminals. Some brief gusts to around 15-20KT are possible this afternoon, but confidence in that occurring is too low to reflect in the TAFs at this time. For coastal terminals (including KBGR and KBHB) a strong sea breeze will develop by early afternoon with winds 10-15G20KT. Gusts should abate at coastal terminals by early evening. Winds should become light and variable throughout late in the evening/by around midnight.

Late tonight: MVFR or lower possible at northern terminals, VFR at southern terminals. LLWS possible.

Tuesday: MVFR or lower likely in any strong to severe convection, otherwise VFR. WSW winds G15-20KT possible.

Tuesday night: MVFR/IFR in showers and possible strong to severe TS, especially for BGR/BHB. W winds 5-10 kts.

Wednesday: Mainly VFR with possible MVFR/IFR north in afternoon showers and TS. W winds 10-15 kts with gust up to 25 kts.

Wednesday night-Friday: Mainly VFR. Possible MVFR north. W/NW winds 10-15 kts.

MARINE

Winds 10 kt or less and seas 3ft or less on all waters this morning. Winds increase on the coastal ocean and outer waters, with gusts of 25-30 kt by late this afternoon and continuing through Tuesday night. This should build seas to 4-7 ft. The intra- coastal waters also should also see gusts to 25 kt Tuesday and Tuesday night. As a result, have hoisted SCAs for the coastal ocean waters from 20Z today - 10Z Wednesday and from 10Z Tuesday - 10Z Wednesday on the intra-coastal waters. There is also a low chance for gusts to gale force on the outer waters from Tuesday into Tuesday evening.

In addition, there is the risk for strong to possibly severe thunderstorms over the waters Tuesday evening.

Winds decrease to 15 kts or less late Tuesday night and remain fairly light through Friday. Seas are a bit slower to come down, with seas down to 2-4 ft by late Wednesday, with these lower seas continuing into Friday.

CAR WATCHES/WARNINGS/ADVISORIES

ME...None. MARINE...Small Craft Advisory from 4 PM this afternoon to 6 AM EDT Wednesday for ANZ050-051. Small Craft Advisory from 6 AM Tuesday to 6 AM EDT Wednesday for ANZ052.