Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Raleigh NC
928 PM EDT sun Mar 29 2015
Synopsis...high pressure overhead will move offshore tonight ahead
of a cold front. This cold front will move through the region
Monday. Another cold front should move through the region overnight
Tuesday into Wednesday.
Near term /through Monday/...
as of 926 PM Sunday...
The main forecast problem this evening is whether or not a frost
advisory would be needed in the southeastern counties along I-95 as
low temperatures are expected to drop into the middle to upper 30s
overnight. After sitting on the fence for a long time...ultimately
have decided that there is not enough evidence to warrant the frost
advisory at this time for several reasons. First the argument for an
advisory stems from the fact that high resolution models were
picking up on an area of higher dewpoints along our eastern counties
that developed rather quickly this evening and did in fact come into
fruition. At rwi for example the dewpoint went from 16 to 26 degrees
in one hour. At the same time temperatures have already dropped into the
upper 30s. The rapid increase in dewpoints and drop in temperatures
supports the possibility of frost...particularly in rural areas
where temperatures are normally cooler. Those same hi-res models
however are showing that the window for temperatures cold enough and
dewpoints high enough for frost is very small...particularly between
6-9z. While dewpoints in the east will continue to rise after this
time period...temperatures are also expected to rise as the high
shifts southeast and light winds pick up out of the southwest. This
not only makes the window for frost very short but the impacts
minimal...especially after last nights hard freeze. Therefore will
forego the advisory at this time. Expect lows earlier than
normal...again around 6-9z with a non-typical hourly temperature
curve thereafter. -Ellis
Moisture and lift will increase through Monday morning. Lift will
increase as the right entrance region of a upper level jet moves in
late tonight. This will result in a band of showers moving through
the area from west to east...roughly between 09-16z. Probability of precipitation will
quickly decrease late Monday morning through early afternoon. Quantitative precipitation forecast
values are prognosticated to be rather light with only a tenth of an inch
or so. -Krd
Short term /Monday night through Wednesday/...
as of 315 PM Sunday...
Monday night and Tuesday... weak surface high pressure will build
into central NC in the wake of the exiting frontal system Monday
night into early Tuesday. The approach of a disturbance in the northwest
flow aloft may initiate a period of orographic cirrus over our
region by early Tuesday. The surface front and wave associated with
the disturbance aloft will cross to our north Tuesday afternoon and
evening. This will set-up a Lee side trough over the western
Piedmont by Tuesday afternoon. The pressure gradient is expected to
tighten in response to this Lee side trough and the approaching surface
low. The resultant SW low level flow will aid to boost temperatures back to
near normal levels. Min temperatures Monday night upper 30s to around 40.
Maximum temperatures Tuesday upper 60s-lower 70s.
Tuesday night and Wednesday...surface cold front will sweep across
central NC pretty uneventful as atmosphere too dry to support precipitation
generation. Bulk of cold air behind the front will remain mostly to
our north. 850mb thermal trough does extend southward into the northern
counties on Wednesday with effects a bit more pronounced over the
northern coastal plain versus the western-southern Piedmont. Min
temperatures Tuesday night middle-upper 40s. High temperatures Wednesday low-middle 60s
NE to the lower 70s SW.
Long term /Thursday through Sunday/...
as of 345 PM Sunday...
Thursday...medium range models in decent agreement...depicting a
weakening middle level short wave in the southern stream lifting across the
deep south into the southeast U.S. Meanwhile a short wave in the northern stream
will progress east across the Great Lakes into the New
England...dragging a cold front toward central NC by Thursday night.
Bulk of showers associated with the southern system will likely
occur more to our west-SW...with shower generation decreasing
farther east as system shears out. SW flow ahead of the approaching
cold front will continue to pull warm air into central NC. The
mixture of sun/clouds and spotty shower coverage should permit temperatures
to rebound into the 70s areawide. If sun is more prevalent than
clouds Thursday afternoon...could see temperatures reach/slightly exceed 80
degrees over teh southeast half.
Friday into Saturday...surface cold front will drift slowly east-southeast
through this period...possibly exiting our eastern counties by middle
day Saturday (based on slower gfs). Appears bulk of showers Friday
will occur west-north of central NC...though increasing across the
Piedmont by late in the day. Shower coverage should maximize Friday
night as the front drifts across the area. Maximum temperatures Friday
dependent on shower coverage and cloud thickness. Potential for
temperatures to reach 80 again in the far southeast Friday afternoon if showers
and clouds are delayed. Should see slightly cooler temperatures Friday in
the far north-northwest due to more extensive cloud coverage. Slightly
cooler temperatures anticipated Saturday with shower threat diminishing northwest-
southeast throughout the day. Easter Sunday at this time appears dry and
seasonably cool as high pressure builds into our region from the northwest.
Aviation /00z Monday through Friday/...
as of 815 PM Sunday...
Current VFR conditions will deteriorate to a short period of MVFR
then IFR conditions Monday morning into early afternoon... with MVFR
visibilities in a period of rain. High pressure over the area this evening
will move offshore as a cold front approaches from the northwest...
bringing poor aviation conditions for 4-6 hours... starting around
12z at int/gso... around 13z-14z at rdu... and around 15z-16z at
rwi/Fay. Improvement back to VFR ceilings/visibilities is expected around 16z
at int/gso... around 18z at rdu... and around 19z-21z at Fay/rwi...
and should persist through the end of the taf valid period. Another
aviation concern will be strengthening winds in the 1200-1800 feet above ground level
layer... potentially up to 40-50 kts from the SW. While we may not
necessarily meet low level wind shear criteria... with surface winds
from the SW at just 8-12 kts... the increase in wind speed with
height may cause mechanical turbulence and difficulty handling some
aircraft. These stronger winds aloft are most likely in the 06z-18z
Looking beyond 00z Tuesday (early Monday evening)... VFR conditions should
dominate through Wednesday night... although another weak cold front will
drop southeast through the area early Wednesday morning causing a shift in
surface winds. The return of this front from SW to NE through the
area as a warm front Thursday afternoon/night may bring a period of MVFR
ceilings with a few showers. -Gih