Possible Severe Weather Outbreak Update One

000

FXUS61 KCAR 271259

AFDCAR

Area Forecast Discussion

National Weather Service Caribou ME

859 AM EDT Thu Jul 27 2023

.SYNOPSIS...

Low pressure will cross the region this afternoon through this

evening. Another cold front will move through the area on

Saturday, with high pressure returning on Sunday. A weak cold

front will cross the area on Monday.

&&

.NEAR TERM /THROUGH TONIGHT/...

900AM Update...Radar scans show the leading edge of the

scattered showers have moved into the Central Highlands slightly

faster than previously forecast. Adjusted the weather forecast

to show this. Heavy rain is still the major concern for this

afternoon in Downeast. Convective activity has slightly

decreased but cannot rule out thunderstorms in the south.

Previous Discussion:

North:

A stationary front stalled across southern Quebec into the St.

John Valley continues to provide a source for showers and

isolated thunderstorms across the northern portion of our

forecast area early this morning. This rainfall will act to

stabilize the area for the day today, with continued rain

showers expected through the day but the threat for thunder

becoming more limited as the day goes on.

Central Highlands through the Downeast coast:

The main story will be that of an MCS propagating northeastward

into our region, bringing another round of thunderstorms and

heavy rainfall. The MCS is currently positioned over the eastern

Great Lakes as seen on current IR satellite imagery, and will

accelerate to the northeast through the day today, reaching our

forecast area by this afternoon.

For convective ingredients, CAPE will be marginal by the time

the MCS arrives with just shy of 500 J/kg at best anticipated

for the Bangor area, and decreasing north and east from there.

The CAPE profile will be generally warm due to the above average

temperatures this week, and the CAPE profile will sit warmer

than the hail growth zone, limiting the potential for hail. Onshore

flow ahead of the MCS will also act to strengthen a marine

layer along the Coastal Downeast region which will further cap

the thunderstorm development potential in this area. That said,

NAM and HRRR are also in agreement that 0 to 6 km Bulk Shear

will sit somewhere between 40 to 60 kts, which is much higher

than has been seen for much of the season so far. Any storms

that do develop will have enough shear to not immediately

collapse as they grow. With a strong LLJ around 40 kts aloft,

the greatest severe threat from any of the strongest storms will

be that of gusty winds.

The warm temps this week have also thickened the warm cloud

layer, which is forecast to sit somewhere between 12 to 14 kft

thick. PWs are also forecast to surge up to or just over 2

inches, which is around the record highest recorded evening PW

for GYX this evening. With so much moisture and effective rain

processes, the threat for heavy rainfall remains across the

Downeast region, with over an inch of rainfall quite possible in

just an hour or two as these storms move through.

Tonight:

All shower and storm threat will rapidly diminish tonight as the

MCS exits to the east overnight and diurnal heating decreases.

Low temperatures will remain above average overnight with lows

in the low to mid 60s across the forecast area......

Hazardous Weather Outlook

National Weather Service Caribou ME

259 AM EDT Thu Jul 27 2023

MEZ005-006-010-280700-

Northern Penobscot-Southeast Aroostook-Central Piscataquis-

259 AM EDT Thu Jul 27 2023

This Hazardous Weather Outlook is for Central Highlands Maine and

Far Eastern Maine.

.DAY ONE...Today and tonight.

There is a marginal threat for severe thunderstorms today. Storms

may produce gusty winds and locally heavy rainfall this afternoon

into the early evening.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

A cold front could produce strong thunderstorms Friday afternoon

into Friday evening. The main threat would be gusty winds with any

storms.

.SPOTTER INFORMATION STATEMENT...

Weather spotters are encouraged to report significant weather

conditions according to Standard Operating Procedures.

$$