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Area forecast discussion...updated 
National Weather Service Jackson Kentucky
149 am EST Friday Jan 30 2015

Update...
issued at 149 am EST Friday Jan 30 2015

Freshened up the hourly temperatures and dew points to better reflect
the current trends. Spotty returns on radar reflect either light rain
or snow showers across the area. The next short wave trough will
rotate in by around dawn...bringing colder air with it and helping to
bolster the snow shower activity into the morning.

Update issued at 711 PM EST Thursday Jan 29 2015

Everything being reported just upstream this evening continues to be
mainly drizzle. This would be supported by model soundings suggesting
very little ice in the clouds through the evening. Model soundings
cool enough (to introduce ice into the clouds) towards midnight to
finally see some snow entering the picture. Adjusted weather through
the evening to reflect more drizzle, before going with rain showers
late evening...before quickly mixing with or changing to snow. Sub-
freezing temperatures are still well upstream and will take a good
chunk of the night to see them get here...but it looks like sometime
after 2 am we should see those subfreezing temperatures working into our
area.

&&

Short term...(this evening through Friday night)
issued at 358 PM EST Thursday Jan 29 2015

A surface cold front was entering the jkl forecast area from the northwest
at middle afternoon. As is often the case...cold air advection will
lead to steep low level lapse rates...and when combined with upslope
flow...shallow convective precipitation should develop. It will be further
aided by the support of the middle/upper level trough axis passing over
tonight and early Friday. Initially...the temperature profile
supports precipitation in the form of rain this evening. As the column
cools...surface temperatures will cool enough to allow snow...and the
upper part of the moisture column will eventually reach -10c and
colder...and precipitation will change to snow. The precipitation amounts will be
light...but the probability is fairly high. Snowfall will generally
be a half inch or less...but some amounts of around an inch may occur
at higher elevations in the southeast. The last of the snow showers
will taper off during the day Friday as high pressure builds in and
upslope flow is lost. Mostly clear skies are expected as the surface
high passes over on Friday night.

Long term...(saturday through thursday)
issued at 358 PM EST Thursday Jan 29 2015

This period starts out quiet with high pressure overhead and
temperatures near 40 degrees...thanks in part to southwesterly
winds. Skies will be mostly clear in the morning with increasing
clouds in the afternoon as the next storm system approaches the
region.

There is still a lot of uncertainty with this late weekend system
due to the model run to run differences. Both the European model (ecmwf)/GFS models
bring southern stream energy from the southwestern US low and try to
phase it with the northern stream energy as it crosses the Tennessee
Valley. However... the track and strength of the surface low that
develops in the models is where there are substantial run to run
differences....especially with the latest 12z/29 GFS run which
deepens the surface low and takes it up across Massachusetts. One thing
the models do have in common is the amount of quantitative precipitation forecast they show. Another
question that remains is how much cold air stays in place and this
will heavily depend on the track of the surface low. That being said...
have leaned a bit toward a colder solution on Sunday. Model
soundings had most of the moist column below zero with surface temperatures
just above freezing until late Sunday night. Overall confidence in
this system remains low. Though...still believe there is a
reasonable chance for measurable snow Sunday into Monday.

As the system departs high pressure once again builds into the
region...along with a cold air mass. This should allow temperatures
to generally be falling throughout the day on Monday. Lows Monday night
could reach the single digits in spots but should mainly be in the
low to middle teens. Temperatures should rebound on Tuesday into the
middle to upper 30s in response to southerly flow from the Gulf
ushering in warmer air. Wednesday another system moves into Kentucky
bringing another chance for a mixed precipitation event ending on Thursday.
An Arctic air mass advects in behind it... dropping temperatures once
again into the low teens and single digits. Friday will be a chilly
but quiet day with highs well below normal.

&&

Aviation...(for the 06z tafs through 06z Friday night)
issued at 149 am EST Friday Jan 30 2015

MVFR/IFR ceilings will continue across the area through the early
afternoon. A passing upper level disturbance should also bring a
window of snow showers to the area generally between 11 and 17z. High
pressure will then build into the region...with VFR conditions
returning by later this afternoon. West to northwest winds of around 10
kts...with occasional gusts in the 15 to 20 knots range will continue
through the day...before diminishing towards dusk.

&&

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

$$

Update...geogerian
short term...hal
long term...jvm
aviation...geogerian

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