Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 210635

Area Forecast Discussion
National Weather Service Raleigh NC
135 AM EST Tue Nov 21 2017

High pressure will drift offshore late tonight and Tuesday. A weak
area of low pressure will develop off the Florida coast on Tuesday,
and then track quickly northeastward along the Southeast coast
Tuesday night. A cold front will move through the area on Wednesday.


As of 1020 PM Monday...

No changes made to previous discussion, slight adjustment to
temperatures based on the latest observations but general forecast
thinking remains the same for tonight.

An area of high pressure at the surface will extend across the
eastern third of NC through the night. While sfc winds will be near
calm east of highway 1, a light sly return flow on the back side of
the high will occur over the southern-western Piedmont. Aloft,
patchy cirrus will traverse overhead in the sw flow. The cirrus will
become thicker towards morning in advance of an upper level
disturbance that will cross the northern Gulf.

Cool dry air associated with the sfc high will permit temperatures
to quickly cool into the 30s by mid-late evening. After midnight,
temperatures should stabilize as the high clouds thicken and a light
sly flow develops over the Piedmont. Min temps should be fairly
uniform, mostly in the lower 30s, and around 30 degrees at the
normally colder locations.


As of 234 PM Monday...

A southern stream short wave, currently located over the western
GOM, will move to the northeast and across the Carolinas during the
afternoon and evening Tuesday.  A resulting sfc low is still progged
to move northeast along the Gulf Stream late Tuesday and Tuesday
night. The latest GFS has trended farther east with the deepest
moisture and best rain chances.  The NAM is a bit farther west, but
it too has shifted slightly east with the better moisture. The
latest ECMWF is about the same as its prev run...generally showing
some light overrunning precip basically from US-1 eastward quickly
moving through Tuesday evening. So for now, will shift highest pops
a bit eastward, basically along and east of I-95 with lesser rain
chances back west toward the Triad. Either way, this light rain
event Tuesday evening will be short lived with limited rainfall
amounts, and other than the usual wet road hazards, should be fairly
low-impact. Given the late-day timing of the rain, we should see
some sunshine during the morning, however clouds will be on the
increase as we head through the afternoon. Highs from the mid-upr
50s northwest to mid 60s southeast.

Tuesday night, the next front will move into our CWA as the next
northern stream short wave moves by to our north. The fropa is
expected to be dry given the drying in the wake of the earlier
southern stream wave. CAA will be somewhat delayed with the next
high delayed, so given prefrontal flow and clouds, look for warmer
lows Tuesday night ranging from the lower 40s northeast to around 50


As of 210 PM Monday...

A surface cold front with limited moisture will be making its way
through the region Wednesday and Wednesday night. High pressure and
its associated cold airmass to the north will expand into North
Carolina on Thursday.  A brief warmup will occur Friday into
Saturday ahead of the next cold front that will pass through
Saturday night.  Very amplified trough in the eastern US Sunday and
Monday will bring a much colder airmass into North Carolina with max
temps Monday only in the 40s.

Precipitation during this time frame will be limited to spotty light
rain with each frontal passage.  Waves of low pressure off the
southeast US coastline will keep more substantial rain to the east
and south of the region.


As of 135 AM Tuesday...

Sfc high pressure over the area this morning will drift eastward and
offshore throughout the day. Low-level dry air associated with this
high will support a continuation of VFR conditions through at least
18z, with the resultant SELY return flow leading to gradual
moistening and broken/overcast ceilings between 3 to 5kt during the
mid to late afternoon.

Strengthening low-level moisture advection in advance of a sfc low
that will move northeast off the SE Coast overnight, is expected to
lead to deteriorating aviation conditions this evening and
overnight, especially at the eastern terminals(KRWI and KFAY).
Model guidance continues to exhibit higher than average spread with
this coastal system, and thus forecaster confidence is lower than
normal. Expect ceilings to lower to IFR to MVFR with patches of
light rain/drizzle from RDU eastward. It`s possible that KINT and
KGSO could also see a period of sub-VFR ceilings during the late
afternoon/early evening, however confidence is too low to include
in TAFS at this time.

A cold front will cross central NC Wednesday. Cold dry air advection
will quickly scour out any sub-VFR ceilings Wednesday morning. VFR
parameters should prevail across central NC Wednesday afternoon
through Saturday.





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