Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Jackson Kentucky
144 am EST Monday Jan 26 2015

issued at 143 am EST Monday Jan 26 2015

Did a quick update to freshen grids with observation and trends. Right now
low pressure continues to track across the region this evening and
most of this is in the form of rain with most sites besides black Montana
in the upper 30s to lower 40s this hour. Best coverage of rain this
hour is across the southern portion of the County Warning Area with more scattered
activity as you move north. Temperatures are dropping across far
western Kentucky tonight and this is expected to be the trend from northwest to southeast
across the state overnight tonight. WSR-88D radar however is not
showing much in the way of returns to our west with generally light
band of precipitation across west and central Kentucky this hour. That said
combine this with hrrr that shows a general weakening trend of the
precipitation as we move into the morning would suggest lighter amts as we
switch to snow in the dawn hour. Right now will only make minor
changes and continue to monitor radar and trends.

Update issued at 1137 PM EST sun Jan 25 2015

Given the well above normal temperatures experienced today /some
locations in the 50s/...we just really Haven/T seen a large cool down
across much of eastern Kentucky through most of the evening. This is
especially true in areas that have not yet received rain...or have
only received a small amount. This being said...other than elevations
above 3000 feet...Don/T expect rain to start changing over quite as fast
as what was in the previous forecast. Worked to adjust the low
temperature for overnight...based on the latest model guidance and well as based on the ongoing conditions with
temperatures and cooling downstream...previous snow pack...etc.
Went with a blend of the current forecast...the latest hrrr /which
seems to have the best initialization for this system/...and a little
influence from the GFS...which trended closer to overall thinking for
the low. Then...adjusted individual locations to get them within
better tolerance...including bumping up Black Mountain to 29 degrees
and other terrain above 2500 feet to between 30 and 32 degrees.
Further more...given the slow progress of temperatures falling...went
ahead and pushed back the timing of the low temperature to 13z
Monday. From here...used a mixture of the cons-short and hand editing
to adjust the diurnal curve for the remainder of the night.

All things considered...the slight uptick in temperature forecast
will result in a several hour difference in the rain changing over to
snow. This will keep any snow accumulations out of the forecast
through 12z /with the exception of Black Mountain/...and less snow
accumulation in for during the day tomorrow. Black Mountain is
currently at 32 they may start to mix with snow at any
time. However...most of the rest of the area will likely not see
snow mixing in until near dawn...then slowly transition to all snow
between noon and 3pm. By this point...model soundings are showing a
strong amount of dry air cutting off some of the best accumulation
potential during the afternoon. Overall...snow totals were lowered
across the County Warning Area. Expect elevations above 3000 feet to pick up the
highest amounts...between 1 and 2 inches. Some of the other ridges
across the area could see between a half an one inch...but a majority
of the County Warning Area will only pick up a half inch or less. Most of this is
still expected to fall between 12 and 18z when the best lift and
moisture and temperatures combine...and surface temperatures finally
fall enough to allow for accumulating snow.

Update issued at 706 PM EST sun Jan 25 2015

Freshened up the grids with the latest observational data for
temperatures...dew points...and winds. This resulted in little overall
change from the ongoing forecast. Based on the current radar
returns...and the precipitable water values overnight being around a half inch or
less...went ahead and reduced any mention of moderate
rainfall/snowfall to light. Just not seeing a whole lot of evidence
at this point for moderate to heavy intensities...though snow could
have some heavier spots at times tomorrow morning. Latest nam12
forecast soundings really start to lose moisture in the upper levels
between 6 and 9 z...with not much lift either...also supporting
lighter intensities. Otherwise...forecast seems to be in pretty good
shape over the next few hours. The center of the low is currently
over south central Kentucky and moving our direction...with the next round
of light rain about to spread across the County Warning Area over the next 1 to 2


Short term...(this evening through Monday night)
issued at 409 PM EST sun Jan 25 2015

Surface analysis as of 20z across the region features a small low
pressure system over the lower Midwest tracking east into the Ohio
Valley this evening. Ahead of this...some shower activity has begun
to move into the area this afternoon with more widespread precipitation back
west into western Kentucky and southern Indiana. Plenty of southwest
flow today and warm air advection into the area has allowed for temperatures to rise into
the upper 40s and even lower 50s across eastern Kentucky today.
Models showing the cold front to move through later tonight after 00z
will have the colder air moving in later. This advection will begin
in earnest just after 06z as the front moves through. Expecting a
change over in the higher elevations with already temperatures at Black
Mountain reaching its high for the day in the upper 30s and is now
beginning to drop off at this hour. Model profiles show a brief
period of good Omega through the last few hours of the event as the
front moves through. With cold enough air moving in...there could be
some quick bursts of snow in the higher elevations and even in the
valleys where colder air has finally moved in. Speaking of
temperatures...late tonight and into the day on Monday...temperatures will
be falling into the morning hours but some slight radiational heating
during the day before the core of the air mass moves in Monday
afternoon and into Monday night will result in temperatures rising a degree
or two or holding steady through the day tomorrow. Temperatures over the
higher terrain should slowly fall through the day.

Winds after frontal passage Monday morning will then switch around to
the northwest for a favorable direction for some upslope snow showers
through Monday afternoon. Moisture depth hangs around through Monday
morning and into the afternoon with some decent lift remaining
according to the NAM and GFS so some decent snow showers will hang
around through the day on Monday before tapering off to flurries from
west to east into Monday night. The core of the air mass moving in
will cause temperatures to plummet into the middle 20s Monday night and will
likely add to the threat of hazardous and slick roads.
Therefore...have issued an Special Weather Statement to highlight this threat.

Long term...(tuesday through sunday)
issued at 420 PM EST sun Jan 25 2015

A rather amplified pattern is expected to begin the period. Models
remain in generally in good agreement for most of the period...with
differences increasing toward the end of the period. At the start of
the period a trough is expected to be in place from the Great Lakes
south into the middle Atlantic sates and off the southeastern US
coast...with a ridge of high pressure from Mexico north into the
Southern Plains and rockies. At the surface the a deep surface low/blizzard
will be moving along the northeast US coast to start the period with
a ridge of high pressure at the surface extending from Ontario into the
Great Lakes and MS valley region. A series of shortwaves in northwest flow
between the two will drop from the Great Lakes and through the Ohio
Valley and Appalachians Tuesday into Tuesday night. This will bring
chances for snow showers and reinforce a cold airmass with 850 mb
temperatures to fall to the -8c to -10c range by late Tuesday afternoon and Tuesday

As the trough axis lifts to the north and east and the surface low moves
further up the eastern Seaboard...high pressure will gradually build
into the lower Ohio Valley region and Appalachians Tuesday night into Wednesday.
The influence of the ridging will wane by late Wednesday night as a
shortwave moving around the ridge over The Rockies and a northern
stream trough begin to join forces and approach the Great Lakes and
MS valley region as well as the lower Ohio Valley region. The
associated surface low should track well north of the area just to the
south of the southern Great Lakes and into the Middle Atlantic States
from Wednesday night into Thursday night. This system will have somewhat
limited moisture...and this should be another event where the
atmosphere moistens from the top down. At the onset...some snow
could mix in pending the strength of warm air advection and moisture
advection late Wednesday night into Thursday morning. The clouds also may not
thicken quick enough to prevent at least a minor Ridge/Valley split
for the valleys on Wednesday evening. At this point...a low in the middle to
upper 20s occurring around 6z on Thursday is expected.

Colder air will wrap back into the region behind this system and
possibly change any precipitation back to snow as it departs. High pressure
should then build in to bring a dry start to the weekend. The European model (ecmwf)
lowers heights more significantly across the region as well as the
Great Lakes and eastern Seaboard at the end of the period and is
thus much colder with the airmass. Any shortwaves at the end of the
period should be rather moisture starved with the model consensus
favoring anything that falls being snow. For temperatures late in the
period...opted to go a tad colder than the consensus blend...more in
line with isc consensus and giving a bit more credit to the past 2
European model (ecmwf) runs.


Aviation...(for the 06z tafs through 06z Monday night)
issued at 1253 am EST Monday Jan 26 2015

Tonight will be tricky in terms of ceilings as sites have been around or
MVFR ceilings thus far tonight. The question then becomes how quickly
to we see IFR conditions overnight and morning hours. Right now have
sites going IFR by 10 to 11 z before sites improve to MVFR this
afternoon. The low pressure that has been poised to move across the
region is tracking over eastern Kentucky this hour and will continue to
move east tonight. This will continue to bring periods of rain and
eventually a changeover to snow as we move into the early morning
hours. This will then transition to more snow shower activity as we
move into the afternoon. This low pressure will also usher in
stronger northwest flow later tonight into tomorrow with gusty winds around
20 knots possible overnight into the day today.


Jkl watches/warnings/advisories...

short term...shallenberger

National Weather Service Glossary of Abbreviations