Flash Flood Watch 5, NWS Morristown, TN

Cherokee County, NC, Clay County, NC, Anderson County, TN, Bledsoe County, TN, Blount County, TN, Bradley County, TN, Campbell County, TN, Carter County, TN, Claiborne County, TN, Cocke County, TN, Grainger County, TN, Greene County, TN, Hamblen County, TN, Hamilton County, TN, Hancock County, TN, Hawkins County, TN, Jefferson County, TN, Johnson County, TN, Knox County, TN, Loudon County, TN, Marion County, TN, McMinn County, TN, Meigs County, TN, Monroe County, TN, Morgan County, TN, Polk County, TN, Rhea County, TN, Roane County, TN, Scott County, TN, Sequatchie County, TN, Sevier County, TN, Sullivan County, TN, Unicoi County, TN, Union County, TN, Washington County, TN, City of Bristol, VA, City of Norton, VA, Lee County, VA, Russell County, VA, Scott County, VA, Washington County, VA, Wise County, VA

Area Forecast Discussion
National Weather Service Morristown TN
415 AM EDT Wed Sep 26 2018

.SHORT TERM...(Today and Tonight)...
Excessive rain and flooding will be our primary weather hazards
for today. A strong upper trough and 120 kt jet across the Great
Lakes will strengthen a surface low as it moves northeastward into
Canada. A surface cold front will move south toward the Tennessee
Valley and Southern Appalachians with a surge of moisture ahead
of the front. Forecast soundings show a saturated vertical
profile, a warm cloud layer depth of 10-12k ft, and PW of 1.9 to
2.1 inches (near the max of climatology). This will favor heavy
rain capable of producing localized flooding. CAM guidance
continues to point toward 2” to 4” totals across southeast
Tennessee with localized higher totals not out of the question.
FFG in this region is already low with 6-hr FFG of less than 3.0
inches, and across parts of Hamilton, Meigs, and Rhea Counties is
less than 2.0 inches. For this reason, will have a Flash Flood
Watch across portions of southeast Tennessee where FFG is lower
and flooding risk is maximized. With widespread rain and clouds,
temperatures will be near normal in the upper 70s.

This front stalls across the Southern Appalachians tonight with
additional periods of heavy rain possible across far southeast
Tennessee and southwest North Carolina with unsettled weather into
Thursday.

.LONG TERM...(Thursday through Tuesday)...
The extended range forecast periods initializes on Thursday
morning amidst broad and nearly full latitude longwave troughing
across the central CONUS, while at the surface weak high pressure
looks to move into the TN valley region from the west behind a
cold front. With that, guidance remains a bit uncertain regarding
the fropa as most sources favor the boundary stalling near/atop
the southern Appalachians on Thursday. Eventually the southern
stream shortwave embedded in the mean longwave flow will lift
northeast across the region Thursday evening, which should work to
drive the front eastward into Friday. Unfortunately antecedent
conditions will be quite degraded across portions of the fcst area
(mainly along/south of I40 as well as the southern mountains),
given expected rainfall today/tonight. The stalled frontal axis,
its associated moisture, and these precursor conditions will at
least extend the heavy rainfall and flash flooding threat
into/through Thursday. Thus a flash flood watch will be issued
through 00z Friday for these areas.

Moving on, by Saturday the old front looks to have pushed southward
while another relatively dry reinforcing cold front approaches from
the northwest.  The jury is still out with regards to how far south
this next front makes it, yet it does look like zonal flow aloft and
some drier llv advection will yield lower pops than days past.  High
pressure north of this frontal boundary will slide by to the north
atop the OH valley, eventually moving quickly off the New England
coastline to start the new work week.  With that, sly llv flow will
return to the TN valley region yielding waa beneath a large upper
ridge centered over the southeast.  All said, pops will return to
more of a diurnal trend to round out the period given no major
synoptic features to affect the area through Wednesday morning.

Temperatures through the extended range will slowly moderate from
below normal levels Thursday/Friday given ample sky cover and
precipitation, to above normal levels amidst a drier airmass and
building heights aloft.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             77  67  76  67 /  90  60  60  60
Knoxville McGhee Tyson Airport, TN  77  66  75  66 /  90  60  80  60
Oak Ridge, TN                       76  65  74  65 /  90  50  60  50
Tri Cities Airport, TN              77  64  73  63 /  80  70  80  60

&&

.MRX WATCHES/WARNINGS/ADVISORIES...
NC...None.
TN...Flash Flood Watch through Thursday evening for Bledsoe-Blount
     Smoky Mountains-Bradley-East Polk-Hamilton-Loudon-Marion-
     McMinn-Meigs-NW Blount-Northwest Monroe-Rhea-Roane-
     Sequatchie-Southeast Monroe-West Polk.

VA...None.
&&

JB/CDG