Area Forecast Discussion
Issued by NWS Grand Forks, ND

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FXUS63 KFGF 181133

Area Forecast Discussion
National Weather Service Grand Forks ND
633 AM CDT Mon Sep 18 2017

Issued at 633 AM CDT Mon Sep 18 2017

Regional radars are showing a few weak echoes moving into
southeast ND. Not sure if any of the echoes are producing rain
that is actually reaching the ground, but will leave some low
shower chances along and south of Interstate 94 through mid
morning to cover this. High resolution models keep some weak
showers around throughout the day, but not much confidence in
that, as they have been overdone so far.


.SHORT TERM...(Today and tonight)
Issued at 404 AM CDT Mon Sep 18 2017

The main forecast challenges will be temperatures, winds, and the
severe weather potential on Tuesday. Currently have a mix of
clouds and clear spots across the FA, but the clouds are all mid
level and above. There is some warm advection and a weak low level
jet focused down into north central and northeast SD, where a few
showers and thunderstorms have formed. Models had been indicating
this potential for a couple of days now, but overall they were a
bit overdone, as they had been indicating these being further
north. High resolution model guidance has not picked up the
current showers/storms over SD very well, so confidence in what
happens with that activity is low. It originally strengthened
pretty quickly, but now the activity has weakened. Therefore will
leave isolated showers in the forecast for areas mainly along and
south of Interstate 94 through early morning. Otherwise, high
temperatures today should be a little warmer than Sundays.
Expecting steady southeast winds tonight with models indicating
quite a bit of cloud cover moving back in.

.LONG TERM...(Tuesday through Sunday)
Issued at 404 AM CDT Mon Sep 18 2017

The biggest question for Tuesday will be cloud trends. The day
looks to start out with quite a bit of cloud cover. However, the
southeast winds will quickly increase through the morning and be
quite gusty by afternoon. This should help to scour out some of
the cloud cover. However, lots of uncertainty with this, and this
plays into the severe weather potential for Tuesday afternoon and
evening. At this point, it appears the frontal boundary will move
into central ND by late afternoon and into eastern ND by early
evening. If enough heating occurs, severe storms are possible
along this boundary. The best likelihood of heating and storms is
over southeast ND, which SPC has upgraded the severe potential to
an enhanced risk. Hail to 1.50 inches, wind gusts to 75 mph or
greater, and isolated tornadoes are the main threats. These storms
should move into MN during the evening and overnight hours, with
a lower threat as they do. However, some storms could become bows
leading to a sustained wind threat. There may still be a few
lingering showers or storms early Wed, otherwise the rest of the
Wed into Wed night time frame looks quiet.

Thursday into Friday, an upper level low over the western Canadian
Prairie will transition to more of an amplified trough over the
western CONUS with stout ridging over the Great Lakes region. This
places the forecast area in deep southwest flow. An upper level jet
max is forecast to round the base of the trough promoting lee
cyclogenesis in the High Plains near CO/WY/NE. Exaggerated
meridional flow aloft over the central US will draw moisture
northward into the Plains states. The CIPS analog for PWAT (using
the 091800Z GFS) valid for Friday evening suggests 2+ standard
deviations over the eastern Dakotas into northern MN. The
aforementioned surface low deepens while traveling north-
northeastward into the Northern Plains/Upper Midwest. GFS/EURO/CMC
brings the surface low through the region Friday with a trailing
cold front gradually moving south through the area into Saturday.
Models suggest a frontal progression towards the south and east out
of the CWA. However, a suggested slow eastward movement of the upper
level trough and associated deep moisture transportation over the
Upper Midwest could suggest the front stalling southeast of the CWA.
Another low is progged to ride this front southeast of the area
towards Sunday.

So what does all of this mean? Rain. Perhaps a decent amount of rain
for some locations too given the amount of expected moisture return
for this time of year. Best chances for rain come Friday as the low
moves through the region. The cold front expected to drop southward
through the region will push the focus of rainfall largely into
Minnesota Saturday into Sunday, but a northward shift could bring
rainfall chances back into the region. With the front advertised to
remain parallel to the mean flow, steady rainfall will be possible,
not to mention the possibility of another low pressure system moving
along this front Sunday. This places areas from around Fargo to
Bemidji and southeastward in best chances for rainfall Friday
through Sunday.

Temperatures are expected to be seasonably mild to warm, especially
for areas around Fargo and southward through much of the period
until around Saturday/Sunday where cooler temperatures may creep
into the region from the north.


.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 633 AM CDT Mon Sep 18 2017

Expect southeast winds to pick up a little throughout the day, but
the really gusty winds should hold off until after 12Z Tuesday.
Should only see SCT to BKN mid clouds through mid morning, and
then some afternoon cumulus. Models are showing low clouds
developing tonight, then expanding across the entire FA, and
lingering into Tuesday morning. Confidence in exactly how low
these clouds may be is low, but at this time will go with MVFR




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