Area Forecast Discussion
Issued by NWS Wilmington, NC

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FXUS62 KILM 300617

Area Forecast Discussion
National Weather Service Wilmington NC
215 AM EDT Sun Apr 30 2017

High pressure will extend across the area from offshore through
early Monday with warm and humid conditions continuing. A cold
front will bring a likelihood of showers and thunderstorms late
Monday into early Tuesday. High pressure will follow for the
mid-week period. A Low pressure system will impact the region
Thursday into Friday amd may bring widespread showers and
thunderstorms and heavy rain.


As of 1000 PM Saturday...Short-term guidance is converging on
the idea of fewer low clouds developing overnight. This may be
due to dewpoints, while still running exceptionally high for
this time of year, are just not high enough relative to the
warmth of the airmass to ensure a good saturated layer develops.
Latest HRRR and GFS-LAMP guidance still shows 1000-2000 foot
stratus inland, but only for a few hours late tonight. I have
trimmed back this potential in the latest sky cover forecast and
tweaked a few temperatures with somewhat more clear skies
anticipated. Discussion from 730 PM follows...

Very few changes were needed to the previous forecast. An
exceptionally humid and warm airmass for this early in the
season will continue to spread onshore tonight. Temperatures
should run a solid 15 degrees above normal with low temps around
70 degrees. Dewpoints will remain in the 60s and lower 70s.
Much like we saw last night, low stratocumulus clouds should
develop and persist through daybreak Sunday. We`re already
seeing some cloudiness develop now in the Cape Fear area,
probably an early sign of what will come. Between 10 PM and 1 AM
expect skies to become cloudy to mostly cloudy area-wide except
perhaps right on the beaches as these clouds will be the result
of humid air lifted up over the shallow nocturnal inversion
near the coast.


As of 315 PM Saturday...Strong mid level ridging which has been
responsible for the summer like conditions of the past few days
will give way to a dampening cyclone moving from the Central
U.S. to the Great Lakes region through the period. At the
surface, Bermuda High pressure will be displaced by a cold front
moving across the area late Monday into early Tuesday. The
timing of the front is becoming more consistent within the
guidance suite and there should be a broken to almost solid line
of showers and thunderstorms moving west to east across the
area from about 0 to 6z Tuesday. Severe potential doesn`t look
overly impressive with 850mb winds only 45-50 knots with the
higher values to the north. Still, the timing could make things
a bit interesting over the western zones early in the evening.
Warm temperatures continue with highs in the 80s monday
following another night with lows in the 60s Monday morning.


As of 315 PM Saturday...Broad high pressure behind Monday night`s
cold front will expand across the Southeast Tuesday creating dry and
seasonable weather with highs and lows right around climo.

This high will remain in place Wednesday with slightly warmer
temperatures but continued dry weather before it shifts offshore
Thursday. This occurs in response to a deep mid-level trough digging
into the middle of the country and then evolving across the eastern
CONUS into the weekend.

There exist two distinct camps in the guidance: the GFS has this low
cutting off and dropping southeast through the end of the period.
The CMC/ECM have a similar pattern initially to the GFS, but the
upper low drifts north before cutting off  overhead the Northeast.
The biggest difference between the guidance appears to be the
evolution of the ridge across the middle of the country. The CMC/ECM
keep the ridge axis aligned N/S, while the GFS produces a more
tilted NE/SW ridge which suppresses the upper low. The agreement
between the ECM/CMC tends to favor that solution a bit more, despite
the fact that the GFS has been consistent and we had a similar setup
just last week so there is precedent. The evolution of this upper
pattern is critical because, while all scenarios support showers and
thunderstorms late Thursday and Friday, the CMC/ECM would dry things
out for the weekend, while the GFS would maintain unsettled and
possibly very wet weather for several days. Without a clear solution
at this time range, will hedge with a WPC favored blend of guidance
but with a bit more weight on the drier ECM by the weekend. This
would also bring much cooler temperatures to the region Fri/Sat with
highs and lows falling below climo.


As of 06z...Although there is a decent low status deck across
many TAF sites south and west of local area, confidence is lower
tonight for prevailing IFR/LIFR ceilings. Soundings and moisture
profile continue to lock in moisture right below 1000 ft in this
unseasonably humid air mass over the area. Have included a tempo
group between 06z and 10z at all TAF sites for LIFR stratus deck
lifting after sunrise, through the morning and maintaining some
MVFR stratocu and also some cirrus through the aftn. Southerly
winds are slightly lower overnight into early this morning and
therefore may see some MVFR fog but have not included in TAFs
for now as winds were remaining up near 4 to 5 kts. Ridge slips
east through this aftn and allows for convection to develop a
bit closer to inland TAF sites but have held it to the west and
therefore did not include any shwrs. Soundings and guidance hint
at another night of low clouds for Sunday night and therefore
put some SCT lower ceilings at the end of TAF period.

Extended outlook...Periods of IFR/MVFR conditions are possible
in showers and thunderstorms late Monday into early Tuesday.


As of 1000 PM Saturday...High pressure well offshore will
maintain a southerly wind tonight around 10 knots. Stronger
winds this afternoon along the coast were the result of the
seabreeze, which produced gusts over 20 knots at times. Seas
around 3 feet should continue overnight in a mix of 5-second
wind waves and 8 second SE swell.

As of 315 PM Saturday...A southerly flow will be in place most of the
period with wind speeds increasing Monday as a cold front approaches
from the west. Initial speeds of 10-15 knots will increase to a
respectable 20-25 knots late Monday and persist into the evening
hours. The front will move across with a modest westerly flow
setting up by early Tuesday. Small craft conditions are likely
for Monday. Significant seas will ramp up as well increasing
from 2-4 feet early to 5-8 feet late.

As of 315 PM Saturday...Broad high pressure builds across the waters
behind a cold front Tuesday. Residual gusty W/NW winds of 15 kts and
4-6 ft seas will fall quickly during Tuesday as winds back to the SW
at 10-15 kts late Tuesday before a secondary surge flips winds
around to the NW by Wednesday at less than 10 kts. As the high
shifts offshore into Thursday, southerly winds will ramp up quickly
becoming 15-25 kts, driving seas back to 4-7 ft after being just 2-3
ft much of Wednesday. An SCA will likely be needed beginning late in
the extended.


NC...Coastal Flood Advisory until 3 AM EDT Sunday for NCZ107.



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