Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Blacksburg Virginia
751 am EDT Tuesday Mar 11 2014
an area of high pressure...centered over the southeast states...
will maintain control of the weather across the middle Atlantic
region though today. Meanwhile...an upper level trough will be
moving across the plains...resulting in the development of an area
of low pressure which will be moving into the Midwest. This low
pressure system is expected to move east...impacting the weather
across the eastern United States on Wednesday. High pressure
follows this system for the end of the week.
Near term /through tonight/...
as of 400 am EDT Tuesday...
Westerly flow surface and aloft will promote another day of above
seasonal temperatures as warm air gets drawn eastward from the
central Continental U.S.. as this air passes over the central Appalachians it
will get an additional temperature boost courtesy of downslope
adiabatic warming. With 850 mb temperatures near +10c surface readings
should easily reach the 60s in the mountains and 70s downwind of
the mountains across the foothills and Piedmont. These
temperatures are 15f-20f warmer than normal.
Dew points today will be a little higher...but still looking at a
dry afternoon with the relative humidity bottoming out between
20 and 30 percent. Any cloud elements today will be of the high
thin variety...from moisture streaming east from the developing
storm system in the middle part of the country.
Clouds will thicken across the area tonight as a surface cyclone
evolves and moves east from the central United States. There are
two pieces of upper level energy that will come into play with the
evolution of the upcoming storm. One is from an upper low that has
been stuck in the southern stream over Mexico and south Texas. The
other is a short wave trough in the northern jet stream which has
crossed The Rockies and is poised to cross the Central Plains
today. All forecast models indicate the southern stream upper low
will get picked up by the stronger northern stream trough...
gaining latitude as it moves across the Gulf Coast states toward
the Carolina coast.
The models never really phase the two energy sources...thus
expecting two separate areas of precipitation...one moving northeast
across the southeast states and potentially skirting our southern
County Warning Area Wednesday...and the other area of precipitation associated with the
northern stream trough which will be moving across the Midwest into
the Ohio Valley...most of this precipitation headed for New England. Not
overly confident we will get a lot of quantitative precipitation forecast with this sort of set-
up...the deeper moisture sources passing north and south of the
forecast area. At the very least we should see rain showers...
beginning daybreak Wednesday...but think quantitative precipitation forecast for the overall
event...which culminates on Wednesday...will average a third of
an inch or less. That said...the main weather hazards from this
upcoming storm will not be the rain...but from the wind and a
blast of cold air that will follow.
Short term /Wednesday through Friday night/...
as of 400 am EDT Tuesday...
Low pressure center around Louisville Wednesday morning with a
trailing cold front will travel northeast reaching the Atlantic
coast by Wednesday evening. The low will intensify as it tracks
northeast to just off the New England coast by Wednesday night. The
upper trough axis eventually passes east of the area by late Thursday
into Thursday night. The best probability of precipitation expected
to be from 12z/8am Wednesday to 00z Thursday/8pm Wednesday.
Used the adjmavbc to generate high temperatures Wednesday from the
upper 50s in the west to the lower 70s in the east. Colder air aloft
coming in late Wednesday will lead to larger lapse rates. In
addition...40 to 55 knot southwest 850 mb winds ahead of the cold
front will result in a large amount of shear. The instability will
be dependent on the cloud cover. The slower the clouds and
precipitation arrive Wednesday...the better the chance for heating
in the morning and instability ahead of the front in the afternoon.
Convective available potential energy around 500 j/kg and healthy shear support convection in
forecast. Swody2 placed a 5 percent chance of severe across eastern
portions of County Warning Area.
Models are fairly close with the timing of the cold front Wednesday
afternoon in the mountains reaching the coast by Wednesday night.
Behind the front...large pressure rises of 7 to 14 mb/6hr and strong
cold air advection will combine with the low level jet to produce
very gusty surface winds. BUFKIT still showing the potential for
Wind Advisory level wind gusts Wednesday night and Thursday morning.
Will highlight the wind potential in severe weather potential statement. Upslope flow and low level
moisture...along with some weak upper support with bring snow
showers into western favored areas in the mountains. Low
temperatures Wednesday night will drop into the teens in the
mountains to the 20s in the east. Wind chills will drop below zero
in the northwest mountains Thursday morning.
Taper off snow showers Thursday morning as high pressure and upper
ridge builds into our region. Went with highs on Thursday from the
the middle 20s in the mountains to the lower 40s in the southeast.
Thursday night surface ridge axis will be directly over the area.
Expecting surface winds to diminish with good radiational cooling.
Low temperatures will be unseasonably cold Thursday night with
readings from the the teens to the lower 20s. A 1026 mb high will
build over the region Friday moderating temperatures. High
temperatures Friday will vary from the around 50 degrees in the
mountains to the middle 50s in the Piedmont.
Long term /Saturday through Monday/...
as of 300 PM EDT Monday...
Next system coming through the northern stream stays north of the
forecast area. Surface low with this system will push a cold front
through the region on Saturday. Any threat of precipitation will be
confined to the northwest County Warning Area.
Long range models become significantly different with the upper
pattern on Sunday and Monday. Will be leaning toward the split
flow of the European model (ecmwf) which holds an upper trough over the Great Lakes
and closes off an upper low over the Southern Plains on Monday.
By day 7...Monday...the European model (ecmwf) is starting to suggest the
potential for a surface low off the Carolina coast. If the large
high that the model has over the Great Lakes is able to wedge down
the east side of the Appalachians...there may be a potential for
winter precipitation Monday night.
Aviation /12z Tuesday through Saturday/...
as of 800 am EDT Tuesday...
VFR through the 24 hour taf period. The only weather concern
through at least 18z/2pm today will be the persistent westerly
downsloping winds over the mountains. Wind gusts vicinity of the mountains
will approach 25 kts this morning. These winds will relax in the
afternoon as pressure gradient weakens.
Sub-VFR conditions return from southwest to northeast late
tonight through Wednesday morning as a warm front lifts through
the area with associated rainfall. Wednesday afternoon and evening
a strong cold front will cross the area with stronger rain showers
and perhaps a few thunderstorms across the Piedmont. Wednesday
night into Thursday...cold air behind the cold front with
lingering moisture will bring snow showers to the
mountains....klwb and kblf. Potential brief IFR conds with MVFR
probable. Also...strong winds are expected Wednesday night into
Thursday behind the front. Wind gusts vicinity of the mountains may
approach 40 kts.
By Friday...high pressure will settle over the area and bring a
decrease in wind speed and a return to VFR conditions for the
long term...air mass