Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wakefield Virginia
657 am EDT sun Mar 29 2015
high pressure settles over the region today and moves offshore
this evening. A weak cold front approaches from the northwest this
evening and moves across the area late tonight through early
Monday morning. High pressure returns Monday afternoon into Monday
night. Low pressure tracks across the northern middle Atlantic
Tuesday with the associated cold front dropping through the region
Near term /until 6 PM this evening/...
the latest surface analysis shows 1030mb high pressure centered
over the upper Ohio Valley. This high is slowly building into the
middle Atlantic with many locations over the Piedmont and interior
coastal plain now decoupling evidenced by calm conditions.
Meanwhile...a gusty northwest wind persists along the coast. Temperatures
over the Piedmont and interior coastal plain have generally
dropped into the low/middle 20s as of 330am with lku showing a
temperature of 18 at 315am. Farther east...temperatures remain in the
upper 20s to low 30s...although wind chill values are in the low
20s. See the climatology section below for record lows for this morning.
High pressure will build across the southeast states today...which
will result in sunny and dry conditions locally along with a light
wind. Mixing will be limited with high pressure overhead...so
highs will only reach the low/middle 40s along the coast...to low 50s
over interior Virginia/NE NC despite full sun. These values will average
about -1.5 St dev below the seasonal mean.
Short term /6 PM this evening through Tuesday/...
high pressure shifts offshore tonight as a middle-level trough
tracks across the Great Lakes. An associated middle-level cold front
then moves across the middle Atlantic late tonight through midday
Monday. Numerical models show a decent band of uvm sliding northwest-southeast
across the local area between about 09-18z. However...moisture
remain very limited below 850mb. Given this have trended probability of precipitation
upward into the high chance category (40-50%) for what should amount
to a light quantitative precipitation forecast event (~0.10in or less).
Temperatures should drop quickly this evening under a clear sky.
Overnight lows should be coldest east (low 30s) where clear
conditions will persist the longest. Farther west...lows should be in
the middle/upper 30s...but surface wet-bulbs will be in the low 30s
so it is possible that the onset of precipitation could include a mix of
-ra/ip. The surface portion of the cold front is mainly a wind
shift...so highs Monday will be warmer averaging from the upper
50s/low 60s along the coast...to the middle 60s inland with downslope
westerly flow in the wake of the boundary.
A fast moving low pressure system driven by zonal flow aloft
tracks across the northern middle Atlantic Tuesday afternoon. Expect
mostly sunny conditions to begin the day with increasing clouds
across the north by afternoon. A ribbon of 20-25% probability of precipitation (for -shra) has
been included for the northern tier counties and this is mainly to
account for uncertainty of the low track. It will be difficult to
get any precipitation S of the low track with deep layered west-southwest flow.
Low-level thickness values support highs approaching 70f on
Tuesday over interior Virginia/NE NC. This is certainly possible with
low pressure tracking north of the region resulting in deep layered
west-southwest flow. Forecast highs have been increased into the upper 60s
over the aforementioned areas...with low 60s over the Eastern
Shore...and locally cooler values along the immediate Atlantic
coast. This will be after morning lows in the upper 30s to low
Long term /Tuesday night through Saturday/...
better agreement in medium range guidance with respect to handling
split flow compared to 24 hours ago. To begin the extended...good
model consensus now with a northern stream wave dropping into the northern middle-
Atlantic region late Tuesday night. Associated surface low prognosticated to track
across northern Virginia/Maryland Tuesday night with a weak cold front sweeping across
the region early Wednesday morning. Best moisture/lift will be north of
the local area...but will introduce slight chance-low end chance
probability of precipitation across the NE zones late Tuesday night closest to best
moisture/lift. Surface low and cold front push well offshore Wednesday as surface
high pressure centers over the region. Modest cold air advection and mostly sunny
skies will result in temperatures in the low-middle 60s inland and middle-upper
50s Eastern Shore and coastal areas. High pressure pushes offshore Wednesday
night-Thursday as a southern stream wave lifts from the Southern Plains into the
Tennessee Valley. Moisture return expected thanks to increasing S-southeast flow.
28/12z European model (ecmwf) quicker with bringing precipitation into the region Thursday
afternoon. Have dropped probability of precipitation Thursday afternoon...but kept slight
chance probability of precipitation across the Piedmont. South-southwest flow will help moderate temperatures
into the upper 60s to around 70 inland to low-middle 60s coastal areas
Thursday. Expect clouds to increase Thursday afternoon.
Thereafter...chance for precipitation ramp up Thursday night-Friday as the southern
stream wave lifts over the region. Northern stream wave over the upper
Midwest also prognosticated to flatten and track across the Great Lakes
region late Thursday-Thursday night. Associated occluded surface low locates
over southeastern Canada Thursday night-Friday morning...with an attendant cold
front crossing the region during the Friday-Sat timeframe. Spatial and
timing differences exist...but will carry chance probability of precipitation through Sat
morning. Slight warmer Friday with highs in the low-middle 70s inland and
low-middle 60s coastal areas.
Aviation /12z Sunday through Thursday/...
VFR through the 12z taf period. Surface hi pressure builds in from the west
today...becoming centered over the Carolinas by this afternoon. This will
allow north-northwest winds...gusty at times this morng...to shift to the S/SW
later in the day. Otws...dry weather expected with just some increasing
hi clouds this eveng.
Outlook...the aforementioned high will move to the S/southeast
tonight...with a weak cold front crossing the area on Monday.
There will be a chance for showers early Monday. High pressure
builds back into the area Tuesday. A chance for showers returns
latest surface analysis reveals broad hi pressure centered over the Ohio
Valley. Strong winds continue this morng with pressure rises and cold air advection
over the local area. Small Craft Advisory headlines continue as planned...ending
later this morng over the Bay...then over the Bay/sound...and
finally over coastal waters midday as seas subside to below 5ft. Improving
marine conds expected this afternoon as the hi centers over the
Carolinas. The next cold front approaches from the west tonight...
crossing the waters late Monday-early Monday night. Prefrontal southerly surge
expected late tonight...with speeds increasing to 15 knots in the Bay
and 20 knots in the coastal waters. Models indicate Small Craft Advisory
conditions...but based on warm air advection and cold water...expect a sharp low
level inversion to prevent strongest winds from mixing to the water.
Have capped speeds below Small Craft Advisory at this time and will continue to monitor as
conds will be close to Small Craft Advisory thresholds. Southerly fetch may push seas to 5
feet in the northern coastal waters Monday morning. Southwesterly flow returns Monday
night-tues. Low pressure tracks across the middle-Atlantic region late
Tuesday with another front crossing the water early Wednesday night. Winds
stay at or below 15 knots. High pressure returns weds-thurs.
record low temperatures for Sunday 3/29:
Marine...Small Craft Advisory until 10 am EDT this morning for
Small Craft Advisory until 1 PM EDT this afternoon for anz650-