NWS Mt.Holly ref: Wednesday thru Saturday.
.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Fairly complicated medium-range forecast today, as a western
Atlantic ridge will steer a weak system currently off the
Florida coast northward into the Mid-Atlantic by Thursday. This
complicates the precipitation forecast Wednesday night through
Friday, with the subsequent approach of a strong cold front
bringing additional chances for convection through Saturday. The
temperature forecast will also be problematic as a result of
these systems.
The 00z model suite poses an interesting set of solutions to our
sensible weather Wednesday through Saturday. Perhaps the most
problematic portion of the forecast is Wednesday and Thursday,
as the operational models consistently depict a weak system off
the Florida coast migrating slowly northward on the upstream
side of a strong western Atlantic ridge into the Mid-Atlantic by
Thursday. Convection looks to accompany the weak surface
reflection, as stronger instability noses northward as deep-
layer southerly flow promotes warm/moist advection along the
East Coast. Timing discrepancies exist amongst the model suite,
with the GFS a bit faster than the ECMWF. There are also slight
differences in the track of the system, and given the rather
compact nature of the system`s associated lift, this track will
be rather important to pinpoint for resultant QPF. Current
thinking is that areas farther inland may have a better shot of
precipitation, so the highest PoPs exist in these areas. Areal-
average QPF, speaking of, is not particularly impressive when
analyzing model solutions generally, but given the source
region of the system and the high-octane air that will advect
into the region (PWs approaching 2 inches by Thursday
afternoon), locally heavy rainfall seems likely with the
stronger convective cores.
Preceding the weak Thursday system, surface flow will continue
to slowly veer to a more south-southeast direction. With
increasing boundary-layer dew points and a continued onshore
component, would expect another round of fog and/or low clouds
Wednesday night.
As might be guessed, the temperature forecast is a little
tricky, especially Thursday with the question marks regarding
precipitation coverage. Although I expect it to be seasonably
warm, the general trend was to nudge highs downward a bit. If
precipitation is lacking and/or periods of reduced cloud cover
occur, highs will be warmer than forecast. However, confidence
is not high enough to stray much warmer than consensus at this
point.
Precipitation chances remain the primary concern Thursday night
and Friday. The weak system on Thursday appears to lift north of
the region by Thursday night, but the proximity of an
approaching trough will allow several midlevel perturbations to
eject northeastward in advance of the primary vort max.
Scattered convection seems probable in much of the eastern U.S.
Thursday night and Friday. Instability will likely gradually
increase through the period as well, especially via diurnal
diabatic heating on Friday. As such, the threat of thunderstorms
looks to increase through this period, likely culminating Friday
night with the approach of a strong cold front. The timing of
the front is still under debate, with the GFS noticeably slower
than the ECMWF/CMC. Tend to think a slower solution is more
probable, owing to the strength of downstream ridging. As such,
tended to keep PoPs a little bit higher than consensus on
Saturday, which has ensemble support. If the slower solutions
verify, Saturday would be another active convective day for
portions of the region (especially the southeastern CWA).
Severe storms are certainly possible on Friday and Saturday,
though ambient shear appears rather weak. Thus, coverage of
severe storms may be fairly sporadic/transient. Locally heavy
rainfall seems probable, particularly in areas of training
(slow-moving features in play), as PWs will remain rather high
(1.6-2.0 inches, generally).
As with Thursday, temperatures Friday and Saturday are a big
question mark, with cloud cover, precipitation coverage, and
frontal timing all playing roles in lowering confidence. Again,
with the expectation that precipitation coverage will be
sufficiently large, think that straying too far from guidance is
unwise at this point.
After the cold front passes through the region Saturday,
temperatures will fall below seasonal averages Sunday into the
following work week as a strong surface high builds into the
region. Another lengthy period of dry weather looks to occur as
well.
&&