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Area forecast discussion...updated 
National Weather Service Jackson Kentucky
232 PM EDT Friday may 29 2015

Update...
issued at 200 PM EDT Friday may 29 2015

Just a quick update to touch up the grids per the latest T/dew point observation
and radar images. These have been sent to the ndfd and web
servers.

Update issued at 1045 am EDT Friday may 29 2015

14z surface analysis shows weak high pressure still holding on over
eastern Kentucky with low pressure out to the west. The earlier
valley fog has cleared out of the area with mainly some middle and
high clouds left behind...especially in the eastern parts of the
County Warning Area. Just a few light showers are lifting north through the area
at this time...but with a lack of debris clouds hindering development
expect convection to be more widespread later today when compared
to yesterday. There remains some questions about the triggers for
convective development today...but differential heating should be
enough for at least scattered activity through the afternoon.
Currently temperatures are in the low to middle 70s most locations
under the partly cloudy skies. Winds have picked up a bit from
the south at 5 to 10 knots...compared to yesterday...while the
dewpoints are in the sticky middle to upper 60s. Have updated the
forecast mainly for near term conditions and trends while also
removing the fog. The updated grids have been sent to the ndfd and
web servers while a freshened set of zones have been issued.

Update issued at 819 am EDT Friday may 29 2015

Freshened up the temperatures...dew points...and sky cover over
the next few hours to jive better with current observational
trends. Also slowed the probability of precipitation a bit more...according to the latest
trends in the hrrr model.

&&

Short term...(today through saturday)
issued at 357 am EDT Friday may 29 2015

Nearly stationary frontal boundary is currently aligned north of
the Ohio River. Eastern Kentucky remains on the more humid side of
the boundary...with the air mass noticeably more sticky compared
to the last few days. A weak impulse or two will once again pass
through the Mississippi Valley in between the upper ridge along
the eastern Seaboard...and the trough established across the
central Continental U.S.. eastern Kentucky will be on the edge of the
trajectory of these impulses...however given the weaker cap in
place and likely more instability building today compared to
yesterday...scattered convection seems like a good bet. Highs
will be warmer compared to yesterday...with less clouds...generally
in the low to middle 80s.

Convection will die off with the loss of heating tonight...with
lows generally in the low to middle 60s...and patchy
fog setting up...particularly at locations that see sustained
rainfall. A cold front will begin to make its push across the Ohio
Valley on Saturday...however there also be drier air in the low to
mid-levels. This will keep more of a gradient of probability of precipitation across the
area...with better storm chances near I-64...and lesser chances to
the southeast. Highs will range from the lower 80s in the
north...to the upper 80s in the southeast.

Long term...(saturday night through thursday)
issued at 412 am EDT Friday may 29 2015

Upper level ridging is expected to continue off the southeast Continental U.S.
Across the western Atlantic through the extended. Meanwhile...
another area of upper level ridging moving into the southwest Continental U.S.
Will help to break down the overall longwave troughing pattern that
has existed over much of the last week across the remainder of the
Continental U.S.. by Saturday night...Kentucky will find itself wedged in between
these two ridges...with upper level troughing amplifying over the
southern Mississippi Valley as it becomes blocked. Expect this
trough to finally close off into a closed low by Monday
night...staying nearly stationary through the remainder of the
extended...while weak ridging slides in just north of the Ohio River
valley. This pattern to our south will keep unsettled weather
across much of Kentucky through much of the extended period.

At the surface...expect a low pressure system to be collocated with
the upper level low...across the southern Mississippi Valley at the
start of the extended. A cold front will extend from this low
newrd...attaching to another low pressure system off the eastern
coast of Canada. As such...this boundary is expected to span
across much of the state of Kentucky through the day Sunday...creating a
driving force for convective development...especially given the
warm moist airmass in place across the region. And given the
blocked nature of this closed upper level low...expect there to be
little movement of the cold front...shifting only slightly
southward towards the Tennessee border throughout the remainder of the
extended. This slight shift will at least allow some influence of
the develop upper level ridging into the northern half of the County Warning Area.

Expect best convective development to be on Sunday...as has been
highlighted in previous forecasts...given the location of the
boundary over much of the state. Little in the way of directional
sheer or speed sheer...and soundings which show high amounts of
moisture throughout the column...will offset any of the higher cape
amounts during the afternoon. Thunderstorms are likely...but
isolated heavy rain and frequent lightning will be the main concerns
with any storms that develop. The boundary then shifts
southward...with high pressure moving into the northern half of the
County Warning Area. This will create a wind shift across much of the County Warning Area...with
cooler and more stable northwest flow taking hold. Temperatures will take a
slight downward trend in this regime...as will the amount of
moisture in the atmosphere. That being said...the boundary will
still be in such a close proximity that afternoon convective
development...especially over the south and southeast County Warning Area...cannot be ruled
out each day. So essentially...probability of precipitation will remain in the forecast
during the daytime hours through the remainder of the forecast
period. Overall coverage across the County Warning Area will increase Thursday and
Friday as southerly flow returns and more moisture is advected into
the County Warning Area.

Given decent model agreement during the extended period...the
superblend of models seemed to handle probability of precipitation and other parameters
fairly well. The only major adjustment to the model blend was to
undercut probability of precipitation some during the late night hours due to loss of
instability in the atmosphere which the superblend 12 hour grids are
just not capable of picking up on. Temperatures...winds...and cloud cover
all seemed quite reasonable and within good agreement of surrounding
offices.

&&

Aviation...(for the 18z tafs through 18z Saturday afternoon)
issued at 230 PM EDT Friday may 29 2015

Scattered convection will not taper off much until early this
evening...warranting at least a thunderstorms in the vicinity mention at all taf
locations. Once the convection will dissipates following dusk some
patchy fog will likely developing again in the valleys after 06z
affecting most of the taf sites with some MVFR visible. Isolated to
scattered convection will be possible by early afternoon on
Saturday with thunderstorms in the vicinity again included. Southerly winds will peak in
the 5 to 10 knots range this afternoon...outside of any storm...
otherwise winds will remain at 5 kts or less through Saturday
morning...picking up again later in the day.

&&

Jkl watches/warnings/advisories...
none.
&&

$$

Update...greif
short term...geogerian
long term...jmw
aviation...greif

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