Scientific Forecaster Discussion
fxus63 kfgf 201506
Area forecast discussion
National Weather Service Grand Forks ND
1006 am CDT sun Oct 20 2019
issued at 1006 am CDT sun Oct 20 2019
Latest radar data shows echoes through much of South Dakota and south
central ND this morning, which will gradually progress into the
region this afternoon. Observed and model forecast soundings
indicate that broad synoptic lift will likely require support from
mid level fgen to overcome a Stout low to mid level layer of dry
air before rain is able to reach the ground this afternoon and
evening. This thinking seems to be in agreement with the latest
runs of high resolution models so delayed the start time of rain
chances back a few hours across the region to account for this.
Update issued at 635 am CDT sun Oct 20 2019
Forecast for today is on track. System continues to organize
across the Wyoming/South Dakota/Nebraska region. Latest
observations and incoming guidance arriving as expected.
Short term...(today through monday)
issued at 300 am CDT sun Oct 20 2019
Main concern this period will be rainfall and wind speeds with the
system expected to affect the region. At 08z, water vapor imagery
indicated circulation (upper level low) over Wyoming with surface
analysis indicating an associated surface low developing. All
guidance is in agreement indicating this system to track due east
into Monday, and then into the northern Great Lakes by Tuesday
morning. This track is a trend slightly south and east from
previous expectations. The end result is that the potential for
2+ inch rainfall and 50+ knot wind gusts has greatly diminished.
Main rain chances will come from synoptic lift associated with
mid-level warm air advection. Deformation zone precipitation
should be mainly east of the region. Total rainfall totals will
be limited by lack of instability and somewhat limited moisture
(pwats ~0.5 inch). Taking into account ensemble guidance and
expected forcing mechanisms along with the environment, anticipate
most areas will receive 0.5 to 1.0 inch of rainfall by Tuesday
morning. Guidance indicates an area of enhanced mid-level fgen
developing by this afternoon across northwest South Dakota into
east central North Dakota. This mesoscale forcing weakens by
Monday morning. Some areas within this region should receive
higher rainfall totals, although the coverage will be limited (to
where any organized banding sets up). With the current expected
track of this system, wind potential is more limited, although
still thinking at least near advisory criteria for a portion of
the region on Monday.
Long term...(tuesday through saturday)
issued at 300 am CDT sun Oct 20 2019
A return to cooler, just below seasonal temperatures is expected
for the mid to late week period with chances for light rain
Wednesday and next weekend.
Tuesday through Wednesday...
Scattered rain showers are possible through the day Tuesday across
northern Minnesota as the Sunday/Monday low lingers across the
northern Great Lakes region. Strong pressure gradient winds
developing over the eastern Dakotas and western Minnesota will allow
gusty winds to linger into the day Tuesday. Colder air filtering
into the region will help cool temperatures to just below seasonal
averages with highs in the low to mid 40s.
Heading into Tuesday night and Wednesday, a weak upper level
shortwave is forecast to propagate southeastward from western Canada
into the northern plains within the mean northwesterly flow regime.
As this occurs, scattered rain showers developing along a low to mid
level baroclinic zone are expected to overspread western to south
central ND. While the better rain chances will remain to the west of
the region, a few showers can't be ruled out for the southern Red
River valley between Fargo and Jamestown. Otherwise, most locations
will remain dry for Wednesday.
Thursday through Friday...
Upper level ridging and surface high pressure will help keep the
region dry for Thursday and Friday. Temperatures will remain below
seasonal normals for Thursday with highs in the low 40s before
warming up to the upper 40s by Friday afternoon.
Ensemble guidance has come into somewhat better agreement about the
timing and evolution of the upper level pattern for the end of the
week/start of next weekend with upper level ridging giving way to an
approaching Canadian low and cold front during the Saturday period.
Although considerable model spread in the exact timing of this
wave/cold front exists, the general idea is that next weekend will
see the passage of a cold front that will bring precipitation
chances to the region.
Aviation...(for the 12z tafs through 12z Monday morning)
issued at 635 am CDT sun Oct 20 2019
Ceilings will slowly lower though the period, reaching MVFR at some
point tonight. Rain will overtake all taf sites at some point this
evening or overnight. Winds will remain relatively light, but
start increasing by Monday morning.
issued at 311 PM CDT Sat Oct 19 2019
Minor to moderate flooding continues across much of the Red River
and some tributaries, with the exception of Oslo remaining in major
flood. River levels have receded a bit at most locations due to
recent dry weather.
A widespread rain event is possible Sunday through Monday, but
confidence is still low regarding where and how much rain is
expected with this system. The latest river forecasts do now account
for precipitation expected through Tuesday.
Inclusion of the impending widespread rain (half inch to one inch)
in the river forecast model yields significant rises to the
Sheyenne, Maple, and Wild Rice (nd) rivers in southeast ND early
this week. This results in mainly minor to moderate flooding along
these basins with the West Fargo diversion reaching major flooding.
Still have notable uncertainty in these forecasts since the rain has
not begun, some sites may have small breakouts to overland flow, and
some sites may be affected by backwater influence downstream (from
mainstem red). Elsewhere along the mainstem Red River and its
tributaries, the main impact will be prolonged High River levels and
perhaps additional crests (mainly in minor to moderate flooding).