Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Jackson Kentucky
1230 am EDT Wednesday Apr 1 2015
issued at 1230 am EDT Wednesday Apr 1 2015
Winds have kept stirring this evening and temperatures have been slower
to drop than was forecast. As surface high pressure continues to
build into the region...winds should further diminish
overnight...and temperatures should finally drop off a bit more.
Have added some modest Ridge/Valley differences toward dawn...with
valleys probably having a brief time to decouple before sunrise.
Update issued at 1055 PM EDT Tuesday Mar 31 2015
The winds are starting to settle more effectively late this
evening along with higher relative humidity levels. Accordingly have updated the
severe weather potential statement to remove the fire weather cautions for the evening period.
Have also touched up the grids via the infusion on the latest
shortblend guidance...obs...and trends. These updates have been
sent to the ndfd and web servers.
Update issued at 810 PM EDT Tuesday Mar 31 2015
23z surface analysis shows a dry cold front dropping through eastern
Kentucky. This is supporting breezy and dry conditions through the
area this evening. This has led to several wild fires developing
through the area earlier in the day that continue...as seen on the
dual pol radar loops...cirrocumulus in particular. The winds will slowly
settle through the rest of the evening as the pressure gradient
relaxes and the mixing heights fall. Accordingly...have allowed
the red flag warning and Special Weather Statement for fire weather concerns expire.
However...did continue the cautious wording in the severe weather potential statement for the
rest of the evening for near critical conditions. Also fine tuned
the T/dew point grids per the latest shortblend guidance...obs...and
trends. Finally...took sky cover down another notch with this
update. These grids have been sent to the ndfd and web servers
while an updated zone forecast product and severe weather potential statement were issued.
Short term...(this evening through Wednesday night)
issued at 345 EDT Tuesday Mar 31 2015
Current conditions across the area feature mainly clear skies
with a an upstream dry cold front moving southeast. As of
19z...the front is moving across the Ohio River and into eastern
Kentucky. With this...a strong gradient will be present with some
20 to 25 knot gusts and this will continue with and behind the
front. Expecting winds to decrease and decouple by 23z this
evening. Profiles this evening continue with a deep dry layer and
will keep skies mostly clear through tonight as well. While the
center of high pressure will not have moved into the area...some
Ridge Valley split will still develop tonight. The dry air this
evening and gusty winds with the cold front will allow for some
hazardous fire weather conditions and will keep this in the severe weather potential statement.
Heading into the day on Wednesday...middle level ridging will be
moving into the area with surface high pressure centered over the
Ohio Valley. Winds will be light during this time and with the
higher sun angle...temperatures will rebound into the middle 60s
despite the cold front passing through on Tuesday evening. Still a
dry air mass will be in place with afternoon relative humidities
dropping into the lower 30 percent range.
For Wednesday night... a strong short wave moves into the MS River
Valley as southerly flow increases into the Tennessee and Ohio Valley. A
weak disturbance moves northeast out of the Gulf and into Kentucky
bringing a chance for showers into eastern Kentucky by dawn on
Thursday. By dawn on Thursday...a strong cold front develops as
this waves moves into the Midwest. Forcing and instability looks
to be strong enough that a few thunderstorms may move into the
area by dawn on Thursday. For now will stay with chance showers as
there will be some dry air to overcome as well.
Long term...(thursday through tuesday)
issued at 357 PM EDT Tuesday Mar 31 2015
The Ohio River valley will find itself in transition during the day
Thursday...as upper level ridging begins to exit...and a subtle
longwave trough over the western half of the Continental U.S. Begins to shift
eastward. Expect this longwave trough to make it into the
Mississippi River valley...and then then Ohio River valley by Friday
evening. Meanwhile...a strong shortwave will traverse southern
Canada just ahead of this longwave trough. Models are in
surprisingly good agreement with these features...other than a few
slight timing differences...and continue to be so throughout the
weekend as the trough axis exits. Zonal flow and general ridging
will then take hold Sunday night through the remainder of the
Two surface low pressure systems will set up along the longwave
trough and shortwave as we head into the extended. By 12z
Thursday...expect these surface low pressure systems to be
located...one...just north of Lake Superior...and 2...along the
Southern Plains. An extensive cold front will link these two
systems...quickly sweeping eastward with the longwave trough
With southerly flow already in place...and a good pull of warm moist
air coming off the Gulf of Mexico...expect convection to begin
developing during the day across Kentucky...well ahead of the cold front.
Coverage and instability will increase as the cold front nears
Thursday night. By Friday morning...the southern-most low pressure
system will be in mi/AR...and the northern one will have raced
farther ahead and northward into far NE Canada. The cold front will
be located along the Ohio River and become nearly stationary as it
becomes further elongated from west to east. This large area of
frontogenesis/instability will increase convective activity Thursday
night and into Friday...with 6 hour precipitable water values well over 1 inch
Thursday afternoon through Friday morning...increasing to over 1.25
inches during the day Friday. As such...expect flash flooding to be
a concern as we head into the day Friday...especially under some of
the larger showers and thunderstorms.
Friday evening...the front will finally make a very quick shift
across Kentucky Friday evening...pulling in much drier and somewhat cooler
northwest flow. This will also kick in a subsidence inversion...preventing
any further thunderstorm development...and quickly cutting off best
quantitative precipitation forecast. Expect showers and any lingering thunder to taper off
overnight. European model (ecmwf) tries to hold onto some upslope flow through the
first half of the day Saturday...while the GFS pulls the front far
enough southeast that there is no lingering moisture influence. Expect it
will likely be a combination of these two solutions...so will keep
with a model blend of precipitation through the day Saturday. Any
additional accumulations will be very light with very little
moisture left in the soundings.
More zonal upper level flow will take hold through the remainder of
the weekend. After a drop in temperatures from the cold frontal passage on
Saturday...expect them to slowly moderate to near or above normal.
However...both the European model (ecmwf) and GFS are trying to develop a weak
frontal boundary along this zonal flow as we head from Monday into
Tuesday...with strong southerly flow and abundant moisture flowing
into the Ohio River valley off of the Gulf of Mexico. If this
continues to organize...could be looking at another chance for rain
and thunderstorms...though there is still quite a bit of
disagreement on intensity and coverage.
Aviation...(for the 06z tafs through 06z Wednesday night)
issued at 1230 am EDT Wednesday Apr 1 2015
VFR conditions and light winds are expected through the period.