Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wakefield Virginia
654 am EST Thursday Mar 5 2015
a cold front will stall over North Carolina today...with a wave
of low pressure moving along the front this afternoon and evening.
This will bring another round of wintry weather to the
area...followed by cold and dry conditions by Friday. Gradually
moderating...milder temperatures are expected late in the weekend
into next week.
Near term /through tonight/...
the primary change to the current forecast reflects slower evolution
of the upcoming system. Start times of the advisories have been
delayed. Additionally...advisories have been raised for southeast Virginia/NE NC
where the potential for a 3-5hr period of sleet exists late this
afternoon and evening. Warnings remain as is.
Latest GOES WV imagery shows the southeast US ridge remaining rather
stubborn...which is keeping deeper moisture well west of the region
back over the Cumberland Plateau. The result of the ridge holding
strong will likely result in a longer period of 'warmer' middle-level
thickness values...which should result in more sleet. As a
result...snow/sleet accumulation has been trimmed back across
central portions of the area. Accumulation (primarily sleet) has
been increased over southeast portions where moisture should linger into
the evening. At the surface...1035mb high pressure is centered over
the plains states. Colder air over the Ohio Valley is spreading eastward
across PA...which has resulted in a change to snow over northern Maryland as of 6
am. Locally temperatures range from the upper 30s northwest...to the low
A strong anti-cyclonic jet remains in place from the middle miss valley
through Atlantic Canada and will translate eastward through the day as a
strong trough digs across the upper Midwest and Great Lakes. It is
at this time that deeper moisture will arrive and rrq forcing will
be idealized, as strong pv anomaly rides across the area this
afternoon through tonight. This forcing should eventually trigger
the onset of wintry precipitation from north-northwest-south-southeast across the area.
Critical 850 mb-7 thickness values (sub 1540m) are not realized until
late in the afternoon tonight over northern half of the area.
However...by this time the strongest uvm will be exiting the coast.
Overall, utilizing roebber slr forecasting tool along with local
thickness chart, forecast slr values will be quite low for much of
the day (perhaps as low as 4:1-8:1). This makes sense given that
there will be a prolonged period of sleet (which will eat into
snowfall totals)...and that middle-level thicknesses will be 'warm'
during the strongest forcing in the early to middle afternoon hours.
Based on all of the above, have continued with a stripe of 3-5" of
wet snow/sleet along a line from Palmyra, Virginia to Tappahannock and
Salisbury, Maryland. This is bordered by a band of 2-3" for other portions
of the northwest Piedmont...Northern Neck...northern ric suburbs and remainder
of the lower Maryland Eastern Shore. Currently 1-2" of sleet/snow is
forecast from the southern sections of the ric metropolitan /Tri-Cities
down through Hampton Roads...with around 1" along the Highway 58
corridor over central Virginia into the Piedmont.
Wintry precipitation should taper off Thursday evening...as top down drying ensues
west/drier air arriving from the northwest during the late evening/early
overnight hours. The advisories will run through midnight...with the
southeast portion lingering through 3 am where drier air will be slower to
Short term /Friday through Saturday/...
high pressure/fair weather to prevail during the short term.
Shortwave exits the NE coast Friday morning with confluence aloft over
the mid-Atlantic. This will allow strong 1030+mb Arctic high
pressure to center over the region Friday. Cold front locates
offshore...extending southwestward into the northern Gulf. Best moisture gets
shunted offshore in increasing westerly flow aloft. The result will be
dry conditions...but well below normal temperatures. Models
consensus attempts to show highs in the 25-30 range Friday.
However...850 mb temperatures ~-8c and low level thicknesses yield temperatures in
the low-middle 30s...with possibly upper 20s over the interior Maryland Eastern
Shore. Will side with the later reasoning given that we are now
into March. The next northern stream shortwave crosses the region Friday
night...resulting in little more than partly cloudy skies. Cold
Friday night with low generally middle teens to around 20...with 10-15
possible from interior S-central Virginia to the Eastern Shore. Zonal flow
develops Sat as high pressure remains over the region. Southwesterly return
flow commences...resulting in moderating low level thicknesses and
temperatures. Thicknesses yield temperatures in the low-middle 50s inland sun...but
guidance running in the middle-upper 40s. Trended toward
thicknesses...with highs in the upper 40s-low 50s inland and low
to middle 40s near the coast...under mostly sunny to partly cloudy
Long term /Saturday night through Wednesday/...
going close to the 12z GFS/CMC in the extended period. Will maintain
dry weather from Sat night through at least Monday night at this time..as hi pressure
will be over the area. There is then a hint of low pressure moving NE out
of the Gulf and across the region Tuesday through Wednesday. For now...just have
slight chance of rain during this time. Temperatures will be closer to
seasonable rdgs through the period. Min temperatures will range from the upper
20s to upper 30s...and maximum temperatures will range from the upper 40s to upper
50s...maybe into the 60s on Wednesday.
Aviation /12z Thursday through Monday/...
as of 12z...frntal boundary located over NE NC continues to slide
S...with gusty northerly winds north of the front across the forecast area. Low ceilings and
visibilities are commonplace this morng as rain overspreads the area. The
rain mixes with sleet/freezing rain later this morng and then
transitions to sleet/snow from northwest to NE during the second half of
the day. IFR/LIFR conds expected over all taf sites with the precipitation.
Two to four inch snow accumulations are expected at ric and sby
with one to two inches or less at the southeast taf sites. Winds will be
gusty from the north much of the day.
Outlook...precipitation moves off to the east this evening/overnight and
VFR conds return. Improving weather is expected Friday into early
a cold front is located near the NC/Virginia border Erly this morng...and
will slowly slide S through midday. North winds will pick up over all
waters...increasing to Small Craft Advisory thresholds by the midday/afternoon hours. Also
hoisted a gale warng for the southern coastal waters where frequent gusts up
to 35 knots are expected this eveng and overnight. Waves over the ches Bay
will build to 3-5 feet...with seas over coastal waters bldng to 6-9 feet. All
marine headlines end during the day Friday as winds/waves/seas decrease
as hi pressure builds in from the west. Benign marine conds continue into the
weekend with the hi remaining in the vicinity.
Maryland...Winter Storm Warning until midnight EST tonight for mdz021>025.
NC...Winter Weather Advisory from 4 PM this afternoon to 3 am EST
Friday for ncz012>017-030>032-102.
Virginia...Winter Weather Advisory from 1 PM this afternoon to midnight
EST tonight for vaz065-066-079>082-084-086>094-100.
Winter Storm Warning until midnight EST tonight for vaz048-049-
Winter Weather Advisory from 10 am this morning to midnight
EST tonight for vaz060>062-067>073-077-078-083-085-099.
Winter Weather Advisory from 4 PM this afternoon to 3 am EST
Friday for vaz095>098.
Marine...Small Craft Advisory until 4 PM EST Friday for anz650-652-654.
Gale Warning until 7 am EST Friday for anz656-658.
Small Craft Advisory until 7 am EST Friday for anz635>637.
Small Craft Advisory until 1 PM EST Friday for anz632>634.
Small Craft Advisory until 10 am EST Friday for anz630-631-638.