982
FXUS61 KRNK 242306
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
606 PM EST Sun Nov 24 2024

.SYNOPSIS...
High pressure will cover the area tonight then move offshore on
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 MONDAY/...
As of 600 PM EST Sunday...

Key message:

   - Above normal temperatures on Monday

Expect a quiet night with thin high clouds at times.
Temperatures with winds subsiding to drop into the 30s most
areas, with some upper 20s in the deeper mountain valleys.

Previous discussion...

Upper ridging over the Ohio Valley moves east across the Mid
Atlantic states tonight then over the western Atlantic on
Monday. This raises heights at 500 mb for the area. At this
surface, high pressure over the Southeast moves offshore
tonight. Surface and low level wind will back to the southwest
by Monday. As a result deeper moisture returns to the area by
Monday afternoon with precipitable water values rising above 0.5
inches and surface dew points rising into the 40s.

Cloud cover will be scattered through Monday afternoon. The wind
will decouple this evening leaving a shallow, surfaced-based
inversion overnight. So conditions will be favorable for good
radiational cooling tonight. Will stay below guidance in the favored
valleys and cold spots. Expecting enough sunshine Monday morning for
highs that are 5 to 15 degrees above normal. Cloud cover will fill
in Monday afternoon. Guidance has the leading edge of
precipitation just reaching the western side of the central
Appalachians shortly after dark Monday evening. Some gusts of 20
to 30 mph are likely at the highest elevations tonight and
Monday as the southwest low-level jet increases.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY NIGHT/...
As of 1230 PM EST Sunday...

Key Points:

1. Showers across mainly the mountains Monday night into early
Tuesday.
2. Dry and cooler Wednesday.
3. Rain/Rain showers arriving west to east Wednesday night.

A look at the 24 Nov 00Z NCEP Ensemble Mean 500 mb Geopotential
heights shows for Monday evening the axis of a shortwave ridge
moving eastward over New England. A shortwave trough will be moving
through the western Great Lakes region. By Tuesday night the
shortwave trough is expected to be negatively tilted from southern
Ontario into the mid-Atlantic region. By Wednesday evening, the
shortwave trough is expected to be over the Canadian Maritimes with
nearly zonal flow across our region.

At the surface on Monday evening low pressure is expected to be
situated near the MI/OH border with a cold front trailing southwest
into the mid-Mississippi Valley and a warm front eastward into PA.
By Tuesday evening, the low is expected to be over central Quebec
with an occluded/cold front extending into ME and then into the
western Atlantic, paralleling the New England coast. Weak high
pressure builds into the mid-West. By Wednesday evening, the center
of an even weaker high center shifts east to over the Southern
Appalachians, while low pressure develops over central TX.

Output from the 24 Nov 00Z Ensemble Situational Awareness Table
shows 850mb temperatures on Monday ranging from around +10C over
northwest sections of the area to around +12C over southeastern
areas. The upper portion of this range corresponds to the 90 to 97.5
percentile of the 30-year CFSR climatology. As the night progresses,
and through the day Tuesday temperatures fall behind a passing cold
front. Look for values on Tuesday afternoon to range from around 0C
across northwest sections to around +6C over southeast areas.
Through Wednesday and Wednesday night, values only see a minor
increase upward to a range of around +2C to +5C.

Precipitable Water (PW) is expect to increase Monday night to around
1.00 inch coincident to the passage of a cold front, with slightly
lower values immediately prior to the passage. After the passage, PW
will begin decreasing quickly the remainder Monday night and through
Tuesday. In fact, by Tuesday afternoon, the region is expected to
see PW less than 0.25 inch. Such low values correspond to the 2.5 to
10 percentile of the 30-year CFSR climatology. Similar values
continue through Tuesday night. PW values for Wednesday are expected
to slowly rise during the day, reaching a value around 0.50 inch by
the evening. The slow increase continue Wednesday night with values
averaging around 0.75 inch by daybreak Thursday.

The above weather patterns suggest showers associated with an
approaching cold front may reach the western half of the region on
Monday night. Increased cloud cover is a good call the entire area.
On Tuesday, the cold front crosses the region early. However, the
best coverage of showers will be associated with the arrival of the
front across western sections of the area late Monday night. Once
the front shifts east of the crest of the Blue Ridge, a developing
west to northwest flow will yield a subsidence effect for this
region of the area, greatly limiting advection/development of
showers eastward. Far eastern portions of the area by see a small
resurgence in coverage within the development zone of a weak lee
trough in areas near or east of roughly a Reidsville to Appomattox
line in the late morning. Slightly gusty winds are expected behind
the front on Tuesday into early Tuesday evening. Dry conditions are
expected for the entire region Tuesday night into Wednesday as high
pressure settles over the area. Wednesday night, light precipitation
begins within the overrunning region in the wake of a northbound
warm front. Timing of the cold front varies enough such that this
overrunning period lasts for different periods of time deepening upon
the individual model. However, there will be a trend probably some
point between late Wednesday night and Thursday morning that the
activity will become more showery as the cold front nears. Variety
of solutions carries over the differences in the low level thermal
profile for northwest sections of the region. For now, our forecast
will offer a basic rain versus snow forecast for any location with
temperatures at or below freezing (and these areas currently are
small in number), but the potential may exist for a greater variety
of winter p-types if conditions are just right.

Confidence in the above weather scenario is moderate.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
As of 1230 PM EST Sunday...

Key Points:

1. Numerous showers on Thanksgiving Day and evening.
2. Lingering upslope rain/snow showers across the mountains Friday
and Friday night.
3. Trending colder through the weekend.

A look at the 24 Nov 00Z NCEP Ensemble Mean 500 mb Geopotential
heights shows a long wave trough strengthening over north central
CONUS with the potential of an associated closed low also forming
near Hudson Bay on Thursday into Thursday night. By Friday night, a
nearly closed low is still in the neighborhood of Hudson Bay with on
associated trough axis extending southeast into the mid-Atlantic
region and potentially a second trough extending southwest into the
Upper Mississippi River Valley. For Saturday night, much of northern
and eastern portions of northern CONUS remain under a dominated long
wave trough with an associated closed low that shifts a bit eastward
to central Quebec. An associated shortwave trough extends southeast
over the Canadian Maritimes and another southwest into the Central
Plains States. Nearly zonal flow is expected over our region. By
Sunday, the upstream shortwave trough within the greater longwave
trough pattern shifts farther east into the Great Lakes and Mid-
Mississippi Valley regions.

At the surface, on Thanksgiving into the overnight hours low
pressure over TX progresses eastward and reaches portions of either
the mid-Atlantic or Southeast US. Ensemble averaging offers a broad
area of low pressure over this region thanks to notable differences
in track and timing of the individual members. By Friday evening, the
ensemble solution offers a more well defined low center just
offshore ME and the Canadian Maritimes with its associated cold
front well offshore the east coast of the US. A building area of
high pressure is expected from central Canada south to the Lower
Mississippi River Valley. By Saturday evening, the central US high
pressure ridge is expected to build eastward to over the Carolinas
and continue strengthening through Sunday.

Output from the 24 Nov 00Z Ensemble Situational Awareness Table
shows 850mb temperatures on Thanksgiving Day around +2C across
northwest sections to +6C over southeast parts. These values are
expected to trend downward in response to the passage of a cold
front. By Friday morning the nw-se range is expected to be -2C to
+3C, and by late Friday night -8C to -4C. Values Friday night for
the vast majority of the region are expected to be within the 2.5 to
10 percentile range of the 30-year climatology. On Saturday and
Saturday night, temperatures show little change as compared to
Friday night. Values on Sunday may be slightly lower within a -9C to
-6C range.

PW values on Thursday are expected to trend higher in
advance of an approaching cold front. Values over SE WV will be just
shy of 0.75 inch with southeast sections of the area around 1.00
inch. Values are expected to start decreasing Thursday night and
continue that trend through Friday. By late Friday afternoon, nw-se
values are expected to range from around 0.25 inch to 0.35 inch. For
Friday night and Saturday, value are expected to be around or under
0.25 inch with similar values on Sunday.

The above weather patterns offer the passage of the cold front
sometime from mid-day Thursday to sometime Thursday evening given
the variability in the model solutions. However, compared to the
output of 24-hours prior, there is a bit of a trend towards a
sooner, rather than later, time of passage. This sooner trend
continues into the forecast Thursday night. Solutions are leaning
towards precipitation directly associated with the front to have
exited all but perhaps the far southeast portion of the forecast
area by daybreak Friday. In the wake of the front, west to northwest
winds will start to increase and start providing for upslope
rain/snow showers across the mountains, with the best coverage over
southeast West Virginia, south into the Northern Mountains of North
Carolina. The upslope precipitation is expected to carry into
Friday, gradually decreasing in coverage throughout the day with
western parts of Greenbrier County, WV the last to have the light
precipitation conclude late Friday night or early Saturday morning.
For Saturday into Sunday, high pressure builds to our south, while
low pressure remains to our northwest. This will continue a general
west to northwest flow across our region. Some of the deterministic
models are offering a shortwave trough to progress through this
flow, helping to re-establish upslope rain/snow showers to western
sections of the area.

Confidence in the above weather scenario is low to moderate, with
the timing of the front and its associated precipitation the biggest
question mark.

&&

.AVIATION /23Z SUNDAY THROUGH FRIDAY/...
As of 604 PM EST Sunday...

FAA communications issues for BLF continues, so keeping AMD NOT
SKED.

VFR conditions expected through the TAF forecast period, with
light west winds, becoming southwest Monday afternoon, with a
few gusts to 20kt at BLF.


Above average confidence for ceiling, visibility, and wind.


EXTENDED AVIATION OUTLOOK...

A cold front will arrive Monday night into Tuesday to bring a
chance of rain and MVFR ceilings. High pressure and dry weather should
return for Wednesday.

Models were still different with the timing and location of low
pressure developing in the Southern Plains on Wednesday. A
majority of the solutions have widespread rain across the area
on Thursday with associated IFR/MVFR ceilings/vsbys.
Precipitation pulls out to the east by Friday, leaving only
upslope rain and snow showers and MVFR flight conditions in the
mountains.

&&

.EQUIPMENT...
As of 600 PM EST Sunday...

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/WP
SHORT TERM...DS
LONG TERM...DS
AVIATION...WP
EQUIPMENT...AMS/WP