Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 131356 AAA
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
956 AM EDT Thu May 13 2021

.UPDATE...
Issued at 955 AM EDT THU MAY 13 2021

13Z sfc analysis shows high pressure still parked to the northwest
of Kentucky with relative low pressure to the south. This kept the
winds light and the skies clear through the night leading to the
formation of patchy fog and areas of mainly valley frost. Now
temperatures are climbing and the frost and fog have cleared off.
Readings are in the upper 40s to lower 50s most places with
dewpoints in the upper 30s to lower 40s. With the temperature
bounce have dropped the frost advisory and updated the forecast to
add in the latest obs and trends. These updates have been sent to
the NDFD servers along with fresh issuances of the HWO and ZFP.

UPDATE Issued at 755 AM EDT THU MAY 13 2021

Hourly grids were updated based on recent observations and trends
to fine tune temperatures and valley fog trends initially. The
fog and frost in some valleys should both dissipate through around
9 AM EDT. Some cumulus development is still expected from midday
into the afternoon particularly in the south and southeast.

&&

.SHORT TERM...(Today through Friday)
Issued at 423 AM EDT THU MAY 13 2021

Early this morning, an upper level trough extended from the
Canadian Maritimes into the northeast Conus and then southwest
into the mid MS Valley region and the southeastern Conus. The
the axis of this trough was just north of the Commonwealth.
Further west, an upper level ridge was centered over the tri state
MN/WI/IA area with an associated sfc ridge of high pressure
extending from MI to IA and extending into the Lower OH Valley
region. Ridging meanwhile extended into the western Conus with
embedded disturbances moving across the northern Rockies into the
central Plains. Southeast of the area, a frontal zone was well
south and southeast of the area and extending across northern
portions of the FL peninsula and into the northern Gulf of Mexico.

The initial concern is some frost developing in the sheltered
valleys through sunrise. This frost should dissipate in all areas
by 9 AM EDT. Otherwise, for today, the northern end of the upper
level trough will move north and northeast of the Northeast Conus
while the southern end of the upper level trough should move to
near the OH River this afternoon to early this evening. Moisture
across the region will be limited with the frontal zone well
southeast of the area. However, a somewhat shallow but extensive
rather high based cumulus field is expected to develop around
midday to early afternoon, especially across central and southern
locations. The cumulus are expected to be too shallow and high
based for precipitation. The airmass will moderate a few degrees
C compared to yesterday which is expected to lead to highs still
below normal but a couple of degrees warmer than Wednesday on
average.

The axis of the upper level trough is expected to move across the
area tonight and into early on Friday while the center of sfc
high pressure moves southeast into the OH Valley region. The
cumulus/cloud cover may be slow to dissipate during the evening
across the south in advance of the trough while clearing should be
more extensive and earlier in the north. Clearing skies, dewpoints
in the low to mid 30s and a decreasing pressure gradient should
again set the stage for patchy frost potential in valleys
tonight.

Height rises ensue during the day on Friday as shortwave upper
level ridging builds into the area. Some diurnally driven cumulus
are again expected to develop but should again be rather shallow
and high based. High could may increase from the northwest late
as a disturbance moves from the Plains toward the MS Valley. The
airmass will moderate further and with sfc and upper level ridging
dominating, temperatures should climb closer to or to the 70
degree mark.

.LONG TERM...(Friday night through Wednesday)
Issued at 316 AM EDT THU MAY 13 2021

High pressure will pull east through the weekend, and this will
lead to warming temperatures under more southerly flow at the
surface. This will also be aided by warming 850mb temperatures and
rising heights in the mid-levels. Then by Sunday a warm front
will lift northward out of the Tennessee Valley. This will be an
anchor for convection in the form of showers across much of
eastern Kentucky late Saturday night into early next week. It
looks like a lack of instability will lead to little if any chance
of thunder and therefore will go with no thunder for now on
Sunday. The cloud cover will also make Sunday a bit cooler despite
the southerly flow.

The operational guidance begins to diverge with respect to the
longer range parts of the forecast. The GFS remains wetter and the
12Z ECMWF remains drier overall in this part of the period. This
seems related to holding onto surface high off the east coast and
more mid-level ridging. The EPS still has several wetter versus
drier members and the new 00Z ECMWF was much wetter and closer to
what the GFS has been advertising. Given this was comfortable
keeping the NBM slight to chance PoPs going late Saturday night
into Wednesday until there is more continuity with respect to
where the boundary sets up. The most confidence exists on the
potential for rainfall along the warm front Sunday into Monday, as
guidance seems to be most in alignment during this time frame.
Either way we are looking at the potential for a more active
pattern to start the new week as several waves progress across the
lower Ohio Valley. We will also see a warming trend back toward
seasonal norms under the southerly flow and increasing 850mb
temperatures. It does look like enough instability will be in
place Monday, Tuesday and Wednesday afternoon for a slight to
chance of a few storms, but not much shear in place to help
organize this convection.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
ISSUED AT 806 AM EDT THU MAY 13 2021

Mainly clear skies were occurring at issuance times for most
locations, though some MVFR and IFR valley fog is initially in
place in some of the river valleys generally along and south of
the Mountain Parkway. A few mid clouds have also spread into the
Big Sandy Region as well. The fog should lift and dissipate
through around 13Z. Otherwise, VFR conditions are expected to
prevail through the period. Some rather high based cumulus in the
5 to 8kft AGL range should develop toward 15Z to 16Z and be most
prevalent across southern and southeastern locations location and
gradually dissipate by the 0Z to 4Z timeframe as an upper level
disturbance approaches the area. For winds, northeast to northeast
winds will initially be 5KT or less, but pick up again from the
northeast to north northeast in the 5 to 10KT range around 15Z and
then slacken toward 0Z as the center of sfc high pressure gets
close to the area.

&&

.JKL WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...GREIF
SHORT TERM...JP
LONG TERM...DJ
AVIATION...JP


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