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Area Forecast Discussion (AFD)

Issued by Jackson, KY (JKL)

                            
000
FXUS63 KJKL 220712
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
212 AM EST Fri Feb 22 2019

.UPDATE...
Issued at 211 AM EST FRI FEB 22 2019

Only made minor changes to blend obs into the forecast

UPDATE Issued at 1040 PM EST THU FEB 21 2019

Updated the forecast mainly to increase PoPs and QPF across the
CWA overnight - more to the north early and then southerly
focused. The QPF is still expected to be light enough not to 
contribute to any renewed flooding, but will keep the ground - 
especially south - saturated setting the stage for trouble as the 
heavy rain bands develop later Friday night. For this next batch
the FFA has been updated and reissued for the entire area. The 
river forecasts have been updated with several having temporarily 
crested and entered a decline. Did also add in the latest 
obs/trends for the T and Td grids. The grid updates have been 
sent to the NDFD and web servers. A freshened set of zones will 
follow, shortly. 

UPDATE Issued at 650 PM EST THU FEB 21 2019

23z sfc analysis shows the temporarily stalled frontal boundary to
our south creeping slowly back north and impacting the Tennessee 
border counties this evening. This is bringing some mainly light 
showers back into the CWA starting in the southwest. Expecting a 
long duration to this rain overnight not accumulating too much or 
adding to the flood concerns compared to the next rain surge 
inbound for later Friday. Otherwise, high and mid level clouds 
cover eastern Kentucky this evening with temperatures generally in
the mid to upper 40s. Dewpoints, meanwhile are running about 10 
degrees below temps, while winds are rather light and variable. 
Have updated the forecast mainly to beef up the near term PoPs in 
the south and add in the latest obs/trends. These updated grids 
have been sent to the NDFD and web servers. 

&&

.SHORT TERM...(This evening through Friday night)
Issued at 310 PM EST THU FEB 21 2019

The focus in the short term portion of the forecast will the
potential for heavy rainfall and flooding across eastern Kentucky
from Friday night through early Sunday morning. There is also an
outside chance for a few severe thunderstorms to move across the
area Saturday night, but we have low confidence in that scenario
playing out at this time. A strong area of low pressure is
forecast to move across the central Mississippi River valley and
Ohio and Tennessee valley regions Friday through Saturday night.
Initially, a warm front associated with this weather system will
move from south to north across the area Friday through Saturday,
bringing with it widespread rain showers. The rain should begin
moving to the southern portion of our forecast area this evening,
and will gradually overspread the entire area overnight. The warm
front will move very slowly at first, and may even stall for a
bit, before finally lifting through and out of the area on
Saturday. 

The showers could be intense at times and could lead to flooding 
across the area Friday night and Saturday. With area rivers, 
creeks, and streams already running high from recent heavy rains, 
there will be an enhanced risk for flooding across the area Friday
night and Saturday. A few thunderstorms will also be possible on 
Saturday and Saturday night. These storms could drop enough rain 
quickly enough to cause localized instances of flash flooding. 
This will be especially the case Saturday night, as a cold front 
moves across the region. We may even see an outside shot at some 
severe weather Saturday night. However, there is a good deal of 
uncertainty as to whether or not conditions will support severe 
weather Saturday, mainly limited instability and the timing of the
passage of the cold front. Because of this uncertainty, we are 
going to focus on the flood risk at this time. A flash flood watch
has been issued to deal with flooding potential.

Temperatures during the period will continue to run well above
normal. Low temperatures the next two nights will range from the
mid 30s to the 40s. Highs on Friday will be fairly mild, with max
readings ranging from the upper 40s to lower 50s across the area.

.LONG TERM...(Saturday through Thursday)
Issued at 520 PM EST THU FEB 21 2019

...Significant Flood Threat Developing Saturday and Saturday 
Night...

Eyes continue to be focused on our next round of weather as a
storm system accelerates across the southern Plains and into the
Great Lakes Region Saturday and Saturday night. Models are in 
reasonably good agreement with the main features but differs
considerably where it counts most...in the details of QPF. Models
are quite variable in where the axis of heaviest rainfall will be
realized as well as in overall totals. Consequently, there is low
confidence in the QPF forecast at this time. Earlier trends were 
taking heaviest precipitation out of the Cumberland and shifting 
it a bit more to the northwest. But a quick look at some of the 
incoming 18Z runs shows that trend reversing back towards the 
Cumberland again. The 12Z ECMWF also places a very uncomfortable 4
inch bullseye down over our south, generally over the London, 
Corbin, Barbourville area. Obviously details in the QPF forecast 
will need to be fine tuned. Regardless, the additional heavy 
rainfall will aggravate the current flooding and high water along 
area creeks, streams. and rivers. At present our forecast suggests
the potential of 2 to 3 inches across just about the entire 
forecast area with highest totals in our southwest closer to the 
Cumberland River Valley.

PWATs rise through the day Friday eventually climbing to between
the 75th and 99th percentile (1-1.5 inches) climatologically
speaking. A baroclinic zone will remain generally over our area 
through this upcoming event, with a slow moving warm frontal 
boundary lifting north across the area during the day Saturday, 
and a cold front sweeping through the area Saturday night. This 
will help steer convection in a band across our area producing 
some training at times. We will see some elevated instability 
develop over the area Saturday into Saturday night. Any 
thunderstorm activity will only increase the potential of locally 
heavier rainfall amounts. 

This system has plenty of dynamics associated with it. Winds 
aloft will climb as an H850 jet with winds of 60 to 75 kts 
develops across the region Saturday night...associated with winds 
along and ahead of the cold frontal zone. There is some very 
impressive environmental shear shear associated with the system as
well. This could help make up for the relatively weaker 
instability which peaks out across the area Saturday night. 
Everything combined means that we could not rule out a few strong 
thunderstorms with the potential that gusty winds could mix down 
in the stronger cells thereby increasing the risk of some damaging
wind gusts. 

We begin to dry out by Sunday, but we will continue to deal with 
some river flooding through the weekend and possibly into early 
next week. Surface high pressure will build into the Oho Valley 
Sunday night into Monday, providing a continuation of the dry 
weather. Thereafter the forecast becomes much more murky as models
differ on the timing and strength of another mid-week to week's 
end system. This is evidenced in the MOS guidance of respective 
parent models with a more progressive ECMWF being cooler through 
the period and the less progressive GFS/FV3 being much warmer. 
Trends suggest that any weather will hold off until later in the 
week. Thus trended up with temperatures just a bit. 

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
ISSUED AT 159 AM EST FRI FEB 22 2019

Conditions varied from IFR to VFR at the start of the period. The
best conditions were generally near and north of the Mountain
Parkway. To the south, light rain was occurring, and conditions
were largely MVFR. However, there were localized occurrences of
IFR and MVFR. This general scenario is expected to hold through  
the period, except rain will become more sparse beginning on 
Friday morning.

&&

.JKL WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch from this evening through Sunday morning for 
KYZ044-050>052-058>060-068-069-079-080-083>088-104-106>120.

&&

$$

UPDATE...HAL
SHORT TERM...AR
LONG TERM...RAY
AVIATION...HAL