Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Duluth Minnesota
643 am CDT Friday Aug 29 2014
Short term...(today through Saturday afternoon)
issued at 349 am CDT Friday Aug 29 2014
Main concerns in the short term remain focused around the
current rain showers tracking northeastward through NE Minnesota this
morning...the next round of showers and storms expected to move in
from the south in the next 2 to 3 hours and spread to the NE
through the day. The main threat from the storms will be heavy
rain and lightning...with the heaviest rainfall likely over northwest WI.
Areal coverage and intensity of storms decreases this evening as
the system exits to the east...but slight chances for weak
convective showers and storms remain through Sat afternoon.
Upper wave currently situated over the Central Plains with decent
warm air advection and moisture transport from the south occurring ahead of the
system across the middle MS River Valley into southern Minnesota. A surface low
positioned around Sioux Falls will track to the east and combine
with a cold front/surface trough moving in across the northern plains
today. An area of MDT-heavy showers and isolated storms has developed
across southern Minnesota this morning...north of a surface warm front draped
over southern Iowa. This area of elevated convection is expected to move
northward into our forecast area in the next 3 hours or so and expand
northeastward through the region. Large scale lift from the incoming upper
trough combined with warm air advection...deep moisture...and increasing
elevated instability will all contribute to an expansion of
showers and storms over the area today. The main concerns will be
heavy rain possible across northwest WI...and lightning. Could see around
an inch of rainfall from Siren to Ashland and areas south and
east. Other locations expecting to receive around a quarter to
The upper low and associated surface low will be positioned over northern
WI late Friday night/early Sat morning and allow showers to linger
across the eastern half of the Northland. High pressure builds in
quickly from the west on Saturday...but not before afternoon
cumulus clouds develop and bring in a slight chance of showers and
weak storms in the afternoon.
Temperatures today will be slightly cool with highs only in the
60s and lower 70s. Strong pressure falls across Western Lake Superior
from the approaching surface trough to the west will induce a modest
lake breeze...winds around 10 to 15 miles per hour...and keep temperatures adjacent
to ls a tad cooler. Lows tonight will only drop into the 50s and
lower 60s due to an abundant amount of cloud cover. Temperatures will be
slightly warmer on Sat with highs in the lower to middle 70s...except
around Lake Superior where another lake wind will keep highs only
in the 60s.
Long term...(saturday night through thursday)
issued at 349 am CDT Friday Aug 29 2014
The extended period will feature periodic chances for showers and
storms with the best chance occurring with a system Sunday into
Monday morning. Confidence is lower tonight than yesterday with a
late period system.
Saturday night should be dry for most areas as a weak shortwave
ridge moves through. The GFS and European model (ecmwf) remain in OK agreement
regarding a shortwave/frontal boundary that will impact the
Northland Sunday into Monday but the NAM is quite a bit slower. We
followed closer to the GFS/ECMWF. A moist airmass will advect into
the region Saturday night...continuing into Sunday with precipitable water values
rising to 1.6 to 1.85 per the GFS/NAM. Showers/storms will develop
and become likely during the day Sunday over western areas...then a
widespread area of precipitation will move east Sunday night and then
diminish from west to east Monday. There will be a heavy rain threat
with such a moist airmass in place and strong forcing. If precipitable water
values rise to 1.75 inches...it will be near 3sd above normal for
this time of year. There will also be a threat for severe
storms...especially later Sunday afternoon into the evening hours.
Deep layer shear is forecast to be from 30-40 knots and ample
instability. The threat for showers/storms will diminish from west
to east Monday.
The upper flow will transition to zonal with several chances for
showers/storms through the rest of the period. No real organized
significant systems look to occur through the rest of the extended.
The models yesterday were in decent agreement developing a
stationary front just south of the Northland. The 00z models are not
in as good agreement and are more progressive late in the period.
Highs for most areas through the period are expected to be in the
seventies...with Sunday the warmest day for most areas.
Aviation...(for the 12z tafs through 12z Saturday morning)
issued at 643 am CDT Friday Aug 29 2014
IFR conditions have developed over most of the Northland and those
conditions will persist through much of the day. Showers and storms
will also occur through the day...diminishing later tonight.
Ceilings may lift for a time in spots this afternoon into the
evening...but are expected to lower again overnight with areas of
Preliminary point temps/pops...
dlh 66 57 69 55 / 70 30 20 10
inl 72 53 73 52 / 50 20 0 10
brd 73 60 74 59 / 60 30 10 20
hyr 71 59 72 57 / 80 70 20 10
asx 72 56 69 54 / 80 70 20 10