Area Forecast Discussion
Issued by NWS Portland, ME

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FXUS61 KGYX 281538

Area Forecast Discussion
National Weather Service Gray ME
1138 AM EDT SAT MAY 28 2016

A hot day is in store for much of New England high
pressure just off the south coast allows for warmth to build
north. Some humidity will even build into parts of New Hampshire
and make it feel a few degrees warmer than what the thermometer
reads. If heat is not your thing...relief is not far away. On
Sunday high pressure builds into the Maritimes...and turns winds
northeast and off the water. That will send a cold front through
eastern parts of the forecast area...dropping temperatures some 15
to 20 degrees from today. That front will hang around the area and
provide the focus for increasing showers and thunderstorms into
Sunday night and Monday as tropical moisture streams northward
into the area.


1130AM UPDATE...
Temperatures have spiked into the mid 80s across a large part of
the area already this morning. Have adjusted the forecast to show
a better temperature trend for the remainder of the day and
increased high temperatures just a few degrees over southern parts
of the area. Dewpoint values are also significantly higher than
expected especially over the coastal plain. Have adjusted the
dewpoint forecast which yielded higher heat index values this
afternoon. Heat index values of 95 to 100 degrees are possible in
southern New Hampshire and southwest Maine. A Special Weather
Statement has been issued for the area of highest heat and
humidity to highlight the threats posed by this first truly hot
day of the year. Winds are light or calm and with strong heating
of inland areas today, a seabreeze can be expected. This will cool
areas along the immediate coastline soon and the hourly
temperature forecast attempts to show this happening.

1015AM UPDATE...
Made some adjustments to the next few hours of the forecast based
on observed temperatures and sky cover. Should see the cumulus
start to build in the mountains and over southern parts of the
area over the next few hours. Morning upper air observation shows
potential instability exists once daytime heating gets going in
full force. Although mid/upper level support for thunderstorms
does not appear to exist, there will be other features which could
aid in the formation of thunderstorms today. Forcing from
differential heating of the terrain will be one source of
potential thunderstorm initiation. In addition, the frontal
boundary which has dropped southward into western Maine could
provide another focus for updraft initiation, particularly where
this front meets the seabreeze. Several models do show convective
activity forming this afternoon in the warm/moist air mass south
of the front and along the seabreeze. If storms form, there is
moderate westerly winds in the mid levels that could help to get
storms more organized. Decided to include small hail in the
forecast wording for today though would not be surprised if a
severe thunderstorm warning might at some point be needed.

Marine fog and stratus will mainly hang tough near and N of PWM
this morning...gradually lifting with daytime heating. Then strong
ridging aloft will build thru the day...and allow skies to clear.
A very warm air mass in place...strong heating...and Wly flow
across the interior will mean afternoon highs reaching the low 90s
for many. With dewpoints in the 60s...some parts of the lower CT
River Valley and ASH-MHT corridor will see heat index values near
95. That will be the main forecast concern today...though there
will be a chance for afternoon showers or storms near the coast.
Some of the higher res model guidance continues to show QPF
developing during peak heating. Given the rising heights...forcing
will be weak and anything more than widely scattered convection
seems unlikely.


Tonight into Sunday...a S/WV trof crossing the Maritimes will see
high pressure build in its wake. As high centers E of Nova
Scotia...the pres gradient will reverse across the region and turn
winds NEly and onshore. A backdoor cold front is expected to move
thru at least eastern zones Sunday. Temps could be some 20
degrees cooler vs today. Air mass aloft will remain quite warm to the W of the front it could be another very warm
day. This may include much of the CT River Valley. At the same
time that warmth aloft may strengthen the inversion and make it
all the more difficult to rid the marine influence near the coast
Sunday. Precip chances will revolve around scattered convection
in the very warm air mass to the W...and any low level rainfall
or drizzle in the marine layer...but overall forcing remains weak


High impact weather: heavy rainfall Sunday night into Monday may
cause localized flash flooding.

A broad ridge of high pressure aloft continues to be the main
large scale feature over the eastern United States through the
next week. This will keep generally mild temperatures in our
region under southerly flow. A weak shortwave will help to
initiate showers to start the week.

Our weather for Sunday and Monday will depend largely on the
strength of a tropical system. While Tropical Depression Two will
remain well to our south and is expected to move into South
Carolina, this tropical moisture will extend into Northern New
England. The strong Bermuda high will couple with an approaching
front to force a plume of very moist air northwards. Precipitable
water will approach 2 inches /near record levels/. Extensive
southerly flow around the Bermuda high will also bring warm air
allowing the freezing level to rise to around 12,000ft. The
tropical moisture and high freezing level will thus set the stage
for heavy rainfall. The moist airmass will yield convective
showers and thunderstorms. However since storm motion vectors
remain very weak /less than 10kts/ there is a risk for localized
flash flooding as any storms which form will have ample moisture
and not move very fast.

The font will push through Monday afternoon allowing for high
pressure to build back in from the Ohio River Valley. The ridge
remains in place through Tuesday and Wednesday bringing seasonable
temperatures with highs in the upper 70s and lows in the 50s.
The upper level pattern begins to shift by the end of the week as
a trough digs into the great lakes at 500mb. At the surface a low
pressure system moves through southern Canada dragging another
cold front through the forecast area for the end of the week.


Short Term...Fog will likely hang just off the coast during the
day. Otherwise VFR conditions prevail. This afternoon could see
widely scattered SHRA or TSRA develop near the coast...but
coverage and location remains uncertain.

Long Term...
Scattered showers and thunderstorms will impact all terminals on
Sunday afternoon into Monday. Brief periods of IFR rain will
occur across inland sites. For coastal sites expect ceilings to
drop to IFR with fog overnight Sunday into Monday. After Monday
afternoon conditions will improve to VFR through the end of the


Short Term...Winds and seas are expected to remain below SCA
thresholds for the weekend. Cold front pushing SWwd across the
waters Sunday may allow for a period of seas approaching 5 ft
outside of the bays.

Long Term...
Large scale high pressure will remain over the region keeping
winds and seas below small craft criteria.


The pattern will remain warmer and humid into early next week. As
a result relative humidity values will remain moderate to high.
Winds will also remain on the lighter side...with high pressure
generally in control.





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