Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Raleigh NC
655 am EDT Sat may 30 2015
Synopsis...high pressure centered over the western Atlantic will
extend into the region through Sunday morning. A cold front will
drop into the middle Atlantic and southern Appalachians on Sunday and
move into the Carolinas on Monday and Tuesday.
Near term /through tonight/...
as of 230 am Saturday...
Surface high pressure will continue to extend into the area from the
western Atlantic today... while a middle/upper level ridge remains over
the area. This will again largely suppress convection today... with
near term guidances showing even less instability than yesterday.
This should generally yield a dry day across the area... with the
best chances of seeing any isolated showers/storms in the far
northwest Piedmont. Otherwise... expect we could see some patchy fog
and low stratus across the area... lifting by middle morning... with
partly to even mostly sunny skies expected today. Low level
thickness values will again be similar to yesterday. Thus... would
expect temperatures to range from the middle 80s northwest to the upper 80s/near 90
elsewhere... similar to friday's highs.
More of the same is expected tonight... with again the potential for
some patchy pre-dawn/early morning fog/stratus and low temperatures
generally in the middle to upper 60s.
Short term /Sunday and Sunday night/...
as of 250 am Saturday...
A weak slow moving middle level trough will slowly shift eastward on
Sunday across the Midwest and deep south. This will allow/cause the
middle level ridge to shift eastward... with increasing southwesterly
flow aloft over central NC. This should lead to a better chance of
seeing some convection on Sunday... mainly in the late
afternoon/evening time frame... with the highest probabilities
across the northwest Piedmont. In fact further eastward across the
central and southern coastal plain we may see dry conditions
continue to prevail. Highs temperatures will again be similar to today...
maybe a few degrees cooler in the northwest Piedmont. Still think we
should see highs ranging from the middle to upper 80s though. Given the
southwesterly middle level flow and potential for weak perturbations to
move across the area and along with the moist airmass in place on
Sunday night we may see afternoon convection linger a bit longer...
along with the potential for at least isolated convection possible
across the western and northern Piedmont all night long... depending
on any weak disturbances aloft in the southwesterly flow. With respect to to any
severe potential... mixed layer cape still appears to be weak to
modest at best... with generally only 500 to 1300 j/kg of MLCAPE.
Given this and still weak deep layer shear... think severe threat will
be quite minimal to none for Sunday afternoon into Sunday night. Lows
by Monday morning are expected to be in the middle to upper 60s again.
Long term /Monday through Friday/...
as of 305 am Saturday...
The approach of a minor short wave and attendant cold front will increase
the threat for showers and thunderstorms Monday into Tuesday as it
interacts with the moist and slightly unstable air mass over central
NC. Based on model timing (and decent consensus)...appears bulk of
lift to initiate/sustain convection will occur in the western
Piedmont late Monday...and over the remainder of central NC Monday
night. Forcing pretty much dependent on upper divergence aloft
attributed to an upper jet lifting NE across the northern middle
Atlantic and a weakening shear axis. Forcing along the 850mb and
700mb fairly anemic. Based on this...will limit pop chance to high
end chance/low end likely.
Looking at severe parameters...wind shear weak while available
instability adequate for some deep convection. Overall severe
weather threat marginal at best as storm type will be multi-
Surface cold front will Glide into the northern-western Piedmont late
Monday night...then drift southeastward Tuesday. This feature will aid to
focus most of the convective activity over the sandhills and coastal
plain...especially Tuesday afternoon. Middle level flow veers to a more
westerly flow by Tuesday. This type of flow pattern usually limits
convective coverage. Will align probability of precipitation from chance northwest to low end
likely in the east and far south...mainly in the afternoon-evening
High temperatures Monday and Tuesday dependent upon the amount of cloud
cover and initiation time of convection. Currently have maximum temperatures
Monday middle-upper 80s...and around 80 north to the middle 80s far south
Tuesday. If convection on Monday does not initiate in the west until
late in the day...maximum temperatures may end up being 2-4 degrees warmer.
Similarly...if overcast skies persist across the northern Piedmont
most of the day...high temperatures may fail to reach 80.
Wednesday through Friday...short wave in the northern stream exits off the
New England coast early Wednesday. This will allow high pressure to
build into the upper Ohio Valley and nose southward toward central NC. Some
of the drier/more stable air will bleed southward into the northern
Piedmont. Former frontal boundary will lie in vicinity of the NC/SC
border and gradually fizzle out. Remnants of this boundary will
still serve as a focus for moisture pooling and probably trigger
isolated to scattered convection over our far southern-southeast counties
Wednesday into Thursday.
00z GFS has intensified an area of low pressure in the northwest Caribbean
and lifts it northward through the Florida Peninsula Thursday. This is a big
departure from its previous runs. 00z European model (ecmwf) fairly consistent with
itself...depicting an inverted trough in this region. Will lean
toward the European model (ecmwf) for now which has a piece of an upper level ridge
leaning eastward across our region. If this verifies...expect probability of precipitation
chances to dwindle Thursday into Friday with high temperatures close to or
slightly above normal.
Aviation /12z Saturday through Wednesday/...
as of 650 am Saturday...
24-hour taf period: VFR conditions are generally expected for the 24
hour taf period... aside from the potential for some patchy sub-VFR
ceilings and/or fog this morning and again Sunday morning during the pre-
dawn/early morning hours (08-15z).
Given the rather patchy nature of the sub-VFR conditions this
morning... will keep mention of MVFR ceilings in a tempo group for now.
Any MVFR ceilings that develop should lift and scatter by middle morning or
so. Otherwise... VFR conditions are expected to prevail today into
tonight in associated/west a persistent upper level ridge along the eastern
Seaboard... which should help to limit afternoon/evening showers and
storms. The best chances of seeing any afternoon/evening showers
and/or storms will again be in The Triad (kgso/kint)... though even
lower probabilities than yesterday. Thus... will not include any
mention of convection in the tafs at this time. Sub-VFR ceilings and/or
visbys will be possible again on Sunday morning in the pre-
dawn/early morning hours of Sunday. Confidence is highest at
kgso/kint... thus have added a predominate group near the end of the
taf period for low end MVFR ceilings at kgso/kint. Elsewhere... outside
of possibly some sub-VFR visbys at fog prone krwi will leave out any
mention of sub VFR ceilings for Sunday morning as confidence is not high
enough to include in the tafs at this time.
Looking ahead: aside from a potential for sub-VFR ceilings on Sunday
morning (08-15z) and convection during the late after/evening (20-
01z)...primarily at the int/gso terminals...expect VFR conditions to
prevail through the weekend. Chances for early morning stratus/fog
and after/evening convection will increase at all terminals (particularly
int/gso) Monday into Tuesday as the upper level ridge weakens and a
slow-moving upper level trough approaches the Carolinas/mid-Atlantic
from the west.