Mesoscale Precipitation Discussion 0733
NWS Weather Prediction Center College Park MD
451 PM EDT Thu Jul 17 2025

Areas affected...Northern Maine

Concerning...Heavy rainfall...Flash flooding possible

Valid 172049Z - 180245Z

Summary...Localized flash flood threat continues through this
evening over northern Maine as rounds of thunderstorms ahead of
low pressure work their way through.

Discussion...A shortwave trough is over north-central Quebec per
mid-level Water Vapor imagery with the surface low approaching the
St. Lawrence between Montreal and Quebec City. The warm sector
ahead is across New England with convection concern north of a
mid-level trough axis that is lifting over central New England.
Strong southerly flow of 25kt is pumping 2" PW air from the
Maine/Mass coast up through northern Maine and over an instability
gradient of 1000 to 2000 J/kg SBCAPE over central Maine. Deep
layer mean flow is veering from SSWly to SWly through the rest of
the afternoon which should continue to allow training of
convection which is ongoing over northern Maine. KCBW has
estimated max hourly rainfall of 2.5" along the Aroostook/
Piscataquis Co border which can be expected to continue in a
localized fashion as the activity lifts northeast making an
isolated flash flood threat rest of the afternoon.

Furthermore, there is a threat for a second round of heavy rain
this evening which could cause greater coverage of flash flood
concern this evening. Recent HRRRs have been slow with the
existing activity, but are clear on a second round which is seen
as scattered convection along and east of the St. Lawrence Seaway
per MRMS mosaics. Given the low flash flood guidance of northern
Maine (generally 2" or less in three hours), flash flooding is
considered likely through 02Z.

Jackson 

ATTN...WFO...CAR...GYX...

ATTN...RFC...TAR...NWC...

LAT...LON   47536894 47186781 46236760 45696837 44856993
            45357110 47147008