Scientific Forecaster Discussion
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Area forecast discussion...updated
National Weather Service Jackson Kentucky
330 am EDT Monday Apr 21 2014
Short term...(today through tuesday)
issued at 330 am EDT Monday Apr 21 2014
06z surface analysis shows a weak area of high pressure holding on over
east Kentucky in the face of approaching low pressure from the
plains. On satellite...patches of high...and mostly thin...clouds
are drifting over east Kentucky early this morning while winds remain
light. This has allowed for a good night of radiational cooling...
establishing a moderate to large ridge to valley temperature
difference across the County Warning Area. Currently...readings range from the lower
40s in the most sheltered valleys in the east to the upper 50s and
lower 60s on the ridges...while more open areas are generally in the
low to middle 50s. Dewpoints...meanwhile...vary from the upper 20s on
the ridges in the east to middle 40s in the west and throughout much of
the Cumberland Valley.
The models continue to be in pretty good agreement with the Transfer
of energy from a dampening Southern Plains trough to a more well
defined one diving southeast from south central Canada later today.
The remnants of the more southern reflection will move through the
Ohio Valley this evening...but the main impetus for weather in
Kentucky will be from the more northern trough...and its height
falls...that cuts through the eastern Ohio Valley by Tuesday evening.
Although there remains some discrepancies with the models as this
pattern adjustment occurs they do agree on the broader features and
timing. As such...a general model blend was favored for the short
term portion of the forecast.
Sensible weather will feature one last pleasant...warm...and mostly
dry day through east Kentucky as a weakening cold front sends
increasing and thickening clouds into the area by afternoon. Moisture
will be increasing ahead of this boundary...but humidities will still
be able to bottom out in the upper 20s and lower 30s across the area
ahead of any showers inbound for the evening. Winds will remain
relatively light...though...limiting fire weather concerns or
opportunities. A few showers will be possible in the evening as the
front presses in and the First Pocket of weak middle level energy
crosses the area. A better chance of measurable rains of any
significance arrives toward dawn as the actual cold front moves into
east Kentucky. This front may be able to pop off a few garden variety
thunderstorms as it passes owing mainly to lifted indices approaching -3 and
convective available potential energy near 1000 j/kg...but we will lack a decent wind field and
stronger surface convergence that could drive better convective
development. Accordingly...have limited the slight chance of thunder
to right along the boundary into the day Tuesday. The front and its
mainly showers moves on through east Kentucky by early afternoon
Tuesday with cooler temperatures to follow. Around a quarter of an
inch of rain on average is expected from this system...so many places
will likely not even see a good soaking...keeping conditions fairly
dry heading into the middle and latter parts of the week.
Used a diurnal from observation scheme for hourly temperatures into the
morning given the wide variance between ridges and valleys currently
under way. After that...favored the curve from the nam12 through the
short term portion of the forecast. Did start out with the bias
corrected consshort guidance for the dewpoints and wind grids for the
first 24 hours of the forecast followed by the British Columbia/consall thereafter.
The dewpoints were adjusted lower through early afternoon per recent
behavior. As for probability of precipitation...ended up most similar to the higher mav
numbers through Tuesday rather than the more meager met guidance.
Long term...(tuesday night through sunday)
issued at 310 am EDT Monday Apr 21 2014
Forecast models are in good agreement through the work week.
Transient ridging will build across our region through Thursday
before giving way to a trough dropping into the Great Lakes region
by Friday. Models then handle this trough differently heading into
the weekend and our confidence in the details of the weekend
forecast drops off quite a bit.
Sensible weather will feature dry and mild conditions on Wednesday
and Thursday. We will likely continue to experience low relative
humidity values each afternoon as well. A strung out cold front is
then prognosticated to pass quickly through our area late Thursday night
into Friday morning. Model generated quantitative precipitation forecast is lean...as is
instability...and only expect scattered showers with perhaps a
thunderstorm or two as the front passes. As mentioned above...
forecast models then paint different scenarios over the
weekend...especially when looking at temperatures. For instance...
raw model temperatures on the 21/00z GFS keep US in the 50s on Sunday while
the 21/00z European model (ecmwf) is around 80. A model blend seems prudent. This
blend results in a dry forecast for Saturday with a return to a
slight chance of showers Saturday night and Sunday.
Aviation...(for the 06z tafs through 06z Monday night)
issued at 135 am EDT Monday Apr 21 2014
VFR conditions will continue over east Kentucky through the forecast
period as high pressure begins to depart. Inconsequential patches of
thin high clouds will drift overhead through the rest of the night.
Moisture will then begin to increase by Monday afternoon ahead of an
approaching cold front. This will likely lead to a cumulus deck developing
between 4 and 6kt feet mean sea level by middle to late afternoon. Clouds will
continue to increase and thicken during the evening...with showers a
possibility before midnight at most places. Winds will be light and
variable through the rest of the night before picking up a bit from
the southwest to west by middle afternoon Monday...continuing at 5 to 10
kts from that direction into the evening.