Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Paducah Kentucky
314 PM CST Thursday Feb 26 2015
Short term...(this evening through saturday)
issued at 120 PM CST Thursday Feb 26 2015
In the immediate near term...a few flurries or scattered light
snows could result in trace amounts to a light dusting through early
evening. Afterward...clouds may linger for much of the
area...even for much of the night (east)...but some clearing may
ultimately occur...particularly late. We tried to collaborate this
gradual west to east trending with our neighbors appropriately.
The main thing about tonight will be the brutally cold Arctic
airmass that plunges in on the strength of the 1040+ mb surface
high pressure system that wedges across the middle Mississippi to
Ohio River valley by 12z Friday. We forecast a record low of 11
at Paducah (record is 14 set in 1963) and a near record low of 8
at Evansville (record is 4 set in 1934). Combined with the
wind...we'll see wind chills near or below zero as well.
The surface high migrates eastward and centers across the Ohio
River valley Friday. Frigid temperatures here mean temperatures only
climb 10 to 15 degrees to their PM highs...even with sunshine.
Upper teens (north) to middle 20s (south) will be commonplace maximum
That sets the stage for another record or near record cold
temperature for Friday night...even with the high pressure center
moving further eastward...with lows in the single digits to lower
teens forecast again. The record low at pah is 17 (1993) and evv
is 4 (1993) for Feb 28th...and we forecast a low of 13 and 10
respectively for our Friday night/Saturday morning lows. Wind
chills late Friday night/early Saturday morning will also be near
or below zero again.
Saturday daytime...we start to moderate. Northern reaches of the
quadrant state will see the Mercury flirt with 32 degrees for their
maximum...while in the south...the Mercury makes a run on hitting the
40 degree mark. It looks like moisture return around the high will
hold off until after 00z Sunday to make its appearance...so at least
a dry start to the weekend appears in order.
Long term...(saturday night through thursday)
issued at 314 PM CST Thursday Feb 26 2015
The long term period will be very active due to a persistent moist
southwest flow aloft. Precipitation chances will be very high late
in the weekend and again Tuesday into Wednesday. The storm track
will initially be to our west through middle week...bringing a
significant intrusion of modified Gulf of Mexico air. By the end
of the long term period...the pattern will revert back to the more
familiar cold pattern of late.
Breaking it down day by day...
precipitation will overspread the region Saturday night as a
strong low level warm advection pattern develops. The 0 degree
isotherm at 850 mb will move north across the lower Ohio Valley in
the evening. A mixed bag of wintry precipitation is
expected...consisting mainly of freezing rain and sleet south of
the Ohio River and more sleet or snow to the north. The precipitation
is expected to change to rain from south to north on Sunday
morning. The liquid equivalents of the wintry precipitation are forecast
to be generally one tenth inch or less south of the Ohio River and
one tenth to one quarter inch north of the river.
Sunday night into Monday...models are in good agreement that
surface high pressure will move east across Illinois and Indiana.
This high pressure will bring a short break in the precipitation
for Monday. There is a chance of some lingering rain or mixed
precipitation in southern areas.
On Monday night into Tuesday...a very moist air mass will spread
northeast across our region ahead of a developing surface low over
the plains. The strong moisture fetch will set the stage for a
potential heavy rainfall event. The extended duration of strong
forcing...deep layer moisture...and elevated instability could
produce two to three inches over a 24 hour period. This could have
a rather high impact given the high water content of snow and ice
on the ground...combined with the saturated and/or frozen ground.
Some thunder appears possible as the 850 mb jet increases to 50 to
70 knots and surface dew points climb into the 50s.
On Tuesday night and Wednesday...a strong cold front will sweep
southeast behind low pressure over the Great Lakes region.
Although the low levels will dry out behind the front...the middle
levels will remain quite moist. Some Post frontal overrunning rain
may linger through Wednesday.
Wednesday night into Thursday...much colder air will filter across
the region. There may be some lingering overrunning precipitation...which
would be in the form of snow by later on Wednesday night. The middle level
flow will finally turn more northwesterly by late Thursday...which
should end the overrunning precipitation threat.
issued at 120 PM CST Thursday Feb 26 2015
MVFR ceilings prevail early with temporary MVFR visibility restrictions in
light snow...mainly North/East. This threat will continue until
around sunset...after which ceilings will linger in the MVFR-low VFR
thresholds. Ceilings should be above extra fuel mins of 2k feet by middle
evening...and may scatter overnight. This trend will occur first
west (kcgi) and move slowly east through the overnight hours...with
some uncertainty as to the extent of clearing as far east as
kevv/kowb. Diurnal heating may reignite a scattered to occasional
broken MVFR deck by late in the planning period. Northerlies will
prevail through the effective valid time of the forecast...but
gusts should curtail overnight.