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000
FXUS62 KRAH 201010
AFDRAH

AREA FORECAST DISCUSSION
National Weather Service Raleigh NC
610 AM EDT Fri Sep 20 2019

.SYNOPSIS...
Canadian high pressure will build southward across the southern
middle Atlantic states through tonight, then offshore this weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 325 AM Friday...

A subtropical ridge centered over the Mid-South this morning will
strengthen and expand ewd across the sern US through tonight.
Underlying surface high pressure centered at 07Z over RIC will
consequently remain anchored across the srn middle Atlantic and
Carolinas. Stratocumulus should be more limited in coverage today
versus Thu owing to a veering of the 925 mb flow to a wly/offshore
component. Temperatures will moderate slightly but remain below
average, with highs in the upr 70s to around 80 degrees and lows,
with strong radiational cooling once again, in the upr 40s to mid
50s.

&&

.SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/...
As of 335 AM Friday...

There will be little change (from the previous 24 hrs) in the
synoptic pattern at the surface and aloft across cntl NC. That
pattern will be characterized by continued surface ridging across
NC, though with a developing Appalachian-lee trough with diurnal
heating, and a 592-593 dm/322-323 dm subtropical ridge remaining
over the sern US at 500 and 700 mb, respectively. The presence and
influence of the subsident subtropical ridge, and otherwise
modification of the antecedent cP airmass, will yield warmer/above
average temperatures mostly in the lwr-mid 80s. Low temperatures are
likely to remain below average, however, given both radiational
cooling potential in the presence of the surface ridge and the
foregoing cP dryness and contribution to a large diurnal range, with
lows mostly in the mid-upr 50s.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
As of 415 AM Friday...

Mostly dry weather and warming conditions can be expected
through the extended with a slight cool down occurring on
Tuesday due to a frontal passage. By the end of the extended
period though models have come into remarkable agreement that a
anomalously strong ridge will begin to take shape across the
southeastern United States with temperatures rising well above
normal towards the end of the next work week.

The extended will open up with a weak sub- tropical ridge
located across the southern United States and an upper level low
heading east over the Midwestern United States. Low level
thicknesses will continue to rise Sunday towards 1400 m putting
high temperatures in the mid to upper 80s. The forecast will
remain dry Sunday as PWATs stay around 1.00", or slightly below
normal for this time of year.

Monday night into Tuesday morning the upper level low that was
over the Midwestern United States Sunday will be crossing the
Great Lakes region. A weak cold front will then attempt to cross
the zones Tuesday morning before getting hung up across central
NC. The ECMWF and GFS are fairly similar here and stall the
front near RDU. The chances of precipitation with the front
still looks rather paltry here as forecast soundings show
multiple layers of remnant dry air from the prior air mass.
Latest GFS soundings are slightly more robust with moisture, as
saturation in the column now exists from ~750 to 600 mb. The
primary 500 mb height rise/fall couplet is well off to the north
though with lift coming in the form of only weak PVA. All of
the above means that the forecast looks dry Monday into Tuesday.

By Wednesday afternoon whatever is left of the stalled
baroclinic zone will loose cohesion allowing warm moist air to
surge north. Thursday afternoon mid-level ridging will begin to
take shape across the southeastern United States as heights
collapse over the Pacific Northwest. 1000/ 850 mb thicknesses on
Thursday are forecast to surge towards ~1430m with highs in the
90s across the Coastal Plain.

&&

.AVIATION /10Z FRIDAY THROUGH TUESDAY/...
As of 610 AM Friday...

Under the influence of Canadian high pressure, mainly VFR conditions
are expected through tonight. However, shallow and localized
radiation fog will be likely again after 06Z mainly at RWI.
Otherwise, surface winds will be light and variable as the center of
the Canadian high builds overhead, with very little cloud coverage.

Outlook: The continued presence of Canadian high pressure will
maintain mainly VFR conditions in cntl NC for the next several days.

&&

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

&&

$$
SYNOPSIS...MWS
NEAR TERM...MWS
SHORT TERM...MWS
LONG TERM...Haines
AVIATION...MWS