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Area forecast discussion 
National Weather Service Jackson Kentucky
933 am EDT Wednesday Jul 23 2014

Update...
issued at 933 am EDT Wednesday Jul 23 2014

Update to increase probability of precipitation a bit sooner through the morning hours for
developing showers. Included the potential of thunderstorms this
morning as 12z soundings indicate enough instability to justify
mentioning once the inversion breaks. Otherwise freshened up wording
in the zone package to remove morning wording and fog. Also tweaked
afternoon highs just a bit based on developing convection...and
trends in sky cover. Finally brought grids in line with hourly observation.

Morning soundings showing decent enough precipitable waters around 1.6 inches...and
satellite sounding data indicating similar values over our area.
Forecast soundings...particularly the higher resolution short term
models which have initialized better than the GFS...are advertising
precipitable waters climbing to around 1.8 inches this afternoon. With storm motion
generally below 10kts this afternoon...some locally heavy rainfall is
a good bet. Gusty winds will also be a possibility with stronger
thunderstorms.

&&

Short term...(today through thursday)
issued at 342 am EDT Wednesday Jul 23 2014

Surface analysis across the region as of 07z feature mostly clear
skies with some increasing cloud cover over the southeast as
southerly moist flow continues to move into the area. This is aided
by high pressure centered over the Carolinas. With dew points in the
lower 70s across much of the area and temperatures only dropping to around
70 for lows...muggy conditions will continue into dawn as well with
some fog development in the valleys. This fog should dissipate as
cloud cover increases during the morning hours.

Heading into the day...models continue to show the closed low will
continue to meander along the la/MS Gulf Coast with a trough axis
extending into the central Appalachians and will assist in some early
development today of some showers and thunderstorms. This will still
be hindered with some middle level warm air but the cap should become
busted in some areas along the counties bordering Virginia.
Meanwhile...the much anticipated cold front will begin to impact the
area into this afternoon. The increased forcing and southwest flow
will allow for increased development during the 18z to 00z time frame
this afternoon into the evening. Model soundings agree with a
deteriorating cap through the afternoon...increased lift...and precipitable waters
in the 1.6 inch to 1.8 inch range will raise some concern for some
cells with heavy rainfall and a few down bursts across the area. Also
there is still a 5% severe risk across the area this afternoon and
into the evening issued by Storm Prediction Center. So will mention some strong storms in
the severe weather potential statement with some heavy rain potential and possibly an isolated
damaging wind from a down burst. Will keep likely probability of precipitation beginning this
afternoon and into the evening centered around the forcing from the
front itself. Since it is possible that with the morning cap...there
may not be any development at all.

Heading into tonight...assisted by the front...precipitation will continue
into tonight with diminishing chances towards dawn as instability
decreases. The forecast challenge for the period will be heading into
late tonight and Thursday. Models have the front pushing through but
the high pressure to the east may hinder the approach of the feature
so bringing an end to precipitation may be a bit later on the day Thursday so
will go with a lower chance but keeping confidence reserved. A few
instances of heavy rain may exist after 06z tonight but the severe
threat...if any should be over. Quite a cooler air mass exists behind
this front with highs in the upper 70s expected on Thursday...nearly
10 degrees below normal. So an unusually overall cool July continues.

Long term...(thursday night through tuesday)
issued at 342 am EDT Wednesday Jul 23 2014

The models are in a bit better agreement tonight with respect to the
pattern aloft through the extended. They all depict a strong ridge
over the southwest part of the nation and a deep trough over the
northeast part of the continent. This eastern trough extends south
through the Appalachians to the Gulf Coast keeping east Kentucky in
a prolonged period of northwest flow. However...the western ridge
does extend east for a time on Friday shifting the shortwave track
to the north of the state as heights rise locally. This ridge
quickly retreats...though...so that by Saturday morning the
northwest flow...and its periodic waves of energy...will again
engulf east Kentucky. This is where the models continue to display
the differences they have exhibited for the past 24 to 48 hours. The
problems center on the handling of the western part of the deep
northeast trough as it shifts southeast and into the states. The 00z
GFS and Gem continue to be quicker than the 12z European model (ecmwf) with this
development....but the latest 00z European model (ecmwf) has narrowed this gap. This
continues the uncertainty about the exact evolution process of
the trough/S renewed shift into the Great Lakes and Ohio Valley.
However...the end point is fairly clear by Monday morning as all
models are on board with an unseasonably very deep and large trough
pivoting through the region. The core of this trough descends well
south into the Great Lakes and Ohio Valley in all the models...
though the GFS ends up between 5 and 10 decameters lower over the
County Warning Area by Tuesday evening owing to its more southern centering of the
trough. This gyre then stays basically parked over the area with
abnormally low summertime heights through the end of the extended.
Given the uncertainty with the middle part of the extended will not
deviate far from a general model blend and continuity for the
forecast.

Sensible weather will feature a fairly active extended period with
times of storms...a threat of heavy rain...and much cooler
temperatures by the start of next week. For Thursday night...showers
and storms will clear out to the east with a departing cold front in
time for the start of the extended. This will be followed by 24 to
36 hours of dry and cooler weather before the front surges back
north with period of convection anticipated...not necessarily
conforming to the diurnal cycle should mesoscale convective system activity set up just
northwest of the County Warning Area. With this...locally heavy rain will be a
concern should any organized thunderstorms affect the same areas on
consecutive days. After a weekend of stormy weather beneath a quasi
stationary frontal boundary and ample heat/humidity...a cold front
will look to settle things down by Monday evening as it drives south
through the area in response to a fairly deep surface low moving through
the eastern Great Lakes. Cooler weather accompanies and follows this
front with Tuesday...possibly ending up similar to the record
setting cool down of last week...especially if the skies clear quick
enough during Monday night and stay that way for Tuesday night.

The CR grid Load provided a good start to the forecast for the
extended...though the ingest of the 12z European model (ecmwf) has likely Hurt the
consensus blend. Accordingly...did adjust the probability of precipitation to hone in on the
prime chances for convection over the weekend and into Monday with
special attention given to the European model (ecmwf) and GFS solutions. Also...
adjusted the low temperature grids a tad to reflect ridge and valley
differences Thursday and Friday night. Finally...went a bit lower on
maxes and mins from Monday night through Tuesday...figuring the
models are playing catchup on the upcoming unseasonable weather.

&&

Aviation...(for the 12z tafs through 12z Thursday morning)
issued at 730 am EDT Wednesday Jul 23 2014

Localized MVFR and IFR visibilities in fog existed early this
morning...including at sme. Visibilities will improve quickly through
14z with VFR conditions prevailing into the afternoon. A cold front
approaching from the northwest will result in increasing clouds and
then numerous showers and thunderstorms this afternoon. Coverage of
showers and thunderstorms should increase considerably after
20z...with mainly isolated to scattered storms in the late morning
and early afternoon. The cold front will move south of the area
between 06z and 12z on Thursday. However...after thunderstorms and
rain move out of the area tonight...low cloud and fog is expected to
result in IFR to MVFR conditions into early Thursday morning.



&&

Jkl watches/warnings/advisories...none.

&&

$$

Update...ray
short term...shallenberger
long term...greif
aviation...sbh

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