Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 040840

National Weather Service Raleigh NC
440 AM EDT Thu Jun 4 2020

A series of mid to upper level disturbances will move from the
northern Gulf of Mexico northeastward across the Carolinas through
Saturday. Otherwise, subtropical high pressure centered east of
Bermuda will direct hot and humid southwesterly flow across the
Southeast until a cold front settles south across the region
Saturday night and Sunday.


As of 350 AM Thursday...

At the base of high latitude blocked flow across the nrn N. Atlantic
wwd across srn Greenland and the Northwest Passages --with a
resultant east-based NAO and above normal temperatures across the
ern US-- the main branch of the mid-latitude westerlies will remain
across the nrn tier of the US and Great Lakes this period. Within a
weaker, srn branch, a positive tilt trough axis will remain quasi-
stationary from the srn Appalachians to the nrn Gulf of Mexico,
tucked between a pair of subtropical ridges extending across nrn
Mexico/the Southwest/srn Rockies and the swrn N. Atlantic,
respectively. A series of perturbations embedded within that
positive tilt trough axis will lift newd across the Carolinas
through tonight. The most prominent of those features was a former
closed low over OK at this time last night, now over srn MS/ern LA,
and which will lift across the Carolinas late tonight.

At the surface, a summer-like pattern of sub-tropical high pressure
centered east of Bermuda and an Appalachian lee trough, the latter
of which will strengthen and drift ewd with diurnal heating across
the NC Foothills and wrn Piedmont, will persist and favor continued
hot and humid conditions over cntl NC today, with generally
persistence high temperatures in the upr 80s to lwr 90s.

Showers and storms will develop with diurnal and differential
heating over the mountains of VA/NC by early afternoon and
subsequently congeal into clusters while moving generally enewd
across nwrn NC and cntl VA through the afternoon and evening. This
convection, or the associated gusty, rain-cooled outflow, will
probably graze the nwrn/nrn NC Piedmont around 00Z. Other more-
isolated activity cannot be ruled out throughout cntl NC,
particularly along the trough over the wrn Piedmont and also the
inland-migrating sea breeze. While generally weak deep tropospheric
flow will limit storm organization to pulse/multi-cellular modes,
moderate to strong instability will favor strong to isolated
damaging wind gusts from precipitation-loaded/wet microbursts.

A separate, second regime of (weaker) showers is likely to spread
newd across the ern Carolinas tonight, including into the srn and
cntl Coastal Plain and Sandhills of cntl NC, after 06Z Fri, related
to the approach of the foregoing prominent perturbation from the
Gulf Coast region.

Otherwise, gradually increasing low level moisture/humidity will
also favor areas of stratus development through Fri morning, with
lows again in the upr 60s to lwr 70s.


As of 430 AM Thursday...

A broad upper-level trough will move across the Great Lakes Region
Friday, then slightly amplify and traverse off the New England Coast
by late Saturday. The upper-level trough will remain to our north,
but switch southwesterly flow aloft to more northwesterly across the
region. A surface trough will remain anchored across the area for
the end of the week, helping to maintain moist, southwesterly flow
into central NC into the early part of the weekend with dewpoints in
the upper 60s to low 70s. Daytime heating will help to generate
diurnal showers and thunderstorms, with some showers lingering
overnight. Highs Friday will be in the upper 80s to near 90, with
lows in the mid to upper 60s.


As of 320 AM Thursday...

Saturday and Saturday night: The weak upper trough sitting over the
eastern US will shift offshore on Saturday as a high builds out
west. A secondary shortwave will traverse the trough, clipping
northeast NC Saturday night into Sunday morning. At the surface, the
lee trough will strengthen on Saturday as high pressure over the
Great Lakes builds south toward the area in the wake of an
approaching backdoor cold front. Increasing southerly flow will
advect warm, moist air into the area Saturday, increasing
instability and moisture across central NC. MUCAPE off the GFS
during the aft/eve is forecast to be around 2000 J/Kg with PWATS in
the 1.5-2.0 inch range, however shear appears limited. Showers and
thunderstorms will be likely Saturday aft/eve as the front interacts
with the existing lee trough and given the diurnal timing and the
parameters listed above, some storms could be strong. Expect highs
in the upper 80s to low 90s and lows in the upper 60s to low 70s.

Sunday through Tuesday: The weather pattern gets a bit more complex
over the weekend as Cristobal moves toward and into the lower MS
Valley from the Gulf. Aloft, Cristobal will help shift the sub-
tropical ridge eastward and over the eastern US. The ridge will
remain over the eastern US through Tuesday night as Cristobal
continues to move northward through the MS Valley, eventually
getting caught in an upper level trough as it progresses eastward
through the Plains and into the MS Valley. At the surface, the high
will migrate southeast from the Great Lakes through and off the mid-
Atlantic/Northeast coast through Tuesday night. Meanwhile, the
backdoor cold front will move through the area on Sunday, stalling
to the south through Monday before lifting northward once again as a
warm front Monday night/Tuesday in response to Cristobal interacting
with the cold front over the Midwest. There is some uncertainty with
respect to exactly when the warm front will make its way back into
central NC. As a result, there is decreasing forecast confidence for
Tuesday into Wednesday for both temperatures and precipitation.
However, given the current model solutions, expect relatively dry
weather across central NC through Tuesday, with the best, albeit
low, chances for rain across the far southwest. Also, temperatures
will be lowest in the northeast and highest in the southwest but
near to slightly below normal.

Beyond Tuesday: As the remnants of Cristobal move north into the
Great Lakes, the cold front will surge eastward toward the eastern
US, potentially getting hung up along the Appalachians on Wednesday.
Cristobal will lift north through the western Great Lakes and become
absorbed in the parent upper low centered over south-central Canada
Wednesday/Wednesday night. While there is still a chance for some
rain across the area Wednesday and Wednesday night, it will depend
on how much moisture is left after the front moves east of the


As of 205 AM Thursday...

VFR. Light sswly surface winds this morning will increase to between
10-15 kts with gusts up to 15-20 kts this afternoon, in the MSL
pressure gradient between high pressure east of Bermuda and an
Appalachian-lee trough that will sharpen with diurnal heating.
Showers and storms will develop with diurnal and differential
heating over the mountains of VA/NC and subsequently congeal into
clusters while moving generally newd across nwrn NC and cntl VA
later this afternoon and evening. These, or their gusty, rain-cooled
outflow, may graze the nwrn/nrn NC Piedmont (INT/GSO) around 00Z.

Outlook: Hot and humid swly flow will result in a chance of mainly
afternoon and evening showers and storms and late night-early
morning stratus through at least Sat.




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