Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service Baltimore Maryland/Washington District of Columbia
400 am EDT Thursday Apr 17 2014


High pressure over New England will ridge southward toward the
middle-Atlantic coast through the remainder of the week. An area of
low pressure and cold front may affect the area Saturday. A second
cold front looks to move through the region Tuesday.


Near term /today/...

As of 07z...1041mb surface high centered over northern Maine with a surface
ridge/cold air damming wedge extending southwest down the Piedmont
to the deep south states. The ridge axis roughly extends down I-95
with Ely flow over the Bay and southern Maryland and mainly calm conditions
elsewhere. Skies are clear with offshore low clouds along the Gulf
Stream/Labrador current boundary off the Delaware-Maryland-Virginia (according to
GOES-east infrared imagery). Temperatures are generally low to middle 30s
with upper 30s for nearshore and urban areas.

The Wedge persists today. Abundant sunshine again...though east of
the ridge axis could see marine layer clouds spread in from the
ocean (the day shift will need to monitor this). The warm middle April
sun will continue to modify the airmass with maximum temperatures generally middle
50s across the balt-wash metropolitan with upper 50s to low 60s over west and
southwest sections of the County Warning Area. Areas west of the Blue Ridge should
be well protected from low clouds and could warm into the middle 60s.


Short term /tonight through Friday/...

The question for tonight is will light flow prevent decoupling and
will low clouds spread across at least eastern sections of the County Warning Area.
NAM forecast soundings are cloudier than GFS ones...and thus met
guidance min temperatures are higher than mav ones. North central
Maryland seems to be the coldest areas with an active growing season
tonight. With mins forecast in the low 30s...went ahead with a
freeze watch for Frederick Maryland to Harford. Day shift will have to
determine if a frost/freeze or neither is necessary.

Friday...modification/moderation continues with maximum temperatures in the upper
50s east to middle 60s west. Cloud cover will continue to play an
important role with the surface ridge axis nearly stationary.


Long term /Friday night through Wednesday/...

Middle Atlantic has xprncd what seemed Lake A neverending series of waves.
But for a change the weather should be rlvtly benign in the extend - no
wintry concerns for one thing. Overall upper level flow could be
characterized as a fairly high znl near the U.S./Canadian border.
This will aid in keeping temperatures on the moderate side - neither too
hot or cold...More Lake what should be occurring in middle Apr. One
short WV is expeceted to push through the northestern U.S. But this is looking
less and less Lake A precipitation producer.

The next precipitation chance looks to be on Tuesday west/ another frontal passage. No cold
temperatures to worry about - highs in the l70s...lows in the u40s/l50s.


Aviation /07z Thursday through Monday/...

VFR at least into the afternoon across the terminals. A surface ridge
will persist over the area with an onshore flow I-95 and east. Ocean
clouds with MVFR ceilings may move in late today/tonight in this onshore
flow. Risk for MVFR ceilings also for Friday.

VFR conds are expeceted for the majority of the extend period.



Onshore flow across the waters. Often times this flow is stronger
than prognosticated by models. So far however...Ely flow has mainly been
gusting to 15 knots...less than prognosticated by models. Still expect it to
increase this morning as northeasterly flow overspreads the waters. A bit of
a lull during the afternoon...then onshore flow increases again. Small Craft Advisory
most of the Maryland part of the Bay this morning...then southern Maryland waters for
the afternoon. Most of the waters in an Small Craft Advisory tonight. Onshore flow
looks to be sub Small Craft Advisory for Friday.

Winds may gust to 20 knots on Sat. No probs foreseen Sunday.



Record lows for April 17...
3 am temperature
BWI...26f in 1962 33
dca...26f in 1875 41
iad...27f in 1983 30



Manassas NWR xtmr is working intermittently. Phone technicians have
been notified.


Lwx watches/warnings/advisories...
District of Columbia...freeze warning until 9 am EDT this morning for dcz001.
Maryland...freeze warning until 9 am EDT this morning for mdz004>007-
Freeze watch from late tonight through Friday morning for
Virginia...freeze warning until 9 am EDT this morning for vaz036>040-042-
Marine...Small Craft Advisory until 3 am EDT Friday for anz532>534-537-
Small Craft Advisory from 6 PM this evening to 3 am EDT Friday
for anz531-536-538-539-542.
Small Craft Advisory until 10 am EDT this morning for anz530-