Area Forecast Discussion
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FXUS62 KRAH 050548
Area Forecast Discussion
National Weather Service Raleigh NC
1245 AM EST Mon Dec 5 2016
Low pressure will cross the Southeast states tonight, before moving
off the Southeast coast Monday morning. High pressure will build in
briefly from the northwest Monday afternoon, then a second stronger
low pressure system will cross the Gulf States and Carolinas Monday
night through Tuesday.
.NEAR TERM /THROUGH MONDAY/...
As of 820 PM Sunday...
Hybrid cold air damming event in progress across central NC this
evening. Dry air ridge shifting slowly east. Meanwhile sting
isentropic upglide centered on the 290K level projected to persist
through 06Z, then weaken thereafter with the passage of a weak mid
level trough. Current forecast on track with categorical PoPs
through 06Z, then decreasing west-to-east during the pre-dawn hours
into the first half of Monday morning. May see areas of fog develop
in the wake of the departing rain across sections of the
western/southern Piedmont with locally dense fog possible.
As is typical for CAD event, expect little movement in temperatures
overnight. Min temps upper 30s to around 40 west to the lower 40s
Monday, areas of fog and low clouds will start Monday morning,
before most guidance suggests scouring out of low clouds from the
NNW Monday afternoon. This occurs only because of some weak
downslope flow from the NNW develops from VA mountains into our
Piedmont damming region (in the rear of the departing initial wave).
Highs Monday will be dependent on the timing of the scouring out of
the low clouds and the extent that the mid/upper level clouds linger
as well. We will go a bit below statical guidance in the north-
central and NE zone where the low clouds should linger longer with
the residual CAD affects. Highs generally in the 50s, some lower 60s
possible in the south. No POP during the day as central NC will be
in between systems.
.SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/...
As of 325 PM Sunday...
CAD again expected Monday night and Tuesday with a chilly rain.
QPF of 1 to 1.5 inches expected Monday night and Tuesday.
Miller B type storm (parent low tracks west of our area - weakens -
the secondary low becomes primary near the Carolina coast Tuesday,
tracks away Tuesday night).
Weak high pressure (less than 1025 mb) is forecast to move from the
TN valley Monday to the mid-Atlantic Monday night setting the stage
for the next significant system to approach our region from the
western Gulf Coast Monday night. Yet another CAD event is expected
even though the high pressure this time is weaker than the one
today. It is still expected to be just strong enough (near 1025 mb)
and in good position (PA to VA) Monday night to allow the
deliverance of CAA/DAA into the Piedmont Damming Region, just before
and early in the development of rain again Monday night. Dew points
in the 30s will feed into the northern Piedmont providing a good
start for evaporative cooling again once the rain arrives in
earnest. Timing for now appears to be near or after midnight in the
SW, spreading NE overnight to cover the area by 12z/Tuesday. Lows
Monday night will likely be at 12z/TUE - and readings will likely
fall further during the morning with the CAD. Lows 42-50 N to S with
falling temps into the upper 30s and 40s all areas during the day
Rain is expected much of the day Tuesday. Highs only in the 40s with
50s in the SE. The chance of the coastal front penetrating well
inland into our region is very low given the expected Damming and
Miller B type storm (and secondary development very near the coast
Tuesday). This would keep the warm sector well to our SE.
The storm system will lift NE and away Tuesday night with low
overcast conditions expected and rapidly ending rain from south to
north early in the evening. Temps should hold nearly steady in the
40s and lower 50s N to SE.
.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
As of 335 PM Sunday...
Look for dry weather to return for Wednesday in the wake of
Tuesday`s system and as high pressure builds to our north. The
airmass will moderate as well as SW flow aloft resumes. Meanwhile,
a deep longwave trough will take shape of the middle of the country,
and will move east through the latter half of the week, pushing a
potent cold front across our area on Thursday. GFS and ECWMF agree
that any rain assoc with the front will be fairly light, generally
less than 1/2 inch, and gone before the colder air arrives. Highs on
Wednesday and Thursday expected to reach the mid-upr 50s in the
prefrontal airmass. Lows Wednesday night in the mid 40s.
The big weather story for the long term will be the cool-down that
comes in the wake of the aforementioned front. Cold high pressure
will build in for Friday through Saturday, resulting in dry weather,
however the accompanying airmass will support highs only in the
upper 30s across the Triad and lower 40s elsewhere, both Friday and
Saturday. Lows Thursday night from the mid 20s nw to lower 30s se.
The coldest night of the weekend now appears to be Friday
night/Saturday morning, with lows expected to bottom out from around
20 NW to mid 20s across the coastal plain.
Otherwise, will be closely watching the pattern evolution late next
weekend into the early part of the following week, as a couple weak
short waves embedded in broad cyclonic flow are progged in the
models to move across the eastern US during that time.
.AVIATION /06Z Monday through Friday/...
As of 1245 AM Monday...
Poor aviation conditions will persist areawide until at least
daybreak. An upper level disturbance passing through the region
combined with low pressure tracking SW to NE over the Southeast
states has brought widespread IFR/LIFR conditions in steady light
rain and drizzle. This will persist until around daybreak, with a
period of LIFR vsbys/cigs in fog not out of the question. Soon after
daybreak, improvement to VFR from NW to SE is likely as the low
moves off the coast and the disturbance exits with rain/drizzle
ending. INT/GSO will see the improvement to VFR occur approximately
11z-13z, RDU at 12z-14z, and RWI/FAY at 13z-16z. VFR conditions and
dry weather will hold through much of today into early evening. The
approach of another stronger disturbance and a stronger surface low
tracking ENE toward the Mid South and Southeast states will bring an
increase in VFR clouds toward the end of the TAF valid period,
although the trend down to MVFR then IFR conditions will likely not
occur until after 06z Tue. Surface winds will be light mainly from
the north this morning, becoming NE this afternoon into tonight.
Looking beyond 06z Tue, a trend to MVFR then IFR conditions is
expected 06z-09z at INT/GSO, 07z-10z at RDU/FAY, and 08z-11z at RWI,
with steady rain spreading in from the SW. IFR/LIFR conditions in on-
and-off rain will persist through all of Tue and Tue evening.
Improvement to VFR is anticipated very late Tue night into Wed
morning as this storm system moves east off our coast, although
areas of fog may linger into early Wed morning in the east. VFR
should dominate much of Wed, then sub-VFR conditions may return Wed
night through much of Thu as a cold front approaches from the NW.
Much colder air and VFR conditions are expected Thu night through