Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston WV
811 PM EDT Tuesday Oct 21 2014
an upper level low pressure system will provide a chance of showers
into Wednesday. Surface high pressure builds from the west Thursday.
A weak front possible over the weekend. High pressure returns Sunday.
Near term /through Wednesday/...
800 PM update...
raised probability of precipitation overnight especially in the mountains...but also focused
on the more organized area of showers back into central WV this
evening. Adjusted evening temperatures and dew points per current
trends...which result in smaller dew point depressions. Forecast
otherwise on track.
northwest flow and cold air advection will keep a stratus deck over
the region into Wednesday. Showers should be most likely this
afternoon due to maximum low level instability...but with cold air
advection continuing tonight...some showers remain a possibility. By
Wednesday...some warm air advection begins which will limit shower
possibilities considerably. Still enough moisture in the northeast
that afternoon instabilities might fire a few showers.
With a stratus deck over the region tonight...will go on the warmer
side of MOS guidance.
Short term /Wednesday night through Friday/...
with the upper level low trough drifting off the middle Atlantic coast
and surface high pressure influences from the west coming into
play...the short term forecast will see a slow clearing through
Thursday night before the next upper level system barrels in Friday.
Looking at the lowest levels reveals a good trajectory for upsloping
precipitation...an extension from the near term forecast...for the
northeast mountains. Good streamlines and the resultant high
humidities in the 1000-850mb layer lends weight to this.
However...will be warm advecting off the surface...so this would
likely be detrimental to precipitation formation. With competing
forces at work...will leave the showers at low end chance instead of
bumping them up into the likely category or higher. Forecast
soundings indicate the low level moisture will become trapped under
an inversion...so leaving them in through Thursday looks to be the
way to go. May need to alter this in upcoming forecasts as drizzle
may end up being a better option. For now...low stratus and damp is
a good bet for places in the Tygart Valley.
The low level moisture will eventually erode Thursday night.
Then...expecting the next upper level trough axis to push from the
northwest for Friday. It will be accompanied by a surface
trough...but indications now are that this system will be moisture
starved. Preferred the sref probabilities of measured precipitation
from this issuance and stick to slight chance for now.
Used the lower side of guidance Friday with the clouds moving back
in and losing a couple degrees at the 850mb level.
Long term /Friday night through Tuesday/...
no major changes necessary to the long term grids. A few weak
shortwaves will cross the area early in the period. Moisture still
appears to be limited...so have continued to maintain a dry forecast
at this time. Upper ridge then builds across the area over the
weekend and into next week...with continued dry and warm conditions.
A cold front approaches Tuesday into Wednesday...creating a chance
for showers...and leading to a drop in temperatures for Wednesday
Aviation /00z Wednesday through Sunday/...
the area remains in deep...moist north to northwest flow around an upper level
low that moves from northern WV to just off the Delaware-Maryland-Virginia peninsula over
the next 24 hours. This will keep lots of clouds in place. Showers
in the mountains and back across central WV at the start of the
period will become increasingly confined to the mountains overnight
and Wednesday. MVFR to IFR visibility with these showers will become less
common overnight through Wednesday. The showers will become more widely
scattered even in the mountains Wednesday afternoon.
Ceilings associated with the clouds will be primarily MVFR
overnight...with IFR at times in the mountains. IFR ceilings are also
possible in any shower. MVFR / IFR ceilings will become less common
Wednesday...with ceilings improving to VFR across much of The Lowlands Wednesday
afternoon. Clearing from the west will reach near the Ohio River late
Surface flow will continue light northwest while flow aloft continues light to
Forecast confidence and alternate scenarios through 00z Thursday...
Forecast confidence: medium to high.
Alternate scenarios: timing of showers and associated restrictions
could vary...especially at nt with brief Post rain fog. Ceiling heights
could vary even outside of the showers.
Experimental table of flight category objectively shows consistency
of weather forecast office 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 Wednesday 10/22/14
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 M M M h h h h h h h h M
heights consistency h h h h h h h M h h h h
bkw consistency h h h h h h h l l l l l
ekn consistency h l l l l l l l l l l l
pkb consistency h h h h h h h h h h h h
ckb consistency h h h h h h h h l l l l
After 00z Thursday...
IFR in low stratus possible in the mountains Wednesday night into
early Thursday...and in valley fog early Thursday morning especially
where it clears.