Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wakefield Virginia
416 PM EDT Friday Mar 27 2015
an upper level disturbance crosses the middle Atlantic region through
Saturday night. High pressure returns for Sunday. A weak cold
front will move across the region Sunday night into early
Monday...with high pressure returning Monday afternoon.
Near term /until 6 am Saturday morning/...
quite a different afternoon across the forecast area.../W cloudiness...widespread
rain...and temperatures avgg 30-35f lower than 24 hours ago. Cold front from earlier
today has settled well to the southeast. One final surface low pressure wave to
track NE and off the CST of NC by lt this evening. Most widespread of
the rain has shifted to mainly along-east of i95 so far this afternoon...will
keep probability of precipitation hi (80-100%) most places through early this evening as temperatures
hover mainly from 40-45f.
Precipitation generally moves offshore after 00z this evening. However...the
approaching upper trough (now extending from lower Michigan S through the Tennessee
vly) will tend to keep enough uvm in place along with lingering
moisture to touch off spotty rain showers through the overnight hours as it
approaches from the west. With very cold air aloft arriving after
mdngt...there could be snow showers or mixed rain/snow showers. No snow
accumulate is expected and travel not likely to be impacted. Low temperatures
tonight from near 30f northwest to the M/u30s southeast.
Short term /6 am Saturday morning through Monday/...
the upper trough moves directly overhead on Sat...then offshore by
Sun morning. Highs on Sat are only expected to reach into the M/u40s.
If there are any lingering showers in the morning...there could
still be a mix of rain and snow. Afternoon instability west/ the trough
overhead will likely result in widespread cumulus which may result
in isolated showers that should stay confined along the coast. All
showers finally come to an end early Sat evening...the sky clears...and
temperatures plummet into the 20s by Sun morning.
Surface high pressure moves across the region on sun. Expecting sunny/dry/cool weather
west/ light winds. Limited mixing will keep temperatures in check with
readings only rising into the M/u40s along the CST to the l/m50s
across interior Virginia and NE NC.
Next trough aloft and accompanying surface cold front to cross the region lt
Sun night/Monday morning...W/ vrb clouds and low probability for precipitation (15-30%).
Expecting more of a deep layered west-southwest low level flow on Monday leading to better
warming. Sky avgg out psny on Monday...W/ hi temperatures from the l/m60s
east...to the l70s west.
Long term /Monday night through Friday/...
split flow pattern prevails through the extended...as northern stream
expected to remain active. The first northern stream shortwave exits the
coast late Monday night...with another shortwave reaching the Ohio Valley
late Tuesday. Associated low pressure expected to lift across New
England Tuesday as high pressure builds across the southeast states.
However...there is a great deal of uncertainty with the exact track
of the northern stream low...with the 27/12z GFS lifting it through NE...the
27/12z European model (ecmwf) through the northern middle-Atlantic region and the 27/12z CMC
through NC. Based on the overall progressive pattern and upper level
flow...prefer the northern track...keeping the forecast area dry. Associated weak
cold front pushes across the region Tuesday night-weds. Limited
moisture and little appreciable forcing will result in a dry frontal
passage. Upper/surface high pressure builds over the eastern Continental U.S. Wednesday.
Thereafter...models diverge with the handling of a southern stream system
lifting from the Southern Plains into the Gulf states Wednesday-Wednesday night.
GFS quicker to return moisture to the region as high pressure
locates off the southeast coast Wednesday-Wednesday night...while its European model (ecmwf) and CMC
counterparts are slower with the moisture return. Thereafter...the
next northern stream system prognosticated to reach the Great Lakes/Ohio Valley
late this week into early next weekend. Significant spatial and
timing differences exist...with the GFS pushing the front through 18
hours before the European model (ecmwf) (fri vs. Sat morning). Will maintain low end
chance probability of precipitation beginning Thursday. Will carry low end chance probability of precipitation through
Friday...but again confidence is not high at this time.
Temperatures to begin the extended will be right around seasonable
norms...in the 60s inland and upper 50s-low 60s Eastern Shore and
coastal areas. Thursday highs will be dependent on potential cloud
cover/precip. Have opted for a blend...resulting in highs in the
upper 60s to near 70 inland and low-middle 60s Eastern Shore and coastal
areas. Lows generally in the low-middle 40s.
Aviation /20z Friday through Wednesday/...
a cold front near the Carolina coast south of Cape Hatteras has a
low pressure system that will move to the northeast out to sea
this afternoon. A deep upper level trough will approach the Middle
Atlantic States from the west Saturday morning. High pressure
builds into the region Saturday night and Sunday.
Conditions at the taf sites have frequently varied from VFR to IFR
with MVFR being the most predominant condition except mostly IFR at
ecg. It has been difficult to nail down the trends but bufr
soundings would indicate an overall decrease in low level moisture
toward evening. The soundings become more saturated again with the
approach of the trough early Saturday morning. Did not lower
ceilings very much during this time frame and any precipitation will be too
sparse and uncertain to include in the taf. An improving trend
returns toward midday Saturday.
Winds diminish late today as the pressure gradient weakens but they
strengthen again Saturday morning as the low off the coast
intensifies with the approach of the upper level trough.
Outlook...mainly dry weather during the next several days should
promote good flying conditions.
cold front has located off the southeast coast this afternoon. An area of
low pressure has developed along the front off the SC coast.
Meanwhile...high pressure has centered over the Great Lakes region.
Current observation over the water indicate northerly winds average 15-20 knots with
waves 2-4 feet and seas 4-6 feet. Surface low lifts northeastward tonight tonight as
high pressure remains over the Great Lakes. This will result in
another surge tonight. Strongest cold air advection arrives after midnight...with
northwest winds increasing to 20-25 knots with gusts to 30 knots over the water.
High pressure slowly builds southeastward through Sat night-Sun
morning...resulting in an extended period of cold air advection. Small Craft Advisory conditions
will likely persist through Sun morning until high pressure finally
builds over the water. Waves generally 3-4 feet and seas 4-6 feet. Northwest
winds subside to 10-15 knots Sun afternoon with seas dropping below 5
feet. Extended Small Craft Advisory headlines through Sun morning. High pressure quickly
passes over the region sun...and then moves offshore Sun night. Flow
shifts to the south-southwest. The next (weak) cold front approaches from the west
late sun. SW flow increases late Sun night...with models indicating
Small Craft Advisory conditions. However...based on warm air advection and cold water...do not
anticipate Small Craft Advisory conditions. Very little cold air advection in wake of the front late
Sun night-Monday morning...so Small Craft Advisory conditions are not anticipated
at this time.
Marine...Small Craft Advisory from 1 am Saturday to 7 am EDT Sunday for
Small Craft Advisory until 11 am EDT Sunday for anz630>634.
Small Craft Advisory until noon EDT Sunday for anz650-652-654-