National Weather Service Baltimore MD/Washington DC
350 PM EDT Sat Oct 10 2026
.WHAT HAS CHANGED...
Given the continued signal of 2 to 3 inches of rainfall, locally
higher along/east of the Blue Ridge Mountains, have issued Flood
Watches for Sunday. These are in effect from the Blue Ridge
eastward to just west of the D.C. metro area. Some further
eastward expansions may be needed. Gale Warnings have been
hoisted over the southern waters for Sunday morning given the
potential for 35 knot southeasterly gusts.
&&
.KEY MESSAGES...
- 1) Remnants of Post-Tropical Cyclone Isaias to bring rain,
breezy to windy conditions, and the threat of tornadoes
Sunday.
- 2) Above normal temperatures Tuesday will fall the second
half of the week as moisture starved fronts move through.
&&
.DISCUSSION...
KEY MESSAGE 1...Remnants of Post-Tropical Cyclone Isaias to
bring rain, breezy to windy conditions, and the threat of
tornadoes Sunday.
Post-Tropical Cyclone Isaias continues to lift northward across
Georgia and Alabama. This system has weakened considerably after
last evening`s landfall while losing all tropical
characteristics. The associated mid-level circulation
strengthens and becomes a large cutoff low later tonight. To the
east, surface high pressure over the northeastern U.S. today
moves offshore off southern New England tonight.
In advance of this broad area of low pressure, a thick high
cirrus shield continues to expand north and east into the Great
Lakes and New England. While this system still looms well to the
southwest of the area, some light scattered showers continue to
lift across I-64 toward the I-66 corridor. However, any amounts
are very light with some radar returns not even reaching the
ground. The thick cloud cover will hold temperatures mainly in
the upper 60s to low 70s this afternoon.
Looking ahead, the interaction of Isaias` remnants to the west
and surface high to the east will create a large area of
convergence / broad frontal zone over the Mid-Atlantic. There is
good model agreement that rain steadily moves from south to
north this evening into tonight as forcing for ascent increases
with some mid-level height falls in response to the approaching
cutoff low. It will take a bit of time for the surface to truly
saturate, so any rainfall this afternoon to evening across
central Virginia will struggle to amount to much. Eventually,
tropical moisture with PWATs at or above 2" surges in after
midnight.
It is worth mentioning again that conditions are favorable for a
widespread soaking rain, and 12Z and 00Z models have responded
with more QPF across the region. Forcing for ascent increases
tonight, and especially Sunday morning into Sunday afternoon as
mid-level heights fall with the approach of the cutoff low.
Enhanced low-level convergence and moisture transport will peak
Sunday morning into early Sunday afternoon. Strengthening
easterly flow into the Blue Ridge could also produce enhanced
rain amounts due to orographic effects. As a result, forecast
rain amounts have increased to 2.0-3.0", with locally higher
amounts of 3-5" possible. With this uptick, Flood Watches were
issued across the Blue Ridge eastward into the central Virginia
Piedmont region. This is in effect on Sunday 5 AM until Monday 2
AM. Some eastward expansion may be necessary if models trends
hold on or show further upticks.
Another noticeable trend in recent guidance is the higher
probabilities for severe weather Sunday afternoon. The main
synoptically forced rain moves north of the area early Sunday
afternoon. Rapid height falls and increasing low-level winds
provide a few hour window where some breaks in the clouds area
possible, leading to pockets of instability. A surface wave of
low pressure moves right through the area Sunday afternoon.
Forecast soundings indicate large, cyclonic hodographs, with
ample shear in place to support organized severe convection.
Clusters of thunderstorms develop along the leading edge of the
surface low pressure, with tornadoes and damaging wind gusts as
the main threats (looks mostly to be east of the Blue Ridge).
The NAM12, RRFS, and 12Z HRRR all show this scenario. The big
question still remains how much instability actually develops.
SPC has maintained a Slight Risk for Sunday, with a recent northward
expansion to just south of I-66 in Virginia.
The strong mid-level circulation is going to bring windy conditions
to the Alleghenies and Blue Ridge, starting late tonight into Sunday
morning. Wind Advisories were issued for downsloping easterly
winds in the Alleghenies (western Garrett, western Grant, and
western Pendleton Counties), and the Blue Ridge. The current
forecast for peak wind gusts is 40-50 mph in the
Alleghenies/Blue Ridge and 20-30 mph elsewhere.
The remnants of Isaias push offshore Monday, bringing an end to any
lingering showers. While conditions return humid and warm Monday,
there likely will not be much in the way of shower activity due
to subsidence behind the departing trough.
