Area Forecast Discussion
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FXUS61 KGYX 202346 AAB
Area Forecast Discussion...UPDATED
National Weather Service Gray ME
746 PM EDT SAT AUG 20 2016
High pressure will ensure mostly dry weather through Sunday along
with seasonably mild temperatures. A strong cold front will move
through the region Sunday night with a period of rain expected
across the region. Behind this...much cooler and drier air will
arrive for Monday and Tuesday as high pressure builds into the
region. As this high shifts offshore by midweek... expect
temperatures and humidity to increase.
.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
-- Changed Discussion --Update...Have adjusted wx grids for the night based on the fog
forecast. Leaning on the NARRE-TL for timing and areal extent of
fog...which brings in the majority after midnight and mainly N of
PWM. Inland patchy valley fog will be possible.
Main forecast issue tonight will be coastal fog/stratus. It was
fairly prevalent around Casco Bay earlier today...but has since
lifted. Most of the Gulf of ME is cloud free at the moment...so
the thinking is that I may have to push back the onset of any
coastal fog some. There is an area S of Nova Scotia noted on
visible satellite imagery pushing Wwd...and NARRE-TL favors this
to arrive for coastal ME after midnight as another round of
fog/stratus. At this time model guidance is focused mainly PWM and
points E up the coast...which seems reasonable at this time.
Previous discussion...High pressure has moved offshore and has
begun to produce a more humid southerly flow. Another quiet night
expected except for the question of when and where fog will
develop. The southerly flow has already begun to develop areas of
fog along coastal waters and during the evening we are expecting
more ocean low clouds and fog to develop and move to coastal
zones. Over the interior more late night valley fog expected once
again. Temperatures will mild tonight with more humidity to be
noted as dewpoints will be slowly on the rise.
-- End Changed Discussion --
.SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...
The valley fog will once again burn off by mid morning but with
high pressure anchored off the coast producing a moist southerly
onshore flow, coastal areas may have low clouds and areas of fog
through the day and into the night. Models show the cold front and
associated showers approaching late Sunday and moving through the
area Sunday night. Used the RFCQPF guidance of between .50 in
southern areas to 2 inches in the mountains. Models in general
agreement with RFC guidance.
Used a blend of models for max/min temps and pops.
.LONG TERM /MONDAY THROUGH SATURDAY/...
High Impact Weather Potential: Minimal.
Pattern: Current teleconnection indices show an ongoing -NAO with
ridging ongoing across Greenland and blocking south of this
feature...albeit a bit far to the north to bottle up anything as far
south of the CONUS...but rather keep ongoing longwave troughing
anchored near Hudson Bay. The PNA has done more oscillating of
late...neutral now trending negative at the moment as shortwave
energy over the Gulf of Alaska/western Canada flattens the
western ridge somewhat...carving out a mobile shortwave trough
that will head east along the US/Canadian border this week. Behind
this feature...there is good EC-ENS/NAEFS agreement that the PNA
returns strongly positive for the second half of the long term
forecast period with a rebuilding of the western ridge.
Overall...this upper level pattern evolution to our west...
combined with semi-permanent ridging over the southeastern
US/western Atlantic suggest that as the troughing over the
northeastern United States to start the period moves east...the
longwave trough position will retrograde somewhat west as next
upstream shortwave merges with Hudson Bay low. Thus...the
transition from northwesterly to southwesterly flow will occur
early in the period with moderating temperatures and gradually
increasing levels of humidity expected in the broad southwesterly
flow. The best widespread precipitation chances will be late in
the period as troughing to our west approaches the Northeastern
states. The pattern does not favor high impact weather with weak
forcing given the dominance of the northern stream and thus
generally weak forcing aloft...typical of this time of year.
Model Trends/Confidence: Overall...model agreement is above
average through the long term forecast period with only slight
timing differences towards the second half of the week.
Thus...confidence in the forecast is above average.
Monday/Monday Night: Deep moisture plume will be exiting stage right
to open the long term forecast on Monday with PWATS falling towards
0.5" by 00Z Tuesday /-1-2 sigma/. Consensus location of the front
suggests that rain may not have completely cleared my Maine zones by
daybreak...so will allow for chance PoPs for a few hours in the
early morning....with PoP focus shifting to upslope regime in far
northern NH/northwest ME as the day unfolds given residual cyclonic
flow and shallow upslope component beneath strengthening subsidence
inversion. Expect clearing south and east of the mountains in
developing subsident regime. Winds look moderate given good cold
advection but little isallobaric help and only a modest gradient.
This will likely yield winds in the 10-15g20-25kt range. T8s
beginning the day near +10 C...but fall 1-3 degrees C during the
day... reaching -1 to -2 sigma values by 00Z Tuesday...with the core
of the cool air /+6-7 C/ settling overhead Monday night. Temps
aloft support highs in the 70s south and east of the mountains with
clouds and a few showers likely keeping spots from the mountains
north in the 60s. This will set up a chilly night Monday night with
core of the cool/dry airmass pretty much overhead and high
pressure ridge axis nosing into the region. 1000 mb geostrophic
winds around 20kts at 00Z Tuesday subside to 10-15kts
overnight...suggesting that our deeper valley locations will
decouple...but the ridges and hilltops will not. For these former
locations...thus...expect temperatures to fall into the 40s...with
our coldest spots near the Canadian border right around the 40F
mark. Given the setup...will go below the guidance consensus on
temps. Expect plenty of valley fog and fog over the inland lakes
given this setup.
Tuesday - Thursday: Very quiet period of weather in store through
the midweek as flow aloft backs westerly and eventually
southwesterly with departing trough...with surface high moving from
a location over the Mid Atlantic early Tuesday to just southeast of
the New England coast Wednesday to south and east of the Canadian
maritimes by Thursday. Only possible chance for precipitation comes
Tuesday night as warm front north of the Great Lakes rides east with
precipitation along the leading edge of the deeper moisture /and
associated low level jet/ moving just north of our region overnight
with more gradual warming/moistening aloft across New England. There
is good consensus for this precip to remain just north of the
region...but worth keeping an eye on for far northern areas.
Otherwise...partly to mostly sunny skies look to be in order with
T8s rising from around +9 C Tuesday to +15 C Wednesday to +16-17 C
on Thursday which is +1-2 sigma by these latter periods...not
terribly abnormal...but likely able to allow locations in southern
NH and far southwestern Maine to again make a run into the upper
80s to around 90 after highs only reach the 70s to around 80 on
Tuesday. Overnight lows warm rapidly...upper 40s/lower 50s Tuesday
morning with most locations at or above 60 by Thursday night.
Friday - Saturday: There is above average deterministic/ensemble
agreement in a frontal passage on Friday associated with weakening
shortwave moving east along the US/Canadian border...with a
relatively thin moisture plume ahead of this feature. Nothing
particularly exciting from a dynamics perspective...but certainly a
warm/humid airmass ahead of this boundary...with thunderstorms
possible depending on frontal timing. While a widespread
precipitation event is possible...there are no signs that this will
result in very significant rains. With the potential
precipitation will keep highs a bit lower on Friday...but still
well above seasonal norms.
Behind this feature...expect temperatures to drop somewhat to end
the forecast period with dry weather Saturday...but with continued
southwesterly flow aloft...expect the period to end warmer than
.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
Short Term...VFR conditions will be variable to IFR/LIFR in
developing areas of coastal stratus and fog as well as some
interior late night valley fog. Valley fog burns off by 15z Sunday
but coastal low clouds may remain. By Sunday night showers
associated with the cold front will produce widespread MVFR/IFR
Long Term...VFR conditions look to dominate flying conditions
through Thursday...with restrictions limited to overnight fog
potential each night HIE/LEB.
Short Term...Light south winds tonight and Sunday will increase
some ahead of the approaching front Sunday night but will remain
below SCA levels. Seas will also remain below 5 feet.
Long Term...Winds and waves to remain below sca levels with
northwesterly winds turning southwesterly for Wednesday and
Thursday. Southwesterly winds may reach SCA levels on Thursday
night and Friday.