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Area Forecast Discussion (AFD)

Issued by Charleston, WV (RLX)

                            
255 
FXUS61 KRLX 200111
AFDRLX

Area Forecast Discussion
National Weather Service Charleston WV
911 PM EDT Sun Aug 19 2018

.SYNOPSIS...
Upper trough crosses tonight. Weak surface front washes out  
Monday. A warm front crosses Monday night, followed by another 
cold front for Tuesday bringing drier end to the week.

&&

.NEAR TERM /THROUGH MONDAY/...
As of 915 PM Sunday...

Radar and satellite imagery suggest a very dry airmass at the
mid to upper levels with only isolated light showers across the
northeast mountains. High resolution models do not show any pcpn
across the lowlands through 12Z Monday. Therefore, trimmed PoPs
across the lowlands, keeping low chances along the eastern 
mountains overnight. Rest of forecast remains on track. 

As of 255 PM Sunday...

A weak cold front over the middle Ohio Valley may mix a bit 
farther into WV this afternoon, before stalling tonight, and 
then wash out on Monday, as a light southeast low level flow 
develops. A warm front will be approaching from the southwest by
late Monday.

Cells in scattered convection that developed south of the front
where the stratus broke up earliest today, may intensify a bit and 
become more numerous, given CAPE up to 2.5 KJ/KG, but bulk shear to 
25 kts should preclude storm organization and limit the strength of 
wind gusts. The cells should remain small and far enough between, 
and moving just quickly enough, to preclude water issues for the 
most part.

An upper level short wave trough will cross tonight, so
convection may be slow to fade, especially farthest to the 
south and east.

Otherwise stratus and fog will form again tonight, but the fog
will be more of a valley fog, and the stratus it lifts into 
Monday morning should not be as persistent as today.

Ridging in the wake of the exiting trough may make for an
otherwise dry start to Monday, but as the warm front 
approaches, the chance for showers and thunderstorms increases 
Monday afternoon. Little drying has taken place with the 
weekend front, and a moist axis is depicted over the area, 
ahead of the warm front, Monday afternoon, to the tune of 
surface dew points near 70, h85 theta e values near 340K, PW 
values approaching two inches, and CAPE values progged to reach 
1.5 KJ/KG.

Temperatures near guidance and still a little above normal for 
tonight and Monday.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY NIGHT/...
As of 330 PM Sunday...

A warm front will lift through Monday night ahead of a 
surface low pressure system moving through the Missouri and
Mississippi River Valleys. The storm system will continue to 
track to the northeast through eastern Canada Tuesday which will
help drive a cold front across the area late Tuesday into 
Tuesday night. Along and ahead of this feature, showers and 
storms are expected. With widespread cloud cover Tuesday 
morning, there is some degree of uncertainty on how much the 
atmosphere will be able to recover in the afternoon. However, 
models still indicate that MLCAPE values around 1,000 J/Kg is 
expected and with bulk shear values of 30-40 kts, strong to 
severe thunderstorms are possible. Agree with the marginal risk
for our entire CWA. It is also worth noting that parts of our 
far northern counties (Tyler, Doddridge, Harrison, and Taylor)
are in a slight risk at this time where the better heating and 
shear is expected. Rainfall rates  with this system as PWAT 
values around 2" are expected.

The cold front will exit the area to the east Tuesday night 
beginning to usher in drier and cooler air. Held on to some
showers through Wednesday as an upper level trough swings 
through. Precipitation activity will diminish Wednesday night as
high pressure builds in from the west.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
As of 330 PM Sunday...

An expansive area of high pressure moving across the Midwest 
will provide a shot of fresher air, ample sunshine and quiet 
weather for the beginning of the extended forecast period. 
Beyond Friday, some uncertainly exists on when precipitation 
returns to the region. The GFS depicts a dry weekend while the 
ECMWF brings the return of showers and storms starting Saturday.
Will go with a consensus blend for now until better agreement 
occurs.

&&

.AVIATION /01Z MONDAY THROUGH FRIDAY/...
As of 735 PM Sunday...

Radar and visible satellite imagery indicate that showers and 
storms activity has moved east of the Appalachians this 
evening, leading to mostly clear skies. Therefore, all sites
will start with widespread VFR conditions through at least 05Z. 

Light flow will become calm as the atmosphere decouples. Weak 
flow in the boundary layer and clear skies will allow for 
radiational cooling to take place, and the formation of dense 
fog, mainly along the river valleys and areas that received 
rainfall. Expect a quick deterioration to IFR/LIFR conditions 
after 06Z under dense fog. Although cannot rule out the 
formation of low stratus, believe dense fog will prevail. 

Removed pcpn and thunder from TAF tonight per poor bouyancy,
marginal deep layered shear of about 30 knots, and strong upper
level winds that decapitate tall updrafts. In addition, dry 
airmass is evident on Water Vapor satellite imagery at the mid 
to upper levels. At the sfc, dewpoints will remain around 70
degrees through the period.  

Any fog and low stratus will gradually lift around 13-14Z at
most sites leading to widespread VFR conditions Monday morning,
except for MVFR stratocu hanging on in the mountains into mid 
morning.

The chance for showers and storms will increase once again
Monday afternoon due to diurnal heating and plenty of sunshine
along an old frontal boundary lying along the tug fork in
southern WV.

FORECAST CONFIDENCE AND ALTERNATE SCENARIOS THROUGH 00Z TUESDAY...
     
FORECAST CONFIDENCE: Medium.

ALTERNATE SCENARIOS: Intensity of dense fog and stratus may 
vary tonight into Monday morning.

EXPERIMENTAL TABLE OF FLIGHT CATEGORY OBJECTIVELY SHOWS CONSISTENCY
OF WFO FORECAST TO AVAILABLE MODEL INFORMATION:
H = HIGH:   TAF CONSISTENT WITH ALL MODELS OR ALL BUT ONE MODEL.
M = MEDIUM: TAF HAS VARYING LEVEL OF CONSISTENCY WITH MODELS.
L = LOW:    TAF INCONSISTENT WITH ALL MODELS OR ALL BUT ONE MODEL.

DATE                                                            MON 08/20/18
UTC 1HRLY       00   01   02   03   04   05   06   07   08   09   10   11
EDT 1HRLY       20   21   22   23   00   01   02   03   04   05   06   07
CRW CONSISTENCY  H    H    H    L    H    L    M    M    M    M    M    M
HTS CONSISTENCY  H    H    H    L    L    L    L    L    M    M    M    M
BKW CONSISTENCY  H    H    H    H    H    H    H    H    M    M    M    M
EKN CONSISTENCY  H    H    H    H    H    H    L    M    M    M    M    M
PKB CONSISTENCY  H    M    M    L    L    L    L    M    M    M    M    M
CKB CONSISTENCY  H    H    H    H    M    M    H    H    L    M    M    M

AFTER 00Z TUESDAY...
IFR in showers and thunderstorms Tuesday into Tuesday night, 
and then in fog and stratus overnight Tuesday night into 
Wednesday morning.

&&

.RLX WATCHES/WARNINGS/ADVISORIES...
WV...None.
OH...None.
KY...None.
VA...None.

&&

$$
SYNOPSIS...TRM/ARJ/MZ
NEAR TERM...TRM/ARJ
SHORT TERM...MZ/RG
LONG TERM...MZ/RG
AVIATION...ARJ