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551
FXUS61 KRNK 210715
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
315 AM EDT Tue May 21 2024

.SYNOPSIS...
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High pressure was over the region this morning and will provide dry
weather for most locations today and tonight as it moves offshore.
Wednesday and Thursday a cold front sinks through the Ohio Valley
and Mid Atlantic region will bring scattered showers and
thunderstorms. Showers and thunderstorms are expected Friday through
the weekend as the low pressure system tracks toward the eastern
United States.
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&&

.NEAR TERM /THROUGH TONIGHT/...
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As of 300 AM EDT Tuesday...

Key messages:

   - Confidence moderate for isolated thunderstorms this afternoon
   - Confidence high for above normal temperatures today and tonight

Night Fog satellite images showed areas of fog in central and
eastern Virginia and North Carolina almost as far west as Lynchburg
and Danville. River valley fog was also developing along the New
River. Expecting continued fog development this morning. The fog
will be shallow and dissipate by mid morning.

Scattered to broken stratocumulus develops this afternoon. Models
have isolated thunderstorms developing mainly after 20Z/4PM in the
mountains and continuing until the sun sets. Fog will form again
overnight in the river valleys and piedmont.

500 MB ridging and 850 MB temperatures in the +12 to +16 range will
result in maximum temperatures 5 to 10 degrees above normal. Lows
will remain mild tonight, mainly due to surface dew points in the 50s
and 60s and little change in the air mass. This keep minimum
temperatures roughly 5 to 10 degrees above normal.
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&&

.SHORT TERM /WEDNESDAY THROUGH FRIDAY NIGHT/...
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As of 200 AM EDT Tuesday...

Key Points:

1. Well above normal temperatures for this time of year.
2. Scattered showers and storms Wednesday mainly across the mountains.
3. Robust coverage of showers and storms Thursday and Friday, especially
during the afternoon hours over the mountains.

A look at the 20 May 00Z NCEP Ensemble Mean 500 mb Geopotential
heights shows for Wednesday high pressure in the western Atlantic,
off the coasts of the Carolinas and a shortwave trough extending
form MN southeast into IN. By Thursday, this axis of the shortwave
trough will be over our region, and by Friday, it will be over the
Canadian Maritimes. At the surface, on Wednesday, low pressure will
be centered near the Ontario/Quebec border with an associated cold
front curving southwest into parts of MI/WI/IA. By Thursday, the low
shifts into northern Quebec with the cold front crossing our region.
On Friday, the low makes additional progress eastward, but its front
is not as progressive and begins to stall over the region.

Output from the 20 May 12Z Ensemble Situational Awareness Table
shows 850mb temperatures around +16C across the area Wednesday and
Thursday, or values with the 90 to 97.5 percentile of the 30-year
climatology. On Friday, values are slightly cooler in the +14 to
+16C range. On Wednesday Precipitable Water values will range from
1.00 to 1.25 inches, for Thursday, 1.50 inch which falls with the 90
to 97.5 percentile of the 30-year climatology, then back to around
1.25 inches by Friday.

The above weather scenario will offer increasing chances of showers
and storms on Wednesday, especially across the mountains. By
Thursday into Friday, look for robust coverage across the region,
especially across the mountains during peak heating of the day as a
cold front crosses and then stalls over the area. Given the above
normal PW values over the are on Thursday, expected rainfall
Thursday into Friday may need to be monitored for locally heavy rain
concerns, especially if the same locations have repeated heavy rain.
Temperatures will be well above normal for this time of year.

Confidence in the above weather pattern is moderate to high.
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&&

.LONG TERM /SATURDAY THROUGH MONDAY/...
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As of 200 AM EDT Tuesday...

Key Points:

1. Temperatures continue above normal for this time of year.
2. Potential for daily chance of showers and storms
3. Confidence in the specific timing and location of the precipitation
is low.

A look at the 20 May 00Z NCEP Ensemble Mean 500 mb Geopotential
heights shows the region in a general southwest flow pattern as a
trough deepens across central CONUS. Concurrently, heights will
trend slightly higher each day over the region. At the surface,
indications are the surface front that began to stall over the area
on Friday, continues over or near the area on Saturday as the parent
low races away to south of Greenland. Sunday and Monday, the
averaging process of the ensemble solution washes out its earlier
weak signature of a front over the area. However, there are good
signs of a generally troughiness across the central US.

Output from the 20 May 12Z Ensemble Situational Awareness Table
shows 850mb temperatures average +16C through the period.
Precipitable Water values will average 1.25 inches through the
period.

The above weather scenario may present a continuation of daily
chances of showers and storms. The challenge in just where the
frontal boundary from Friday moves to, or doesn`t move.
Additionally, the prevailing southwest flow aloft could help escort
shortwave troughs across the region from the generally area of
troughiness across the center of the nation. While this general
pattern may end up being accurate, at this time, nailing down the
details in the timing of the best chances of precipitation each day
is the biggest question mark. As such, confidence in this portion of
the forecast is low on these details. There is better confidence in
the continuation of above normal temperatures
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&&

.AVIATION /07Z TUESDAY THROUGH SATURDAY/...
As of 205 AM EDT Tuesday...

Areas of fog over central and eastern Virginia and North
Carolina were resulting in MVFR to LIFR visibilities early this
morning. LIFR stratus moving onshore in eastern Virginia is
expected to stay east of KLYH and KDAN this morning. River
valley fog is also likely to develop along the Greenbrier and
New Rivers, impacting KLWB before 12Z/8AM this morning.

The fog will dissipate by 14Z/10AM, then scattered to broken VFR
stratocumulus will develop this afternoon over the mountains
and foothills. Isolated showers and thunderstorms are expected,
especially along the southern Blue Ridge. Because the coverage
will be isolated, local TAF sites may not be impacted by these
storms. For now only have VCSH mentioned at KBLF and KLWB.

Any showers and thunderstorms will erode this evening, after
00Z/8PM with the loss of heating. MVFR/IFR fog will form again
overnight in the piedmont.


Average confidence for ceiling, wind, and visibility.


EXTENDED AVIATION OUTLOOK...

VFR conditions will continue into Wednesday with the wind turning
to the southwest. The chance of showers and thunderstorms will
gradually increase in the mountains by Wednesday afternoon and
become more widespread by Thursday as a front arrives.

This front will stall by Friday across the Mid Atlantic and
linger through Saturday. Waves of low pressure riding along this
boundary will spark more showers and thunderstorms and increase
the likelihood of low ceilings during this time.

&&

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

&&

$$

SYNOPSIS...AMS
NEAR TERM...AMS
SHORT TERM...DS
LONG TERM...DS
AVIATION...