986
FXUS61 KRNK 240147
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
847 PM EST Sat Nov 23 2024

.SYNOPSIS...
Low pressure off the New England coast will pull northeast away from
the area as high pressure moves over the central and southern
Appalachians tonight into Monday. A cold front crosses the area
Monday night and Tuesday with a chance of precipitation mainly in
the mountains. A complex low pressure system over the southeast
United States will bring widespread precipitation to the area
Wednesday night through Thursday night.

&&

.NEAR TERM /THROUGH SUNDAY/...
As of 815 PM EST Saturday...

Key message:

   - Mostly quiet weather with some winds continuing to weaken
     overnight

Not much has changed with the evening forecast update. Clouds
have receded from the east, with low to mid-clouds remaining
over the mountains of WV. Precipitation has ended and shouldn`t
resume overnight as heights continue to rise and the front
moving into New England takes forcing further away.

From the previous discussion...

Starting with upper troughing over the northeast United States
and a couple weak short waves will bring periods of high clouds
across the Mid Atlantic region this afternoon and evening. Low
clouds remain in the western upslope side of the central
Appalachians for the rest of the day, then will gradually erode
from northwest North Carolina this evening northeast to
southeast West Virginia by early Sunday morning.

As the surface low off of New England tracks farther away, the
pressure gradient will weaken and the low-level jet also decreases.
Plus, surface and low level wind will back to the west. All these
factors will result in less upslope lift into the mountains. By
Sunday morning, surface high pressure will be centered over the
southern Appalachians and wind speeds will be less than 10 mph.

The 500 MB flattens on Sunday with a slight rise in heights. At
850mb, temperatures warm back into the +6 to +8 range Sunday. While
clouds are limiting the temperature rise in the mountains today,
Sunday will see highs mainly in the 50s.

Since the wind will still be producing some light mixing tonight and
with the remaining cloud cover, only those areas with new snow
will have a local effect of a cooler minimum temperature. Will
lower the mins at the higher elevations and in spots that still
have snow on the ground, otherwise will stay close to NBM
guidance.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/...
As of 1245 PM EST Saturday...

Key Points:

1. Dry Sunday night into Monday with milder temperatures.
2. Showers, mainly over the mountains, Monday night.
3. Cooler and dry Tuesday into Tuesday night.

A look at the 23 Nov 00Z NCEP Ensemble Mean 500 mb Geopotential
heights shows a shortwave ridge crossing the Great Lakes region
early Sunday evening and a shortwave trough over the Dakotas. By
Monday evening, the axis of the ridge is expected to be centered
over New England, with the upstream shortwave trough centered over
the Upper Mississippi Valley. By Tuesday evening, the shortwave
trough is expected to have moved through our region, and slightly
negatively tilted extending from southern Quebec to the Delmarva
Peninsula. The northern extent of the trough may actually deepen a
close off as a low center.

At the surface Sunday evening, low pressure is expected to be near
Iowa, with a cold front extending southwest into North Texas. A warm
front is expected to extend eastward into the Ohio Valley. By Monday
evening, the low is expected to be near the Thumb of Michigan, with
the cold front extending southwest into the Lower Ohio Valley and
Mid Mississippi Valley. By Tuesday evening, the low is expected to
be over eastern Quebec with the cold front curving through Maine and
the western Atlantic. The center of surface high pressure is
expected to be over western Kentucky by Tuesday evening.

Output from the 23 Nov 00Z Ensemble Situational Awareness Table
shows 850mb temperatures of roughly +8C to +11C Sunday night into
Monday, with the high end of this range touching the 90 to 97.5
percentile of the 30-year CFSR climatology. Monday night into
Tuesday, temperatures trend lower post cold front, reaching a range
of -2C to +4C by Tuesday afternoon. Similar values are expected to
continue into Tuesday night. Precipitable Water values Sunday night
are expected to average 0.35 to 0.50 inch across the region. On
Monday, values are expected to trend higher, reaching a range of a
little over 0.50 inch to just shy of 1.00 by the late afternoon,
with the highest values in the northwest sections of the area.
Monday night, values the evening between 0.75 and 1.00 inch, and
then fall quickly through the night, especially in the west post
cold front to a range of 0.35 west to 0.75 inch east. The drop in
values continues during the day Tuesday with afternoon values under
0.25 inch for the entire region. These low value correspond to the
2.5 to 10 percentile of the 30-year climatology. Values around or
under 0.25 inch continue Tuesday night.

The above weather pattern offers a warming trend as the center of an
upper ridge builds over the region, and then shifts east of the
region Sunday night into Monday. Low level flow will trend more
southwest, conducive of warm air advection. The approach of a cold
front and the progression a warm front north of the area, will
continue the trend of milder air arriving over the area heading into
Monday into Monday night. Additionally, the increase in Precipitable
Water ahead of the cold front will also be promising for the
development of showers coincident to and in advance of the front as
it progresses across the region. However, as the prevailing flow
behind the front trends more westerly and northwesterly, coverage of
the showers should wane as subsidence increases across the Piedmont,
and the front also encounters lower amounts of low level moisture.
Unlike our last similar system, temperatures look as if they will
remain mild enough for rain showers rather than snow showers. If
there are any snow showers, they most likely would be over the
highest peaks of southeast West Virginia or northwest North Carolina
early Tuesday morning just prior to the conclusion of the
precipitation. Building high pressure will bring dry conditions
Tuesday and Tuesday night along with cooler temperatures.

Confidence in the above weather scenario is moderate.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
As of 1245 PM EST Saturday...

Key Points:

1. Trending milder into Friday.
2. Better chances of a wet rather than dry Thanksgiving for most
folks.
3. Breezy plus mountain rain/snow showers on Friday.
4. Dry and colder for Saturday.

A look at the 23 Nov 00Z NCEP Ensemble Mean 500 mb Geopotential
heights shows an upper low centered just north of the Canadian
Maritimes. Nearly zonal flow is expected across our region. A
shortwave trough is expected to be over the Central Rockies. On
Thanksgiving Day, the upper shortwave trough is expected to head
east into central CONUS where it is expected to strengthen and gain
amplitude from the Upper Mississippi River Valley to near the
Arklatex region. On Friday, the axis of the trough becomes washed
out in the averaging process of the ensemble solution. However, a
more dominate closed low is expected to be situated over western
Ontario with a broad pattern of circulation around the low covering
much of the northern sections of central and eastern CONUS. On
Saturday, the average center of the primary closed upper low shift
closer to the Ontario/Quebec border, while a broad circulation
remain around the feature into much of northern sections of central
and eastern CONUS.

At the surface, a ridge of high pressure is expected to over the
Ohio Valley on Wednesday with low pressure developing over west
Texas. On Thursday, high pressure is expected to be centered over
southwest Canada with its axis extending southeast into the Plains
States of CONUS. Over the eastern US, ensemble averaging does not
offer anything than a general relative weakness in pressure, rather
than a defined trough or closed low. By Friday, the central CONUS
ridge axis expands in width and extends farther southeast to along
the northwest Gulf of Mexico. A trough of low pressure is depicted
off the coast of New England. On Saturday, the ridge axis expands
more into the Mid-Atlantic region and the southeast US. A closed low
deepens over the Canadian Maritimes.

Output from the 23 Nov 00Z Ensemble Situational Awareness Table
shows 850mb temperatures of around 0C to +3C on Wednesday and
Thursday. Values trend lower post cold front Thursday night into
Friday, reaching a range of -4C to 0C by Friday afternoon.
Temperatures continue to slide a bit heading into Saturday, reaching
a range of -5C to -2C by the afternoon. Precipitable Water values on
Wednesday are expected to average around 0.35 inch. Values trend
higher Wednesday night into Thursday with afternoon values in the
0.50 to 0.75 inch range. Similar values continue into Thursday
night. On Friday, values trend lower post cold front with afternoon
values around 0.35 inch. Values continue trending lower into
Saturday with values around 0.25 inch for much of the area.

The above weather pattern offers dry weather for the area on
Wednesday. While the ensemble averaging offered no definite low
pressure pattern in the east for Thursday, deterministic solutions
offer a quick moving wave approaching and then crossing the region
Wednesday night into Thanksgiving Day. After Thursday, timing varies
as to how prompt the system exits the area, and if any other
disturbance moving through the southwest flow acts to slow the
buckle the feature back over the region for at least some period of
time Thursday night. Ultimately, a the feature has a kicker to the
north which exits the feature southeast of the area by Friday
morning. A remaining healthy northwest flow may continue upslope
mountains rain/snow showers into Friday and Friday night. High
pressure is expected to return the whole area to a dry forecast by
Saturday. Temperatures will trend milder through Friday before
falling on Saturday.

Confidence in the above weather scenario is low to moderate.

&&

.AVIATION /01Z SUNDAY THROUGH THURSDAY/...
As of 135 PM EST Saturday...

Due to FAA communications issues, amend not sked for BLF will
continue.

Wind speeds have reduced considerably from earlier in the day,
and will continue to drop as a low level jet associated with the
previous system exits the area. This trend will continue, and
through the TAF valid period expect winds to remain in the 5-8
kt range for all sites.

As mid-level troughing weakens and we see more zonal flow
occurring, in addition to increasing surface pressure, any
chances of precipitation, even in the mountains, will become
slim to none. Conditions are currently MVFR or VFR around the
area, with a deck around 1-2kft keeping a few mountain airports
under VFR. As we enter tomorrow morning, these cigs will
continue to lift and thin out, leading to widespread VFR by late
Sunday morning, lasting through the remainder of this period.

Confidence in the above scenario is above average.


EXTENDED AVIATION OUTLOOK...

Good flying weather should continue through Monday, but a cold
front will arrive by Monday night into Tuesday to bring a chance
of rain and MVFR ceilings. High pressure should return for
Wednesday.

&&

.EQUIPMENT...
As of 1040 AM EST Saturday...

National Weather Service Radar, KFCX is offline for maintenance
for the rest of the day.

Observations from the KBLF ASOS are not available due to a FAA
communications circuit outage.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...None.
NC...None.
WV...None.

&&

$$

SYNOPSIS...AMS
NEAR TERM...AMS/VFJ
SHORT TERM...DS
LONG TERM...DS
AVIATION...AMS/VFJ
EQUIPMENT...AMS