Waterville Valley

000
FXUS61 KGYX 281040
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
640 AM EDT Tue Jul 28 2026

.WHAT HAS CHANGED...
Update to the Aviation section for the 12Z TAFs.

&&

.KEY MESSAGES...
1. The recent dry stretch of weather ends today with increasing
chances for slow moving showers and thunderstorms by Tuesday 
afternoon and evening.

2. A cut-off low develops over the region Tuesday night and 
Wednesday and remains in the vicinity through Friday.  This will 
bring multiple rounds of rainfall with locally heavy rainfall 
possible.

3. Some periods of drier weather this weekend with warmer 
temperatures, but daily chances for precipitation continue, 
especially Sunday.

&&

.DISCUSSION...
KEY MESSAGE 1 DESCRIPTION...

Today opens with a large trough over Hudson Bay with shortwaves
rotating around this feature. A robust shortwave will reach the
eastern Great Lakes by this morning helping to close off a H5 
low by this evening over upstate New York. The result will be 
building southerly flow to the east of this feature with 1.5" 
PWAT plume pushing east into NH and far western ME by Tuesday 
night. Mid level forcing lags that moisture plume so expect best
potential for afternoon/evening storms to be over NH. The CAMs 
show a decent setup for locally heavy rain with narrow CAPE 
profiles, MBE vectors with less than 10kts net storm motion and 
deep warm cloud depths in the presence of PWATs locally over 
1.75". Current depictions show a decent storm motion given that 
the llevel jet is not all that strong and only 
isolated/scattered coverage...so...while there are some 
ingredients for flash flood potential...agree with the previous 
shift that given such dry antecedent conditions this event will 
likely only serve as a primer for the larger event on Wednesday.
Cannot rule out an isolated instance of flash flooding but feel
the overall threat is low. Clouds will be on the increase 
through the day with highs cooler than on Monday...close to 80 
in most locations. 

KEY MESSAGE 2 DESCRIPTION...

Cutoff low slowly moves from upstate NY on Wednesday morning...to 
southern New England on Thursday morning to the Gulf of Maine by 
Friday morning.  Most impactful weather period is expected to be 
Wednesday as surface low should drive a band of moderate to locally 
heavy rainfall through the region...with additional rainfall 
developing near the low again Thursday.  Given clouds and 
precipitation...temperatures will be below normal through the 
period.  

For Wednesday...the arriving low will strengthen the southeastern 
LLJ which may allow for more backbuilding of embedded convective 
elements in a precip-efficient environment.  However...instability 
looks to be less than the day previous.  The guidance suite has a 
decent amount of spread on the exact timing/orientation of the 
rainfall...but feel that by late morning and through the afternoon 
moderate to locally heavy rainfall is possible and there will be a 
threat of isolated flash flooding if training cells can materialize. 
While it will be humid...clouds and rainfall will keep temperatures 
in check with most locations remaining in the lower 70s...and 
perhaps some spots not reaching 70. Showers will likely continue 
through Wednesday night with fog also likely given the moist airmass 
in place.

Shower activity continues for the day on Thursday though placing the 
heaviest/most persistent shower activity is not possible at this 
range with a fair amount of spread in the guidance.  With the axis 
of the upper low overhead...rainfall activity may be very slow 
moving and while the overall column will have cooled a bit...the 
threat for flash flooding /now with increasingly saturated soils/ 
may increase if the activity is organized/widespread enough.  Expect 
that as the llevel flow turns more northeasterly Thursday night 
that any flooding threat will end but some isolated/scattered 
showers will likely continue.

Reviewing the ensemble probabilities...2" probabilities are 
generally restricted to far SW ME and NH along/south of the 
mountains.  With flash flood guidance well above this /6 hour 
guidance over 3" for nearly all of the area and greater than 4" for 
the NH mountains...lakes region and SE ME/ it suggests that any 
possible flash flooding for the Wednesday-Thursday period will be 
isolated.  There is not expected to be any river flooding with this 
event with plenty of storage given a much drier than normal July to 
date so far.  

The cutoff low finally opens up Friday and begins to pull east which 
should allow more sunshine...and warmer temperatures though the 
threat for scattered showers will continue. 

KEY MESSAGE 3 DESCRIPTION...

Global models are in surprisingly good agreement on the 500 mb 
pattern going into next week. Low pressure finally loses its grip on 
the region by Saturday while essentially dissipating offshore. 
Should note there is still some split guidance on how quickly this 
happens, and given cutoff lows are generally not handed well by 
global guidance, still a bit uncertain how fast this happens. 
Regardless, most guidance keeps Saturday on the dry side, with some 
subsidence behind the coastal low likely playing a role.

Sunday onward may be a different story, as guidance suggests the 
Hudson Bay upper-level low reorganizes, lifting another 500 mb 
trough towards New England by Sunday night, with subtle height 
falls. With southwest flow ahead of this feature developing, as well 
as a possible surface low somewhere in the Ohio Valley, signs are it 
will turn humid and possibly rainy once again, although that is 
about the most we can say with confidence six days out. So in a 
nutshell, Saturday is likely the drier of the two days, while Sunday 
brings increasing chances for showers late, especially across the 
interior.

&&

.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
Through tonight...

Summary: Increasing moisture has brought low clouds across 
southern NH and coastal Maine early this morning with cigs 
likely lifting later this morning. Shower and thunderstorm 
chances increase this afternoon and evening for NH terminals. 
Low cigs and patchy fog are likely tonight with chances for 
showers

Restrictions: IFR to LIFR cigs across southern NH and PWM likely
mid morning. Increasing moisture will allow clouds to thicken 
and lower across NH and coastal Maine later this morning into 
the afternoon. Restrictions are again possible this afternoon 
and evening due to SHRA/TSRA primarily for NH terminals. IFR to 
LIFR is likely across all sites in low cigs and visibility 
restrictions in fog tonight.

Winds: Light winds through day break will strengthen again to 
10-15kts late morning...diminishing to less than 10kts tonight.

LLWS: No LLWS is expected through the TAF period and through Tuesday 
night.  

Thunder: Isolated to scattered slow moving /movement generally 
from south to north/ thunderstorms are possible this afternoon 
and evening, particularly for NH terminals. 


Outlook:

Wednesday - Thursday: Slow moving low pressure will bring multiple 
rounds of rainfall to the region with a prolonged period of IFR/MVFR 
restrictions. Winds at or below 10kts.  

Friday - Saturday:  Expect conditions to slowly improve on Friday as 
low pressure moves away from the region though scattered showers and 
a thunderstorm are possible.  VFR conditions should dominate 
Saturday outside of an isolated afternoon shower/storm. Winds at
or below 10kts.

&&

.MARINE...
Conditions remain below SCA levels through at least the first half 
of Wednesday...though there will be increasing potential for fog 
over the waters by late tonight and continuing through much of the 
week.  Low pressure passing south of the region Wednesday night and 
Thursday will bring strengthening easterly winds and building wave 
heights with SCAs likely necessary Wednesday afternoon and 
continuing through Thursday.  Improving conditions arrive to end the 
week Friday and persist through the weekend.

&&

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

&&

$$

DISCUSSION...Arnott/Barker/Schroeter