Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
313 PM EDT Sat Apr 25 2015
low pressure over Kentucky will track east this afternoon and
then move southeast across the Carolinas tonight and off the coast
Sunday morning. The low remains offshore as high pressure
gradually builds in from the west for the first half of the week.
Another low may impact the region for the latter half of the week.
Near term /through Sunday/...
for rest of this afternoon...at 1830z radar showing some scattered
returns over lower southern Maryland...but the remainder of the County Warning Area was
cloudy but precipitation free mostly. Leading edge of precipitation along an
Elkins-Staunton Virginia-Charlottesville line. This area is moving east
at a pretty good clip...and will overspread the region in the next
2-4 hours...except NE Maryland could take until 7-8pm for precipitation to start.
Low levels still quite dry across northern 2/3rds of County Warning Area. Precipitation
reaching surface will create low level cooling...so temperatures will
keep on the cool side remainder of this afternoon especially for
this late in April.
For tonight...precipitation associated with warm frontal system lifting
across the region will impact the region mainly through 06z...then
models suggest bulk of precipitation will lighten considerably after
then. Earlier timing of precipitation suggested lingering light precipitation
would impact entire County Warning Area through 10-12z Sunday morning. But
guidance today suggests a faster timing which is reflected in the
forecast. Temperatures will not fall much overnight and basically
trended min temperatures to adjusted met guidance.
Forecast rainfall amounts generally line up pretty well with wpc
quantitative precipitation forecast amounts and will be generally heavier across the SW portion
with amounts around one half inch...District of Columbia metropolitan around one- quarter
of an inch...Baltimore between 1-2 tenths.
Hi res cam models show good agreement with 12z NAM/GFS/sref on
timing of precipitation across area. Latest hrrr guidance suggest the
precipitation could even be more scattered in coverage this evening.
For Sunday...there could be lingering light precipitation across the southern
tier of the County Warning Area just after 12z...but clouds and precipitation will push
south as high pressure builds into the region from the Great
Lakes. High temperatures still cool for this time of year...and used a
blend of MOS/adjacent mav.
Short term /Sunday night through Monday night/...
region remains positioned under upper level low centered over the
Canadian Maritimes while surface low settles well offshore to start
the work week. Generally expecting dry conditions Sun night with a
break in the shortwave energy...though a surface trough could generate
isolated showers second half of the night. Temperatures dropping into the 30s
for lows Sun night could result in any precipitation near daybreak being a
rain/snow or even all snow...with little to no accumulate.
The region will be sandwiched between high pressure over the Great
Lakes and the low offshore Monday...resulting in elevated
winds...with gusts 25-30 miles per hour. Probability of precipitation increase aftr 12z Monday as next
shortwave/vorticity maximum rounds the low...with the better chance western and
eastern fringes of the County Warning Area. The strong shortwave will extend across
the middle Atlantic for most of the day...producing scattered showers.
Precipitation tapers off Monday evening as upper level low pivots offshore. As the
high builds in...expecting to see warming temperatures...with temperatures nearing
normal by Monday night.
Long term /Tuesday through Saturday/...
despite the cool start and continued cold air advection behind the cold
front...temperatures will rebound a few degrees Tuesday as decreasing clouds
allow the late April sun to do its work. This slow warming trend
continues into Wednesday...with temperatures back to near normal...as a weak area
of high pressure builds in.
Model divergence increases substantially by late Wednesday into Thursday with
regards to developing low over gom. Latest model guidance appears to
shunt main impacts to our south...with little quantitative precipitation forecast over County Warning Area. 12z GFS
far different from 00z European model (ecmwf)...as GFS has no coastal low off the
Carolina coast and European model (ecmwf) does. Have lowered probability of precipitation some for
Thursday...although for consistency and to avoid jumping on one model
cycle still kept chance probability of precipitation...although that might be too high.
High pressure returns by Friday...bringing near normal temperatures.
Aviation /19z Saturday through Thursday/...
expect VFR conditions through middle to late day. Precipitation
will move in and ceilings will lower. This evening expect MVFR to
locally IFR ceilings in precipitation...expect BWI/iad/dca ceilings to range from
2-3 kft this evening...locally down to 1kft in heavier precipitation.
Overnight...BWI and iad could see ceilings below 1kft. Winds will be
under 10 kts through the period.
VFR conditions sun-Sun night. Sub-VFR conditions possible Monday with any
rain shower. Gusty northwest winds with gusts 20-25 kts possible as well
during the day Monday...diminishing aftr sunset. MVFR ceilings may linger
through Monday night.
Not expecting aviation concerns Tuesday/Wednesday with VFR conditions.
winds expected to be below 10 kts across the waters today and
variable in direction. Rain will overspread the waters this
afternoon into this evening. Winds remain less than 10 kts through
Sun morning...increasing Sun afternoon. Gusts could briefly touch 18-20
kts Sun afternoon with northerly channeling.
Sub-Small Craft Advisory conditions initially sun evening...with incrsg
winds overnight. Small Craft Advisory conditions with gusts up to 20 kts as early as
the second half of Sun night...becoming more likely aftr daybreak Monday.
Gusts up to 30 kts possible on the Chesapeake Bay during the day. Small Craft Advisory
gusts continue through Monday night.
Small Craft Advisory is possible Tuesday until the pressure gradient weakens with
departing low. Pressure gradient relaxes enough for a return to
light winds by Wednesday.
District of Columbia...none.