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223
FXUS62 KRAH 220127
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
927 PM EDT Fri Jun 21 2024

.SYNOPSIS...
High pressure aloft will remain in control ahead of a weak upper
level trough that will move across the Middle Atlantic on Sunday. A
pre-frontal trough and weak cold front will move into NC Monday
afternoon and night, then lift northeastward across the Middle
Atlantic as a warm front Tuesday and Wednesday.

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
As of 925 PM Friday...

No major changes with the evening update. The 00Z upper air analyses
show the 596 dam H5 high over the mid-MS Valley, with central NC on
the eastern periphery of the high. At H7 and H85, the area of low
pressure sits just off the FL/GA coast, almost due east of the state
line. There is a tight gradient in the H7 moisture from the southern
Coastal Plain to the northern Piedmont of NC. At the surface, the
low was located about 40 miles southeast of Brunswick, GA at 8 PM.
The 00Z surface analysis shows a tight dewpoint gradient across
central NC, with some upper 50s/low 60s over the northern Piedmont
and low/mid 70s over the Sandhills and Coastal Plain. The higher
dewpoint air will continue to migrate nwwd through the area this
eve/tonight, with dewpoints in the upper 60s/low 70s expected by
daybreak Sat. Still expect lows to bottom out in the upper 60s/low
70s, with max RH values overnight near/at 100 percent. As mentioned
in the earlier discussion, there is a good chance for fog/low
stratus tonight, especially across the Sandhills and Coastal Plain.
-- End Changed Discussion --

&&

.SHORT TERM /SATURDAY AND SATURDAY NIGHT/...
As of 400 PM Friday...

Slightly hotter yet, with forecast high temperatures about 6-12 F
above average and centered in the middle 90s, or about a category on
average higher than those of Fri.

A mid-level high now over the srn Appalachians and TN Valley will
continue to gradually weaken while retreating swwd across the lwr MS
Valley and srn Plains through 12Z Sun. An associated ridge axis will
continue to extend from the center of the high newd and across the
srn Appalachians and wrn Carolinas, while a weak mid-level
trough/low now just offshore the NC coast will meander there and
promote weakly cyclonic flow and slightly cooler mid-level
temperatures over the ern Carolinas. Observed 500 mb temperatures
were minus 7 C at MHX this morning versus minus 5 C at GSO, for
example; and that should remain the case on Sat.

At the surface, on the wrn periphery of high pressure that will
become anchored near and just northeast of Bermuda, an Appalachian-
lee trough will develop and remain over the srn Middle Atlantic
Foothills and wrn Piedmont. Surface flow, which in recent days has
maintained a considerable ely to nely component around the Bermuda
high, will assume a sly direction and favor both warming
temperatures and increasing moisture/humidity. That sly flow will
also favor appreciable inland penetration of a sea breeze across
sern and cntl NC through Sat evening.

The aforementioned increasing low-level moisture/humidity will favor
areas of morning fog and stratus through the srn/cntl Coastal Plain
and ern Sandhills, with surface dewpoints mostly in the lwr 70s in
the morning (except for lingering 60s F probable over the nw
Piedmont). That moisture will remain somewhat shallow and prone to
vertical advection/"mixing out" for one more day, however, such that
the 70s of the morning should decrease into the mid/upr 60s with
strong diurnal heating/mixing during the afternoon (except a
lingering 70-72 F from CTZ to GSB) As such, despite the increasingly
hot temperatures, related Heat Index values are apt to remain mostly
in the mid to upr 90s, to around 100 F in climatologically-favored
areas roughly east of US 1.

It will also remain mainly dry, though with a slight-small chance of
afternoon showers/storms over the srn-cntl Coastal Plain and
Sandhills (similar to that now over sern NC), where sea breeze
forcing and the aforementioned slightly cooler mid-level
temperatures will coincide. It will become increasingly muggy and
warm overnight, with the development of areas of stratus
accompanying a resurgence of surface dewpoints in the the lwr-mid
70s, and with similar low temperatures.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
As of 300 PM Friday...

...Dangerously hot temperatures expected this weekend and into early
next week...

Sunday/Monday...Fairly high confidence heat forecast for
Sunday/Monday, with a few caveats as precip chances return to the
forecast for the first time in a while.

Synoptically...Sunday will see the upper ridge responsible for the
widespread heat begin a slow migration westward toward the Four
Corners. This will result in somewhat lower heights aloft across the
area as the flow becomes increasingly northwesterly, yet
temperatures and heat indices will still approach dangerously high
values Sunday afternoon. At the surface, the combination of
increased southerly flow from the Bermuda High, along with increased
remnant moisture from the weak trough over GA/SC will push dewpoints
well into the mid 70s by Sunday morning, with little hope of mixing
out much below the lower 70s later in the day. This, along with
afternoon temps in the mid 90s, will likely translate to heat
indices generally in the 102-105 degree range, especially for areas
along and east of US-1 although arguably the entire forecast area
(even the western Piedmont) could be within a degree or two of
triple digit heat indices. One caveat at this point is the potential
for cloud cover with the weak trough over GA/SC as it moves
northward, along with the potential for some much-needed scattered
showers and storms across the Sandhills/southern Coastal Plain later
in the day. If these showers develop (probabilities in the 20-30
percent range), it`s likely they won`t occur until after we`ve
reached out high temperature for the day. We will continue to
message the potential for dangerously hot temperatures not only
Sunday, but into Monday as well.

At the same time, a weak synoptic surface boundary will be making
its way through the Ohio Valley, gradually crossing the mountains
and arriving in NC at some point during the day on Monday. Strong
southerly flow ahead of the front will allow for another dangerously
hot/humid day on Monday. There is a signal in the guidance for a
period of cloud cover/showers/isolated storms coincident with the
frontal passage, but the exact timing at which this will happen is
still unclear. Most of the guidance advertises a decaying line of
showers moving through the area overnight, eventually redeveloping
across the Coastal Plain Monday afternoon. Thu guidance is clear
that somewhat drier air will follow the front, with dewpoints in the
Triad retreating in the mid 60s by the afternoon while remaining in
the low to mid 70s to the east. Thicknesses behind this front aren`t
notably lower, thus temperatures will once again top out in the
mid/upper 90s. However with drier air in place to the west, the
primary threat area for heat-related concerns appears to once again
be located from US-1 eastward.

Tuesday/Wednesday: Tuesday will see limited precip chances across
the area as the influences of subsidence in the wake of Monday`s
departing trough take hold over the area, not to mention the
intrusion of lower dewpoints (mid 60s) across the area. Once again,
thicknesses remain relatively unchanged and temps within the post-
frontal regime will reach the mid to upper 90s. Return flow around
the Bermuda High will allow dewpoints to return to the 70s on
Wednesday and with temps once again in the mid/upper 90s, heat
indices are likely to make another return into the triple digits
Wednesday afternoon. Scattered showers will be possible especially
across the western Piedmont and Sandhills Wednesday as moisture
returns to the area, although chances remain low in the 20-30
percent range.

Thursday/Friday: Another longwave trough and associated surface
convergent boundary appear on target to cross the mountains and
sweep through the Mid Atlantic late in the week, at this point with
the highest probabilities Thursday afternoon/evening. Grand ensemble
precip probabilities are generally in the 40-50 percent range for
Thursday and this seems more than reasonable at this stage given an
approaching surface boundary, abundant moisture, and instability.
Much like the boundary earlier in the week, somewhat lower dewpoints
will be drawn into the area to close out the week, but this time
also accompanied by slightly lower temps in the upper 80s/lower 90s.

&&

.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
As of 730 PM Friday...

24-hour TAF period: Moist easterly flow continues between high-
pressure off the Carolina coast and a wave of low pressure off the
Georgia coast. Guidance suggest better low-level moisture surging
inland tonight as the low level flow becomes more south-
southeasterly and higher probability of fog and low clouds.  With
sub-VFR ceilings already apparent along the coast, confidence is
highest at FAY where at least IFR seems likely. Further north and
inland confidence is not as high at RWI and RDU , but there is
enough of a signal in the models to include IFR at RWI and a tempo
for IFR at RDU after 09Z.

Cloud should scour relatively quickly Saturday morning and once
again yield some scattered VFR cumulus clouds with winds continuing
to swing more southwesterly.

Outlook:  An approaching cold front will support a slight chance of
showers and storms and related sub-VFR restrictions on Sunday, with
better coverage on Monday. Tuesday should be mostly dry before
isolated showers and storms may return on Wednesday especially west.

&&

.CLIMATE...

Record High Temperatures:

June 22:
KRDU: 100/2022
KFAY: 101/2022

June 23:
KRDU: 100/1986
KFAY: 102/1981

June 24:
KRDU: 99/2010
KFAY: 102/1914

June 25:
KRDU: 100/1952
KFAY: 102/1914

June 26:
KRDU: 102/1952
KFAY: 101/1951


Record High Minimum Temperatures:

June 22:
KGSO: 75/1981
KRDU: 78/1933

June 23:
KGSO: 74/2015
KRDU: 77/1890
KFAY: 77/2017

June 24:
KGSO: 76/2015
KRDU: 76/1888
KFAY: 79/2010

June 25:
KGSO: 75/2015
KRDU: 77/2010
KFAY: 75/1952

June 26:
KGSO: 74/2010
KRDU: 76/1902
KFAY: 76/1997

June 27:
KGSO: 76/1969
KRDU: 76/1952
KFAY: 77/1998

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$
SYNOPSIS...CBL/MWS
NEAR TERM...KC
SHORT TERM...MWS
LONG TERM...Leins
AVIATION...BLS/Danco
CLIMATE...RAH