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FXUS62 KRAH 210700

Area Forecast Discussion
National Weather Service Raleigh NC
300 AM EDT Mon May 21 2018

A moist and slightly unstable air mass will remain entrenched across 
central NC through the middle of the week.


As of 210 AM Monday... 

Primary drivers of weather today include a weak backdoor surface 
front moving in from the north and minor mid level shear axes 
shifting in from the south. The latest surface map shows a fairly 
uniform air mass across much of the Carolinas and Southeast, albeit 
with lingering instability over the eastern CWA, and a weak backdoor 
front stretches W-E across central VA. This front is expected to 
drop southward into N NC this morning before washing out and 
ultimately dissipating as it starts to shift back N tonight. This 
front is more of a temporary wind shift, with minimal change in low 
level thicknesses, so impacts should be little more than weak low 
level mass convergence over the N Piedmont this afternoon. But this 
resultant forcing in tandem with afternoon heating and subsequent 
destabilization (tempered a bit by considerable mid and high clouds 
across the region) should allow scattered afternoon convection to be 
focused over the N Piedmont and N/C Coastal Plain starting in the 
mid afternoon, perhaps dropping into the Sandhills, S Coastal Plain 
and S Piedmont late afternoon into early evening, although this will 
depend to a large degree on cold pool propagation and a possible 
inland-moving sea breeze. While moderate CAPE is expected over the N 
and E CWA, other forcing mechanisms will be absent or very weak, 
including the aforementioned surface frontal convergence and subtle 
mid level waves tracking northward through the area between the 
offshore-centered mid level anticyclone and low pressure over the FL 
panhandle. Latest model runs are favoring pretty good convective 
coverage along the frontal zone, and will retain the trend up to 
likely pops across the N/E with lower coverage in the SW. Rather 
slow storm motion will raise the risk of locally higher rainfall 
totals. Storm intensity will be limited by the weak deep layer 
shear, although forecast soundings suggest elevated D-CAPE with 
potential for strong wind gusts, and high values of normalized CAPE 
favor high lightning activity. Expect highs in the low-mid 80s, with 
some upper 80s SW. Storms should decrease gradually in coverage and 
strength during the evening and into the overnight hours, although 
residual surface heat flux and high dewpoints necessitate keeping 
chance pops in through the night. Lows in the upper 60s to near 70 
under mostly cloudy skies. -GIH


.SHORT TERM /Tuesday through Tuesday night/...
As of 250 AM Monday...

Today's weak backdoor front should be mostly gone by Tue morning, 
leaving central NC within a light SW surface flow and light W mid 
level flow, as deep offshore ridging re-asserts its influence over 
the Southeast Coast. We will see passage of a mid level shortwave 
trough to our north Tue/Tue night, in conjunction with a surface 
trough crossing into the Mid Atlantic region Tue/Tue night NW to SE. 
Models depict a minimum in PW translating NE through the area during 
much of the day, and with a general lack in dynamic forcing for 
ascent and slightly lower forecast MUCAPE on the 3 km NAM with poor 
deep layer shear, storms may be fewer overall and focused across the 
far N and NW CWA, just ahead of the surface trough where CAPE will 
be greater (1500-2000 J/kg vs. the 500-1000 J/kg over much of the 
remaining CWA). Will have chance pops, highest N and W and lower SE, 
peaking in the afternoon. Pops should decrease in the evening and 
overnight, although will hold onto scattered showers over the NW 
through Tue night with an improving wind field resulting from 
digging of the mid level shortwave trough over the Northeast. Expect 
highs again in the low-mid 80s under partly to mostly cloudy skies. 
Lows Tue night in the upper 60s. -GIH


As of 300 AM Monday... 

A continuation of the wet weather pattern is expected during the 
long term forecast with chances for rain each day of the forecast. A 
couple of features continue to drive this pattern including a 
frontal zone to the north of the area that is expected to remain 
close to our northern border and a low pressure system coming out of 
the Gulf of Mexico. While the frontal zone to the north with be a 
bigger player in the weather in the short term, a cold front is 
expected to pass through on Thursday. After this point attention 
will switch to the low coming out of the Gulf of Mexico as this 
feature is expected to bring large amounts of moisture transport to 
the Carolinas, especially late Memorial Day weekend. While it is 
unclear how this feature will ultimately evolve, a couple things 
remain true. We will have chances for showers and thunderstorms 
throughout the long term forecast. Temperatures will rise into the 
80s each day with mid to upper 60s for lows. 


As of 125 AM Monday...

VFR conditions will dominate at central NC terminals through the 
next 24 hours, although there is a good chance of MVFR to IFR 
conditions 08z-12z this morning at FAY/RWI with a lower chance at 
RDU. Considerable mid level cloudiness based above 8 000 ft AGL is 
expected today through tonight, with scattered to periodically 
broken clouds based at 3 500 - 6 000 ft AGL this afternoon. Light 
winds and high humidity early this morning may induce development of 
stratocumulus based at 500-800 ft agl across the eastern sections in 
the hours before and around daybreak this morning. Scattered showers 
are possible near RDU/RWI 15z-18z, then scattered to numerous storms 
are possible 18z-00z later today at RDU/RWI/FAY, with a lower chance 
near INT/GSO. Shower/storm chances will decrease quickly after 00z.

Looking beyond 06z Tue, VFR cigs/vsbys will dominate through Tue 
morning, with a slight chance of sub-VFR cigs 08z-12z. Another round 
of scattered showers/storms with local sub-VFR conditions is 
expected 18z-00z Tue. This pattern is expected to repeat through the 
week, with storm chances from mid afternoon through mid evening and 
low clouds or fog possible late each night through dawn. -GIH






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