Scientific Forecaster Discussion
fxus63 kfgf 201435
Area forecast discussion
National Weather Service Grand Forks ND
935 am CDT Fri Sep 20 2019
issued at 930 am CDT Fri Sep 20 2019
Storm continue to develop across far NE ND this morning where the
strongest llj around 40kts is feeding into better forcing aloft.
Will keep mention of slight chance through the morning. Still
expecting a break in the activity before more storms this
afternoon and evening.
Update issued at 649 am CDT Fri Sep 20 2019
Seeing a lot of small speckles on radar currently, but the
slightly stronger storms are up across the Langdon area. Not sure
how long the morning activity will last, but it could go until
mid to late morning. Late afternoon and evening storm potential
may be even later than previously advertised, but will monitor
that through the morning.
Short term...(today and tonight)
issued at 323 am CDT Fri Sep 20 2019
Lots of issues to monitor for this portion of the forecast, so
will break up this discussion to match more specific segments.
Through sunrise...starting out, there are already some echoes on
radar in the Devils Lake region. This appears to be associated
with the broad low level jet and steady 850mb warm advection.
Showalter indices are highest over western North Dakota (where
several warnings were issued a few hours ago), but really taper
back as they move back into eastern North Dakota. None of the high
resolution models have picked up on this current activity,
instead there is a cluster of solutions favoring some sort of
development in the next 1 to 3 hours over southeast North Dakota
into adjacent areas of west central Minnesota. Meanwhile the
latest hrrr runs have no longer been showing the development over
southeast North Dakota into west central Minnesota. Therefore
confidence is fairly low in any one solution, but it is hard to
ignore what is already occurring over the Devils Lake region. This
current activity is more showers with isolated thunder, and will
keep a mention of this in the Devils Lake forecast through
sunrise. As some showers and storms have also formed in northeast
South Dakota and southeast North Dakota, will maintain isolated
precipitation chances into the Red River valley as well.
Sunrise through mid afternoon...for the most part, this portion
of the forecast should be relatively quiet. South-southeast winds
will increase again by mid morning and stay fairly gusty through
the day. Highs will again be very mild for mid September. Some
of the high resolution models linger some isolated showers or weak
thunderstorms across portions of the forecast area through the morning hours.
Confidence pretty low on if, when, and where this isolated
activity will occur. Will keep the mention of isolated showers and
weak thunderstorms across most of the forecast area through the morning, but
may be able to fine tune them with the next update if confidence
Late afternoon through the evening...this is the time frame with
the highest confidence on thunder development, with severe storms
and localized flooding possible. As for the set up, the deep 500mb
trough will move into the Montana rockies, with fairly steep
south-southwest flow aloft. At the surface, by 00z Saturday, low
pressure should stay over the western Dakotas, with the warm front
well north in southern Canada. MLCAPE and precipitable water
values become quite impressive for mid September, although
effective shear seems to still lag behind, not quite as strong as
the other two parameters. A steady, strong southerly low level
jet remains over the fa, but models show a slight increase again
by late afternoon into the early evening, especially focused up
into the Devils Lake region and the northern Red River Valley.
High resolution model guidance has been showing stronger
convection breaking out over central North Dakota around 6 to 7
PM, and rolling slowly eastward into the evening. Overall model
trends seem to be slower and further west with this development,
so will likely be fine tuning it through the day today as well.
Storm Prediction Center day 1 discussion mentions the possibility of this development
evolving into a linear mesoscale convective system. Agree with previous shift forecaster
that this could also evolve into shower/storm clusters that
gradually weaken by late evening. So will see. With the 500mb flow
nearly parallel to the expected storm development, heavy rainfall
remains possible as well. Storms could form and reform along the
line, bringing several periods of heavy rain.
After midnight...more uncertainty comes back again into this
period. Depending on whether the storms become a linear mesoscale convective system or
begin to weaken, there is more uncertainty in the lingering severe
storm threat. The slower trend with the recent models also comes
into play here, as some models do not even bring any storms into
our Minnesota forecast area until several hours after midnight. However, even
if storms were not longer severe, they could still drop some
heavy rain rates.
Long term...(saturday through thursday)
issued at 323 am CDT Fri Sep 20 2019
Quite a bit of uncertainty holds into Saturday as well. However,
models are showing a potential dry slot working into some portions
of the forecast area. The best afternoon chances of rain may be over the
Devils Lake region, closer to the mid level low. Southern portions
of the forecast area may actually be dry.
Long wave pattern showing troughing over region early in the period
as strong wave impacting early weekend weather resides over northern
tier. Long wave ridge then slides over region late Sun night into
Mon before transitioning to a split flow regime for early next week.
Best chances for precip will be northeast zones Sat night into sun,
however threat for convection decreases quickly aft 03z sun as
depicted by rising showalters indices. Sunday highs fall into the
60s behind this next cold front, before rebounding into the 70s on
By mid-day Tuesday zonal flow across the northern tier will result
in a progressive pattern. Main feature next week appears to be a
srn mb cold frontal passage Tue aftn, which will drop afternoon
highs into the upper 50s to lower 60s for the latter half of the
week. Most precip with this frontal passage will be across the north, and with
showalters ranging +2 to +4, will not mention ts at this time.
Aviation...(for the 12z tafs through 12z Saturday morning)
issued at 649 am CDT Fri Sep 20 2019
There are a few storms around the area this morning. Looking like
some will hit the kgfk taf briefly, and will monitor to see if
they will affect any of the other taf sites. Southeast winds will
be pretty gusty again today, especially by late morning through
the afternoon. Low level wind shear will also be an issue
throughout the taf period. Confidence low on the late afternoon
and tonight thunder chances. Each model run keeps coming in with a
later and further west solution. Trying not to make wholesale
changes at this point, but would not be surprised if each forecast
update adjusts the timing for any storms even more. For now,
pushed the storm chances back to the evening time frame, but
confidence is pretty low on exact details.