Area Forecast Discussion
Issued by NWS Charleston, WV

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FXUS61 KRLX 281037
AFDRLX

Area Forecast Discussion
National Weather Service Charleston WV
637 AM EDT SAT MAY 28 2016

.SYNOPSIS...
Slow moving convection with heavy downpours again today. Moist
southeast flow will raise shower chance Sunday in the mountains.
Upper level ridge rebuilds next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
630 AM UPDATE...

Tweaked pops this aftn a bit given recent trends in hi res
models...with more of an emphasis over SE OH. NAM remains by
itself in blowing up convection over central WV today.

PREVIOUS DISCUSSION BELOW...

Another warm and somewhat humid day on tap with isolated to
widely scattered tsra this aftn and early evening. Such is life on
the edge of the ridge.

It remains difficult to hone in on any specific area for
convection later today. However...outside of any isolated mtn
convection...NAM model continues to indicate sct convection
firing over the Kanawha Valley by 21z and slowly propagating off
to the NW early this evening. The previous fcster looks to have
handled this well on the day shift and only some fine tuning was
made to the pops...mainly to increase to around 40ish for POP
flanked with slight chance. Another area to potentially hone in
on is across portions of SE OH. Expect downpours in any convection
with locally heavy rain given the light flow thru the column and
high moisture levels. Added a degree to highs today from observed
values yesterday yielding mid to upper 80s in the lower
elevations. Suspect a spot 90 will be observed in the urban
centers...especially in and around HTS/CRW.

Any evening convection will slowly wane as attention turns to low
pressure along the SE coast. With an approaching upper
trof...models are trying to pull in deeper moisture from the
tropical/subtropical system Sat night. This will result in an
increase in clouds with a few shra possible toward morning.

&&

.SHORT TERM /SUNDAY THROUGH TUESDAY NIGHT/...
There are only very minor models differences in the exact track and
timing of the two synoptic scale systems affecting our area this
period...with the biggest forecast challenge coming in the QPF
fields...as the models have trouble with convection in the summer
like moist and unstable atmosphere. Handling of the QPF will again
be handled on a diurnal basis outside of the main synoptic features.

First is the tropical/subtropical low pressure system that tracks
northwestward to the South Carolina coast this weekend...and then
just sits there through early next week...as the supporting upper
trough is sheared north and northeast thru the Mid Atlantic states
on Sunday. This shearing out of the upper trough on Sunday is
caused by the current Plains upper low opening up and moving east
across the Great Lakes. This second system is strong enough to
drive a weak front across the area Sunday night and Monday
morning.

The best chance of showers and storms comes with the upper trough on
Sunday...mainly in the mountains...as the upper trough lifts north
and then northeast through the Mid Atlantic states. Just diurnally
driven low pops mainly in the afternoon over much of the low
lands...as the deepest moisture and lift remains in the east. This
swath of precip then shifts east early Sunday night with the
upper trough. The following frontal system that comes across
Sunday night and Monday morning has less moisture to work
with...thanks to the previous system taking the deeper moisture
with it. So we will play low pops with this front...especially
given the loss of heating to support convection. Behind the
front...look for drying and some clearing from northwest to
southeast with any lingering showers ending in the mountains
Monday afternoon. Thereafter...weak high pressure and upper
ridging will bring dry weather Tuesday.

Only minor changes to high temperatures this period...with no really
cooler air moving in behind the front. However...behind the
front...the muggier air will exit with lows Monday night and Tuesday
night somewhat cooler.

&&

.LONG TERM /WEDNESDAY THROUGH FRIDAY/...
Upper level ridging over the central Appalachians and middle
Atlantic seaboard leads to a dog day summer pattern for the
middle portion of the short work week, with increasing diurnally
driven thunderstorms tending to favor the mountains per elevated
heat source.

Models begin to diverge on the strength and timing of the ridge,
which is stronger and peaks later, on Thursday, in the GFS
solution, while weaker and peaking on Wednesday in the ECMWF
solution. This model divergence continues on Friday, as the ECMWF
rolls an upper level low across southern Canada during the week,
which then pushes a cold front through the area on Friday. The GFS
has divorced itself from this solution, instead shearing out the
southern Canadian low, and dropping another southeastward through
the plains states toward the lower Mississippi valley.

The forecast does not bite on the left turn taken by the GFS, and
instead picks up on an increasing chance for showers and
thunderstorms Thursday into Friday, before turning slightly drier
and cooler late Friday and Friday night.

Temperatures close to central guidance with little change through
day 6, and then the trend toward slightly lower values.

&&

.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
SCT/BKN CU field will quickly develop as the morning
progresses. Isolated convection will be noted this
aftn...primarily over SE OH. Confidence not high enough to put
VCTS at any terminal with this issuance.

Mid and high clouds will overspread the area from the SE tonight
as moisture from low pressure along SE coast advects into the
region. As such...not forecasting fog attm.

FORECAST CONFIDENCE AND ALTERNATE SCENARIOS THROUGH 12Z SUNDAY...

FORECAST CONFIDENCE: Medium.

ALTERNATE SCENARIOS: Extent and coverage of convection this
afternoon remains in question...especially regarding any location
that may be affected.

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.

UTC 1HRLY       10   11   12   13   14   15   16   17   18   19   20   21
EDT 1HRLY       06   07   08   09   10   11   12   13   14   15   16   17
CRW CONSISTENCY  H    H    H    H    H    H    H    H    H    H    H    H
HTS CONSISTENCY  H    H    H    H    H    H    H    H    H    H    H    H
BKW CONSISTENCY  H    H    H    H    H    H    H    H    H    H    H    H
EKN CONSISTENCY  M    M    M    H    H    H    H    H    H    H    H    H
PKB CONSISTENCY  M    M    M    H    H    H    H    H    H    H    H    H
CKB CONSISTENCY  M    M    H    H    H    H    H    H    H    H    H    H

AFTER 12Z SUNDAY...
No widespread IFR conditions expected.

&&

.HYDROLOGY...
The river gauge...and forecast point...at the South Side Bridge
in downtown Charleston has not be reading correctly. The NWS
hydrologist is working to correct this problem.

&&

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

&&

$$
SYNOPSIS...JMV/30
NEAR TERM...30
SHORT TERM...JMV
LONG TERM...TRM
AVIATION...30

HYDROLOGY...



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