Area Forecast Discussion
Issued by NWS Portland, ME
FXUS61 KGYX 211053
Area Forecast Discussion
National Weather Service Gray ME
653 AM EDT THU JUL 21 2016
High pressure will remain anchored to our southeast through
Friday. The circulation around this high will circulate warm and
increasingly humid air into the region ahead of a cold front. The
cold front will approach the area on Friday, producing showers and
thunderstorms, before sliding offshore Saturday morning. Some of
the thunderstorms late Friday and Friday night will produce gusty
winds, hail, and frequent lightning. The front stalls over the
area Saturday with another round of scattered thunderstorms. Weak
high pressure moves through Sunday and Sunday night. Another
rounds of showers ands storms is possible late Monday and Monday
night as a cold front approaches the region, and the may stall
over the area Tuesday.
.NEAR TERM /UNTIL 7 PM THIS EVENING/...
650 AM...Minor ESTF update to ingest the current mesonet into near
At 06z...a 1023 millibar high was anchored southeast of the
forecast area. GOES infrared imagery showed clear skies across the
region. The clear skies and light winds were allowing patchy fog
to develop over interior valleys. For today, little change as the
surface high remains in control. Some high clouds will spill into
the region from Quebec, courtesy of the convective complex
vicinity of the southern tip of Hudson bay, otherwise it`ll be a
mostly sunny day. Highs today will be in the 80s and lower 90s, but
with comfortable humidity levels for one last day. The westerly
flow will turn onshore by late afternoon from Casco Bay and points
east allowing some late day relief from the heat. It should be
another dry day with any convection over Quebec province remaining
to our north.
.SHORT TERM /7 PM THIS EVENING THROUGH 6 PM FRIDAY/...
For tonight...dewpoints should gradually rise in the southwest
flow. Can`t rule out a late night shower or thunderstorm near the
international border ahead of a weak surface trough. Otherwise...a
partly cloudy night with patchy fog and haze developing. It`ll be
milder then this morning with lows mainly in the 60s.
On Friday...southwest flow ahead of the approaching surface cold
front and a prefrontal trough will allow dewpoints to rise through
the 60s while temperatures warm well into the 80s. An approaching
shortwave impulse during the afternoon, coupled with peak heating
should produce cape values in the 1500 to 2000 j/kg. In response,
expect strong to severe convection to develop across the forecast
area by afternoon then continue into Friday night. I`ve left
enhanced wording in the grids and public products beginning Friday
.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
Chance of high impact Wx: Increasing confidence for severe
thunderstorms Friday afternoon and evening. There is a chance for
more isolated severe storms on Saturday.
The strong ridging at 500mb over most of the CONUS and the
western Atlantic will hold through the long term forecast period,
with the one weakness in the ridge still straddling the intl
border from the Great Plains to New England. This should make for
a more active period with the threats of showers/storms at least
every other day. Moving lower in the atmosphere, it`s hard to much
air below normal at 850 mb outside of the Arctic circle thru this
period, so expected temps to continue to run mostly above normal.
As we get into the low levels, flow becomes fairly stagnant, with
only small differences in air masses on either side of sfc fronts,
and very little dry air to to tap into to lower humidity levels
much. So, in summary, expect very warm and humid conditions over
the weekend and into the middle of next week, with frequent
potential for scattered showers and storms.
The most interesting part of the extended will be Friday night as
ongoing convection Friday afternoon to our west has the potential
to organize into convective line or MCS and move across the
region, especially between 0Z and 6Z. Whether a line forms or not
there will be enough instability and presence of elevated mixed
layer, along with strong bulk shear to continue the severe threat
thru the evening hours. Fri night will be warm and humid with lows
mostly in the mid to upper 60s, and maybe not dropping below 70 in
urban areas of southern NH.
On Saturday, frontal boundary looks to stall or slowly move south across
the CWA as the 500 mb trough hangs back a bit. It will be a
possible that with presence of frontal boundary and potential NW
flow a loft, could see more strong to severe storms on Saturday,
but for now, will not mention in zones/grids as confidence is too
low. Highs Saturday will be hotter south of the front in southern
NH where they will reach into the low 90s, with TDs in the mid to
upper 60s, which will produce heat indices in the mid 90s.
Elsewhere it will remain on the warm and humid side.
It starts clear out later Sunday night as the front finally pushes
just south of the CWA and fades out. Some drier air moves in , and
will push dew points down to the upper 50s to lower 60s late
Saturday night into Sunday. Sunday should be dry with highs back
in the 80s to around 90 in southern NH. Sfc humidity increases Sun
night and Monday with another threat for showers storms as another
front approaches and tries to cross the region Monday night or
Tuesday. Temps and humidity may drop off a bit on Wednesday.
.AVIATION /12Z THURSDAY THROUGH MONDAY/...
Short Term /through Friday/...Lcl ifr psb through 12z at khie and
kleb...otw vfr. Sct mvfr psb aft 08z Fri in mtn -shra/-tsra. Aft
16z Fri...areas of mvfr in shra/tsra with lcl ifr psb in +tsra.
Long Term...Friday night will be a busy period with the potential
for severs storms, coastal status and fog. Some flight
restrictions are expected, but conditions will be changeable. VFr
returns on Saturday, but there will be the htreat for another
round of TSRA. Mainly VFR Sat night through Monday with night
Short Term /through Friday/...Southwest flow will continue with
seas gradually building. We may reach marginal small craft
conditions during Friday outside the bays.
Long Term...SCA possible outside the bays friday evening, but
otherwise should remain below SCA through Monday. thunderstorms
frinight could produce very strong gusts and frequent lightning.