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Area forecast discussion
National Weather Service Grand Forks ND
1032 am CDT Thursday Apr 24 2014
issued at 1025 am CDT Thursday Apr 24 2014
Latest rap/hrrr indicate surface trough and clearing axis to remain
maybe a tad west of where it was earlier thought. 21-00z period
rap has area of showwalters of -2/-3c and 700 j/kg mu cape in an
axis from Rolla through Devils Lake to Valley City to Lisbon-
Hankinson. It is this region where enough sun will break out and
on western edge of cold pool with 500 mb trough for scattered thunderstorm formation.
Will need to keep an eye for low topped supercells as paramters
favor them. Will needd maximum temperatures to rise into the 55-60 degree
range in sun area for instability to be realized.
Farther east very tight gradient where clouds will hold and temperatures
much lower and than appears to run from Cavalier through Grand
Forks to just east of Fargo to Fergus Falls.
In the meantime area of rain spreading north up the Red River
valley and eastward so wet day in sore for northwest Minnesota.
Short term...(today through friday)
issued at 330 am CDT Thursday Apr 24 2014
Many challenges through the short and into the long term as active
and at times complex pattern continues. Considering active pattern
models in pretty good agreement.
Interesting day ahead with temperatures...rain...thunderstorm and
accumulating snow potential all contributing to challenging
forecast. Subsidence in the wake of shortwave lifting into Canada
has diminished showers in the near term. However elevated boundary
over the central Dakotas will propagate east across forecast area along with
band of frontogenetic forcing and warm advection. Global and
mesoscale models all support showers becoming more organized from
valley east this morning. Precipitation area will then shift east mainly across
western Minnesota. In the wake of this elevated trough drying will move
into areas mainly west of the valley and could see some solar
there which would help boost temperatures close to average where
areas in the rain will likely hold in the 40s. In the mean time
upper low and associated cold pool will propagate southeast reaching forecast area
at prime heating. With cold pool will see some pretty steep lapse
rates along with sufficient instability and around 400j/kg of
mixed layer cape. Associated surface low will also be over forecast area at
same time providing low level convergence. So even with drying
allowing precipitable water values to drop to around a half inch
there will be potential for thunderstorm development. With upper
and surface low over forecast area cannot rule out potential for a few spin-
ups under stronger storms.
Tonight could continue to see some spotty convection mainly either
side of the valley until loss of heating. Best lift tonight will
be across the far NE ahead of sharp shear axis. With column cold
enough will need to monitor the Lake of The Woods region for some
Friday should be relatively quiet with any precipitation confined to the NE
forecast area closer to departing surface boundary. Models in disagreement on
how far south colder air will spread with GFS the coldest. At any
rate looks to be a respectable NE-SW oriented thermal gradient
across the forecast area which will make the temperature forecast tricky.
Long term...(friday night through wednesday)
issued at 330 am CDT Thursday Apr 24 2014
On Saturday band of warm advection lifts north through the western
forecast area as next area of low pressure organizes over the Central High
plains. With good model agreement increase probability of precipitation across the west.
Surface low deepens Saturday night over Central High plains as
next upper low crosses the central rockies. Will maintain current
probability of precipitation as broad area of isentropic lift and lowering condensation
pressure deficits sets up.
Sunday-Wednesday...high latitude blocking will set up over eastern
Canada...with an intense upper wave expected to lift into the
Central High plains on Sunday before slowly meandering into the
upper Mississippi Valley/Great Lakes for mid-week. A main source of
uncertainty is the details of the evolution of the upper low and
downstream ridge. Models suggest deep relatively moist
south/southeast flow upstream from the ridge axis into the northern
plains will help to promote widespread precipitation in this region
into early next week...with drier air associated with surface high
pressure over eastern Canada potentially inhibiting precipitation farther
east for at least some time period...especially if the amplified
upper ridge ends up displaced slightly west. Thermal fields vary
somewhat among models...but kept the idea of primarily rain during
the daytime hours with perhaps some mixed snow at night. Temperatures are
generally expected to remain on the cool side through the period.
Aviation...(for the 12z tafs through 12z Friday morning)
issued at 643 am CDT Thursday Apr 24 2014
Taf forecasts will be a challenge today with wide variety of ceilings
across the forecast area. Some dense fog possible at dvl for a few hours this
morning. Primary rain area today expected to be from valley east
and will see mainly MVFR ceilings. Some drying will be working into
areas west of the valley this afternoon which could break out
clouds however will be seeing potential for some afternoon thunderstorms and rain to
valley and adjacent areas.