Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Grand Forks ND
1007 am CDT Wednesday Aug 20 2014
issued at 1005 am CDT Wednesday Aug 20 2014
Visible satellite loop indicated some cirrus blow off over
northwestern parts of ND. Elsewhere cirrus was over southern ND
which lowers to middle level clouds over the far western ND. Middle level
clouds not expect to move into western zones until late this
afternoon or early evening. Tweaked high temperatures up a degree or so for
today. No other changes made.
Update issued at 636 am CDT Wednesday Aug 20 2014
Most of the fog has remained east of the area overnight...with
just a few patches of fog and low clouds east of the valley. This
will erode after sunrise.
Short term...(today through thursday)
issued at 350 am CDT Wednesday Aug 20 2014
The main forecast concern will be convective chances and potential
heavy rainfall late today into Thursday.
So far this morning...most of the area has remained free of fog
with light southeasterly winds. The far eastern areas will need to
be monitored through the next few hours though given the light or
calm winds in this area.
The region remains under the influence of shortwave ridging this
morning with surface low pressure developing over the High Plains
under developing southwest flow aloft. The feature of interest
over the next 24 hours will be a shortwave trough currently over
The Rockies which will lift northeastward. 850 mb temperatures will warm
a few degrees from yesterday...which should allow temperatures to climb a
little higher...despite some increase in middle/high cloud cover.
Winds will also be a bit breezy at times from the southeast. Think
the majority of the day will be dry over the area. Expect
convection to get going later this afternoon to the southwest
nearer to the surface low/warm front within strong warm
advection/moisture transport and also farther west in ND.
Precipitation chances will begin to increase late afternoon and tonight
across the area. There still is some uncertainty in where the
heaviest precipitation will occur. However...precipitable water values will rapidly
increase to over 1.80 inches by this evening. With deep warm cloud
depths...the potential for locally heavy rainfall will need to be
monitored where stronger convection does occur. In terms of
location...one favored area of precipitation may be into the dvl
basin...closer to the upper wave. Meanwhile...the strongest warm
advection signal appears to be across southeast ND this evening lifting
northeastward overnight. The day 1 Storm Prediction Center outlook does include far
southeast ND in a slight risk for severe. This area will be closest to
the instability axis and warm front. Based upon current forecasts
of surface features...the greatest severe threat would be just south
of the region. Given the strong forcing...a few strong storms are
possible throughout the area...but expect locally heavy rain to be
the greatest threat.
Convection will continue especially across northwest Minnesota on Thursday as
the shortwave trough continues to lift northeastward...with
overall drier conditions farther southwest. Thermal profiles are
not a great deal cooler...but clouds and precipitation likely will
affect temperatures...especially across northwest Minnesota.
Long term...(thursday night through tuesday)
issued at 350 am CDT Wednesday Aug 20 2014
Models continue to differ on timing and location of weak shortwave
troughs ejecting out of the deepening long wave trough to the west
Thursday night and Friday. Thus...confidence is on the low side.
With light northerly flow and the surface boundary south of the
area...currently not seeing any strong forcing signal. Model
consensus keeps the highest precipitation chances farther west. Temperatures on
Friday still appear to be near normal...but dependent on
For the weekend...00z model runs have taken a bit farther west track
with storm system and 500 mb upper low than previous days and also
slowed timing of main wave about 24 hours. It appears main 500 mb
low will track over far eastern Montana into western North Dakota
into southeastern Saskatchewan and western Manitoba. Thus the most
widespread and heaviest rainfall will be concentrated in that area
Sat night-Sun night time period. A bit more scattered nature to
showers and storms farther east in our forecast area for that
period. Cooler air will move in behind the system as 850 mb temperatures
cool into the single digits...with coolest air remaining in Canada.
Precipitation chances look lower early next week but increase a bit toward
middle week as another wave moves into the northern plains. Temperatures will drop
to below normal values early next week.
Aviation...(for the 12z tafs through 12z Thursday morning)
issued at 636 am CDT Wednesday Aug 20 2014
High/middle clouds will increase through the day with increasing southeast
winds gusting at times to 20 knots this afternoon. Still expect
showers and storms to increase from the southwest by this evening.
Maintained vicinity thunder due to low confidence in timing at
each site. Gusty winds and visibility/ceilings below VFR thresholds possible
with stronger storms.