Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 251152

Area Forecast Discussion
National Weather Service Duluth MN
652 AM CDT Tue Jul 25 2017

.SHORT TERM...(Today through Wednesday)
Issued at 326 AM CDT Tue Jul 25 2017

Chances of showers and thunderstorms will increase through the
morning hours today, especially over our southern counties as a mid-
level shortwave sweeps over our southern periphery. There could be a
brief respite from precipitation chances across the Northland later
this afternoon before ramping up again by the late afternoon and
evening hours as a cold front boundary dives south over the region.
This will set the stage for another shot of showers and storms
across a good portion of the Northland, with some storms possibly
strong to severe. There is some uncertainty regarding the severe
extent for this afternoon and evening as the risk will be
conditional on if we can get a sufficient amount of daytime heating.
This will impact how much instability builds to support these
thunderstorms. MLCAPE values between the synoptic models have a good
bit of range, with values generally between 500 to 1500 J/kg, with
the NAM model going much higher than these values, and 0-6 km bulk
shear values are progged between 30 to 40 kts. Rich boundary layer
moisture is expected to exist ahead of the cold front, with sfc dew
points in the lower to mid 60s across most of the Northland, with
perhaps values near 70 over the Brainerd Lakes area. Southerly flow
will help increase moisture transport, with Pwat values in the 1.5
to 2.0" range, which are >90% of climatology, according to the NAEFS
Pwat climatological anomalies. Large hail and damaging winds look to
be the main threats for this system, along with small risk of a
tornado, especially from the Twin Ports and points southwest towards
Brainerd where the richer boundary layer moisture and stronger low-
level jet will be. Some flash flooding will also be possible given
the Pwat values, and the potential for some training convection due
to Corfidi storm-motion forward propagation vectors are progged to
run parallel to the cold front boundary. There is a Slight Risk for
severe weather southwest of a line from Hackensack, MN to Virginia,
MN to Tofte, MN, and all of the head of Lake Superior. There is at
least a Marginal Risk of severe weather elsewhere across the
Northland. The best timing of severe thunderstorms should be after 9
PM CDT and 5 AM CDT tonight.

There may be a small lingering chance of a strong to severe storm
over northwest Wisconsin for Wednesday morning as portions of
northwest Wisconsin is in a Day 2 Marginal Risk of severe weather.
However, once the cold front boundary moves southward, which should
be late Wednesday morning, the thunderstorm threat will move out.
Then, sfc high pressure will build in behind the cold front, leading
to a very nice afternoon across the Northland, with mostly sunny
skies expected. There may be some lingering showers over northwest
Wisconsin in the afternoon, but these should move out as the high
builds in. Wednesday`s highs look to be near seasonal normal, with
values in the upper 70s and lower 80s.

.LONG TERM...(Wednesday night through Monday)
Issued at 326 AM CDT Tue Jul 25 2017

A digging upper level short wave trof will be dropping over the
forecast area Wednesday night. Moisture is lacking ahead of the
trof, but increases behind the trof. With this lack of moisture and
the best forcing ahead of the trof, only have a slight chance of
showers over southern Price county in the evening. Dry overnight as
surface high pressure covers the area. As the upper trof exits on
Thursday, this allows mid level and surface ridging to cover the
region and linger through Saturday. Model differences show up
Saturday night through Monday. A weakening upper short wave trof
will move across the area Saturday night with an associated
vorticity maxima. Best chance of showers will be over the western
half of the region in the anticipated path of the vort max. Another
short wave follows on Sunday. Timing, strength of the trof, QPF are
all in question and used a blend for pops/timing/QPF. By Monday, the
GEM closes off an upper low over the forecast area which is not
featured in the ECMWF or GFS and was ignored. Blended the GFS/ECMWF
to handle differences with embedded impulses in a west northwest
flow aloft.


.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 652 AM CDT Tue Jul 25 2017

Mainly VFR through the morning ahead of an area of low pressure in
South Dakota. Isolated MVFR cigs are possible in the vicinity of
showers near BRD east to HYR. Later this afternoon, showers and
some thunderstorms will develop and affect all terminals but INL
as the low pressure moves slowly east and a cold front approaches
from the northwest. Cigs will drop into the MVFR range with the
showers and thunderstorms into the evening. As the cold front
begins to move across the terminals later tonight, look for the
cigs to improve to VFR at INL/BRD/HIB after midnight. The MVFR
cigs will hang on until near the end of the forecast at DLH and


DLH  75  63  80  58 /  60  60  10   0
INL  78  58  77  56 /  10  10  10  10
BRD  81  65  80  59 /  70  50  10   0
HYR  79  65  81  58 /  60  60  40  10
ASX  79  65  82  59 /  40  60  30  10




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