Flash Flood in New Hampshire, July 26, 2021

Area Forecast Discussion
National Weather Service Gray ME
950 PM EDT Mon Jul 26 2021

.SYNOPSIS...
A warm and humid air mass will last through Tuesday before a
cold front moves through late in the day. This front will be
the first in a series that will bring cool and dry air into the
region through the end of the week and the weekend. Showers and
thunderstorms are possible with the front Tuesday night High
pressure will pass through on Wednesday, before another chance
of showers late Thursday with another frontal passage. High
pressure builds in for Saturday, with another front possible by
late Sunday.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
945 PM Update... Adjusted PoPs some to better align the area of
higher PoPs to where showers and thunderstorms are currently
located. Although an isolated strong storm will remain a
possibility through around 04Z, the threat for severe weather is
very low and continuing to diminish as CIN continues to
increase over the area. Generally weighted the HRRR pretty
heavily for PoPs through the remainder of tonight as it has done
a decent job with the ongoing convection. Some minor
adjustments to temperatures, winds, and sky cover were also made
but overall the ongoing forecast remains on track.

Previously... 7:00 PM
Update...Have increased pops across Northern NH and Western
Maine as a pre- frontal 500mb shortwave trough begins to
approach the region from Quebec province. Convection is
beginning to fire across VT ahead of a large cluster of storms
in the Saint Lawrence river valley area. WV sat imagery shows
the trough that the CAMs are picking up on with the RAP and HRRR
keeping activity going until at least midnight across the
northern areas. A few strong cells could be possible, and a
isolated SVR can't be ruled out at this time, but that is a low
prop at this point with a setting sun and decreasing surface
instability.

The classic triple H this afternoon: Hazy, hot and humid as smoke
from wildfires in Manitoba combines with a warm and sticky airmass.
While the Haze is thick enough to reduce visibility to 5 miles and
may be keeping us just slightly cooler most of the region is still
at or above 80F.

A glace to the Northwest shows what's to come. The thickest portion
of the haze ends at the St. Lawrence valley and just behind it
convection is beginning to fire ahead of another short
wave/cold front just starting to drop into southern Quebec.
Timing out this boundary, we've still got most of the afternoon
to go in the hot haze before any of the convection can reach the
US/Canada border, which should occur around sunset. This
morning's sounding out of Maniwaki shows a region of steep lapse
rates around 700mb which should help to increase instability.
That said, there is also quite a bit of dry air aloft. Overall
it's a marginal environment for severe storms, but some gusty
winds can't be ruled out in Northwestern Maine late this
evening.

Well behind the front we have much drier air moving in but we'll
need it to get here first. While the northern parts of NH and
western Maine may see that benefit tonight the Maine coast will
likely wait out almost until sunrise, and thus continued fog
overnight along the midcoast is expected.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/...
Tuesday a second stronger short wave will push through the
region. This will bring scattered showers and thunderstorms to
especially the southern Maine and NH south of the White
mountains. Forecast soundings suggest some marginal severe
storms are possible, with gusty winds being the main threat.
Have kept a mention of gusty winds in for the highest PoP.

Overnight behind the front the drier air will come in allowing
temperatures to drop. Have leaned on the cooler side of the
distribution putting the mountains into the upper 40s.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
The long term pattern will continue to be dominated by troughing
across eastern North America, with generally below normal
temperatures and frequent frontal passages through the next week.
The pattern doesn't look particularly rainy, but the chances for
showers will increase with the frontal passages roughly every other
day.

Breaking it all down, a frontal boundary will be south of the area
by Wednesday morning, but lingering showers may still remain across
southern New Hampshire. These will diminish by the afternoon hours
as high pressure builds into the area. Highs will mainly be in the
low to mid 70s.

The influence of the high pressure will be short lived however, as
low pressure rides northwest of the area on Thursday. Thursday will
start off dry, but a triple point low is likely to develop across
the eastern Great Lakes south of the parent low, bringing widespread
showers and likely a few thunderstorms into the region later
Thursday afternoon through Friday morning. They should move out by
Friday mid-morning, but the trough will be deepening on Friday, with
cooling temperatures aloft likely leading to some pop up afternoon
showers.

The low pressure will strengthen as it moves through the Canadian
Maritimes on Friday and Saturday, becoming anomalously strong for
this time of the year. This will likely lead to some breezy
conditions late Friday afternoon, and then resuming again on
Saturday once daytime heating resumes. A weak ridge will build
in at the surface for Saturday yielding sunshine, but the upper
level trough will reach its maxima on Saturday and Sunday as
cool Canadian air pours into the region.

Another front will likely approach the region late Sunday and into
Monday, bringing another threat of showers and a fresh shot of cool
air for early next week.

&&

.AVIATION /02Z TUESDAY THROUGH SATURDAY/...
Short Term... MVFR visibilities in Haze will continue through
evening before the residual smoke plume moves off shore,
thereafter VFR and clear skies will be the rule, although a few
scattered showers are possible in the north tonight. Valley fog
will drop conditions to LIFR for LEB and HIE, with additional
IFR fog along the coast for RKD. tomorrow sunny skies with just
a chance for scattered afternoon across southern New Hampshire.

Long Term...
Some lingering showers are possible across southern New
Hampshire Wednesday morning. A few pop up showers are possible in
the afternoon, but otherwise VFR conditions are expected
through midday Thursday. A frontal boundary will likely bring
widespread showers late Thursday through early Friday. VFR
conditions return midday Friday outside of a few afternoon pop
up showers and remain through Saturday. Some gusty northwest
winds are possible late Friday and again on Saturday. Scattered
showers likely return late Sunday.

&&

.MARINE...
Short Term...Hazy skies will continue across the waters this evening as
weak southwesterly flow continues. A cold front will cross the
region tomorrow afternoon switching winds to northwesterly.

Long Term...
High pressure will build into the area on Wednesday through
early Thursday, before an area of low pressure moves in from the
west late Thursday through early Friday. A period of SCA
conditions with southerly winds are possible Thursday afternoon
and night ahead of the system. The low will move into the
Canadian Maritimes on Friday and strengthen, possibly bringing
SCA conditions with northwesterly winds late Friday through
early Saturday. High pressure builds across the waters during
the day on Saturday.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...None.
NH...None.
MARINE...None.

&&

NEAR TERM...Dumont/Tubbs

Hazardous Weather Outlook
National Weather Service Gray ME
929 AM EDT Mon Jul 26 2021

MEZ007>009-012>014-019>022-024>028-033-NHZ001>004-271330-
Northern Oxford-Northern Franklin-Central Somerset-Southern Oxford-
Southern Franklin-Southern Somerset-Central Interior Cumberland-
Androscoggin-Kennebec-Interior Waldo-Coastal Cumberland-Sagadahoc-
Lincoln-Knox-Coastal Waldo-Interior Cumberland Highlands-
Northern Coos-Southern Coos-Northern Grafton-Northern Carroll-
929 AM EDT Mon Jul 26 2021

This Hazardous Weather Outlook is for Maine, south central Maine,
southwest Maine, west central Maine, western Maine and northern New
Hampshire.

.DAY ONE...Today and tonight.

Isolated thunderstorms are expected this afternoon. A few strong to
severe storms are possible, with gusty winds being the primary
concern.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday.

Hazardous weather is not expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

MEZ018-023-NHZ005>015-271330-
Interior York-Coastal York-Southern Grafton-Southern Carroll-
Sullivan-Merrimack-Belknap-Strafford-Cheshire-Eastern Hillsborough-
Interior Rockingham-Coastal Rockingham-
Western And Central Hillsborough-
929 AM EDT Mon Jul 26 2021

This Hazardous Weather Outlook is for southwest Maine, New
Hampshire, central New Hampshire, northern New Hampshire and
southern New Hampshire.

.DAY ONE...Today and tonight.

No hazardous weather is expected at this time.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday.

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

ANZ150>154-271330-
Coastal Waters from Stonington, ME to Port Clyde, ME out 25 NM-
Penobscot Bay-
Coastal Waters from Port Clyde, ME to Cape Elizabeth, ME out 25 NM-
Casco Bay-
Coastal Waters from Cape Elizabeth, ME to Merrimack River, MA out
25 NM-
929 AM EDT Mon Jul 26 2021

This Hazardous Weather Outlook is for Atlantic coastal waters.

.DAY ONE...Today and tonight.

No hazardous weather is expected at this time.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday.

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.