textproduct: Caribou

WHAT HAS CHANGED

Strong to severe storms possible Wednesday afternoon.

Excessive Heat Watch and Heat Advisories Issued for mid to late week.

Confidence increasing in the potential for strong to possibly severe convection late Thursday/Thursday night.

KEY MESSAGES

1) Very warm to hot temperatures and high humidity Wednesday through Friday make hazardous heat likely, with little reprieve each night.

2) Hard to time storms possible through the middle of the week.

3) Thunderstorms remain possible Thursday through Saturday. Storms could be on the stronger side.

DISCUSSION

KEY MESSAGE 1... Very warm to hot temperatures and high humidity Wednesday through Friday make hazardous heat likely, with little reprieve each night.

KEY MESSAGE 1 DESCRIPTION... Wednesday will see the heat begin to build as 595dm hipres over the TN Valley noses toward the area. Heights will rise to 580+ during the afternoon. With H8 temps rising to near +20C over swrn zones temps will climb to near 90 degrees for highs and coupled with dwpts in the lower 70s expecting heat index values to climb to between 95-100 degrees in the Dover-Foxcroft, Bangor, Dedham and Aurora areas.

The region remains on the northern periphery of a strong upper level high anchored across the Mid Atlantic states Thursday- Friday. This will allow for 850 temperatures of 17-21C and high temperatures from the mid 80s-mid 90s away from the immediate coast. Highs on Friday should be a few degrees lower than on Thursday due to the passage of a weak cold front.

These high temperatures coupled with dewpoints from the mid 60s to mid 70s (highest near the coast on Thursday), should yield heat indices from the low 90s to mid 100s on Thursday and from around 90 to the lower 100s (with a low chance at mid 100s) on Friday. Low temperatures Thursday night should only fall of to the mid 60s to mid 70s, so there should be little in the way of recovery at night. As a result have issued the following heat headlines for Thursday-Friday:

Extreme Heat Watch 11am-8pm Thursday: Southern Piscataquis and Penobscot and all of Hancock County for heat indices around 105F potentially a little higher in coastal Hancock.

Heat Advisory 11am-8pm Thursday: Northern Penobscot and Southeast Aroostook for heat indices in the mid-upper 90s.

Heat Advisory 11am Thursday - 8pm Friday Central Penobscot and all of Washington County for heat indices in the upper 90s to low 100s.

For now have held off on issuing an excessive heat watch on Friday as it is uncertain exactly how much temperatures and dewpoints fall off behind the cold front on Friday.

KEY MESSAGE 2...Hard to time storms possible through the middle of the week.

KEY MESSAGE 2 DESCRIPTION... Expansive upr lvl high over the TN Valley will continue to build with ridge axis nosing up into the CWA. Area will be on the northern periphery of the ridge and timing varies on when these storms may roll through. Guidance is now bringing MCS through during the overnight hours tonight. Latest models with the NAM core bringing system across the north after 09z tonight with other models diving it to our south and west. Of concern is the 14z HRRR currently bringing thru more of a broken MCS around the same time. Gut feeling is that MCV located with the system to the south of James Bay will begin to dive south late tonight into better axis of instability, missing CWA to the west. However have included likely pops with storms over portions of the Central Highlands around 06z.

Plenty of instability exists on Wednesday but with capping inversion aloft, think anything that develops should be isolated. With CAPES between 2000-3000 J/kg and 0-6km shear of 25-35kts, cannot rule out a severe storm producing damaging winds.

KEY MESSAGE 3...Thunderstorms remain possible Thursday through Saturday. Storms could be on the stronger side.

KEY MESSAGE 3 DESCRIPTION... The region remains between a strong upper level high anchored over the Mid Atlantic states and an upper level low over Labrador/Newfoundland and Southern Quebec Thursday-Friday. The upper level high begins to exit to the east Friday night and Saturday allowing for the upper level low to move towards or over the region Friday night and Saturday. This will bring the potential for Mesoscale Convective Systems mainly at night during this time frame. This will be the best chance for any strong to possibly severe storms. At this time, the timing for a cold frontal passage for Friday night or Saturday is uncertain, so while there could be storms on Saturday, the confidence in occurrence is not high. However, if the cold front were to delay until Saturday, this could be the best chance for widespread strong to possibly severe storms, if the frontal passage held off until afternoon.

AVIATION /18Z TUESDAY THROUGH SUNDAY/

Through 00z this evening...VFR all terminals. SSW wind 5-10kts.

Tonight...BHB starting off at low MVFR, immediately dropping to IFR/MVFR in stratus and fog. BGR diminishes to MVFR after 06z, dropping to IFR/LIFR toward daybreak. Aroostook terminals drop to MVFR cigs, and possibly IFR by daybreak. S winds 5-10kts.

Wednesday...IFR/MVFR in the morning will give way to VFR in the afternoon. Cannot rule out brief MVFR restrictions in any showers or storms that develop during the afternoon. SSW winds 5-10kts. gusting to 15 kts.

Wednesday night...Mainly VFR. WSW winds 5-10kts.

Thursday-Saturday: Mainly VFR, except for a chance of MVFR or lower in any fog late at night/early in the morning and a brief chance for MVFR in any thunderstorms. WSW-W winds G15-20KT possible during the day Thursday and Friday. LLWS possible Thursday night.

Saturday night-Sunday: Becoming VFR throughout Saturday night.

MARINE

Southwest winds increase to aoa 25kts from 25-60NM tonight through Wednesday night with seas also increasing over this area to 5ft. Intracoastal and waters out to 25NM will remain below small craft levels through the period. Humid airmass will keep visibilities reduced in fog tonight and again Wednesday night.

Sustained winds should be 15 kt or less (20 kt or less in the outer waters) and seas 5 ft or less Thursday-Saturday. The highest seas should be on Sunday. The outer waters could see gusts to around 25 kt on Thursday with gusts to 20kt possible on the coastal ocean waters.

Fog reducing visibilities to 1nm or less is possible Thursday- Friday.

CAR WATCHES/WARNINGS/ADVISORIES

ME...Heat Advisory from 11 AM to 8 PM EDT Thursday for MEZ005-006. Heat Advisory from 11 AM Thursday to 8 PM EDT Friday for MEZ011-017-030-032. Heat Advisory from 11 AM to 8 PM EDT Wednesday for MEZ015-016- 031. Extreme Heat Watch from Thursday morning through Thursday evening for MEZ015-016-029-031. MARINE...None.