593
FXUS63 KFGF 150250
AFDFGF

Area Forecast Discussion
National Weather Service Grand Forks ND
950 PM CDT Wed Aug 14 2024

.KEY MESSAGES...

- Showers and thunderstorms will increase in coverage through
  this evening and last into Thursday. Heavy rain and lightning
  are the main impacts.

- Wildfire smoke from Canada may return to the region Friday,
  with a chance for air quality impacts.

&&

.UPDATE...
Issued at 950 PM CDT Wed Aug 14 2024

As expected, storms entering southeastern ND have been on a
weakening trend, no longer SPS worthy but bringing rain and
lightning to our area. Northern shield of precip has been
falling apart as the stronger cells from the south have been
taking over, but there are still plenty of showers to bring rain
to most of our counties. System will continue to slowly wrap up
and push northeastward throughout the night. Should see
decreasing instability and any lingering convection will be
weakening.

UPDATE
Issued at 659 PM CDT Wed Aug 14 2024

Rain has pushed northeastward into the Devils Lake Basin,
northern Red River Valley, and western MN. A bit of elevated
instability in the 500-1000 J/kg range has entered southeastern
ND, so we are getting some thunderstorm activity in that area.
With the better CAPE remaining to the south and effective shear
around 25 kts, think that we won`t see any severe impacts, but
will monitor for heavy rain and anything popping up to produce
some small hail. Adjusted for timing and placement of POPs but
otherwise no major changes to overall messaging.

&&

.DISCUSSION...
Issued at 334 PM CDT Wed Aug 14 2024

...Synopsis...

A mid/upper level trough is slowly deepening over the Northern
Plains, with a 700MB/500MB low eventually closing off over our
region tonight into Thursday before moving east. A plume of deep
moisture highlighted by PWATs in the 1.5-1.8" range extends over our
CWA and several areas of showers and embedded thunderstorms will
track through or develop over our area through tonight before
coverage becomes more scattered Thursday. We remain on the northern
fringe of  centered over the southwest US, and
progressive flow will returns in several shortwave ridge and trough
passages. The amplitude of the ridging does vary in time between
ensemble clusters with stronger ridging supporting drier and warmer
conditions, while more clusters keep flow flatter/more progressive.
This keeps near seasonal highs in place next week and allows for
progressive waves and shower/thunderstorm chances.

Regarding thunderstorm impacts today-Thursday:

This afternoon/evening features an axis of steep to marginal mid
level lapse rates and marginal instability (1000 J/KG) near our west
and south through sunset. Deep layer shear is weak. There may be
enough forcing for a few marginal cores/smaller hail, and eventually
a linear MCS may pass to our south (as shown by some CAMs), but with
the main axis of instability south and 0-3km shear is less than
20kt/DCAPE less than 1000 J/KG wind organized severe this evening.
PWATs are very high but broader areas of moderate showers and
embedded thunderstorms/locally heavy rain. As thunderstorm activity
will tend to be more progressive/embedded within larger areas of
moderate rain the signal has continued to decrease within CAMs for
higher totals above 3" and 24hr PMM show a very "spotty" signal for
1.5"+, which lowers confidence in even localized excessive runoff.
Signal is still there for many locations to see above 0.25"+
rainfall over the next 24hr, with swaths over 1".

It is a low probability, but it is worth monitoring the track/depth
of the mid level low Thursday. Stratus may persist and any dry slot
may fill in, however if there is clearing the high vorticity
environment in place may support funnels or conditionally
landspout/weak tornado potential (particularly near surface
low/boundaries. As this is highly dependent on clearing an
mesoscale/smaller scale evolution the probabilities are low and
ultimately funnels would be favored over landspouts in the most
likely scenario.

Smoke potential Friday:

As the mid/upper low transitions east RAP/Canadian smoke models are
showing a dense plume of wildfire smoke that is currently bottled up
over northern Canada advecting south into our region. This is far
enough out in time, however dense the smoke will be an any potential
air quality impacts are uncertain, however the signal in near
surface smoke fields is there and it is worth monitoring, especially
if part of a sensitive group health-wise.

&&

.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 659 PM CDT Wed Aug 14 2024

Conditions a mix of VFR to IFR with rain pushing north and east
across the forecast area. Some convection getting going south of
KFAR which will bring some VCTS to at least the Red River
airports later this evening. There will be -RA or VCSH for most
of the night, with those locations seeing VFR ceilings currently
gradually decreasing to MVFR then IFR towards morning. Winds
will shift around to the northwest at least on the ND side of
the Red River by tomorrow. Some slight improvements possible by
the end of the period, but overall clouds and scattered showers
are expected to stick around through much of the day on
Thursday.

&&

.FGF WATCHES/WARNINGS/ADVISORIES...
ND...None.
MN...None.

&&

$$

UPDATE...JR
DISCUSSION...DJR
AVIATION...JR