Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Raleigh NC
739 am EDT Wednesday Jun 3 2015
Synopsis...a middle level low pressure trough and surface cold front
extending along the central and southern Appalachians will drift
slowly eastward then stall over the Carolinas through the rest of
the work week...bringing unsettled weather.
Near term /through tonight/...
as of 330 am Wednesday...
Plume of moisture with high precipitation water values will remain over
central NC today and tonight as the upper level low to our west
slowly spins over the southern Appalachians. Lobes of vorticity
rotating around this feature will cause periods of showers and
scattered thunderstorms at most anytime though coverage will likely
peak in the late afternoon-early evening coincidental with peak
heating. One notable change today compared to yesterday is that a
surface cold front has edge southward into the northern Piedmont-
northern coastal plain. Northerly flow behind this boundary has advected a
more stable air mass into our far northern counties. Thus thunder
potential will be less over the northern counties compared to the
south. As stable air mass begins more firmly entrenched later today
(hybrid cad?)...character of precipitation across the far north-northwest may
become more stratiform in nature (rain/drizzle versus showers).
Best focus for showers and storms will occur along and ahead of the
surface boundary (southern counties). This feature will aid to focus low
level convergence...leading to an enhance probability of training
echoes and associated heavy/locally excessive rainfall. Similar to
the past few days...potential will exists for a few strong to
locally severe storms. However...model parameters today are weaker
with available low level instability though 0-6km bulk shear
slightly stronger...possibly supporting formation of banded
convection across the south-se. Again...main severe weather threat
will be locally damaging downburst winds along with torrential
downpours which may lead to street/low lying flooding.
Tonight...presence of middle-upper low to our west-SW and the plume of
moisture over our region will likely maintain areas of showers for a
good part of the night...especially over our eastern and southern
counties...and areas of rain/drizzle over the northern Piedmont.
Maximum temperatures today will be cooler than Tuesday...especially across the
north. Maximum temperatures near 70 northwest to near 80 far southeast. Mins tonight upper
50s/around 60 northwest to the middle 60s southeast.
Short term /Thursday and Thursday night/...
as of 330 am Wednesday...
Middle-upper level low projected to be overhead Thursday. This will
shift the moisture plume more to our east along with better upper
divergence. This should begin a downward trend in shower/rain
coverage...most notable in the west. Extensive clouds and presence
of the low aloft will result in a lower than normal diurnal temperature
recovery. Maximum temperatures Thursday afternoon may remain in the 60s over a
large part of the Piedmont. For now will go with temperatures near 70-lower
70s...warming to the upper 70s over th far south-se. Best chances
for rain will be over our eastern counties...trending lower to our
west-SW. At this time...atmosphere appears too stable and the bulk
shear too weak to support any strong-severe storms. If there is a
threat..it will be over sections of our southeast ( namely Sampson county).
Rain chances will dwindle Thursday night as the middle-upper level low
is ushered east-NE in response to an amplification in the northern
stream across the Great Lakes into New England.
Long term /Friday through Tuesday/...
as of 400 am Wednesday...
Friday: a cut-off upper low centered in vicinity of Knoxville Tennessee at
06z this morning will gradually become progressive over the next 48
hours...tracking eastward through the Carolinas Thursday night into Friday.
Latest guidance suggests the upper low will be centered in vicinity
of the I-95/Highway 17 corridor in eastern NC on Friday...with an
attendant surface low offshore the Carolina coast. Diurnal
destabilization will be hampered by cloud cover (particularly east)
and relatively weak low-level moisture (dewpoints upper 50s to lower
60s) via northerly flow on the western periphery of the offshore
low. Furthermore...subsidence on the western periphery of the upper
level low will increase across central NC during the day...
especially along/west of Highway 1...as the upper low progresses slowly
eastward to the Carolina coast. With the above in mind...expect
chances for thunder to largely remain confined to the Carolina
coast...though some chance for convection will likely persist in the
coastal plain early/middle afternoon where marginal destabilization
coupled with small amplitude waves /DPVA/ rotating cyclonically
around the northwest/west periphery of the upper low could conceivably support
shower activity. Light northwest flow aloft could conceivably support
convection along/west of the mountain ridges as well...though
activity east of the foothills is unlikely per reasoning above.
Expect highs ranging from the middle 70s NE to lower 80s SW.
Saturday/sunday: a pronounced surface ridge axis is prognosticated to extend
southward from the middle-Atlantic into the Carolinas Sat/sun...in
associated/west pressure rises attendant subsidence on the western periphery
of the departing upper level low...along with ridging aloft
extending eastward from the lower Midwest into the Tennessee Valley/deep
south. Chances for convection will likely remain outside of central
NC...to the east in associated/west the seabreeze and to the west in associated/West
Mountain convection...the latter of which may be aided by weak DPVA
or upstream mesoscale convective system activity rounding the top of the lower Midwest ridge
from the central MS River Valley into the Tennessee Valley/Appalachians.
Will indicate slight to low chances for convection in the far northwest
Piedmont and far southeast coastal plain with highs in the 80s and lows in
Monday-Wed: expect a more active pattern to arrive by the end of this
period (tue into wed) as an amplifying upper level trough digs
southeast from Canada into the mid-Atlantic/southeast. -Vincent
Aviation /12z Wednesday through Sunday/...
as of 735 am Wednesday...
A very moist air mass over the Carolinas coupled with the approach
of a low pressure system and its attendant surface cold front will
result in adverse aviation conditions across much of central NC
through Thursday night.
Widespread LIFR/IFR ceilings will persist across much of central NC
through the morning hours. Meanwhile a surface cold front will edge
southward across the Piedmont and coastal plain....and into the sandhills. This
surface boundary expected to stall near or just north of the SC border.
Behind this feature...ceilings lower into the
IFR/LIFR category. Once the ceilings drop...guidance is suggesting
that the ceilings will remain low through much of today and into
tonight...especially in vicinity of The Triad terminals. At krdu and
krwi...guidance suggests that ceilings may lift into the MVFR
category by early afternoon...but confidence is low that this will occur.
Farther south in the kfay vicinity...clusters of showers and an
isolated storms will maintain MVFR/low end VFR conditions through much of the
morning. There may be a temporary break in the convection by late
morning with showers and storms redeveloping in the middle-late
afternoon. If the surface front is able to drift into the
sandhills...then ceilings may lower into the IFR category as well.
The adverse aviation conditions will persist Thursday through early
Friday as the upper level low drifts overhead. Conditions are
expected to improve this weekend as the low opens up and lifts northeastward
away from our region and a slightly drier air mass overtakes our