Saint Paul, Virginia Weather Forecast Discussion

358
FXUS64 KMRX 220026 AAA
AFDMRX
Area Forecast Discussion...UPDATED
National Weather Service Morristown TN
826 PM EDT Sun Sep 21 2025
...New UPDATE, AVIATION...
.KEY MESSAGES...
Updated at 814 PM EDT Sun Sep 21 2025
-  Above normal temperatures will persist through early next
    week.
-  Scattered showers and storms will be possible especially in
    the afternoons today through Tuesday. A few storms may produce
    strong gusty winds.
-  Cooler temperatures and increasing chances of showers and
    storms are expected Wednesday into late week. There is potential
    of isolated severe storms and flooding concerns but
    confidence is low at this time.
-  Next weekend will likely see decreasing chances for showers
    and storms, with temperatures a bit below normal.
&&
.UPDATE...
Issued at 814 PM EDT Sun Sep 21 2025
No significant changes for the evening update. Main change was to
add in some patchy fog tonight. I`m not terribly confident in this
given how much convective debris cloudiness there will likely be
left overnight. However, with widespread rainfall in the valley
this evening, I would expect there to be some patchy fog or low
clouds develop rather quickly should the cloud cover clear out.
Otherwise, evening convection continues to weaken/move out of the
area and expect rain free conditions across the CWA by 10pm
onward.
&&
.DISCUSSION...
Issued at 1229 PM EDT Sun Sep 21 2025
We start the period under quasi-zonal flow aloft, with some weak
short wave energy traversing the area sponsoring isolated to
scattered showers and storms this afternoon to go along with above
normal temperatures. MLCAPE values generally less than 1500 J/kg,
weak shear, and modest DCAPE values all suggest that chances for
any severe storms will be very limited, but a few storms may
produce gusty winds upwards of 40 mph this afternoon.
This general pattern will persist into Tuesday, with very warm
afternoons both Monday and Tuesday and scattered showers and storms
expected each day. The best coverage of convection will likely be
during the afternoon hours, although this will be influenced by the
exact timing of the weak shortwaves moving across the area. Models
show one of these weak waves approaching late Monday and an area of
increased upper jet forced divergence clips our northwest counties
late Monday into the evening. Effective bulk shear ticks up slightly
for late Monday afternoon/evening through Tuesday (approaching 20
kts Monday evening then more in the 20 to 25 kt range Tuesday),
and any convection early Monday evening and again Tuesday
afternoon and evening will be have a better opportunity to
organize with a few strong to severe storms possible. Damaging
winds will be the primary severe threat. The highest chance for
any severe storms late Monday looks to be over our northwest
counties especially along and near the northern Plateau where the
better upper divergence will be located.
By Wednesday, an upper low will be amplifying over the northern
half of the Mississippi Valley region. This upper low will drift
slowly east, with additional short wave energy rounding the base
of the trough and enhancing our chances for showers and storms
during Wednesday into Friday. Moisture will be increasing, with
NAEFS mean PW values reaching or exceeding the 90th percentile for
this time of year across much of our area during this period.
While it has been dry of late, repeated days of showers and storms
combined with these high PW values will necessitate monitoring
flooding concerns. How much convective energy will be available is
still questionable, but enough effective shear is likely to be
present to suggest the potential for a few strong to severe storms
given enough CAPE.
Models are in poor agreement for the latter periods, with questions
about how quickly the upper low exits the region. Right now it
appears that at least some drying can be expected for the weekend
along with temperatures a bit below normal. However, we will still
have low PoPs in the forecast for the weekend per the NBM given the
uncertainty that far out.
&&
.AVIATION...
(00Z TAFS)
Issued at 814 PM EDT Sun Sep 21 2025
Have basically VFR conditions in for the 00z package, except for
KTRI. There will likely be some patchy fog develop tonight in the
valley, but exactly where I`m not very confident about. If we lose
some of the debris cloudiness, KTRI seems the most likely to see
it and the LAMP and other numerical guidance suggest this to be
the case. Put some TEMPO 3SM in at KTRI to account for this.
Otherwise tomorrow will likely be similar, with SCT SHRA/TSRA
again tomorrow afternoon. Will let future shifts nail down timing
a bit better for any PROB30 or TEMPO inclusions.
&&
.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             67  87  66  88 /  30  40  20  30
Knoxville McGhee Tyson Airport, TN  64  86  63  86 /  20  40  20  30
Oak Ridge, TN                       64  85  64  85 /  20  50  20  50
Tri Cities Airport, TN              61  83  59  82 /  20  40  10  40
&&
.MRX WATCHES/WARNINGS/ADVISORIES...
NC...NONE.
TN...NONE.
VA...NONE.
&&
$$
DISCUSSION...CD
AVIATION...CD

NWS MRX Office Area Forecast Discussion