Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service Wakefield Virginia
218 PM EDT Wednesday Apr 16 2014

Synopsis...
cool high pressure builds in from the northwest this morning and
settles over the middle Atlantic and northeast states this afternoon
through tonight. The high will become centered from New England to
the Canadian Maritimes Thursday and Friday...maintaining northeast
flow and much cooler than average temperatures across the region.

&&

Near term /through tonight/...
latest analysis showing surface high pressure centered from Michigan south
into northern Kentucky...and beginning to ridge east of the Appalachians
early this morning. Winds remain gusty...particularly along the
coast due to rapid pressure rises and strong cold advection but
wind speeds have dropped off somewhat over the past few hours. Skies
have generally cleared except across Hampton Roads and NE NC where broken
cloud cover persists through middle morning. Perhaps even more
impressive will be how cold today's highs will be even with ample
sunshine. Low level thicknesses suggest guidance values of the
middle-upper 40s at the immediate coast to the lower 50s over
interior southern Virginia should be about as warm as it will get (this
is around 20 f below avg). Have included a climate section as this
may rival record low maximum temperatures at Norfolk.



High pressure settles over the area later this afternoon into this
evening and winds will subside. Will likely need another freeze
warning for portions of the area tonight/Thursday morning. With SW flow
aloft and the surface high becoming centered over northern New England
overnight...there will tend to be increasing low level moisture
and cloud cover from the southeast. BUFKIT soundings show increasing low
level moisture across southeast Virginia and NE NC overnight so temperatures should
remain well above freezing there (lows in upper 30s to lower 40s)...with
a freeze more probable over central and south central Virginia where
skies generally stay mostly clear and winds decouple.

&&

Short term /Thursday through Friday/...
the trend that starts tonight/early Thursday morning looks to continue
on Thursday. Setup supports a strong inversion above 900 mb which will
tend to trap any developing marine layer cloudiness. Not much
chance for measurable precipitation given a very dry airmass above the
inversion...but do think skies will end up mostly cloudy over most
of the County Warning Area from I-95 east. This will keep highs well below
average...mainly in the lower to middle 50s...with upper 50s to around 60
f over the Piedmont. A deeper layer of moisture from 950 to about
800 mb will eventually move into all areas Thursday night/Friday as a
coastal trough continues to push closer to the coast. Will carry a
slight chance (20%) probability of precipitation Thursday night through Friday. While the overall
airmass warms quite a bit on Friday...have sided on cooler edge of
guidance for highs due to clouds and persistent NE flow. Lows
mainly in the 40s Thursday night with highs Friday generally 55-60 f.

&&

Long term /Friday night through Tuesday/...
an area of surface low pressure is expected to develop on a stalled
boundary off the southeast coast Friday night. The low should track NE
well off the Carolina coast on Sat. This feature may bring a few
rain showers to far southeast Virginia/NE NC during this timeframe.
Meanwhile...an upper level trough over the upper Midwest will swing
into the eastern Great Lakes Friday night and skirt across northern Virginia on Sat. A
weak surface low will be associated with this feature and may bring a
brief round of showers to far northern portions of the forecast area (including the
Maryland/Virginia eastern shore) Sat afternoon/early evening before moving offshore
and dissipating. The surface low associated with the Great Lakes trough
is expected to phase with the aforementioned coastal low Sat
night...but this should occur over New England and have very little
impact to the Middle Atlantic States. Surface high pressure builds into the
region sun...then slides offshore by sun evening as a relatively
flat (west to east oriented) frontal boundary sags down into the
area Monday night into Tuesday. Weak shortwave energy and a subsequent surface
low traveling along this boundary may bring another shot of
precipitation to the area on Mon/Tue. GFS precipitation-generation and
general movement is a bit aggressive versus the European model (ecmwf)...therefore
tried to split the difference with the pop forecast and limited
coverage to no higher than 40 percent.

Temperatures are expected to be straight-forward Sat night through
Sun night as high pressure crosses the region. Expect lows near
normal both nights in the 40s (lower 50s possible immediate southeast Virginia/NE
NC coasts). Highs Sat/sun range from roughly 65 degrees far NE to 70
degrees SW. As the flat frontal boundary starts to sag into the Middle
Atlantic States Monday through Tuesday...the temperature forecast becomes tricky
in regard to where exactly the warm sector develops. With precipitation
expected to approach the area on Monday...increasing cirrus should keep
high temperatures in the upper 60s west of I-95 with warmer temperatures in the
lower 70s east of I-95 (mid-upper 60s Maryland/Virginia eastern shore). Highs
Tuesday should be in the lower 70s inland and in the upper 60s near the
immediate ches Bay and Atlantic coasts. Low temperatures areawide on
Monday/Tuesday night should also be warm with readings in the 50s (or about
10 degrees above normal).

&&

Aviation /18z Wednesday through Monday/...
a mainly clear sky is expected through early Thursday morning. Gusty
north winds become NE this afternoon and slowly diminish toward
evening. Winds have tended to be slightly backed from MOS forecasts
and made adjustments accordingly. NE winds may be gusty once again
Thursday. Stratocu clouds which could go MVFR develop over southeast
sections Thursday morning associated with onshore flow.

Outlook...as high pressure strengthens over New England and the
Canadian Maritimes...the chances for MVFR conds increase through
Friday night...especially southeast portions. There will also be a chance
for showers late Friday and Friday night. A cold front moves through
early Saturday but the trend toward onshore flow will continue into
early next week.

&&

Marine...
update...remaining gale warnings have been converted into Small Craft Advisory
flags through at least early Thursday morning. As high pressure
slides across New England tonight into Friday...winds turn to the
NE and result in persistent seas of 5 feet or higher. Another but
weaker push of cold air is anticipated to occur overnight into
early Thursday...which will increase winds into Small Craft Advisory thresholds
during this time. It is likely that Small Craft Advisory conditions due to seas
above 5 feet will continue beyond early Thursday morning. Will have
a final decision made regarding headlines by the afternoon forecast
package (issued by 4 PM today).

Previous discussion...hi pressure slides NE across New England and
into the Canadian Maritimes tonight into Friday...as a weak coastal trough
develops off the southeast and middle Atlantic CST. This will result in a
prolonged period of NE winds and elevated seas through the end of
the week.

&&

Climate...
record low maximum temperatures today 4/16:

Ric...45 (1929)
orf...46 (1935)
sby...45 (1935)
ecg...52 (1962 & 1952)

Record lows Thursday 4/17:

Ric...31 (1949)
orf...34 (1875)
sby...26 (2008)

&&

Akq watches/warnings/advisories...
Maryland...none.
NC...none.
Virginia...none.
Marine...Small Craft Advisory until 5 PM EDT this afternoon for
anz635>637.
Small Craft Advisory until 8 am EDT Thursday for anz630>634-
638-650-652-654-656-658.

&&

$$
Synopsis...lkb
near term...lkb/jab
short term...lkb/lsa
long term...bmd
aviation...lsa
marine...bmd/tmg
climate...