textproduct: Caribou

WHAT HAS CHANGED

- 5:52AM UPDATE...Watching Canadian Doppler Radar data as a large bow echo is pushing SE through Quebec towards the St. Lawrence Valley. This complex is producing excessive cloud to ground lightning and maintaining strength. This bow has been following an area of elevated instability and expected to move towards Northern Somerset, Moosehead Region over the next 2-3 hours. The bow echo has drifted slightly more east of southeast as instability advects eastward. In addition a large precip shield exists east of the bow and therefore have increased POPs this morning and increased thunderstorm chances. Will continue to monitor this threat.

Previous Changes... - A Heat Advisory was added for the Bangor region, as well as the Upper Penobscot Valley and portions of the Central Highlands on this afternoon.

KEY MESSAGES

1) Severe thunderstorms are possible late today into tonight areawide. The greatest chance for severe winds, hail, and isolated tornadoes occurs around sunset through midnight.

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

3) Cooler Wednesday through the weekend, with a chance for showers and storms mainly Wednesday and Thursday.

DISCUSSION

KEY MESSAGE 1...Severe thunderstorms are possible late today into tonight areawide. The greatest chance for severe winds, hail, and isolated tornadoes occurs around sunset through midnight.

KEY MESSAGE 1 DESCRIPTION... The Storm Prediction Center continues their enhanced risk (level 3 of 5) for severe thunderstorm development across our forecast area. This is the first time an enhanced risk has been issued for our CWA. Ingredients are favorable for severe thunderstorm development late Tuesday into Tuesday night.

The first feature to watch will be a decaying MCS that has developed over Quebec. While rather strong now, the expectation is that this feature will weaken markedly as it drifts into northern Maine later this morning. However, what it will do is bring substantial cloud cover and stable air that will last longer into the morning.

The key with the severe potential later this afternoon/evening will be how the atmosphere recovers after the morning showers/clouds. There is reasonably good agreement that we will have sufficient warm/moist flow to scour out enough clouds to destabilize this afternoon. Most guidance gives us around 2000+ J/kg of CAPE by the mid-late afternoon timeframe ahead of the next system. Additionally, a tightening pressure gradient surrounding the low pressure system passing well to the north and a ridge of high pressure approaching from the west will deliver west to northwest winds aloft increasing in strength through time, which could generate 0-6 km shear of at least 40 kts. Especially for convection in the Central Highlands down through the Bangor region, these winds aloft may also be perpendicular to any convective lines, creating bowing segments and generating supercell structures. This amount of shear and instability is also favorable for a few discrete supercell structures.

Damaging winds in excess of 60 mph will be the primary threat with storms on Tuesday given 40-50 knots of wind shear and sufficient low-level lapse rates to mix that wind down in any semi-organized storms. Any bowing segments could have the potential for some 70+ mph gusts should they become well- organized especially. With substantial shear of 40 to 50 kts, and strong instability, large hail 1 to 2 inches in size remains possible in the strongest storms, especially the further southwest you are. Finally, several runs from a variety of convective allowing models have indicated 0-1 km SRH values exceeding 200 m2/s2, 0-1 km shear over 30 kts, and favorably low LCL heights. These values indicate strong helicity that could be supportive of tornadic development, particularly within any well-developed supercells in the area. The tornado risk is limited, but present enough to warrant extra caution.

With the greatest chance for severe storms occurring after sunset, lack of ambient light will present a threat of its own, as incoming storms may not be as visible. Stay weather aware and have a way to receive critical warning information overnight.

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

KEY MESSAGE 2 DESCRIPTION... Southwest winds will continue to advect warm moist air into the forecast area tonight through Tuesday and into Tuesday night. Tuesday will be the hottest day of the week, with max temperatures lifting into the mid 80s to upper 80s in the north and into the lower 90s in the Bangor and Downeast regions. Combined with increased relative humidity, apparent temperatures will run into the mid to upper 90s for the Central Highlands down through the Bangor region. A Heat Advisory has been issued for these areas as a result through Tuesday evening.

KEY MESSAGE 3...Cooler Wednesday through the weekend, with a chance for showers and storms mainly Wednesday and Thursday.

KEY MESSAGE 3 DESCRIPTION... Cooler weather pattern setting up mid to late week, with a deep, cool upper level low pressure centered north of the area. We could see some primarily afternoon showers and storms Wednesday and Thursday, with the better chance being Thursday. However, we don't anticipate severe storms. Can't rule out some small hail Thursday though with the cold air aloft. More uncertainty from Friday onward, but tentatively looking fairly dry. High temperatures will be fairly close to average, with low temperatures a bit cooler than average. The coolest day will likely be Friday, when highs may struggle to reach 70 in the north. Some 40s at night in cooler northern valleys are likely from Friday night through Saturday night.

AVIATION /09Z TUESDAY THROUGH SATURDAY/

Rest of Tonight...Mainly VFR. TEMPO for BR/FG at several terms possible. Confidence is low to moderate due to weak stirring winds. Winds light and variable. VCSH/-SHRA possible by 12z but confidence is low.

Tuesday...Variable conditions with showers and thunderstorms. Afternoon thunderstorms could produce strong wind gusts of at least 40 to 50 kts along with large hail. Otherwise, VFR/MVFR. South/southwest winds 10 to 15 knots with gusts up to around 20 knots.

Tuesday night...Variable conditions with showers and thunderstorms. Thunderstorms could produce strong wind gusts of at least 40 to 50 kts along with large hail through early morning. Southwest winds 10 to 15 knots, becoming west/northwest.

Wednesday to Saturday: Mainly VFR with possible MVFR at times mainly in the north due to either cigs or afternoon showers/storms. Better chance for afternoon storms is Wednesday and Thursday. in afternoon showers and TS. W winds 10-15 kts with gusts up to 25 kts.

MARINE

SW winds will increase overnight tonight, with gusts increasing to 20 to 25 kts and seas gradually responding to 3 to 5 ft through the night. Cold sea surface temps will help keep boundary layer stable and limit wind gusts overnight. Swell will continue to increase through the day on Tuesday, and seas will lift to 4 to 8 ft across all waters by Tuesday night. Gusts will remain marginal for SCA at around 20 to 25 kts. Strong thunderstorms may move over the waters late Tuesday night, which could bring localized gusts over 40 kts possible.

W winds generally 10-20 kts Wednesday through Saturday with minimal fog threat. Seas 2-5 ft Wed to Sat, generally on the lower side of the range toward Saturday.

CAR WATCHES/WARNINGS/ADVISORIES

ME...Heat Advisory from 11 AM this morning to 8 PM EDT this evening for MEZ011-015-031. MARINE...Small Craft Advisory until 6 AM EDT Wednesday for ANZ050-051. Small Craft Advisory until 6 AM EDT Wednesday for ANZ052.