Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service Baltimore Maryland/Washington District of Columbia
347 am EDT sun Apr 20 2014

Synopsis...

Low pressure off the Georgia coast continues to spread high
clouds into the Middle Atlantic States. High pressure over Quebec
will build into the area today as the low tracks further offshore.
The high will remain in control of the regions weather through
Monday. A cold front will bring showers to the area Tuesday and
Tuesday night. High pressure builds back in for the second half of
the work week.

&&

Near term /today/...

As west/ yesterday...the weather story for the middle Atlantic region is the battle between
low pressure - which migrated from northern Florida yesterday to about 160 Michigan east of sav
this morning...and an area of high pressure over southern Quebec. What this
meant to the forecast yesterday...and today...is high clouds over VA/MD/DC. These
could either be classified as broken or thin overcast...as is evidenced by
the moon being dimly vsbl at 3 am...but these should be moving to the east
along west/ the low by late afternoon.

High today in the u60s - right around climatology norms.

&&

Short term /tonight/...

We are still xpctg a period of clearing tonight as the low pulls moves
further offshore. Lows in the mu30s...which is probably a degree or two
above the required needed values for a frost advisory.

&&

Long term /Monday through Saturday/...

Monday while we are experiencing another quiet weather day across the
region...a couple of fast-moving shortwaves will be drifting across
southern Canada. The western shortwave will be sliding toward the northern plains
and will pick up a dissipating cut off low over the Central Plains.
Combining the moisture from the two and phasing them into one much
longer shortwave trough will occur during the daytime hours on Monday.
This wave will be a series of smaller zones of forcing/lift - so not
a steady line of convection or stratiform precipitation but instead merely
batches of them all along the trough axis. By late Monday...the trough
axis will be on the doorstep of the Appalachians...ready to through our
region on Tuesday. Before then...we'll top out again in the u60s/l70s
over the area on Monday afternoon for daytime highs. Temperatures ahead of the
upper trough will only drop into the l50s Monday night.

As low level moisture increases ahead of the trough passage early
Tuesday...it will help to add some instability - along west/ another
relatively warm day. Clouds will stream over the region in earnest
Tuesday morning...which may limit heating a few degrees ultimately and help
slightly inhibit a stronger convective potential for the day. Only a
couple hundred j/kg of cape appearing on area models soundings for
Tuesday...for multiple models and over the best potential part of the
day for thunderstorms. Unlike the other convective and a few non-convective
events so far this year...shear will be lacking - less than 20kt
bulk and mean layer shear at the height of the afternoon heating. Add to
that the latest model trend of nearly disintegrating the precipitation
along the surface boundary as it has moved across our area late Tuesday
aftn/eve. Still some residual activity across Delaware-Maryland-Virginia and the
Tidewater Tuesday night....but a quick drop off in precipitation chances toward
and after sunset.

A modest region of subsidence will then spread across the area on
Wednesday...bringing gusty northwest winds and drier/cooler air. Not nearly as
potent as the storm system a week ago at the same time...but still
only allowing temperatures to rise barely into the l60s across much of the
area west/ a brisk 15-25mph northwest wind. A potent cut-off upper low over
the northern rockies will lose some of its punch as it slides east of the
miss river late this week...as high pressure again gives the middle Atlantic
another quiet weather day on Thursday. Another cold and closed upper low will
barrel across the northern plains and the Great Lakes Thursday into Friday. By
the time the tail end of the associated cold front swings across the
region...it should be losing much of its precipitation west/ only scattered
batches moving across the area Friday into Sat.

&&

Aviation /07z Sunday through Thursday/...

VFR conditions expeceted today through Monday morning.

High pressure will hang tough for much of Monday...but the upper
cirrus will overcome the area later in the day - just ahead of
another storm system. The frontal system looks relatively weak for
Tuesday aftn/eve...though a few thunderstorms across still possible for
scattered areas of the middle Atlantic region. The frontal system will then
work its way off the coast into the late night hours. High pressure
and some gusty northwest winds on Wednesday - quieting down our weather for Thursday
briefly before a frontal boundary sweeps through the area on Friday.

&&

Marine...

On the waters at this time - light winds on the ptmc and NE 5-10 knots on the
ches Bay. These are expeceted to increases aftr daybreak as the pressure gradient
between the southeastern coastal low and the northestern high pressure grows stronger. Small Craft Advisory
is in effect for the daylgt hours then winds weaken tonight.

Winds will slack off over the waters by early Tuesday...as the center of
surface high moves off the coast and winds turn southerly. A cold front will
push through the region late Tuesday...bringing some scattered showers and
possibly some isolated thunderstorms just south of the metropolitan District of Columbia area. Breezy
northwest winds of Wednesday afternoon...though high pressure will again overtake the
region for the second half of the week.

&&

Lwx watches/warnings/advisories...
District of Columbia...none.
Maryland...none.
Virginia...none.
WV...none.
Marine...Small Craft Advisory from 6 am this morning to 2 PM EDT this
afternoon for anz530-535-536-538>540.
Small Craft Advisory until 8 PM EDT this evening for
anz531>534-537-541>543.

&&

$$
Products...Woody!/Gms